Mission Status Center

All testing of the various systems that run through the replaced Aft Load Control Assembly No. 2 power switchbox has been successfully completed. Shuttle Endeavour's aft engine compartment is being buttoned up once again in preparation for launch and the access doors on either side of the orbiter will be installed today.

The six-man astronaut crew is completing some last-minute refresher training at the Johnson Space Center. They are scheduled to arrive at the Kennedy Space Center on Thursday around 9 a.m. EDT in advance of the countdown clocks starting to tick Friday at 7 a.m.

"Heading back to Florida tomorrow. Hopefully this is it," commander Mark Kelly tweeted this afternoon.

Liftoff remains on schedule for next Monday at 8:56 a.m. EDT.

With shuttle Endeavour's repairs now complete, technicians at launch pad 39A are moving forward with plans for next week's liftoff. Ordnance installation and connections were completed this morning and the pad tower's access arm to the external fuel tank was retracted.

"We are done with all the troubleshooting of the problem and we're into our standard pre-countdown pad closeout work," shuttle launch director Mike Leinbach says. "We'll get into the aft closeout in earnest, and that sets us up for beginning launch countdown Friday morning."

Endeavour's six astronauts went back into medical quarantine on Monday to prepare for their mission. They spent time with more launch simulations and reviewing spacewalk procedures.

"Right now we're in good shape. Endeavour is looking good, the team is upbeat," Leinbach says. "Hopefully this time the heaters will work and we'll be able to launch on-time next Monday morning."

NASA managers met Monday and cleared the shuttle Endeavour for a second launch try May 16 after weekend work to re-wire and re-test hydraulic power system fuel line heaters blamed for derailing an April 29 launch attempt.

Read our full story.

NASA will host a live news conference from the Kennedy Space Center today at 3 p.m. EDT (1900 GMT) to provide a status update on Endeavour's repairs and plans to launch the space shuttle next Monday. We'll have live streaming video coverage right here on this page.

Launch of the shuttle Endeavour, grounded April 29 by an electrical glitch in the ship's hydraulic system, will be delayed until at least May 16 pending additional troubleshooting and repairs, NASA managers said Friday.

Read our full story.

Engineers have not yet pinned down the cause of a short circuit that vaporized fusing in a heater control power switch April 29, delaying launch of the shuttle Endeavour on its 25th and final flight. But a replacement power switching box has been installed and NASA managers have approved a plan to replace wiring between the box and the heaters in question to clear the way for a second launch attempt.

Read our full story.

Engineers inspecting a suspect electrical distribution box removed from the shuttle Endeavour after a launch scrub last week have found blown internal fusing that could be the result of an external, yet-to-be-identified short circuit somewhere in the ship's complex electrical system, officials said Wednesday. But they cautioned that troubleshooting is not yet complete and a problem with the box itself has not yet been ruled out.

Read our full story.

A new power switching box was installed into the space shuttle's rear compartment this morning, taking the Aft Load Control Assembly No. 2 (ALCA-2) position aboard Endeavour that serves critical systems throughout the vehicle. The team is awaiting further data from the old box's failure analysis before fully plugging in the replacement, however.

Positioned in the overhead avionics bay just inside the right-aft entrance doorway on Endeavour, technicians manhandled the 45-pound device into its slot with the help of guide rails.

"The work itself to replace the box is really quite easy, relatively speaking. Access is good," shuttle launch director Mike Leinbach told reporters Sunday. "It's standard work. It's just unfortunate it happened to us in (the) countdown and it's getting all this attention."

The replacement was ordered after a string of fuel line heaters on Auxiliary Power Unit No. 1 failed during last Friday's launch attempt for Endeavour's final spaceflight. Troubleshooting indicated power wasn't reaching the heaters because of a faulty component in the ALCA-2. The old box, which was removed Monday night, is undergoing full forensics at the malfunction laboratory to figure out exactly what went wrong.

There's three such Load Control Assemblies in the shuttle's aft that switch electrical feeds to various systems from the main power buses. They also enable the power paths to be changed as needed and take alternate courses for redundancy sake.

The ALCA-2 box that's been replaced controls approximately 75 functions in 9 different parts of the shuttle including the auxiliary power units, environmental control and life support, electric power distribution, solid rocket booster electronics, the water spray boilers, the main propulsion system, the main engines, orbital maneuvering system and flight controls, Leinbach said.

Although only that single set of heaters weren't working last Friday, NASA's flight rules prohibited a launch given the criticality of the hydrazine fuel in those APU-1 lines freezing in orbit.

Once the new unit is completely hooked up, a two-day checkout process will begin to verify all the systems routed through the box are working properly again.

"Any time you break a connection to a box like this, you essentially invalidate testing we did up to that point. You could take the tack of saying all you're doing is replacing the box, everything downstream of that box should be fine. Well, that's true, but the way we do business is when we break a connection we go back and retest it. It's just the prudent thing to do," Leinbach said.

The launch pad was closed for work this afternoon while technicians disconnected and safed the shuttle's ordnance systems. When the complex is reopened tonight, further inspections of the cold plate will be performed. This structure is part of the shuttle's Freon cooling system that keeps electronics from overheating. Installation of the new Aft Load Control Assembly No. 2 won't happen until sometime Wednesday.

Check out a photo gallery showing the old ALCA-2 being removed from Endeavour last night.

Endeavour's old Load Control Assembly No. 2 electronics box was removed from the space shuttle last night by technicians working in the cramped quarters of the aft compartment.

Subsequent inspections of the cold plate where the unit is mounted inside the shuttle revealed a spot of raised metal. Engineers are studying that situation to determine if any repairs are necessary before the new box can be installed.

Preps on the spare ALCA 2 are complete and the unit is set to go, once the pad crew is ready to receive it.

Meanwhile, the astronauts are back in the simulator this morning for launch training. Mission specialist Mike Fincke tweeted: "With the slip we get more sims. Welcome aboard. Oh yeah- we started at 6am" and linked to this photo.

Work to replace and retest an electrical distribution box in the shuttle Endeavour's engine compartment will push the crew's next launch attempt to at least May 10, agency managers said Monday. An official launch date is expected Friday, after repairs are complete.

Read our full story.

Mission specialist Mike Fincke just tweeted: "Now we are no earlier than Tuesday, May 10 for our launch. No worries-- we have plenty to study and the teams at the Cape are awesome."

As expected, the space shuttle and International Space Station programs met today to assess launch date options for rescheduling Endeavour's mission. Although officials still aren't sure when the shuttle will be repaired and ready to fly again, the earliest possible launch date has slipped to May 10 at 11:21 a.m. EDT (1521 GMT).

Removal of the Aft Load Control Assembly No. 2 will occur today inside the space shuttle Endeavour. Technicians were spending this morning performing additional troubleshooting on the external wiring from the ALCA 2 box to look for contributing causes for the failure.

Once the unit -- weighing between 40 and 50 pounds -- is pulled out of the shuttle, full testing of the aft compartment circuitry will be performed to ensure that was the failed component before the new box is installed tomorrow. The team will "double-check all that to ensure that there is no downstream wiring damage that might have been a cause so we don't put another (ALCA) in there and blow it too," Mission Management Team chairman Mike Moses said.

Meanwhile, the astronauts got to home Sunday night before returning into pre-flight medical quarantine this morning. Endeavour pilot Greg Johnson just tweeted: "Enjoyed an 18 hour reprieve in Houston spending an evening at home. Now we're back in quarantine ... reminds me of the movie "Groundhog Day"

Engineers have traced an electrical problem blamed for grounding the shuttle Endeavour Friday to an avionics box in the ship's engine compartment, officials said Sunday. Replacing the box will delay launch until at least May 8 -- Mother's Day -- and possibly later.

Read our full story.

We've posted a YouTube video showing technicians working inside shuttle Endeavour's cramped aft compartment this morning.

Endeavour's astronauts will be getting back into the Houston simulators for some refresher training before they return to Kennedy Space Center later this week.

The launch team are breaking out of the countdown sequence and will be starting all over again three days before next liftoff attempt.

The old Aft Load Control Assembly No. 2 box will come out of Endeavour tomorrow and be sent to the malfunction laboratory for study. The new box gets installed on Tuesday. The system retesting then takes two full days, shuttle launch director Mike Leinbach says.

The next potential launch date would appear to be Sunday, May 8 at 12:09 p.m. EDT (1609 GMT), Mike Moses says. But officials caution that they aren't making that the real target date yet.

The pre-launch Mission Management Team chairman Mike Moses says the failure does appear to reside inside the box of switches that controls power feeds through the shuttle. Schedules for performing the replacement work, the retesting after installing the new box and the failure analysis of the old unit are being refined.

His team will meet either tomorrow or Tuesday to look at options for picking a new launch date. There isn't an official launch target date yet. But liftoff likely won't happen until next weekend.

And check out some illustrations the show were the faulty load control assembly box is located in the shuttle.

See this collection of images from shuttle Endeavour's first launch attempt.

The astronauts have arrived back in Houston.

NASA is targeting 2 p.m. EDT (1800 GMT) for today's space shuttle news conference.

The astronauts are boarding the Shuttle Training Aircraft to leave Kennedy Space Center and return home to Houston for this extended delay. Endeavour pilot Greg Johnson just tweeted: "Things happen fast. We are now all aboard an STA for return to Houston. Be back in a few days. More to follow."

Engineers have traced an electrical problem blamed for grounding the shuttle Endeavour Friday to an avionics box in the ship's engine compartment, officials said Sunday. Replacing the box will delay launch past Monday, but NASA managers have not yet determined when another attempt might be possible.

Read our full story.

NASA plans to hold a news conference from the Kennedy Space Center later today to provide a full update on shuttle Endeavour's launch. A start time hasn't been set.

Launch of space shuttle Endeavour will be postponed several more days so technicians can remove and replace the faulty load control assembly switchbox in the orbiter's aft compartment. Engineers believe this device is responsible for the electrical glitch with a string of fuel line heaters on the Auxiliary Power Unit No. 1 that scrubbed last Friday's initial countdown attempt.

DELAY. NASA officials confirm that launch of space shuttle Endeavour will not happen tomorrow because additional time needed to correct the electrical troubles. A new launch date has not been established yet.

A morning engineering meeting is underway to review yesterday's test results and determine the plan for resolving Endeavour's heater problem. It appears hope is fading for launching the space shuttle tomorrow and that a further delay is likely.

The thermostats inside Endeavour failed to respond in initial low-temperature tests today. See our udpated story.

Engineers troubleshooting an electrical glitch that grounded the shuttle Endeavour Friday have verified that a cockpit fuse panel is working normally, officials said Saturday, indicating the problem likely is either an open circuit in a hydraulic system fuel line heater thermostat or a controller assembly in the shuttle's aft engine compartment.

Read our full story.

Technicians have just opened up Endeavour's aft engine compartment as they seek the cause of the heater malfunction that scrubbed yesterday's launch.

Launch pad 39A was reopened for regular work a few moments ago with confirmation that the last traces of explosive liquid hydrogen and liquid oxygen within the shuttle's external fuel tank are now fully vented.

Efforts will start to gain entry to Endeavour's aft engine compartment to determine the cause of the heater problem on Auxiliary Power Unit No. 1.

If the problem lies with the thermostats associated with that heater, replacements could be installed in time to support a launch on Monday.

NASA plans to hold a news conference at 10:30 a.m. EDT tomorrow to discuss the repair effort.

The preliminary weather forecast for shuttle Endeavour launching early next week predicts an 80 percent chance of acceptable conditions on Monday and Tuesday with only slight concerns for cumulus clouds and low ceilings. The odds drop to 60 percent on Wednesday because of greater concerns for cumulus clouds and rain showers.

"KSC will have breezy easterly winds over the weekend, with the winds gradually veering southeasterly by Monday. No other significant weather is expected. The onshore flow Monday causes a slight concern for cumulus clouds and a low cloud ceiling. Our primary concerns for launch are cumulus clouds and a low-cloud ceiling, and conditions are similar Tuesday," forecasters report.

"Wednesday, the winds shift to the southwest and the atmosphere becomes more moist as a front moves into North Florida causing a concern for isolated showers within 20 nautical miles of the Shuttle Landing Facility (SLF) and cumulus clouds within 10 nautical miles of the launch pad."

A listing of the shuttle's available launch windows is posted.


Read our earlier status center coverage.