BY SPACEFLIGHT NOW

Follow the mission of space shuttle Columbia on the fourth servicing call to the orbiting Hubble Space Telescope. Reload this page for the very latest. A text only version is also available for faster access.

SATURDAY, MARCH 9, 2002

Scientists around the world are standing in line for a chance to use the Hubble Space Telescope's new camera and other instruments. In fact, in recent months the Space Telescope Science Institute has been flooded with eight times as many observing proposals as the telescope can accommodate. Read full story.

1038 GMT (5:38 a.m. EST)

Flying 900 feet above the Hubble Space Telescope, Columbia has just performed a thruster firing to accelerate the separation from the vicinity of the observatory.

Hubble is in the hands of its flight control team to slowly begin returning to science operations over the next few weeks.

For our Spaceflight Now Plus subscribers, here is a clip of today's Hubble deployment:

Video coverage for subscribers only:
   VIDEO: HUBBLE DEPLOYED FROM COLUMBIA QT or RV

1004 GMT (5:04 a.m. EST)

The overhauled Hubble Space Telescope -- sporting new solar arrays, electrical heart, advanced camera and infrared cooling system -- is once again flying on its own. The astronauts released the observatory from the end of shuttle Columbia's robotic arm at 5:04 a.m. EST today after the completely successful fourth servicing of the 12 year old telescope.

The astronauts will be interviewed by reporters later today. Sunday will largely be an off-duty day. Monday will be spent packing up and prepping Columbia for return to Earth. Landing is scheduled for 4:30 a.m. EST Tuesday at Kennedy Space Center, Florida to end the 11-day mission.

0953 GMT (4:53 a.m. EST)

The Space Telescope Operations Control Center has given its "go" to deploy Hubble. The shuttle flight control team then issued its approval for release, calling the astronauts with the news to proceed with an on-time deployment 11 minutes from now.

0940 GMT (4:40 a.m. EST)

The main door on the end of the Hubble Space Telescope is now swinging open, allowing starlight into the observatory once again.

Deployment of Hubble remains targeted for 5:04 a.m. EST, the start of a 19-minute window of opportunity for release.

0930 GMT (4:30 a.m. EST)

Hubble ground controllers are quite busy readying the telescope for its upcoming deployment. The astronauts have positioned Hubble in the release orientation on the end of the robotic arm.

0900 GMT (4:00 a.m. EST)

Hubble, riding on Columbia's arm, has been released from the servicing platform in the rear of the shuttlle's payload bay. The telescope will be maneuvered to the proper position for the upcoming deployment.

0756 GMT (2:56 a.m. EST)

With Hubble's six batteries fully charged, the power stream provided by the shuttle can be disconnected. The umbilical from Columbia to the telescope will be unplugged as activities continue in advance of Hubble's release, just over two hours from now.

0708 GMT (2:08 a.m. EST)

Columbia's robotic arm, operated by astronaut Mike Massimino, has just grappled the Hubble Space Telescope. Later this morning the observatory will be lifted out of the shuttle's payload bay and deployed back into space.

0530 GMT (12:30 a.m. EST)

The Columbia astronauts are gearing up to release the rejuvenated Hubble Space Telescope back into open space early today, wrapping up a surprisingly successful five-spacewalk flight to upgrade the $2 billion observatory's electrical system and scientific instruments. Read full story.

FRIDAY, MARCH 8, 2002

Astronauts John Grunsfeld and Richard Linnehan began repressurizing the shuttle Columbia's airlock at 11:06 a.m. EST today, officially ending a seven-hour 20-minute spacewalk, the crew's fifth and final excursion devoted to servicing the Hubble Space Telescope. Read spacewalk wrap-up story.

1609 GMT (11:09 a.m. EST)

Grunsfeld and Linnehan are back in the airlock and their space walk officially came to an end at 11:06 a.m. EST. Their excursion had a duration of 7 hours and 20 minutes. With the conclusion of this spacewalk, STS-109 has achieved a new record for the most EVA hours in a single shuttle flight: 35 hours and 55 minutes. The previous record of 35 hours and 26 minutes was set on the first Hubble servicing mission in 1993. The total number of EVA hours spent servicing Hubble is 129 hours 10 minutes. (Statistics provided by Bill Harwood.)

1555 GMT (10:55 a.m. EST)

Hubble's twin High Gain Antenna are being deployed.

1540 GMT (10:40 a.m. EST)

After paying tribute to their ground support teams, Grunsfeld and Linnehan returned to the airlock but Linnehan has left the airlock briefly to check a cover on the flight support structure is correctly positioned over an antenna cover.

1442 GMT (9:42 a.m. EST)

The astronauts are now moving on to pack up their tools and equipment as the fifth and final spacewalk of this mission draws to a close.

1441 GMT (9:41 a.m. EST)

Flight controllers have decided the radiator skirt position is adequate and not to work on it any longer.

"Better is the enemy of good enough," said CAPCOM Mario Runco. "We're going to press ahead and call it a day."

1425 GMT (9:25 a.m. EST)

Mission control has asked Grunsfeld to try to reposition the skirt that keeps light from warming the back side of the newly installed NICMOS cooling system radiator.

1416 GMT (9:16 a.m. EST)

The aft shroud doors are verified closed.

1400 GMT (9:00 a.m. EST)

The two spacewalkers are working to close the doors to the aft shroud area where they have been working to install the experimental NICMOS cryo cooler device.

1352 GMT (8:52 a.m. EST)

Linnehan continues to work ensuring the cryo cooler cabling is correctly placed, while Grunsfeld is finishing up work the capillary pump loop evaporator, part of the cooler system.

1332 GMT (8:32 a.m. EST)

Grunsfeld and Linnehan are working to attach the bundle of connectors from the radiator to the cooling box they installed in Hubble's aft shroud earlier in the spacewalk.

1306 GMT (8:06 a.m. EST)

Linnehan is feeding the bundle of connectors through a hole in the aft shroud of the telescope. The attachment of these connectors to the cryo cooler will complete installation of the device.

1254 GMT (7:54 a.m. EST)

Grunsfeld is preparing a bundle of connectors on the cooler radiator that will be snaked through the base of the telescope's aft shroud for attachment to the newly installed cooler device.

1247 GMT (7:47 a.m. EST)

Grunsfeld and Linnehan continue to work routing cables for the NICMOS Cryo Cooler.

1224 GMT (7:24 a.m. EST)

The radiator is now securely in place and the astronauts will move on to the installation of electrical cables for the NICMOS cooler device.

1220 GMT (7:20 a.m. EST)

The radiator has been reinstalled to the aft shroud of Hubble. Although the astronauts say the alignment isn't perfect, Mission Control says it is acceptable.

1206 GMT (7:06 a.m. EST)

The alignment of the radiator panel is off a bit. So the spacewalkers are unlatching it and will try attaching it again.

1156 GMT (6:56 a.m. EST)

The radiator has been placed on the side of the Hubble Space Telescope. The spacewalkers will now engage latches to hold the panel in position.

1142 GMT (6:42 a.m. EST)

Grunsfeld is holding onto the radiator panel while riding on the end of Columbia's robotic arm. The spacewalkers released the panel from its launch carrier in the rear of the shuttle's payload bay. They will soon mount it to the observatory as part of the NICMOS cryocooler system.

The spacewalkers are nearly three hours into this planned 6 1/2-hour EVA. Mission Control reports the crew is virtually right on the timeline.

1120 GMT (6:20 a.m. EST)

Rick Linnehan is getting off the robot arm; John Grunsfeld will get on for the next phase of the cryocooler installation work. Upcoming will be the retrieval of the NICMOS radiator panel from its launch carrier in Columbia's payload bay for attachment to the side of Hubble.

1109 GMT (6:09 a.m. EST)

The spacewalkers have now electrically connected the new cryocooler. For more on the cryocooler, here is the NASA fact sheet:

The Near Infrared Camera and Multi-Object Spectrometer (NICMOS), dormant since January of 1999, will be reactivated by a high tech cooling system, the NICMOS Cryocooler.

Installed on Hubble in February of 1997, NICMOS used infrared vision to probe dark, dusty, never-before-seen regions of space with the optical clarity that only Hubble can provide. Its infrared detectors operated at a very cold temperature (minus 352 degrees Fahrenheit, which is minus 272 degrees Celsius, or 60 degrees Kelvin). To keep the detectors cold, NICMOS was encased in a thermos-like container filled with solid nitrogen ice. Unfortunately, the nitrogen ice was consumed more quickly than planned due to a very small heat leak. In anticipation of this shortened lifespan, NICMOS's subscribed observations were tripled in order to get the most usage of this instrument before it ran out of coolant. In 1999-with its supply of ice exhausted-NICMOS became dormant.

Scientists and engineers at NASA's Goddard Space Flight Center in Greenbelt, MD, devised a way of adding a new, high-tech refrigeration device to NICMOS to re-cool its detectors and other components. The Hubble team developed the NICMOS Cryocooler-a state-of-the-art, mechanical, cryogenic cooler that is expected to return NICMOS to active duty.

Using non-expendable neon gas as a coolant, this closed system delivers high cooling capacity, extremely low vibration and high reliability. It employs a miniature cryogenic circulator to remove heat from NICMOS and transport it to the cryocooler. The system uses a tiny turbine turning at up to 400,000 rpm (over 100 times the maximum speed of a typical car engine). The NICMOS Cryocooler is virtually vibration-free - which is very important for Hubble. Vibrations could affect image quality in much the same way that a shaky camera produces blurred pictures.

The new cryogenic system is expected to re-cool the NICMOS infrared detectors to about minus 334 degrees Fahrenheit (minus 203 degrees Celsius or 70 degrees Kelvin). This is an ideal temperature for the detectors and will make NICMOS more sensitive to incoming light, thereby allowing it to collect more light. Engineers expect it to increase the life span of NICMOS to more than 5 years.

In 1998, the Hubble team successfully demonstrated this new cooler technology aboard the Space Shuttle Discovery on STS-95. This was the first on-orbit test of a high performance, high efficiency, mechanical cryocooler. The test took place less than 18 months after development began-an extremely short time for successfully developing a new space technology.

Retrofitting NICMOS with the new cryocooler will more than double its lifetimeŅensuring a greater scientific return on the original investment. This revolutionary technology paves the way for exciting advances in infrared astronomy on Hubble and beyond.

In the case of NICMOS, the cryocooler is replacing the solid nitrogen cooler that originally encased the instrument. But this advanced type of cryocooler can replace both liquid and solid nitrogen-based cooling systems on Earth as well as in space.

The cyrocooler offers earthly benefits in electronics manufacturing, medical imaging, and magnetic field detection. One particularly important application is in brain imaging. Magnetic encephalograms, which measure brain waves, allow doctors to determine if the various parts of the brain are functioning properly. This new cooler technology could make such brain imaging equipment more "user friendly," compact and affordable.

1048 GMT (5:48 a.m. EST)

The cryocooler has been positioned on the floor of the instrument bay, just in front of NICMOS. The spacewalkers will latch it in place.

1029 GMT (5:29 a.m. EST)

With the cryocooler in hand, Linnehan is riding the robot arm up out of payload bay and back to Hubble for the installation.

1018 GMT (5:18 a.m. EST)

Robot arm operator Scott Altman has maneuvered Linnehan back to Columbia's payload bay to retrieve the NICMOS cryocooler from its launch container.

1010 GMT (5:10 a.m. EST)

Linnehan is now preparing the hole on the bottom of the telescope through which the plumbing from the cryocooler will be fed.

0955 GMT (4:55 a.m. EST)

With the telescope opened, the spacewalkers have several activities to perform before the cryocooler is actually installed. They are currently working on disconnecting a ground strap and the cryo vent line to NICMOS.

0940 GMT (4:40 a.m. EST)

Riding on the end of Columbia's 50-foot robot arm, spacewalker Rick Linnehan is now swinging open the large aft shroud doors nearly an hour into today's planned 6 1/2 hour EVA.

0915 GMT (4:15 a.m. EST)

The spacewalkers are moving through preparatory steps for today's EVA. They will soon open up the aft shroud doors on Hubble for the installation of the NICMOS cryocooler.

0846 GMT (3:46 a.m. EST)

EVA 5 BEGINS. The fifth and final planned spacewalk of shuttle Columbia's mission to rejuvenate the Hubble Space Telescope has officially begun.

Astronauts John Grunsfeld and Rick Linnehan switched their suits from shuttle-provided power to internal batteries at 3:46 a.m. EST, marking the start of this planned 6 1/2-hour EVA to mount an experimental refrigerator to the observatory designed to revive a dormant infrared camera-spectrometer.

We have posted a comprehensive spacewalk preview story. And check out our detailed timeline of today's activities in space.

We'll update this page from time to time as the spacewalk progresses.

0843 GMT (3:43 a.m. EST)

The depress is now complete and Columbia's outer airlock hatch has been opened by the astronauts.

0834 GMT (3:34 a.m. EST)

The depressurization of Columbia's airlock is now underway. The start of today's spacewalk is running a few minutes behind schedule.

0330 GMT (10:30 p.m. EST Thurs.)

Mission Control has announced that the Columbia astronauts will be allowed to sleep in tonight by about a half-hour. So that will push back the day's activities accordingly, putting the target start time of the spacewalk at 3:22 a.m. EST.

0100 GMT (8:00 p.m. EST Thurs.)

Columbia's astronauts are scheduled to be awakened at 10:22 p.m. EST tonight for Flight Day 8 -- the day devoted to the fifth and final spacewalk of the mission. Spacewalk preparations for John Grunsfeld and Rick Linnehan will begin about two hours later, leading to the start of a 6 1/2-hour EVA at 2:52 a.m. EST.

In a pre-flight interview, Grunsfeld described the objectives of this spacewalk to install an experimental cooling system on Hubble to revive the NICMOS science instrument:

"This mission, STS-109, is a little bit different than any of the previous Hubble missions because we're doing a number of things that folks never thought we would do on Hubble. Although they've talked about the power control unit change-out before, I don't think anybody ever thought we'd really do it. It's just too hard.

"On EVA day 5, (we're) putting on the cooling system. And so, we're going to hang on handrails a large 12-foot-by-4-foot radiator on the outside of the telescope. (Nobody ever thought we'd do anything like that.) And, we're going to snake through the bottom of the telescope a bunch of plumbing that contains electronic control lines but also cooling lines. That's kind of like installing an external air conditioner in a house for the first time. And, plumbing it through a hole in the bottom of the telescope that was essentially a vent line previously.

"So Rick and I are first going to open up the big doors on the bottom of the telescope and we'll put in the cryo cooler (that's the refrigerator). And it's a relatively large box that goes on the floor of the telescope and clamps into handrails, again, that nobody ever thought would be used for putting items. And, Rick will get that all plumbed up; and we'll start some of the connections.

"Jim and Mike will have fed through a large cable harness from the Advanced Camera for Surveys side that's hooked up to the electronics for the cryo cooler. And then, we'll hook up the rest of that. At that, while Rick's hooking up all of the components on the inside of the telescope, a very delicate area again (everything inside is a scientific instrument, and he'll have to be very careful there), I'm going to go to the back of the payload bay and start taking the bolts off of the radiator.

"After that, Rick and I are going to switch places. I'll be on the arm; Rick will become the free-floater. And, I'll go back and hold on to the radiator, and Rick will undo the final latch. At which point, Nancy will drive me out over the port wing, holding this large 12-foot-long radiator. And I'll bring it around to the front of the telescope and hang it on the handrails. And Rick and I together will clamp it down.

"After that, Rick is going to climb underneath the telescope and get into a foot restraint so that he's looking straight up through this little hole (it's about that big) in the bottom of the telescope. And, I'll swing the cables around and underneath to him, and then he'll start feeding them up through the hole. I'll go inside the telescope and start pulling it up. And, we'll try and get this very, very long - I think it's ten feet or so of cable - through the bottom of the telescope.

"We've trained this many times in the pool; but nobody's done anything like this on Hubble. Once it's through, we'll clamp down a little holder in the bottom of the telescope that keeps any light from getting into the telescope from the bottom; and so that'll still be dark inside the telescope. (It's good to have no light inside the telescope from other than the place where the mirror is.) And, we'll hook up all the connections and close the doors."

THURSDAY, MARCH 7, 2002

Spacewalkers James Newman and Michael Massimino successfully installed a new $75 million camera inside the Hubble Space Telescope today, accomplishing the primary scientific goal of the fourth Hubble servicing mission. Read full story.

1632 GMT (11:32 a.m. EST)

Today's spacewalk has been officially clocked at 7 hours and 30 minutes in duration. It began at 4 a.m. EST and concluded at 11:30 a.m. EDT.

1628 GMT (11:28 a.m. EST)

Repressurization of the airlock is underway.

1624 GMT (11:24 a.m. EST)

The spacewalkers are back inside the airlock and the outer hatch is now closed.

1616 GMT (11:16 a.m. EST)

The two spacewalkers have completed an inventory of the tools they used during today's spacewalk and are returning to the shuttle's airlock.

1550 GMT (10:50 a.m. EST)

The two spacewalkers continue to work to remove shades and covers installed to protect the telescope while it was shutdown on Wednesday for the Power Control Unit replacement. They are running well over an hour behind schedule.

1530 GMT (10:30 a.m. EST)

Massimino is checking that equipment bays opened during yesterday's replacement of the Power Control Unit are properly latched shut, while Newman is removing a thermal shade placed over a bay to protect its contents during yesterday's telescope shutdown.

1511 GMT (10:11 a.m. EST)

The first functional test of the newly installed electronics support module for the NICMOS Cryo Cooler has gone well according to Hubble ground controllers.

1504 GMT (10:04 a.m. EST)

The spacewalkers have closed the aft shroud doors and are working to latch them closed.

1448 GMT (9:48 a.m. EST)

The electronics support module for the NICMOS Cryo Cooler is now hooked up to Hubble's power supply and Newman and Massimino are making sure the associated cables do not snag on any of the equipment inside the telescope's aft shroud.

1421 GMT (9:21 a.m. EST)

Massimino is now hooking up cables to the new electrical box.

1405 GMT (9:05 a.m. EST)

The spacewalkers are busy hooking up an electrical harness that will route power to the NICMOS Cryo Cooler.

1343 GMT (8:43 a.m. EST)

The spacewalkers are bolting down the electrical box for NICMOS Cryo Cooler inside the aft-shroud of the Hubble Space Telescope. Once the box is in place Newman will unplug four electrical connectors from the COSTAR corrective optics device and connect them to a harness that will power the NICMOS cooler. COSTAR, installed in 1993 to fix Hubble's blurred vision, is no longer needed as all instruments are now fitted with their own corrective optics.

1329 GMT (8:29 a.m. EST)

Riding the shuttle's robot arm, Mike Massimino is carrying the electrical box for the NICMOS Cryo Cooler to the aft shroud of the Hubble Space Telescope.

1306 GMT (8:06 a.m. EST)

The functional test of the Advanced Camera for Surveys is getting underway while the astronauts prepare for their next task, the installation of an electrical box for the NICMOS Cryo Cooler.

1250 GMT (7:50 a.m. EST)

The Faint Object Camera has now latched down in its cargo bay carrier for the return to Earth. The next task for the two spacewalkers is to install an electrical box for the NICMOS Cryo Cooler. The spacewalk officer in mission control reports the astronauts are running about 30 minutes behind schedule.

1246 GMT (7:46 a.m. EST)

Newman and Massimino are working to latch down the Faint Object Camera in its cargo bay carrier.

1233 GMT (7:33 a.m. EST)

The newly installed $75 million Advanced Camera for Surveys has passed an "aliveness" test according to Hubble flight controllers at NASA's Goddard Space Flight Center.

1220 GMT (7:20 a.m. EST)

Spacewalker Jim Newman has lifted the Faint Object Camera off the temporary stowage fixture on the side of the payload bay. He will maneuver it into the carrier that the Advanced Camera for Surveys had been launched in.

1209 GMT (7:09 a.m. EST)

Spacewalker Mike Massimino is now hooking up the ground strap and four electrical cables to the Advanced Cameras for Surveys. Once this is completed, Hubble ground controllers can conduct an "aliveness test" on the new instrument.

1158 GMT (6:58 a.m. EST)

The latches have been tightened. The Advanced Cameras for Surveys is now locked down inside the Hubble Space Telescope following this morning's successful installation by the spacewalking astronauts.

The spacewalkers will now load the old Faint Object Camera into the carrier vacated by ACS for the ride back to Earth.

1143 GMT (6:43 a.m. EST)

The Hubble Space Telescope has a new scientific instrument. The Advanced Camera for Surveys has been installed into the observatory by the spacewalkers. After checking the alignment, the crew will then engage latches to hold the phone booth-sized instrument in place.

1138 GMT (6:38 a.m. EST)

ACS is being loaded into Hubble.

1134 GMT (6:34 a.m. EST)

The spacewalkers are checking alignments before sliding the ACS into the Hubble Space Telescope. Newman is holding the instrument in his hands while riding on the robot arm; Massimino is free-floating to give guidance cues to Newman.

Mission Control reports the astronauts are currently 25 minutes behind the timeline.

1124 GMT (6:24 a.m. EST)

Still riding on the end of Columbia's Canadian-built robotic arm, spacewalker Jim Newman is slowly lifting the phone booth-sized Advanced Camera for Surveys out of its launch carrier.

1112 GMT (6:12 a.m. EST)

The spacewalkers have now moved on to the job of preparing the Advanced Camera for Surveys to be lifted out of the carrier in the middle of Columbia's cargo bay.

1105 GMT (6:05 a.m. EST)

With the Faint Object Camera now removed, Massimino has floated into the aft shroud of the telescope to install a wiring harness that will be used by the NICMOS electronics module, which will be installed later in this spacewalk.

1052 GMT (5:52 a.m. EST)

Newman has parked the Faint Object Camera atop a special fixture on the left side of the payload bay, basically getting the instrument out of the way in preparation for lifting the Advanced Camera for Surveys out of its launch container and installing it into the telescope. The Faint Object Camera ultimately will be stowed into the ACS's container for return to Earth.

1042 GMT (5:42 a.m. EST)

The Faint Object Camera, the last of Hubble's original science instruments, is now being removed from the observatory. Jim Newman is sliding the FOC out. He will then temporarily stow the instrument to a fixture on the side of Columbia's payload bay while the Advanced Camera for Surveys is installed.

0954 GMT (4:54 a.m. EST)

The aft shroud doors are open. Massimino will now unhook connectors and release latches holding the Faint Object Camera inside Hubble. Once that work is completed, Newman will pull the instrument out of the telescope while riding on the end of Columbia's robot arm.

0940 GMT (4:40 a.m. EST)

Hubble ground controllers report the Faint Object Camera has been powered down in preparation for its removal from the telescope by the spacewalkers. Meanwhile, Jim Newman is about to open the aft shroud doors for the FOC removal and subsequent installation of the Advanced Camera for Surveys this morning.

0901 GMT (4:01 a.m. EST)

EVA 4 BEGINS. The fourth of five spacewalks to overhaul the Hubble Space Telescope during this flight of space shuttle Columbia has officially begun.

Astronauts Jim Newman and Mike Massimino switched their suits from shuttle-provided power to internal batteries at 4:00 a.m. EST, marking the start of this planned 6 1/2-hour EVA that will see the no-longer-used Faint Object Camera removed from Hubble and the new Advanced Camera for Surveys installed into the orbiting observatory. The spacewalkers will also install the NICMOS electronics support module.

We have posted a comprehensive spacewalk preview story. And check out our detailed timeline of today's activities in space.

We'll update this page from time to time as the spacewalk progresses.

0851 GMT (3:51 a.m. EST)

Airlock depressuziation is underway for this morning's spacewalk to enhance the scientific reach of the Hubble Space Telescope. The official start time of the spacewalk will be clocked with Newman and Massimino switch their suits to internal battery power.

0841 GMT (3:41 a.m. EST)

Mission Control has given the "go" for airlock depress, which is now expected in a few minutes.

0820 GMT (3:20 a.m. EST)

Astronauts Jim Newman and Mike Massimino are sealed inside Columbia's airlock, preparing for the start of today's spacewalk. Depressurization is expected to start in 15 to 20 minutes.

0525 GMT (12:25 a.m. EST)

Flush with success after upgrading the Hubble Space Telescope's power system, the Columbia astronauts now turn their attention to beefing up the observatory's scientific horsepower with installation of a $75 million camera during the mission's fourth spacewalk today. The 6 1/2-hour EVA begins at around 3:30 a.m. EST. Read full story.

WEDNESDAY, MARCH 6, 2002

NASA managers, elated at the successful replacement of the Hubble Space Telescope's central power controller, will delay the start of the next two servicing spacewalks to give Columbia's astronauts time to catch up on their rest after getting off to a late start today. Read full story.

1517 GMT (10:17 a.m. EST)

Columbia's airlock is now being repressurized. Today's spacewalk lasted 6 hours 48 minutes.

1510 GMT (10:10 a.m. EST)

The functional test of the newly installed PCU device is now underway.

1457 GMT (9:57 a.m. EST)

Grunsfeld and Linnehan are returning to the airlock as this spacewalk draws to a a close.

1442 GMT (9:42 a.m. EST)

Controllers at the Space Telescope Operations Control Center report that the aliveness test of the new Power Control Unit has been successfully completed.

1438 GMT (9:38 a.m. EST)

Grunsfeld is removing thermal shades from the telescope's star trackers.

1424 GMT (9:24 a.m. EST)

Power from Columbia is flowing to the telescope. The full revival of the observatory will begin shortly, starting with the activation of the Wide Field Planetary Camera.

1423 GMT (9:23 a.m. EST)

Hubble's six batteries have now been reconnected.

1421 GMT (9:21 a.m. EST)

The aliveness test of the new PCU continues and is reported to be going well.

1402 GMT (9:02 a.m. EST)

Hubble has a heart beat! Telemetry is once again being received from the telescope's newly installed PCU. The spacewalkers are now working to hook up the telescope's batteries.

1331 GMT (8:31 a.m. EST)

Grunsfeld is now connecting fuse plugs to the four power distribution units. This will allow the new PCU to route power to the various telescope systems.

1318 GMT (8:18 a.m. EST)

All 36 cables are now connected to Hubble's new Power Control Unit.

1300 GMT (8:00 a.m. EST)

28 of the 36 cables are now connected to Hubble's new PCU.

1255 GMT (7:55 a.m. EST)

Grunsfeld has now mated 24 of the 36 electrical connectors for the new PCU.

1242 GMT (7:42 a.m. EST)

Mission commentator Rob Navias reports that 20 out of the 36 PCU connectors have now been reconnected. The telescope has now been without power for about three hours.

1230 GMT (7:30 a.m. EST)

Grunsfeld has now connected one third of the cables to the new PCU box.

1220 GMT (7:20 a.m. EST)

Six connectors on the new PCU now mated. 30 left to go.

1214 GMT (7:14 a.m. EST)

Two more cables are now connected. 32 remain.

1211 GMT (7:11 a.m. EST)

Grunsfeld has connected the first two cables to the PCU. They are located on the bottom of the box. The remaining 34 connectors run down the left side of the box.

1204 GMT (7:04 a.m. EST)

Grunsfeld is about to start work to hook up the 36 electrical connectors to the new PCU. The old box is now secured in the payload bay for the return to earth.

1154 GMT (6:54 a.m. EST)

John Grunsfeld has inserted the new PCU in equipment bay 4 and will now start work to bolt it down.

1143 GMT (6:43 a.m. EST)

Grunsfeld handed the old PCU to Linnehan down in the payload bay and picked up the new unit. He is headed back up to the telescope to begin the process of installing the new PCU.

1134 GMT (6:34 a.m. EST)

Just over three hours into today's spacewalk, John Grunsfeld has pulled the old PCU, the electrical heart of the Hubble Space Telescope, out of the observatory. Riding on the end of the shuttle's robot arm, Grunsfeld will carry the unit down to the payload bay to be stowed for the ride home. He will then pick up the new PCU to be installed into the telescope as the spacewalk continues.

1128 GMT (6:28 a.m. EST)

Linnehan and Grunsfeld have switched places. Grunsfeld has now finished getting the final connectors unhooked and will now unbolt the PCU.

1051 GMT (5:51 a.m. EST)

More than half of the connectors -- 23 of the 36 -- have been demated from the old PCU. Linnehan will do seven more before letting Grunsfeld finish the job. Mission Control reports Linnehan is right on the timeline.

1026 GMT (5:26 a.m. EST)

After some prep work around the PCU, Linnehan has started unhooking the 36 connectors.

0936 GMT (4:36 a.m. EST)

The Hubble Space Telescope has been completely powered off. The observatory is now without a heart beat.

The power down is considered risky -- the observatory has never been turned off in its 12-year life in orbit. Although engineers are confident Hubble, the crown jewel of astronomy, will power back up at the end of today's spacewalk, obviously there is drama.

Hubble was built to be serviced by astronauts in orbit, but removal of the PCU was never planned. As a result, the spacewalkers will have only limited vision into the area where the box is located as they work to disconnect 36 cables and other umbilicals.

The spacewalkers must complete the Power Control Unit replacement and restore power by the end of the day, or Hubble's critical systems could be damaged by the effects of the normal temperature extremes of space.

While NASA managers typically downplay the drama associated with key events like this one, Anne Kinney, director of astronomy and physics at NASA headquarters, said she was "nervous as hell" about the PCU swap out.

The spacewalk preview story has full details on the power down.

Meanwhile, spacewalker Rick Linnehan has gained access to the Power Control Unit in Bay 4. He will remove the first 30 connectors. Then John Grunsfeld will take over to remove the final six connectors and pull out the PCU. This removal work will take a couple of hours.

0930 GMT (4:30 a.m. EST)

As soon as Grunsfeld finishes installing thermal covers over Hubble's fixed head star trackers, Hubble will be powered down. The "go" to turn Hubble off has been given by Mission Control as soon as Grunsfeld completes his work.

0925 GMT (4:25 a.m. EST)

Spacewalker Linnehan has completed disconnecting the three batteries in Bay 2. Hubble is now one command away from being turned off.

0910 GMT (4:10 a.m. EST)

The three batteries in Hubble's Bay 3 have been disconnected. Linnehan, riding on the end of Columbia's robot arm, is now moving to Bay 2 to unhook the remaining three batteries.

0905 GMT (4:05 a.m. EST)

Linnehan is now working to disconnect six batteries in Hubble while Grunsfeld deploys thermal covers on parts of the observatory -- all preparatory steps to the replacement of the PCU.

0900 GMT (4:00 a.m. EST)

We have updated our timeline of today's spacewalk based on the actual start time.

0828 GMT (3:28 a.m. EST)

EVA 3 BEGINS. Running two hours late after a water leak forced astronaut John Grunsfeld to change into a new spacesuit, the spacewalk considered the riskiest and most challenging ever attempted on the Hubble Space Telescope has now started. The planned seven-hour excursion began at 3:28 a.m. EST when Grunsfeld and fellow spacewalker Rick Linnehan switched their suits from shuttle-provided power to internal batteries.

Over the next hour the spacewalkers will move through prep work in advance of replacing Hubble's Power Control Unit, the electrical heart of the observatory. Also upcoming will be the power down of Hubble.

Read a comprehensive spacewalk preview story.

0827 GMT (3:27 a.m. EST)

The airlock is at vacuum and the outer hatch is now being opened.

0811 GMT (3:11 a.m. EST)

Airlock depressurization is now beginning. Meanwhile, steps are underway to power down the Hubble Space Telescope for the first time since it was launched in April 1990. The telescope is being turned off so its Power Control Unit can be replaced by the spacewalkers today.

0755 GMT (2:55 a.m. EST)

Depressurization of Columbia's airlock is expected in about 15 minutes. Grunsfeld is nearing completion of the procedure to breathe pure oxygen to purge his blood stream of nitrogen to prevent "the bends" during the spacewalk. The official start time of the spacewalk is clocked when the astronauts switch their suits to internal battery power, now expected around 3:30 a.m. EST.

0725 GMT (2:25 a.m. EST)

Spacewalk preparations are underway for John Grunsfeld in his new suit. Mission Control now projects the start time of today's spacewalk will be around 3:40 a.m. EST (0840 GMT). The EVA is scheduled to last at least seven hours.

0654 GMT (1:54 a.m. EST)

After discussions between the shuttle flight control team and Hubble project officials, it was decided to keep with the plan to replace the Power Control Unit today, albeit a couple hours later than planned.

0642 GMT (1:42 a.m. EST)

At the moment it appears flight controllers are favoring the plan of pressing ahead with Power Control Unit replacement today. The spacewalk is now estimated to start at around 3:30 a.m. EST, two hours later than planned. The EVA will last about seven hours, making for an incredibly long workday for the crew. They would get to bed late, then sleep in and push back the start of tomorrow's spacewalk to install the Advanced Camera for Surveys.

The spacewalk team in Mission Control suspects that a valve in the suit's cooling system popped open for some reason, causing the water leak.

The astronauts are currently working to re-size another spacesuit onboard to fit Grunsfeld.

0630 GMT (1:30 a.m. EST)

Grunsfeld is making his way out of the old suit and into the new suit. The other astronauts are working to mop up the water in the airlock from the leak, which remains unexplained.

Meanwhile, Hubble remains powered up. Controllers had not yet progressed to the point of turning off the observatory for this morning's intended replacement of the Power Control Unit.

Since it will obviously take some time for Grunsfeld to don the other suit and complete the pre-spacewalk preparatory work, NASA officials are discussing whether to keep with the game plan of replacing the Power Control Unit today or instead jumping to the work scheduled for Thursday's spacewalk. The PCU spacewalk is expected to last seven hours from start to finish, making it a long day for the crew. This suit problem is delaying the start of the spacewalk by at least an hour, making the PCU replacement today an even longer workday than envisioned.

0616 GMT (1:16 a.m. EST)

Given the delay in the start of the spacewalk, Mission Control is now talking about how this impacts the overall timeline for the day and whether the lengthy task of replacing the Power Control Unit can still be accomplished. There is the option, NASA says, of performing the tasks of spacewalk No. 4 of installing the Advanced Camera for Surveys this morning and deferring the spacewalk No. 3 job of the PCU replacement until tomorrow.

0612 GMT (1:12 a.m. EST)

The shuttle crew has just been instructed by Mission Control to get John Grunsfeld out of his current spacewalking spacesuit and into another as a result of the water leak with his cooling garment system. It is not clear what caused the leak. The spacewalkers were in the airlock preparing to start the EVA about a half-hour from now.

NASA estimates this suit switch will delay the start of this morning's spacewalk by approximately an hour -- to 2:30 a.m. EST. But that is just an estimate at this point.

0610 GMT (1:10 a.m. EST)

Flight controllers are discussing options to recover from this problem involving water seeping from John Grunsfeld's suit.

0607 GMT (1:07 a.m. EST)

The astronauts report John Grunsfeld's spacesuit has leaked some water from the cooling system. Mission Control is discussing the situation. It is possible Grunsfeld will have to switch to another suit, which would delay the start of today's EVA by approximately an hour.

0530 GMT (12:30 a.m. EST)

Since it was launched in 1990, the Hubble Space Telescope has undergone eye surgery to correct its flawed vision, an electronic brain transplant and numerous other upgrades and repairs to replace aging or broken components and to install new instruments. On Wednesday, the $2 billion observatory faces its riskiest operation yet, the equivalent of open heart surgery to replace its central power system controller. Read a comprehensive spacewalk preview story.

0200 GMT (9:00 p.m. EST Tues.)

Columbia's seven astronauts have been awakened for the most challenging day of their mission to overhaul the Hubble Space Telescope. Tonight, the observatory will be powered down for the first time since it was launched in April 1990 so spacewalkers John Grunsfeld and Rick Linnehan can replace Hubble's Power Control Unit, the electrical heart of the telescope.

Hubble was built to be serviced in orbit but removal of the PCU was never planned. As a result, the spacewalkers will have limited vision into the area where the box is located as they work to disconnect 36 cables and other umbilicals.

"What makes it difficult is, as you're facing the PCU, those connectors are on the left-hand side, they're not staring right at you, they're on the left face," lead flight director Bryan Austin said. "And that's on the side that that bay door is hinged. For the suited crewman to reach his hand in there, he's pretty much reaching in there blind.

"I kind of equate it to changing out spark plugs on your car. There's always those spark plugs down there where you sort of can't see real well, you've just got to go down and feel and make sure you're oriented such that you're unscrewing it without a lot of offset force."

Once Hubble is shut down for the PCU change out, an imaginary "thermal clock" will start ticking. The astronauts must complete the PCU replacement and restore power by the end of the day, or Hubble's critical systems could be damaged by the effects of the normal temperature extremes of space.

Also making this spacewalk dramatic is the potential of a problem turning Hubble back on after the new Power Control Unit is installed.

"That scares me a lot, it kind of violates a long-standing policy in the space business that if something's working well you turn it off and just hope it comes back on," said Ed Weiler, NASA's associate administrator for space science.

"We're not doing that cavalierly, we fully anticipate that everything will work just fine," he said. "But it is a risk that we've never faced before. So this mission is no cakewalk."

Despite the risk of replacing the PCU, officials say it is necessary job because the current unit cannot provide enough power to run all of Hubble's instruments at the same time and it has suffered an internal problem that could one day cripple the observatory if it gets worse.

The spacewalk begins at about 1:30 a.m. EST. See a timeline.

Grunsfeld previewed the spacewalk in this pre-flight NASA interview:

"Even while Rick and myself are in the airlock on the EVA-3, the activity will have already started. Up in the flight deck, Jim (Newman) and Mike (Massimino) will have started to work their steps on the avionics on Hubble, to start powering it off. And, the folks on the ground are going to kick off a procedure called the "super proc." You know, I imagine that there's some guy at a computer console with a big "S" on the shirt, you know, in a cape and his hands madly clicking on the keys. Of course, it's not really like that. But, they're going to send a large program up to Hubble to tell it to start turning things off.

"Once we egress the airlock, Rick and I are in turbo mode because we have to go out and there's various times that we have to hit (gates, if you will) to get Hubble in position to change out the Power Control Unit. We have to get thermal covers on some of the bays because, once Hubble's unpowered, space is a very cold place; and it's going to start radiating to space, cooling off, and some of the equipment can't get cold. It's just a limit on the mechanical components, on electronic components. It's kind of like if you live in Minnesota, where our pilot Duane Carey comes from, you know, if you leave your car out at a restaurant, in the bitter cold and come out and expect it to turn on, it may or may not turn on. Hubble's the same way. We don't want it to get too cold.

"And so, Rick and I are going to be speedily getting Hubble ready, to change out the Power Control Unit. And that, as I said, includes putting some thermal covers on. Rick is going to start disconnecting batteries. They're the same batteries that I worked on, on STS-103, so we have a little bit of experience in that area. And then, Rick is going to start disconnecting connectors on the Power Control Unit, as soon as he can get there. We're going to try and stay ahead of the power curve, so to speak, because this is an EVA that could go long. There's so many unknowns in it, that it, if any of these EVAs on our flight are going to be long ones, this would be the one to look for.

"We're prepared if necessary to swap out roles if it becomes too tedious. This is the kind of task that Mark Lee said was very difficult, so we're preparing for that. So, while Rick is disconnecting connectors, I'm going to be just by his side relaxing, as if, you know, I'm sort of on deck, in a, you know, just keeping, you know, warm but ready to go. If Rick gets tired, I'll jump in his place and disconnect until we get all the connectors off.

"Then we'll swap the PCU. It's about halfway up the telescope in a little electronics bay. So, I'll take it out. Nancy (Currie) will take me down to meet Rick. In the payload bay, we'll change it out for the new box. I'll put the new box in, and then start connecting. While I'm connecting the connectors, Rick is going to be by my side relaxing. In case I get too tired, he can jump in and take a few connectors.

"And, that's the plan; but we're ready for anything."

"And then, we'll continue back undoing all the things that we did earlier by putting the batteries back on line, taking thermal covers off. And once we have the batteries back on line, you know, then the man with the big S and the fast fingers is going to send commands up to start Hubble systems back on."

TUESDAY, MARCH 5, 2002

Astronauts James Newman and Michael Massimino began repressurizing the shuttle Columbia's airlock at 8:56 a.m. this morning, officially ending a seven-hour 16-minute spacewalk. The astronauts installed a second solar array on the Hubble Space Telescope and a new reaction wheel to help it move from target to target. Initial tests show both components are healthy and operating normally. Read full story, which includes a preview of tonight's third spacewalk.

1400 GMT (9:00 a.m. EST)

Today's spacewalk ended at about 8:56 a.m. and had a duration of 7 hours and 16 minutes.

1355 GMT (8:55 a.m. EST)

Newman and Massimino are back in the airlock as their spacewalk comes to a close.

1311 GMT (8:11 a.m. EST)

Mission control has informed the Columbia crew that the functional test of the new Reaction Wheel Assembly was successful.

1257 GMT (7:57 a.m. EST)

One of the Hubble Space Telescope's aft shroud latches has checked out fine. The second latch will require replacement. This should be a fairly swift task, according to mission commentator Rob Navias.

1237 GMT (7:37 a.m. EST)

Newman has successfully installed a new installation panel over the telescope's equipment bay 6 -- an unplanned activity added to today's outing after the spacewalker got ahead of schedule. The astronauts are now finishing up tests on two of the telescope's aft shroud latches.

1212 GMT (7:12 a.m. EST)

A functional test of the new Reaction Wheel Assembly is now underway.

1204 GMT (7:04 a.m. EST)

With the spacewalkers running ahead of schedule, Flight Director Bryan Austin has instructed the astronauts to conduct at least two extra tasks: the installation of a thermal blanket panel on equipment bay 6 and a drive test on two bolts on the aft shroud doors behind which are located the NICMOS and STIS instruments. The test is designed to check if a new latching mechanism will be required for the door.

Meanwhile, Hubble flight controllers report a successful aliveness test of the newly installed Reaction Wheel Assembly.

1158 GMT (6:58 a.m. EST)

Massimino has completed the installation of the new Reaction Wheel Assembly and closed the door to the equipment bay where it is housed. Hubble flight controllers will now conduct an "aliveness test" to ensure it is working properly.

1140 GMT (6:40 a.m. EST)

Now five hours into today's spacewalk. Massimino is now installing the new Reaction Wheel Assembly.

The spacewalkers are running about 20 minutes ahead of schedule. So Mission Control is considering adding some low-priority tasks to this EVA.

1133 GMT (6:33 a.m. EST)

Handoff of the Reaction Wheel Assemblies has occurred. Massimino, riding on the end of the shuttle's robot arm, took the old wheel down to the payload bay carrier where Newman had unbolted the new unit. They traded wheels and Massimino is headed back to up to Hubble to install the new RWA. Newman will now stow the old wheel for return to Earth.

1125 GMT (6:25 a.m. EST)

The spacewalkers have removed the suspect Reaction Wheel Assembly on the Hubble Space Telescope in preparation for installation of a fresh unit. This job is actually the highest priority item on NASA's list of things to be accomplished on this Hubble servicing mission.

The Reaction Wheel Assembly in question -- RWA-1 -- is one of four gyroscopic devices used in moving, or "slewing", the observatory from one astronomical target to the next.

Last November, gyro speed telemetry from RWA-1 briefly dropped out, the result of an internal electrical problem. Although the device has worked properly ever since, NASA officials became concerned it could fail. Hubble can operate with just three RWAs, but another problem would leave the telescope unable to slew and thus, unable to accomplish any scientific observations. As a result, the space agency decided to add the RWA replacement to Columbia's mission, albeit at the last minute.

1116 GMT (6:16 a.m. EST)

Spacewalker Massimino is working to remove the old Reaction Wheel Assembly from Hubble, while Newman is unbolting the new unit from its launch carrier in Columbia's payload bay.

1105 GMT (6:05 a.m. EST)

Hubble ground controllers report the "aliveness test" of the newly installed port solar array was successfully completed. And the spacewalkers have been given a "go" to disconnect the old Reaction Wheel Assembly for replacement.

1050 GMT (5:50 a.m. EST)

The spacewalkers have completed their work to deploy the Hubble Space Telescope's new port-side power-generating solar array. The observatory now has two new, more powerful arrays following the installation of the starboard one yesterday. Ground controllers will run a series of tests this morning confirm the port array's health.

The next major task upcoming for the spacewalkers is replacement of a Reaction Wheel Assembly on Hubble.

1042 GMT (5:42 a.m. EST)

The new port solar array has been unfolded. The spacewalkers will now tighten some locking bolts on the array.

1032 GMT (5:32 a.m. EST)

The spacewalkers are beginning to deploy the new port-side solar array, opening it up like a book.

1025 GMT (5:25 a.m. EST)

Just like yesterday's spacewalk, there was a bit of trouble getting the old array fully locked down on the payload carrier. But after some extra effort, Massimino has successfully secured the array for its trip back to Earth. Massimino, still on the end of the arm, is now headed back up to the new array for deployment.

1000 GMT (5:00 a.m. EST)

While Jim Newman continues working with electrical connectors between Hubble and its new port solar array, Mike Massimino is back in the cargo bay to fully secure the old array to the carrier for return to Earth. Once both complete their current jobs, they will then open up the new array.

0948 GMT (4:48 a.m. EST)

The spacewalkers have attached the new solar array to the Hubble Space Telescope. Newman will now bolt the array into place to firmly secure it to the observatory.

0916 GMT (4:16 a.m. EST)

The new solar array has been lifted from its launch carrier. Massimino is holding on to the array as he rides from the payload bay up to Hubble. Newman will now climb back up to the telescope to bolt the array into place when it arrives shortly.

0901 GMT (4:01 a.m. EST)

With the new diode box installed, Newman joined Massimino in the cargo bay to assist is releasing the new solar array from the carrier structure. Massimino, riding on the end of the robot arm, has the new array in hand now and is beginning to lift it out of the carrier. He will ferry it up to the telescope for installation.

0840 GMT (3:40 a.m. EST)

Now two hours into today's spacewalk. Newman is working to hook up all the connectors between the new diode box and the telescope. Meanwhile, Massimino has stowed the old box in the payload bay and is now preparing release latches holding the new array in its launch carrier aboard Columbia.

Mission Control says the spacewalkers are about 25 minutes ahead of the timeline.

0828 GMT (3:28 a.m. EST)

Jim Newman has unbolted the old diode box from the Hubble Space Telescope and handed it to Mike Massimino for transport to the shuttle's payload bay for return to Earth. Massimino had the new box in his hand and gave it to Newman for installation on the telescope. The new unit is suited to handle the additional power the new solar array will generate.

0803 GMT (3:03 a.m. EST)

The spacewalkers have bolted the old array to a carrier structure in Columbia's payload bay. Massimino will later engage some latches to firmly hold the array in place for its ride home. Now the spacewalkers will turn their attention to replacing the diode box assembly on Hubble's port side to support the new, more powerful array.

0751 GMT (2:51 a.m. EST)

Hubble's port solar array has been detached from the observatory by the spacewalkers. Jim Newman unbolted the array from the telescope and Mike Massimino, riding on the end of the shuttle's robot arm, has the free array in his hands. The array will be stowed back in Columbia's payload bay for the return to Earth.

So the two second-generation solar arrays delivered to Hubble during the first servicing mission in December 1993 have been removed during the first two spacewalks of this fourth servicing mission. Spacewalkers installed one of the smaller but more powerful third-generation arrays yesterday to the starboard side of the observatory. The new port array will be installed later this morning.

0735 GMT (2:35 a.m. EST)

While Jim Newman works to disconnect cabling with the diode box assembly for the old solar array, Mike Massimino is loosing a series of bolts on three access doors on the side of Hubble as a get-ahead task for tomorrow's spacewalk to replace the observatory's Power Control Unit.

0725 GMT (2:25 a.m. EST)

Now 45 minutes into today's spacewalk. The port-side solar array, which had been sticking straight out from the body of the telescope, has been folded upright against Hubble in preparation for removal. Mission Control reports the spacewalkers are running about a half-hour ahead of the timeline.

0640 GMT (1:40 a.m. EST)

EVA 2 BEGINS. For the second straight day astronauts from space shuttle Columbia have embarked on a spacewalk to give the Hubble Space Telescope an overhaul.

Astronauts Jim Newman and Mike Massimino switched their suits from shuttle-provided power to internal batteries at 1:40 a.m. EST, marking the start of this planned 6 1/2-hour EVA.

The spacewalkers plan to remove Hubble's port-side solar array and install of a new array that will allow the telescope to generate more power to run its new generation set of science instruments. They will then replace one of the telescope's four Reaction Wheel Assemblies used for pointing during science observations.

After initial setup work, the array replacement is expected to take about four hours, followed by the hour-long job of switching out the reaction wheel, some other quick tasks and then cleanup of the payload bay.

The mission's first spacewalk, successfully completed early Monday by John Grunsfeld and Rick Linnehan, replaced Hubble's starboard array. This morning's EVA will complete the solar array replacement work by installing the new port-side array.

"Mike and I have a similar day on the second spacewalk, but we don't have as much initial configuration to do," Newman said in a NASA pre-flight interview. "Since John and Rick are the first ones out the door, they have to do a little bit of initial configuration in order to set up the payload bay for the rest of the spacewalks. And they'll do some final de-configuration on the very last spacewalk.

"When Mike and I go outside, I'll immediately head back and get to work and Mike will take a couple of minutes, just to get his space legs. He will have an opportunity to translate a little bit around in the payload bay in order to become familiar with what it's like to be a spacewalker, and then we're going to put him right to work as well."

This is the fifth spacewalk for Newman, who is wearing the suit with horizontal broken red stripes, and first for Massimino who has the suit with diagonally broken red stripes.

We'll update this page periodically during the spacewalk.

0637 GMT (1:37 a.m. EST)

The airlock has been depressurized and the astronauts have just opened the outer hatch.

0624 GMT (1:24 a.m. EST)

Airlock depressurization has now started.

0615 GMT (1:15 a.m. EST)

Mission Control has given the Columbia crew a "go" for airlock depressuziation for this morning's spacewalk. The official start time of the spacewalk will be clocked with Newman and Massimino switch their suits to internal battery power.

0330 GMT (10:30 p.m. EST Mon.)

The shuttle crew was awakened for Flight Day 5 at 8:53 p.m. EST by the children's song "Floating in the Bathtub," by Tonya Evetts Weimer.

Astronauts Jim Newman and Mike Massimino will take their turn as the spacewalking duo tonight, heading into Columbia's payload bay at about 1:30 a.m. EST for a 6 1/2-hour EVA to replace Hubble's other power-generating solar array and swap out a suspect gyroscopic device, called a Reaction Wheel Assembly, that is used to point the observatory.

The work to remove the old port-side solar array and install a new, more powerful one will be quite similar to the job performed early Monday by the mission's other spacewalking team of John Grunsfeld and Rick Linnehan.

Tonight will see Newman as the "free floating" astronaut and Massimino as the crewman riding on the end of the shuttle's robotic arm. Newman will work to disconnect the old array and later bolt the new one in place and hook up cabling. Massimino will transport the old structure to the payload bay to be stowed for the return to Earth and hand-carry the new array to the telescope. Mission specialist Nancy Currie will be the robot arm operator.

After the array replacement is completed, the spacewalkers will turn their attention to changing out the Reaction Wheel Assembly in the telescope's Bay 6. Massimino will ride the arm to Bay 6, remove the old wheel and then carry it to the payload bay where Newman will be waiting with the new component. They will exchange wheels and Massimino will take the new device back to Bay 6 for installation, while Newman stows the old wheel for the ride home.

MONDAY, MARCH 4, 2002

Shuttle Columbia astronauts John Grunsfeld and Rick Linnehan removed the Hubble Space Telescope's starboard solar array this morning and installed a new, more powerful array during a successful seven-hour spacewalk. It was the first of five consecutive days of spacewalks scheduled for Columbia's mission to rejuvenate the observatory. Read our full story.

1348 GMT (8:48 a.m. EST)

Today's spacewalk came to an official end at 8:38 a.m. EST (1338 GMT) and had a duration of seven hours and one minute.

1340 GMT (8:40 a.m. EST)

Repressurization of the airlock is underway. Controllers are about to move the newly installed solar array as part of its functional test.

1330 GMT (8:30 a.m. EST)

The airlock outer hatch is closed.

1326 GMT (8:26 a.m. EST)

The two spacewalkers have returned to Columbia's airlock as they wrap up their spacewalk to install Hubble's first new solar array.

1322 GMT (8:22 a.m. EST)

Mission control reports the aliveness test of the new solar array was successful. A functional test to check the array can turn to track the sun will follow shortly.

1304 GMT (8:04 a.m. EST)

The two spacewalkers have completed all their major tasks for this spacewalk. Linnehan has successfully installed thermal covers on two of the telescope's equipment bays to ensure crucial components don't get too cold when the observatory is switched off on Wednesday for the replacement of the power control unit. They are now stowing and checking their tools before returning to the airlock.

1245 GMT (7:45 a.m. EST)

The final major cable has been connected by Grunsfeld to route power from the new solar array to Hubble. An "aliveness test" can now be performed to verify the health of the new array. Meanwhile, Linnehan continues the installation of thermal blankets on the telescope.

1237 GMT (7:37 a.m. EST)

Now six hours into today's spacewalk.

1208 GMT (7:08 a.m. EST)

The two spacewalkers are swapping places. Grunsfeld will take up position on the robot arm, while Linnehan works free-floating. Mission control's EVA officer reports the spacewalkers are running about 30 minutes behind schedule.

1149 GMT (6:49 a.m. EST)

The locking bolts have been tightened, completing most of the work to install the first new solar array.

Linnehan will now move on to install an insulation cover over the telescope's equipment bay 10. This is to keep warm the scientific instrument command and data handling computer while the observatory is switched off during the replacement of the power control unit, scheduled for Wednesday.

Meanwhile, Grunsfeld will connect a cable to connect the new array to route power to Hubble's batteries.

1143 GMT (6:43 a.m. EST)

The EVA officer in mission control reports the spacewalkers are running about 20 minutes behind schedule, but they have plenty of consumables to finish all their planned tasks.

1141 GMT (6:41 a.m. EST)

The new array is now completely unfolded and Linnehan will start work tightening the bolts to lock the array open.

1136 GMT (6:36 a.m. EST)

Linnehan is now carefully unfolding the brand new solar array on the starboard side of the Hubble Space Telescope.

1125 GMT (6:25 a.m. EST)

After some extra effort, Linnehan has finally gotten all four latches secured to hold down the old array. And Mission Control has given the spacewalkers a "go" to deploy, or open up, the new array.

1100 GMT (6:00 a.m. EST)

Cables are being connected with the new starboard solar array by spacewalker Grunsfeld. Meanwhile, spacewalker Linnehan is having some difficultly locking a fourth and final clamp that will hold the old array to the carrier aboard Columbia for return to Earth. All four clamps are required to be secured.

1030 GMT (5:30 a.m. EST)

Hubble has received the first of two new, more powerful solar arrays. The spacewalkers have physically attached the starboard array and work to connect cabling is underway before it is opened up.

The new arrays are the third set built for the observatory. Hubble's first two pairs were flexible and rolled up like window shades. The newest ones are flat and rigid and fold up like a book rather than roll up.

Here is the NASA fact sheet on the new arrays:

Though one third less solar cell area, these third-generation arrays will produce 20 percent more power than the current set. The new arrays collect the extra electricity needed to power a new generation of science instruments. This added power enables all the science instruments to be powered on and ready to operate simultaneously -- allowing for more discoveries in less time.

The high efficiency solar panels have supporting frames made of aluminum-lithium, which is stronger and lighter than the type of aluminum commonly used in spacecraft construction. These supports are much less sensitive to the extreme temperature changes of Hubble's harsh environment.

During each 97-minute orbit, Hubble spends about two-thirds of its time in searing sunlight and the other third in the frigid darkness of Earth's shadow. These brutal, rapidly cycling conditions cause the temperature of the solar panels to fluctuate between minus 94 degrees Fahrenheit (minus 70 degrees Celsius) and 187 degrees Fahrenheit (86 degrees Celsius). The solar arrays reach their hottest temperature just ten minutes after leaving the chill of Earth's shadow.

Such dramatic, repeated temperature changes may cause tiny vibrations and movements within a spacecraft's solar array structure. If these movements are large enough, they cause motion of the main body of the telescope, and may affect the sensitivity of Hubble's pointing control instruments and interfere with long-term science observations.

This excessive movement was observed with Hubble's original solar arrays, which were replaced in 1993 with a much more stable pair. Since then, advances in solar cell technology and spacecraft design have led to the development of even more stable and efficient solar arrays.

These smaller, stiffer arrays are easier for the astronauts to work around during servicing missions -- easier to fold up and move out of their way. Their smaller size decreases on-orbit drag and slows the rate at which Hubble's orbit decays. Over time, all low Earth orbiting satellites feel the effects of atmospheric drag and lose altitude. These new arrays will slow that rate of altitude loss.

The Hubble program bought these solar panels from the production line of a commercial system of communications satellites. At NASA's Goddard Space Flight Center in Greenbelt, Md., four of these panels were attached to an aluminum-lithium support wing structure to create each of the complete structures called "wings." A total of 8 panels were used in the construction of these two wings. Hubble team members at Goddard fabricated the support wing structures, the composite mast assembly, and the electrical assembly for these wings. By using these off-the-shelf panels and fabricating the support systems at Goddard the Hubble program saved considerable time and expense.

Hubble's new solar arrays are just the latest chapter in a longstanding, international partnership between NASA and the European Space Agency (ESA). ESA built Hubble's first two sets of solar arrays. For the newest pair, ESA designed, developed and tested the Solar Array Drive Mechanisms, which maneuver the arrays to keep them constantly pointed at the Sun.

ESA also provided the ability to test the new arrays in a unique, never-before-done way. ESA's world-class test facility in The Netherlands features a huge test chamber that can realistically simulate the extreme temperature cycles of Hubble's orbit -- including sunrise and sunset. This chamber, combined with the size of the new array and ESA's vast Hubble experience, made this facility the only place in the world capable of performing this test.

In October of 2000, one of the new arrays was shipped to the ESA test site, located at the European Space Research and Technology Center (ESTEC) in Noordwijk, The Netherlands. Here the combined ESA/NASA team conducted the special thermal test to measure the amount of movement produced within the solar array due to the harsh extremes of Hubble's environment. After extensive evaluation, the team verified that Hubble's new arrays would stay steady throughout the extreme temperature cycles of each orbit.

1025 GMT (5:25 a.m. EST)

The spacewalkers have soft-mated the new solar array to the Hubble Space Telescope. A clamp band will now be tightened to firmly hold the array in place. Then some cabling will be connected between the array and observatory. The astronauts will open the array later in this EVA.

0951 GMT (4:51 a.m. EST)

The new array is being carried from the payload bay to Hubble in the hands of spacewalker Linnehan, who is riding on the end of Columbia's robot arm.

0930 GMT (4:30 a.m. EST)

With the new diode box installed on Hubble, the two spacewalkers are working to remove the new array from the carrier aboard the shuttle.

0910 GMT (4:10 a.m. EST)

Continuing to ride on the end of the shuttle's Canadian-built robot arm, Rick Linnehan is down in the payload bay to release the new solar array from its launch carrier.

0903 GMT (4:03 a.m. EST)

The old diode box has been removed. It will be stowed on the array carrier in the payload bay to be returned to Earth.

0847 GMT (3:47 a.m. EST)

John Grunsfeld is currently disconnecting the old solar array diode box from Hubble. Rick Linnehan is preparing the new box for installation to go along with the new solar array.

0837 GMT (3:37 a.m. EST)

Now two hours into the spacewalk. The old array has been clamped down to the carrier in Columbia's payload bay for return to Earth.

0822 GMT (3:22 a.m. EST)

The starboard solar array has been removed from the Hubble Space Telescope. It is now in the hands of spacewalker Rick Linnehan, who will transport the structure to a carrier in the payload bay where it will be stowed for the trip back to Earth.

This array and its twin on the other side of the observatory were installed during the first Hubble servicing mission in 1993. They weigh 339 pounds each and measure 40 feet long by 10.8 feet wide, delivering about 4,600 watts of power from silicon solar cells.

Due to the wear and tear of temperature extremes and normal space radiation, these flexible panels now provide just 63 percent of their original power. In addition, they suffer from structural problems and some shorted circuitry in the wiring connecting all the solar cells.

Hubble's new arrays are heavier -- 640 pounds per wing -- and more powerful, generating some 5,270 watts. But they are smaller than Hubble's flexible panels, measuring just 23 feet long and 8.5 feet wide.

The additional power generated by the new gallium arsenide solar cells will enable astronomers for the first time to operate all of Hubble's instruments simultaneously for multi-disciplinary observations. In addition, their smaller size will reduce the atmospheric drag that constantly acts to reduce Hubble's altitude.

The old array on the port side of Hubble will be replaced tomorrow.

0818 GMT (3:18 a.m. EST)

The spacewalkers have folded up the old solar array boom, moving it from its perpendicular configuration to an orientation parallel to the telescope's body. Grunsfeld has also disconnected a series of cables in preparation for the actual removal of the array from Hubble.

0737 GMT (2:37 a.m. EST)

Now one hour into today's spacewalk. Grunsfeld and Linnehan are running about 10 minutes ahead of the spacewalk timeline. Since the EVA started about 10 minutes late, everything is balancing out.

The spacewalkers have moved through the early chores of this EVA, including the gathering of tools and equipment. The main task of this spacewalk -- removal and replacement of starboard solar array -- will be starting shortly.

0637 GMT (1:37 a.m. EST)

EVA 1 BEGINS. The first of five challenging spacewalks to give the 12-year old Hubble Space Telescope a makeover during this flight of shuttle Columbia has officially begun.

Astronauts John Grunsfeld and Rick Linnehan switched their suits from shuttle-provided power to internal batteries at 1:37 a.m. EST, marking the start of this planned 6 1/2-hour EVA that will see one of Hubble's solar arrays removed and replaced with one that will allow the telescope to generate more power to run its new generation set of science instruments.

Grunsfeld will disconnect the old array and Linnehan will temporarily mount it on a cargo carrier in the payload bay. Grunsfeld then will install a diode box needed to ensure power from the arrays flows to Hubble's batteries and not vice versa while Linnehan pulls the new array, folded in half, from its carrier.

Grunsfeld will attach the new solar wing, crank it open and wire it to the diode box. Another cable, known as P601, will be connected to route power to a diode box controller.

The spacewalkers also will do a bit of preparatory work needed before Hubble can be powered down for replacement of the power control unit during the third spacewalk. They will install a light shield over Hubble's star trackers and thermal covers over the Wide Field-Planetary Camera-2 and equipment bays five and 10.

This is the third spacewalk for Grunsfeld, which is wearing the suit with red stripes, and first for Linnehan who has the all-white suit.

See our update below, from 0200 GMT, for a preview of the spacewalk timeline by Grunsfeld.

We'll update this page from time to time as the spacewalk progresses.

0632 GMT (1:32 a.m. EST)

The hatch from the airlock to the payload bay has been opened.

0621 GMT (1:21 a.m. EST)

Airlock depressuziation is underway for this morning's spacewalk to service the Hubble Space Telescope. The official start time of the spacewalk will be clocked with Grunsfeld and Linnehan switch their suits to internal battery power.

0614 GMT (1:14 a.m. EST)

The hatch from the shuttle's middeck to the airlock is being closed in preparation for airlock depressurization.

0445 GMT (11:45 p.m. EST Sun.)

Mission specialists John Grunsfeld and Rick Linnehan are donning their spacesuits in preparation for the spacewalk to replace one of the power-generating solar arrays on the Hubble Space Telescope. This will be the first of five consecutive days of spacewalks to rejuvenate the observatory. Mission Control reports the astronauts are just about on the scheduled timeline, with the 6 1/2-hour spacewalk now expected to start at around 1:20 a.m. EST.

0200 GMT (9:00 p.m. EST Sun.)

The astronauts were awakened to the sounds of "Twinkle, Twinkle Little Star" a few minutes ago as the crew begins Flight Day 4 -- a day devoted to the first of five spacewalks for Columbia's mission to service the Hubble Space Telescope.

The EVA is scheduled to begin at about 1:30 a.m. EST, but could start as much as an hour early for spacewalkers John Grunsfeld and Rick Linnehan. The excursion's main goal is the removal of Hubble's starboard solar array and installation of a new, more powerful one.

In a pre-flight interview, Grunsfeld previewed this spacewalk:

"The first EVA day I think will set the stage for all five of our spacewalks. It's in the beginning of the EVA day, first of all I'll come out of the airlock. And then, Rick Linnehan will come out of the airlock. And for me that's very exciting; he's a classmate of mine. This is his third flight but his first spacewalk. And so, I'll get to see my friend and my spacewalking buddy come out of the airlock for the first time on his first spacewalk. But, we won't have much time to enjoy the view because this is a very busy day.

"This is the day where we have to set up the payload bay. We've gotten to orbit; we've grappled Hubble; put it on the servicing structure; and now we have to go and get the payload bay and Hubble ready for servicing. And, that involves a number of activities with putting a special support post under the telescope to rigidize it (the BAPS post). I'm going to put an antenna cover over a small, delicate antenna at the bottom of the telescope so that we don't inadvertently hit it. Rick is going to be setting up the shuttle robotic arm, the robotic manipulator system, with a special foot-plate that we can stand on and that holds our tools. So we'll both be very busy right at, right from the start. That'll take about an hour or so.

"Now from there, we move straight into the solar array change-out. If all goes well, the solar arrays will be all rolled up; and we'll go up on the telescope about halfway up; and we'll take off those flexible arrays that are now rolled up, we'll take them off and put them into the payload bay on the shuttle. And then, we'll take out the new solar arrays. And, they're quite a bit different than the old ones. Instead of being rolled up, they're actually rigid arrays; and they open like a book.

"So, we're going to take these roughly 9-foot-by-12-foot arrays out; and Rick is going to hold on to the array; and Nancy Currie will lift Rick up out of the payload bay, using the robotic arm, with a 640-pound solar array in front of him. Rick is then going to steer it around towards the telescope, and then together Rick and I will insert it into the fitting onto Hubble.

"And then Rick is going to open up the solar array, like a book, exposing it to sunlight. And, we'll cinch that down, clean up a little bit of the payload bay, and come back in.

"There are a few other little things that we're going to do. We're going to wrap some cables in preparation for the next EVA day where we'll put the second solar array on."

Watch this page for periodic updates throughout the spacewalk.

SUNDAY, MARCH 3, 2002
1815 GMT (1:15 p.m. EST)

NASA officials are Mission Control say this morning's retrieval of the Hubble Space Telescope and retraction of the observatory's twin solar arrays all went as planned. Read our full story.

1505 GMT (10:05 a.m. EST)

Hubble has been moved into position on its payload bay craddle for the first of five planned spacewalks to service the orbiting observatory.

1455 GMT (9:55 a.m. EST)

Flight controllers earlier today asked the crew to isolate one of the shuttle's water storage tanks because of a potential problem with one of the electricity-generating power plants. Controllers believe fuel cell No.3 might be seeping hydrogenated water and controllers want to preserve prestine water supplies needed for the space suits.

"We would like to isolate tank C until we understand the problem exactly," CAPCOM Steve MacLean told mission commander Scott Altman. "No impact right now. We are just being conservative."

The shuttle's fuel cells mix liquid oxygen and liquid hydrogen to generate electricity and water. The fuel cells are critical components and any problem with them is worth following closely.

1446 GMT (9:46 a.m. EST)

Hubble's port solar array appears to have successfully retracted, clearing the way for the first spacewalk of the mission and the installation of new more powerful, electricity-generating panels. Once again, one of two microswitches does not indicate a complete retraction and controllers are working to tighten the array.

1440 GMT (9:40 a.m. EST)

The port solar array has begun to retract.

1439 GMT (9:39 a.m. EST)

Once again a microswitch failure has stalled the retraction. The switch is being reset.

1438 GMT (9:38 a.m. EST)

The Space Telescope Operations Center has sent commands to retract the observatory's port solar array.

1437 GMT (9:37 a.m. EST)

Columbia has orbited into daylight and has been given a "go" for free-drift prior to the retraction of the port solar array.

1419 GMT (9:19 a.m. EST)

Columbia should sail into sunlight in about 15 minutes. Controllers will allow about three more minutes to allow the array to warm in the sun before retraction begins.

1415 GMT (9:15 a.m. EST)

Flight controllers are waiting for Columbia to orbit into daylight before starting the retraction of the Hubble Space Telescope's port solar array.

1349 GMT (8:49 a.m. EST)

Hubble is being rotated to bring the port solar array into view.

1342 GMT (8:42 a.m. EST)

Both microswitches are now giving a "stowed" indication. Next the telescope will be rotated 180 degrees for the port solar array retraction.

1340 GMT (8:40 a.m. EST)

Flight controllers have not received a "stowed" indication from one of two microswitches. The Space Telescope Operations Center will attempt to drive the array once more to get that second microswitch to give a "stowed" signal. This does not appear to be a significant problem as mission control's EVA officer reports that the array is sufficiently retracted for spacewalk activities.

1328 GMT (8:28 a.m. EST)

The starboard solar array blankets appear to have successfully retracted.

1323 GMT (8:23 a.m. EST)

The solar array appears to be retracting now.

1322 GMT (8:22 a.m. EST)

Mission control believes a failed microswitch might have prevented the retraction of the array. That microswitch will be reset and commands will be sent again.

1320 GMT (8:20 a.m. EST)

Commander Scott Altman reports no sign of motion in the solar array despite the fact commands were sent to retract the array.

1317 GMT (8:17 a.m. EST)

The shuttle is now in "free drift" so its maneuvering jets don't distrub the retraction of the arrays. Space telescope controllers are about to send the retraction command.

1315 GMT (8:15 a.m. EST)

The crew has been given a "go" by mission control for the retraction of the starboard array.

1314 GMT (8:14 a.m. EST)

We are standing by for the retraction of the first solar array. The crew has positioned payload bay TV cameras to observe the operation and is waiting for any motion in the arrays to dampen out before proceeding.

1307 GMT (8:07 a.m. EST)

The telescope is now in position for the retraction of the starboard solar array.

1257 GMT (7:57 a.m. EST)

The crew has been given a "go" to turn the Hubble Space Telescope into position for the starboard solar array retraction. This will allow the crew to observe the array retraction through the aft cockpit windows.

1243 GMT (7:43 a.m. EST)

The solar array slew is now complete. The crew has been given a "go" to pivot the Hubble Space Telescope on its craddle to the 75 degree position in readiness for the solar array retraction. It will take about four minutes to reach this position.

1227 GMT (7:27 a.m. EST)

The Hubble Space Telescope's solar arrays are being turned to the correct position for their retraction later today. The move should take about 14 minutes. The arrays will be parallel to Columbia's payload bay once they reach their intended position.

1051 GMT (5:51 a.m. EST)

The motorized power umbilical has been plugged into the base of Hubble from Columbia. Also, the robot arm has ungrappled the telescope, now that is berthed on the servicing platform in the shuttle's payload bay. The arm, which is fitted with several video cameras, now will be used to conduct a survey of Hubble's exterior, giving ground controllers their first close-up look at the observatory in over two years.

1032 GMT (5:32 a.m. EST)

The Hubble Space Telescope is now firmly locked down on the Flight Support System servicing platform in the rear of shuttle Columbia's payload bay.

Basically the workbench for Hubble, the platform features a Lazy Susan-like ring that the telescope actually sits on, allowing the observatory to be rotated and pivoted as needed to provide the best available access to various worksites for spacewalkers and the upcoming retraction of the solar arrays.

The craft's arrays are to be rolled up starting in about three hours.

But before the retraction occurs, the shuttle will be maneuvered to an attitude where the arrays can recharge Hubble's onboard batteries. The arrays were positioned for the retrieval in such a way that they weren't able to collect enough sunlight to properly recharge the batteries. An umbilical will also be attached to Hubble to supply power from the shuttle.

1017 GMT (5:17 a.m. EST)

Hubble now 15 inches above the servicing platform.

1014 GMT (5:14 a.m. EST)

Mission Control reports robot arm operator Nancy Currie has now maneuvered Hubble to within three feet of the service ring in the payload bay.

0950 GMT (4:50 a.m. EST)

The shuttle's Canadian-built robotic arm is slowly moving Hubble to the rear of the payload bay where it will be lowered onto a servicing platform. Once locked down, an umbilical will be remotely connected to the telescope to provide power. And then at around 8:30 a.m. EST, the observatory's twin solar arrays will be rolled up in preparation for their replacement during the spacewalks on Monday and Tuesday. If the arrays fail to retract, then spacewalkers will toss the structures overboard as was the case with one array during the first Hubble servicing in December 1993.

0931 GMT (4:31 a.m. EST)

Columbia has retrieved the Hubble Space Telescope, setting the stage for five spacewalks to service and upgrade the observatory starting Monday morning.

Speeding along at five miles a second, some 362 miles above the Pacific Ocean southwest of Central America, the shuttle's robotic arm reached out and captured the 12 1/2-ton, 43-foot tall observatory at 4:31 a.m. EST (0931 GMT).

Robot arm operator Nancy Currie will now maneuver Hubble into the payload bay of Columbia and mount the telescope to a Lazy Susan-type service platform where it will reside for the servicing work over the next six days.

0930 GMT (4:30 a.m. EST)

The robot arm is moving in to retrieve Hubble.

0928 GMT (4:28 a.m. EST)

Commander Scott Altman has completed the approach to Hubble, flying right up to the telescope from below. The observatory is now just above the payload bay, in arm's reach for the shuttle's robotic arm to grab.

0918 GMT (4:18 a.m. EST)

Columbia continues to slowly inch ever closer to Hubble. The rendezvous is taking a bit longer than planned, so the retrieval has been delayed from the advertised time. But there is no requirement to grapple the telescope at any specific time.

0911 GMT (4:11 a.m. EST)

Now 100 feet between Columbia and Hubble.

0907 GMT (4:07 a.m. EST)

Now inside the final 150 feet to capture, closing at one-tenth of a foot per second.

0852 GMT (3:52 a.m. EST)

Distance separating the two spacecraft is now just 300 feet.

Astronaut John Grunsfeld has radioed to Mission Control that the Hubble Space Telescope appears to be in good shape. This is the first time that humans have seen the observatory up close since the last servicing mission in December 1999, a flight that Grunsfeld was also aboard.

0840 GMT (3:40 a.m. EST)

Space shuttle Columbia is currently 600 feet directly beneath the Hubble Space Telescope and continuing to close in. Commander Scott Altman is manually flying this final approach to Hubble. Retrieval of the observatory is expected in about a half-hour.

The telescope, meanwhile, has acted on commands sent from ground controllers to maneuver itself to the proper orientation for capture by the shuttle's robot arm.

0703 GMT (2:03 a.m. EST)

The Terminal Initiation burn by Columbia has been performed, putting the shuttle on a course to directly intercept the Hubble Space Telescope over the next orbit of Earth. Grapple of the telescope by the shuttle's robot arm is about two hours away.

0520 GMT (12:20 a.m. EST)

Columbia is currently 45 miles below and behind the Hubble Space Telescope, still closing in for the planned retrieval at about 4:13 a.m. EST this morning.

Mission Control reports the rendezvous is going well. The longest rendezvous maneuver ever performed by a space shuttle -- a 3 1/2 minute firing that slowed the ship by about 225 mph -- occurred over an hour ago, boosting the low point of Columbia's orbit by over 200 miles to more closely match that of the Hubble Space Telescope.

The next major event will be the Terminal Initiation burn, scheduled for 2:01 a.m. EST. That burn will occur when the shuttle is about 50,000 feet, or 9 1/2 miles behind the telescope, putting Columbia on the final approach to Hubble over the next orbit of Earth.

0155 GMT (8:55 p.m. EST)

Columbia's seven astronauts have been awakened for Flight Day 3 by Mission Control with the "Mission Impossible" theme music.

This is rendezvous day. In just over seven hours, the crew will pluck the Hubble Space Telescope out of orbit in preparation for five spacewalks to rejuvenate the 12-year old observatory.

Columbia began the two-day chase to catch Hubble at the moment of launch, which was timed to put the shuttle on the proper course to reach the telescope. Strategically performed engine firings since Friday morning have refined the trek.

As Columbia closes in the final miles, the shuttle's rendezvous radar system will begin tracking Hubble and providing range and closing rate information to the crew. During the approach toward the telescope, the shuttle will have an opportunity to conduct four, small mid-course corrections at regular intervals. As the shuttle closes in, mission specialist Nancy Currie will maneuver Columbia's robotic arm up above the payload bay to a position where it is poised to grab a capture fixture on the telescope for the actual retrieval.

Just after Columbia's fourth small course correction engine firing is completed, the shuttle will reach a point about a half-mile below the telescope. At that time, about an hour before the scheduled grapple of Hubble, commander Scott Altman will take over manual control of the approach. During the rendezvous, pilot Duane Carey will assist Altman with navigation. Mission specialist Rick Linnehan will operate a handheld laser range-finding device, aiming it through the shuttle windows at the telescope to provide Altman with supplementary distance and closing rate information. Mission Specialist Jim Newman will oversee a laptop computer program aboard Columbia, fed by real-time navigation information, which will provide Altman with additional cues to aid in controlling his approach.

Altman will slow Columbia's approach and fly up toward the telescope. When he is within 1,500 feet of the observatory, Altman will switch the shuttle's thrusters to a mode called "low-Z." In that mode, jets offset to the direction of the telescope are fired to continually slow the shuttle's approach, avoiding potential contamination of Hubble by shuttle jet exhaust. As Columbia moves within 600 feet of the observatory, it will approach the telescope at less than a half-mile per hour. As the distance between Columbia and Hubble decreases to about 200 feet, the space telescope operations ground crew will command Hubble to perform a final roll maneuver to position itself for capture. The telescope's solar arrays will remain fully deployed parallel to Hubble's optical axis.The shuttle will creep toward the observatory as it closes the final 100 feet, moving at a speed of only a few feet per minute.

Altman will fly Columbia to within 35 feet of the telescope and hold position while Currie, using a view from a camera mounted at the end of the robotic arm to gauge alignment, latches on to the telescope. The grapple is targeted for 4:13 a.m. EST as the two spacecraft fly over the South Pacific Ocean, just east of Australia.

Using views from a camera centered in the ring where the telescope will be berthed in the shuttle bay, Currie will then lower Hubble into a special cradle, called the Hubble Space Telescope Flight Support System, in Columbia's payload bay. The telescope will be latched to the FSS for the duration of the servicing work.

The Lazy Susan-type service platform can be rotated and pivoted as needed to provide the best available access to various worksites for spacewalkers or to prepare for a reboost of the telescope by Columbia.

Once on the FSS, an umbilical from Columbia will be remotely connected to Hubble to provide transmission of electrical power from the shuttle to the telescope. Then, Altman will maneuver the shuttle to allow Hubble's solar arrays to track the sun, fully charging the telescope's batteries.

About four hours after Hubble is captured, once the batteries are fully charged, commands will be sent to retract the telescope's solar arrays. These arrays will be removed and replaced with new, more powerful ones during the first two spacewalks.

SATURDAY, MARCH 2, 2002
2145 GMT (4:45 p.m. EST)

NASA managers decided this afternoon that a problem with one of space shuttle Columbia's two coolant loops will not force an early end to an ambitious mission to overhaul the Hubble Space Telescope. Read the full story.

Here are some of the latest movies from the mission for our Spaceflight Now Plus service subscribers.

Video coverage for subscribers only:

   VIDEO: DITTEMORE SAYS MISSION TO PROCEED QT or RV
   VIDEO: SATURDAY'S MISSION STATUS BRIEFING QT or RV
   VIDEO: DITTEMORE ON FREON PROBLEM QT or RV
   VIDEO: POWERFUL TRACKING CAMERA VIEW OF LAUNCH QT or RV
   VIDEO: JETTISONED EXTERNAL TANK FALLS AWAY QT or RV
   VIDEO: WATCH ENTIRE POST-LAUNCH NEWS CONFERENCE QT or RV

2030 GMT (3:30 p.m. EST)

NASA's mission management team has concluded that a blockage in Columbia's freon coolant loop No.1 will not curtail the shuttle's ambitious mission to service the Hubble Space Telescope, shuttle program manager Ron Dittemore said this afternoon.

"The decision of the management team was that we have the confidence that freon coolant loop 2 is good and stable and that the flow rate that we see in freon coolant loop 1 is large enough that it would be able to support a full nominal entry if called upon to do it all by its own. So the team decided that we would press on with the nominal mission."

Engineers believe the vibrations of launch would have exposed any problems with Columbia's coolant loop No.2 which is working normally. Also loop No.1 -- which has the blockage -- is not expected to deteriorate further.

"The guys will continue to monitor the loops very carefully," Dittemore said. "I suspect that the engineering teams will go back and scrutinize all their calculations one more time, but other than that I think this is behind us."

1958 GMT (2:58 p.m. EST)

Mission managers have completed their review of Columbia's Freon coolant loop problem and decide to proceed as planned with the mission. More details as we get them.

1922 GMT (2:22 p.m. EST)

NASA's Mission Management Team is meeting now to discuss the problem with the shuttle's freon coolant loop. The meeting begain at 2 p.m. EST (1900 GMT), later than previously advertised. At the conclusion of the meeting, shuttle manager Ron Dittemore is expected to provide an update on the outcome of the meeting on NASA Television. We'll update this page as soon as we receive further information.

1525 GMT (10:25 a.m. EST)

NASA managers are increasingly optimistic problems with one of the shuttle Columbia's two coolant loops will not force an early end to a dramatic mission to overhaul the Hubble Space Telescope. Read the full story.

1302 GMT (8:02 a.m. EST)

The Hubble Space Telescope's aperture door has been closed in readiness for the upcoming service call by shuttle Columbia.

0630 GMT (1:30 a.m. EST)

The seven Columbia astronauts are settling into their first full work day in orbit, a day devoted to preparing for retrieval of the Hubble Space Telescope and the five subsequent spacewalks to service and upgrade the observatory.

Activities on tap include testing of Columbia's 50-foot robotic arm, which will be used to grapple Hubble and place the telescope into the payload bay, as well as moving the spacewalkers around. The astronauts will also check out the spacesuits to be worn during the spacewalks and the tools needed to work on Hubble. And the shuttle's cabin air pressure will be lowered from 14.7 psi to 10.2 psi. The lower pressure will help spacewalkers purge nitrogen from their bloodstreams, a routine preparatory step for EVAs.

0225 GMT (Fri. 9:25 p.m. EST)

The crew of space shuttle Columbia was awakened by mission control at 9:22 p.m. EST this evening with the song "Blue Telescope" by John Hiatt to begin its first full day in orbit. At the time the Hubble Space Telescope was over the South Pacific about 8,000 miles behind the orbiter.

0010 GMT (Fri. 7:10 p.m. EST)

Shuttle program manager Ron Dittemore says a potential problem with Columbia's freon loop is unlikely to force the shuttle home early. NASA's mission management team met today at 6 p.m. EST and will reconvene tomorrow at 1 p.m. to further review the problem.

"We believe we are safe to continue on orbit for the next 24 hours, while we continue to look at further information and to refine our analysis," Dittemore said. "This analysis, we firmly believe, will conclude that we are safe to continue the mission for the full duration."

FRIDAY, MARCH 1, 2002
1727 GMT (12:27 p.m. EST)

A few moments ago, CAPCOM Steve MacLean gave shuttle commander Scott Altman this update on the orbiter's freon loop problem: "We on the ground are looking at the degraded flow in Freon loop 1 and at present we are pressing on with the nominal timeline. However, there is an MMT [Mission Management Team meeting] at 5 p.m. where they will discuss the details and impacts of the degraded flow. So first thing in the morning we will give you the outcome of their discussion and we are all hoping that we can rendezvous with the Hubble and fix it."

See our earlier update below for further details on this potential problem.

1630 GMT (11:30 a.m. EST)

This from Bill Harwood:

Flight controllers are troubleshooting apparent problems with one of the Freon coolant loops used to carry away heat generated by the shuttle Columbia's electronics systems. While the trouble has not yet had any impact on Columbia's mission to upgrade the Hubble Space Telescope, NASA's mission management team plans to meet late today to discuss the issue.

Columbia's crew, meanwhile, has completed its post-launch work to rig the space shuttle for orbital flight. Other than a bit of trouble coaxing the shuttle's inner airlock hatch open, the astronauts have not had any major problems. Following a short rocket firing to fine tune their approach to Hubble, the astronauts plan to call it a day and go to bed around 1:22 p.m. They will be awakened at 9:22 p.m. to begin their first full day in orbit.

The shuttle's ascent today was virtually flawless. But just before the ship's cargo bay doors were opened, when coolant loop radiators on the inner side of each door were still being bypassed, data indicated the flow of coolant through one loop was sharply reduced.

Once Columbia's cargo bay doors were opened and Freon-21 began flowing through a radiator in the left-side payload bay door, the cooling rate returned to normal. But the reduced flow presumably will show back up when the cargo doors are closed for landing and the radiators are once again in bypass mode. From that point forward, the heat carried away by the Freon-21 must be dissipated by boiling water or, depending on the shuttle's altitude, ammonia.

NASA flight rules require a minimum coolant flow rate of 211 pounds of Freon-21 per hour in each coolant loop. Just before Columbia's cargo bay doors were opened today, engineers saw the flow rate in one loop drop to near the flight rule redline.

The shuttle must have active cooling for re-entry. To protect against the possibility of a second failure, NASA's flight rules call for landing at the earliest U.S. opportunity if one of the coolant loops is declared failed. That's not the case here, but with a flow rate so close to the redline, NASA's mission management team plans to meet at 6 p.m. this evening to discuss the problem and possible workarounds. While there is no mission impact at present, this is an issue that will bear watching over the next few days.

Here are some movies of today's launch for our Spaceflight Now Plus service subscribers. More clips are on the way!

Video coverage for subscribers only:

   VIDEO: TOWER VIEW OF LAUNCH QT or RV
   VIDEO: 3-MINUTE REPLAY OF COLUMBIA'S LAUNCH QT or RV
   VIDEO: SPECTACULAR VIEW WITH RISING SUN BEHIND QT or RV
   VIDEO: LAUNCH AS SEEN FROM VAB ROOF QT or RV
   VIDEO: PAD PARAMETER CAMERA'S LAUNCH VIEW QT or RV
   VIDEO: LAUNCH VIEW FROM COMPLEX 39 PRESS SITE QT or RV
   VIDEO: ASTRONAUTS DEPART CREW QUARTERS FOR PAD QT or RV
   VIDEO: PILOT CAREY CLIMBS INTO HIS SEAT QT or RV
   VIDEO: MASSIMINO CRAWLS TO HIS MIDDECK SEAT QT or RV

1322 GMT (8:22 a.m. EST)

T+plus 2 hours. Columbia's two 60-foot long payload bay doors have been swung open and Mission Control has given the astronauts the "go" for on-orbit operations following today's successful launch into space. Next up will be deployment of the Ku-band radar and TV antenna.

1251 GMT (7:51 a.m. EST)

T+plus 89 minutes. Mission Control has given the Columbia crew a "go" to open the payload bay doors.

NASA officials report the shuttle's climb to orbit was flawless and no problems are being addressed with the vehicle at this time.

Columbia returns to space for the first time since July 1999. Over the past couple of years the oldest ship in the fleet underwent a major overhaul.

1207 GMT (7:07 a.m. EST)

T+plus 45 minutes. The twin Orbital Maneuvering System engines on the tail of Columbia have been fired successfully to propel the shuttle the rest of the way to orbit. Columbia is now circling Earth in a 357 by 121 statute mile orbit, NASA reports.

The next major event will be opening Columbia's payload bay doors in about an hour.

1153 GMT (6:53 a.m. EST)

T+plus 31 minutes. Mission Control reports the Orbital Maneuvering System engine firing to boost the shuttle from its current sub-orbital trajectory to a safe orbit will occur in about 12 minutes.

1142 GMT (6:42 a.m. EST)

T+plus 20 minutes. The official launch time this morning was 6:22:02.080 a.m. EST.

1137 GMT (6:37 a.m. EST)

T+plus 15 minutes. Columbia's three APU hydraulic-powering units have been shut down. They won't be needed until an entry system checkout on the day before landing, and then again for Columbia's high-speed return to Earth and touchdown.

1130 GMT (6:30 a.m. EST)

T+plus 8 minutes, 50 seconds. The emptied external tank has been jettisoned from the belly of space shuttle Columbia. The tank will fall back into the atmosphere where it will burn up harmlessly.

1130 GMT (6:30 a.m. EST)

T+plus 8 minutes, 30 seconds. MECO! Confirmation that Columbia's main engines have cutoff as planned, completing the powered phase of the launch. Space shuttle Columbia has safely embarked on its two-day chase to rendezvous with the Hubble Space Telescope on Sunday at 4:14 a.m. EST.

1130 GMT (6:30 a.m. EST)

T+plus 8 minutes. The main engines beginning to throttle back to ease the force of gravity on the shuttle and astronauts.

1129 GMT (6:29 a.m. EST)

T+plus 7 minutes, 30 seconds. Columbia remains on the proper course. A good launch so far.

1128 GMT (6:28 a.m. EST)

T+plus 6 minutes, 30 seconds. Three good main engines, three good fuel cells, three good hydraulic power units. Velocity 10,000 miles per hour, downrange distance 405 miles.

1127 GMT (6:27 a.m. EST)

T+plus 5 minutes, 15 seconds. Columbia can now reach a orbit on the power of two main engines should one fail. But all three continue to fire properly.

1126 GMT (6:26 a.m. EST)

T+plus 4 minutes, 20 seconds. Altitude 62 miles, downrange distance 165 miles.

1126 GMT (6:26 a.m. EST)

T+plus 4 minutes, 10 seconds. Negative return. The shuttle is traveling too fast and is too far downrange so it can no longer return to the launch site in the event of a main engine problem.

1125 GMT (6:25 a.m. EST)

T+plus 3 minutes. All systems continue to function normally. Altitude 42 miles, downrange distance 61 miles, speeding along at 3,400 miles per hour.

1124 GMT (6:24 a.m. EST)

T+plus 2 minutes, 10 seconds. The twin solid rocket boosters have done their job and separated from the space shuttle Columbia. The shuttle continues its climb to orbit on the power of the three liquid-fueled main engines.

1123 GMT (6:23 a.m. EST)

T+plus 90 seconds. All systems of Columbia are performing well as the shuttle accelerates to orbit. Burning propellant at remarkable rates, the shuttle weighs half of what it did at liftoff.

1123 GMT (6:23 a.m. EST)

T+plus 70 seconds. Columbia's engines have throttled back up.

1122 GMT (6:22 a.m. EST)

T+plus 35 seconds. Columbia's three main engines are being throttled down to ease the shuttle's passage through the dense lower altitude.

1122 GMT (6:22 a.m. EST)

T+plus 20 seconds. The shuttle has rolled to a heads-down, wings-level attitude and the proper due east heading for a 28.5 degree inclination orbit. Houston has taken control of the Columbia mission.

1122 GMT (6:22 a.m. EST)

LIFTOFF! Liftoff of Columbia on a service call to the Hubble Space Telescope -- our window on the Universe. And the shuttle has cleared the tower!

1121 GMT (6:21 a.m. EST)

T-minus 31 seconds. Auto sequence start. Columbia's onboard computers have assumed control of the countdown.

In the next few seconds the solid rocket booster hydraulic power units will be started and the orbiter's body flap and speed brake will be moved to their launch positions. The main engine ignition will begin at T-minus 6.6 seconds.

1121 GMT (6:21 a.m. EST)

T-minus 1 minute. Computers verifying that the main engines are ready for ignition. Sound suppression water system is armed. System will activate at T-minus 16 seconds to suppress the sound produced at launch. Residual hydrogen burn ignitors have been armed. They will be fired at T-minus 10 seconds to burn off any hydrogen gas from beneath the main engine nozzles. And the solid rocket booster joint heaters have been deactivated.

Shortly the external tank strut heaters will be turned off; Columbia will transition to internal power; the liquid oxygen and liquid hydrogen outboard fill and drain valves will be closed; the payload bay vent doors will be positioned for the launch; and the gaseous oxygen vent arm will be verified fully retracted.

1119 GMT (6:19 a.m. EST)

T-minus 2 minutes, 30 seconds. Orbiter steering check now complete -- the main engine nozzles in their start positions. The external tank liquid oxygen vent valve has been closed and pressurization of the LOX tank has started. Standing by to transfer Columbia's power-producing fuel cells to internal reactants. The units will begin providing all electricity for the mission beginning at T-50 seconds. And pilot Duane Carey has been asked to clear the caution and warning memory system aboard Columbia.

In the next few seconds the gaseous oxygen vent hood will be removed from the top of the external tank. Verification that the swing arm is fully retracted will be made by the ground launch sequencer at the T-37 second mark.

Coming up on T-minus 2 minutes. The astronauts will be instructed to close and lock the visors on their launch and entry helmets. At T-minus 1 minute, 57 seconds the replenishment of the flight load of liquid hydrogen in the external tank will be terminated and tank pressurization will begin.

1118 GMT (6:18 a.m. EST)

T-minus 3 minutes, 30 seconds. The main engine nozzles are now being moved through a computer controlled test pattern to demonstrate their readiness to support guidance control during launch today.

1118 GMT (6:18 a.m. EST)

T-minus 4 minutes. Activation of the APUs complete. The three units are up and running. The final helium purge sequence is under way in the main propulsion system. This procedure readies fuel system valves for engine start. In the next few seconds the aerosurfaces of Columbia will be run through a pre-planned mobility test to ensure readiness for launch. This is also a dress rehearsal for flight of the orbiter's hydraulic systems.

1117 GMT (6:17 a.m. EST)

T-minus 5 minutes. Go for Auxiliary Power Unit start. Pilot Duane Carey is now flipping three switches in Columbia's cockpit to start each of the three APU's. The units, located in the aft compartment of Columbia, provide the pressure needed to power the hydraulic systems of the shuttle. The units will be used during the launch and landing phases of the mission for such events are moving the orbiter's aerosurfaces, gimbaling the main engine nozzles and deploying the landing gear.

Over the course of the next minute, the orbiter's heaters will be configured for launch by commander Scott Altman, the fuel valve heaters on the main engines will be turned off in preparation for engine ignition at T-6.6 seconds and the external tank and solid rocket booster safe and arm devices will be armed.

1116 GMT (6:16 a.m. EST)

T-minus 5 minutes, 30 seconds. APU pre-start is complete and the units are ready for activation. The orbiters flight data recorders now in the record mode to collect measurements of shuttle systems performance during flight.

1116 GMT (6:16 a.m. EST)

T-minus 6 minutes. Pilot Duane Carey has been asked by Orbiter Test Conductor Jeff Lauffer to pre-start the orbiter Auxiliary Power Units. This procedure readies the three APU's for their activation after the countdown passes T-minus 5 minutes.

1114 GMT (6:14 a.m. EST)

T-minus 7 minutes, 30 seconds. The ground launch sequencer is now pulling the orbiter access arm away from the crew hatch on the port side of the vehicle. The arm was the passage way for the astronauts to board Columbia a few hours ago. The arm can be re-extended in about a quarter of a minute should the need arise later in the countdown.

1114 GMT (6:14 a.m. EST)

T-minus 8 minutes and counting. Pilot Duane Carey has flipped the switches in the cockpit of Columbia to directly connect the three onboard fuel cells with the essential power buses. Also, the stored program commands have been issued to the orbiter for the final antenna alignment and management for today's launch.

1113 GMT (6:13 a.m. EST)

T-minus 9 minutes and counting. The ground launch sequencer is now controlling the final phase of today's countdown to launch of space shuttle Columbia at 6:22 a.m. EST. The GLS will monitor as many as a thousand different measurements to ensure they do not fall out of predetermine red-line limits.

The launch of STS-109 will mark the 108th flight in the space shuttle program since 1981, the 83rd since return-to-flight after Challenger, the 27th for Columbia and the first shuttle flight of 2002.

1112 GMT (6:12 a.m. EST)

One minute remaining in this built-in hold. All systems are "go" for launch today at 6:22:02 a.m. EST.

Once the countdown picks up, the Ground Launch Sequencer will be initiated. The master computer program is located in a console in Firing Room 1 of the Complex 39 Launch Control Center. The GLS is the master of events through liftoff. During the last 9 minutes of the countdown, the computer will monitor as many as a thousand different systems and measurements to ensure that they do not fall out of any pre-determine red-line limits. At T-minus 31 seconds, the GLS will hand off to the onboard computers of Columbia to complete their own automatic sequence of events through the final half minute of the countdown.

1109 GMT (6:09 a.m. EST)

NASA Launch Director Mike Leinbach has polled senior officials and no technical problems were announced. And the local weather conditions will be acceptable for launch this morning; the low clouds won't be a problem.

Countdown will resume from the T-minus 9 minute mark in four minutes.

1108 GMT (6:08 a.m. EST)

The final readiness poll by NASA Test Director Steve Altemus has been completed with all launch team members reporting "go", including the orbiter, external tank, solid rocket boosters, safety personnel, Eastern Range and the astronaut crew. Mission Control also has given its "go" which indictates weather at the Shuttle Landing Facility and other abort landing sites will not be a factor against launch today.

1106 GMT (6:06 a.m. EST)

Range is now "go" for launch.

Final readiness polls of the launch team and managers will be performed shortly to determine if all is in readiness to resume the countdown for an on-time liftoff today at 6:22 a.m. EST. There is optimism the weather will cooperate after all.

1104 GMT (6:04 a.m. EST)

Range just announced it is "no go" for launch. Countdown clock is scheduled to resume in 9 minutes.

1102 GMT (6:02 a.m. EST)

Now 20 minutes from launch.

1050 GMT (5:50 a.m. EST)

At the moment, the weather is reported to be acceptable for launch. But the low clouds over Central Florida appear to be in bands, so the situation remains a bit dynamic.

Chief NASA astronaut Charlie Precourt continues to feed real-time weather observations to meteorologists as he pilots the shuttle training aircraft in the skies over Kennedy Space Center.

1047 GMT (5:47 a.m. EST)

Now 35 minutes away from Columbia's planned launch from Kennedy Space Center in Florida to begin the fourth Hubble Space Telescope servicing mission, weather permitting.

After the 8 1/2-minute launch, Columbia should achieve a suborbital trajectory with a high point of 303 nautical miles and low point of 30 nautical miles. A two-minute firing of the twin orbital maneuvering system engines on the tail of Columbia about 43 minutes into flight will raise the orbit's low end as the shuttle races to catch Hubble. The rendezvous is scheduled to conclude at about 4:14 a.m. EST Sunday with the grapple of the telescope by the shuttle's robotic arm.

1032 GMT (5:32 a.m. EST)

T-minus 9 minutes and holding. Countdown clocks have gone into the planned 41-minute, 2-second built-in hold. Today's launch remains set for 6:22:02 a.m. EST. There are no significant technical problems being reported. Weather continues to be watched, however, with low clouds a real concern at the moment. This hold will be extended if the weather prohibits an on-time launch this morning.

The flow rate of conditioned air into the payload bay of Columbia has been adjusted and the fuel cell load has been tweaked per the normal plan.

1030 GMT (5:30 a.m. EST)

The Orbital Maneuvering System/Reaction Control System crossfeed valves are configured for launch. The Main Propulsion System helium system has been reconfigured. The gaseous nitrogen purge to the aft skirts of the solid rocket boosters is starting.

1029 GMT (5:29 a.m. EST)

Mission Control in Houston is loading Columbia's onboard computers with the proper guidance parameters based on the projected launch time. Pilot Duane Carey is configuring the displays inside Columbia's cockpit for launch while commander Scott Altman enables the abort steering instrumentation.

1021 GMT (5:21 a.m. EST)

T-minus 20 minutes and counting. The countdown has resumed after a 10-minute hold. Clocks will tick down for the next 11 minutes to the T-minus 9 minute mark where the final planned hold is scheduled to occur. The hold length will be adjusted to synch up with today's launch time of 6:22:02 a.m. EST. Today's launch window extends to 7:23:53 a.m. EST if needed.

There are no technical problems but the weather is very iffy due to low clouds developing around the area.

Columbia's onboard computers are now transitioning to the Major Mode-101 program, the primary ascent software. Also, engineers are dumping the Primary Avionics Software System (PASS) onboard computers. The data that is dumped from each of PASS computers is compared to verify that the proper software is loaded aboard for launch.

In about one minute, the astronauts will configure the backup computer to MM-101 and the test team will verify backup flight control system (BFS) computer is tracking the PASS computer systems.

1011 GMT (5:11 a.m. EST)

T-minus 20 minutes and holding. The countdown has paused for a 10-minute built-in hold. Launch remains scheduled for 6:22:02 a.m. EST. There are no technical problems, but the weather suddenly has become iffy. There are low clouds around the space center and conditions are presently "no go" for launch. Today's available launch window extends 7:24 a.m. EST.

During this built-in hold, all computer programs in Firing Room 1 of the Complex 39 Launch Control Center will be verified to ensure that the proper programs are available for the countdown; the landing convoy status will be verified and the landing sites will be checked to support an abort landing during launch today; the Inertial Measurement Unit preflight alignment will be verified completed; and preparations are made to transition the orbiter onboard computers to Major Mode 101 upon coming out of the hold. This configures the computer memory to a terminal countdown configuration.

1009 GMT (5:09 a.m. EST)

T-minus 22 minutes and counting. Standing by to go into a built-in hold at the T-minus 20 minute mark.

The shuttle's backup flight control system (BFS) computer has been configured. It would be used today in the event of emergency landing.

Also, the primary avionics software system (PASS) is transferring to Columbia's BFS computer so both systems can be synched with the same data. In case of a PASS computer system failure, the BFS computer will take over control of the shuttle vehicle during flight.

Commander Scott Altman is pressurizing the gaseous nitrogen system for Columbia's Orbital Maneuvering System engines, and pilot Duane Carey has activated the gaseous nitrogen supply for the orbiter's Auxiliary Power Units' water boilers.

1004 GMT (5:04 a.m. EST)

Chief astronaut Charlie Precourt, flying weather reconnaissance around Kennedy Space Center this morning, reports some low clouds are forming to the south of the launch site. Range Safety says it is currently "no go" for launch due to low cloud ceilings restricting the view of the shuttle during its initial portion of flight.

At this time in the countdown, the ground pyro initiator controllers (PICs) are scheduled to be powered up. They are used to fire the solid rocket hold-down posts, liquid oxygen and liquid hydrogen tail service mast and external tank vent arm system pyros at liftoff and the space shuttle main engine hydrogen gas burn system prior to engine ignition.

Columbia's two Master Events Controllers have been tested. They relay the commands from the shuttle's computers to ignite, and then separate the boosters and external tank during launch.

And the Orbiter Closeout Crew has completed its job today with the hatch of Columbia sealed for flight. The crew is now preparing to depart launch pad 39A and head back to the safety roadblocks.

0958 GMT (4:58 a.m. EST)

The Orbiter Closeout Crew reports the hatch is now latched for flight, a few minutes late due to a latch glitch.

0950 GMT (4:50 a.m. EST)

The hatch has been re-closed.

Mission Control has just announced that the precise liftoff time today will be 6:22:02 a.m. EST (1122:02 GMT) based upon the latest radar tracking of the Hubble Space Telescope's orbit. The window extends to 7:23:53 a.m. EST.

The observatory will be over Sarasota, on the west coast of Florida, at the time of launch. It will pass directly over Kennedy Space Center about three minutes later.

At this point in the countdown the Ground Launch Sequencer mainline activation has been completed.

0946 GMT (4:46 a.m. EST)

The Orbiter Closeout Crew is currently checking that the latches on the hatch are working correctly. They did not get the expected indication from two of the latches when the hatch was closed initially.

0942 GMT (4:42 a.m. EST)

Columbia's side hatch has been reopened after the Orbiter Closeout Crew did not receive the proper latch indication a short time ago. Engineers are looking at the situation.

0931 GMT (4:31 a.m. EST)

T-minus 1 hour and counting. The countdown continues to this morning's scheduled 6:22 a.m. EST launch. There are two planned holds still to come -- at T-minus 20 minutes and T-minus 9 minutes.

The pre-flight alignment of Columbia's Inertial Measurement Units is now beginning, and will be completed by the T-minus 20 minute mark. The IMUs were calibrated over the past few hours of the countdown. The three units are used by the onboard navigation systems to determine the position of the orbiter in flight.

Meanwhile, the S-band antennas at the MILA tracking station here at the Cape are shifting from low power to high power. The site will provide voice, data and telemetry relay between Columbia and Mission Control during the first few minutes of flight. Coverage then is handed to a NASA Tracking and Data Relay Satellite in space.

0927 GMT (4:27 a.m. EST)

Columbia's crew module hatch is now swinging shut. Pressure and leak checks will be performed shortly to ensure a good seal on the hatch for today's launch.

0922 GMT (4:22 a.m. EST)

Now two hours away from launch time. The countdown continues extremely smoothly this morning with no problems at all.

0921 GMT (4:21 a.m. EST)

The Orbiter Closeout Crew reports all non-flight items have been removed from Columbia's crew module in preparation for closing the hatch for flight.

0857 GMT (3:57 a.m. EST)

The final Columbia astronaut has boarded the shuttle today. Nancy Currie, mission specialist No. 2 and flight engineer, has now entered the hatch. She will sit in the flight deck center seat, giving an extra set of eyes to aid the commander and pilot watch displays and switches during launch and landing.

You can read Currie's biography in our Crew Report.

Meanwhile, the ground launch sequencer software that will control the final nine minutes of the countdown is being initialized as the clock continues to today's planned launch at 6:22 a.m. EST.

Also, the solid rocket boosters' gas generator heaters in the hydraulic power units are turned on, the aft skirt gaseous nitrogen purge is starting and the rate gyro assemblies (RGAs) are being activated. The RGAs are used by the orbiter's navigation system to determine rates of motion of the boosters during the first-stage flight.

0844 GMT (3:44 a.m. EST)

Mission specialist No. 4 Jim Newman has boarded the shuttle. He will sit in the middeck center seat.

You can read Newman's biography in our Crew Report.

0840 GMT (3:40 a.m. EST)

John Grunsfeld, Columbia's mission specialist No. 1 and payload commander, has boarded the shuttle. He will sit in the flight deck aft right seat.

You can read Grunsfeld's biography in our Crew Report.

0824 GMT (3:24 a.m. EST)

Mission specialist No. 3 Rick Linnehan has boarded the shuttle. He will sit in the middeck left seat.

You can read Linnehan's biography in our Crew Report.

0822 GMT (3:22 a.m. EST)

Columbia pilot Duane Carey has entered the shuttle's hatch. He will sit in the flight deck forward right seat.

You can read Carey's biography in our Crew Report.

0808 GMT (3:08 a.m. EST)

Mission specialist No. 5 Mike Massimino has boarded Columbia. Massimino will sit in the middeck right seat.

You can read Massimino's biography in our Crew Report.

0804 GMT (3:04 a.m. EST)

Columbia commander Scott Altman has become the first astronaut to enter the shuttle this morning. He will sit in the flight deck forward left seat.

You can read Altman's biography in our Crew Report.

0757 GMT (2:57 a.m. EST)

The crew has taken the elevator to the 195-foot level of the pad structure where the Orbiter Access Arm is located with the White Room. In the White Room the crew will be outfitted with the rest of their suit gear and communications hat before entering Columbia's crew module hatch.

The countdown continues on schedule this morning with no problems to speak of. In the past few minutes the MILA tracking station here at the Cape reported that alignment of antennas with the launch pad had been completed. Also, the launch team verified there are no Launch Commit Criteria rules being violated.

0755 GMT (2:55 a.m. EST)

The shuttle astronauts have arrived at launch pad 39A. They will take the elevator up to the 195-foot level of the fixed service structure to enter Columbia's crew cabin.

0738 GMT (2:38 a.m. EST)

Columbia's astronauts have left their quarters at the Operations & Checkout Building in Kennedy Space Center's Industrial Area bound for launch pad 39A. The seven crew members walked out of the O&C Building at 2:37 a.m. EST and boarded the "AstroVan" for the 20-minute ride to the pad located on the edge of the Atlantic Ocean, about 10 miles away.

The AstroVan convoy will stop at the Launch Control Center for some members of NASA management and astronaut Charlie Precourt to exit the Astrovan. The managers will take their positions in the Firing Room while Precourt heads over to the Shuttle Landing Facility to begin weather reconnaissance flights in a T-38 jet. He will later switch to the modified Gulfstream jet, which is known as the Shuttle Training Aircraft because its flying characteristics are very similar to the space shuttle.

0731 GMT (2:31 a.m. EST)

T-minus 3 hours and counting. The countdown has resumed on scheduled from this planned two-hour built-in hold. Clocks will now tick down to T-minus 20 minutes when the next hold is planned. A final hold is scheduled at the T-minus 9 minute mark. Liftoff remains set for 6:22 a.m. EST.

The Final Inspection Team recently completed its work at launch pad 39A and has headed to the fallback area. The team did not report any problems or concerns during their inspections this morning. There was some light frost noted on the external tank but no ice.

Standing by for departure of the astronauts from crew quarters in a few minutes.

0700 GMT (2:00 a.m. EST)

The crew of space shuttle Columbia are suiting up following a routine pre-flight weather briefing with flight controllers in Houston. Weather continues to look generally acceptable, but officials will be keeping a close watch on low clouds that could form a ceiling.

The launch time forecast is calling for a few clouds at 4,000 feet, scattered clouds at 6,500 with the chance that deck could become more wide spread across the sky to be considered at "broken" status, 7 miles visibility, northeasterly winds from 040 degrees at 8 peaking to 13 knots, equating to a crosswind of 12 knots at the Kennedy Space Center Shuttle Landing Facility runway that Columbia could use if an emergency forced an abort during the first minutes of flight.

0601 GMT (1:01 a.m. EST)

The seven Columbia astronauts -- commander Scott Altman, pilot Duane Carey and mission specialists John Grunsfeld, Nancy Currie, Rick Linnehan, Jim Newman and Mike Massimino -- have finished a snack and are now posing for the traditional pre-launch photo in the dining room. They are seated around a table and have a cake decorated with the mission patch.

A weather briefing for the commander Altman, pilot Carey and flight engineer Currie is planned for 1:58 a.m. EST. At the same time, the rest of the crew will start donning their launch and entry spacesuits. Once the weather update concludes, all seven astronauts will be reunited in the suit-up room.

Departure from the crew quarters for the 20-minute ride to launch pad 39A is expected at around 2:38 a.m. EST. After arriving at the seaside pad, the astronauts will immediately begin boarding Columbia. The crew module hatch should be closed for flight at 4:22 a.m. EST.

There are no technical problems being worked by the launch team at this point in the countdown. The weather is also favorable, with just a 30 percent chance that clouds could move onshore from the Atlantic Ocean and create a low ceiling.

The launch time forecast calls for some scattered clouds in the area, winds from the northeast at 14 to 20 knots, a temperature of 55 degrees F and a relative humidity of 86 percent.

0545 GMT (12:45 a.m. EST)

Columbia stands fully fueled at launch pad 39A. The loading of liquid oxygen and liquid hydrogen into the external tank officially began at 9:17 p.m. EST. The operation went smoothly and hydrogen loading was completed at 11:57 p.m., followed by oxygen tanking at 12:15 a.m. A stable replenishment mode then started to continuously top-off the respective tanks within the external tank through the final minutes of the countdown.

Following tanking procedures, a team called the Final Inspection Team was dispatched to the pad to check the vehicle one last time prior to liftoff. The six-person team, comprised of five engineers and one safety official, is currently performing the inspections at pad 39A. At the conclusion of their two-hour tour-of-duty, they will have walked up and down the entire 380-foot fixed service structure and mobile launcher platform.

The team is on the lookout for any abnormal ice or frost build-up on the vehicle that could break-off during ignition and damage the spacecraft. The team is also searching for any loose debris that could possibly fly up and strike the vehicle at launch. And the third item of interest to the team is the thermal integrity of the external tank foam insulation.

The team uses a portable infrared scanner that gathers temperature measurements on the surface area of the shuttle and can spot leaks. The scanner will be used to obtain temperature data on the external tank, solid rocket boosters, space shuttle orbiter, main engines and launch pad structures. The scanner can also spot leaks of the cryogenic propellants, and due to its ability to detect distinct temperature differences, can spot any dangerous hydrogen fuel that is burning. One team member is also responsible for photo documentation.

Each member of the Final Inspection Team is in constant contact with the NASA Test Director in the Firing Room.

The team wears the highly visible day-glow orange coveralls that are anti-static and flame resistant. Each member also has a self-contained emergency breathing unit that holds about 10 minutes of air.

Following the Final Inspection Team's activities, they will meet with NASA Launch Director Mike Leinbach, the Mission Management Team, and engineering directors in the launch control center, providing a detailed report on the inspections and findings at the pad 39A.

A full inspection of the vehicle and pad was performed yesterday and the external tank received a thorough check prior to fueling last night.

An inspection of the launch pad and beach will be made following launch. That inspection will be to look for anything unusual, particularly anything that could have fallen off of the vehicle during the first few seconds of flight. Later, there will be a meeting to review high-speed videotape and film of the launch and early ascent to determine if there was any damage to the vehicle.

0531 GMT (12:31 a.m. EST)

T-minus 3 hours and holding. The countdown has just entered a two-hour planned built-in hold at the T-minus 3 hour mark. Activities remain on schedule for liftoff at 6:22 a.m. EST.

Columbia's external fuel tank is now full with 528,000 gallons of super-cold liquid oxygen and liquid hydrogen. Tanking was officially completed at 12:15 a.m. EST.

But given the cryogenic nature of the oxidizer and propellant, the supplies naturally boil away. So the tanks are continuously topped off until the final minutes of the countdown in a procedure called "stable replenishment."

With the hazardous tanking operation completed, the Orbiter Closeout Crew and Final Inspection Team are being dispatched to the pad to perform their jobs. The closeout crew will ready Columbia's cockpit for the astronauts' boarding in a couple of hours; and the inspection team will give the entire vehicle a check for any ice formation from fueling.

0400 GMT (11:00 p.m. EST)

The high-speed pumping of super-cold rocket fuel into the space shuttle Columbia continues at Kennedy Space Center's launch pad 39A. The loading of cryogenic oxygen and hydrogen takes about three hours and the process is about half-way completed at this point.

0225 GMT (9:25 p.m. EST)

The three-hour operation to fuel space shuttle Columbia for launch has begun. More than a half-million gallons of super-cold liquid oxygen and liquid hydrogen are being pumped into the shuttle's bullet-shaped external tank. The so-called tanking process began at 9:20 p.m. EST (0220 GMT).

There are actually two tanks inside the orange tank. The liquid oxygen tank fills the top third of the external tank. It will be filled with 143,000 gallons of liquid oxygen chilled to minus 298 degrees Fahrenheit (minus 183 degrees Celsius). The liquid hydrogen tank is contained in the bottom two-thirds of the external tank. It holds 385,000 gallons of liquid hydrogen chilled to minus 423 degrees Fahrenheit (minus 253 degrees Celsius).

The cryogenics are pumped from storage spheres at the pad, through feed lines to the mobile launcher platform, into Columbia's aft compartment and finally into the external fuel tank.

The fueling process is being orchestrated by engineers in the safe confines of the Kennedy Space Center's Launch Control Center located about 3 1/2 miles from Columbia at launch pad 39A.

0216 GMT (9:16 p.m. EST)

The Mission Management Team has completed its routine "pre-tanking meeting" at Kennedy Space Center to review status of the shuttle, countdown, ground systems and the weather forecast. Also of importance during this meeting was the final discussion of the main landing gear bearing concern.

In the end, officials concluded all was in readiness to continue the countdown and to begin fueling Columbia for launch on the fourth Hubble Space Telescope servicing mission. Liftoff is set for 6:22 a.m. EST.

The weather forecast is still predicting a 70 percent chance of acceptable conditions. The main concern will be a low cloud ceiling.

A NASA spokesman says engineers studying the bearing issue said the hardware on Columbia is safe to fly as-is.

At launch pad 39A, fueling should begin momentarily.

The seven astronauts, meanwhile, were awakened for launch day activities at about 8:30 p.m. EST. They will have breakfast at around 9:45 p.m. After a couple of hours, they will have a snack and pose for the traditional pre-launch photo in the dining room of crew quarters at 12:34 a.m. The suit-up process will start at around 2 a.m., followed by walkout from the O&C Building for the ride to the launch pad, which is targeted for 2:38 a.m. EST.

0150 GMT (8:50 p.m. EST)

The Mission Management Team meeting is underway to give a "go" to begin fueling Columbia.

THURSDAY, FEBRUARY 28, 2002
1815 GMT (1:15 p.m. EST)

The shuttle launch team is preparing to resume Columbia's countdown this afternoon following the 24-hour postponement ordered because of cold weather at Kennedy Space Center. Liftoff remains scheduled for 6:22 a.m. EST (1122 GMT) on Friday.

Air Force meteorologists are calling for a 70 percent chance of acceptable weather conditions during Friday's 62-minute launch window that extends to 7:24 a.m. EST (1224 GMT). The main concern will be low cloud ceilings.

The predicted launch time conditions include scattered stratocumulus clouds with 3-to-5/ths sky coverage at 4,000 feet and tops at 6,000 feet, visibility of 7 miles, northeasterly winds from 030 degrees at 14 peaking to 20 knots, a temperature of 55 degrees F, relative humidity of 86 percent and a dewpoint of 51 degrees F.

Should the launch be delayed to Saturday for some reason, the forecast degrades to a 40 percent chance of favorable weather due to low clouds, thick clouds and rainshowers. The forecast is even worse for Sunday with just a 30 percent chance of launching due to low clouds, thick clouds, showers, thunderstorms and anvil clouds.

The Mission Management Team will meet at about 8:30 p.m. EST tonight to review the status of the countdown and weather forecast before giving approval to begin fueling Columbia with a half-million gallons of liquid hydrogen and liquid oxygen. It is during this meeting that officials will receive a presentation from the engineers working the main landing gear bearing concern. At this point, all indications are the issue will be put to rest, clearing Columbia for launch on Friday.

The three-hour fueling process should begin around 9:30 p.m.

WEDNESDAY, FEBRUARY 27, 2002
2020 GMT (3:20 p.m. EST)

SCRUB! The forecast of cold temperatures at launch time Thursday has prompted NASA officials to delay liftoff of space shuttle Columbia by 24 hours. The launch has been rescheduled for 6:22:02 a.m. EST (1122:02 GMT) Friday when the weather is predicted to be warmer.

The space agency made the decision to postpone the launch a short time ago because meteorologists were calling for a temperature of 38 degrees F for Thursday's launch attempt. That temperature is right at the limit for being too cold to launch the shuttle given the other weather factors expected tomorrow.

The rule governing the acceptable temperature for launch is a complex one, taking into account not only the temperature but also humidity, wind speed and wind direction. See a chart of the temperature criteria.

Meanwhile, engineers continue to review the technical concern involving the shuttle's main landing gear.

1600 GMT (11:00 a.m. EST)

What should be the final day of Columbia's countdown to launch on the fourth Hubble Space Telescope servicing mission is progressing at Kennedy Space Center, but NASA is working a technical concern involving the shuttle's main landing gear that has the potential of delaying the mission.

The issue was raised late yesterday when engineers reported that wheel bearings on the shuttle's gear might not have been tested properly.

NASA said this morning that indeed all eight bearings in Columbia's main landing gear were part of manufacturing a lot that were heat treated at 300 degrees instead of 500 degrees as required.

Three engineering teams are reviewing data today and conducting tests to determine whether such bearings can perform normally under the loads of a 225-mph shuttle landing.

Engineers will present their findings to the Mission Management Team at about 9 p.m. EST tonight during a regularly scheduled meeting that is designed to give a "go" to begin fueling Columbia for launch.

The bearings cannot be replaced or even inspected at the launch pad. So if officials order such work, the shuttle would have to be rolled back to the hangar, delaying launch indefinitely.

The weather forecast is still calling for a 60 percent chance of acceptable conditions for Thursday's 66-minute launch window that opens at 6:48 a.m. EST. The main concern is the cold temperatures predicted. Air Force meteorologists are now expecting a temperature of 38 degrees F at launch time, which is the bottom limit.

Other conditions are expected to include a few clouds at 3,000 feet, visibility of 7 miles, northwesterly winds from 320 degrees at 7 gusting to 10 knots, relative humidity of 73 percent and dewpoint of 30 degrees F.

The forecast for Friday calls for an 80 percent chance of good weather. Low cloud ceilings would be the concern. For Saturday, low clouds, thick clouds, showers and thunderstorms are all in the forecast, dropping the probability of launching to just 30 percent.

TUESDAY, FEBRUARY 26, 2002

Columbia's three electricity-generating fuel cells were loaded with liquid hydrogen and liquid oxygen reactants on Tuesday as the countdown continued at Kennedy Space Center for Thursday's launch from pad 39A.

The main concern for the 6:48 a.m. EST blastoff, however, remains unseasonably cold temperatures forecast Thursday morning. Air Force meteorologists predict the temperature at launch time will be 39 degrees F, just one degree above NASA's low-temperature safety limit for the expected conditions.

The rule governing the acceptable temperature for launch is a complex one, taking into account not only the temperature but also humidity, wind speed and wind direction. See a chart of the temperature criteria.

Chilly conditions are a concern because ice can form on the shuttle's external fuel tank, which will be loaded with a half-million gallons of super-cold hydrogen and oxygen rocket fuel. Chunks of ice breaking off and falling away during liftoff could damage the orbiter.

Once the launch team begins filling the external tank at about 9:58 p.m. Wednesday, meteorologists will carefully monitor the temperature at the pad. If the temperature limit for the observed weather (including humidity and wind) is violated for 35 minutes in a row, then the launch would have to be scrubbed. But if conditions become acceptable at any point during the 35-minute period, then the violation clock is reset to zero.

Forecasters are predicting winds out of the northwest at seven knots with gusts to 10 knots at launch time. The temperature is expected to be 39 degrees with a relative humidity of 62 percent and the dewpoint at 27 degrees. Given those conditions, the shuttle would be "go" for launch. But if the temperature drops one degree lower than currently predicted and stays there for 35 minutes - and if all the other variables stay the same - the launch would be scrubbed.

2245 GMT (5:45 p.m. EST)

The Mission Management Team met this afternoon and tentatively cleared shuttle Columbia for launch Thursday. Officials formally put to rest an issue with hydraulic pump bolts that had been under review for a couple of weeks. However, a new issue involving Columbia's main landing gear wheel bearings has come to light. Technicians are sifting through records to determine if the bearings were subjected to required tests and inspections.

1700 GMT (12:00 p.m. EST)

Some valve trouble has delayed the start of loading Columbia's fuel cells for flight. The equipment was replaced and the situation is not expected to impact launch. Also, the weather forecast has been downgraded slightly to a 60 percent chance of acceptable conditions for Thursday's 6:48 a.m. EST liftoff. The change is based on the new temperature prediction at launch time of 39 degrees F, that is one degree above the limit.

For our Spaceflight Now Plus subscribers, here is the entire 18-minute countdown status briefing from this morning for a full update on progress of pre-launch activities and the weather forecast.

Video coverage for subscribers only:

   VIDEO: TODAY'S COUNTDOWN STATUS BRIEFING QT or RV
   MORE: COMPLETE SFN+ VIDEO INDEX

TUESDAY, FEBRUARY 26, 2002

The Hubble Space Telescope has cost U.S. taxpayers more than $6 billion in the quarter century since the project was approved. But to astronomers around the world, the 24,000-pound satellite is, quite simply, priceless. Read a comprehensive five-part preview of the most technically challenging - and risky - overhaul and upgrade of Hubble that NASA has ever attempted.

MONDAY, FEBRUARY 25, 2002
1500 GMT (10:00 a.m. EST)

Countdown clocks have begun ticking at Kennedy Space Center for Thursday's sunrise blastoff of shuttle Columbia on the fourth Hubble Space Telescope servicing mission. The weather forecast is calling for a 30 percent chance cold temperatures will delay the launch.

Thursday's 66-minute launch window extends from 6:48 to 7:54 a.m. EST (1148-1254 GMT).

"After an extensive modification period that spanned over two-and-a-half years, during which over 133 modifications were incorporated into (the shuttle), Columbia is poised on the launch pad with all ground and flight systems ready to go," NASA Test Director Steve Altemus told reporters at a briefing in the past hour.

Shuttle Weather Officer Ed Priselac says unseasonably cold temperatures are expected across Central Florida on Thursday morning following the passage of a cold front on Wednesday.

The launch time forecast predicts scattered stratocumulus clouds at 3,000 feet with 3/8ths sky coverage and tops at 4,500 feet, visibility of 7 miles, northwesterly winds from 320 degrees at 7 peaking to 10 knots at launch pad 39A, relative humidity of 70 percent, a temperature of 40 degrees F and dewpoint of 31 degrees F.

Meteorologists factor in the wind and humidity to determine how low the temperature can go and still be acceptable for launch. Temperatures can dip as low as 36 degrees and still be acceptable for launch as long as the winds are gusty. With winds of at least 5 to 7 knots on Thursday, the temperature needs to be at least 38 degrees.

Should the launch slip to Friday for some reason, Priselac says there is a 20 percent cold temperatures or low cloud ceilings would prohibit liftoff. The forecast for Saturday is much worse with a 70 percent chance of bad weather due to low clouds, thick clouds, showers and thunderstorms.

The countdown was started from the T-43 hour mark. Over the next three days, there are several planned holds in the countdown lasting for a total of 26 hours and 36 minutes.

Activities scheduled for today include starting the final close-outs of the shuttle and launch pad for launch, tests of back-up flight systems, reviewing flight software stored in mass memory units and display systems, loading backup flight system software into Columbia's general purpose computers, removing mid-deck and flight-deck platforms and activating and testing shuttle navigational systems. Columbia's payload bay doors are slated to be closed for flight at about 8 p.m. EST tonight.

1315 GMT (8:15 a.m. EST)

The crew of space shuttle Columbia arrived at the Kennedy Space Center overnight to begin final pre-launch preparations for an ambitious mission to service the Hubble Space Telescope. The countdown for Thursday's launch is due to get underway at 10 a.m. EST. NASA will hold a countdown status briefing for the news media at 9 a.m. EST. Check this page for updates throughout the countdown.

THURSDAY, FEBRUARY 14, 2002

Shuttle managers on Thursday affirmed plans to launch Columbia on a challenging Hubble Space Telescope servicing mission on February 28, assuming an ongoing technical analysis of bolts used in the ship's hydraulic units doesn't uncover a last-minute concern.

A "Risk Assessment Team" is conducting an investigation to determine whether dry lubrication that shouldn't have been applied to bolts will cause any problems during the upcoming mission. The bolts are used to attach the hydraulic pumps to shuttle's three Auxiliary Power Units. Engineers are trying to understand whether the lubrication would compromise the bolts' structural integrity.

As it stands now, NASA doesn't believe there is a concern with the bolts. But the analysis must be completed to show there isn't any risk in launching with the lubricated bolts.

The cargo to be launched aboard Columbia will be delivered to pad 39A early Friday. The new Reaction Wheel Assembly steering device, a late addition to the servicing mission, will be delivered to the Cape from Goddard Space Flight Center on Saturday. The wheel that had been prepped to fly was recently deemed suspect, forcing officials to call up another spare. The hardware will be installed into the shuttle's payload bay on Sunday.

Columbia, America's first space shuttle, will embark on its third decade of flight with the 6:48 a.m. EST liftoff February 28. The ship will return to orbit fresh from two years of work that have left it safer and more capable than ever before.

"This year will be as challenging, complex and exciting as any we have ever had," said Space Shuttle Program Manager Ron Dittemore. "We have more spacewalks planned in the next 12 months than we have ever done in a single year. We are going to fly diverse missions, dedicated to satellite maintenance, research and Space Station assembly, showcasing capabilities unique in the world. The shuttle team has done a great job in preparing for this mission. Returning Columbia to orbit to improve the Hubble Space Telescope is a fitting start to what will be a busy and vital year in space."

A maintenance and upgrade period completed last year installed a new "glass cockpit" in Columbia, increased its cargo capacity, strengthened its crew cabin and enhanced the protection of its cooling system from orbital debris. Columbia's new cockpit replaced mechanical instruments with 11 full-color, flat-panel displays. The new cockpit is lighter, uses less electricity and sets the stage for the next generation of improvements -- a "smart cockpit" under development that will make the cabin even more user-friendly. Columbia is the second of NASA's four space shuttles to be fitted with the new "glass cockpit." Technicians also performed comprehensive inspections of Columbia's more than 200 miles of electrical wiring, installing protection to prevent future damage in high-traffic areas. Intensive structural inspection of Columbia also was performed as well as 133 modifications and upgrades.

Columbia will fly under the command of Scott Altman (Cmdr., USN). Duane Carey (Lt. Col., USAF) will serve as pilot. Mission specialists will be John Grunsfeld, Nancy Currie (Lt. Col., USA), Richard Linnehan, James Newman and Michael Massimino. Grunsfeld, Linnehan, Newman and Massimino will work in alternating teams of two to perform the five planned spacewalks.

Columbia's flight is scheduled to end with landing back at the Kennedy Space Center on March 11. STS-109 marks the 27th mission for Columbia and the 108th in shuttle program history.

MONDAY, JANUARY 28, 2002

Columbia arrived on the launch pad early this afternoon at Kennedy Space Center following a smooth rollout from the Vehicle Assembly Building. Launch of STS-109 -- the first shuttle flight of 2002 -- remains set for 6:48 a.m. EST on February 28.

The three-day launch countdown will begin on February 25. Here is an overview of the countdown and major events. All times are EST.

Monday, Feb. 25
10:00 a.m....Countdown begins at T-minus 43 hours
10:00 a.m....BFC test and cockpit display verification
06:00 p.m....Display verification complete; fuel cell loading preps

Tuesday, Feb. 26
02:00 a.m....Countdown enters a four-hour BIH at T-minus 27 hours
03:00 a.m....Shuttle vehicle PIC resistance test
06:00 a.m....Countdown resumes
06:00 a.m....Fuel cell hydrogen/oxygen loading begins
02:00 p.m....Fuel cell loading complete
02:00 p.m....Countdown enters a four-hour BIH at T-minus 19 hours
06:00 p.m....Countdown resumes at T-minus 19 hours

Wednesday, Feb. 27
02:00 a.m....Begin a 13-hour 58-minute BIH at T-minus 11 hours
06:22 a.m....Communications system activation begins
12:00 p.m....Rotating service structure retraction
02:58 p.m....Countdown resumes at T-minus 11 hours
05:00 p.m....Clear pad
07:58 p.m....Countdown enters two-hour BIH at T-minus six hours
08:58 p.m....Mission Management Team meets to assess countdown
09:58 p.m....Countdown resumes at T-minus six hours
09:58 p.m....Fueling begins

Thursday, Feb. 28
12:58 a.m....Fueling complete
12:58 a.m....Countdown enters a two-hour BIH at T-minus three hours
02:58 a.m....Countdown resumes at T-minus 3 hours
03:05 a.m....Astronauts depart crew quarters for pad 39-A
03:35 a.m....Astronauts begin strapping in
05:38 a.m....Countdown enters a 10-minute BIH at T-minus 20 minutes
05:48 a.m....Countdown resumes at T-minus 20 minutes
05:59 a.m....Countdown enters a 40-minute BIH at T-minus nine minutes
05:59 a.m....MMT gives final "go" for launch
06:39 a.m....Countdown resumes at T-minus 9 minutes
06:43 a.m....Hydraulic power system start
06:48 a.m....Launch

1500 GMT (10:00 a.m. EST)

Running five days late because of steering troubles with its transporter, space shuttle Columbia is making the 3.5-mile trip to launch pad 39A today at Kennedy Space Center. The move began at 6:38 a.m. EST and should take about six hours to complete.

The shuttle is scheduled for blastoff February 28 on the fourth mission to service and upgrade the Hubble Space Telescope.

FRIDAY, JANUARY 25, 2002
1810 GMT (1:10 p.m. EST)

With a favorable weather forecast for Monday, NASA has decided against rolling Columbia to the launch pad on the weekend. Officials have rescheduled the move for 7 a.m. EST Monday.

THURSDAY, JANUARY 24, 2002
2230 GMT (5:30 p.m. EST)

Rollout of Columbia from Kennedy Space Center's 525-foot tall Vehicle Assembly Building to launch pad 39A has been tentatively rescheduled for no sooner than Saturday morning. The extended wait has been ordered "due to requirements to continue troubleshooting and verifying a faulty bearing in the steering linkage on one of the crawler-transporter's four 'trucks,'" NASA said in a statement late today.

NASA officials are also requiring that all of the trucks on the transporter be inspected and verified before commencing rollout activities.

The delayed rollout will not scuttle the planned February 28 launch of Columbia on the fourth Hubble Space Telescope servicing mission. The space agency said there is about a week of padding in the pre-launch processing schedule.

The launch time on February 28 is currently targeted for 6:48:14 a.m. EST (1148:14 GMT). The daily window extends 64 minutes. The timing will be revised until the final 90 minutes of the countdown based upon radar tracking of the Hubble Space Telescope's orbit.

2040 GMT (3:40 p.m. EST)

NASA public affairs said this afternoon that rollout won't occur on Friday after all as work continues to repair the crawler transporter needed to move Columbia to the launch pad. A new rollout date is pending.

1640 GMT (11:40 a.m. EST)

Efforts to repair the faulty steering system on the crawler transporter continue at Kennedy Space Center, a NASA spokesman said. Rollout of Columbia from the Vehicle Assembly Building to launch pad 39A has been tentatively rescheduled for Friday, but that assumes the crawler will be fixed in time.

Yesterday NASA had hoped the repairs would be quick, allowing Columbia to make the 3.5-mile move to the pad this morning.

1320 GMT (8:20 a.m. EST)

Shuttle Columbia's rollout to launch pad 39A has been postponed another 24 hours and is now scheduled to take place no earlier than Friday. We will post additional details on this page when information becomes available.

WEDNESDAY, JANUARY 23, 2002

Today's planned rollout of Columbia was scrubbed because of a steering problem with the massive transporter used to carry space shuttles from the Vehicle Assembly Building to the seaside launch pads at Kennedy Space Center.

The so-called "crawler-transporter" began the planned 3.5-mile trek this morning, only to have the move to pad 39A stopped a few feet later as Columbia was about to emerge from the 52-story VAB.

The Apollo-era transporter was originally built to carry the Saturn 5 moon rockets from the VAB to the Complex 39 launch pads more than 30 years ago. The diesel-powered crawler was given a new lease on life with the space shuttle program.

The 5.5-million pound, eight-track crawler hauls the shuttles at a top speed of one-mile per hour. The combined weight of the transporter, shuttle and mobile launch platform tips the scales at nearly 12 million pounds.

Engineers troubleshooting today's problem believe a bearing in the crawler's Drive Truck D is to blame, Kennedy Space Center spokesman Bruce Buckingham said.

Plans call for the crawler to be put in reverse, driving the shuttle back into the VAB so repair efforts can be attempted. If the repairs are successful, rollout could occur early Thursday morning.

Buckingham said the option of replacing the crawler with its identical twin is also possible. The swap, however, would delay rollout until Friday.

In any event, the trouble will have no impact to Columbia's planned February 28 launch on an 11-day mission to service and upgrade the Hubble Space Telescope. NASA has nine days of "contingency time" built into the schedule, giving plenty of padding to take care of problems.

Columbia's mission is a high-stakes five-spacewalk flight to install new solar arrays, a critical power switching unit and a new camera to extend the observatory's scientific reach. Read our detailed mission preview.