BY JUSTIN RAY

December 27, 1999 -- Follow the launch and mission of space shuttle Discovery to repair the Hubble Space Telescope. Reload this page for the very latest on the mission.

1828 GMT (1:28 p.m. EST)

Discovery's two 60-foot long payload bay doors have been closed and latched, a major milestone in today's preparations for entry and landing.

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

The left-hand payload bay door is now swinging closed.

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

The astronauts have bypassed Discovery's cooling from the radiators on the payload bay doors to the flash evaporator system. This allows the payload bay doors to be closed.

1808 GMT (1:08 p.m. EST)

Entry flight director Wayne Hale, after completing a poll of his team in Mission Control, has given a "go" to close the payload bay doors of shuttle Discovery on schedule in about 20 minutes. The latest Kennedy Space Center weather forecast for landing at 5:18 p.m. EST (2218 GMT) calls for clear skies, unrestricted visibility and northwesterly winds 9 peaking to 17 knots. The winds are currently forecasted to be within limits to allow Discovery to return to Earth, ending a triumphant eight-day mission to repair the Hubble Space Telescope.

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

The astronauts stepped into their deorbit timeline about 30 minutes ago in preparation for landing. Activities completed so far include setting onboard timers to countdown to the deorbit burn, maneuvering the shuttle to the cold-soak attitude, installing the mission specialist seats and wrapping up stowage of equipment inside the crew module.

The latest weather update continues to show generally favorable conditions for the first landing attempt at 5:18 p.m. EST (2218 GMT). The current weather is acceptable and the forecast is also within limits. Crosswinds will be watched, but meteorologists say the winds should continue to decrease as the day goes on.

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

The entry team of flight controllers has arrived on console for today's scheduled landing of space shuttle Discovery. The team is led by Flight Director Wayne Hale.

Within the hour, Hale will receive a full weather briefing on conditions expected at Kennedy Space Center for the three landing opportunities available today. That will be followed at about 12 noon EST by the astronauts beginning their deorbit preparation timeline, a four-hour block of time to finish configuring the shuttle for entry, suiting up and strapping into their seats.

The crew's day began with a wake-up call from Mission Control in the form of "The Cup of Life," sung by Ricky Martin. The music was the official song of France '98 World Cup Soccer and was played for mission specialist Jean-Francois Clervoy of the European Space Agency at the request of his son.

At this point, all remains set for Discovery to fire its twin orbital maneuvering system engines to begin the trek from orbit at 4:06:40 p.m. EST (2106:40 GMT). Landing would then occur at 5:18:50 p.m. EST (2218:50 GMT).

A backup landing opportunity at KSC is available one orbit later with a deorbit burn ignition time of 5:49:27 p.m. EST (2249:27 GMT) and touchdown at 7:01:14 p.m. EST (0001:14 GMT Tuesday).

Should weather or some technical problem scrub the earlier tries, there is one final shot into KSC today on the third consecutive orbit. However, it is unlikely NASA would try for all three straight. They would have to give up on the first attempt before closing the payload bay doors, which is about 2 1/2 hours away. In any event, the third attempt would begin with the deorbit burn at 7:32:12 p.m. EST (0032:12 GMT) and landing at 8:43:23 p.m. EST (0143:23 GMT).

Discovery is currently in an orbit of 329 by 301 miles with no problems reported.

0310 GMT (10:10 p.m. EST)

Shuttle Discovery is packed up and ready to return home late Monday afternoon, ending a highly successful eight-day mission to repair the crippled Hubble Space Telescope.

NASA mission managers say good weather conditions should greet Discovery during a sunset touchdown on Kennedy Space Center's three-mile-long shuttle runway.

However, meteorologists will be keeping a close eye on crosswinds that could keep Discovery in space for an extra orbit or two, or an additional day.

Entry flight director Wayne Hale says if weather does prevent Discovery from landing on Monday, NASA would likely keep the shuttle in orbit for one more day and shoot for KSC on Tuesday afternoon.

But the decision to delay landing a day and not immediately divert to the backup landing site at Edwards Air Force Base in California on Monday would only come if the weather forecast looks favorable for both sites on Tuesday, which is currently the case.

Officials like to avoid landing at Edwards to save the $1 million it costs to ferry the shuttle back to Florida atop a modified Boeing 747 jet.

The space agency wants Discovery on the ground no later than Wednesday so the ship can be safed and ground computers turned off before the Y2K rollover.

Hale will have three opportunities to get Discovery into KSC on Monday. The first would begin with a deorbit burn at 4:06 p.m. EST (2106 GMT) and landing at 5:18 p.m. EST (2218 GMT). The second attempt would feature a deorbit burn ignition at 5:49 p.m. EST (2249 GMT) and landing at 7:00 p.m. EST (0000 GMT). The last shot would begin with deorbit at 7:32 p.m. EST (0032 GMT) and touchdown at 8:43 p.m. EST (0143 GMT). The second two attempts would be nighttime landings.

The forecast for landing time at KSC on Monday calls for a few clouds at 25,000 feet, unrestricted visibility and winds from the west at 9 peaking to 14 knots. Earlier in the day, winds could be gusting upwards of 18 knots. However, the winds are predicted to decrease as the evening goes on.

The astronauts are scheduled to be awakened at 8:20 a.m. EST (1320 GMT) to begin final work before entry and landing. The deorbit preparation timeline will start just after 12 noon EST (1700 GMT). Discovery's 60-foot long payload bay doors should be closed and locked at about 1:30 p.m. EST (1830 GMT) to support the first landing opportunity.

SUNDAY, DECEMBER 26, 1999
2110 GMT (4:10 p.m. EST)

Space shuttle Discovery has just completed an orbit adjust maneuver, setting up for Monday's landing opportunities at Kennedy Space Center in Florida or Edwards Air Force Base in California.

The burn further reduced the low point of Discovery's orbit by 16 nautical miles. The shuttle is now circling the Earth in an orbit of 329 by 300 nautical miles.

The maneuver also will increase the distance between Discovery and the Hubble Space Telescope. Before the burn, the two were about 53 nautical miles apart, and moving away at 4 miles per orbit. Now, they will be separating at 70 miles per orbit, or ever 96 minutes.

Earlier this afternoon the crew successfully completed checks of the shuttle's flight control systems and reaction control thusters.

We will have a complete landing preview following a news briefing from NASA at 9:30 p.m. EST tonight (0230 GMT Monday).

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

The shuttle astronauts were awakened at 1350 GMT (8:50 a.m. EST) today to begin their final full day in space. Today's orbital wake up music was the song "We're So Good Together" by Reba McEntyre, played for pilot Scott Kelly at the request of his wife.

The next event in this STS-103 mission will be the traditional in-flight news conference. The 40-minute media briefing will begin at 1650 GMT (11:50 a.m. EST) with reporters at NASA centers in the U.S. and European Space Agency facilities in Geneva and Paris.

Later today commander Curt Brown and Kelly will test Discovery's flight control systems and aerosurfaces that will be used during Monday's reentry and landing. Also, the crew will pack up the shuttle's crew module, stowing equipment and materials. Near the end of the crew's day at 0245 GMT (9:45 p.m. EST), the dish-shaped Ku-band antenna will be retracted for landing, ending live television from Discovery.

Discovery is scheduled to perform the deorbit burn to leave orbit at 2111 GMT (4:11 p.m. EST) tomorrow. That would set up for a landing at Kennedy Space Center at 2221 GMT (5:21 p.m. EST).

The current landing time weather forecasts are generally favorable. KSC is calling for a few clouds at 25,000 feet, visibility of 7 miles and northwesterly winds 9 peaking to 14 knots. At the backup site - Edwards Air Force Base in California - conditions are expected to include a few clouds at 8,000 feet, scattered clouds at 12,000 and 22,000 feet, 7 miles visibility and northeasterly winds 6 peaking to 12 knots.

SATURDAY, DECEMBER 25, 1999
2339 GMT (6:39 p.m. EST)

The second of two separation maneuvers has been completed by Discovery to move the shuttle away from Hubble. This was a seven-second firing of the shuttle's reaction control thrusters.

The rest of the crew's day will be spent having a meal and participating in several interviews with reporters. Sunday will see the astronauts preparing for Monday's entry and landing by packing up Discovery's crew compartment and testing the flight control systems.

2327 GMT (6:27 p.m. EST)

With Hubble back in normal mode under gyroscope control for the first time in over two months, Discovery continues to move away. Distance between the two craft is now 850 feet and continuing to expand.

2317 GMT (6:17 p.m. EST)

Hubble controllers report very tiny rates were imparted on the telescope. Shortly the fine guidance electronics will be activated and the star trackers will determine the craft's field of view. In less than 20 minutes, pilot Scott Kelly will begin the separation burn to move Discovery out of Hubble's orbit.

2312 GMT (6:12 p.m. EST)

Discovery is now 500 feet away from Hubble.

2306 GMT (6:06 p.m. EST)

Hubble Space Telescope controllers report the spacecraft has moved to a sun-point mode as planned.

2305 GMT (6:05 p.m. EST)

Discovery is backing away from the Hubble Space Telescope at about one foot per second.

2303 GMT (6:03 p.m. EST)

A refurbished and working Hubble Space Telescope has been set free from Discovery after a long-distance servicing call by the shuttle's astronauts. The $3 billion telescope, the first of NASA's Great Observatories, was set released at 2303 GMT (6:03 p.m. EST) as Discovery sailed high above the South Pacific northeast of Australia.

Over the past three days, four shuttle astronauts logged 24 1/2 hours of spacewalking time in three excursions to repair the telescope's crippled pointing system and install of new electronics.

Soon controllers will issue commands to Hubble to maneuver the telescope to the desired attitude. The controllers will also reconfigure Hubble's low gain antenna to resume communications through NASA's Tracking and Data Relay Satellites, allowing data from HST to be transmitted to the STOCC control center.

Scientists anticipate to resume science observations in the visible spectrum with Hubble in about two weeks. That will be the first work the telescope has performed since shutting down in mid-November due to the broken pointing system. Observations in the ultraviolet range should start in about three weeks.

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

Power to Discovery's aft control station is now on. That is where commander Curt Brown will fly Discovery away from Hubble after deployment in about three minutes.

2241 GMT (5:41 p.m. EST)

Lead STS-103 flight director Linda Ham has given the final "go" for release of the Hubble Space Telescope from shuttle Discovery at 2303 GMT (6:03 p.m. EST).

2238 GMT (5:38 p.m. EST)

The Space Telescope Operations Control Center reports it is go for deployment of Hubble in 25 minutes.

2235 GMT (5:35 p.m. EST)

The aperture door has been opened and final commanding sequences are being uplinked to the Hubble Space Telescope in preparation for re-deployment at 2303 GMT (6:03 p.m. EST).

2134 GMT (4:34 p.m. EST)

As Discovery begins its 90th orbit of Earth, Hubble is now being maneuvered to the release position over the side of the shuttle's payload bay. Deployment is now about 90 minutes away, and live television of the event is expected from Discovery.

2123 GMT (4:23 p.m. EST)

Hubble is on its way out of the Discovery's payload bay. Riding on the robotic arm, the telescope will be moved to staging point above the bay, then later over the side of Discovery for release.

2120 GMT (4:20 p.m. EST)

The three berthing latches holding Hubble to the lazy-susan support structure in Discovery's payload bay have been retracted. With this completed, the telescope now will be lifted out of the bay. Deployment of Hubble is now targeted to occur at 2303 GMT (6:03 p.m. EST).

2110 GMT (4:10 p.m. EST)

The electrical umbilical connecting the Hubble Space Telescope to space shuttle Discovery has been disconnected. The telescope is running on its internal power now.

The next step will be to release three latches to free Hubble from the platform it is sitting on in Discovery's payload bay. That will clear the way for Jean-Francois Clervoy to hoist the 4 1/2-story tall telescope out of the bay for deployment into space.

2000 GMT (3:00 p.m. EST)

French astronaut Jean-Francois Clervoy has grappled the Hubble Space Telescope using Discovery's robotic arm in preparation for today's deployment. In about an hour, the telescope will be lifted out of the payload bay and maneuvered into position for release.

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

For the first time in its near 19-year history, a space shuttle is orbiting the Earth on Christmas Day. Discovery's mission to service the Hubble Space Telescope, now entering the home stretch, will see the seven international astronauts spend this holiday redeploying the $3 billion observatory back into space.

Checks of Hubble's newly installed elctronics have gone well, and this third servicing mission of the 9 1/2-year old telescope has been declared a complete success.

"What a Christmas for Hubble!" program manager John Campbell said last tonight during a press conference. "Six gyros, new ones, not normally found under the tree, a new computer, better batteries - everybody needs batteries on Christmas - more storage, new clothes, better fine guidance - and everybody needs better guidance on Christmas - and a new radio transmitter. So we're leaving Mom tomorrow and going back to work."

The crew was awakened by Mission Control just a few moments ago to the song "I'll Be Home for Christmas."

"Good Christmas morning, Discovery. It is time to return Hubble to the heavens," CAPCOM Chris Hadfield said.

"Hubble will be home for Christmas," commander Curt Brown responded.

Over the next couple of hours the crew will get dressed, have a quick bite to eat and then begin preparing to set Hubble free.

The work will underway at about 1945 GMT (2:45 p.m. EST) when mission specialist Jean-Francois Clervoy grapples Hubble with Discovery's 50-foot robotic arm. About an hour and 10 minutes later, Hubble will be gently lifted out of the shuttle's payload bay, away from a lazy-susan table platform the 12 1/2-ton telescope has been resting on since Tuesday. The large aperture door on Hubble will be swung open at 2135 GMT (4:35 p.m. EST). Release of Hubble to resume its mission to observe our universe should occur at about 2250 GMT (5:50 p.m. EST).

The seven Discovery astronauts will join eight other Americans as having spent Christmas in space. The three-man Apollo 8 crew orbited the moon in 1968; three men were on Skylab in 1973 and astronauts John Blaha and Dave Wolf were aboard the Russian space station Mir in 1996 and 1997, respectively.

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

Space shuttle Discovery's astronauts have completed a successful Christmas Eve spacewalk, ending three days of work to repair and enhance the $3 billion Hubble Space Telescope. The stage is now set to relaunch Hubble into orbit from Discovery on Christmas Day at 2303 GMT (6:03 p.m. EST).

This third spacewalk officially ended at 0325 GMT (10:25 p.m. EST). Mission Control decided to leave Grunsfeld's suit on internal battery power and repressurize the airlock anyways. This spacewalk lasted eight hours and eight minutes, bringing the total EVA time on STS-103 to 24 hours and 33 minutes. The spacewalk also goes into the history books as the fourth longest in history behind the STS-49 EVA No. 3 in 1992 and the first two EVAs from this shuttle mission.

0323 GMT (10:23 p.m. EST)

John Grunsfeld is having difficulty switching his spacesuit to shuttle-provided power. Mission controllers are discussing the problem.

0310 GMT (10:10 p.m. EST)

The spacewalking duo is back in Discovery's airlock. The spacewalk will officially end when Smith and Grunsfeld switch their suits from battery to shuttle power.

Meanwhile, Hubble's two high gain antennas and their deployable arms have been released in preparation for tomorrow's release of the telescope back into space.

0209 GMT (9:09 p.m. EST)

On this Christmas Eve in Mission Control, CAPCOM Steve Robinson just radioed the Discovery crew to announced that full mission success has been achieved on STS-103. Hubble's precision pointing system has been fixed, an advanced computer was added, plus other electronics planned to be replaced during this third servicing mission have been swapped.

Also, the optical control unit installed earlier on this spacewalk has completed a functional test, ensuring it is working properly. Currently, the spacewalkers are completing a tool inventory and cleaning up the payload bay before returning to the airlock in less than an hour.

In Mission Control, Santa Claus has arrived on console, overseeing Discovery's systems.

0146 GMT (8:46 p.m. EST)

Spacewalkers Steve Smith and John Grunsfeld have installed new thermal insulation on two of Hubble's equipment bay doors tonight, adding further protection to the electronics contained within the compartments.

Other bays that had been earmarked for additional insulation on this servicing mission will have to rely on the temporary materials installed during the last Hubble visit in 1997. This spacewalk is running behind schedule and NASA feels comfortable leaving the other insulation as is until the fourth servicing in the summer of 2001. Mission Control has instructed the spacewalkers to begin putting away their tools and preparing to return to the shuttle over the next hour.

0055 GMT (7:55 p.m. EST)

Steve Smith is cutting away the temporary insulation material strapped onto Hubble's outer surface during the last servicing mission nearly three years ago. Once this material is removed, the new insulation will be attached to Hubble. The insulation is important because it protects the sensative electronics inside the telescope's equipment bays. Now over 5 1/2 hours into this spacewalk. Mission Control wants the spacewalkers to finish the insulation installation work within the next hour, leaving an additional hour for cleaning up the payload bay before returning to Discovery's crew cabin.

0040 GMT (7:40 p.m. EST)

Spacewalkers Steve Smith and John Grunsfeld are beginning work to attach semi-hard thermal insulation blankets over Hubble's equipment bays 9 and 10. These bays were covered with some thrown-together materials on the last servicing mission in 1997 after the astronauts found Hubble's original insulation to be toren and degraded. Now over five hours into this third and final spacewalk for the STS-103 mission.

0019 GMT (7:19 p.m. EST)

The remaining task tonight is the installation of thermal blankets over a couple of Hubble's compartments.

0005 GMT (7:05 p.m. EST)

The Hubble project reports the aliveness test with the new data recorder has been successful, ensuring the device was correctly installed aboard the telescope. The spacewalkers are wrapping up work to close out that area of the telescope, and soon will move clear so ground controllers can conduct a transmission test of the new S-band antenna system installed earlier in this EVA.

FRIDAY, DECEMBER 24, 1999
2355 GMT (6:55 p.m. EST)

The spacewalkers have finished installing the new solid state recorder aboard Hubble. The go has now been given to telescope ground controllers to perform an aliveness test to verify the recorder is properly connected.

Meanwhile, Mission Control has just told the crew they would like the spacewalk to be completed with a duration no longer than 7 1/2 hours, or about 0237 GMT (9:37 p.m. EST).

2310 GMT (6:10 p.m. EST)

The old reel-to-reel tape recorder has been removed and the astronauts are now working to install the new solid state recorder.

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

Having completed the replacement of the S-band transmitter, Smith and Grunsfeld are now working to install a solid state recorder.

Here is some text from NASA's fact sheet on the solid state recorder:

To communicate with its operators on the ground, the Hubble Space Telescope uses a group of NASA satellites called the Tracking and Data Relay Satellite System (TDRSS). By way of TDRSS, Hubble sends the data from its science instruments and spacecraft systems to the Space Telescope Operations Control Center at NASA's Goddard Space Flight Center in Greenbelt, Md. When the TDRSS link is not available, Hubble stores its science and engineering data in onboard recorders for playback at a later time. Hubble records all of its science data to prevent any possible loss of unique information.

Prior to the Second Servicing Mission, Hubble used three 1970s-style, reel-to-reel tape recorders. In February 1997, Astronauts replaced one of these mechanical recorders with a digital Solid State Recorder. During Servicing Mission 3A Astronauts will remove a second mechanical tape recorder and install a second Solid State Recorder.

Unlike the reel-to-reel recorder it replaces, the Solid State Recorder has no reels, no tape, and no moving parts to wear out and limit lifetime. Data is digitally stored in computer-like memory chips until Hubble's operators command its playback. Although the Solid State Recorder is about the same size and shape as the reel-to-reel recorder, it can hold approximately ten times as much data. It stores 12 gigabits of data, while the tape recorder it replaces can hold only 1.2 gigabits. This ten times greater storage has proven essential in allowing Hubble's new, high-tech scientific instru-ments to be fully productive.

State-of-the-art electronics provide the Solid State Recorder with more capability and flexibility than reel to-reel recorder. This digital recorder is designed to perform the tasks of two separate mechanical recorders. Unlike a mechanical recorder, the Solid State Recorder can record and play back data simultaneously.

Another advantage is its ability to record two data streams at the same time, allowing both the science and engineering data streams to be captured on a single recorder. Unlike the reel-to-reel recorders, data can be played back without having to rewind the tape, and information can be instantly accessed.

Reel-to-reel tape recorders can fall victim to single-point failures, such as a break in the tape or a mechanical defect. The Solid State Recorder does not have mechanically moving parts, and its memory modules have a very low failure rate. This digital recorder is designed to grow old gracefully, compensating for situations such as a bad chip or a bad module.

The recorder automatically detects, corrects and reports random errors in memory. If the failure is too difficult to correct, the affected area can be isolated and skipped over, leaving the rest of memory fully functional. The old, mechanical recorders also had to be sealed in a pressurized enclosure to protect the tape and the delicately lubricated mov-ing parts from the hazards of a space vacuum. This special packaging is not necessary for the Solid State Recorder.

NASA successfully tested this Solid State Recorder during a 10-day Space Shuttle Mission (STS-95) in October 1998. Based on these results and the on-orbit performance of the unit already aboard Hubble, NASA expects this new recorder to last the life of the Telescope. The Solid State Recorder was developed at Goddard.

2200 GMT (5:00 p.m. EST)

After some fiddly hand work, John Grunsfeld has successfully removed the old S-band transmitter and is installing the new transmitter. Fitting the new device will be much easier because it has bolts designed to be turned by a spacewalking astronaut.

2129 GMT (4:29 p.m. EST)

Grunsfeld is now using a pistol grip power tool to loosen the eight bolts that attach the S-band transmitter to the telescope's equipment bay. These bolts are non-captive and could float free if not carefully removed. After loosening the bolts, a special tool will be used to remove and capture them.

2122 GMT (4:21 p.m. EST)

John Grunsfeld is disconnecting the thin cables that connect to Hubble's S-band transmitter. He has already disconnected two and is working on a third.

2054 GMT (3:54 p.m. EST)

Next up for the spacewalking duo is probably the most difficult task of the mission, the replacement of the telescope's failed S-band transmitter. The transmitter was not designed to be replaced by spacewalking astronauts and requires the astronauts to work with tiny bolts and thin coax cables.

The transmitter, which failed in 1998, is one of two aboard the telescope. Since the failure, the other transmitter has been able to shoulder the load and the observatory's scientific work has not been affected. Hubble can operate with one transmitter by making additional commands to rotate the telescope, but optimally the telescope operates with two S-band transmitters.

2049 GMT (3:49 p.m. EST)

Flight controllers report a good aliveness test of the optical control electronics package.

2038 GMT (3:38 p.m. EST)

The astronauts are taking pictures of bay C to document the newly installed optical control electronics package.

2024 GMT (3:24 p.m. EST)

The optical control electronics package is installed and the astronauts have instructed flight controllers to conduct an "aliveness" test of the package. The system will allow controllers to make adjustments to a mirror inside the telescope's newly installed fine guidance sensor.

2024 GMT (3:24 p.m. EST)

Smith and Grunsfeld are working to install an optical control electronics package which will enhance the performance of Fine Guidance Sensor installed yesterday. The package will be installed in equipment bay C located close to one of the telescope's solar arrays.

1959 GMT (2:59 p.m. EST)

The spacewalkers have finished setting up their equipment for today's work on the Hubble Space Telescope. Grunsfeld is perched at the end of the shuttle's robot arm and Smith is free-floating.

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

The astronauts have left the airlock to begin the third spacewalk of the mission.

1917 GMT (2:17 p.m. EST)

Discovery's airlock is now depressurised and Smith and Grunsfeld have switched their spacesuits to battery power.

1825 GMT (1:25 p.m. EST)

Astronauts Steve Smith and John Grunsfeld are breathing oxygen to purge their bodies of nitrogen prior to their spacewalk. The pre-breathe activity is designed to ward off the condition commonly known as the "bends".

Meanwhile, in mission control, the lead flight control team, led by flight director Linda Ham, is coming on duty.

1655 GMT (11:55 a.m. EST)

The astronauts have completed the half-hour task to resize the spare space suit, designated EMU 3, to fit John Grunsfeld. The space suit was used during yesterday's EVA by Mike Foale.

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

Mission control has instructed Grunsfeld to use the spare space suit because of the electrical problem noted earlier.

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

The crew is reporting an electrical problem with John Grunsfeld's space suit that could force the astronaut to switch to a spare suit. The crew is resizing the suit to fit Grunsfeld. Flight controllers are discussing the problem.

1605 GMT (11:05 a.m. EST)

Hubble Space Telescope controllers at the Goddard Space Flight Center report they are delighted with the performance of the orbiting observatory's new 486 computer, installed during yesterday's spacewalk. Testing has not revealed any sofware bugs. They also say that, the check out of the new Fine Guidance Sensor has gone very well.

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

The Discovery astronauts were woken by mission control at about 1450 GMT (9:50 a.m. EST) to begin the sixth day of their mission, the highlight of which will be the third and final spacewalk.

"The crew is ready to go back and work on Hubble one more time," mission commander Curt Brown said.

The astronauts were woken to the sounds of Steppenwolf's 'Magic Carpet Ride', played for Smith, and the children's song 'Skinnamarink' by Kimbo for Grunsfeld.

Steve Smith and John Grunsfeld are scheduled to venture out into the shuttle's cargo bay at about 1920 GMT (2:20 p.m. EST), but, based on previous experience, will probably start their spacewalk a little earlier.

During today's spacewalk, which is expected to last no more than 7 1/2 hours, the spacewalkers will install a solid-state data recorder, a replacement data transmitter and insulation panels to keep Hubble's equipment bays from getting too hot or too cold.

0318 GMT (10:18 p.m. EST)

The second of three spacewalks to service Hubble has been completed by the crew of shuttle Discovery. Over the past two days the $3 billion telescope has received new gyroscopes, battery protection kits, an advanced main computer and refurbished guidance sensor. All the tasks have gone as planned with no serious problems experienced. This work completes the primary tasks planned for this third visit to Hubble. However, another spacewalk is planned for Friday afternoon to add an electronic control unit on the new fine guidance sensor, replace a failed S-band radio transmitter, change out one of Hubble's data recorders and install additional thermal blanket material on the telescope's outer surface.

Today's spacewalk officially concluded at 0316 GMT (10:16 p.m. EST), some eight hours and 10 minutes after it started. That makes this spacewalk the third longest in history. The longer ones were EVA No. 3 on STS-49 in May 1992 lasting eight hours and 29 minutes and yesterday's spacewalk at eight hours and 15 minutes.

0307 GMT (10:07 p.m. EST)

Discovery's airlock hatch to space has been closed and locked, now over eight hours into this spacewalk.

0305 GMT (10:05 p.m. EST)

The thermal cover has been closed and the spacewalkers are now swinging the airlock hatch shut so repressurization can begin.

0302 GMT (10:02 p.m. EST)

The "go" has been given to the spacewalkers to enter the airlock after cleaning up the payload bay. The spacewalk will officially end when Foale and Nicollier switch their suits from battery to shuttle-provided power.

0230 GMT (9:30 p.m. EST)

Payload bay clean up work is still continuing. The spacewalkers have encountered a problem locking a foot restraint in place in the bay. So Mission Control has told the crew to begin the platform inside Discovery's crew cabin tonight for closer inspection and troubleshooting. In any event, there is a second foot restraint onboard the shuttle. Now about 7 1/2-hours into this spacewalk, which will probably last another half-hour or more.

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

Spacewalkers Mike Foale and Claude Nicollier are finishing up their spacewalk aboard Discovery, which is now reaching seven hours in duration. The telescope has been closed out after the FGS installation and the old unit has been placed in its carrier box for return to Earth. The crew had asked to perform a task planned for tomorrow's spacewalk, but Mission Control said they needed to clean up the payload bay and return to the shuttle over the next half-hour or so.

0123 GMT (8:23 p.m. EST)

The doors that cover the Fine Guidance Sensor compartment of Hubble are now being closed. Nicollier will have to drive three bolts to lock the doors in place.

0120 GMT (8:20 p.m. EST)

An aliveness test of the newly installed Fine Guidance Sensor has been completed, ensuring the unit was correctly hooked up to the telescope.

0111 GMT (8:11 p.m. EST)

The new Fine Guidance Sensor has been connect to the Hubble Space Telescope, clearing the way for an "aliveness" test to verify the unit is properly connected.

The planned objectives of this spacewalk are now completed, just over six hours since it started. Work left to be accomplished by the spacewalkers includes taking pictures of the new unit, closing the compartment doors, placing the old FGS in the carrier box mounted in Discovery's payload bay, cleaning up the bay and putting their tools away.

0058 GMT (7:58 p.m. EST)

Claude Nicollier has removed the handrail from the new Fine Guidance Sensor as electrical hookups continue.

0043 GMT (7:43 p.m. EST)

After fixing an alignment problem, Swiss astronaut Claude Nicollier, riding on Discovery's robot arm under the control of French astronaut Jean-Francois Clervoy, has inserted the new Fine Guidance Sensor into the Hubble Space Telescope.

This new FGS is a refurbished unit that has an enhanced on-orbit alignment capability. This is the same FGS that was returned to Earth from Hubble on the second servicing mission in February 1997. The one removed from the telescope tonight will be refurbished and upgraded for reinstallation during Hubble's fourth servicing.

Hubble has three guidance sensors that work with the gryoscopes replaced during yesterday's spacewalks to precisely point the telescope during science observations of the universe.

The spacewalkers will now attach the new FGS to Hubble with eight electrical connectors. Then they will close the doors to that compartment. This is the last scheduled task for today's spacewalk, already about 5 1/2-hours in duration.

0036 GMT (7:36 p.m. EST)

Nicollier now pulling the Fine Guidance Sensor back out of Huuble in an effort to correct the apparent misalignment during the first installation attempt.

0031 GMT (7:31 p.m. EST)

Spacewalker Mike Foale says it appears the FGS is not seated properly on the tracks to insert it into the telescope. Nicollier is trying to realign the FGS.

0028 GMT (7:28 p.m. EST)

The astronauts are having some difficultly installing the new Fine Guidance Sensor into Hubble. This is a very delicate task and they are trying to be very careful.

0021 GMT (7:21 p.m. EST)

Foale now removing the protective mirror cover on the new Fine Guidance Sensor.

0019 GMT (7:19 p.m. EST)

Mike Foale has inspected the bay where the new sensor will be inserted in Hubble.

0017 GMT (7:17 p.m. EST)

Claude Nicollier has removed the new Fine Guidance Sensor from its container aboard Discovery.

0002 GMT (7:02 p.m. EST)

The handrail has been attached to the new FGS. Shortly, the spacewalkers will release the latch holding the FGS inside the carrier box.

THURSDAY, DECEMBER 23, 1999
2357 GMT (6:57 p.m. EST)

The box in Discovery's payload bay that contains the new Fine Guidance Sensor has been opened. Riding on the end of the shuttle's robotic arm, Claude Nicollier is moving in to attach the handrail on the new unit to maneuver it toward Hubble.

2346 GMT (6:46 p.m. EST)

The FGS has been removed from the telescope's structure. The unit will now be stowed on a support structure until it can be placed in the carrier box currently occupied by the new FGS.

2341 GMT (6:41 p.m. EST)

The Fine Guidance Sensor is now being pulled out of Hubble. The box is 5.5 x 4 x 2 feet and weighs 478 pounds on Earth.

2335 GMT (6:35 p.m. EST)

Claude Nicollier is now loosening knobs to release the old Fine Guidance Sensor from Hubble.

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

Now well over four hours into this spacewalk. Claude Nicollier is positioning the handrail against the old Fine Guidance Sensor for attachment.

2306 GMT (6:06 p.m. EST)

The connectors and ground strap have been demated from the old FGS. A handrail will now be mounted on the unit so Nicollier can pull the large box out of the telescope. Here is NASA's description of the Fine Gudiance Sensor:

The Fine Guidance Sensor (FGS) is an optical sensor used on the Hubble Space Telescope to provide pointing information for the spacecraft and also as a scientific instrument for astrometric science.

A FGS consists of a large structure housing a collection of mirrors, lenses, servos, prisms, beam-splitters and photomultiplier tubes. There are three fine guidance sensors on Hubble located at 90-degree intervals around the circumference of the telescope. Two FGSs are used to point the telescope at an astronomical target and hold that target in the scientific instrument's field of view. The third FGS can then be used as a scientific instrument for astrometry.

The fine guidance sensors are one of the sensors used by Hubble's pointing control system to point the telescope at a target with an accuracy of 0.01 arcsec. What is an arcsec? An arcsec is the width of a paperclip wire viewed from the distance of two football fields. With this fine precision, the guidance sensors lock on to a star and then measure any apparent motion to an accuracy of 0.0028 arsec. This gives Hubble the ability to remain pointed at that target with no more than 0.007 arc-sec of deviation over long periods of time. This level of stability and precision is comparable to being able to hold a laser beam focused on a dime that is 200 miles away (the distance from Washington D.C. to New York City).

Astrometry is the science that deals with the determination of precise positions and motions of stars. The FGS's can provide star positions that are about 10 times more precise than those observed from a ground based telescope.

When used for astrometric science the fine guidance sensors will let Hubble:

• Search for a wobble in the motion of nearby stars that could indicate the presence of a planetary companion.
• Determine if certain stars really are double stars.
• Measure the angular diameter of stars, galaxies and other celestial objects.
• Refine the positions, distances and energy output of stars.
• Help determine the true distance scale for the universe.

2303 GMT (6:03 p.m. EST)

Mike Foale and Claude Nicollier have start unhooking the old FGS inside Hubble.

2249 GMT (5:49 p.m. EST)

The doors covering the Fine Guidance Sensor compartment have been opened.

2237 GMT (5:37 p.m. EST)

The go has been given to demate the connectors on the Fine Guidance Sensor inside Hubble.

2215 GMT (5:15 p.m. EST)

This job of Fine Guidance Sensor replacement calls for the astronauts to open and secure the FGS bay doors and demate the FGS connectors and ground strap. Nicollier will install four guide studs on the FGS, mount a handhold and loosen the A latch.

With Foale in the portable foot restraint and Nicollier holding the FGS handhold, the team removes the baby grand piano-sized sensor as Foale gives guidance instructions. The old unit will be placed on a fixture for the time being while the new one is installed.

Foale will remove the mirror cover on the new FGS. After maneuvering the unit in place, Nicollier will slide it into the telescope, attach the ground strap and mate the electrical connectors.

2210 GMT (5:10 p.m. EST)

The spacewalkers have switched places - Nicollier has climbed into the foot restraint on the end of the robot arm and Foale is free floating.

2201 GMT (5:01 p.m. EST)

Rotation of Hubble is complete.

2154 GMT (4:54 p.m. EST)

The Hubble Space Telescope rotation on its lazy-susan table in Discovery's payload bay is under way. This rotation is necessary to present the next work area - where the Fine Guidance Sensor is located on the telescope - so the robot arm can reach and the crewmembers inside Discovery can oversee the job.

2150 GMT (4:50 p.m. EST)

The spacewalkers have moved away from Hubble so that the telescope can be rotated 90 degrees for access to the compartment that houses the Fine Guidance Sensor.

2147 GMT (4:47 p.m. EST)

A test of Hubble's new computer has been completed successfully, ensuring the new unit was connected properly by spacewalker Mike Foale. "Hubble not only has new brains, it is thinking," CAPCOM Steve Robinson told the crew from Mission Control.

Foale has added a new panel of insulation over the door that covers the computer compartment, and now will trade places with Nicollier on Discovery's robot arm for the next spacewalk task. That job will be to install the new Fine Guidance Sensor.

2134 GMT (4:34 p.m. EST)

The door to Hubble's Bay 1 compartment has been closed and locked. The Hubble team will now run the aliveness test on the new computer.

2127 GMT (4:27 p.m. EST)

Mike Foale is now swinging the door shut on Hubble's Bay 1 where the computer is installed.

2123 GMT (4:23 p.m. EST)

The spacewalkers are taking pictures and video of the new computer for documentation purposes.

2120 GMT (4:20 p.m. EST)

"The brains of Hubble have been replaced," the Discovery crew just reported. The job required Foale to engage six J-hooks, mate two Y-harness connectors and seven wiring harnesses.

Hubble ground controllers will soon perform an "aliveness" test of the new computer to ensure it is connected properly.

2108 GMT (4:08 p.m. EST)

The new computer is already inside Hubble and spacewalker Mike Foale is connecting the new unit to the observatory.

2105 GMT (4:05 p.m. EST)

Hubble's new computer is 20 times faster and has six times as much memory as the previous one. The computer was built using commercial equipment and tested in space aboard the John Glenn's mission in October 1998 to make sure it would work properly in the harsh environment of orbit. That test went well, clearing the way for this "brain transplant" today.

The computer is 18.8 x 18 x 13 inches and weighs 70.5 pounds on Earth. The greater capabilities of the new computer will increase productivity for Hubble by performing more work in space and less work by people on the ground, NASA says. The computer software will be programmed in a modern programming language. The result will be decreased cost for software maintenance.

2050 GMT (3:50 p.m. EST)

Work continues to go well and on schedule aboard space shuttle Discovery. Now approaching two hours into this spacewalk. Claude Nicollier has stowed the old computer in a carrier for return to Earth. The spacewalkers are now preparing to install the new computer brain into Hubble.

2024 GMT (3:24 p.m. EST)

With the old computer out of Hubble, Mike Foale is now installing "connector converters" in preparation for hooking up the new computer.

2015 GMT (3:15 p.m. EST)

One hour and nine minutes into this spacewalk, Mike Foale has pulled the old computer out of the Hubble Space Telescope. This "brain transplant" will continue with installation of the new computer over the next hour or so.

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

Foale is now unbolting the old computer from Hubble.

Hubble's main computer is responsible for monitoring the health of its many systems, for controlling the movement of the telescope from target to target, and for holding the telescope steady when observing. The old computer, called the DF-224, was designed in the late 1970's and its capabilities are much less than today's modern computers. Programming requires very specialized skills, unique to this computer, and maintaining the software is difficult and expensive.

The DF-224 computer has degraded over time and during the First Servicing Mission in 1993 it was augmented with an additional computer called a co-processor. The design of the co-processor was based on the Intel 80386 microchip.

2004 GMT (3:04 p.m. EST)

Mike Foale reports all the connectors to the old computer have been undone.

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

The go has been given to start disconnecting the old computer aboard Hubble. Once that is completed, Foale will hand the old computer to Nicollier for stowage aboard Discovery. Nicollier will then give Foale the new 486-computer for installation.

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

Spacewalker Mike Foale has opened the bay door where Hubble's main computer is located. This is the first step in today's computer transplant.

1943 GMT (2:43 p.m. EST)

Live television is now being received from Discovery showing the spacewalkers are work in the payload bay.

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

The first job today will be setting up the tools the spacewalkers will need. They will then move on to switching out Hubble's main computer, basically the telescope's brain. For the task, Mike Foale will be riding on Discovery's robot arm and Nicollier will be free floating. Later, the Fine Guidance Sensor will be replaced. The spacewalking duo will reverse positions for that task - Nicollier on the arm and Foale floating.

1915 GMT (2:15 p.m. EST)

"Welcome to the EVA faternity." That is what Steve Smith inside Discovery just radioed to spacewalker Claude Nicollier. The Swiss astronaut is making his first spacewalk today. Foale has two previous walks under his belt - one on shuttle mission STS-63 in February 1995 and one from the Russian space station Mir when he was a resident there in the summer of 1997.

During this spacewalk, Jean-Francois Clervoy will be operating the robot arm to move the spacewalkers around the payload bay and Smith will direct the action.

1914 GMT (2:14 p.m. EST)

Mission Control says Nicollier's suit is working as expected, too. So now the duo is set to begin setting up the tools they will need for today's spacewalk.

1911 GMT (2:11 p.m. EST)

The spacewalkers are reading data from their suits to mission controllers. Officials report Foale's suit is in good shape. Nicollier is now reading his data. This is done before the two leave the airlock and venture into Discovery's payload bay.

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

The second spacewalk of this third Hubble Space Telescope servicing mission has officially begun. Mike Foale and Claude Nicollier switched their spacesuits to battery power at 1906 GMT (2:06 p.m. EST), starting the 6 or 6 1/2-hour spacewalk.

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

Depressurization is complete and spacewalker Claude Nicollier has been given the "go" to open the airlock hatch.

1844 GMT (1:44 p.m. EST)

The airlock pressure is now at about 2 psi. After depressurization is completed, the hatch will be opened and the spacewalkers will disconnect the power umbilicals to their suits.

1842 GMT (1:42 p.m. EST)

Pressure in the airlock is now down below 3 psi.

1841 GMT (1:41 p.m. EST)

After a brief pause in the depressurization, the pressure in the airlock is now falling again. The pressure level started at 10.2 psi, which is equal to Discovery's crew cabin. Pressure was taken to 5 psi so the spacewalkers could check for leaks in the their suits.

1830 GMT (1:30 p.m. EST)

Mission Control has given "Discovery" the go to begin depressurizing the airlock for today's spacewalk. The walk will officially start when Mike Foale and Claude Nicollier switch their suits to battery power.

1802 GMT (1:02 p.m. EST)

Spacewalkers Mike Foale and Claude Nicollier have completed breathing pure oxygen in preparation for beginning today's EVA. They are running significantly ahead of the timeline, and could start depressurizing Discovery's airlock in about 30 minutes.

Read our overview of this spacewalk.

Meanwhile, Hubble Space Telescope project officials report that extensive functional testing overnight confirmed the six new gyroscopes installed yesterday are performing as expected. Also, the Hubble team spent the night looking over the extensive amount of photographic data the astronauts have collected. There are now over 450 photographs, all taken over the past two days.

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

Preparations have begun for today's spacewalk, the second of three planned for this servicing mission to the Hubble Space Telescope. Mike Foale and Claude Nicollier are running ahead of schedule and could begin the spacewalk in about two hours from now.

This spacewalk will see the installation of a new main computer aboard Hubble, replacing the 1970s-era brain with a 486-computer. The new computer is 20 times faster and has six times the memory of the outdated unit. The duo will also change out one of Hubble's three Fine Guidance Sensors used to precisely point the telescope. The one being installed today is a refurbished FGS that was removed and returned to Earth by the STS-82 crew during its servicing of the telescope in February 1997.

If time permits, the space walkers also may perform some optional "get ahead" tasks.

During the spacewalk, Foale can be recognized by the broken red stripes on the legs of his EVA suit, and Nicollier by the diagonally broken red stripes on his suit.

This morning's wake up music from Mission Control honored the two spacewalkers. Traditional Swiss music was played for Nicollier and the song "Only When I Sleep" by The Corrs was played for Foale.

0314 GMT (10:14 p.m. EST)

The first of three spacewalks to repair and service NASA's Hubble Space Telescope during this mission of shuttle Discovery is complete. It was one for the record books, becoming the second-longest in the shuttle program history with a duration of 8 hours, 15 minutes. The longest was on STS-49 in May 1992, lasting 8 hours, 29 minutes.

The spacewalk ended tonight at 0310 GMT (10:10 p.m. EST). Although there were a few bumps in the road with minor glitches, all the planned tasks were completed by Steve Smith and John Grunsfeld.

The main goal of this 96th shuttle mission and third to service Hubble was the installation of six fresh gyroscopes that will revive the telescope's idle pointing system. The precision system was shut down in mid-November when the fourth gryo failed, ending all science observations by Hubble. Initial testing after the new gyros were installed indicated the units were connected properly. However, further checks by ground controllers will be needed to ensure the gyros are functioning as planned.

Smith has now logged 27 hours, 25 minutes of spacewalking time in four excursions; this was Grunsfeld's first trip outside the shuttle's crew cabin.

The stage is now set for EVA No. 2 to continue this series of three consecutive days of spacewalks. The walk is expected to begin at around 1900 GMT (2:00 p.m. EST) Thursday. Astronauts Michael Foale and Claude Nicollier are slated to install a new fine guidance sensor and advanced main computer aboard the $3 billion telescope.

0302 GMT (10:02 p.m. EST)

Discovery's airlock hatch has been closed and latched by the spacewalkers. Tonight's spacewalk will official conclude when Smith and Grunsfeld switch their suits from battery to shuttle power.

0254 GMT (9:54 p.m. EST)

Now 8 full hours into this spacewalk. The astronauts are back in the airlock. They will soon close the hatch and begin repressurizing the airlock from the vacuum of space to the 10.2 psi of the shuttle's crew cabin.

0240 GMT (9:40 p.m. EST)

With their spacewalking tasks complete, Steve Smith and John Grunsfeld are cleaning up the payload bay and preparing to return to the shuttle Discovery. The spacewalk duration will approach or pass 8 hours, one of the longest in shuttle program history. The longest was on STS-49, the three-man spacewalk to manually grab the Intelsat 6 communications satellite, that lasted 8 hours, 29 minutes.

0208 GMT (9:08 p.m. EST)

The final three voltage regulators have been installed into Hubble to protect the telescope's aging batteries from overcharging or overheating. Astronaut John Grunsfeld is now locking the Bay 2 door back in place after completing the job. Hubble ground controllers will later perform an aliveness test to verify all is well with the batteries and power charging system after the regulators were added.

0150 GMT (8:50 p.m. EST)

Spacewalker John Grunsfeld has moved over to Hubble's Bay 2 for installation of the other three VIKs. Meanwhile, Steve Smith is finishing up adding handrail covers to Hubble.

Also, the decision has been made to leave the Rate Sensor Unit No. 1 in its box in the payload bay. There was earlier concern that since the box's door would not shut, perhaps that was a safety issue for landing.

Now nearly 7 hours into this first of three spacewalks for Discovery's mission.

0135 GMT (8:35 p.m. EST)

The "go" has been given to install the other three voltage regulators for Hubble's batteries tonight.

0131 GMT (8:31 p.m. EST)

Mission controllers are discussing the possibility of having John Grunsfeld go ahead and install the other three voltage kits tonight as originally planned. Officials had earlier decided to complete just half of the kits tonight because the spacewalk was running late. But since Grunsfeld completed the first three fairly quickly, they could have him complete the job during this spacewalk.

0129 GMT (8:29 p.m. EST)

All three of the voltage kits have now been installed tonight by spacewalker John Grunsfeld. He will now begin closing out Hubble's Bay 3. Now 6 hours, 35 minutes into this spacewalk.

0120 GMT (8:20 p.m. EST)

Spacewalker John Grunsfeld has installed the first Voltage/Temperature Improvement Kit. Each kit is basically one jumper cable running between the charging unit and one of Hubble's batteries.

0112 GMT (8:12 p.m. EST)

While John Grunsfeld is hooking up the new battery voltage kits, Steve Smith has moved on to install covers on some of Hubble's handrails. This spacewalk has been under way for about 6 1/4 hours.

0108 GMT (8:08 p.m. EST)

Mission Control has given Discovery the "go" for battery connector demate in preparation for installing three voltage regulator kits. The other three will be installed on a later spacewalk.

0105 GMT (8:05 p.m. EST)

Hubble's Bay 3 door has been opened, allowing access for the spacewalkers to install the voltage improvement kits to the telescope's batteries. The kits will protect the 10-year old batteries from overcharging and overheating.

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

Now extactly three days to the minute since Discovery's launch and six hours into this spacewalk, John Grunsfeld and Steve Smith have Hubble's aft shroud doors closed and locked.

0040 GMT (7:40 p.m. EST)

The spacewalkers are finishing efforts to tighten bolts on Hubble's aft shroud door latches. NASA officials say they will likely have the crew install just three of the six voltage regulators on Hubble's batteries tonight. They won't be able to complete all six tonight because of the extra time spent opening the NICMOS cooling valves.

0016 GMT (7:16 p.m. EST)

Having completed work to open coolant valves on the NICMOS instrument, the shuttle spacewalkers are closing the large doors on Hubble's aft shroud. The doors have been open for the past few hours while the new gyroscopes were installed into the telescope and the valves were opened so any residual coolant in lines to NICMOS can vent into space. That venting will allow an experimental cooling system to be added to NICMOS on Hubble Servicing Mission 3B.

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

Success on the NICMOS valves. Steve Smith and John Grunsfeld have managed to open a pair of coolant valves on the NICMOS instrument inside the Hubble Space Telescope. Officials wanted the valves opened on this shuttle mission to prepare for installation of a new cooling system on the next Hubble servicing in mid-2001.

WEDNESDAY, DECEMBER 22, 1999
2359 GMT (6:59 p.m. EST)

Well there is some good news and some bad news so far from Discovery's spacewalkers. They were able to remove the caps covering the NICMOS cooling valves. However, now the valves are not turning. The duo of Steve Smith and John Grunsfeld is still trying.

2333 GMT (6:33 p.m. EST)

NASA officials have just decided to send the spacewalkers back inside the telescope to attempt again to open a pair of valves on the telephone booth-sized NICMOS instrument.

2329 GMT (6:29 p.m. EST)

Spacewalkers Steve Smith and John Grunsfeld are swinging the large aft shroud doors closed on Hubble.

2317 GMT (6:17 p.m. EST)

The three Rate Senor Units have checked out and Hubble's pointing system should be back in business. This is the minimum task needed to declare STS-103 a successful mission. While the crew sleeps over, more functional tests will be conducted on the RSUs via controllers.

2311 GMT (6:11 p.m. EST)

The spacewalkers report the valve caps on the NICMOS instrument aboard Hubble will not turn. Mission controllers have told Discovery to give up and forget about this task on STS-103. The crew plans to take some photos of the valves for engineers to troubleshoot. The aft shroud doors of Hubble will now be closed. The next task of this spacewalk will be the installation of six Voltage/Temperature Improvement Kits to protect Hubble's batteries.

2251 GMT (5:51 p.m. EST)

While awaiting word on the aliveness test for the third RSU, spacewalkers Steve Smith and John Grunsfeld are now moving on the next task: opening valves on Hubble's Near Infrared Camera and Multi-Object Spectrometer to purge nitrogen coolant from the instrument. This is being done in preparation for NICMOS maintenance on the next Hubble servicing in the summer of 2001.

2243 GMT (5:43 p.m. EST)

The third and last Rate Sensor Unit has been installed aboard the Hubble Space Telescope, completing the main task of this servicing mission to the orbiting observatory. Controllers will now conduct an activation test to ensure the RSU is working as expected.

2235 GMT (5:35 p.m. EST)

The third old Rate Sensor Unit with two gyroscopes inside has been removed from Hubble.

2227 GMT (5:27 p.m. EST)

Spacewalker John Grunsfeld has been given the "go" from Mission Control to disconnect the third and final old Rate Sensor Unit. Grunsfeld is removing this RSU by himself; Steve Smith has removed the previous two with Grunsfeld's help.

2215 GMT (5:15 p.m. EST)

Hubble Space Telescope officials report the second new Rate Sensor Unit has passed its aliveness test, verifying it is connected and working properly.

2156 GMT (4:56 p.m. EST)

Just over three hours into this spacewalk, the second old Rate Sensor Unit has been removed from the Hubble Space Telescope. The spacewalkers are now preparing to install the new unit.

2145 GMT (4:45 p.m. EST)

Mission Control has given Discovery the go to disconnect the second old Rate Sensor Unit inside Hubble.

2142 GMT (4:42 p.m. EST)

Hubble Space Telescope officials report the first Rate Sensor Unit to be installed today has passed its aliveness test. The old unit has been stowed aboard Discovery and now the spacewalkers are preparing to remove the second unit from Hubble.

2135 GMT (4:35 p.m. EST)

While Hubble controllers check the newly installed Rate Sensor Unit, spacewalkers John Grunsfeld and Steve Smith are retrieving the second RSU for installation.

2133 GMT (4:33 p.m. EST)

One down and two more to go. Space shuttle Discovery's crew just reported the first Rate Sensor Unit has been changed out and Hubble ground controllers have been given a "go" to perform an aliveness test on the new box. The test will ensure the RSU with its two gyroscopes has been connected properly to Hubble.

2119 GMT (4:19 p.m. EST)

The first old Rate Sensor Unit containing two gyroscopes have been removed and spacewalker Steve Smith has begun hooking up the new one. Discovery is crossing over Central America on the start of its 44th orbit of Earth. So far, this spacewalk has been going according to plan and schedule since its early start at 1854 GMT (1:54 p.m. EST).

2050 GMT (3:50 p.m. EST)

After a bit of trouble opening of the aft shroud door of the Hubble Space Telescope, the astronauts have the latches unbolted and will soon begin work to remove the first of three Rate Sensor Units, or RSUs. Each unit contains two gyroscopes. The units together service as Hubble's precision pointing system needed to keep the telescope positioned for observations of stars, planets and its other astronomical targets. Three of the six gyros are needed for science observations, but four have now failed, halting Hubble's work over a month ago.

When the old units are removed, they will be stowed aboard Discovery for return to Earth. Once each new unit is installed, controllers will begin tests to ensure they are connected properly and working.

2015 GMT (3:15 p.m. EST)

The spacewalking astronauts have completed their setup tasks in the payload bay and are now getting down to business - replacing Hubble's failed gryoscopes.

Meanwhile, Hubble ground controllers have sent commands to spin down the gryos in preparations for their removal.

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

Live television is now being received from space shuttle Discovery showing the spacewalk under way. The spacewalkers have installed a foot restraint on the end of the shuttle's robot arm.

1912 GMT (2:12 p.m. EST)

Smith and Grunsfeld are floating in Discovery's open payload bay beginning chores to set up the tools they will need for this 7-hour spacewalk. This is Smith's fourth spacewalk and Grunsfeld's first.

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

"Hubble needs us." With that the spacewalking duo of Steve Smith and John Grunsfeld are preparing to exit Discovery's airlock. The crew spent the morning getting ready for the spacewalk in which Smith and Grunsfeld donned their EMUs, climbed into the airlock and depressurized it.

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

The first of the three spacewalks for shuttle mission STS-103 is officially under way. Spacewalkers Steve Smith and John Grunsfeld switched their spacesuits to internal battery power at 1854 GMT (1:54 p.m. EST), beginning the excursion that calls for the installation of six fresh gyroscopes to restore Hubble's prescision pointing system to working order.

1700 GMT (12:00 p.m. EST)

Discovery's astronauts are awake and already preparing for today's spacewalk to repair Hubble's crippled pointing system. Mission Control beamed the song "Hucklebuck" by Beau Jocque and the Zydeco Hi-Rollers to awaken the crew, a tune that the spacewalkers heard many times while training hundreds of hours for the mission in the 6.5-million gallon water tank at the Johnson Space Center in Houston.

Prime task today will be the replacement of three Rate Sensor Units, each containing two gyroscopes. Once the new ones are installed, the two spacewalkers will open valves on the telescope's Near Infrared Camera and Multi-Object Spectrometer to purge nitrogen coolant from that instrument in preparation for its servicing on the next shuttle maintenance mission in the summer of 2001. Next, they will install six Voltage/Temperature Improvement Kits for the Hubble's batteries to increase efficiency and reduce a potential for overcharge and heating.

Discovery is circling the Earth in an orbit of 380 by 365 statute miles with no significant problems.

0130 GMT (8:30 p.m. EST)

Robot arm operator Jean-Francois Clervoy has lowered the Hubble telescope into its carrier at the back of the shuttle's payload bay, where it will remain until Saturday. Spacewalks to repair the telescope are scheduled to begin tomorrow.

0104 GMT (8:04 p.m. EST)

With the shuttle's Ku-band antenna no longer needed for rendezvous operations, live pictures of the Hubble Space Telescope, last seen in 1997, are now being broadcast on NASA TV. Repairs on the telescope, which has been dormant since Nov. 13, are scheduled to begin tomorrow and continue during three spacewalks on consecutive days. Hubble is scheduled to be released back into orbit on Saturday.

0047 GMT (7:47 p.m.EST)

All is quiet in Mission Control. The shuttle's steering jets have been powered back on.

0037 GMT (7:37 p.m.EST)

The Hubble Space Telescope, now safely affixed to the end of the shuttle's robot arm, is being put into position to be latched into its carrier in the back of Discovery's payload bay.

0035 GMT (7:35 p.m.EST)

Telescope has been captured. Grapple took place at 7:34 p.m. ET as Discovery and Hubble sailed 369 miles over the Gulf of Mexico.

0035 GMT (7:35 p.m.EST)

With Discovery hovering about 35 feet from the Hubble Space Telescope, robot arm operator Jean-Francois Clervoy is preparing to extend the shuttle's 50-foot-long crane to snatch the observatory.

TUESDAY, DECEMBER 21, 1999
2358 GMT (6:58 p.m.EST)

Discovery's commander Curt Brown is beginning the final stages of the rendezvous with the Hubble Space Telescope. The spaceship is about 1,000 feet from the observatory, closing at about two feet per second. Discovery's upward firing steering jets have been shut down to prevent plumes from hitting the telescope. Once Brown has positioned the shuttle to within 35 feet of Hubble, robot arm operator Jean-Francois Clervoy will extend the shuttle's payload bay crane and snatch the telescope from orbit. Grapple is expected at about 7:41 p.m. EST.

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

Space shuttle Discovery is closing the gap between itself and the Hubble Space Telescope for the scheduled retrieval of the 12 1/2-ton observatory in about eight hours. The astronauts were awakened to the song "Rendezvous" by Bruce Springsteen at 10:20 a.m. EST (1520 GMT). Discovery is currently about 240 miles behind the telescope.

Upcoming is a firing of Discovery's jet thrusters at 1:38 p.m. EST (1838 GMT) that will raise the shuttle's orbital altitude and slow the closing rate with HST. Another engine firing will follow 48 minutes later to put Discovery on course to reach a point 8 miles behind the telescope. The final phase of rendezvous will begin at 5:28 p.m. EST (2228 GMT).

Commander Curt Brown will begin flying Discovery once the shuttle is a half-mile away and directly beneath Hubble, edging the shuttle within 35 feet of the telescope. Then robot arm operator Jean-Francois Clervoy will capture the orbiting telescope at about 7:41 p.m. EST (0041 GMT Wednesday) and maneuver it into Discovery's payload bay over the following half-hour.

0800 GMT (3:00 a.m. EST)

Discovery's seven astronauts are now asleep after a productive day completing tests of the equipment and tools needed to captured and repair the crippled Hubble Space Telescope.

The crew spent Monday flexing the 50-foot robot arm that will grab Hubble and checking the four spacesuits to be used during the spacewalks. No major problems were reported during the tasks.

According to NASA officials, Discovery is less than 1,100 statute miles behind Hubble, closing at a rate of 150 statute miles per orbit.

Discovery is circling Earth in an orbit with a high point of 367 statute miles and a low point of 352 miles.

The astronauts are scheduled to be awakened at 10:20 a.m. EST (1520 GMT) to begin retrieval day. The rendezvous begins at 1:18 p.m. EST (1818 GMT). The terminal initiation burn is expected to occur at 5:28 p.m. EST, setting the stage for Discovery's final approach to the $3 billion observatory. Astronaut Jean-Francois Clervoy is scheduled to grapple the telescope at 7:41 p.m. EST (0041 GMT Wednesday), and then position Hubble on a special platform in Discovery's payload bay about 20 minutes later.

Hubble controllers reported Monday that the telescope was stable and ready for the rendezvous.

Meanwhile, workers at Kennedy Space Center say launch pad 39B received only minimal damage from Sunday night's launch.

At sea, the solid rocket booster recovery ships began towing the spent SRBs back toward Cape Canaveral just before 12 noon EST Monday from their impact points in the Atlantic Ocean. The ships are expected to arrive at Hangar AF today at 4:30 a.m. EST (0930 GMT). NASA said the twin boosters were in good condition.

MONDAY, DECEMBER 20, 1999
1600 GMT (11:00 a.m. EST)

Discovery's seven astronauts have been awakened to begin their first full day in space, known as Flight Day 2. Mission Control gave the seven Hubble fix-it men a musical wake up call at 10:50 a.m. EST (1550 GMT).

Today will be spent preparing for tomorrow's rendezvous and retrieval of the orbiting Hubble Space Telescope. In about 3 1/2 hours, mission specialist Jean-Francois Clervoy will power up and test Discovery's 50-foot robotic arm that will be used to pluck Hubble from space on Tuesday at about 7:41 p.m. EST (0041 GMT Wednesday).

Later, the airlock, spacesuits and tools will be readied for the three spacewalks planned on this mission.

Discovery is in good shape with no problems being worked by ground controllers.

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

NASA's Mission Management Team chairman Don McMonagle says Discovery is working flawlessly in the first two hours of its 27th flight.

"We have what I believe is a darn near perfect vehicle on orbit right now, things are going extremely well. We have a vehicle that has absolutely no anomalies, not a single one. We couldn't ask for a more perfect vehicle and a more perfect scenario to execute this mission."

After two months of delays due to a series of technical troubles, the $2 billion spaceship lifted off at precisely 7:50:00.069 p.m. EST on a shortened 8-day mission to fix the crippled Hubble Space Telescope. Discovery is currently a half-orbit behind Hubble, and will catch up to the telescope for retrieval on Tuesday at 7:41 p.m. EST (0041 GMT Wednesday).

The three spacewalks to replace broken and aging electronics aboard the observatory are planned for December 22, 23 and 24. Hubble will be redeployed into space on Christmas Day at about 6:03 p.m. EST (2303 GMT). Discovery is then due home to the Kennedy Space Center at 5:24 p.m. EST (2224 GMT) on December 27.

0241 GMT (9:41 p.m. EST)

The Ku-band antenna has been deployed and activated without problem.

0235 GMT (9:35 p.m. EST)

Mission Control has given Discovery the "go" for on-orbit operations. The ship's 60-foot payload bay doors have been opened and the crew is preparing to deploy the Ku-band antenna. The antenna is used to relay data and television to Earth. It also will be a critical tool during rendezvous with Hubble because it can serve as a radar system.

0140 GMT (8:40 p.m. EST)

NASA commentator Kyle Herring has corrected himself on the result of this OMS-2 burn. Discovery's orbit will not be circularized until a later rendezvous burn to reach Hubble. This burn simply raised the orbit's low point to a safe altitude - 170 nautical miles. Discovery's current orbit is 317 by 170 nautical miles, or 362 by 195 statute miles.

Watch a movie of the launch. The movie is a 596K QuickTime file.

0137 GMT (8:37 p.m. EST)

The OMS-2 burn is complete and good. Discovery has achieved the desired orbit on its way to catch the Hubble Space Telescope.

0135 GMT (8:35 p.m. EST)

About 90 seconds to go in the OMS-2 burn. This is a 168-mile per hour boost for Discovery.

0134 GMT (8:34 p.m. EST)

The 2 1/2-minute firing of Discovery's twin orbital maneuvering system engines has begun. This burn will nearly circularize the shuttle's orbit about 315 nautical miles above Earth, according to NASA commentator Kyle Herring.

0131 GMT (8:31 p.m. EST)

Discovery is about to pass into daylight for the first time in space. Coming up on the OMS-2 burn in about three minutes. The external tank umbilical doors have been closed and no problems have been reported so far during the STS-103 mission.

0102 GMT (8:02 p.m. EST)

T+plus 12 minutes. The next event will occur in about 30 minutes. That will be the firing of Discovery's orbital maneuvering system engines on the ship's tail. The burn will circularize Discovery's current elliptical orbit of 317 by 30 miles. The low point will be raised to 315 nautical miles.

0059 GMT (7:59 p.m. EST)

T+plus 9 minutes. Discovery has safely reached orbit today following a flawless launch. The OMS-1 orbit boost is not required.

0058 GMT (7:58 p.m. EST)

T+plus 8 minutes, 35 seconds. MECO! Discovery's main engines have cutoff as planned.

0058 GMT (7:58 p.m. EST)

T+plus 8 minutes. Discovery has rolled to a heads-up position. Communciations coming through the TDRS satellite system.

0057 GMT (7:57 p.m. EST)

T+plus 7 minutes, 30 seconds. Discovery is now 65 miles up. Main engine cutoff will occur at T+plus 8 minutes, 26 seconds.

0057 GMT (7:57 p.m. EST)

T+plus 7 minutes. Velocity up to 11,000 miles per hour, downrange distance 487 miles.

0056 GMT (7:56 p.m. EST)

T+plus 6 minutes. Velocity now 6,000 miles per hour. Discovery's fuel cells, hydraulic systems and main engines all functioning as expected.

0055 GMT (7:55 p.m. EST)

T+plus 5 minutes. Three and a half minutes of powered flight left. Altitude is 67 miles, downrange distance is 270 miles.

0054 GMT (7:54 p.m. EST)

T+plus 4 minutes, 30 seconds. Discovery could now make a safe orbit if one of the main engines were to shut down.

0054 GMT (7:54 p.m. EST)

T+plus 4 minutes. Negative return. Discovery can no longer make an emergency landing at Kennedy Space Center. All systems are reported healthy as the shuttle continues streaking to orbit.

0052 GMT (7:52 p.m. EST)

T+plus 2 minutes, 30 seconds. Solid rocket boosters have separated. Altitude 40 miles, downrange distance 55 miles.

0052 GMT (7:52 p.m. EST)

T+plus 2 minutes. Coming up on SRB sep.

0051 GMT (7:51 p.m. EST)

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

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

LIFTOFF. Liftoff of space shuttle Discovery on a mission to reopen Hubble's eye on the universe.

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

0049 GMT (7:49 p.m. EST)

T-minus 31 seconds. Go for auto sequence start. Discovery'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.

0049 GMT (7:49 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; Discovery will transition to internal power and the liquid oxygen and liquid hydrogen outboard fill and drain valves will be closed.

0047 GMT (7:47 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 Discovery'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 Scott Kelly has been asked to clear the caution and warning memory system aboard Discovery.

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.

0046 GMT (7:46 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.

0046 GMT (7:46 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 Discovery 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.

0045 GMT (7:45 p.m. EST)

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

Over the course of the next minute, the orbiter's heaters will be configured for launch by commander Curt Brown, 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.

0044 GMT (7:44 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.

0044 GMT (7:44 p.m. EST)

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

0042 GMT (7:42 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 Discovery 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.

0042 GMT (7:42 p.m. EST)

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

0041 GMT (7:41 p.m. EST)

T-minus 9 minutes and counting. The countdown is ticking again. The ground launch sequencer is now up and running for today's launch of Discovery on the third Hubble Space Telescope servicing mission.

0040 GMT (7:40 p.m. EST)

Standing by to pick up the countdown clocks in one minute.

The launch of STS-103 will mark the 96th flight in the space shuttle program since 1981, the 71st since return-to-flight after Challenger, the 27th for Discovery and the third and final shuttle flight of 1999.

0037 GMT (7:37 p.m. EST)

The final management poll has been completed by Launch Director Dave King. All systems are go for launch at 7:50 p.m. EST.

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

0036 GMT (7:36 p.m. EST)

The launch team has been polled by NASA Test Director Steve Altemus and all systems were reported go.

0031 GMT (7:31 p.m. EST)

The Mission Management Team has been polled by chairman Don McMonagle and all parties reported "go" for launch.

0021 GMT (7:21 p.m. EST)

Now 20 minutes through this built-in hold. Still no problems to speak of. Launch remains set for 7:50 p.m. EST (0050 GMT).

0001 GMT (7:01 p.m. EST)

T-minus 9 minutes and holding. A planned 40-minute hold has started for the countdown. This hold has been extended from the typical 10-minute duration for shuttle countdowns due to the short launch window tonight. Holds are built into the countdown to allow the launch team time to work any problems that may arise.

Tonight the weather is go, the shuttle is ready and the Range is green. So far, this has been a textbook countdown.

SATURDAY, DECEMBER 19, 1999
2356 GMT (6:56 p.m. EST)

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

2355 GMT (6:55 p.m. EST)

T-minus 15 minutes. The Orbital Maneuvering System/Reaction Control System crossfeed valves are now being configured for launch.

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

The launch danger area has been cleared, and pilot Scott Kelly is configuring the displays inside Discovery's cockpit for launch. Also, Mission Control in Houston is loading Discovery's onboard computers with the proper guidance parameters.

2350 GMT (6:50 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 is now one hour away.

Discovery'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.

2345 GMT (6:45 p.m. EST)

Now half-way through this built-in hold. NASA Test Director Steve Altemus is now giving his pre-launch briefing to the launch team. Today's window will extend from 7:50 to 8:32:16 p.m. EST. The liquid oxygen drain back limit is 5 minutes, 0 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.

2340 GMT (6:40 p.m. EST)

T-minus 20 minutes and holding. The countdown has paused for a 10-minute built-in hold. Launch remains scheduled for 7:50 p.m. EST (0050 GMT). Weather looks good and there are no problems being worked by the launch team.

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

2335 GMT (6:35 p.m. EST)

The simultaneous air-to-ground voice communications between the astronauts and Mission Control have been checked.

2334 GMT (6:34 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 Curt Brown has pressurized the gaseous nitrogen system for Discovery's Orbital Maneuvering System engines, and pilot Scott Kelly has activated the gaseous nitrogen supply for the orbiter's Auxiliary Power Units' water boilers.

2321 GMT (6:21 p.m. EST)

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 Discovery and Mission Control during the first few minutes of flight. Coverage then is handed to a NASA Tracking and Data Relay Satellite in space.

2317 GMT (6:17 p.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 fina nine minutes of the countdown to launch.

2312 GMT (6:12 p.m. EST)

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

2309 GMT (6:09 p.m. EST)

NASA commentator Bruce Buckingham reports the Shuttle Training Aircraft with chief astronaut Charlie Precourt has taken to the skies to "orbit" Kennedy Space Center through the remainder of the countdown. The STA is used for weather reconnaissance during shuttle countdowns.

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

T-minus 1 hour. The countdown continues smoothly and without problems tonight at Kennedy Space Center for launch of space shuttle Discovery at 7:50 p.m. EST (0050 GMT Monday). 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 Discovery'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.

2238 GMT (5:38 p.m. EST)

The Orbiter Closeout Crew reports Discovery's hatch is closed and latched. Crew cabin pressure and leak checks will now be performed.

2233 GMT (5:33 p.m. EST)

Discovery's crew module hatch is now swinging closed.

2222 GMT (5:22 p.m. EST)

A camera that will capture the view of launch from inside the shuttle's cockpit is being set up at this time.

2220 GMT (5:20 p.m. EST)

The sun is slowly fading toward the horizon in Florida this evening as the countdown continues on schedule for launch of space shuttle Discovery in 2 1/2 hours. The astronauts are all onboard the shuttle and no problems are being worked.

2207 GMT (5:07 p.m. EST)

The final Discovery astronaut has boarded the shuttle this afternoon. Mission specialist No. 2 and flight engineer Jean-Francois Clervoy will sit in the flight deck aft center seat. Read a biography of Clervoy.

2205 GMT (5:05 p.m. EST)

The lead spacewalker and mission specialist No. 1 and spacewalker Steve Smith has boarded Discovery. He will sit in the middeck center seat. Read a biography of Smith.

2153 GMT (4:53 p.m. EST)

Discovery's mission specialist No. 3 and spacewalker John Grunsfeld is now aboard. He will sit in the flight deck aft right seat. Read a biography of Grunsfeld.

2148 GMT (4:48 p.m. EST)

Mission specialist No. 4 and spacewalker Michael Foale has boarded Discovery. He will sit in the middeck left seat. Read a biography of Foale.

2141 GMT (4:41 p.m. EST)

Discovery's rookie pilot, Scott Kelly, has entered the shuttle's hatch. He will sit in the flight deck forward right seat. Read a biography of Kelly.

2133 GMT (4:33 p.m. EST)

Mission specialist No. 5 and spacewalker Claude Nicollier is now aboard Discovery. He will sit in the middeck right seat. Read a biography of Nicollier.

2129 GMT (4:29 p.m. EST)

Discovery commander Curt Brown has become the first astronaut to enter the shuttle this afternoon. He will sit in the flight deck forward left seat. Read a biography of Brown.

2123 GMT (4:23 p.m. EST)

The shuttle astronauts have arrived at launch pad 39B.

2107 GMT (4:07 p.m. EST)

Discovery'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 39B, 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 1 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.

2100 GMT (4:00 p.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 7:50 p.m. EST (0050 GMT). The weather looks promising and there are no technical problems being worked by the launch team.

Standing by for departure of the astronauts from their quarters in about five minutes.

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

A weather briefing to the astronauts from the Spaceflight Meteorology Group at Mission Control shows favorable conditions at Kennedy Space Center and abort landing sites in the U.S. and across the Atlantic. KSC is forecasting scattered clouds at 3,000 and 25,000 feet, good visibility and light winds. Edwards and White Sands look good, too. For TAL weather, the prime site is Ben Guerir in Morocco and conditions are predicted to be acceptable.

2011 GMT (3:11 p.m. EST)

The Final Inspection Team has completed its work at launch pad 39B. The team is leaving the pad and will return to the firing room to give management a briefing on the vehicle inspections.

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

Discovery's astronauts have just been seated for lunch in the dining room at the Operations & Checkout Building. Following the meal, the crew will receive a weather briefing and begin suiting up for launch.

1915 GMT (2:15 p.m. EST)

Discovery stands fully fueled and ready for launch from pad 39B at Kennedy Space Center, Fla. The loading of 528,000 gallons of liquid oxygen and liquid hydrogen into the external tank began at 10:30 a.m. EST (1530 GMT). The operation went smoothly and was completed three hours later. 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 at pad 39B performing their inspections. 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 lead 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 orbit, 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 potentially dangerous hydrogen fuel that is burning.

Each member of the Final Inspection Team is in constant contact with NASA Test Director Steve Altemus in Firing Room 1.

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. He will give the managers a full and detailed report on the team's inspections and findings at the pad 39B.

A full inspection of the vehicle and pad was performed earlier in the countdown, and the external tank received a thorough check prior to fueling.

An inspection of the launch pad and beach will be made following launch tomorrow. That inspection would 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.

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

T-minus 3 hours and holding. The countdown has entered a two-hour planned hold.

1820 GMT (1:20 p.m. EST)

Good afternoon from Kennedy Space Center in Florida. It is a warm, sunny day here today as work to fuel space shuttle Discovery is continuing. There are no problems to report and launch remains set to occur at 7:50 p.m. EST tonight (0050 GMT Monday).

The weather forecast for launch time calls for scattered clouds at 3,000, 8,000 and 25,000 feet, 7 miles visibility, southwesterly winds at 10 knots, a temperature of 65 degrees F and relative humidity of 63 percent. The overall chance of not meeting the launch weather rules is just 20 percent because of cumulus clouds and the chance of low cloud ceilings.

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

Space shuttle Discovery is being fueled with a 528,000 gallons of supercold liquid hydrogen and liquid oxygen at launch pad 39B. The operation will take three hours to complete. Mission managers have cleared the shuttle for launch tonight at 7:50 p.m. EST (0050 GMT Monday) on a shortened 8-day mission to service the Hubble Space Telescope. This will be the final try to launch Discovery in 1999.

1501 GMT (10:01 a.m. EST)

NASA officials have formally approved the plan to launch space shuttle Discovery tonight on an 8-day mission to service the Hubble Space Telescope. The observatory will be grappled by the shuttle on December 21; the three spacewalks will follow on December 22, 23 and 24; and Hubble deployment should occur on December 25. Landing at Kennedy Space Center is expected on December 27. Two backup days for landing would be possible if bad weather kept Discovery in space. NASA says the plan is doable and will still protect against Y2K.

A separate meeting of the Mission Management Team is beginning at this time. The MMT will give the final "go" to begin fueling Discovery in about an hour. Liftoff is scheduled for 7:50 p.m. EST (0050 GMT Monday), the opening of a 42-minute window.

U.S. Air Force weather forecasters say there is an 80 percent chance of acceptable conditions for launch. The only concern is low cloud ceilings.

SATURDAY, DECEMBER 18, 1999
1738 GMT (12:38 p.m. EST)

Tonight's launch of space shuttle Discovery has been scrubbed due to the forecast of poor weather at Kennedy Space Center. NASA officials will meet in the morning to decide whether to make another attempt to launch on Sunday at 7:50 p.m. EST (0050 GMT Monday).

1615 GMT (11:15 a.m. EST)

NASA mission managers will meet again in about 45 minutes to decide whether or not to proceed with another launch attempt tonight for space shuttle Discovery. The traditional pre-fueling meeting of the Mission Management Team that started over an hour ago concluded with the decision to reconvene again at 12 noon EST (1700 GMT).

Fueling of Discovery's external fuel tank was scheduled to begin at this point, but the work could be delayed as much as an hour before impacting the scheduled launch time.

Officially, there is a 70 percent chance of bad weather during the launch window from 8:21 to 9:03 p.m. EST (0121-0203 GMT Sunday). Currently at Kennedy Space Center, it is raining, very windy and I cannot see the top of the 52-story Vehicle Assembly Building because of the low clouds hanging over the Space Coast this morning.

If Discovery does not launch tonight, officials say they may try again in 24 hours.

0258 GMT (9:58 p.m. EST)

Discovery's astronauts have climbed out of the shuttle and the launch team is draining the super-cold propellants from the external tank following the scrub. Officials are working toward another attempt in 24 hours, which was supposed to be the last try for Discovery in 1999 due to Y2K computer concerns.

However, Joe Rothenberg, NASA's chief of human spaceflight, says the space agency will decide on Saturday morning if they could squeeze another attempt in on Sunday night Eastern Time (Monday morning GMT). "There is not a glimmer of a hope beyond Sunday and Sunday is only a possibilty."

If Discovery launches on Saturday night local time, the mission is expected to be shortened to just 8 days with only three of the four spacewalks performed. Landing would occur on December 26, with two backup days for landing in the event of bad weather. Safing of the shuttle would then be performed and an orderly shutdown of ground computers would follow.

But officials are looking to see if the post-landing safing work could be shortened. If so, Discovery could launch on Sunday night on an 8-day mission leading to landing on December 27. Backup landing days would be on the 28th and 29th.

Discovery's mission must last at least 8 days in order to perform three spacewalks to repair the Hubble Space Telescope's broken pointing system and install new electronics. NASA says it will not launch Discovery if it could not perform at least an 8-day flight, have backup landing attempts and complete an orderly shutdown of computers before the new year.

The weather forecast for Saturday's attempt looks similar to tonight's with a 70 percent chance of not meeting the launch rules. Low clouds and rain are the main threats.

0152 GMT (8:52 p.m. EST)

SCRUB! NASA launch director Dave King has just decided to scrub this attempt to launch space shuttle Discovery due to numerous weather constraints. Launch has been rescheduled for Saturday at 8:21 p.m. EST (0121 GMT Sunday) and extend for 42 minutes.

0130 GMT (8:30 p.m. EST)

NASA Test Director Steve Altemus has just announced that the countdown will not resume as planned at 8:38 p.m. EST (0138 GMT). That means Discovery will not lift off at 8:47 p.m. EST (0147 GMT) because of the bad weather here at Kennedy Space Center. The count will remain holding at T-minus 9 minutes in hopes the weather would clear in time to launch before 9:33 p.m. EST (0233 GMT), the end of today's opportunity.

0124 GMT (8:24 p.m. EST)

Adding insult to injury, the field mills used to measure the potential for lightning around Kennedy Space Center are now "red" for launch.

0119 GMT (8:19 p.m. EST)

Here is an update on the troublesome weather at Kennedy Space Center. For launch weather, conditions are "no go" due to the threat of triggered lightning from cumulus clouds and thick layered clouds, the ceiling is currently 6,500 feet and must be at 8,000 feet or greater so tracking cameras can document the shuttle's early ascent and there is rain in the flight path, which could damage the Discovery's thermal protection tiles.

For the weather conditions at the shuttle's emergency landing strip at Kennedy Space Center, which must be acceptable in case a problem forces Discovery back to the Cape during launch, the situation is not good. Triggered lightning is a concern, rain is currently falling at the runway and is forecast to continue and the forecast calls for unacceptable cloud ceilings. In addition, the crosswind is right at the acceptable limit.

Finally, the high altitude weather balloons used to gather upper level wind data are not working tonight due to icing conditions. Mission Control is looking for other ways to determine the loads Discovery would experience during launch.

0058 GMT (7:58 p.m. EST)

T-minus 9 minutes and holding. A planned 40-minute hold has started for the countdown. During this time, officials will watch the weather conditions in the local Kennedy Space Center area to determine if the launch will be able to occur at 8:47 p.m. EST (0147 GMT). However, conditions are currently unacceptable because of cumulus clouds, rain in the flight path, disturbed weather, thick clouds and low cloud ceilings.

0053 GMT (7:53 p.m. EST)

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

0052 GMT (7:52 p.m. EST)

T-minus 15 minutes. The Orbital Maneuvering System/Reaction Control System crossfeed valves are now being configured for launch. Also, Mission Control in Houston is loading Discovery's onboard computers with the proper guidance parameters.

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

The launch danger area has been cleared, and pilot Scott Kelly is configuring the displays inside Discovery's cockpit for launch.

0047 GMT (7:47 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.

Discovery'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.

0037 GMT (7:37 p.m. EST)

T-minus 20 minutes and holding. The countdown has paused for a 10-minute built-in hold. Launch remains scheduled for 8:47 p.m. EST (0147 GMT), however it continues to rain at Kennedy Space Center.

During this hold, all computer programs in Firing Room 1 of the 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.

0033 GMT (7:33 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 Curt Brown has pressurized the gaseous nitrogen system for Discovery's Orbital Maneuvering System engines, and pilot Scott Kelly has activated the gaseous nitrogen supply for the orbiter's Auxiliary Power Units' water boilers.

0030 GMT (7:30 p.m. EST)

The Orbiter Closeout Crew has departed launch pad 39B at the edge of the Atlantic Ocean. Discovery's crew is now alone at the pad.

0020 GMT (7:20 p.m. EST)

NASA officials have decided that they may elect to use the second "pane" of tonight's launch window. That would permit launch as late as 9:33:32 p.m. EST (0233:32 GMT). However, launch between 9:29:22 and 9:33:32 p.m. EST would mean Discovery will rendezvous with Hubble on Flight Day 4 as opposed to Flight Day 3 for the rest of the window.

0017 GMT (7:17 p.m. EST)

The Orbiter Closeout Crew reports Discovery's hatch has been closed and locked for flight. Also, commander Curt Brown has completed a cabin vent test. The Eastern Test Range shuttle range safety system terminal count closed-loop test is also been performed.

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 Discovery and Mission Control during the first few minutes of flight. Coverage then is handed to a NASA Tracking and Data Relay Satellite in space.

FRIDAY, DECEMBER 17, 1999
2357 GMT (6:57 p.m. EST)

T-minus 1 hour. The countdown continues smoothly and without problems tonight at Kennedy Space Center for launch of space shuttle Discovery at 8:47 p.m. EST (0147 GMT Saturday). 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 main concern continues to be weather conditions in the local KSC area. The forecast is calling for thick low clouds and rain. It is currently raining at KSC and U.S. Air Force weather officials are not too hopeful for launching Discovery before the end of the 42-minute window.

At launch pad 39B, Discovery's astronauts have been strapped in their seats, the hatch has been closed and communications checks were completed.

The pre-flight alignment of Discovery'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.

2340 GMT (6:40 p.m. EST)

Work to close Discovery's crew compartment hatch for launch is under way.

Officials have announced there are two COLAs, or collision avoidance periods, in which the shuttle cannot launch tonight. The available launch window extends from 8:47 to 9:29 p.m. EST (0147-0229 GMT). However, the COLAs will prohibit liftoff from 9:20 to 9:21 and 9:22 to 9:24 p.m. EST.

2309 GMT (6:09 p.m. EST)

The final Discovery astronaut has boarded the shuttle tonight. Mission specialist No. 2 and flight engineer Jean-Francois Clervoy will sit in the flight deck aft center seat. Read a biography of Clervoy.

2305 GMT (6:05 p.m. EST)

The lead spacewalker and mission specialist No. 1 and spacewalker Steve Smith has boarded Discovery. He will sit in the middeck center seat. Read a biography of Smith.

2256 GMT (5:56 p.m. EST)

Discovery's mission specialist No. 3 and spacewalker John Grunsfeld is now aboard. He will sit in the flight deck aft right seat. Read a biography of Grunsfeld.

2249 GMT (5:49 p.m. EST)

Mission specialist No. 4 and spacewalker Michael Foale has boarded Discovery. He will sit in the middeck left seat. Read a biography of Foale.

2242 GMT (5:42 p.m. EST)

Discovery's rookie pilot, Scott Kelly, has entered the shuttle's hatch. He will sit in the flight deck forward right seat. Read a biography of Kelly.

2232 GMT (5:32 p.m. EST)

Mission specialist No. 5 and spacewalker Claude Nicollier is now aboard Discovery. He will sit in the middeck right seat. Read a biography of Nicollier.

2228 GMT (5:28 p.m. EST)

Discovery commander Curt Brown has become the first astronaut to enter the shuttle this evening. He will sit in the flight deck forward left seat. Read a biography of Brown.

2224 GMT (5:24 p.m. EST)

The shuttle astronauts have arrived at launch pad 39B after a drive through the rain at Kennedy Space Center.

2203 GMT (5:03 p.m. EST)

Discovery'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 39B, 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 the Firing Room while Precourt will head 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.

2157 GMT (4:57 p.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 8:47 p.m. EST (0147 GMT), but weather does not appear favorable at Kennedy Space Center. The forecast calls for thick low clouds, rain and crosswinds at the shuttle landing facility.

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

The Final Inspection Team has completed its work at launch pad 39B and they did not report any problems. A briefing on the team's inspections will be given to management shortly.

2115 GMT (4:15 p.m. EST)

Latest weather update continues to look lousy for launch tonight at Kennedy Space Center. The forecast calls for rainshowers, broken clouds at 3,000 and 5,000 feet and overcast skies at 10,000 feet, 7 miles visibility and northeasterly winds at 10 knots gusting to 18, which would be a crosswind. However, the hope is that the weather, which is associated with a front, may clear as the system moves back northward.

The abort landing sites are certainly more favorable. Edwards Air Force Base is calling for just a few clouds at 25,000 feet, northeasterly winds 4 to 7 knots; White Sands expects a few clouds at 25,000 feet, north-northeasterly winds 7 to 12 knots; overseas at Ben Guerir the forecast is for a few clouds at 5,000 and 20,000 feet, good visibility and east-northeasterly winds 10 to 15 knots.

2100 GMT (4:00 p.m. EST)

Discovery stands fully fueled and ready for launch from pad 39B at Kennedy Space Center, Fla. The loading of 528,000 gallons of liquid oxygen and liquid hydrogen into the external tank began at 11:49 a.m. EST (1649 GMT). The operation went smoothly and was completed three hours later. 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 at pad 39B performing their inspections. 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 lead 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 orbit, 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 potentially dangerous hydrogen fuel that is burning.

Each member of the Final Inspection Team is in constant contact with NASA Test Director Steve Altemus in Firing Room 1.

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. He will give the managers a full and detailed report on the team's inspections and findings at the pad 39B.

A full inspection of the vehicle and pad was performed earlier in the countdown, and the external tank received a thorough check prior to fueling.

An inspection of the launch pad and beach will be made following launch tomorrow. That inspection would 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.

1957 GMT (2:57 p.m. EST)

T-minus 3 hours and holding. The countdown has entered a two-hour planned hold. During this time, the final inspection team will be dispatched to launch pad 39B to examine the shuttle one last time prior to liftoff. In addition, the astronauts will suit up and prepare to depart for the pad. Launch still scheduled for 8:47 p.m. EST (0147 GMT Saturday), weather permitting.

1946 GMT (2:46 p.m. EST)

The liquid oxygen tank inside the external tank has been loaded. The LOX and liquid hydrogen tanks are now in stable replenishment mode with more cryogenics being added to replace what naturally boils away during the countdown.

1935 GMT (2:35 p.m. EST)

Fueling of shuttle Discovery is nearing completion at launch pad 39B as rain falls over Kennedy Space Center this afternoon. The liquid hydrogen tank inside the external fuel tank has been filled with 385,000 gallons of rocket fuel. The liquid oxygen operations are not yet done, the tank is still being loaded in the fast-fill mode. The tanks' supplies of the super-cold cryogenics will naturally boil away over the course of the countdown. That means the tanks will be topped off until minutes for launch.

Other than a poor weather forecast, there are no problems being worked. Liftoff remains scheduled for 8:47 p.m. EST tonight (0147 GMT Saturday).

1755 GMT (12:55 p.m. EST)

Tanking operations are reported to be going well at launch pad 39B. Fueling transitioned to the fast-fill mode at 12:40 p.m. EST (1740 GMT).

The seven Discovery astronauts were awakened for launch at 11 a.m. EST (1600 GMT). The crew has cycled its sleep to the schedule in which they will be on duirng the 9-day mission. They will be seated for lunch in the dining room at the Operations & Checkout Building at 3:53 p.m. EST (2053 GMT), the start of a brief photo opportunity to be carried live on NASA Television. Following lunch, commander Curt Brown, pilot Scott Kelly and flight engineer Jean-Francois Clervoy will receive a weather briefing on conditions expected at Kennedy Space Center and abort landing sites in California, New Mexico, Spain and Morocco. Meanwhile, mission specialists Steve Smith, John Grunsfeld, Mike Foale and Claude Nicollier will begin suiting up. The entire crew will be reunited in the suit up room following the weather update. Departure from the crew quarters for launch pad 39B is expected at 5:03 p.m. EST (2203 GMT). After the 30-minute ride to the pad, the astronauts will begin boarding Discovery for launch.

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

With a last-minute concern with welding put to rest, NASA managers have cleared space shuttle Discovery for launch tonight on a 9-day mission to service the Hubble Space Telescope. However, there is still one problem that threatens the scheduled 8:47 p.m. EST (0147 GMT Saturday) launch -- the weather. Forecasters say there is an 80 percent chance thick clouds and rain could keep Discovery on Earth for another day.

Fueling of Discovery's external fuel tank with 528,000 gallons of super-cold liquid oxygen and liquid hydrogen began at 11:49 a.m. EST today (1649 GMT). The operation will take three hours to complete.

THURSDAY, DECEMBER 16, 1999
1830 GMT (1:30 p.m. EST)

Shuttle Discovery's long-delayed mission to repair the Hubble Space Telescope is on hold again for at least a day.

A last-minute question on Wednesday about a possible manufacturing flaw on the shuttle's external fuel tank had threatened Thursday's planned launch. With a sigh of relief the Discovery's tank was found to be free of the welding defects.

However, managers on Thursday became aware that the same manufacturer had also done work on welds in Discovery's main engine compartment and ordered a 24-hour hold to try to ascertain if there are any defects in those welds, said a NASA spokeswoman.

The launch has been reset for 8:47 p.m. EST Friday (0147 GMT Saturday). Landing will remain scheduled for Dec. 26 so the shuttle will be safely secured in its processing hangar before the end of the year. NASA wants to avoid flying during the transition to the year 2000 because of potential computer problems.

If the shuttle is launched Friday, the crew will have to give up their day-off in orbit to accommodate all the work planned on four spacewalks to repair and service the dormant Hubble Space Telescope.

If launch is delayed until Saturday, one of the spacewalks will be cut. If Discovery is not off the ground by then, the flight will be rescheduled for next year.

1802 GMT (1:02 p.m. EST)

NASA has scrubbed tonight's planned launch of Shuttle Discovery. The mission has been postponed at least 24 hours because of concerns about welds in the shuttle's aft engine compartment. Details to follow.

1500 GMT (10:00 a.m. EST)

While the early focus today is on a California launch pad where an Atlas rocket sits ready to carry NASA's Terra satellite, work continues on schedule at Kennedy Space Center in Florida for tonight's launch of shuttle Discovery.

Overnight the rotating service structure was retracted from the shuttle at pad 39B. Earlier this morning the power-generating fuel cells on Discovery were activiated and personnel were cleared from the danger area. Countdown clocks are scheduled to enter a planned hold at the T-minus 6-hour mark at 1628 GMT (11:28 a.m. EST). If mission managers do not find any problems during a meeting at lunchtime, the go will be given to load 528,000 gallons of liquid oxygen and liuqid hydrogen into the shuttle's external fuel tank beginning at about 1730 GMT (12:30 p.m. EST).

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

Shuttle program managers believe space shuttle Discovery's external tank does not have a welding flaw found on different tank slated for future use. The problem involved suspect material used in welding external tank pressure lines. The issue will be put to rest during the Mission Management Team meeting prior to fueling Discovery at midday today.

WEDNESDAY, DECEMBER 15, 1999
2200 GMT (5:00 p.m. EST)

NASA tonight is checking paperwork to ensure space shuttle Discovery's external tank has not have faulty welds. A paperwork review was prompted after another tank was found to have suspect material used in the construction of liquid oxygen lines. Engineers are examining records to make sure the suspect batch of material was not used on Discovery's tank before launching the shuttle on Thursday night. This issue might not be resolved until the Mission Management Team meeting at lunchtime tomorrow, local time.

Otherwise, the countdown is proceeding on schedule and without any other problems.

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

NASA officials say they are tracking no problems and the countdown is still on schedule for space shuttle Discovery at pad 39B. Launch of the third Hubble Space Telescope servicing mission remains set for Thursday at 9:18 p.m. EST (0218 GMT on Friday).

Yesterday the shuttle test team completed checkout of Discovery's avionics, electrics and landing system. Last night the liquid oxygen and liquid hydrogen was loaded aboard the shuttle's fuel cell storage tanks. The eight-hour operation was completed early this morning. The reactants will be combined to generate electricty and drinking water for the shuttle and crew in space.

Today the activities planned include final main engine tests, powering up NASA's worldwide communications systems and installation of the mission specialists' seats aboard Discovery.

The weather forecast has improved to a 90 percent chance of acceptable conditions. The only slight concern will be a low cloud ceiling below 3,000 feet. Should the launch slip to Friday or Saturday there is 80 percent chance of good weather on both days with cloud ceilings being the main threat.

TUESDAY, DECEMBER 14, 1999
2230 GMT (5:30 p.m. EST)

The warning alert has been sounded to clear personnel from launch pad 39B. The launch team is preparing to perform the pyrotechnic initiator controllers in the next hour. Later tonight the cryogenic liquid oxygen and liquid hydrogen will be loaded aboard Discovery's fuel cells. There are no problems to report and launch remains on schedule for Thursday at 9:18 p.m. EST (0218 GMT on Friday).

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

Eight hours into the countdown and things are going well. Officials told reporters this morning that there are no problems being worked and Discovery remains scheduled for launch on Thursday during a window of 9:18 to 9:59 p.m. EST (0218-0259 GMT on Friday). "The vehicle's in great shape, the launch team is once again well prepared and it looks like the weather is going to cooperate," NASA test director Steve Altemus said.

Discovery's launch countdown is the first in five months for NASA's shuttle program. The shuttle fleet was grounded in late summer for wiring inspections, and then Discovery was plagued by other wiring defects, a broken drill bit lodged in a main engine and a damaged liquid hydrogen recirulation line. This mission is running two months behind schedule, and Endeavour's radar mapping flight originally to fly before Discovery has been delayed until mid-to-late January.

"It is good to be back in countdown again," Altemus said. "Over the past several weeks, as you are aware of, we worked through a significant number of nonstandard work items."

Discovery's aft engine compartment was closed for flight last night before the countdown was started. Today, workers are preparing for tonight's eight-hour loading of liquid oxygen and liquid hydrogen into Discovery's fuel cell storage tanks. The cryogenics will be used to generate power and drinking water for the shuttle and crew once in space. Launch pad 39B will be cleared of all personnel at 5:30 p.m. EST (2230 GMT) to test the pyrotechnic initiator controllers, which will ignite the solid rocket boosters and release the umbilicals to the shuttle at liftoff. Loading of the fuel cells is expected to begin at 9:30 p.m. EST (0230 GMT Wednesday).

There are no middeck or secondary payload work during this countdown and no apparent constraints that would prevent NASA from conduct three consecutive launch attempts should Discovery not fly Thursday night.

The weather forecast for Thursday looks favorable with high pressure building over the area after a cold front moves through. Shuttle Weather Officer Ed Priselac says there is an 80 percent chance of acceptable conditions. The main concern is the threat of a cloud ceiling at 3,000 feet, which could violate the 5,000-foot ceiling limit at the emergency shuttle runway at KSC and the Range Safety visible tracking requirement for launch. In addition, the forecast calls for a temperature in the lower 50s F, which might cause ice to form on the external fuel tank.

Conditions on Friday night appear similar with an 80 percent of meeting the weather rules. On Saturday, there is a 70 percent of good weather with the concerns being low clouds and the chance of rainshowers.

Emergency landing sites at Edwards Air Force Base in California, White Sands in New Mexico and the TALs across the Atlantic all look favorable. The only site with a concern is Ben Guerir because of crosswinds.

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

T-minus 43 hours and counting. The countdown is scheduled to begin at this time for Thursday night's launch of space shuttle Discovery. NASA will start clocks ticking down from the T-minus 43 hour mark. The count includes 24 hours and 48 minutes of built-in hold time leading toward liftoff on Thursday at 9:18 p.m. EST (0618 GMT on Friday).

One-half hour ago launch team members were called to their stations in Firing Room 1 of the Complex 39 Launch Control Center to begin the count. Over the next few hours work will start to close out the vehicle and ground facilities for launch. Also, the the backup flight system software will be loaded into Discovery's general purpose computers.

Our next update will be posted following a countdown status news briefing scheduled for 9 a.m. EST this morning.

MONDAY, DECEMBER 13, 1999
2100 GMT (4 p.m. EST)

At long last the countdown is about to begin for space shuttle Discovery and the STS-103 mission. After two months of delays because of wiring defects, an engine swap and replacement of a crushed liquid hydrogen recirculation line, NASA is ready to send Discovery into space to fix the crippled Hubble Space Telescope.

The shuttle launch team will gather at Kennedy Space Center tomorrow at 1 a.m. EST (0600 GMT) in preparation to begin the three-day countdown. Clocks will start ticking backwards from T-minus 43 hours at 1:30 a.m. EST (0630 GMT). If all stays on track, Discovery will lift off from KSC's pad 39B at 9:18 p.m. EST on Thursday (0218 GMT on Friday), the opening of a 41-minute launch window.

Discovery's 10-day mission will feature four spacewalks to install six fresh gyroscopes into Hubble, restoring the observatory's precision pointing system to working orbit. Hubble has been shut down since mid-November when the fourth gyro failed; three of the six are needed to keep the telescope pointed to stars, planets and its other astronomical targets during observations. In addition, a new main computer, guidance sensor and other equipment will be added to the 9 1/2-year old telescope.

The seven international astronauts for mission STS-103 arrived at Kennedy Space Center from their home base in Houston one week ago today. They were preparing for launch last Saturday, but the flight was postponed due to the hydrogen line replacement work. The crew is led by commander Curt Brown, with rookie pilot Scott Kelly, robot arm operator Jean-Francois Clervoy and spacewalkers Steve Smith, John Grunsfeld, Michael Foale and Claude Nicollier.

Discovery's mission will be the the third and final shuttle launch of 1999. This year will have the smallest number of missions since two flights were completed in 1988 when NASA resumed the shuttle program after the Challenger accident.