BY JUSTIN RAY

February 21, 2000 -- Follow the launch and mission of space shuttle Endeavour on an 11-day radar mapping mission. Reload this page for the very latest on the mission.

MONDAY, FEBRUARY 21, 2000
1515 GMT (10:15 a.m. EST)

Mission Control just told Endeavour's crew to take a break and get some lunch. Engineers on the ground are evaluating further options.

Now nearly two hours since retraction was first started. Space agency officials said over the weekend that if the mast retraction could not be completed within five hours, the boom would have to be jettisoned due to thermal constraints on the shuttle. Endeavour was placed into "free drift" prior to starting the retraction in which steering and control jet thrusters were turned off. The jets cannot be reactivated until after retraction operations are completed.

1508 GMT (10:08 a.m. EST)

Some positive movement was seen when the drive motors will turned back on, pulling the mast into the canister at full torque. However, the mast lid is still not fully closed and the latches are not locked. Commander Kevin Kregel aboard Endeavour says the lid moved about a quarter-inch toward the canister's mouth then moved outward a tiny bit after the motors were turned off.

"Back to the drawing board," astronaut Steve Robinson radioed to Endeavour from Mission Control.

1503 GMT (10:03 a.m. EST)

NASA says they are going to try closing the mast canister lid again, this time with more force. The drive motors will be operated at maximum torque. It is thought that the cables that run inside the 197-foot long accordion-like mast are stiffer than thought, causing the boom to not fully fold up inside the 9-foot long canister.

1449 GMT (9:49 a.m. EST)

Mission Control just told Endeavour's astronauts that the ground team is working on a "big picture" plan that will be finished shortly.

See a picture of the unlatched mast.

1445 GMT (9:45 a.m. EST)

The latches have been opened. The astronauts reported some tiny movement but the mast lid has not fully closed. The heaters on the mast have been turned off.

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

The astronauts are beginning efforts to try again to latch the mast into a canister aboard Endeavour. The three latches were passive during the first locking attempt just like a door's latches on Earth -- they should simply lock. The latches are being powered open for the second re-stow. Also, engineers think warming up the mast by heaters and the sun might loosen any stiffness encountered during the first retraction attempt.

1433 GMT (9:33 a.m. EST)

Mission Control has developed a plan to drive the latches open and then attempt to re-stow the mast. Steps to carry out this effort are being read up to the astronauts.

1422 GMT (9:22 a.m. EST)

The benefit of a video replay shows the mast retracting normally but stopped just an inch or two short and seemed to bounce slightly outward again. NASA says the three latches should have locked automatically once the accordion-like mast was fully retracted into a 9-foot long canister. But none of the latches closed. The NASA flight rule says two of the three latches have to be locked.

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

Commander Kevin Kregel, awakened from his scheduled sleep time, says the mast is retracted enough to allow Endeavour's 60-foot long payload bay doors to be closed for tomorrow's entry and landing. He also said he would like to keep potential spacewalkers Janet Kavandi and Gerhard Thiele asleep for now. Mission Control says it does not expect a spacewalk to be ordered and is discussing other options following today's mast retraction problem.

1410 GMT (9:10 a.m. EST)

NASA says it is looking at "various options" today after the 197-foot long radar antenna mast failed to lock into place after being retracted. The boom appeared to reel in without incident before running into trouble during the last few moments.

1404 GMT (9:04 a.m. EST)

There is nothing new to report at this point. Mission Control continues to troubleshoot why the three latches on the mast's canister lid did not lock. The latches keep the mast safely in the stowed position during launch and landing. NASA says at least two of the three latches must be locked.

1354 GMT (8:54 a.m. EST)

Ground controllers are still using a camera mounted in Endeavour's payload bay to study the latches on the mast canister. The video appears to show the mast did not fully retract, stopping an inch or two shy. The canister lid is not flush against the rest of the container. None of the three latches locked either, and NASA requires at least two of them to be locked for landing.

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

Mission Control is using video cameras in Endeavour's payload bay to visually inspect the three latches that are supposed to lock, keeping the mast stowed. Indications are the three latches did not lock.

1345 GMT (8:45 a.m. EST)

NASA says the 197-foot long mast has been retracted. However, none of the three latches appear to have locked the mast into the canister. Flight rules dictate two of the three latches must be locked in order to safely keep the mast in position aboard the shuttle for entry and landing.

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

Mission controllers say they are looking into an "anomaly" seen when the latches where supposed to lock the mast into the stowed position. The mast must be latched before Endeavour can return to Earth. If it does not latch, NASA has said the mast would have to be jettisoned.

1339 GMT (8:39 a.m. EST)

The mast has been retracted and the drive motor has been turned off. Mission Control and the astronauts are trying to determine if the mast has been locked into position.

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

Mission Control says the mast retraction is going very smoothly with over half of 197-foot long structure stowed aboard Endeavour. Fifty of the mast's 86 deployed segments have been retracted.

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

So far so good aboard Endeavour as the astronauts retract the 197-foot long radar mapping mast. The structure is folding up like an accordion inside a canister mounted in the shuttle's payload bay. Thirty of the 86 external sections, or bays, of the mast have been retracted. About 10 minutes remain in the retraction.

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

About one minutes into the mast retraction. Mission Control reports seeing good voltage currents on the retraction motors. The mast stowage will take approximately 17 minutes to complete.

1319 GMT (8:19 a.m. EST)

The 197-foot long antenna mast aboard shuttle Endeavour, the longest structure ever extended in space, is now being retracted.

1316 GMT (8:16 a.m. EST)

Mission Control says the lightning conditions are acceptable aboard Endeavour and has given the astronauts "go" to begin retraction in about one minute.

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

Since the mast stow will occur while Endeavour orbits in darkness, Mission Control is discussing the lightning conditions and options to ensure good TV of the retraction.

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

The NASA press kit gives this overview of the outboard antenna mast, which will be retracted back into Endeavour's payload bay beginning in about 10 minutes.

Made of carbon fiber reinforced plastic (CFRP), stainless steel, alpha titanium, and Invar, the mast is a truss structure that consists of 87 cube-shaped sections called bays. Unique latches on the diagonal members of the truss allow the mechanism to deploy bay-by-bay out of the mast canister to a length of 60 meters (200 feet), about the length of five school buses. The canister houses the mast during launch and landing and also deploys and retracts the mast.

The mast will be deployed and retracted by a motor-driven nut within the mast canister. This nut will pull the mast from its stowed configuration and allow it to unfold like an accordion.

The mast technology enables the SRTM system to perform at the high precision necessary to achieve the desired mapping resolution. The mast supports a 360-kilogram (792-pound) antenna structure at its tip and carries 200 kilograms (440 pounds) of stranded copper, coaxial, fiber optic cables, and thruster gas lines along its length.

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

Mission Control reports mast retraction is set to begin at 1317 GMT (8:17 a.m. EST). The operation should take about 17 minutes to complete as the 197-foot long structure is folded up into a compact canister inside Endeavour's payload bay.

If the mast jams or some other problem occurs that prevents the mast from retracting, NASA has the backup option of jettisoning the entire structure from Endeavour. Paul Dye, the STS-99 lead flight director, explains how the jettison would occur:

"The jettison is actually extremely simple. There is a rotary switch that selects about four different sequences of pyros that sever the connections to the mast. If we have to jettison it, we basically let the whole canister go. The procedure doesn't take very long.

"The mission specialist will throw the switch to sever the mast, it's a simple activity with essentially no relative motion. Once it's separated, the commander takes a look at it, he thrusts downward with the shuttle, backs away from it and in a matter of about eight to 10 feet of motion we're completely clear of the mast. We pulse away a little bit more then we ... do a series of three burns that gets us away from the mast. At that point, it's gone. It's a very simple jettison, it's almost an undocking."

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

Endeavour's crew says the alignment check of the mast using the outboard antenna as the reference was successful. Alignment was within fractions of centimeters.

1238 GMT (7:38 a.m. EST)

Next up, the astronauts will use the attitude and orbit determination system to verify proper mast alignment with Endeavour before retraction starts.

You can watch an animation clip of the antenna mast being deployed from Endeavour with narration from lead flight director Paul Dye. We also have an animation slip showing the retraction procedure with Dye describing the event. Both are QuickTime files.

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

The outboard radar antenna has been flipped 180 degrees from its mapping position to the stow position. Work leading up to mast retraction is going smoothly aboard shuttle Endeavour this morning.

Live television was received from Endeavour during the flip, and Mission Control expects the downlink to continue through mast retraction over the next hour.

1223 GMT (7:23 a.m. EST)

The "milkstool" device the was used to position the outboard radar antenna has been stowed. Mission Control has given Endeavour the "go" to flip the outboard antenna 180 degrees to the launch and landing position.

1205 GMT (7:05 a.m. EST)

Astronauts Dom Gorie, Janice Voss and Mamoru Mohri are beginning the mast stow checklist with retraction just over one hour away. Early tasks in the checklist include turning on heaters, disabling various systems and checking switches in Endeavour's cockpit.

1155 GMT (6:55 a.m. EST)

Mapping of our home planet by the Shuttle Radar Topography Mission is over. Astronauts aboard shuttle Endeavour, circling 150 miles above Earth, ended radar mapping operations at 1153 GMT (6:53 a.m. EST) after sweeping across Australia, at a mission elapsed time of nine days, 18 hours and 10 minutes. By all accounts, the SRTM project has been a success, collecting data that will be used to generate the finest surface elevation map of nearly 80 percent of the Earth's surface. Mapping time was 222 hours and 23 minutes, NASA says.

The astronauts will now prepare to retract the 197-foot long radar mast extending from Endeavour. Mast stowage is scheduled to start at 1314 GMT (8:14 a.m. EST), taking just under 20 minutes to complete if all goes well. The radar system and SRTM pallet will be deactived a few minutes after mast retraction is completed.

0600 GMT (1:00 a.m. EST)

The final six hours of mapping operations are underway aboard space shuttle Endeavour. The astronauts will continue using the Shuttle Radar Topography Mission payload to map the Earth until 1153 GMT (6:53 a.m. EST) today.

The last nine hours of mapping was added into the shuttle's schedule on Friday. However, by extending the mapping time, NASA was forced to give up the option to send two spacewalking astronauts into Endeavour's payload bay to manually retract the 197-foot long outboard antenna mast. Officials decided the additional science was worth the minor risk of losing the mast if it does not retract properly.

Once mapping is completed later this morning, the astronauts will stow the mast beginning at 1314 GMT (8:14 a.m. EST). It will take just under 20 minutes for the telescoping structure to fold back up into a canister aboard Endeavour. The radar system and carrier pallet should be deactivated by 1350 GMT (8:50 a.m. EST).

"We've had everybody look at the mast, the mast deployment, we've looked at data, we've looked pictures, it's in exactly the shape we expected it to be," said Paul Dye, lead flight director for STS-99. "We saw no anomalies during deploy so we expect no anomalies during retraction."

See animation of the mast retracting. The 221k QuickTime file runs 32 seconds.

As of midday Sunday, 99 percent, or about 47 million square miles of the target area had been mapped once by SRTM. More than 87 percent of the target area -- nearly 42 million square miles -- had been twice.

At the conclusion of mapping, Endeavour's mission will have imaged 99.96 percent of the planned coverage area. The coverage area extends from Hudson Bay in the north to the tip of South America, an area equal to 47.6 million square miles. Only 80,000 square miles of the target area -- about the size of West Virginia -- will remain unmapped. However, the majority of this unmapped area is in North America and already has been accurately surveyed.

Researchers will use the wealth of data from this shuttle mission to create the best 3D surface elevation map of the Earth's surface.

"It's really difficult to comprehend the magnitude of what we're about to accomplish," said Earnest Paylor, SRTM program manager. "This truly is a magnificent accomplishment."

The astronauts will spend Monday afternoon testing Endeavour's aerosurfaces and control system jet thrusters in preparation for Tuesday's entry and landing at the Kennedy Space Center. Touchdown on the three-mile long shuttle runway in Florida is planned for 2152 GMT (4:52 p.m. EST) on Tuesday to complete the 11-day, 4-hour mission.

SUNDAY, FEBRUARY 20, 2000
1700 GMT (12:00 p.m. EST)

NASA officials have given space shuttle Endeavour's radar mapping work another extension -- this time adding 10 minutes. That will mean mapping of Earth will conclude at a mission elapsed time of nine days, 18 hours and 10 minutes, or 1153 GMT (6:53 a.m. EST) on Monday. The 197-foot long outboard antenna mast will be retracted into Endeavour's payload beginning about 80 minutes after mapping ends.

See animation of the mast retracting. The 221k QuickTime file runs 32 seconds.

Mission controllers added the time to permit one more mapping pass across Australia. The radar would have been turned off as Endeavour approached the Australian coastline without the extra 10 minutes.

So far, the Shuttle Radar Topography Mission has imaged 44.7 million square miles, or about 93.9 percent of the target area, at least once. About 33.4 million square miles or 70.1 percent of the target area has been imaged at least twice. The target area extends from 60 degrees north latitude to 56 degrees south latitude. That covers all the Southern Hemisphere landmasses except Antarctica, and Northern Hemisphere land south of Hudson Bay and St. Petersburg, Russia. It is home to about 95 percent of Earth's population.

At the scheduled end of mapping operations on Monday, more than 99.9 percent of the area will have been imaged at least once. More than 94.6 percent of it will be covered at least twice, and almost half will be imaged at least three times. All but about 80,000 square miles of targeted land will have been covered. The areas that will not be covered are in small, scattered segments, mostly in North America and most of them already accurately mapped.

Endeavour's radar, gathering data in 140-mile-wide swaths as the spacecraft orbits at 17,500 miles per hour, images 40,000 square miles each hour. Data from this mission will, after a year or more of processing, produce the most accurate and most uniform global topography maps ever made.

0050 GMT (7:50 p.m. EST)

From Saturday night's NASA mission status report:

Following Friday's decision by mission managers to extend mapping operations, Endeavour's astronauts are set to continue collecting data until 1144 GMT (6:44 a.m. EST) Monday. At that point preparations will begin to stow the 200-foot-long mast for the remainder of the mission. This 9-hour extension allows for almost 100 percent of the planned coverage of the Shuttle Radar Topography Mission.

The mission's target mapping area includes about 47.6 million square miles. As of midday Saturday, 92 percent, or about 44 million square miles, of the target area had been mapped once. More than 65 percent of the target area ­ nearly 31 million square miles -- has been mapped with two or more passes. Only 80,000 square miles of the target area, mostly in North America, will remain unmapped by the end of mapping operations. Highly accurate topographic maps of these areas already exist.

"I have to believe that scientists all over the world are giving a standing ovation to the SRTM team," observed Dr. Jeffrey Plaut, a research scientist at the Jet Propulsion Laboratory. He said that maps resulting from SRTM data would help archaeologists study ancient cultures and the lands they inhabited, and better understand the reasons for their demise.

Science operations continued on schedule through the mission's ninth day, with all radar and orbiter systems continuing to work smoothly.

Endeavour's crew carried out the seventh trim burn of the mission earlier Saturday. This "flycast maneuver" keeps the spacecraft at the proper altitude for mapping and is designed to reduce the stresses on the mast and minimize the loads at the tip. This was the last flycast maneuver planned during the mission.

Earlier, Commander Kevin Kregel and European Space Agency astronaut Gerhard Thiele spoke to reporters gathered at the German Space Operations Center in Oberpfaffenhofen and in Munich.

Endeavour's systems continue to perform flawlessly as it circles the Earth at an altitude of about 150 statute miles.

SATURDAY, FEBRUARY 19, 2000
0100 GMT (8:00 p.m. EST)

NASA officials decided late Friday to extend space shuttle Endeavour's Earth radar mapping work an additional nine hours to collect more data. The plan scraps any ability to perform an emergency spacewalk to retract the 197-foot long radar antenna mast extended from the shuttle's payload bay. The extension will provide an extra 6 1/2 orbits around Earth.

"We spent a lot of time working to save propellant and we've done a very good job with that," flight operations representative Milt Heflin told reporters Friday afternoon. "Part of this has to do with the propellant savings that we've had. A lot of it has to do with the performance of the radar system and what we're doing. We don't want to just rest on our laurels right now, we'd like to see if there's anything we can possibly do to squeeze out a little more time."

In January, the space agency opted to shorten the original 10-day, 10-hour data-collecting mapping mission to 9 days and 9 hours to ensure the astronauts would have the chance to perform the contingency spacewalk if the mast jammed or retraction motors failed. A spacewalk performed after 10 1/2 days of mapping would have used up one of Endeavour's backup landing days, something NASA did not want to risk.

If the mast fails to retract under the new game plan, the astronauts will have no choice but to jettison the $35 million structure to fall back into Earth's atmosphere. NASA says it has no plans to refly the radar payload in the future.

"We're greatly buoyed by the fact that (the mast) deployed perfectly, it's operated perfectly, it's matching our predicts spot on," Michael Kobrick, SRTM project scientist, said Friday. "We have no indication that there's going to be any problem. The motors look like they're going to start right up. I feel like Joe Namath in that second Superbowl. It's going to stow. We're going to win."

The radar mast is now planned for retraction on Monday after 6:44 a.m. EST (1144 GMT).

"That's super news," commander Kevin Kregel said after being told of the extension. "I'm sure the folks at the Jet Propulsion Lab and NIMA are really ecstatic about that."

As of midday Friday, 88 percent, or more than 42 million square miles of the target area had been mapped once. More than 57 percent of the target area -- over 27 million square miles -- has been mapped with two or more passes. Endeavour images 40,000 square miles of land every minute. At that rate, it can image an area the size of Rhode Island in just 2 seconds.

Scientists and researchers will use the data gathered during Endeavour's mission to generate the highest resolution 3D map of Earth's surface, covering just under 80 percent of the planet's land masses.

"Every hour we get toward our original objective (10 days, 10 hours) is getting us closer to our uniform data set that we envisioned," said program scientist Earnest Paylor.

Endeavour remains scheduled for landing at Kennedy Space Center on Tuesday at 4:52 p.m. EST (2152 GMT).

FRIDAY, FEBRUARY 18, 2000
1700 GMT (12:00 p.m. EST)

From this morning's NASA mission status report:

With unprecedented detail of well over half of the world's terrain already safely stored aboard, Endeavour's crew continued mapping the Earth uninterrupted this morning, marching toward more than nine full days of radar observations thanks to successful fuel conservation measures.

Early today, Endeavour completed its sixth "Flycast Maneuver" trim burn, a gentle engine firing that maintains the Shuttle's altitude at around 150 statute miles for the precise mapping work. Today's burn gave the Shuttle a slightly larger boost than previous daily firings, a measure that will allow controllers to save fuel by eliminating a subsequent firing on Sunday. The next trim burn is now planned for midday on Saturday.

So far, the Space Radar Topography instruments aboard Endeavour have mapped 83 percent, or almost 40 million square miles, of the target area once, an area larger than the Americas, Africa and Australia combined. More than 50 percent of the target area, over 24 million square miles, has been mapped with two or more passes. Endeavour images 40,000 square miles of land every minute, a rate that would allow the Shuttle to map the state of Alaska in 15 minutes and the state of Rhode Island in less than two seconds.

In addition to the changes in trim burns, other fuel conservation measures aboard Endeavour have included changing the way waste water is dumped overboard, slightly relaxing the spacecraft's stringent attitude control guidelines and limiting the use of some equipment. Early in the mission, the failure of a tiny thruster at the end of the 197-foot mast protruding from Endeavour's cargo bay resulted in increased use of the Shuttle's steering jets and fuel. On Thursday, flight controllers noted that the small nitrogen gas thruster on the mast now appeared to be again providing some thrust, a trend that could further improve the Shuttle's predicted fuel consumption.

While the radar mapping continues, a student-operated camera mounted in one of Endavour's windows also has set a record pace. So far, the experiment, called EarthKAM, has sent down almost 1,400 photos of Earth to middle school students. On four previous shuttle flights combined, EarthKAM sent down a total of about 2,000 photos.

THURSDAY, FEBRUARY 17, 2000
2130 GMT (4:30 p.m. EST)

Space shuttle Endeavour has conserved enough fuel to allow its Earth radar mapping mission to be completed as planned, NASA officials determined today. Earlier, mission controllers were concerned the shuttle might run out of fuel and cut short the mapping work.

The trouble was caused by a broken thruster on the end of the 197-foot long radar antenna mast extending from Endeavour's payload bay. Without that nitrogen gas thruster working, Endeavour's onboard thrusters have been used instead to keep the shuttle pointed properly during mapping.

"My optimism has changed to reality," said Milt Heflin, flight operations representative. "We have crossed this bridge. We are now at the point we wanted to be as far as saving propellant to be able to do the nine-days, nine-hour mapping mission. We're there. We're not taking any days off of the mission."

0300 GMT (10:00 p.m. EST)

From Wednesday evening's NASA mission status report:

With growing confidence that fuel-saving measures onboard Endeavour will permit the radar mapping mission to run its full duration, flight controllers and crew members today marked the mission¹s mid-way point. "We're almost there," stated Milt Heflin, NASA¹s Deputy Chief Flight Director.

Science operations progressed flawlessly through the halfway point of the 11-day mission. "You have six smiling faces up here," remarked Gerhard Thiele after being told how well the mapping was going. As of noon today, more that 73 percent, or 35 million square miles, of the target area has been mapped once. That exceeds the land area of the Americas, Africa and Australia combined. More than 38 percent of the target area -- 18 million square miles -- has been mapped with two or more passes. Endeavour collects data on 40,000 square miles every minute it is over land.

New radar images of the Kamchatka Peninsula in Russia's Far East, and of northwestern Mongolia were released today. Shuttle Radar Topography Mission images hold the promise of helping scientists and planners better understand such potential problems as river flooding and soil erosion.

While continuing to troubleshoot the balky small thruster on the tip of Endeavour's 200-foot mast, flight controllers are implementing steps to conserve the propellant used by the orbiter's reaction control system jets to maintain the mast¹s attitude. With pilot Dom Gorie cycling the cold gas line, Janice Voss reported seeing a small, white object moving out of Endeavour¹s payload bay. The object is suspected to be a small piece of ice. The remaining Blue Team member, Mamoru Mohri, took some time out of his day to talk with students in his native country of Japan. Later today, Thiele answered questions from reporters at the German Space Operations Center in Oberpfaffenhofen.

Meanwhile, EarthKam has processed 1,033 images -- more than from any other shuttle mission. Using a camera mounted in Endeavour¹s overhead window, school students are taking pictures of the Earth. On four previous flights, EarthKam took about 2,000 photos.

Endeavour's continues to provide an excellent platform for the most accurate and unified topographical mapping of the Earth ever produced.

WEDNESDAY, FEBRUARY 16, 2000
0300 GMT (10:00 p.m. EST)

With more than half of Endeavour's radar mapping mission completed, shuttle engineers have implemented five steps to save precious propellant. The conservation effort is needed to ensure Endeavour has enough fuel to keep the shuttle oriented properly during the full 9 days of mapping work. The concern was created by a failed steering thruster on the end of the 197-foot long radar antenna boom extending from the shuttle. Without that thruster working, Endeavour has to complete all the pointing maneuvers.

Steps already implemented include easing the requirements for maintaining the mast's attitude due to the better-than-expected stability of the boom, the longest structure ever extended in space. Officials are looking at additional steps that could be taken later this week. NASA remains hopeful the fuel-saving efforts will allow Endeavour to complete the mapping mission's full duration.

"I'm optimistic we're not going to fold our tent early," said Milt Heflin, a mission operations representative. "But I've got to tell you also, I'm probably a couple of days away from coming here and telling you we're there. But we're well on our way."

Mapping operations continued smoothly into the mission's fifth day, with both radar and orbiter systems working flawlessly. By Tuesday afternoon, more than 29 million square miles had been mapped, representing more than 61 percent of the planned coverage for the mission. That's equivalent to the combined area of North America, South America and Africa.

Endeavour is gathering data four times faster than its advanced data communications system can send it to Earth. "Quick look" data sent down, with less detail than will be available from the high-density tapes being filled aboard the shuttle, already has revealed features not shown on even the best maps available today, NASA says.

All of Endeavour's systems are functioning normally as it circles the Earth every 90 minutes at an altitude of about 150 miles.

TUESDAY, FEBRUARY 15, 2000
0400 GMT (11:00 p.m. EST)

Space shuttle Endeavour's Earth radar mapping mission continues successfully with over 24 million square miles over the planet having been mapped once and 9 million square miles surveyed twice.

Shuttle Radar Topography Mission project scientist Dr. Michael Kobrick says that Endeavour is mapping 100,000 square kilometers every minute and that after only three days of flight, the mission has tripled the world's supply of digital terrain elevation data.

The nitrogen thruster problem encountered with the radar payload has not impacted the mapping operations. Endeavour's thrusters have been used to keep the shuttle properly oriented during the flight. NASA officials said Sunday that Endeavour might not have enough propellant to last the planned 9 days of mapping, possibly cutting short the science mission. However, the space agency on Monday said it was too soon to tell if the shuttle will run out of fuel early.

"This is going to evolve over time," said Milt Heflin, mission operations representative. "That's why we're not ready to state that science mission duration is (some) number because this is going to occur over the next two or three days. And I also would like to emphasize again - because I've been here before - we are now dealing with reality. And that's great, because after two or three days of reality we might see something that's even better than expected. So we've got to let all that play out."

Mission controllers are looking at ways to use Endeavour's precious fuel more efficiently.

"I can't tell you today what mission impact we might have," Heflin said. "Right now, we are full duration as far as our mapping is concerned until we know otherwise."

Back at the launch site, engineers say inspections of pad 39A and the mobile launcher platform revealed no abnormal damage following Friday's liftoff. Endeavour's twin solid rocket boosters arrived at Cape Canaveral Air Force Station's Hangar AF on Sunday after being recovered from the Atlantic Ocean by two ships. The boosters are undergoing full inspections but early checks show they are in good condition. Work to disassemble the boosters will occur this week and shipment by rail to Utah will follow. The boosters will be refurbished in Utah for reuse on a later shuttle launch.

MONDAY, FEBRUARY 14, 2000
0300 GMT (10:00 p.m. EST)

A problem has arisen aboard space shuttle Endeavour that could impact the Earth radar mapping mission currently underway. The shuttle astronauts and Mission Control are troubleshooting a suspected leak in the nitrogen gas thruster system designed to keep the 197-foot long antenna mast positioned properly during the flight. A small thruster is mounted on the tip of the outboard antenna. Data from the system indicates nitrogen is flowing but little or no thrust is being produced from the thruster, leading officials to believe there is a leak somewhere in the system.

As a result of the problem, Endeavour's onboard thrusters are being used as a susbstitute. However, predictions show Endeavour's propellant reserve might be too short to allow a full-duration mapping mission. Officials say it will take a few more days before they will know how much, if any, of the mission must be cut. If a shortening is required, it would not be more than one day.

NASA has already reduced the mapping from an original 10-day plan to 9, cutting the amount of data returned by 10 percent. Space agency management made that decision last month to ensure time would be available for spacewalking astronauts to manually retract the 197-foot long mast if it jammed during retraction.

Meanwhile, scientists says about 17.7 million square miles of the Earth's surface having been mapped by 0100 GMT today (8 p.m. EST Sunday). Scientists also reported that 38 percent of landmasses had been mapped thus far in the flight.

See the second image released from SRTM.

"We are starting to see the first 'quick look' results from the X-band and C-band antennas and the details are fantastic," said Dr. Michael Kobrick, SRTM project scientist. "Even in this lower resolution, quick-look results, we can see many topographic features that were completely invisible in the best maps we have today."

Two members of the Blue Team -- Dom Gorie and Mamoru Mohri -- spent a few minutes early Sunday morning talking to Dr. Bob Ballard, discoverer of the RMS Titanic and founder of the JASON Foundation, an educational program designed to spark students' interest in science and technology. They also took questions from the Fox News Network.

There are no problems with Endeavour's system as the shuttle circles the planet every 90 minutes at an altitude of about 150 miles.

SUNDAY, FEBRUARY 13, 2000
1500 GMT (10:00 a.m. EST)

The latest NASA mission status report:

The first "flycast maneuver" trim burn was completed without a hitch by members of the Endeavour crew early Sunday. A little later, the Payload Operations Center reported that the Shuttle Radar Topography Mission had successfully mapped 7.64 million square miles as of very early Sunday morning.

The flycast maneuver is designed to reduce strain on the almost-200-foot mast extending from Endeavour's cargo bay. The orbiter, which flies tail-first during mapping operations, is moved to a nose-first attitude with the mast extending upward. A brief reaction control system pulse begins the maneuver. The mast deflects slightly backwards, then rebounds forward. As it reaches vertical, a stronger thrust is applied, arresting the mast’s motion and increasing the orbiter's speed.

For this mission Endeavour is in a comparatively low orbit, and is slowed by the upper fringes of the Earth’s atmosphere, which causes it to lose altitude. The crew will make daily flycast maneuver trim burns to keep the spacecraft in the proper altitude for mapping.

Endeavour's Red Team, Commander Kevin Kregel, and Mission Specialists Janet Kavandi and Gerhard Thiele, began their eight-hour sleep period shortly after the trim burn. Blue Team members went on duty at about 12:30 a.m. Sunday.

Working around the clock in the two shifts, crewmembers will map an area from 60 degrees north to 56 degrees south. The area includes all the southern continents except Antarctica, and northern continents south of a line from the southern tip of Greenland, southern Alaska and through St. Petersburg, Russia. The area includes about 95 percent of the Earth's population.

All of the orbiter's systems continue to function normally. Crewmembers and flight controllers in Houston continue to look at the cold gas jet on the end of the SRTM's outboard antenna. They are looking at consumption of propellant and the lack of thrust from that jet, designed to help maintain the attitude of the mast. The balky jet is having no impact on the mission's mapping activities.

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

The first image has been released from this Shuttle Radar Topography Mission. Check it out here. The latest NASA mission status report:

By the time members of Endeavour's Red Team had reached lunchtime on this first full day in space for the Shuttle Radar Topography Mission, the radar antennas in the payload bay and at the end of a 200-foot mast had mapped about 1.7 million miles (4.5 million kilometers) of the Earth's surface, or the equivalent of about half the area of the United States.

The Red Team -- Kevin Kregel, Janet Kavandi and Gerhard Thiele -- took over the mapping operations from their Blue Team counterparts shortly after waking up about 7 this morning Central Time. Dom Gorie, Janice Voss and Momoru Mohri turned in shortly after 2 this afternoon and are to be awakened at 10:14 tonight. For a few minutes this morning -- while Japanese astronaut Mohri conducted mapping operations – Gorie and Voss discussed the mission with CNN and NBC's Today Show.

The crew is working around the clock, in two shifts, to collect data that will produce maps of the Earth with unprecedented accuracy and uniformity. Mapping operations will continue for 10 days, and are proceeding very smoothly. SRTM will cover the area between 60 degrees north and 56 degrees south, roughly the area between St. Petersburg, Russia to the north and the tip of South America to the south. The area to be mapped is home to about 95 percent of the Earth's population. In all, more than 70 percent of the Earth's surface will be mapped.

The first X-band image -- of the area near White Sands, New Mexico -- was released this afternoon, and scientists expressed their delight with the quality of the image. X-band images will be posted to the German Space Agency web site at www.dfd.dlr.de/srtm/html/newtoday_en.htm. Both the C-band and X-band radars continue to perform as expected.

"The data we’ve seen so far looks just terrific," said Dr. Michael Kobrick, project scientist at NASA's Jet Propulsion Laboratory in Pasadena, CA. "The mapping plan is right on schedule."

Early this afternoon, Kregel fired the shuttle's thruster jets in a series of pulsed burns to measure the movement of the rigid mast extending over Endeavour's left wing. Flight controllers reported the tip of the mast moved only 11 inches, just as predicted, despite the fact the antenna's dampers remained locked in position. The firings were necessary to determine how they affect the mast, prior to upcoming maneuvers to raise Endeavour's orbit.

Endeavour’s crew also downlinked launch video from an in-cabin camera, providing a unique perspective of yesterday's flawless launch.

All of Endeavour’s payload and spacecraft systems are continuing to function normally.

SATURDAY, FEBRUARY 12, 2000
1600 GMT (11:00 a.m. EST)

This morning's NASA mission status report:

Endeavour astronauts began mapping operations on the Shuttle Radar Topography Mission, which will provide maps of the Earth unprecedented in accuracy and uniformity. The first swath was begun as the orbiter crossed over southern Asia and continued until Endeavour flew over the continent’s eastern coast and moved over the northern Pacific Ocean. The mapping will continue through the mission until the antenna mast is retracted before landing.

Because of the 24-hour-a-day activity aboard Endeavour, the six crewmembers are divided into two teams. Blue Team members Dom Gorie, Janice Voss and Mamoru Mohri began the first mapping swath, covering a 140-mile-wide path, at about 11:31 p.m. Friday. It was the beginning of coverage of more than 70 percent of the Earth's land surface. The mapping will cover an area between 60 degrees north and 56 degrees south, where about 95 percent of the Earth's population lives.

The Red Team, led by Mission Commander Kevin Kregel, includes Mission Specialists Janet Kavandi and Gerhardt Thiele. Their first shift was intense. It included deployment and checkout of the almost 200-foot mast supporting the outboard antenna structure. It is the largest rigid structure ever deployed in space. The Red Team began its sleep period at about 10:45 p.m. Friday and are scheduled to be awakened at 6:44 this morning.

After mast deployment, tests revealed that the mast's damping system, designed as a kind of a shock absorber for the mast, was not working as expected. Flight controllers decided to leave the dampers in their locked position. Calculations showed that the mast was at no risk without the dampers activated.

All planned science data takes have been acquired successfully and all indications from the telemetry show that the radars are performing nominally. Data has been sent to JPL for analysis and early indications are that the data is of excellent quality. Additional reports about mapping results are expected about 12:00 noon CST.

Saturday is scheduled to be the first full day of Shuttle Radar Topography Mission mapping. Endeavour systems continued to function normally.

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

Space shuttle Endeavour began mapping the Earth with radar a few hours ago, even ahead of the planned timeline after deployment and checkout the SRTM went smoothly.

Here is the NASA mission status report released at 9 p.m. EST last night:

Space shuttle astronauts deployed the longest rigid structure ever built in space today and continued work to check out the equipment they will use to produce unrivaled three-dimensional images of the Earth's surface.

Red Team leader Commander Kevin Kregel, and colleagues Janet Kavandi and Gerhardt Thiele initiated extension of the radar mast at 5:27 p.m. CST. After 17 minutes, all 87 cube-shaped bays of the carbon fiber-reinforced plastic, stainless steel, alpha titanium, and Invar structure were deployed by 5:44 p.m. Total length of the mast was 60.95 meters, or just under 200 feet.

The crew also maneuvered the shuttle into the proper attitude, or orientation, for mapping. This orientation points the shuttle payload bay -- and its inboard and outboard radar antennas -- at the Earth. Endeavour’s tail is leading the way as the shuttle orbits about 150 statute miles above the surface. The Red Team then began a series of jet thruster firings to test the ability of dampers to absorb the force of planned maneuvering jet firings and keep the inboard and outboard antennas properly aligned. This alignment is crucial for scientists who will need to combine the radar images received by the two sets of antennas.

The Shuttle Radar Topography Mission will record radar data in both C-band and X-band radar wavelengths. This data eventually will be processed into 3-D maps of the Earth that are 30 times more exact that those currently available. These maps will be important to scientists in many disciplines, ranging from ecology to geology to hydrology, as well as a number of military and commercial applications.

As the Red Team performed the checkout procedures, Blue Team members Dom Gorie, Janice Voss and Mamoru Mohri set up the shuttle's network of portable computers and began an abbreviated six-hour sleep period at 3:44 p.m. They'll be awakened at 9:44 p.m to begin radar mapping operations late tonight.

Endeavour is orbiting the Earth in an orbit inclined 57 degrees to either side of the Equator for the radar mapping of a majority of the Earth's surface. The shuttle completes one orbit every 90 minutes at an altitude of about 150 statute miles.

See a photo of the mast fully extended.

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

A series of thruster tests and shock absorber evaulations have been ongoing in space aboard Endeavour to check the 197-foot long radar antenna mast now extended.

We have posted a video clip of the mast beginning its deployment from a canister inside Endeavour's payload bay.

0018 GMT (7:18 p.m. EST)

Further measurements of the extended mast and outboard antenna show everything is right where it should be. The antenna was flipped 180-degrees to the mapping configuration. The next task in preparing for mapping operations will be activating the Global Positioning System receivers used on the SRTM payload.

0006 GMT (7:06 p.m. EST)

The outboard radar antenna has now been flipped to the mapping configuration.

FRIDAY, FEBRUARY 11, 2000
2358 GMT (6:58 p.m. EST)

Endeavour is now being maneuvered to the mapping orbit with the tail facing the direction of travel and the payload bay facing Earth. Also, the outboard radar antenna on the end of the 197-foot long mast is now being flipped from its stowed position to the mapping configuration.

2353 GMT (6:53 p.m. EST)

Mission controllers report readings indicate the mast is within the expected structural integrity following extension.

2344 GMT (6:44 p.m. EST)

The mast, equipped with the radar antenna on the end, has been extended to its full length of nearly 200 feet. The deployment took about 18 minutes to complete and went without any problems noted by the astronauts or ground controllers. This is a major point of success for the mission because without the mast deployed, Endeavour would not have been able to complete its 3D mapping.

2326 GMT (6:26 p.m. EST)

Extension of the 197-foot long antenna mast has started aboard space shuttle Endeavour. When fully extended in about 20 minutes, the mast will be longest structure deployed in space.

2325 GMT (6:25 p.m. EST)

Endeavour and Mission Control report all is "go" for mast deployment.

2300 GMT (6:00 p.m. EST)

Work to activate the various elements of the Shuttle Radar Topography Mission payload are going very well aboard Endeavour and the astronauts will start extending the 197-foot long mast in about 15 minutes. Live TV downlink from Endeavour during the deployment is expected.

2040 GMT (3:40 p.m. EST)

The activation of the Shuttle Radar Topography Mission payload is well underway aboard Endeavour. Also, Endeavour's Ku-band antenna has been activated, allowing live television to be downlinked to Earth a short time ago. There are no major problems being discussed in these early hours of the STS-99 mission.

We have added two additional video clips from today's launch. One view is from the VAB roof due west of the pad. The other provides a front view of shuttle at liftoff.

1930 GMT (2:30 p.m. EST)

The astronauts have fixed their earlier problem with cockpit computer screen.

Looking ahead to other events today the Shuttle Radar Topography Mission pallet and other systems will be activated later this hour. An orbit adjust burn will be performed four hours into the mission to tweak the shuttle's altitude. Deployment of the 197-foot long SRTM mast is expected to start at 2303 GMT (6:03 p.m. EST) and take about 70 minutes to complete.

1920 GMT (2:20 p.m. EST)

Endeavour's two 60-foot long payload bay doors have been opened and Mission Control has given the shuttle astronauts the "go" for on-orbit operations. One problem has been found with Endeavour -- a computer screen is frozen. It is one of five such CRTs inside the shuttle's cockpit. The astronauts are troubleshooting this problem but it is not a major issue. However, it could the slow down the crew during activation of the radar payload later today.

1840 GMT (1:40 p.m. EST)

See our launch video of Endeavour's spectacular liftoff from Kennedy Space Center, Florida.

In space, the Endeavour astronauts have completed their ascent checklist and will open the payload bay doors in next half-hour or so.

1823 GMT (1:23 p.m. EST)

T+plus 40 minutes. The orbital maneuvering system engine firing has been completed successfully to place Endeavour into a safe orbit around the Earth about 150 statute miles high. The shuttle is now comfortably in space to begin its 11 day radar mapping mission of the planet.

1818 GMT (1:18 p.m. EST)

Endeavour and its six astronauts are preparing for the upcoming engine firing to circularize the shuttle's orbit.

1759 GMT (12:59 p.m. EST)

T+plus 15 minutes, 30 seconds. The Endeavour astronauts are now shutting down the three auxiliary power units. They won't be used until entry and landing.

1753 GMT (12:53 p.m. EST)

T+plus 10 minutes. The next event will occur in about 30 minutes. That will be the another firing of Endeavour's orbital maneuvering system engines on the ship's tail. The burn will circularize the shuttle's orbit.

1752 GMT (12:52 p.m. EST)

T+plus 9 minutes. Mission Control confirms the spent external fuel tank has separated from Endeavour.

1752 GMT (12:52 p.m. EST)

T+plus 8 minutes, 40 seconds. MECO! Endeavours's main engines have cutoff as planned.

1751 GMT (12:51 p.m. EST)

T+plus 7 minutes, 30 seconds. One minute from main engine shutdown. Altitude is 69 miles and distance is 625 miles northeast of Kennedy Space Center.

1750 GMT (12:50 p.m. EST)

T+plus 6 minutes, 30 seconds. The shuttle has reached a speed of 11,000 miles per hour. About two minutes left in powered flight today.

1749 GMT (12:49 p.m. EST)

T+plus 6 minutes, 10 seconds. Endeavour now rolling to a heads-up position.

1749 GMT (12:49 p.m. EST)

T+plus 5 minutes, 30 seconds. Endeavour can now make a lower than planned but safe orbit should one main engine fail.

1748 GMT (12:48 p.m. EST)

T+plus 5 minutes. Altitude 67 miles, downrange distance 215 miles.

1747 GMT (12:47 p.m. EST)

T+plus 4 minutes. Negative return. Endeavour can longer return to Kennedy Space Center if an emergency is declared. All systems continue to operate normally.

1746 GMT (12:46 p.m. EST)

T+plus 3 minutes. The twin orbital maneuvering system engines on Endeavour's tail have ignited for an extra boost. Altitude 41 miles, downrange distance 68 miles.

1746 GMT (12:46 p.m. EST)

T+plus 2 minutes, 30 seconds. Solid rocket boosters have separated. Endeavour continues it climb to orbit on the power of three liquid-fueled engines.

1744 GMT (12:44 p.m. EST)

T+plus 1 minute, 15 seconds. Go at throttle up!

1744 GMT (12:44 p.m. EST)

T+plus 1 minute. Engines have throttled down to ease Endeavour into the dense lower atmosphere.

1744 GMT (12:44 p.m. EST)

T+plus 30 seconds. One mile in altitude. Roll maneuver completed placing Endeavour on the proper launch heading.

1743:40 GMT (12:43:40 p.m. EST)

LIFTOFF. Liftoff of the first human space flight of the new century as Endeavour begins a mission to map our home planet.

Vehicle has cleared the tower; Houston now controlling the mission; roll program initiated.

1743:09 GMT (12:43:09 p.m. EST)

T-minus 31 seconds. Go for auto sequence start. Endeavour's computers now controlling 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.

1742 GMT (12:42 p.m. EST)

T-minus 1 minute. Computers verifying that the main engines are ready. 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 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; Endeavour will transition to internal power and the liquid oxygen and liquid hydrogen outboard fill and drain valves will be closed.

1741 GMT (12:41 p.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 Endeavour'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 Dom Gorie has been asked to clear the caution and warning memory system aboard Endeavour.

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.

1740 GMT (12:40 p.m. EST)

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

1739 GMT (12:39 p.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 Endeavour 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.

1738 GMT (12:38 p.m. EST)

T-minus 5 minutes. Go for Auxiliary Power Unit start. Pilot Dom Gorie is now flipping three switches in Endeavour's cockpit to start each of the three APU's. The units, located in the aft compartment of Endeavour, 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 Kevin Kregel, 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.

1738 GMT (12:38 p.m. EST)

T-minus 5 minutes, 25 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.

1737 GMT (12:37 p.m. EST)

T-minus 6 minutes. Pilot Dom Gorie has been asked by the Orbiter Test Conductor to pre-start the orbiter Auxiliary Power Units. This procedure readies the three APU's for their activation at T-minus 5 minutes.

Liftoff is planned for 12:43:40 p.m. EST.

1736 GMT (12:36 p.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 Endeavour 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.

1735 GMT (12:35 p.m. EST)

T-minus 8 minutes and counting. Pilot Dom Gorie has flipped the switches in the cockpit of Endeavour to directly connect the three onboard fuel cells with the essential power buses. Also, the stored program commands have been issued to the orbiter.

The launch of STS-103 will mark the 97th flight in the space shuttle program since 1981, the 72nd since return-to-flight after Challenger, the 14th for Endeavour and the first shuttle flight of 2000.

1734 GMT (12:34 p.m. EST)

T-minus 9 minutes and counting. The ground launch sequencer is now up and running. Now in the final phase of today's countdown to launch of space shuttle Endeavour for liftoff at 12:43:40 p.m. EST.

"We are ready to map the world," Endeavour commander Kevin Kregel just said.

1734 GMT (12:34 p.m. EST)

The final management poll has been completed by Launch Director Dave King. All systems are go for launch.

Once the countdown picks up, the Ground Launch Sequencer will be initiated. The master computer program is located in a console in Firing Room 3 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 Endeavour to complete their own automatic sequence of events through the final half minute of the countdown.

1731 GMT (12:31 p.m. EST)

The launch team has been polled by NASA Test Director Doug Lyons and all systems were reported go to proceed with the countdown. The three last-minute technical glitches have been put to rest -- a hydraulic circulation pump concern, a propulsion system meter reading and the crew cabin pressure level.

1730 GMT (12:30 p.m. EST)

The final issue has been resolved.

1727 GMT (12:27 p.m. EST)

Once the final problem is resolved, polls of the launch team and management will be performed to verify everyone's readiness to resume the countdown for liftoff.

1725 GMT (12:25 p.m. EST)

Analysis to clear one final issue continues. The two other technical problems have been put to rest. A new liftoff time has not been set. Countdown clocks still holding at T-minus 9 minutes.

1720 GMT (12:20 p.m. EST)

Again, the countdown will not restart in one minute as originally planned. NASA Test Director Doug Lyons says it will take a few additional minutes to resolve three minor glitches that have been seen in the last little while in the countdown.

1719 GMT (12:19 p.m. EST)

The countdown hold will be extended at least a few minutes. This will delay liftoff beyond 1730 GMT (12:30 p.m. EST). The launch team is working three issues, but there are minor.

1718 GMT (12:18 p.m. EST)

The air purge rates to Endeavour's payload has been set for launch.

1716 GMT (12:16 p.m. EST)

Now half-way through this planned 10-minute hold. Launch remains scheduled for 1730 GMT (12:30 p.m. EST), the opening of today's two-hour, 10-minute window.

1711 GMT (12:11 p.m. EST)

Endeavour's vent valves are now closed.

1711 GMT (12:11 p.m. EST)

T-minus 9 minutes and holding. Countdown clocks have gone into the planned 10-minute built-in hold leading toward liftoff at 1730 GMT (12:30 p.m. EST).

1708 GMT (12:08 p.m. EST)

The shuttle's main propulsion system helium system has been reconfigured for launch. Also, the launch danger area has been cleared.

1706 GMT (12:06 p.m. EST)

The Orbital Maneuvering System/Reaction Control System crossfeed valves have been configured for launch.

1706 GMT (12:06 p.m. EST)

Pilot Dom Gorie is configuring the displays inside Endeavour's cockpit for launch. Also, Mission Control in Houston is loading Endeavour's onboard computers with the proper guidance parameters.

1700 GMT (12:00 p.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 T-minus 9 minutes where the final planned hold is scheduled to occur. Launch remains set for 1730 GMT (12:30 p.m. EST).

Endeavour'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.

1658 GMT (11:58 a.m. EST)

The Orbiter Closeout Crew reports they have stowed the platforms and equipment in the White Room next to the crew hatch of Endeavour. The OCC will now depart launch pad 39A.

1650 GMT (11:50 a.m. EST)

T-minus 20 minutes and holding. The countdown has paused for a 10-minute built-in hold. Launch remains scheduled for 1730 GMT (12:30 p.m. EST).

During this hold, all computer programs in Firing Room 3 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.

1640 GMT (11:40 a.m. EST)

Mission managers have decided the one psi difference in the pressure level inside Endeavour cabin is acceptable for launch.

At this time, 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. Endeavour's two Enhanced Master Events Controllers will be tested, too. They relay the commands from the shuttle's computers to ignite, and then separate the boosters and external tank during launch.

Also, commander Kevin Kregel has pressurized the gaseous nitrogen system for Endeavour's Orbital Maneuvering System engines, and pilot Dom Gorie has activated the gaseous nitrogen supply for the orbiter's Auxiliary Power Units' water boilers.

Earlier, the Eastern Test Range shuttle range safety system terminal count closed-loop test is currently being performed. Other activities scheduled at this point in the countdown include shifting the S-band antennas at the MILA tracking station here at the Cape from low power to high power. The site will provide voice, data and telemetry relay between Endeavour and Mission Control during the first few minutes of flight. Coverage then is handed to a NASA Tracking and Data Relay Satellite in space.

1625 GMT (11:25 a.m. EST)

NASA launch commentator Joel Wells says the Orbiter Closeout Crew will troubleshoot a pressure-level issue seen during the leak checks of Endeavour's crew module. The launch team did not see the pressure buildup inside the crew cabin that is normally expected. However, Wells said this is not a big problem.

1617 GMT (11:17 a.m. EST)

NASA astronaut Kent Rominger has taken off in the the Shuttle Training Aircraft to flight weather reconnaissance. Rominger has been flying around earlier this morning in a T-38 jet. Precourt plans to stay aloft through the remainder of the countdown.

We have posted our countdown photo gallery with images of today's events.

1610 GMT (11:10 a.m. EST)

T-minus 1 hour. The countdown continues smoothly and without problems today for launch of Endeavour at 1730 GMT (12:30 p.m. EST). The countdown clock is ticking toward T-minus 20 minutes where a 10-minute long hold is planned. A final built-in hold is scheduled at T-minus 9 minutes and will last for 40 minutes.

The pre-flight alignment of Endeavour'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.

Also in the countdown, the booster test conductor will verify the chamber pressure in the twin solid rocket motors. Sensors measure pressure in the thrust chambers at nozzles of the boosters. The data tells onboard computers when the boosters have consumed their solid-fuel propellant and should be separated in-flight.

1608 GMT (11:08 a.m. EST)

The Final Inspection Team has completed its analysis of the ice noted earlier on the large external fuel tank of Endeavour. The team has concluded that this is more like frost than ice, and the four superficial cracks to the tank's foam insulation do not pose a problem for launch.

1556 GMT (10:56 a.m. EST)

Endeavour's hatch has been verified closed and latched. Now cabin leak checks will be performed.

1549 GMT (10:49 a.m. EST)

The Orbiter Closeout Crew has closed Endeavour's hatch.

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

T-minus 90 minutes and counting. The countdown continues toward a planned 1747 GMT (12:30 p.m. EST) launch today of shuttle Endeavour if the weather cooperates. There are two planned holds remaining in the countdown at T-20 and T-9 minutes.

Voice checks between the astronauts, the launch team and Mission Control have been completed.

1524 GMT (10:24 a.m. EST)

Initialization of the ground launch sequencer has been completed. The GLS is the master computer program that will control the final nine minutes of the countdown to launch.

Also, the Orbiter Closeout Crew has been cleared to begin readying Endeavour's crew module for flight now that the astronauts are all aboard.

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

The latest weather forecast continues to show very favorable conditions for launch today at 1730 GMT (12:30 p.m. EST). There is some haze around Kennedy Space Center but astronaut Kent Rominger flying the weather reconnaissance plane says it is not a problem.

1512 GMT (10:12 a.m. EST)

Mission specialist No. 2 and flight engineer Janet Kavandi has entered the shuttle, becoming the final astronaut to board Endeavour today. She will sit in the flight deck aft center seat.

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

The final inspection team has completed its briefing to mission managers. The team says it found four minor cracks in the external fuel tank's foam insulation. This is not a concern since the foam has not debonded and the tank's outer skin is not damaged. Earlier this morning the team completed a two-hour inspection of the shuttle and launch pad after fueling operations were completed.

1459 GMT (9:59 a.m. EST)

Five of Endeavour's six astronauts are now aboard the shuttle. European Space Agency astronaut, known as mission specialist No. 1, Gerhard Thiele has entered Endeavour's hatch. Thiele will sit in the flight deck aft right seat.

1451 GMT (9:51 a.m. EST)

Mission specialist No. 3 and payload commander Janice Voss has boarded Endeavour. She will sit in the middeck left seat.

We have posted a video clip of the astronauts departing their quarters for the launch pad today.

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

Endeavour's pilot, Dom Gorie, has entered the shuttle's hatch. He will sit in the flight deck forward right seat.

Meanwhile, voice checks between commander Kevin Kregel and ground controllers have begun. Kregel reported "it is a beautiful day."

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

Mission specialist No. 4 and Japanese astronaut Mamoru Mohri has boarded Endeavour. Mohri will sit in the middeck right seat.

1436 GMT (9:36 a.m. EST)

Endeavour commander Kevin Kregel has become the first astronaut to enter the shuttle today. He will sit in the flight deck forward left seat.

1432 GMT (9:32 a.m. EST)

Endeavour's six astronauts have taken the elevator up the fixed service structure at launch pad 39A to the 195-foot level. This is 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 gear and communications hat before entering Endeavour's crew module hatch.

1430 GMT (9:30 a.m. EST)

The shuttle astronauts have arrived at launch pad 39A.

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

Endeavour's astronauts are on their way to the launch pad. They have departed the Operations & Checkout Building, which serves as the living quarters for the flight crew while at Kennedy Space Center. The ride out to pad 39A, on the edge of the Atlantic Ocean, will take about 20 minutes.

The convoy will stop at the Launch Control Center for the NASA management and NASA astronaut Kent Rominger to exit the Astrovan. The managers will take their positions in Firing Room 3 while Rominger heads over to the Shuttle Landing Facility to begin weather reconnaissance flights in a T-38 jet. Later he will 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.

1410 GMT (9:10 a.m. EST)

T-minus 3 hours and counting. Countdown clocks have resumed following this two-hour planned hold. The count will continue to T-minus 20 minutes where the next built-in hold will occur. Launch is still scheduled for 1730 GMT (12:30 p.m. EST. There and no technical problems being worked and weather is expected to be near-perfect today.

The astronauts are expected to depart their quarters for the launch pad in about five minutes.

The two solid rocket booster recovery ships are currently on station in the Atlantic Ocean about 140 miles northeast of Kennedy Space Center, off the coast of Jacksonville, Florida. The ships will retrieve and return the spent boosters to the Cape for disassembly and shipment back to Utah for refurbishment and reuse on a future shuttle launch.

The ships sailed from Port Canaveral yesterday at about 1730 GMT (12:30 p.m. EST). In about one hour, they will be verified in position about 7 1/2 miles from the predicted impact area. Later they will perform an electronic search of the area to ensure it is cleared of all shipping traffic.

Follow the boosters' parachuted descent and splashdown in the Atlantic, the recovery teams will configure the SRBs for tow back to Port Canaveral, with arrival expected on Sunday morning.

The weather forecast at the impact zone calls for just a few clouds and light wind.

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

A weather briefing from the Spaceflight Meteorology Group based at Mission Control is underway for the Endeavour's astronauts. This weather update is for the abort landing sites at Kennedy Space Center, California, New Mexico, Africa and Spain. Conditions are looking good and weather should not be a factor today.

The final inspection team has completed its work at launch pad 39A. The team has noted some minor ice buildup on the backside of Endeavour's external tank. However, that is not expected to be a concern for launch.

The countdown continues holding at T-minus 3 hours with 30 minutes left in this two-hour build-in hold. Launch remains on schedule for 1730 GMT (12:30 p.m. EST).

1301 GMT (8:01 a.m. EST)

Endeavour's astronauts have just been seated for a final pre-launch meal in the dining room at the Operations & Checkout Building. This is breakfast for the Red Team of Kregel, Thiele and Kavandi and lunch for Blue Team of Gorie, Voss and Mohri. They appeared in good spirits and ready for this second launch attempt of their mission. The first attempt on January 31 ended in a scrub due to a faulty avionics box and poor weather.

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

Now inside the final five hours to the launch of space shuttle Endeavour and the first human spaceflight adventure of the new millennium.

Endeavour stands fully fueled and ready for launch from pad 39A at Kennedy Space Center, Fla. The loading of 528,000 gallons of liquid oxygen and liquid hydrogen into the external tank officially began at 0849 GMT (3:49 a.m. EST). The operation went smoothly and was completed at 1137 GMT (6:37 a.m. EST). A stable replenishment mode has now started to continuously top-off the respective tanks within the bullet-shaped 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. Currently, the six-person team, comprised of five engineers and one safety official, is 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, which is headed by Greg Katnik of the Kennedy Space Center, is also looking for any loose debris that could possibly fly up and strike the launch vehicle. 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 vehicle 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 teammember is also responsible for photo documentation.

Each member of the Final Inspection Team is in constant contact with NASA Test Director Doug Lyons in Firing Room 3.

The team wears the highly visible day-glo-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, Greg Katnik will meet with NASA Launch Director Dave King, the Mission Management Team, and engineering directors in the launch control center. Katnik will give the managers a full and detailed report on the team's inspections and findings at the pad 39A.

A full inspection of the vehicle and pad was performed on Sunday and the external tank received a thorough check prior to fueling.

An inspection of the launch pad and beach will be made following launch today. 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.

1210 GMT (7:10 a.m. EST)

T-minus 3 hours and holding. The countdown has entered a two-hour planned hold. During this time, the final inspection team and orbiter closeout crew will complete their work at launch pad 39A. The inspection team will check the shuttle and launch pad for any ice or debris following fueling. The closeout crew will ready Endeavour's crew module for the astronauts' arrival.

All six astronauts are now awake for launch. The Red Team of commander Kevin Kregel and mission specialists Gerhard Thiele and Janet Kavandi was awakened a short time ago. The Blue Team of pilot Dom Gorie and mission specialists Janice Voss and Mamoru Mohri were awakened about seven hours ago, and they will next sleep about four hours into the mission.

The six astronauts are divided into the two shifts to allow round-the-clock, 24-hour radar mapping during the mission.

It is beautiful morning at Kennedy Space Center. Skies are clear, the sun is rising and the forecast is very promising for an on-time liftoff today at 1730 GMT (12:30 p.m. EST), the opening of a two-hour, 10-minute launch window.

1205 GMT (7:05 a.m. EST)

The loading of the space shuttle Endeavour has been completed this morning as the countdown continues very smoothly toward liftoff at 1730 GMT (12:30 p.m. EST).

The shuttle launch team completed "tanking" 528,000 gallons of liquid oxygen and liquid hydrogen into Endeavour's external fuel tank at 1137 GMT (6:37 a.m. EST). The super-cold cryogenics will be replenished continously throughout the remainder of the countdown to replace that which naturally boils away.

Forecasters are currently indicating less than a 10 percent chance of bad weather today. At launch time conditions at pad 39A are predicted to include a few clouds at 2,500 and 25,000 feet, 7 miles visibility, south-southwest winds at 12 peaking to 15 knots and temperature of 75 degrees. At the nearby emergency shuttle landing strip at Kennedy Space Center, winds should be from south-southwest at 8 peaking to 12 knots. Earlier, there had been a concern about crosswinds at the runway above the 15-knot limit.

0855 GMT (3:55 a.m. EST)

T-minus 6 hours and holding. NASA managers met early this morning and gave the launch team a "go" to begin fueling of shuttle Endeavour's bullet-shaped external fuel tank.

The three hour operation to load 500,000 gallons of liquid oxygen and liquid hydrogen got underway at about 0849 GMT (3:49 a.m. EST), a little earlier than planned.

NASA spokesman George Diller said the launch team was not working any technical problems and there was less than a 10 percent chance of weather holding up the launch. The only concern is just a slight chance of high crosswinds at the shuttle's emergency landing strip.

0307 GMT (10:10 p.m. EST)

T-minus 11 hours and counting. The countdown has resumed following a planned 12-hour, 40-minute hold. Clocks will continue ticking down to T-minus 6 hours where a one-hour built-in hold is scheduled. Launch of Endeavour remains scheduled to occur at 1730 GMT (12:30 p.m. EST), the opening of a two-hour, 10-minute window.

At launch pad 39A, workers rolled the rotating service structure away from Endeavour about 3 1/2 hours ago. The shuttle is now sitting brightly illuminated on the pad, awaiting fueling operations that will occur before dawn.

Over the next few hours, the shuttle's three power-generating fuel cells will be activated and Endeavour's purge air will be switched to gaseous nitrogen. The Mission Management Team will convene at 0815 GMT (3:15 a.m. EST) for the traditional pre-tanking meeting. The review will cover countdown status, the weather forecast and any outstanding issues or concerns. If there are no significant problems, officials will clear the launch team to begin loading a half-million gallons of super-cold liquid hydrogen and liquid oxygen into the shuttle's external fuel tank after 0900 GMT (4 a.m. EST). The operation will take three hours to complete.

The six Endeavour astronauts are divided into two shifts to allow round-the-clock radar mapping during the mission. Right now, the Red Team of commander Kevin Kregel and mission specialists Gerhard Thiele and Janet Kavandi are preparing to go to bed in about an hour. The Blue Team of pilot Dom Gorie and mission specialists Janice Voss and Mamoru Mohri will be awakened in about two hours. The astronauts will be joined for a final pre-launch meal at 1300 GMT (8:00 a.m. EST). Later, they will receive a weather briefing and don their spacesuits before heading to the launch pad.

THURSDAY, FEBRUARY 10, 2000
1730 GMT (12:30 p.m. EST)

Space shuttle Endeavour has only 24 hours to wait before its 14th trip to space is scheduled to begin. NASA officials report all systems are go for liftoff on Friday at 1730 GMT (12:30 p.m. EST), the opening of a two-hour, 10-minute launch window. The weather forecast calls for a 90 percent chance of good conditions.

At launch pad 39A, Endeavour's three electricity producing fuel cells were loaded with liquid oxygen and liquid hydrogen reactants yesterday. The cryogenics will be combined during the shuttle's mission to generate power for the orbiter, radar payload and astronauts, while making drinking water as a by-product.

This morning work is underway to activate the shuttle's Inertial Measurement Units and communications systems. The gantry-like rotating service structure will be rolled away from Endeavour just after sunset tonight at 2330 GMT (6:30 p.m. EST).

Mission managers will convene a meeting at 0815 GMT (3:15 a.m. EST) tomorrow to review the status of the countdown, vehicle systems and the weather. If there are no major problems, officials will clear the launch team to begin loading Endeavour's external fuel tank with a half-million gallons of liquid oxygen and liquid hydrogen starting at about 0910 GMT (4:10 a.m. EST).

WEDNESDAY, FEBRUARY 9, 2000
1800 GMT (1:00 p.m. EST)

The launch countdown continues on schedule for Friday's launch of space shuttle Endeavour.

At launch pad 39A today, a Global Positioning System receiver inside the shuttle's crew compartment failed a self test. Officials have decided to replace the unit beginning this evening. No impact to the launch date is expected. The GPS unit is used by the radar payload being carried into space by Endeavour.

Also this morning, tests of Endeavour's pyrotechnic initiator controllers confirmed that the safe and arm device indicator located in the left hand solid rocket booster's forward skirt is functioning as expected and is ready for launch, NASA said. This was a confidence test for engineers who yesterday completed inspections of a cable that supports the device. Inspections revealed only superficial scuffing to exterior tape and confirmed that the cable was intact.

The weather forecast still shows an 80 percent chance that conditions will be acceptable for launch on Friday. At the 12:30 p.m. EST (1730 GMT) liftoff time, the forecast calls for scattered clouds at 3,000 and 25,000 feet, visibility of 7 miles, southwest winds at 14 peaking to 20 knots, a temperature of 75 degrees F, relative humidity of 45 percent, dew point at 52 degrees F and zero chance of precipitation. The 24-hour delay forecast indicates a 60 percent chance of favorable weather.

TUESDAY, FEBRUARY 8, 2000
2330 GMT (6:30 p.m. EST)

The countdown started one hour ago for launch of space shuttle Endeavour on Friday at 12:30 p.m. EST (1730 GMT).

After further inspections today, NASA has determined that a scuffed cable, located in the forward skirt of the left solid rocket booster, is safe for launch. NASA says a functional test of the booster ignitor's safe and arm device is scheduled to occur tomorrow. This standard countdown test gives engineers confidence that the device is functioning as expected.

1600 GMT (11:00 a.m. EST)

NASA is preparing to start the second countdown for shuttle Endeavour's STS-99 mission to map the Earth's surface. Clocks are slated to begin ticking backwards at 5:30 p.m. EST (2230 GMT) today in Firing Room No. 3 of the Complex 39 Launch Control Center. Launch remains on schedule for Friday at 12:30 p.m. EST (1730 GMT).

There is one technical issue to report. Technicians have found a scuffed tape wrapper on a solid rocket booster wiring harness. Work is underway to determine if the wiring beneath the cover could be damaged. The cabling is used to verify the position of the Safe and Arm device on the left-hand booster. While in the safe position, the device prohibits ignition of the SRB. When armed, the motor is allowed to ignite. If the wiring is not damaged, there should be no impact to launch. However, if replacement work is required, some delay is possible.

The weather forecast for Friday indicates an 80 percent chance of good conditions.

MONDAY, FEBRUARY 7, 2000
2300 GMT (6:00 p.m. EST)

Endeavour's six astronauts returned to Kennedy Space Center today in preparation for their planned launch on Friday. Following last week's launch postponement, the crewmembers flew back to Houston to complete some additional training to sharpen their skills.

See our QuickTime video of the crew's arrival.

"It seems like we were only just here a week ago," commander Kevin Kregel jokingly said to reporters. "We're really glad to be back. The weather looks like it's going to be favorable for our launch attempt on Friday. The vehicle's clean, they went ahead and replaced the master events controller, so we're getting ready to get back in the saddle and do the mapping mission."

During the stay at KSC, the astronauts will undergo routine health checks, take flights in the Shuttle Training Aircraft and perform final crew equipment checks.

At launch pad 39A, work to close the shuttle's aft compartment is wrapping up. That area of Endeavour was reopened late last week so the suspect Enhanced Master Events Controller No. 2 could be replaced.

Over the weekend technicians replaced a cable located in an umbilical harness aboard Endeavour. Otherwise, NASA says there are no problems being worked that should stand in the way of launch on Friday.

The new countdown is poised to begin at 5:30 p.m. EST (2230 GMT) on Tuesday, leading toward a liftoff on Friday at 12:30 p.m. EST (1730 GMT).

SATURDAY, FEBRUARY 5, 2000
0501 GMT (12:01 a.m. EST)

A faulty avionics control unit that scuttled this week's shuttle launch has been replaced aboard Endeavour. Read our full story.

THURSDAY, FEBRUARY 3, 2000
0501 GMT (12:01 a.m. EST)

NASA has secured February 11 as space shuttle Endeavour's new launch date after a scheduling conflict with an unrelated rocket test at Cape Canaveral was resolved, NASA officials confirmed late Wednesday. Read our full story.

WEDNESDAY, FEBRUARY 2, 2000
0501 GMT (12:01 a.m. EST)

The next attempt to launch space shuttle Endeavour may not come until February 12. Read our full story.

TUESDAY, FEBRUARY 1, 2000
0838 GMT (3:38 a.m. EST)

NASA has decided to delay the launch of shuttle Endeavour until at least February 9 to replace the suspect Master Events Controller (MEC) that puzzled engineers during yesterday's countdown. "They don't know exactly what's wrong with it," said NASA spokesman George Diller. "But they're pretty sure there's something wrong inside that box."

Space agency officials said they will request a February 9 launch slot from the U.S. Air Force, which coordinates all liftoffs from Cape Canaveral. A Boeing Delta 2 rocket has already reserved that day, but at this stage it is unclear whether NASA will have to wait or if the Delta will slip and make way for Endeavour.

MEC-2 failed a test at the T-29 minute mark during yesterday's launch attempt. Although engineers were unable to duplicate the glitch in retests they were convinced that there was indeed a problem within the device. "They knew it would happen again, they just didn't know when," Diller said.

The controller, which is located in the shuttle's aft engine compartment, is responsible for relaying critical commands to separate the twin solid rocket boosters and external fuel tank. The shuttle is equipped with a backup MEC device but they are considered so critical that both have to be fully operational before NASA will commit the shuttle for launch.

Replacement of the box will begin on Thursday after engineers have drained the shuttle's fuel cell tanks and disconnected explosive devices hooked up to the MEC. The new MEC will then undergo testing before the shuttle is cleared to make another launch attempt.

MONDAY, JANUARY 31, 2000
2300 GMT (6:00 p.m. EST)

NASA managers have deferred a decision on Endeavour's Master Events Controller No. 2 until early tomorrow morning before fueling the shuttle for launch. Officials met a short time ago to assess the MEC problem seen during the countdown today.

At T-minus 29 minutes, the MEC No. 2 failed a health check when an erroneous response was given back to Endeavour's main computers. A later test was performed successfully, stumping the engineers troubleshooting the problem. The management team decided to allow the troubleshooting to continue over the next several hours and convene again at 0730 GMT (2:30 a.m. EST). That overnight meeting will review the progress was made in examining the problem and determine whether the avionics box will need replacement.

Endeavour carries two MECs to perform such crucial functions as igniting the solid rocket boosters and jettisoning the boosters and external fuel tank during launch.

"If we don't understand (the problem) to the point we know we are safe for the MEC to function properly, we will not launch," shuttle program manager Ron Dittemore told reporters in a brief news conference. "We can always take the time to change out the box. That would result in, probably, a week's delay."

If Endeavour is not off the ground by the end of Tuesday's launch window of 1744-1948 GMT, the next attempt might not come before February 6 due to the planned Atlas rocket launch from nearby Cape Canaveral Air Station. The planned February 6 launch of a Boeing Delta 2 rocket from the Cape has been delayed until February 9 to replace the rocket's main guidance computer.

Also, the weather forecast for Tuesday remains questionable.

2017 GMT (3:17 p.m. EST)

The astronauts, riding inside the AstroVan, have departed launch pad 39A bound for the crew quarters to wait out the postponement.

Tentatively, the launch of Endeavour has been rescheduled for Tuesday. However, that plan is pending resolution of the problem with Endeavour's Master Events Controller No. 2. NASA mission managers will meet in less than two hours to further discuss the situation and the poor weather forecast for tomorrow.

Looking into the history books, NASA says a Master Events Controller failure aboard Columbia in October 1995 caused a one-week delay of STS-73 to replace the unit. In August 1984, a MEC problem on Discovery was fixed with a software patch, delaying STS-41D one day.

We will update later today following the Mission Management Team meeting.

Watch our video of NASA Launch Director Dave King announcing today's scrub.

2014 GMT (3:14 p.m. EST)

Commander Kevin Kregel and pilot Dom Gorie have climbed out of Endeavour, completing the egress of the astronauts.

2009 GMT (3:09 p.m. EST)

A Mission Management Team meeting has been scheduled for 2200 GMT (5 p.m. EST) to discuss today's scrub and the Master Events Controller No. 2 problem. A press conference is planned once the meeting concludes.

2007 GMT (3:07 p.m. EST)

Flight engineer Janet Kavandi and European astronaut Gerhard Theile have left the shuttle.

2001 GMT (3:01 p.m. EST)

The astronauts are now beginning to egress from Endeavour. Janice Voss and Mamoru Mohri have climbed out.

1954 GMT (2:54 p.m. EST)

Endeavour's hatch is swinging open to allow the six astronauts to exit the shuttle following today's launch scrub.

The launch team is pressing ahead with plans for another attempt at flying Endeavour tomorrow. However, when the next launch attempt occurs will be based on final resolution of the Master Events Controller No. 2, which displayed some unexplained behavior during the countdown.

1948 GMT (2:48 p.m. EST)

The Orbiter Closeout Crew has arrived at pad 39A's White Room next to Endeavour's hatch. They will get the hatch open and help the astronauts out of Endeavour over the next half-hour or so.

1938 GMT (2:38 p.m. EST)

The off-loading of liquid oxygen from the shuttle's external tank has started.

The latest weather forecast shows a slight improvement tomorrow compared to conditioned experienced today. Overall, meteorologists say there is a 40 percent chance of good weather.

Meanwhile, NASA managers are still discussing the problem encountered earlier with Mission Events Controller No. 2. The issue has not been put to rest, and must be resolved before Endeavour will be cleared for another launch attempt on Tuesday.

1925 GMT (2:25 p.m. EST)

Operations to safe space shuttle Endeavour are underway. The astronauts will begin unstrapping and climbing out of the shuttle over the next little while once the pad is safe. The Orbiter Closeout Crew, which helped the astronauts during ingress, will head back to the pad to assist the crewmembers out of Endeavour. Officials plans to recycle the countdown and make another launch attempt on Tuesday.

1908 GMT (2:08 p.m. EST)

SCRUB! NASA Launch Director Dave King has just decided to scrub today's attempt to launch Endeavour due to the weather. The launch team has been told to plan for another try on Tuesday. The launch window will extend from 1744 to 1948 GMT (12:44-2:48 p.m. EST).

The Master Events Controller No. 2 issue has not been resolved, but the weather was simply not going to cooperate today.

1906 GMT (2:06 p.m. EST)

The latest weather report indicates no positive changes in conditions are expected any time soon. Standing by to enter the next hold point at T-minus 9 minutes.

1904 GMT (2:04 p.m. EST)

The Orbital Maneuvering System/Reaction Control System crossfeed valves are configured for launch.

1903 GMT (2:03 p.m. EST)

The shuttle's main propulsion system helium system has been reconfigured for launch.

1902 GMT (2:02 p.m. EST)

Mission Control in Houston is loading Endeavour's onboard computers with the proper guidance parameters.

1901 GMT (2:01 p.m. EST)

The launch danger area has been cleared, and pilot Dom Gorie is configuring the displays inside Endeavour's cockpit for launch.

1900 GMT (2:00 p.m. EST)

Weather conditions remain very poor at Kennedy Space Center courtesy of a stalled cold front over the Central Florida region. Currently, the cumulus cloud, thick cloud, flight through precipitation, ceiling and visibility weather rules are being violated. Today's window closes in 49 minutes.

1858 GMT (1:58 p.m. EST)

T-minus 20 minutes and counting. The countdown has resumed after this extended delay that lasted one hour and 41 minutes, or a total hold of one hour, 51 minutes. The count will hold at T-minus 9 minutes to further discuss the MEC problem and weather.

Endeavour'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.

1856 GMT (1:56 p.m. EST)

NASA Test Director says following another test with the Master Events Controller No. 2, the countdown will be restarted. The count will be taken to T-minus 9 minutes to hold again.

1849 GMT (1:49 p.m. EST)

Now one hour remaining in today's available window to launch space shuttle Endeavour on a radar mapping mission of Earth. Discussions and analysis of Endeavour's Master Events Controller No. 2 problem continue. Also, the weather remains unchanged and unacceptable.

1829 GMT (1:29 p.m. EST)

NASA spokesman Joel Wells said the special test with the Master Events Controller No. 2 did not repeat the problem seen earlier in the countdown. However, further analysis is ongoing to ensure the MEC will work properly during launch.

1824 GMT (1:24 p.m. EST)

Now over an hour into this unplanned, extended hold at T-minus 20 minutes. Troubleshooting and analysis of the Master Events Controller No. 2 problem continues by the launch team. If this problem can be cleared up, NASA would be 30 minutes away from launch because of the 10-minute planned hold at T-minus 9 minutes. Today's available launch window extends until 1949 GMT (2:49 p.m. EST). Just to repeat ourselves, the weather still looks lousy and it continues to rain at launch pad 39A. Not the type of weather you want for a space shuttle launch day.

1807 GMT (1:07 p.m. EST)

The launch team has decided to perform a special test to further troubleshoot the Master Events Controller No. 2 problem. The test will verify the "on" and "off" commands are transmitted between the shuttle's main computers and the MEC No. 2.

Meanwhile, we have verified that the upcoming Boeing Delta 2 rocket launch planned for February 6 from Cape Canaveral Air Station has been delayed a few days. This is significant to NASA and Endeavour because it would allow launch attempts to become available beginning around the 6th if the shuttle does not fly today or tomorrow. Previously, it was thought if Endeavour had not launched by Tuesday, the next attempt would not be possible until around February 9.

The Air Force-controlled Range needs 48 hours between launches of different vehicles from Kennedy Space Center and Cape Canaveral to reset tracking and computer equipment. There is a Lockheed Martin Atlas rocket launch planned for February 3, too.

1800 GMT (1:00 p.m. EST)

The Range computer problem has been fixed, but the Air Force is "no go" due to weather.

1757 GMT (12:57 p.m. EST)

The U.S. Air Force reports the Range computer problem is nearly complete. In addition, the Range says that some additional requirements have been put in place due to a power problem with a command destruct relay station, but that will not affect launch. Also, all ground optics sites around the Cape used to document the shuttle's launch are buttoned up due to the rain.

1747 GMT (12:47 p.m. EST)

The launch window has now opened for today's attempt. However, the countdown is stuck at T-minus 20 minutes. NASA Test Director Doug Lyons just radioed Endeavour commander Kevin Kregel to update the astronauts on the ongoing delay. Lyons said the Range is reconfiguring and that computer issue could be close to being resolved. Meanwhile data analysis of the Master Events Controller No. 2 problem is continuing and the launch team is nearing a recommendation on how to proceed. And of course the weather still looks very poor.

1740 GMT (12:40 p.m. EST)

The troubleshooting continues to understand why a data loss or data garbling occurred during a standard pre-flight test between Endeavour's onboard General Purpose Computers and Master Events Controller No. 2.

1732 GMT (12:32 p.m. EST)

Now 15 minutes beyond the scheduled time the countdown should have picked up from T-minus 20 minutes.

The launch team members troubleshooting the master events controller problem report they now believe MEC No. 2 is suspect. The two MECs aboard Endeavour are required to be working properly before launch can occur. They control such critical events as jettisoning the solid rocket boosters during launch. The error seen earlier occurred somewhere between MEC No. 2 and the associated data bus.

Also, the Range says it is working a computer problem. Last but not least, weather conditions remain unacceptable. It is currently raining at launch pad 39A.

1727 GMT (12:27 p.m. EST)

NASA Test Director Doug Lyons has been told that the console that went down earlier is now restored.

1723 GMT (12:23 p.m. EST)

The countdown continues to hold at T-minus 20 minutes and there is no estimation on when clocks will resume ticking. Another planned hold is scheduled at T-minus 9 minutes and will last for 10 minutes.

This unplanned hold has officially delayed the launch time. Liftoff at 1747 GMT (12:47 p.m. EST) will not be possible.

1719 GMT (12:19 p.m. EST)

A console in the Launch Control Center has gone down, a launch team member just informed NASA Test Director Doug Lyons. However, this console is not required for launch.

1718 GMT (12:18 p.m. EST)

The launch team reports it is working a pre-flight byte error with one of Endeavour's master events controllers, NASA commentator Joel Wells said.

1717 GMT (12:17 p.m. EST)

The countdown clock has not restarted following what should have been a 10-minute hold. The launch team is working a technical problem.

1715 GMT (12:15 p.m. EST)

The countdown will not be restarted at the end of this hold due to a problem. No further details are available.

Meanwhile, NASA Test Director Doug Lyons has given his pre-launch briefing to the launch team. The liquid oxygen drain back limit is 4 minutes, 10 seconds. That is the maximum amount of time the countdown can hold once LOX drain back to the external tank is started inside T-minus 5 minutes due to main engine performance.

1709 GMT (12:09 p.m. EST)

NASA Launch Director Dave King has just been updated on the latest weather forecast, which continues to worsen. Currently, weather conditions are "no go" for launch due to cumulus clouds and cloud thickness, which raise the threat of triggered lightning. In addition, the flight rule for flight through precipitation is being violated. At the Kennedy Space Center's Shuttle Landing Facility, where Endeavour could return in the event of a problem during launch, conditions are unacceptable due to rainshowers within 20 miles and low cloud ceilings.

1707 GMT (12:07 p.m. EST)

T-minus 20 minutes and holding. The countdown has paused for a 10-minute built-in hold. Launch remains scheduled for 1747 GMT (12:47 p.m. EST). However, weather conditions do not look promising.

During this hold, all computer programs in Firing Room 3 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.

1704 GMT (12:04 p.m. EST)

At this time, 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.

Also, commander Kevin Kregel has pressurized the gaseous nitrogen system for Endeavour's Orbital Maneuvering System engines, and pilot Dom Gorie has activated the gaseous nitrogen supply for the orbiter's Auxiliary Power Units' water boilers.

Earlier, the Eastern Test Range shuttle range safety system terminal count closed-loop test is currently being performed. Other activities scheduled at this point in the countdown include shifting the S-band antennas at the MILA tracking station here at the Cape from low power to high power. The site will provide voice, data and telemetry relay between Endeavour and Mission Control during the first few minutes of flight. Coverage then is handed to a NASA Tracking and Data Relay Satellite in space.

1653 GMT (11:53 a.m. EST)

The Orbiter Closeout Crew reports they have stowed the platforms and equipment in the white room next to the crew hatch of Endeavour. The OCC will now depart launch pad 39A.

1644 GMT (11:44 a.m. EST)

The main line activation of the ground launch sequencer has been completed. The GLS is the master computer program that will control the final nine minutes of the countdown to launch.

1639 GMT (11:39 a.m. EST)

Chief astronaut Charlie Precourt has taken off in the the Shuttle Training Aircraft to flight weather reconnaissance. Precourt has been flying around earlier this morning in a T-38 jet. Precourt plans to stay aloft through the remainder of the countdown.

Weather continues to be the main problem today. Thick clouds and rain are serious threats again an on-time liftoff of Endeavour at 1747 GMT (12:47 p.m. EST).

1627 GMT (11:27 a.m. EST)

T-minus 1 hour. The countdown continues smoothly and without problems today for launch of Endeavour at 1747 GMT (12:47 p.m. EST). The countdown clock is ticking toward T-minus 20 minutes where a 10-minute long hold is planned. A final built-in hold is scheduled at T-minus 9 minutes and will last for 40 minutes.

The pre-flight alignment of Endeavour'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.

Also in the countdown, the booster test conductor will verify the chamber pressure in the twin solid rocket motors. Sensors measure pressure in the thrust chambers at nozzles of the boosters. The data tells onboard computers when the boosters have consumed their solid-fuel propellant and should be separated in-flight.

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

Endeavour's hatch has been verified closed and latched. The weather continues to look lousy at Kennedy Space Center for today's space shuttle launch. A NASA spokesman says a measurement a little while ago indicated cloud thickness of 8,000 feet. The limit for the launch is no greater than 4,500 feet. Thick clouds are of concern because they could trigger a lightning strike as the shuttle launches. Forecasters say the weather will likely be best towards the end of today's two-hour, two-minute window that extends from 1747 to 1949 GMT (12:47-2:49 p.m. EST).

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

The Orbiter Closeout Crew is now closing and locking Endeavour's hatch, a bit ahead of schedule.

1557 GMT (10:57 a.m. EST)

T-minus 90 minutes and counting. The countdown continues toward a planned 1747 GMT (12:47 p.m. EST) launch today of shuttle Endeavour if the weather cooperates. There are two planned holds remaining in the countdown at T-20 and T-9 minutes.

Voice checks between the astronauts, the launch team and Mission Control have been completed.

1532 GMT (10:32 a.m. EST)

Mission specialist No. 2 and flight engineer Janet Kavandi has entered the shuttle, becoming the final astronaut to board Endeavour today. She will sit in the flight deck aft center seat.

1520 GMT (10:20 a.m. EST)

Some additional troubleshooting has been successfully completed at launch pad 39A by a special "Red Crew". The team was dispatched to fix a trickle charge purge, which serves as the secondary side vent support. This was not a constraint to launch, but officials decided to fix the problem since time was available to do so.

1518 GMT (10:18 a.m. EST)

Five of Endeavour's six astronauts are now aboard the shuttle. European Space Agency astronaut, known as mission specialist No. 1, Gerhard Thiele has entered Endeavour's hatch. Thiele will sit in the flight deck aft right seat.

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

Mission specialist No. 3 and payload commander Janice Voss has boarded Endeavour. She will sit in the middeck left seat.

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

Endeavour's pilot, Dom Gorie, has entered the shuttle's hatch. He will sit in the flight deck forward right seat.

We have added a QuickTime video file of the astronauts departing their quarters.

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

Mission specialist No. 4 and Japanese astronaut Mamoru Mohri has boarded Endeavour. Mohri will sit in the middeck right seat.

1454 GMT (9:54 a.m. EST)

Endeavour commander Kevin Kregel has become the first astronaut to enter the shuttle today. He will sit in the flight deck forward left seat.

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

The shuttle astronauts have arrived at launch pad 39A.

1434 GMT (9:34 a.m. EST)

Endeavour's astronauts are on their way to the launch pad. They have departed the Operations & Checkout Building, which serves as the living quarters for the flight crew while at Kennedy Space Center. The ride out to pad 39A, on the edge of the Atlantic Ocean, will take 20 to 25 minutes.

The convoy will stop at the Launch Control Center for the NASA management and Chief Astronaut Charlie Precourt to exit the Astrovan. The managers will take their positions in Firing Room 3 while Precourt heads over to the Shuttle Landing Facility to begin weather reconnaissance flights in a T-38 jet. Later he will 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.

1427 GMT (9:27 a.m. EST)

T-minus 3 hours and counting. Countdown clocks have resumed following this two-hour planned hold. The count will continue to T-minus 20 minutes where the next built-in hold will occur. Launch is still scheduled for 1747 GMT (12:47 p.m. EST. The weather remains the primary concern today.

The astronauts are expected to depart their quarters for the launch pad in about five minutes.

1410 GMT (9:10 a.m. EST)

With the replacement of a few fuses, the redundant power supply to a main engine liquid hydrogen pump has been restored. A special "Red Crew" was sent to pad 39A to complete the work.

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

A weather briefing from the Spaceflight Meteorology Group based at Mission Control is underway for the Endeavour's astronauts. This weather update is for the abort landing sites at Kennedy Space Center, California, New Mexico, Africa and Spain.

The latest forecast for KSC at launch time is calling for scattered clouds at 3,000 feet and broken at 10,000 and 25,000 feet, 7 miles visibility and northwesterly winds 10 peaking to 15 knots. The concerns are with the chance of the 3,000-foot cloud deck becoming broken and constituting a ceiling and the possibility of showers within 20 nautical miles of the shuttle runway.

For TALs, overall they are looking good today. White Sands also appears more favorable for an Abort-Once-Around landing site.

Currently at KSC, a cold front has passes just south of the launch site. The entire Central Florida area has awakened to dark, cloudy skies, fog and little mist this morning. Behind the front, in northern Florida, is a large area of rain. Weather forecasters hope the conditions will push through the local area by the end of today's two-hour, two-minute launch window that opens at 1747 GMT (12:47 p.m. EST). Officially, there is a 40 percent chance conditions will allow Endeavour to launch today.

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

Endeavour's astronauts have just been seated for a final pre-launch in the dining room at the Operations & Checkout Building. This is lunch of Blue Team and breakfast for the Red Team.

Meanwhile, officials have decided to send a special team to launch pad 39A to troubleshoot a problem with a redundant power supply for a main engine liquid hydrogen recirculation pump. If this problem cannot be fixed, it will not be a constraint to launch because the primary power supply is working just fine. The team's time at the pad should last about one hour.

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

Endeavour stands fully fueled and ready for launch from pad 39A at Kennedy Space Center, Fla. The loading of 528,000 gallons of liquid oxygen and liquid hydrogen into the external tank officially began at 0910 GMT (4:10 a.m. EST). The operation went smoothly and was completed at 1204 GMT (7:04 a.m. EST). A stable replenishment mode has now started to continuously top-off the respective tanks within the bullet-shaped 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. Currently, the six-person team is 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, which is headed by Greg Katnik of the Kennedy Space Center, is also looking for any loose debris that could possibly fly up and strike the launch vehicle. 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 vehicle 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.

Each member of the Final Inspection Team is in constant contact with NASA Test Director Doug Lyons in Firing Room 3.

The team wears the highly visible day-glo-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, Greg Katnik will meet with NASA Launch Director Dave King, the Mission Management Team, and engineering directors in the launch control center. Katnik will give the managers a full and detailed report on the team's inspections and findings at the pad 39A.

A full inspection of the vehicle and pad was performed on Sunday and the external tank received a thorough check prior to fueling.

An inspection of the launch pad and beach will be made following launch today. 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.

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

T-minus 3 hours and holding. The countdown has entered a two-hour planned hold. During this time, the final inspection team and orbiter closeout crew are dispatched to launch pad 39A to begin their work. The inspection team will check the shuttle and launch pad for any ice or debris following fueling. The closeout crew will ready Endeavour's crew module for the astronauts' arrival.

In the next few minutes, the Red Team of commander Kevin Kregel and mission specialists Gerhard Thiele and Janet Kavandi will be awakened after an eight-hour sleep period. The Blue Team of pilot Dom Gorie and mission specialists Janice Voss and Mamoru Mohri were awakened about seven hours ago, and they will next sleep about four hours into the mission.

The six astronauts are divided into the two shifts to allow round-the-clock, 24-hour radar mapping during the mission.

A little mist continues to fall at Kennedy Space Center. There are a lot of clouds and fog around the launch site, too. The launch pad is completely hidden by the weather from the KSC Press Site located just over three miles away. Officially, meteorologists say there is a 60 percent chance the weather will prohibit launch today.

Launch of Endeavour remains planned for 1747 GMT (12:47 p.m. EST).

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

The shuttle launch team has just completed loading 528,000 gallons of liquid oxygen and liquid hydrogen into Endeavour's external fuel tank. The super-cold cryogenics will be replenished continously throughout the remainder of the countdown to replace that which naturally boils away.

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

Tanking operations are continuing smoothly at launch pad 39A and no problems have been reported.

0935 GMT (4:35 a.m. EST)

Fuel is flowing into Endeavour at launch pad 39A. The shuttle launch team in Firing Room No. 3 has commenced the three-hour tanking process to load space shuttle Endeavour's external tank with 528,000 gallons of super-cold liquid hydrogen and liquid oxygen.

The cryogenics are being pumped from a pair of storage spheres located at the pad's parameter through fuel lines to the mobile launcher platform. From there, the propellants are fed into Endeavour's aft engine compartment via umbilicals and make their way into the external tank through the shuttle's plumbing.

The countdown has resumed from the one-hour built-in hold at T-minus 6 hours and clocks are ticking toward T-minus 3 hours where another hold is planned.

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

The Mission Management Team has given approval to begin fueling space shuttle Endeavour for launch later today. The loading over over a half-million gallons of super-cold rocket fuel into the shuttle's bullet-shaped external tank will start shortly at Kennedy Space Center's pad 39A.

The weather forecast remains unchanged with a 60 percent chance of unacceptable conditions today. The main concern is thick clouds associated with a passing cold front.

There are no technical problems being discussed and launch remains scheduled for 1747 GMT (12:47 p.m. EST).

0327 GMT (10:27 p.m. EST)

T-minus 11 hours and counting. The countdown has resumed following a planned 12-hour, 57-minute hold. Clocks will continue ticking down to T-minus 6 hours where a one-hour built-in hold is scheduled. Launch of Endeavour remains scheduled to occur at 1747 GMT (12:47 p.m. EST), the opening of a two-hour, two-minute window.

At launch pad 39A, workers rolled the rotating service structure away from Endeavour about 3 1/2 hours ago. The shuttle is now sitting brightly illuminated on the pad, awaiting fueling operations that will occur before dawn.

Over the next few hours, the shuttle's three power-generating fuel cells will be activated and Endeavour's purge air will be switched to gaseous nitrogen. The Mission Management Team will convene at 0830 GMT (3:30 a.m. EST) for the traditional pre-tanking meeting. The review will cover countdown status, the weather forecast and any outstanding issues or concerns. If there are no significant problems, officials will clear the launch team to begin loading a half-million gallons of super-cold liquid hydrogen and liquid oxygen into the shuttle's external fuel tank after 0900 GMT (4 a.m. EST). The operation will take three hours to complete.

The six Endeavour astronauts are divided into two shifts to allow round-the-clock radar mapping during the mission. Right now, the Red Team of commander Kevin Kregel and mission specialists Gerhard Thiele and Janet Kavandi are preparing to go to bed in about an hour. The Blue Team of pilot Dom Gorie and mission specialists Janice Voss and Mamoru Mohri will be awakened in about two hours. The astronauts will be joined for a final pre-launch meal at 1322 GMT (8:22 a.m. EST). Later, they will receive a weather briefing and don their spacesuits before heading to the launch pad.

SUNDAY, JANUARY 30, 2000
2245 GMT (4:45 p.m. EST)

NASA officials today cleared space shuttle Endeavour for launch on Monday despite a lack of paperwork to verify the craft's fuel turbopumps are not equipped with suspect parts.

The concern was raised this week when NASA found a two-inch area on a nickel tip seal segment that debonded from its backing inside a turbopump that flew aboard Discovery last month. The tip seals are used to direct hot gases into the turbopump's turbine blades for proper engine performance. During Discovery's launch, the debonded section of nickel material was hit be the fast-spinning turbine blades.

The debonded segment was deemed unusable during manufacturing and should have been thrown away, but accidently found its way into a shuttle main engine. The suspect seal and turbopump were used during six engine firings, three of which were actual shuttle missions, NASA officials said today, a change from information provided yesterday.

In a paperwork chase to verify the 18 segments on Endeavour were certified for use, NASA says manufacturing records cannot be found for two of those segments. One was made in 1979, the other in 1993.

In explaining the rationale for flying the shuttle without further action, such as inspecting the turbopump seals, shuttle program director Ron Dittemore says there is very low probability the two nickel tip seal segments aboard the shuttle are faulty. In addition, he said even if the segments were to debond like on Discovery, the risk of failing the engine during launch is considered remote based upon analysis and previous experience.

"The main engine team throughout the country continued to work for the last 24 hours to review the data and analysis to support the flight," Dittemore told reporters in an informal news conference. "We just met in the capacity of the mission management team, reviewed the information they had collected and concluded the engines are safe to fly. We will be picking up the count on schedule."

Launch of Endeavour, weather permitting, is planned to occur at 1747 GMT (12:47 p.m. EST), the opening of a two-hour, two minute-window.

The forecast continues to show a 60 percent chance of bad weather at Kennedy Space Center on Monday.

1515 GMT (10:15 a.m. EST)

The weather forecast for Monday's scheduled launch of space shuttle Endeavour has taken a turn for the worse as the countdown ticks on at Kennedy Space Center.

U.S. Air Force meteorologists say there is now only a 40 percent chance of acceptable weather conditions during Monday's launch window extending from 1747-1949 GMT (12:47-2:49 p.m. EST). The main concern will be thick clouds. Earlier, there had been a 70 percent chance of good weather.

The change was caused by a frontal system, which was expected to be well south of KSC on Monday. But that front has slowed and may not be as far south as originally predicted. Forecasters say the closer the front is to KSC, the greater the chance of having thick clouds and rain showers around the launch site.

The launch time forecast calls for scattered to broken clouds at 3,000 feet, and broken clouds at 10,000 and 25,000 feet, 7 miles visibility, northwesterly winds 12 peaking to 16 knots, a chance of rain showers in the vicinity and a temperature of 62 degrees F.

As predicted yesterday, the weather at abort landing sites in California and New Mexico are also a concern for Monday. High crosswinds are still forecasted for Edwards Air Force Base and White Sands. The sites could be used by Endeavour in an emergency if the shuttle had to return to Earth before completing a full orbit of Earth.

However, mission officials at Johnson Space Center in Houston say those sites will not be required for launch because Endeavour could abort to orbit if one main engine shuts down early. That means NASA has another option instead of ordering the abort landing at Edwards or White Sands. If an engine should fail earlier in flight, Endeavour would be diverted to a landing facility in Spain or Africa.

At launch pad 39A, Endeavour's fuel cells have been loaded with liquid oxygen and liquid hydrogen. The reactants will be combined to generate electricity and drinking water during the space mission.

Senior shuttle managers plan to meet at 1900 GMT (2 p.m. EST) today to further discuss the main engine turbopump problem encountered during the launch of Discovery last month. The meeting is expected to either clear Endeavour for flight as is, or announce some sort of launch delay. See an image of a tip seal segment like the one that caused the problem during the last shuttle mission.

If the launch plans remain on track, the gantry-like rotating servicing structure will be retracted at 2330 GMT (6:30 p.m. EST) tonight. The launch pad will be cleared of all workers about six hours later. Managers will meet again at 0830 GMT (3:30 a.m. EST) on Monday to review the status of countdown, the latest weather forecast and give the OK to begin fueling Endeavour for launch. Loading of 528,000 gallons of liquid oxygen and liquid hydrogen into the external fuel tank should start at around 0930 GMT (4:30 a.m. EST) and take three hours to complete.

SATURDAY, JANUARY 29, 2000
2330 GMT (6:30 p.m. EST)

NASA mission managers today decided to continue with the countdown for Monday's launch of space shuttle Endeavour. However, they will meet again Sunday afternoon at 2 p.m. EST (1900 GMT) to further discuss the main engine turbopump problem seen during the last shuttle launch. The second meeting will allow engine experts another day to review data and analysis.

Shuttle program chief Ron Dittemore says the braze debond of nickel plating experienced on the turbine tip seal in the high-pressure fuel turbopump on Discovery last month was caused by a vendor snafu. The suspect part installed into the turbopump was not certified for use during a shuttle launch. Instead, it was rejected during manufacture and should have been scraped. "It was an honest mistake," he said. Reviews of paperwork show the part flew six times, but only debonded during the STS-103 mission in December.

Checks of records documenting the hardware on Endeavour show that 16 of the 18 tip seal segments are certified for flight. However, two cannot be verified through paperwork.

Officials feel confident that the debonding seen during Discovery's launch would not have compromised the safety of the engine. But they will meet on Sunday to debate the risks of flying as is.

"The folks have done a great job in gathering the data that supports flight. However, we have decided to give the team 24 hours to have more time and self life on the rationale that they have presented today."

Each turbopump contains two tip seals, or six segments. They run the circumference of the pump housing, about 18-thousandths-of-an-inch away from each of the two turbine blade wheels. The seals prevent airflow above the turbine blades to direct hot gases into the turbine machinery.

We have posted a QuickTime video clip from this evening's NASA press conference.

2140 GMT (4:40 p.m. EST)

NASA mission managers are continuing their standard Launch Minus-2 Day meeting today, which began over 2 1/2 hours ago. Officials are getting an update on the fuel turbopump problem seen on space shuttle Discovery's most recent mission and may decide today what actions, if any, need to be made to ensure Endeavour can fly safely. Sources say engine experts will recommend Endeavour be cleared for launch as is. However, managers will have the final say in the matter.

At launch pad 39A, the countdown has resumed from a planned hold and loading of the shuttle's fuel cells with cryogenic reactants has started.

A press conference originally planned for 4 p.m. EST is being delayed until after the management team meeting concludes. We will post additional information has soon as it becomes available.

1430 GMT (9:30 a.m. EST)

T-minus 27 hours and counting. The STS-99 countdown has the entered the first in a series of holds leading up to Monday's planned launch of space shuttle Endeavour. This hold will last for four hours.

NASA officials told reporters at a countdown status briefing minutes ago that no additional information was available on the engine problem that threatens to delay Endeavour. However, engine experts working the problem are expected to provide their insights to senior NASA managers this afternoon during a meeting that will start at 2 p.m. EST (1900 GMT). A full press conference is planned for no earlier than 4 p.m. EST (2100 GMT) at the Kennedy Space Center. We will post any information as soon as it is available.

Meanwhile, preparations are continuing at launch pad 39A. Since the countdown started yesterday, technicians have started final work to ready the shuttle's electronics and avionics for launch. The pad will be cleared of all non-essential personnel shortly so the launch team can perform a test of the pyrotechnic initiator controllers, which will fire the ordnance to separate the shuttle from the launch pad at ignition. Later today, Endeavour's three fuel cells will be loaded with liquid hydrogen and liquid oxygen reactants. The cryogenics will be used to generate power and drinking water during the 11-day shuttle mission.

The weather forecast for KSC continues to look favorable with a 70 percent chance of good conditions on Monday and Tuesday. The only concern will be thick clouds that could trigger a lightning strike during launch. However, meteorologists are watching the potential of unacceptably high crosswinds at abort-once-around landing sites at California's Edwards Air Force Base and New Mexico's White Sands on Monday and Tuesday. Either site would be used as an emergency landing facility if the shuttle had to return to Earth before completing one orbit. NASA will require at least one site have acceptable weather conditions before Endeavour can launch.

NASA only has launch attempts available on Monday and Tuesday before having to wait until around February 8 or 9 before trying again. The reason is other unmanned launches at nearby Cape Canaveral Air Station planned for February 3 and 6. The U.S. Air Force-run Eastern Range needs 48 hours between launches of different vehicles to reconfigure its tracking, communications and safety systems.

If the shuttle isn't off the ground by around February 16, NASA likely will have to wait until mid-March because the Range has scheduled a down period for upgrades, preventing any launches from KSC or Cape Canaveral.

FRIDAY, JANUARY 28, 2000
2230 GMT (5:30 p.m. EST)

T-minus 43 hours and counting. The countdown has begun for the launch of space shuttle Endeavour and the first human spaceflight of the new century. Countdown clocks are ticking toward a scheduled 1747 GMT (12:47 p.m. EST) liftoff on Monday despite an ongoing concern with a main engine turbopump found after shuttle Discovery's launch last month. NASA opted to start the countdown as planned today to preserve the option of launching on schedule if the engine problem can be resolved in time.

The STS-99 countdown, controlled from Firing Room No. 3 of the Complex 39 Launch Control Center, will feature 24 hours and 17 minutes of built-in hold time.

This shuttle mission, the first of 2000, will be the 14th flight of Endeavour and the 97th flight overall in NASA's shuttle program. It will also mark the 72nd shuttle flight since the Challenger accident 14 years ago today.

1450 GMT (9:50 a.m. EST)

Monday's launch of space shuttle Endeavour could be postponed after technicians this week found unusual wear on a key engine component that flew aboard sistership Discovery last month.

Read our full story on the problem. We have also posted a QuickTime video clip from today's mission status briefing.

Boroscope inspections show rubbing on a seal used to direct hot gases through the engine's turbopump. The suspect hardware has been shipped from Kennedy Space Center to the engine manufacturer Rocketdyne in Canoga Park, California, for further analysis.

NASA hopes the tests will be completed by Saturday, allowing managers to debate the issue during a regularly scheduled meeting.

The impact, if any, to Endeavour's launch date is not yet known. NASA has two attempts to get Endeavour off the ground, on Monday and Tuesday, before having to wait until around February 9 because other rocket launches planned from nearby Cape Canaveral Air Station.

"It is too early to say now. We got to go and see what really is going on there," NASA test director Doug Lyons told reporters this morning. "At this point, what we are doing is planning on proceeding with the countdown timeline."

The countdown is slated to begin at 2230 GMT (5:30 p.m. EST) today.

THURSDAY, JANUARY 27, 2000
1706 GMT (12:06 p.m. EST)

The Endeavour astronauts have just touched down at Kennedy Space Center in their T-38 jet trainers. The crew flew from their home base in Houston, Texas, to the Cape this morning to begin final pre-launch preparations.

NASA says all systems remain go to start the STS-99 launch countdown on Friday at 2230 GMT (5:30 p.m. EST). Liftoff remains set for 1747 GMT (12:47 p.m. EST) on Monday

The early weather forecast indicates a 70 percent chance of good weather with the main threat being thick clouds.

We will have a complete report later with comments from the astronauts. We have posted a QuickTime movie of the crew's comments to the press.

0250 GMT (9:50 p.m. EST)

Space shuttle Endeavour remains scheduled to launch Monday from the Kennedy Space Center on the Shuttle Radar Topography Mission, a 10-day flight that will make an unprecidented map of the Earth in three dimensions. Liftoff is slated for 1747 GMT (12:47 p.m. EST) at the opening of a two hour, two minute launch window.

The six astronauts will depart the homes in Houston this morning and fly to KSC. Their arrival at the Shuttle Landing Facility is expected at about 1700 GMT (12 noon EST).

NASA plans to begin the three-day launch countdown at 2230 GMT (5:30 p.m. EST) on Friday.

Here is an update on pre-launch preparations from the official Kennedy Space Center shuttle status report:

Preparations for Shuttle Endeavour's upcoming launch continue on schedule at Launch Pad 39A. Aft compartment close-outs are complete. Replacement of the four payload bay camera assemblies is complete and retesting concluded today. While the payload bay doors are open, workers will clean the optics on the SRTM Attitude and Orbit Determination Assembly (AODA). Door closure is slated to occur tonight. Endeavour remains in the standard cold weather configuration with the reaction control system heaters powered up.