BY JUSTIN RAY

Follow the countdown and launch of the Delta 2 rocket with Jason 2 ocean surface measurement spacecraft. Reload this page for the very latest on the mission.

MONDAY, JUNE 30, 2008

Initial concerns about the performance of the Delta 2 rocket that launched the Jason 2 oceanography satellite from California earlier this month have proven unfounded, officials say.

Immediately after the joint U.S. and European spacecraft was deployed into orbit from the booster on June 20, NASA said the first stage appeared to have fired short of expectations and forced the second stage to make up the difference.

Further analysis, however, shows the rocket performed well within specification and that a lag in data caused early confusion about the second stage firing noticeably longer than planned.

It was the 82nd consecutive successful Delta 2 rocket launch dating back to May 1997. The Delta 2's overall history since debuting in 1989 has achieved 135 successes in 137 flights.

The venerable rocket has five more missions planned this year, including a pair of commercial launches from California's Vandenberg Air Force Base carrying the GeoEye 1 Earth-imaging satellite on August 22 and the third Italian COSMO-SkyMed radar spacecraft on October 23.

Three military flights from Florida's Cape Canaveral to loft the final two Global Positioning System Block 2R satellites and a demonstration for the Space Tracking and Surveillance System are expected in the Fourth Quarter.

FRIDAY, JUNE 20, 2008

NASA partnered with European scientists to launch an ocean research satellite from California early Friday, giving forecasters a new tool to make more accurate predictions of weather patterns and climate change.

Read our full story.

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1100 GMT (7:00 a.m. EDT; 4:00 a.m. PDT)

The Jason spacecraft unfurled its two solar arrays, a post-launch NASA statement says, and ground controllers successfully acquired signals from the satellite.

"Initial telemetry reports show it to be in excellent health."

"Together with our NASA customer, we are honored to have successfully launched this important mission which will assist meteorologists and scientists better understand global climate changes affecting our planet," said Jim Sponnick, United Launch Alliance's vice president, Delta Product Line.

A quick photo from our sound-activated camera at the launch pad is posted here. Photo credit: Chris Miller/Spaceflight Now.

Video coverage is available in our Spaceflight Now Plus service here.

Check back later today for more photos and video.

0858 GMT (4:58 a.m. EDT; 1:58 a.m. PDT)

NASA launch manager Omar Baez says engineers will be carefully studying the data from today's mission.

"There were some things in (the data) that we need to go look at. It seemed like that the first stage went a little short and it looks like the second stage had to make up for some of that. This is a high-performance mission, in other words it is a very light spacecraft for this type of rocket," Baez said.

"So maybe it's nothing, but we do have to look at the data a little bit. It looks like the satellite is in the proper orbit, but maybe some of our predicts were a little bit off and we just need to go look at that."

0844 GMT (4:44 a.m. EDT; 1:44 a.m. PDT)

Deployment of Jason's power-generating solar arrays is underway.

0841 GMT (4:41 a.m. EDT; 1:41 a.m. PDT)

T+plus 55 minutes, 14 seconds. SPACECRAFT SEPARATION! The Jason 2 spacecraft has been released from the Delta 2 rocket's second stage, completing today's launch!

0835 GMT (4:35 a.m. EDT; 1:35 a.m. PDT)

T+plus 49 minutes, 30 seconds. SECO 2. Confirmation has been received that the second stage has completed its second burn.

0835 GMT (4:35 a.m. EDT; 1:35 a.m. PDT)

T+plus 48 minutes, 45 seconds. The second stage engine firing is in progress.

0834 GMT (4:34 a.m. EDT; 1:34 a.m. PDT)

T+plus 48 minutes. Hartebeesthoek has picked up the rocket's signal as it flies northeasterly.

0831 GMT (4:31 a.m. EDT; 1:31 a.m. PDT)

T+plus 45 minutes. The next firing by the Delta rocket's second stage is coming up in four minutes. The Hartebeesthoek tracking station in South Africa should acquire the rocket shortly. The site will relay the rocket's signal back to Vandenberg to provide confirmation of the second stage burn and release of the Jason satellite.

0826 GMT (4:26 a.m. EDT; 1:26 a.m. PDT)

T+plus 40 minutes. The rocket is coasting until the second stage restarts its engine at T+plus 48 minutes, 51 seconds for a brief 24-second firing to put the vehicle into a near-circular orbit above Earth. Deployment of Jason 2 from the launch vehicle is expected 55 minutes after liftoff.

0811 GMT (4:11 a.m. EDT; 1:11 a.m. PDT)

T+plus 25 minutes. The Range liftoff time was 12:46:25.192 a.m. PDT.

0801 GMT (4:01 a.m. EDT; 1:01 a.m. PDT)

T+plus 15 minutes. The rocket has reached a 716 by 99 nautical mile orbit inclined 66.4 degrees as planned.

0757 GMT (3:57 a.m. EDT; 12:57 a.m. PDT)

T+plus 11 minutes. SECO 1. The second stage's Aerojet-made engine completed its initial burn for the launch. Delta has reached a parking orbit where it will coast until about T+plus 48 minutes.

0755 GMT (3:55 a.m. EDT; 12:55 a.m. PDT)

T+plus 9 minutes. A P-3 instrumented aircraft over the Pacific is tracking the rocket's telemetry signal as the Delta flies beyond Vandenberg's horizon.

0754 GMT (3:54 a.m. EDT; 12:54 a.m. PDT)

T+plus 7 minutes, 50 seconds. The Delta 2 rocket is 644 miles south from the launch pad and traveling at 12,400 mph.

0753 GMT (3:53 a.m. EDT; 12:53 a.m. PDT)

T+plus 6 minutes, 15 seconds. The second stage is firing normally.

0752 GMT (3:52 a.m. EDT; 12:52 a.m. PDT)

T+plus 5 minutes, 40 seconds. The Delta 2 rocket is 76 miles in altitude, 310 miles downrange, traveling over 10,500 mph.

0751 GMT (3:51 a.m. EDT; 12:51 a.m. PDT)

T+plus 5 minutes, 30 seconds. The rocket's nose cone enclosing the spacecraft has been jettisoned.

0751 GMT (3:51 a.m. EDT; 12:51 a.m. PDT)

T+plus 4 minutes, 40 seconds. The Delta's second stage engine has ignited!

0751 GMT (3:51 a.m. EDT; 12:51 a.m. PDT)

T+plus 4 minutes, 36 seconds. MECO. The first stage main engine cutoff is confirmed, and the spent stage has been jettisoned!

0750 GMT (3:50 a.m. EDT; 12:50 a.m. PDT)

T+plus 4 minutes, 10 seconds. The vehicle is 45 miles in altitude, 95 miles downrange from the launch pad and traveling at 7,200 mph.

0750 GMT (3:50 a.m. EDT; 12:50 a.m. PDT)

T+plus 3 minutes, 30 seconds. The first stage main engine continues to burn normally. The Pratt & Whitney Rocketdyne powerplant consumes kerosene fuel and liquid oxygen to produce about 200,000 pounds of thrust.

0749 GMT (3:49 a.m. EDT; 12:49 a.m. PDT)

T+plus 3 minutes, 5 seconds. The Delta 2 rocket is 32 miles in altitude, appearing as a fiery star streaking southward.

0748 GMT (3:48 a.m. EDT; 12:48 a.m. PDT)

T+plus 2 minutes, 15 seconds. The first stage main engine continues to burn normally.

0748 GMT (3:48 a.m. EDT; 12:48 a.m. PDT)

T+plus 1 minute, 40 seconds. The ground-lit boosters have jettisoned from the first stage. They remained attached until the rocket cleared off-shore oil rigs.

0747 GMT (3:47 a.m. EDT; 12:47 a.m. PDT)

T+plus 1 minute, 5 seconds. All three ground-start solid rocket boosters have burned out. The Delta 2's first stage RS-27A main engine is providing the sole thrust for the next few minutes.

0747 GMT (3:47 a.m. EDT; 12:47 a.m. PDT)

T+plus 50 seconds. The rocket has flown through the area of maximum aerodynamic pressure in the lower atmosphere. The vehicle is riding the power of its first stage main engine and the three strap-on boosters.

0746 GMT (3:46 a.m. EDT; 12:46 a.m. PDT)

T+plus 15 seconds. Delta is maneuvering on course to deliver the Jason 2 satellite into orbit to replace the aging Jason 1 spacecraft to continue a growing legacy of global sea surface measurements.

0746:25 GMT (3:46:25 a.m. EDT; 12:46:25 a.m. PDT)

LIFTOFF! Liftoff of the Delta 2 rocket with the Jason 2 satellite to observe the dynamics of Earth's oceans. And the vehicle has cleared the tower!

0745:55 GMT (3:45:55 a.m. EDT; 12:45:55 a.m. PDT)

T-minus 30 seconds. SRB ignitors will be armed at T-minus 11 seconds.

The launch ignition sequence will begin at T-minus 2 seconds when a launch team member triggers the engine start switch. The process begins with ignition of the two vernier thrusters and first stage main engine start. The three ground-lit solid rocket motors then light at T-0 for liftoff.

0745:25 GMT (3:45:25 a.m. EDT; 12:45:25 a.m. PDT)

T-minus 1 minute. The Range has given its final clear-to-launch.

0745 GMT (3:45 a.m. EDT; 12:45 a.m. PDT)

T-minus 80 seconds. First stage liquid oxygen topping to 100 percent is underway.

0744 GMT (3:44 a.m. EDT; 12:44 a.m. PDT)

T-minus 1 minute, 45 seconds. The launch pad water suppression system is being activated.

0744 GMT (3:44 a.m. EDT; 12:44 a.m. PDT)

T-minus 2 minutes. The first stage liquid oxygen vents are now being closed so the LOX tank can be pressurized for launch. Puffs of vapor from a relief valve on the rocket will be seen in the remainder of the countdown as the tank pressure stabilizes.

0743 GMT (3:43 a.m. EDT; 12:43 a.m. PDT)

T-minus 2 minutes, 30 seconds. The Jason 2 satellite has been declared "go" for launch.

0743 GMT (3:43 a.m. EDT; 12:43 a.m. PDT)

T-minus 2 minutes, 45 seconds. Vehicle ordnance is being armed.

0743 GMT (3:43 a.m. EDT; 12:43 a.m. PDT)

T-minus 3 minutes. All remains "go" for launch.

0742 GMT (3:42 a.m. EDT; 12:42 a.m. PDT)

T-minus 3 minutes, 45 seconds and counting. The Delta 2 rocket's systems are now transferring to internal power for launch. And the launch pad water system is being enabled.

0742:25 GMT (3:42:25 a.m. EDT; 12:42:25 a.m. PDT)

T-minus 4 minutes and counting! Clocks are ticking down the final moments for liftoff of Delta 2 rocket with the Jason 2 spacecraft and ANSA's Ocean Surface Topography Mission. Launch is set for 12:46:25 a.m. local time (3:46:25 a.m. EDT; 0746:25 GMT) from Vandenberg Air Force Base, California.

0741 GMT (3:41 a.m. EDT; 12:41 a.m. PDT)

Now five minutes from launch! The "go" has been given for release of the hold in one minute.

0738 GMT (3:38 a.m. EDT; 12:38 a.m. PDT)

The launch team was just polled and all systems were reported "ready."

0736 GMT (3:36 a.m. EDT; 12:36 a.m. PDT)

Now 10 minutes from launch. All appears to be ready for today's liftoff. Upper level winds are accepable and there are no technical problems being reported.

0735 GMT (3:35 a.m. EDT; 12:35 a.m. PDT)

The NASA management team has been polled and the agency is "go" for launch.

0732 GMT (3:32 a.m. EDT; 12:32 a.m. PDT)

T-minus 4 minutes and holding. The countdown has entered the final planned built-in hold. This is a scheduled 10-minute pause leading to today's liftoff time of 12:46:25 a.m. local time (3:46:25 a.m. EDT; 0746:25 GMT) for the Delta 2 rocket with Jason 2.

During the hold, officials will poll the various team members in the "soft blockhouse," Range Operations Control Center and Mission Directors Center to verify all systems are ready to enter into the final phase of the countdown.

0728 GMT (3:28 a.m. EDT; 12:28 a.m. PDT)

The first stage's kerosene fuel tank is being pressurized for launch.

0727 GMT (3:27 a.m. EDT; 12:27 a.m. PDT)

The launch weather officer has confirmed conditions are "go" for liftoff. It is a beautiful night with a star-filled sky for the Delta's ascent.

0721:25 GMT (3:21:25 a.m. EDT; 12:21:25 a.m. PDT)

T-minus 15 minutes and counting. Countdown clocks are running again following the planned 20-minute hold. The count will continue to the T-minus 4 minute mark where another hold is scheduled. Launch remains set to occur at 12:46:25 a.m. local time (3:46:25 a.m. EDT; 0746:25 GMT).

0717 GMT (3:17 a.m. EDT; 12:17 a.m. PDT)

The launch team members were just polled. All responded with a "ready" to press ahead with the countdown for liftoff 29 minutes from now.

0711 GMT (3:11 a.m. EDT; 12:11 a.m. PDT)

Now half-way through this built-in hold at T-minus 15 minutes. Once the countdown resumes, clocks will tick down to the T-minus 4 minute mark where a 10-minute hold is planned.

0708 GMT (3:08 a.m. EDT; 12:08 a.m. PDT)

The Jason 2 spacecraft atop the Delta rocket is switching to internal battery power for launch.

0701 GMT (3:01 a.m. EDT; 12:01 a.m. PDT)

T-minus 15 minutes and holding. Clocks have entered the first of two planned hold periods during the final quarter of the Terminal Countdown for today's launch. This pause will last 20 minutes in duration.

These holds are designed to give the launch team a chance to deal with any problems and catch up on work that could be running behind schedule.

0656 GMT (2:56 a.m. EDT; 11:56 p.m. PDT)

The first stage engine steering checks are complete.

0653 GMT (2:53 a.m. EDT; 11:53 p.m. PDT)

The second stage engine slews are complete. First stage tests have begun.

0651 GMT (2:51 a.m. EDT; 11:51 p.m. PDT)

The launch team is beginning the "slew" or steering checks of the first and second stage engines. These are gimbal tests of the nozzles on the first stage main engine and twin vernier engines and second stage engine to ensure the rocket will be able to steer itself during launch.

0646 GMT (2:46 a.m. EDT; 11:46 p.m. PDT)

Now one hour until liftoff. Today's launch will be:

• The 334th Delta rocket launch since 1960
• The third Delta of 2008
• The 137th Delta 2 rocket mission since 1989

0643 GMT (2:43 a.m. EDT; 11:43 p.m. PDT)

Inhibited checks are now beginning for the Range Safety command destruct receivers that would be used in destroying the Delta rocket should the vehicle veer off course or malfunction during the launch.

0636 GMT (2:36 a.m. EDT; 11:36 p.m. PDT)

T-minus 40 minutes and counting. Countdown clocks are continuing to the T-minus 15 minute mark where a 20-minute built-in hold is planned. A final 10-minute hold at T-minus 4 minutes will lead to the target liftoff time of 12:46:25 a.m. local time (3:46:25 a.m. EDT; 0746:25 GMT).

0629 GMT (2:29 a.m. EDT; 11:29 p.m. PDT)

Loading of the Delta 2 rocket's first stage liquid oxygen tank was completed at 11:29:26 p.m. local time. The operation took 26 minutes and 36 seconds today. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

The rocket is now fully fueled for launch. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel earlier today. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels on Tuesday. And the three strap-on booster rockets are solid-propellant.

0623 GMT (2:23 a.m. EDT; 11:23 p.m. PDT)

Liquid oxygen loading has been underway for 20 minutes. Once the first stage tank is 95 percent full, the "rapid load" valve will be closed and the slower "fine load" phase will continue to fill the rocket.

0616 GMT (2:16 a.m. EDT; 11:16 p.m. PDT)

Liftoff is just 90 minutes away. The Delta 2 rocket is poised to soar away from California at 12:46 a.m. local time to deliver the Jason 2 spacecraft into orbit tonight.

0613 GMT (2:13 a.m. EDT; 11:13 p.m. PDT)

Now 10 minutes into this approximate 25-minute process to fill the first stage liquid oxygen tank. A bright white plume of vapors have begun streaming from a vent on the rocket and the bottom of the vehicle is icing over as the super-cold liquid oxygen continues to flow into the first stage.

0603 GMT (2:03 a.m. EDT; 11:03 p.m. PDT)

LOX LOADING BEGINS. Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from a 28,000-gallon storage tank at Space Launch Complex-2 West, through plumbing and into the bottom of the Delta 2 rocket. The LOX will be consumed by the first stage main engine during the first four-and-a-half minutes of flight along with the 10,000 gallons of RP-1 kerosene already loaded aboard the vehicle.

0557 GMT (1:57 a.m. EDT; 10:57 p.m. PDT)

The launch team has a "go" to begin preparations for loading the rocket's first stage liquid oxygen tank as planned.

0550 GMT (1:50 a.m. EDT; 10:50 p.m. PDT)

NASA launch manager Omar Baez just polled the agency team for a "go" to begin loading the rocket's first stage liquid oxygen tank. No constraints were voiced and Baez reported all systems are in good shape right now.

0545 GMT (1:45 a.m. EDT; 10:45 p.m. PDT)

There is a 100 percent chance of acceptable launch weather tonight. At liftoff time, the Air Force launch weather officer predicts just a few cirrus clouds at 20,000 feet, 7 miles of visibility, a temperature around 60 degrees F and northerly winds at 10 knots.

Engineers are monitoring the upper level wind conditions in the atmosphere, however, that were showing close to the limits during early weather balloon runs.

0506 GMT (1:06 a.m. EDT; 10:06 p.m. PDT)

Typically at this point in a Delta 2 rocket countdown, the launch team begins loading 10,000 gallons of highly refined kerosene fuel into the first stage. However, this operation was completed earlier in the day prior to rollback of the mobile service tower.

The early fuel loading was performed to give the rocket added weight and stability in the high wind conditions experienced after the tower was retracted, leaving the Delta exposed to the weather.

The kerosene, called RP-1, will be guzzled along with liquid oxygen by the first stage RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

Filling of the stage with cryogenic liquid oxygen will begin about an hour from now.

0455 GMT (12:55 a.m. EDT; 9:55 p.m. PDT)

A collection of photos taken at the launch pad today can be seen here.

0446 GMT (12:46 a.m. EDT; 9:46 p.m. PDT)

T-minus 150 minutes and counting. The Terminal Countdown has been initiated for tonight's launch of the Jason 2 spacecraft aboard the Delta 334 vehicle.

Pre-flight activities are proceeding apace for the evening liftoff from Vandenberg Air Force Base in California. The site is on the Pacific coastline, about 140 miles northwest of Los Angeles.

Following liftoff, the vehicle will head southward as it climbs into orbit on a 55-minute flight to deploy the Jason satellite cargo.

The countdown clocks currently stand at T-minus 150 minutes and counting. Two planned holds -- at the T-minus 15 minute and the T-minus 4 minute points -- will give the launch team some time to catch up on any work running behind. The first hold will last 20 minutes in duration, the second extends 10 minutes.

Today's 9-minute launch window opens at 12:46 a.m. local time (3:46 a.m. EDT; 0746 GMT).

0438 GMT (12:38 a.m. EDT; 9:38 p.m. PDT)

The launch team has been polled to ensure all stations are manned and systems are ready to proceed with the countdown. The first stage kerosene fuel tank stands loaded for launch and the pad has been cleared of all workers.

0431 GMT (12:31 a.m. EDT; 9:31 p.m. PDT)

"Man stations for Terminal Count." That was the message just announced to the launch team in preparation for starting the Terminal Countdown some 15 minutes from now. Liftoff of the Delta 2 rocket remains targeted to occur at 12:46 a.m. local time (3:46 a.m. EDT; 0746 GMT).

0416 GMT (12:16 a.m. EDT; 9:16 p.m. PDT)

Now 30 minutes through this scheduled hour-long hold in the countdown. Mission managers and launch team members have gathered at their stations. A readiness check prior to starting the Terminal Count is coming up shortly.

0346 GMT (11:46 p.m. EDT; 8:46 p.m. PDT)

T-minus 150 minutes and holding. The countdown has just entered a planned 60-minute built-in hold at Vandenberg Air Force Base in California. The Terminal Countdown will begin once this hold is concluded. Launch remains scheduled for 12:46 a.m. local time (3:46 a.m. EDT; 0746 GMT).

0145 GMT (9:45 p.m. EDT; 6:45 p.m. PDT)

With a beautiful setting sun as backdrop, the mobile service tower has wheeled away from the ULA Delta 2 rocket at Vandenberg Air Force Base's Space Launch Complex-2 West pad. The 177-foot tall mobile service tower reached its park spot by 6:40 p.m. local time, completing a crucial step in the preparations for liftoff later this tonight.

The gantry was used to stack the two-stage vehicle, the three strap-on solid rocket motors and the Jason 2 payload atop the pad's launch mount. The tower also provided the primary weather protection and worker access to the rocket during its stay at the oceanside complex on North Vandenberg.

Ground teams will spend the next couple of hours getting the pad secured in advance of the Terminal Countdown. Launch remains targeted for 12:46 a.m. local time (3:46 a.m. EDT; 0746 GMT).

Check back later tonight for photos and video of the tower rollback.

0125 GMT (9:25 p.m. EDT; 6:25 p.m. PDT)

Rollback of the mobile service tower at the Space Launch Complex-2 West pad just got underway about 6:25 p.m. local time. Crews are moving the tower into its launch position, revealing the Delta 2 rocket for tonight's countdown.

0105 GMT (9:05 p.m. EDT; 6:05 p.m. PDT)

The Air Force meteorology team at Vandenberg recently completed another briefing to senior managers on the latest weather conditions and forecast for rollback of the mobile service tower.

The wind situation is improving. So the game plan calls for the tower to begin driving away from the rocket in about 30 minutes.

The launch team, meanwhile, is working to rearrange pre-flight tasks to keep preparations proceeding despite this delay in rolling the tower today.

0000 GMT (8:00 p.m. EDT; 5:00 p.m. PDT)

Still worried about gusty winds, rollback of the pad gantry remains on hold this afternoon. The latest retraction time is projected to be no earlier than 6:30 p.m. local time (9:30 p.m. EDT).

2015 GMT (4:15 p.m. EDT; 1:15 p.m. PDT)

Crews at Vandenberg's Space Launch Complex 2 pad are making final preparations for today's rollback of the mobile service tower from around the Delta rocket and the evening countdown to liftoff.

Weather forecasters have removed the chance of fog and clouds at the 12:46 a.m. PDT (3:46 a.m. EDT) launch time, however gusty afternoon winds have forced officials to shift the pre-flight timelines a bit.

A weather update is planned for 3 p.m. PDT (6 p.m. EDT) to assess the winds and determine when the gantry can be safely moved away and expose the rocket for launch. The tentative move time is about 6 p.m. PDT (9 p.m. EDT), based on when the winds will ease and be acceptable. The rollback would need to be underway by around 7 p.m. PDT (10 p.m. EDT) to ensure an on-time launch tonight, a NASA spokesman said.

There are no technical issues being worked.

"High pressure dominating the region continues to keep the skies clear along the Central Coast. The offshore flow has caused above average temperatures and gusty winds throughout the region," Air Force weather officials reported this morning.

"Strong northwest winds are the main concern for MST roll. Winds will increase from 20 knots at 12 p.m. local to near 30 knots by 5 p.m. local before dying down after 7 p.m. local.

"At T-0, winds at SLC-2 will be northerly at 10-15 knots. Partly cloudy skies are expected for T-0 with a few mid and high clouds. Max upper-level winds will be southwest at 65 knots near 40,000 feet with no considerable wind shear."

WEDNESDAY, JUNE 18, 2008

A joint American and European oceanography satellite designed to continue a growing legacy of monitoring changes in sea levels and the impacts on the global climate awaits an overnight blastoff Friday morning from California.

Liftoff of the United Launch Alliance Delta 2 rocket carrying the Jason 2 spacecraft is scheduled for 12:46 a.m. local time (3:46 a.m. EDT; 0746 GMT) from Vandenberg Air Force Base. The days launch opportunity extends 9 minutes.

Once placed in its orbit high above the planet, the craft will replace the aging Jason 1 satellite for the long-term tracking of the planet's oceans. The data record began with the TOPEX/Poseidon spacecraft in 1992 and continued with Jason 1's launch in 2001.

Jason 2 will fly in formation with Jason 1 for the next several months so scientists can synchronize the data from the new satellite to keep the records of ocean research consistent.

The satellite series measure ocean surface topography -- the small hills and valleys on the ocean surface that are crucial to studying global ocean circulation.

Measurements from TOPEX/Poseidon and Jason 1 have shown that mean sea level has risen by about three millimeters (0.12 inches) a year since 1993, twice the rate estimated from tide gauges in the past century.

Partners in the Jason 2 mission include NASA, NOAA, the French space agency and Europe's weather satellite agency. NASA refers to its portion of the Jason 2 project as the Ocean Surface Topography Mission.

"OSTM/Jason 2 will help create the first multi-decadal global record for understanding the vital roles of the ocean in climate change," said project scientist Lee-Lueng Fu of NASA's Jet Propulsion Laboratory. "Data from the new mission will allow us to continue monitoring global sea-level change, a field of study where current predictive models have a large degree of uncertainty."

The final launch readiness review was held Wednesday and gave approval to begin the countdown on Thursday afternoon.

"We are set to fly," said Omar Baez, the NASA launch manager.

Weather forecasters predict an 80 percent of acceptable conditions at launch time, with gusty winds posing the only threat for violating liftoff rules. But there is a chance of fog and low clouds ruining the view of the 12-story Delta rocket roaring away from its coastal pad.

Launch activities begin with retraction of the protective mobile service gantry from around the Delta rocket at the Space Launch Complex-2 West pad. Rollback is expected to occur in the mid-afternoon, after crews load 10,000 gallons of kerosene propellant into the first stage. The early fuel loading will give the rocket extra weight and stability in the windy conditions expected Thursday.

The Delta rocket will be flying in its configuration known as the 7320-10 vehicle. The two-stage launcher is fitted with just three strap-on solid-propellant motors and a 10-foot diameter composite nose cone.

After quickly climbing away from its coastal pad, the rocket will soar southward over the Pacific Ocean. The three solid boosters burn out and separate less than 100 seconds into the flight, leaving the kerosene-powered main engine to continue pushing the rocket to an altitude of 56 miles. The spent stage then jettisons to let the hydrazine-fueled second stage ignite.

Within 11 minutes, the vehicle settles into an initial parking orbit along a trajectory the cruises above the South Pacific before looping around the globe. The second stage reignites its engine for about 25 seconds off the southeastern coast of Africa.

The payload is expected to be released from the rocket 55 minutes after blastoff.

Watch this page for live updates throughout the final hours of the countdown and Jason 2's trek to orbit aboard the Delta rocket.