BY JUSTIN RAY

December 18, 1999 -- Follow the countdown and launch of a Lockheed Martin Atlas 2AS rocket and NASA's Terra spacecraft. Reload this page for the very latest on the mission.

FRIDAY, DECEMBER 17, 1999
1810 GMT (1:10 p.m. EST)

At Vandenberg Air Force Base in California a pair of meetings are scheduled for today to determine when the next attempt will be made to launch an Atlas 2AS rocket and the Terra spacecraft for NASA. The U.S. Air Force Western Range will decide early this afternoon if it can support an attempt on Saturday. The Range provides tracking, communications and safety services for all Vandenberg launches. Later, a 4 p.m. EST (2100 GMT) engineering meeting is planned for Lockheed Martin officials to review the work completed to fix a computer software problem responsible for Thursday's scrub. The problem, obviously, much be fixed before the countdown can go forward.

We will provide further updates as news becomes available.

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

Lockheed Martin has determined it will take at least another day to resolve a ground software problem that cancelled Thursday's launch attempt. The extra day also will allow launch team members to rest before resuming the countdown. So the launch of the Atlas 2AS rocket and NASA's Terra spacecraft is now scheduled for no earlier than Saturday during a window of 1833:25 to 1857:49 GMT (1:33:25-1:57:49 p.m. EST).

The software problem caused the ground launch sequencer, the master computer program running the countdown, to incorrectly determine the Atlas rocket had not switched to internal power. The countdown was halted at T-minus 39 seconds. To correct the problem the software logic will be changed.

However, to ensure a similar problem does not exist in the software for the remainder of the countdown, officials decided late Thursday check the rest of the program.

THURSDAY, DECEMBER 16, 1999
2315 GMT (7:15 p.m. EST)

Lockheed Martin engineers have determined that a software error in the ground launch sequencer caused today's scrub of the Atlas 2AS rocket. The sequencer controls the final 100 seconds of the countdown.

During an automatic software check of rocket systems at T-minus 40 seconds, the sequencer did not confirm that the Atlas stage had switched to internal power. That resulted in a computer-commanded cutoff of the countdown at T-minus 39 seconds. The launch team used other methods to show the rocket was, in fact, on internal power and that the problem was with the ground software and not Atlas. But given the short launch window officials were not able to determine why the software acted the way it did and recycle the countdown.

Work is now under way to correct the ground launch sequencer software logic and test it in Lockheed Martin's software verification laboratory. This work should be completed in time to support another launch attempt on Friday during a window of 1833:25 to 1857:49 GMT (1:33:25-1:57:49 p.m. EST).

U.S. Air Force weather forecasters say there is a 90 percent chance of acceptable conditions on Friday.

1945 GMT (2:45 p.m. EST)

The glitch that stopped today's launch countdown at T-minus 40 seconds appears to be software problem with the ground support system used to monitor the Atlas rocket. A meeting is scheduled for 2100 GMT (4 p.m. EST) today to discuss the results of troubleshooting efforts currently under way. The launch has been tentatively rescheduled for Friday, NASA spokesman George Diller said. The weather forecast for tomorrow is very favorable.

1905 GMT (2:05 p.m. EST)

Officials have tentatively rescheduled to launch of a Lockheed Martin Atlas 2AS rocket with NASA's Terra spacecraft for Friday during a window of 1833:25 to 1857:49 GMT (1:33:25-1:57:49 p.m. EST). However, the 24-hour scrub turnaround is depending on the successful resolution of a problem detected in the final minute of today's countdown. Management and engineers plan meetings later today to discuss the problem.

At Space Launch Complex-3 East, the liquid oxygen and liquid hydrogen will now be drained from the Atlas rocket and Centaur upper stage. Later the mobile service tower will be returned to around the rocket.

1854 GMT (1:54 p.m. EST)

The official announcement that today's launch attempt has been scrubbed was just made. The countdown cutoff was triggered by a redline limit monitor at T-minus 40 seconds. We will await further details on the problem and news of when the next launch attempt will be made.

1853 GMT (1:53 p.m. EST)

The countdown has not been restarted and so launch will not occur today before the close of the window.

1850:49 GMT (1:50:49 p.m. EST)

The countdown would have to pick up from T-minus 5 minutes within the next two minutes in order to still launch today. A decision has not been made on the fate of today's launch attempt.

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

Still no official word on what problem caused the countdown to be stopped in the final minute. It takes seven minutes to safe the rocket and recycle the countdown back to T-minus 5 minutes for another attempt. It is unclear if this problem can be resolved and the countdown restarted to launch today before the end of the window.

1847 GMT (1:47 p.m. EST)

Today's available launch window extends for another 10 minutes. The launch team is trying to recycle the countdown back to T-minus 5 minutes in order to try to get the rocket airborne by the end of the window at 1857:49 GMT (1:57:49 p.m. EST).

1845 GMT (1:45 p.m. EST)

The ground computer controlling the countdown has detected a program. That resulted in an automatic cutoff of the countdown. Safing of the rocket has started.

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

CUTOFF! Countdown has stopped. Safing in progress.

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

T-minus 1 minute. All systems are go for launch.

1843 GMT (1:43 p.m. EST)

T-minus 1 minute, 40 seconds. Launch commit start. Computers are now controlling the remainder of the countdown to launch.

The Atlas booster stage is now going to internal power.

1843 GMT (1:43 p.m. EST)

T-minus 2 minutes. Coming up on the handover to the launch sequencer in 20 seconds.

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

T-minus 3 minutes. Western Range reports go for launch.

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

T-minus 3 minutes, 30 seconds. The solid rocket boosters are armed.

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

T-minus 4 minutes. The rocket's Flight Termination System is on internal power and armed for launch. The Centaur upper stage also has switched off ground power and gone to internal battery.

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

T-minus 5 minutes and counting. The Lockheed Martin launch team has picked up the countdown for launch today. The Atlas rocket is about to conclude its 27-month wait atop Space Launch Complex-3 East and carry NASA's Terra satellite into near-polar orbit.

1838 GMT (1:38 p.m. EST)

The "go" has been given by Mark Ware, Lockheed Martin's directior of operations at Space Launch Complex-3, to pick up the countdown in two minutes.

1837 GMT (1:37 p.m. EST)

A repeat of Tom Heter's management poll is complete and all was reported go for launch.

1835 GMT (1:35 p.m. EST)

The launch time has been changed again to 1845 GMT (1:45 p.m. EST). The countdown will resume at T-minus 5 minutes at 1840 GMT (1:40 p.m. EST).

Also, the intruder aircraft was a glider, officials say.

1834 GMT (1:34 p.m. EST)

The U.S. Air Force, which runs the Western Range, reports the aircraft has left the restricted area. The Range is now go for launch.

1831 GMT (1:31 p.m. EST)

The launch team has set 1841 GMT (1:41 p.m. EST) for the new liftoff time today. However, that is based on the intruder aircraft being cleared from the restricted safety zone around Vandenberg.

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

The countdown is now in an extended hold at T-minus 5 minutes. It is believed the aircraft will be cleared from the restricted airspace around the launch site very shortly. In any event, today's available window in which to launch the Atlas rocket extends for 24 minutes and 24 seconds, closing at (1857:49 GMT) 1:57:49 p.m. EST.

1827 GMT (1:27 p.m. EST)

The decision has been made to extend this built-in hold at T-minus 5 minute. The aircraft inside the restricted area around Vandenberg will not be cleared from the area in time to allow the count to pick up as planned.

1826 GMT (1:26 p.m. EST)

Lockheed Martin launch director Tom Heter has completed his management poll and all systems were "go" for liftoff. However, the Western Range, not part of the poll, is still working the intruder aircraft problem.

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

Terra spacecraft is on internal power.

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

The Western Range reports there is an aircraft inside the restricted launch danger area. If the plane cannot be cleared in time, this hold at T-minus 5 minutes could be extended.

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

The Terra spacecraft is scheduled to transfer to internal power at this time, now 10 minutes from launch.

1822 GMT (1:22 p.m. EST)

The Lockheed Martin launch team has been polled and all reported "go" status.

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

NASA mission director Ray Lugo has completed a poll of his launch team. No problems were reported. Lugo will then put this input into the Lockheed Martin management poll upcoming shortly.

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

Now 15 minutes away from the scheduled launch of a Lockheed Martin Atlas 2AS rocket from Vandenberg Air Force Base along Central California's Pacific coastline.

The mission to place Terra into the proper low-Earth orbit will take less than 14 minutes. At separation, the apogee altitude should be 376 nautical miles, perigee of 354 nmi and inclination of 98.3 degrees

1814 GMT (1:14 p.m. EST)

The flight control pre-launch preparations are completed and the steering programs have been loaded aboard the rocket's guidance computer.

1813:25 GMT (1:13:25 p.m. EST)

T-minus 5 minutes and holding. Countdown clocks have entered the final planned built-in hold for today's launch attempt. During this 15-minute period, the launch team will have a chance to catch up on any work that could be running behind schedule. In addition, managers will poll various members of the launch team to ensure all systems are ready for liftoff. The count should resume at 1828:25 GMT (1:28:25 p.m. EST).

The Atlas booster and Centaur upper stage are now fully fueled for launch, work that has been on going over the past 90 minutes. But given the super-cold temperatures of the liquid oxygen and hydrogen aboard the vehicle, the cryogenics will be replenished as the countdown continues. The Atlas was loaded earlier with its RP-1 fuel, a highly refined kerosene.

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

The weather conditions are perfect at Vandenberg Air Force Base in California. There is a zero percent chance of violating the launch weather rules. In addition, the Range Safety weather criteria is being met. At launch time the forecast calls for some thin, high-level cirrus clouds, north-northeasterly winds at 8 knots and a temperature of about 60 degrees F.

1803 GMT (1:03 p.m. EST)

Now 30 minutes from the launch of Terra aboard the Atlas 2AS rocket from Vandenberg. Countdown clocks are continuing toward the T-minus 5 minute mark where a 15-minute hold is planned.

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

The Atlas launch team reports the Centaur liquid hydrogen tank is at flight level.

1758 GMT (12:58 p.m. EST)

While things have are going according to plan in California for the launch of a Lockheed Martin Atlas rocket, NASA officials have scrubbed tonight's liftoff of space shuttle Discovery. Shuttle managers say they need 24 hours more to completed a paperwork review of suspect welding work. See our STS-103 Mission Status Center for further details later today.

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

Atlas liquid oyxgen and helium loading operations have been completed.

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

Liquid hydrogen and liquid oxygen topping to the Centaur upper stage is now beginning.

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

The anomaly team says the temperature in the Atlas thrust section is 19 degrees F and the limit is 15 degrees F. The plan is to increase the temperature of the section's heater.

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

A team of engineers are discussing the low temperatures in the Atlas thrust section. The temperatures are becoming too cold for launch. The team will develop a plan to warm up the section.

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

Eighty percent of the Centaur liquid hydrogen tanking is complete.

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

Centaur's liquid hydrogen tank is now half full.

1733:25 GMT (12:33:25 p.m. EST)

Now one hour away from launch of the Atlas rocket and NASA's Terra spacraft. Fueling of the Atlas-Centaur rocket continues to go smoothly and there are no problems reported with the vehicle, payload, Range or weather today.

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

Centaur liquid hydrogen now at 20 percent.

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

Five percent of the liquid hydrogen tank on Centaur has been filled. Today's launch will mark the first time a liquid hydrogen-fueled rocket has flown from Vandenberg Air Force Base. Centaur's twin engines will consume the hydrogen and liquid oxygen to boost Terra into the intended orbit around Earth.

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

The Atlas stage liquid oxygen tank is now 60 percent full.

1721 GMT (12:21 p.m. EST)

The customary light coating of frost and ice is being to form on the Atlas stage. Just minutes ago the stage was bright and shiny silver, now it is becoming snow white.

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

Final alignment of the rocket's guidance computer has been completed.

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

T-minus 60 minutes. The countdown continues on schedule for today's launch of a Lockheed Martin Atlas 2AS rocket and NASA's Earth Observing System Terra spacecraft from Vandenberg Air Force Base in California. Fueling of the rocket is under way and no problems have been reported. The count has one additional built-in hold at T-minus 5 minute leading to liftoff at 1833:25 GMT (1:33:25 p.m. EST).

1714 GMT (12:14 p.m. EST)

Loading of liquid oxygen into the Atlas first stage has started. The tank is 5 percent full.

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

The chilldown conditioning of plumbing for loading liquid oxygen into the Atlas booster stage is now beginning.

1705 GMT (12:05 p.m. EST)

The Centaur liquid oxygen tank has been filled to 95 percent.

1703:25 GMT (12:03:25 p.m. EST)

Now 90 minutes away from the scheduled liftoff time for the Atlas rocket and Terra spacecraft.

Today's launch will occur from Space Launch Complex-3 East at Vandenberg Air Force Base in California. Since its last launch in May 1995, the pad has undergone complete reconstruction to support the larger, more complex Atlas 2-series of rockets and their Centaur upper stages. The renovation contract was signed in late 1992 to build the new pad so Atlas 2 rockets could launch secret spy satellites for the National Reconnaissance Office from the U.S. West Coast, placing the craft into orbits that cannot be reached with launches from Cape Canaveral in Florida.

The old tower was demolished and rebuilt from the ground up. Construction was completed in September 1996 and the first Atlas rocket, the one flying today, was stacked on the pad in September 1997.

SLC-3E consists of the 230-foot tall mobile service tower that enclosed the rocket when it is at the pad, providing access and weather protection; the 170-foot tall fixed umbilical tower that supports lines connected to the rocket through which propellants are pumped to the rocket, as well as electrical power and conditioned air; the launch support building is a two-story structure contains support equipment; and the launch operations building where the countdown is controlled, located about 7 miles from the pad.

To date, there are three scheduled launches from the new pad: Terra today and two NRO payloads next summer and one about a year later.

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

Richard Ho, the Terra mission director, has just reported the spacecraft is ready for launch.

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

Preparations for the starting of liquid hydrogen fueling of Centaur are now under way. Meanwhile, the Centaur liquid oxygen tank is 65 percent full.

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

The Centaur liquid oxygen tank is now 40 percent full.

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

Confirmation has been received that liquid oxygen is flowing into the Centaur upper stge.

1638 GMT (11:38 a.m. EST)

The go has been given to start loading super-cold loquid oxygen into the Centaur upper stage. This is the first of three propellant loading operations during today's countdown. The Atlas stage will be loaded with LOX starting in about 35 minutes. Liquid hydrogen fuel will then be pumped aboard the Centaur starting at 1724 GMT (12:24 p.m. EST).

1635 GMT (11:35 a.m. EST)

The Centaur upper stage's engines and liquid oxygen transfer lines are being chilled at this time to prepare for fueling operations. Also, the Atlas rocket's RP-1 fuel tank is being pressurized.

1633 GMT (11:33 a.m. EST)

T-105 minutes and counting. Countdown clocks have been released for the 30-minute built-in hold. Activities are going as planned today at Vandenberg Air Force Base for launch since the countdown was started at 1018 GMT (5:18 a.m. EST).

The latest weather forecast has been improved to a 100-percent chance of acceptable conditions today. The launch time forecast calls for just some scattered cirrus clouds at 24,000 feet, a temperature of 59 degrees F and northeasterly winds at 8 to 12 knots.

1603 GMT (11:03 a.m. EST)

T-105 minutes and holding. The countdown has entered the first of two planned holds today. This will be a 30-minute pause. Five minutes before resuming the count, a readiness poll will be conducted of the launch team to verify members are ready for loading of super-cold fuel and oxidizer into the rocket.

It is a clear, beautiful morning in California. There are no problems being reported and launch remains scheduled to occur on time in 2 1/2 hours at 1833:25 GMT (1:33:25 p.m. EST).

1535 GMT (10:35 a.m. EST)

The 230-foot tall mobile service tower that has protected the Atlas rocket during its record setting 27-month stay at Space Launch Complex-3 East is retracted to the launch position. Preparations are continuing on schedule at Vandenberg Air Force Base in California for today's scheduled 1833:25 GMT (1:33:25 p.m. EST) launch.

The Atlas rocket to be launched today was assembled at SLC-3E in September 1997 to support pathfinder exercises at the newly rebuilt pad. Those tests to check the pad, ground support equipment and launch team were completed in April of 1998. However, the Terra satellite was grounded due to software problems, forcing the Atlas rocket to be placed in extended storage.

Lockheed Martin officials decided the best place to keep the Atlas was on the launch pad enclosed in the mobile service tower. The MST at Vandenberg is unlike the more open towers at Cape Canaveral Air Station's Complex 36 Atlas pads. The Vandenberg tower is often referred to as a building, fully enclosed and environmentally controlled. In addition, workers closed off the base of the tower and erected a tent around the base of the Atlas to protect the engines. Dry, warm air was also pumped into the tent.

Throughout the past two years the rocket has been coated with WD-40 to prevent corrosion. WD-40 was originally created 40 years ago for the Atlas ICBMs. X-ray tests were also performed every 90 days to check the structural integrity of the rocket's fuel tanks.

In May of this year when the decision was made to resume the launch campaign for Terra, Lockheed Martin reperformed tests and checkout of the pad and rocket for for today's mission, said Mark Ware, manager of launch operations at SLC-3. Launch pad validations were completed as if the rocket was never there. "It was like starting fresh."

When the work resumed the launch was planned for late July. However, when the Boeing Delta 3 rocket failed on May 4, another delay for Terra was triggered. The upper stage engine that caused the Delta 3 mishap is a similar version to the engines on the Atlas rocket's upper stage - Centaur. To ensure the engines on Centaur were safe to use, a pair of ultrasonic inspections were performed at the launch pad to check the engines' combustion chambers to see if the problem that doomed Delta 3 would affect Terra's ride. The inspections and later analysis concluded that the Centaur was ready for flight. The launch was rescheduled for today.

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

The countdown for launch of a Lockheed Martin Atlas 2AS rocket remains on schedule at Vandenberg Air Force Base in California. Atlas has been powered on and preparations are continuing for retraction of the mobile service tower in about two hours.

The latest weather forecast calls for clear skies, unrestricted visibility, a temperature of 55 degrees and a 90 percent chance of meeting the launch weather rules.

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

The day has arrived for a $140 million Lockheed Martin Atlas 2AS rocket to write a bit space history. After resolving a final technical concern, officials have cleared the rocket to launch NASA's Terra satellite on a $1.5 billion mission to study Earth's environment from orbit. The launch will mark the first time a Centaur upper stage has been used by an Atlas rocket from the Vandenberg Air Force Base launch site, the first time liquid hydrogen rocket fuel - consumed by Centaur - has used at Vandenberg, the first launch from Space Launch Complex-3 East since it was rebuilt to support Atlas 2-series rockets, the liftoff will end the longest time a commercial Atlas has waited on the launch pad - some 27 months - and Terra will become the heaviest payload ever carried by Atlas.

The only problem being worked Wednesday was with a remote interface controller, a piece of ground hardware that allows the launch processing system in the control center to communicate with launch pad systems to service the rocket and monitoring Atlas systems. During a test Tuesday, a system shut down and a backup did not take over as it should have. However, engineers troubleshooting the problem determined late Wednesday that an error in procedures caused the glitch. The RIC was properly initialized and rebooted Wednesday, clearing the problem at SLC-3E.

So with no other problems and a near-perfect weather forecast officials are pressing ahead with liftoff at 1833:25 GMT (1:33:25 p.m. EST), the opening of a 24-minute, 24-second launch window that will extend to 1857:49 GMT (1:57:49 p.m. EST).

"We are basically in a ready state with the launch vehicle, space vehicle, the facilities and launch team," said Ray Lugo, NASA's mission director for the Terra launch.

Final pre-launch activities will get under way with a weather briefing at 1000 GMT (5 a.m. EST) for management before entering countdown operations. The Atlas will be powered up at 1018 GMT (5:18 a.m. EST). A communications test between NASA's Tracking and Data Relay Satellite System and Terra will be performed at 1200 GMT (7 a.m. EST). About 90 minutes later the launch team will switch the purge into the payload fairing from air to gaseous nitrogen. Another weather briefing will be held at just after 1500 GMT (10 a.m. EST) so managers can decide whether to roll the protective mobile service tower away from the rocket. Tower retraction is planned to begin at 1533 GMT (10:33 a.m. EST). Following a built-in hold in the countdown, fueling of the Centaur upper stage with liquid oxygen and liquid hydrogen and Atlas with liquid oxygen will occur in steps. A final hold will take place at T-minus 5 minutes.

We will have complete comprehensive updates throughout the final hours of the countdown and the 14-minute flight by Atlas to place Terra into orbit.

WEDNESDAY, DECEMBER 15, 1999
1930 GMT (2:30 p.m. EST)

The launch readiness review was completed today at Vandenberg Air Force Base for Thursday's mission of a Lockheed Martin Atlas 2AS rocket to carry NASA's Terra environmental research satellite into space. There are no problems reported with the rocket, payload or weather for Thursday's 1833 GMT (1:33 p.m. EST) scheduled liftoff time. However, engineers are assessing a ground support equipment issue. A meeting planned for later today is expected to clear the problem.

TUESDAY, DECEMBER 14, 1999
2345 GMT (6:45 p.m. EST)

The first Atlas-Centaur rocket to launch from Vandenberg Air Force Base in California stands ready for liftoff on Thursday. The Lockheed Martin Atlas 2AS vehicle, known as AC-141, will carry NASA's Terra satellite into near-polar orbit from the refurbished Space Launch Complex-3 West. Launch is planned for 1833 GMT (1:33 p.m. EST), the opening of a 25-minute window.

Workers today performed final closeouts of the electrical and mechanical systems on the Atlas booster and Centaur stage thrust sections. Final pre-launch work to prepare the spacecraft is also beginning. The launch readiness review is planned for Wednesday morning.

U.S. Air Force weather forecasters say there is a 90 percent chance of acceptable conditions for launch on Thursday. The only slight concern will be layered clouds. The launch time forecast calls for scattered altostratus clouds at 18,000 feet and scattered cirrus clouds at 24,000 feet, visibility of 7 miles, northerly winds 8 to 12 knots and a temperature between 52 and 56 degrees F.

Launch weather officer Capt. Joe Kurtz provided this summary in today's forecast:

"An upper level ridge and surface high pressure continue to build into the west coast. The Vandenberg area will have partly cloudy skies over the next few days. Scattered mid and high clouds will move over the ridge into California on launch day. Winds will be gusty around base Tuesday morning, but they should decrease as we go through the week. On launch day, surface winds will be out of the east early in the count, becoming northeasterly for liftoff. Overnight low temperatures this week will range in the upper 30's to around 40 F, with the highs in the upper 50's to lower 60's. Maximum upper level winds will be 30 knots from the northwest at 30,000 feet."

Terra is a $1.5 billion mission that will serve as NASA's flagship for the Earth observing system, a multi-satellite program designed to study the global environment over the next decade.