BY JUSTIN RAY

May 24, 2000 -- Follow the countdown and launch of the inaugural Lockheed Martin Atlas 3A rocket with Eutelsat's W4 communications satellite. Reload this page for the very latest on the mission.

2145 GMT (5:45 p.m. EDT)

The Range reports there is just one boat in the restricted launch danger area in the Atlantic Ocean. The boat is being chased away by the Air Force and Coast Guard, and Lockheed Martin hopes to be ready for launch at 6:15 p.m. EDT (2215 GMT).

See a diagram of the restricted waters for launch.

2142 GMT (5:42 p.m. EDT)

ANOTHER NEW LAUNCH TIME! The hold at T-minus 5 minutes will be extended another 16 minutes, producing a new launch time of 6:15 p.m. EDT (2215 GMT).

2139 GMT (5:39 p.m. EDT)

NEW LAUNCH TIME! Launch has been delayed another 10 minutes to 5:59 p.m. EDT (2159 GMT) due to boats in the downrange restricted area. They are expected to be cleared, hopefully, very soon. Saturday's launch attempt was delayed, in part, due to over 70 boats inside the launch safety zone that were participating in a celebrity fishing tournament.

2138 GMT (5:38 p.m. EDT)

No additional information to pass along from Lockheed Martin at this point. Standing by for word on the LOX depletion error.

2134 GMT (5:34 p.m. EDT)

The Anomaly Team has been convened to look at a liquid oxygen depletion error message with the Atlas booster stage.

2129 GMT (5:29 p.m. EDT)

T-minus 5 minutes and holding. The countdown has entered the planned built-in hold at T-minus 5 minutes. This 15-minute period gives launch team members time to catch up the countdown timeline, managers will poll various the launch team to ensure all systems are ready for liftoff.

2124 GMT (5:24 p.m. EDT)

T-minus 10 minutes and counting. Now five minutes away from entering the built-in hold at T-minus 5 minutes, and 25 minutes away from liftoff. The rocket, W4 satellite, weather, Range and ground support systems are all reporting "go" status for launch.

The loading of the Atlas booster and Centaur upper stage with super-cold cryogenic propellant is now completed. Given the cold nature of the liquid oxygen and liquid hydrogen, however, the cryogenics naturally boil away during the countdown. As a result, the tanks will be topped off until just minutes prior to liftoff. RP-1 fuel, a highly refined kerosene, was loaded aboard the Atlas stage earlier during a countdown dress rehearsal.

2119 GMT (5:19 p.m. EDT)

Now 30 minutes away from today's launch of the first Atlas 3A rocket. Liftoff will occur from pad 36B at Cape Canaveral Air Force Station in Florida.

2116 GMT (5:16 p.m. EDT)

The final weather briefing for launch management has just been completed by Launch Weather Officer Jim Sardonia. There are no concerns with all weathr conditions acceptable and expected to remain that way. Liftoff remains scheduled for 5:49 p.m. EDT (2149 GMT). Upper level winds are also favorable.

2110 GMT (5:10 p.m. EDT)

The Centaur liquid hydrogen is now at flight level.

The Flight Termination System self-test check was recently completed, with inhibits in place to ensure safety of the Atlas 3A rocket pad pad 36B. The FTS would be used to destroy the rocket should problem occur during the launch.

Also, the pogo suppression system at the pad has been readied. The system will be used to dampen the "bounce" of the rocket during engine ignition.

And the C-band beacon on the rocket is reported "go" for launch. The beacon will be used by the Eastern Range to track the rocket during flight.

2103 GMT (5:03 p.m. EDT)

The Atlas liquid oxygen tank is now being topped off to flight level.

The report from Lockheed Martin is upper level winds are acceptable for launch today. There was concern earlier about a wind shear between 47,000 and 49,000 feet.

2054 GMT (4:54 p.m. EDT)

T-minus 40 minutes and counting. Launch remains scheduled for 5:49 p.m. EDT (2149 GMT). The Centaur liquid hydrogen tank is 60 percent full. The Atlas liquid oxygen tank is being maintained 98 percent full. Topping to flight level will begin shortly.

2048 GMT (4:48 p.m. EDT)

Fueling operations are continuing without problem today for the first Atlas 3A rocket. The Centaur liquid oxygen tank has reached flight level, Centaur liquid hydrogen is at 10 percent and Atlas liquid oxygen now at 90 percent.

2043 GMT (4:43 p.m. EDT)

Chilldown conditioning of the liquid hydrogen propellant systems at pad 36B have been completed, and the "go" was given by Launch Conductor Ed Christiansen to begin loading the fuel into Centaur.

2041 GMT (4:41 p.m. EDT)

The liquid oxygen tank inside the Atlas booster stage is now 60 percent full. Launch remains set for the rescheduled time of 5:49 p.m. EDT (2149 GMT).

2038 GMT (4:38 p.m. EDT)

The launch team has verified the the Russian-made RD-180 engine at the base of the Atlas 3 rocket is within temperature limits after liquid oxygen chilldown.

2035 GMT (4:35 p.m. EDT)

At launch pad 36B, the Atlas liquid oxygen tank is now 20 percent full. The rocket's shiny exterior has turned a frosty white as a thin layer of ice forms from the super-cold liquid oxygen. The Atlas 3A rocket features a liquid oxygen tank nearly 10 feet longer than the older Atlas 2-series vehicles because of the extra LOX needed by the RD-180 engine.

Also, topping of the Centaur liquid oxygen tank to flight level has started.

2026 GMT (4:26 p.m. EDT)

The final alignment of the Atlas 3A rocket's inertial navigation unit guidance computer has been completed. Final pre-launch preparations of the rocket's control system now begins.

2024 GMT (4:24 p.m. EDT)

T-minus 70 minutes and counting. The countdown has been restarted toward launch of the first Atlas 3A rocket at 5:49 p.m. EDT, 10 minutes later than planned.

The consensus of engineers is the dropping gaseous nitrogen pressure and supplies at the pad was caused by a computer-monitoring error. That has been fixed. Also, the pad's rocket hold-down cylinder pressure problem was a temperature-related issue and the previously-dropping pressure is expected to stabilize.

With the countdown running again, the "go" has been given to start loading liquid oxygen into the Atlas stage. And "chilldown" conditioning of liquid hydrogen propellant feed lines at pad 36B is now starting. This is done to thermally prepare the plumbing before the super-cold cryogenic flows through the pipes and into the rocket.

Also at this time, the Complex 36 Blockhouse doors are being sealed, protecting the 120-plus-member launch team. The Blockhouse is located just 1,400 feet away from the Atlas 3A rocket at pad 36B, and serves as the control center for the countdown to launch.

On Friday, May 12, Spaceflight Now toured the historic Complex 36 Blockhouse. Now you can step inside through the eyes of our virtual reality camera. (286k QuickTime file).

2020 GMT (4:20 p.m. EDT)

Launch Weather Officer Jim Sardonia just reported the latest weather balloon has found a significant drop in upper level wind conditions. Winds are currently at 34 knots at 47,000 but fall to nearly zero knots at 49,000 feet. It is unknown at this time if that will be a problem for the rocket during flight. The second launch attempt for the Atlas 3 last Tuesday was scrubbed by upper level wind shear.

2016 GMT (4:16 p.m. EDT)

Engineers are troubleshooting a couple of problematic measurements that are of concern today involving falling pressures in systems at launch pad 36B. The issues are being discussed and the countdown remains holding at T-minus 70 minutes. Liftoff has been delayed at least 10 minutes to 5:49 p.m. EDT (2149 GMT).

2014 GMT (4:14 p.m. EDT)

T-minus 70 minutes and holding. The countdown has entered an unplanned hold for at least 10 minutes while officials and engineers examine a couple of pressure problems at pad 36B. Fueling activities for the Centaur liquid hydrogen tank and Atlas liquid oxygen are also being delayed.

2012 GMT (4:12 p.m. EDT)

Countdown clocks will hold in two minutes due to the pressure measurement problems at the pad.

2009 GMT (4:09 p.m. EDT)

The Centaur liquid oxygen tank has reached 95 percent full where it is being held. Topping to 100 percent will be completed later.

Meanwhile, the Anomaly Team has started looking at a pressure problem at launch pad 36B. Also, a technician reports another pressure measurement is decreasing, suggesting a regulator problem.

2002 GMT (4:02 p.m. EDT)

The Centaur liquid oxygen tank is now 50 percent full.

1958 GMT (3:58 p.m. EDT)

The Centaur liquid oxygen tank has been filled above 20 percent. The super-cold liquid oxygen will be consumed along with liquid hydrogen by the stage's single RL-10 main engine built by Pratt & Whitney. Liquid hydrogen will be loaded aboard the stage in about 35 minutes.

1949 GMT (3:49 p.m. EDT)

Chilldown condition of the liquid oxygen transfer lines at pad 36B has been completed and the launch team is now beginning to fill the Centaur upper stage with its its supply of liquid oxygen for launch today at 5:39 p.m. EDT.

1944 GMT (3:44 p.m. EDT)

The latest steering program is being loaded into the rocket's guidance computer based upon the upper level wind conditions. Also, the wind damper arm connecting the Atlas 3A rocket with the launch tower has been completed.

1940 GMT (3:40 p.m. EDT)

The "chilldown" procedure has started to thermally condition the liquid oxygen propellants lines at pad 36B in advance of loading the Centaur upper stage. Chilldown is a process in which a small amount of the super-cold liquid oxygen is released from the pad's storage tank into the feed lines that lead to the rocket.

1939 GMT (3:39 p.m. EDT)

T-minus 105 minutes and counting. And the countdown clocks are running again toward the scheduled launch of the Atlas 3A rocket and its history-making flight to space with the first Russian-made engine for an American booster. Liftoff is two hours away.

1935 GMT (3:35 p.m. EDT)

Launch Conductor Ed Christiansen has been polled the launch team to verify readiness to begin fueling the Atlas/Centaur rocket shortly. All systems were reported "go" and launch pad 36B is being cleared of all workers. The mobile service tower is fully retracted and secured for today's 5:39 p.m. EDT (2139 GMT) launch. Countdown clocks are scheduled to resume from the T-minus 105 minute hold in about four minutes.

1909 GMT (3:09 p.m. EDT)

T-minus 105 minutes and holding. Clocks have entered a planned 30-minute hold period for the countdown this afternoon at Cape Canaveral Air Force Station for launch of the maiden Atlas 3A rocket. Launch remains scheduled for 5:39 p.m. EDT (2139 GMT).

The Air Force has announced two collision avoidance, or COLA, cutouts of today's launch window. Liftoff will be prohibited from 6:35:43 to 6:39:54 p.m. EDT and 6:50:15 to 6:51:05 p.m. EDT to avoid passing too close to another orbiting object. Today's window extends from 5:39 to 7:58 p.m. EDT.

1903 GMT (3:03 p.m. EDT)

The mobile service tower has been retracted and technicians are now securing the structure for launch. Road blocks are being set up at Complex 36 while technicians at pad 36B are beginning test stand checks. Also, the final alignment test of the rocket's inertial navigation unit guidance computer has been completed and the pre-launch alignment is starting.

Countdown clocks are about to enter the T-minus 105 minute hold at 3:09 p.m. EDT. There is nothing amiss today at Cape Canaveral.

1844 GMT (2:44 p.m. EDT)

A test of the C-band beacon system is starting. This system is used by the Eastern Range to track the rocket during flight.

1839 GMT (2:39 p.m. EDT)

Retraction of the mobile service tower from around the Atlas 3A rocket is starting at Cape Canaveral's launch pad 36B. The tower will be fully retracted to the "maintenance area" for launch.

The launch team reported preps for the Atlas and Centaur propulsion systems are complete, as were the hydraulic preps for Atlas.

1824 GMT (2:24 p.m. EDT)

T-minus 150 minutes and counting. The entire launch team is now manning stations at Cape Canaveral's Complex 36 for the Integrated Launch Operations. Activities are proceeding well on this fifth launch attempt for the Atlas 3A rocket. Liftoff remains scheduled for 5:39 p.m. EDT (2139 GMT).

Countdown clocks will pause twice over the next three hours and 15 minutes in advance of launch. Built-in holds are planned at T-minus 105 for 30 minutes and at T-minus 5 minutes for 15 minutes.

At launch pad 36B, access platforms and equipment inside the mobile service tower have been stowed, and technicians are preparing to retracted the structure from around the rocket in about 15 minutes.

1754 GMT (1:54 p.m. EDT)

The Integrated Launch Operations for the countdown to liftoff of Atlas 3 will being in a half-hour and retraction of the mobile service tower will start in 45 minutes.

Meanwhile, Range Safety is currently conducting a holdfire test to ensure it could stop the launch moments before liftoff if necessary.

1710 GMT (1:10 p.m. EDT)

With promising weather and no technical problems, countdown clocks are ticking along smoothly this afternoon at Cape Canaveral's Complex 36 for launch of the Atlas 3A rocket and the Eutelsat W4 satellite.

Over the past two hours or so, internal power tests of the Atlas and Centaur stages were completed, as were the checks of the liquid oxygen and liquid hydrogen systems at pad 36B, the helium purge to Centaur began and the Centaur main engine ignitor was checked.

Launch remains scheduled for 5:39 p.m. EDT (2139 GMT), the opening of a two-hour, 19-minute window extending to 7:58 p.m. EDT (2358 GMT).

1530 GMT (11:30 a.m. EDT)

The countdown is underway at Cape Canaveral for this afternoon's attempt to launch the first Atlas 3A rocket. No problems are being reported, officials say, and activities remain on scheduled for liftoff at 5:39 p.m. EDT.

The latest weather forecast now indicates a 90 percent chance of favorable conditions, a slight improvement from yesterday's prediction. Launch Weather Officer Jim Sardonia gave this overview this morning:

"Very dry conditions will persist today allowing for an excellent opportunity for launch. Winds will be southwesterly and brisk today, preventing an east-coast seabreeze to form until very late in the afternoon if at all. If a seabreeze forms, there will be a slight chance of enhanced cumulus clouds forming along the coast and within 10 nautical miles of SLC 36. Similar conditions are expected Thursday and Friday. The main concern today will be the slight chance of enhanced cumulus clouds within 10 nm of SLC 36 during the launch window."

TUESDAY, MAY 23, 2000

Lockheed Martin is ready to try again Wednesday to launch its inaugural Atlas 3A rocket from Cape Canaveral to place a European telecommunications satellite into orbit. It will be the fifth attempt for the Atlas 3A since May 15, of which the previous delays were caused by a variety of technical and weather problems. Liftoff from pad 36B at the Cape is scheduled for 5:39 p.m. EDT, the opening of a launch window that extends to 7:58 p.m. EDT (2139-2358 GMT).

The countdown will get started Wednesday at 8:49 a.m. EDT as the launch team begins readying the rocket for flight. The vehicle will be powered up and three hours of electrical and mechanical checks should get underway.

The Integrated Launch Operations -- the final portion of the countdown in which all members of the launch team participate -- will start at 2:24 p.m. EDT (1824 GMT). Retraction of the mobile service tower from around the rocket is slated for 2:39 p.m. EDT (1839 GMT).

Fueling operations will commence at 3:53 p.m. EDT (1953 GMT) with super-cold liquid oxygen flowing into the Centaur upper stage. Loading of liquid oxygen into the Atlas booster stage should start at 4:14 p.m. EDT (2014 GMT). The final segment of fueling will begin at 4:33 p.m. EDT (2033 GMT) when liquid hydrogen is pumped into the Centaur. The Atlas stage was previously fueled with its supply of RP-1 kerosene.

Weather forecasters are calling for an 80 percent chance of acceptable conditions. Launch Weather Officer Jim Sardonia gave this overview today:

"Expect a slight chance of an isolated rainshower or thunderstorm along the east-coast sea breeze this afternoon. The atmosphere is fairly dry however, so the number of storms will be few and the coverage will be minimal. Expect similar conditions on Wed for the launch countdown, with a slight chance of an isolated rainshower or thunderstorm forming west of CCAFS along the east-coast sea breeze. If a cell forms due west of the Cape, there will be a slight chance of Anvil clouds drifting back east within 10 nautical miles of SLC 36. Winds are expected to be southerly and light on Wednesday.

"The main concern on Wednesday will be the slight chance of isolated rainshowers and thunderstorms forming along the east-coast sea breeze, with a chance of Anvil clouds within 10 nm of SLC 36."

The launch time forecast calls for scattered cumulus clouds at 3,000 feet with 2/8ths sky coverage, scattered altocumulus clouds at 10,000 feet with 3/8ths sky coverage and broken cirrus clouds at 25,000 feet with 5/8ths sky coverage, visibility of 7 miles, southerly winds 10 gusting to 16 knots at the pad, a temperature of 76 to 78 degrees F, relative humidity of 80 percent and isolated rainshowers and thunderstorms in the interior portions of Florida.

Should the launch be delayed for some reason, there is a 90 percent chance of good conditions on Thursday with the concern being rainshowers and thunderstorms in the area. On Friday, there is an 80 percent of acceptable weather due to the same threat.

We will provide extensive coverage of the launch with our Mission Status Center reports and a live streaming video broadcast that will include views from two cameras mounted onboard the rocket.

MONDAY, MAY 22, 2000
1625 GMT (12:25 p.m. EDT)

The maiden voyage of Lockheed Martin's Atlas 3A rocket -- the first American launcher to be powered by a Russian-made engine -- will have to wait until Wednesday, one day later than originally envisioned. Citing the need to replace critical batteries on the rocket and a glitch-prone valve at the launch pad, Lockheed Martin officials today decided to slip the liftoff another day.

"When you started putting all those activities together and the work crews taking a rest, and the weather looked bad for Tuesday, we decided to give everyone a breather," said Adrian Laffitte, Lockheed Martin's director of Atlas launch operations at Cape Canaveral.

Liftoff from Cape Canaveral Air Force Station's pad 36B on Wednesday will be possible during a launch window of 5:39 to 7:58 p.m. EDT (2139-2358 GMT).

Weather forecasters are calling for an 80 percent chance of favorable weather on Wednesday with the only concern being cloud tops from thunderstorms drifting within 10 miles of the launch pad. Launch Weather Officer Jim Sardonia gives this overview:

"With some instability in the area due to the remnants of a cold front in north Florida, expect a slight chance of an isolated rainshower or thunderstorm along the east-coast sea breeze this afternoon and Tuesday afternoon. The atmosphere is fairly dry however, so the number of storms will be few and the coverage will be minimal. Expect similar conditions on Wed for the launch countdown, with a slight chance of an isolated rainshower or thunderstorm forming west of CCAFS along the east-coast sea breeze. If a cell forms due west of the Cape, there will be a slight chance of Anvil clouds drifting back east within 10 nautical miles of SLC 36. Winds are expected to be southeasterly and light on Wednesday.

"The main concern on Wed will be the slight chance of isolated rainshowers and thunderstorms forming along the east-coast sea breeze, with a chance of Anvil clouds within 10 nautical miles of SLC 36."

Should the launch be delayed to Thursday for some reason, the forecast indicates a 70 percent of good conditions with the concern being rainshowers and thunderstorms in the area. On Friday, there is the same threat but an 80 percent chance of launching.

Saturday's launch attempt, the fourth conducted since last Monday, was spoiled when over 70 boats strayed into the restricted danger zone off the coast of Cape Canaveral, delaying the liftoff until the final minute of the launch window. A last-minute computer glitch then halted the countdown at T-minus 2 minutes, 15 seconds, causing the launch to be automatically scrubbed for the day.

The computer error was solved within 18 minutes and another shot at launching the rocket could have been made on Saturday had it not been for the boats, which were part of a celebrity fishing tournament.

After the postponement, a worn out gasket in a liquid oxygen topping valve caused a leak as the super-cold oxidizer was being drained from the Atlas booster stage. Officials opted to let the oxygen naturally boil off over night, with the tank dropping from 52 percent to 8 percent, Laffitte said. On Sunday, technicians returned to pad 36B and replaced the faulty gasket, allowing the launch team to properly "de-tank" the remaining 8 percent.

Today, engineers are systematically going through the batteries aboard the rocket for replacement. Some of the batteries are reaching the end of their life, and fresh ones will permit additional launch attempts if needed.

In addition, the troublesome liquid oxygen dump valve at the pad is being replaced. This is the valve that created delays last Wednesday and again on Saturday while the launch team was trying to fuel the rocket. The valve was not closing properly on those attempts.

The Atlas 3 has experienced four unsuccessful countdowns with a variety of technical and weather problems to blame. Before Saturday's bizarre countdown, Monday's attempt was called off because of a faulty Range tracking radar in Bermuda; Tuesday saw unacceptable high altitude winds; and Wednesday's effort got to T-minus 29 seconds before a computer timing error aborted the count.

"It is a little bit frustrating but on the other hand we are a totally dedicated team and we are working through the problems," Laffitte said. "This is sort of expected with a new vehicle. But we still have our sense of humor."

1545 GMT (11:45 a.m. EDT)

Lockheed Martin officials have decided to reschedule the next launch attempt for the first Atlas 3A rocket to Wednesday, bumping back the liftoff by one additional day. A spokeswoman says the extra time is needed so technicians can replace a troublesome valve at the Cape Canaveral launch pad.

Wednesday's launch window will extend from 5:39 to 7:58 p.m. EDT (2139-2358 GMT).

SUNDAY, MAY 21, 2000
1740 GMT (1:40 p.m. EDT)

The maiden voyage of Lockheed Martin's Atlas 3A rocket will be delayed until at least Tuesday so workers can replace a faulty valve gasket at Cape Canaveral Air Force Station's pad 36B.

The gasket is part of the liquid oxygen topping check valve inside the pad's plumbing. The gasket created a problem Saturday night in which liquid oxygen could not be drained properly from the Atlas booster stage. An alternate "de-tanking" method was employed but the rocket was not completed drained of fuel until around 12 noon EDT today, nearly 16 hours after the launch attempt was scrubbed, a Lockheed Martin spokeswoman said.

Technicians plan to replace the gasket, the spokeswoman reported, to get the valve working correctly in preparation for another launch attempt on Tuesday -- the fifth for the first Atlas 3A rocket. If officials approve a Tuesday shot, the liftoff will be possible during a window of 5:38 to 7:58 p.m. EDT (2138-2358 GMT).

The launch team will also get some time to rest before starting the next countdown early Tuesday morning at 8:48 a.m. EDT.

1510 GMT (11:10 a.m. EDT)

Lockheed Martin announced this morning it would postpone the debut launch of the Atlas 3A rocket until no earlier than Tuesday afternoon from Cape Canaveral, Florida. Officials had hoped to attempt the inaugural launch later today but a defueling problem experienced last night caused the additional delay, a spokeswoman said.

Further details are expected to be released this afternoon, and we will update this page as soon as possible.

Tuesday's window extends from 5:38 to 7:58 p.m. EDT (2138-2358 GMT).

Saturday's launch try -- the fourth this week -- was scrubbed after virtually the entire window was used up waiting for the Range to clear nearly 70 boats from the restricted danger zone in the Atlantic Ocean. Then a last-minute computer error message cropped up as the launch team prepared the Russian-made RD-180 engine for ignition. Read our full story.

0401 GMT (12:01 a.m. EDT)

A celebrity fishing tournament and a last-minute software problem conspired to scrub Lockheed Martin's fourth try at launching its inaugural Atlas 3A rocket during a bizarre countdown Saturday at Cape Canaveral. Launch has been rescheduled for Sunday at 5:38 p.m. EDT (2138 GMT). Read our full story.

Meanwhile, Launch Weather Officer Jim Sardonia reports there is a 40 percent chance thunderstorm anvil clouds will be a problem on Sunday courtesy of disturbed weather in Western Florida. Sardonia gave this forecast Saturday night:

"A significant cold front is expected to move into the eastern Gulf of Mexico on Sunday producing strong thunderstorms just west of Tampa, Florida. These thunderstorms are expected to produce a broad band of Anvil clouds that could reach within 10 nautical miles of SLC 36 by the beginning of the launch window.

"There will be no threat from lightning or thunderstorms on station for Tower removal and Tanking operations, however the anvil clouds may violate the triggered lightning Launch Commit Criteria during the launch window. Winds are expected to be southerly and below the 29 knot constraint.

"Conditions deteriorate even further in the event of a 24 hour delay (Monday). The frontal system is expected to move into central Florida producing numerous thunderstorms and rainshowers in the area especially along the east-coast seabreeze."

If the launch is delayed to Monday, there is a 70 percent chance of bad weather due to rainshowers and thunderstorms over Cape Canaveral.

0027 GMT (8:27 p.m. EDT)

Engineers troubleshooting the last-minute problem encountered during tonight's countdown report a "minor software glitch" is to blame, Lockheed Martin commentator Don Spencer says. The problem is on its way to resolution and officials have rescheduled launch for Sunday at 5:38 p.m. EDT (2138 GMT), the opening of a two-hour, 19-minute window.

0007 GMT (8:07 p.m. EDT)

Lockheed Martin says a computer error message was detected during the fuel-fill sequence for the RD-180 engine. That prompted the countdown to be stopped at T-minus 2 minutes, 15 seconds. At this time, engineers are troubleshooting the situation to understand if it is simply a software glitch or an actual problem with the engine or ground support systems.

Officials are tentatively preparing for another launch attempt on Sunday afternoon -- the fifth for the maiden Atlas 3A rocket. However, a Sunday try is pending resolution of the engine issue. Sunday's window extends from 5:38 to 7:57 p.m. EDT (2138-2357 GMT). Generally favorable weather conditions are forecast.

At pad 36B, the liquid oxygen and liquid hydrogen supplies are being drained from tanks inside the Atlas and Centaur stages. The rocket will be safed tonight and the mobile service tower rolled back into position to shield the vehicle.

We will update this page as more information becomes available.

0000 GMT (8:00 p.m. EDT)

We are standing by for an announcement by Lockheed Martin as to when the launch will be rescheduled. It is not yet known if launch can occur on Sunday.

SATURDAY, May 20, 2000
2354 GMT (7:54 p.m. EDT)

SCRUB! The countdown was stopped at T-minus 2 minutes and 15 seconds when an unexplained problem was detected as RP-1 fuel was loading into the Atlas rocket's Russian-made RD-180 engine. Since the liftoff was planned at the very end of today's available launch window, the launch team did not have any time to examine the problem.

Tonight's launch was delayed 2 1/2 hours because of over 70 boats strayed into the restricted danger area beneath the rocket's flight path in the waters off the coast of Cape Canaveral. The Coast Guard was able to clear the boats at the last minute, but the delay used up all the launch window.

2354 GMT (7:54 p.m. EDT)

HOLD! Problem was noted during the fuel-fill sequence with the RD-180 engine.

2354 GMT (7:54 p.m. EDT)

T-minus 3 minutes. RP-1 kerosene fuel is now flowing into the RD-180 engine -- the first Russian-made engine to power an American rocket to space. The water system is being readied for activation at launch pad 36B.

2353 GMT (7:53 p.m. EDT)

T-minus 4 minutes. The Atlas booster stage and Flight Termination System are going on internal power.

2352 GMT (7:52 p.m. EDT)

T-minus 5 minutes and counting. The countdown has resumed for launch of AC-201 -- the inaugural Lockheed Martin Atlas 3A rocket with the Eutelsat W4 communications satellite. There are now no problems standing in the way of liftoff at 7:57 p.m. EDT from pad 36B at Cape Canaveral Air Force Station, Florida.

2351 GMT (7:51 p.m. EDT)

The boats have been cleared, finally, from the danger area and the Range is "go" for launch at 7:57 p.m. EDT. Countdown will resume in one minute for liftoff at 7:57 p.m. EDT.

2350 GMT (7:50 p.m. EDT)

Range is "GO" fo launch.

2349 GMT (7:49 p.m. EDT)

Launch Conductor Ed Christiansen has completed a readiness poll of his launch team to ensure all systems are "go" to pick up the countdown at 7:52 p.m. EDT.

2347 GMT (7:47 p.m. EDT)

The fuel-fill sequence is starting to prepare the Russian-made RD-180 engine for launch.

2343 GMT (7:43 p.m. EDT)

"We have no substantive information to pass along," the Range just reported on the situation with the fishing boats in the launch danger area. This problem was first noted over two hours ago.

2337 GMT (7:37 p.m. EDT)

The Eutelsat W4 communications satellite is now switching from ground power to internal power for launch. Again, the plan of attack calls for the countdown to be restarted at T-minus 5 minutes at 7:52 p.m. EDT. If the Range remains "no go" for launch, the count will be safely halted at T-minus 40 seconds.

There were reported to be upwards of 73 boats or more in the launch danger area off the coast of Cape Canaveral today as part of an annual fishing tournament. The boats need to be cleared from the area for their own safety in case the rocket explodes during the early portions of flight.

2334 GMT (7:34 p.m. EDT)

The Lockheed Martin launch team is planning to resume the countdown at 7:52 p.m. EDT from the T-minus 5 minutes even if the Range remains "no go" for liftoff. This will be done to give the Range every moment to clear the danger area of the boats. Should the Range stay "red" for launch, a holdfire will be called and countdown stopped at T-minus 40 seconds.

2331 GMT (7:31 p.m. EDT)

Nothing new to report from the Range. Efforts to clear the dozens and dozens of fishing boats from launch danger area in the Atlantic Ocean continue. Launch is currently scheduled for 7:57 p.m. EDT, the end of today's available window.

Should the Range not be cleared by close of the window, launch will be postponed until Sunday. The weather forecast for tomorrow indicates a 70 percent chance of acceptable conditions during a window of 5:38 to 7:57 p.m. EDT.

2325 GMT (7:25 p.m. EDT)

ANOTHER NEW LAUNCH TIME. The Range says the danger area remains cluttered with boats. Launch has been pushed back to 7:57 p.m. EDT, the very last moment the Atlas can lift off tonight or else be delayed until tomorrow afternoon.

2320 GMT (7:20 p.m. EDT)

The launch of AC-201 -- the Lockheed Martin Atlas 3A rocket and the Eutelsat W4 communications satellite -- is currently scheduled for no sooner than 7:40 p.m. EDT (2340 GMT). The rocket must be airborne by 7:57 p.m. EDT or else wait until Sunday afternoon because the available launch window will close.

This is the fourth attempt to launch the first Atlas 3 rocket. The first try on Monday was scrubbed due to a different Range problem -- a faulty tracking radar in Bermuda. Tuesday saw unacceptable high altitude wind shears. The countdown made it to T-minus 29 seconds on Wednesday before a computer timing error aborted the attempt.

Lockheed Martin then had to wait until after the space shuttle Atlantis launched from nearby Kennedy Space Center on Friday morning before rescheduling the Atlas 3 flight.

2314 GMT (7:14 p.m. EDT)

The Range just told Lockheed Martin that there are still many boats in the restricted area from the Cal Dixon Offshore Classic fishing tournament. In addition, the Coast Guard is trying to determine exact location of a disabled boat. And even more, there is a U.S. Navy ship sailing toward the danger zone and efforts are underway to contact that vessel.

2306 GMT (7:06 p.m. EDT)

For all the launch delays experienced at Cape Canaveral, this one is unique. The countdown to the debut launch of Lockheed Martin's Atlas 3A rocket is stalled at T-minus 5 minutes due to dozens of boats located inside the restricted danger area east of the Cape in the Atlantic Ocean. The boats are part of the Cal Dixon Offshore Classic fishing tournament. The Coast Guard is continuing its attempt to clear the boats -- perhaps as many as 73 -- from the area so the Atlas can be cleared for launch by the end of today's window at 7:57 p.m. EDT (2357 GMT).

Organizers of the fishing event say they informed the participants of the launch and where not to stray. The Air Force says the tournament was supposed to end over three hours ago.

2257 GMT (6:57 p.m. EDT)

NEW LAUNCH TIME. Launch has been delayed until at least 7:28 p.m. EDT, but officials are not optimistic the Range can be cleared by then given the extremely high number of boats located in the danger area east of Cape Canaveral. Today's available launch window extends to 7:57 p.m. EDT (2357 GMT).

Here is the latest report from the U.S. Air Force and Range via a spokeswoman: The 73-boat number is based on the number of participants from the fishing tournament that have not reported back to Port Canaveral. Exactly how many boats are actually inside the restricted area off Cape Canaveral is not known, the Air Force says, pointing out there are too many to count. The boats are scattered from just off the coastline to 40 miles east of Cape. Some are cluster 20 miles out.

The Air Force says that it did not believe the fishing tournament -- the Cal Dixon Offshore Classic -- would cause a problem today because the event was scheduled to conclude at 4 p.m. EDT, or 90 minutes before launch time. But dozens of boats remain at sea on this beautiful Saturday afternoon and evening.

2243 GMT (6:43 p.m. EDT)

The number of boats have been revised, and the new figure is much greater than previously announced by officials. There are eight vessels within the area directly below the rocket's flight path. No boats are permitted in that area during launch. Meanwhile, a separate safety area surrounding the flight path currently has 73 boats that have not responded to Coast Guard warning to leave. Less than 15 are allow to be in that zone during launch for safety reasons.

The U.S. Air Force-run Range says that it did not believe the fishing tournament would cause a problem today because the event was scheduled to conclude at 4 p.m. EDT with a weigh-in at Port Canaveral. However, there is obviously a great deal of boats still in the Atlantic Ocean and have not returned to Port Canaveral.

Launch is currently scheduled for no sooner than 7:08 p.m. EDT (2308 GMT).

2234 GMT (6:34 p.m. EDT)

The Range now estimates another 20 minutes to clear the launch danger area. As a result, Launch Conductor Ed Christiansen has instructed the launch time to be delayed another 20 minutes. Liftoff is now scheduled for 7:08 p.m. EDT (2308 GMT). Tonight's launch window extends to 7:57 p.m. EDT.

There is a fishing tournament underway this Saturday afternoon. The Coast Guard continues its efforts to contact 40 boats and chase them from the restricted area so the Atlas rocket can be cleared for launch.

2228 GMT (6:28 p.m. EDT)

The Eastern Range is expected to provide an update on the boat situation momentarily.

2214 GMT (6:14 p.m. EDT)

NEW LAUNCH TIME. As the Range continues to clear fishing boats out of the restricted danger east of Cape Canaveral, Lockheed Martin has pushed the launch time back another 20 minutes. Liftoff is now scheduled for 6:48 p.m. EDT (2248 GMT). That means today's launch will be delayed a full hour by this problem.

Officials say there is a fishing tournament underway today, of which these boats are part.

The Atlas 3A rocket remains fueled and ready at pad 36B, just waiting for the countdown to resume from T-minus 5 minutes.

2209 GMT (6:09 p.m. EDT)

Lockheed Martin has clarified the boat situation. There is one boat in an area that must be completely cleared of all people for safety reason. And that vessel is currently disabled. The Coast Guard has been dispatched to tow the boat out of the area.

Meanwhile, there are 40 boats in a separate zone where Range Safety limits the number to 15. So the boats are being contacted and told to leave.

Launch is still scheduled for 6:28 p.m. EDT, but may be delayed again given this Range problem.

2202 GMT (6:02 p.m. EDT)

The U.S. Air Force now says there are as many as 40 boats in the restricted danger area east of the Cape Canaveral beneath the rocket's flight path. The area must be clear of the boats for safety sake in case the Atlas rocket malfunctions during the launch.

There is a fishing tournament underway this afternoon that is creating this problem.

The RD-180 fuel-fill sequence in which RP-1 kerosene fuel is released from its storage tank into the Atlas rocket to flow in the engine remains on hold. This procedure, conducted to ready the engine for ignition, won't be performed until 11 minutes before liftoff. Also, the Eutelsat W4 satellite remains on external ground power.

2158 GMT (5:58 p.m. EDT)

The Range reports there are still a number of boats located in the downrange launch danger area in the Atlantic Ocean. The boats are believed to be part of a fishing tournament underway this afternoon. Liftoff is currently scheduled for 6:28 p.m. EDT (2228 GMT), if the boats can be cleared in time.

The launch team has until 7:57 p.m. EDT to get the Atlas 3A rocket off the ground tonight.

2150 GMT (5:50 p.m. EDT)

ANOTHER NEW LAUNCH TIME. Officials have been forced to again shift the launch time because of boats inside the restricted danger area. Launch is now planned for 6:28 p.m. EDT. Efforts are continuing to clear the boats while the countdown remains holding at T-minus 5 minutes.

2143 GMT (5:43 p.m. EDT)

Countdown clocks remain holding at T-minus 5 minutes while the Eastern Range clears a half-dozen boats from the restricted area in the Atlantic Ocean beneath the Atlas rocket's projected flight path. Launch is currently scheduled for 6:03 p.m. EDT (2203 GMT).

There are no technical problems being reported and weather conditions are perfect for this Saturday afternoon launch of the first Atlas 3A rocket carrying the Eutelsat W4 communications satellite.

2136 GMT (5:36 p.m. EDT)

NEW LAUNCH TIME SET. Lockheed Martin has established 6:03 p.m. EDT (2203 GMT) as the new planned liftoff time. The extra 15-minute delay will allow five or six boats to be chased out of the launch danger area in the Atlantic Ocean.

In addition, this new time is after the COLA, or collision avoidance period, that extends from 5:57:27 to 6:02:07 p.m. EDT to avoid passing too close to the orbiting Russian space station Mir.

2129 GMT (5:29 p.m. EDT)

The Range has gone "red" due to several boats in the launch danger area in the Atlantic Ocean east of the Cape Canaveral. It is not know at this time if the boats can be cleared in time to allow the Atlas 3A rocket to launch at 5:48 p.m. EDT. In any event, today's available window extends to 7:57 p.m. EDT if needed.

2128 GMT (5:28 p.m. EDT)

T-minus 5 minutes and holding. The countdown has entered the planned built-in hold at T-minus 5 minutes. 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.

2123 GMT (5:23 p.m. EDT)

T-minus 10 minutes and counting. Now five minutes away from entering the built-in hold at T-minus 5 minutes, and 25 minutes away from liftoff. The rocket, W4 satellite, weather, Range and ground support systems are all reporting "go" status for launch.

The loading of the Atlas booster and Centaur upper stage with super-cold cryogenic propellant is now completed. Given the cold nature of the liquid oxygen and liquid hydrogen, however, the cryogenics naturally boil away during the countdown. As a result, the tanks will be topped off until just minutes prior to liftoff. RP-1 fuel, a highly refined kerosene, was loaded aboard the Atlas stage earlier during a countdown dress rehearsal.

2118 GMT (5:18 p.m. EDT)

Now 30 minutes away from today's launch of the first Atlas 3A rocket. Liftoff will occur from pad 36B at Cape Canaveral Air Force Station in Florida.

2114 GMT (5:14 p.m. EDT)

The final weather briefing for launch management has just been completed by Launch Weather Officer Jim Sardonia. There are no concerns and a 100 percent chance of meeting the weather rules for liftoff at 5:48 p.m. EDT (2148 GMT). Upper level winds are also favorable.

The launch time forecast calls for just a few thin clouds, southeasterly winds and a temperature around 78 degrees F.

Given the very dry conditions at Cape Canaveral, Sardonia says there is a chance of brush fires around the pad after launch today.

2109 GMT (5:09 p.m. EDT)

The Flight Termination System self-test check was recently completed, with inhibits in place to ensure safety of the Atlas 3A rocket pad pad 36B. The FTS would be used to destroy the rocket should problem occur during the launch.

Also, the pogo suppression system at the pad has been readied. The system will be used to dampen the "bounce" of the rocket during engine ignition.

And the C-band beacon on the rocket is reported "go" for launch. The beacon will be used by the Eastern Range to track the rocket during flight.

2059 GMT (4:59 p.m. EDT)

The Atlas liquid oxygen tank is being maintained 98 percent full. Topping to flight level will begin shortly.

2056 GMT (4:56 p.m. EDT)

The Centaur liquid oxygen tank is now at flight level, Atlas liquid oxygen is at 90 percent.

2054 GMT (4:54 p.m. EDT)

The Centaur liquid hydrogen tank is almost full, reaching the 97 percent level. A slower process will now be used to top off the tank through the remainder of the countdown.

2050 GMT (4:50 p.m. EDT)

Half of the liquid oxygen tank in the Atlas stage has been filled and Centaur liquid hydrogen is 80 percent loaded.

Again, the new launch time is 5:48 p.m. EDT (2148 GMT).

2045 GMT (4:45 p.m. EDT)

The Atlas liquid oxygen tank is over 30 percent full and the Centaur liquid hydrogen tank has been loaded past the 50 percent level.

2040 GMT (4:40 p.m. EDT)

With super-cold liquid oxygen now flowing toward the Atlas stage, the rocket's shiny exterior has turned a frosty white as a thin layer of ice forms from the cryogenic. The Atlas 3A rocket features a liquid oxygen tank nearly 10 feet longer than the older Atlas 2-series vehicles because of the extra LOX needed by the RD-180 engine.

Also, topping of the Centaur liquid oxygen tank from 98 percent to flight level has started.

2038 GMT (4:38 p.m. EDT)

T-minus 55 minutes and counting. The countdown has just resumed. One additional hold is planned at T-minus 5 minute for 15 minutes in duration. Liftoff is now set for 5:48 p.m. EDT. To recap, the liquid oxygen dump valve problem was short-lived and loading of liquid oxygen into the Atlas stage has started. The Centaur liquid oxygen tank has been loaded to 98 percent, and the stage's liquid hydrogen tank is now being filled with 5 percent already.

Otherwise, there have not been any other significant problems to report and weather conditions are beautiful this afternoon here at Cape Canaveral.

2035 GMT (4:35 p.m. EDT)

NEW LAUNCH TIME SET. Atlas liquid oxygen tanking is starting and the countdown will resume in three minutes after an unplanned hold of 10-minutes. Liftoff is now slated for 5:48 p.m. EDT (2148 GMT).

2033 GMT (4:33 p.m. EDT)

The "go" was just given to load liquid oxygen into the Atlas booster stage now that the dump valve appears to be working.

2032 GMT (4:32 p.m. EDT)

The launch team reports the troublesome liquid oxygen dump valve is now working again -- cycling from the open position to closed. Standing by on word of the Anomaly Team recommendation.

2028 GMT (4:28 p.m. EDT)

T-minus 55 minutes and holding. Lockheed Martin launch officials have ordered the countdown stopped at this time while engineers troubleshoot the liquid oxygen dump valve in the main transfer line at pad 36B. This is the same valve that is experiencing the same problem that was seen during Wednesday's launch attempt.

2023 GMT (4:23 p.m. EDT)

T-minus 60 minutes and counting. Liquid hydrogen chilldown has been completed at pad 36B but loading of the Centaur is on hold. Chilldown -- the thermal conditioning of the propellant systems -- will be maintained while officials examine a problem with the non-functioning liquid oxygen dump valve at the pad. For now, launch remains scheduled for 5:38 p.m. EDT.

2021 GMT (4:21 p.m. EDT)

The Anomaly Team has just recommended that the liquid hydrogen chilldown activities continue but stopping short of loading the super-cold propellant into the Centaur. This will plan will be implemented while troubleshooting continues with the liquid oxygen dump valve at pad 36B.

2013 GMT (4:13 p.m. EDT)

The launch team has just reported a problem with the liquid oxygen dump valve at pad 36B. The valve is not closing when commanded to do so, which is the same problem experienced at this point in the countdown on Wednesday. The Anomaly Team has been convened to discuss what to do. The valve must be closed in order for liquid oxygen tanking of the Atlas stage to begin.

2009 GMT (4:09 p.m. EDT)

The final alignment of the Atlas 3A rocket's inertial navigation unit guidance computer has been completed. Final pre-launch preparations of the rocket's control system now begins.

2008 GMT (4:08 p.m. EDT)

T-minus 75 minutes and counting. The countdown remains on schedule toward today's launch time of 5:38 p.m. EDT (2138 GMT). The Centaur liquid oxygen tank has reached 95 percent full where it is being held. Topping to 100 percent will be completed later. And the launch team has been given approval to start loading liquid oxygen into the Atlas booster stage.

2006 GMT (4:06 p.m. EDT)

The Centaur liquid oxygen tank is 90 percent full.

2002 GMT (4:02 p.m. EDT)

The "chilldown" conditioning of liquid hydrogen propellant feed lines at pad 36B is now starting. This is done to thermally prepare the plumbing before the super-cold cryogenic flows through the pipes and into the rocket.

Also at this time, the Complex 36 Blockhouse doors are being sealed, protecting the 120-plus-member launch team. The Blockhouse is located just 1,400 feet away from the Atlas 3A rocket at pad 36B, and serves as the control center for the countdown to launch.

Last Friday, Spaceflight Now toured the historic Complex 36 Blockhouse. Now you can step inside through the eyes of our virtual reality camera. (286k QuickTime file).

2000 GMT (4:00 p.m. EDT)

The Centaur liquid oxygen tank is now 50 percent full.

1954 GMT (3:54 p.m. EDT)

Ten percent of the Centaur liquid oxygen tank has been filled. The super-cold liquid oxygen will be consumed along with liquid hydrogen by the stage's single RL-10 main engine built by Pratt & Whitney. Liquid hydrogen will loaded aboard the stage in about 35 minutes.

1947 GMT (3:47 p.m. EDT)

Chilldown condition of the liquid oxygen transfer lines at pad 36B has been completed and the launch team is now beginning to fill the Centaur upper stage with its its supply of liquid oxygen for launch today at 5:38 p.m. EDT.

1943 GMT (3:43 p.m. EDT)

The latest steering program is being loaded into the rocket's guidance computer based upon the upper level wind conditions.

1939 GMT (3:39 p.m. EDT)

The "chilldown" procedure has started to thermally condition the liquid oxygen propellants lines at pad 36B in advance of loading the Centaur upper stage. Chilldown is a process in which a small amount of the super-cold liquid oxygen is released from the pad's storage tank into the feed lines that lead to the rocket.

1938 GMT (3:38 p.m. EDT)

T-minus 105 minutes and counting. And the countdown clocks are running again toward the scheduled launch of the Atlas 3A rocket and its history-making flight to space with the first Russian-made engine for an American booster. Liftoff is two hours away.

1934 GMT (3:34 p.m. EDT)

Launch Conductor Ed Christiansen has been polled the launch team to verify readiness to begin fueling the Atlas/Centaur rocket shortly. All systems were reported "go" and launch pad 36B is being cleared of all workers. The mobile service tower is fully retracted and secured for today's 5:38 p.m. EDT (2138 GMT) launch. Countdown clocks are scheduled to resume from the T-minus 105 minute hold in about four minutes.

1908 GMT (3:08 p.m. EDT)

T-minus 105 minutes and holding. Clocks have entered a planned 30-minute hold period for the countdown this afternoon at Cape Canaveral Air Force Station for launch of the maiden Atlas 3A rocket. There are no technical problems being discussed and the weather is very promising for today's scheduled 5:38 p.m. EDT (2138 GMT) liftoff time.

1907 GMT (3:07 p.m. EDT)

The Air Force has announced today's two collision avoidance, or COLA, cutouts of the launch window. Liftoff will be prohibited from 5:57:27 to 6:02:07 p.m. EDT and 7:33:26 to 7:37:47 p.m. EDT to avoid passing too close to the Russian space station Mir. Today's window extends to 5:38 to 7:57 p.m. EDT.

1903 GMT (3:03 p.m. EDT)

Road blocks are being set up at Complex 36 while technicians at pad 36B are beginning test stand checks. Also, the final alignment test of the rocket's inertial navigation unit guidance computer has been completed and the pre-launch alignment is starting.

1855 GMT (2:55 p.m. EDT)

The mobile service tower has been rolled back from the Atlas 3A rocket at pad 36B as the countdown continues on schedule towards liftoff at 5:38 p.m. EDT. Weather conditions are favorable with bright blue skies over the Cape.

1845 GMT (2:45 p.m. EDT)

A test of the C-band beacon system is starting. This system is used by the Eastern Range to track the rocket during flight.

1838 GMT (2:38 p.m. EDT)

Retraction of the mobile service tower from around the Atlas 3A rocket is starting at Cape Canaveral's launch pad 36B. The tower will be fully retracted to the "maintenance area" for launch.

The launch team reported preps for the Atlas and Centaur propulsion systems are complete, as were the hydraulic preps for Atlas.

1826 GMT (2:26 p.m. EDT)

A readiness poll of the launch team has been completed and all parties were "go" for retraction of the mobile service tower at 2:38 p.m. EDT.

1823 GMT (2:23 p.m. EDT)

T-minus 150 minutes and counting. Man stations for Integrated Launch Operations. The entire launch team is now reporting on console at Cape Canaveral's Complex 36. Two built-in holds -- one for 30 minutes at T-minus 105 and 15 minutes at T-minus 5 minutes -- remain in advance of today's planned 5:38 p.m. EDT (2138 GMT) launch. The mobile service tower is scheduled to be retracted from around the rocket in about 15 minutes at pad 36B.

1750 GMT (1:50 p.m. EDT)

Range Safety has just completed its holdfire checks. This feature allows safety personnel the ability to stop the countdown in the final seconds if a problem is noted.

1730 GMT (1:30 p.m. EDT)

Activities are proceeding at pad 36B and inside the Complex 36 Blockhouse this afternoon on a picturesque Florida day for launch of the debut Atlas 3A rocket in just over four hours. The launch team is continuing with system preps and tests in advance of beginning the integrated countdown at 2:23 p.m. EDT. Launch still set for 5:38 p.m. EDT.

1600 GMT (12:00 p.m. EDT)

The countdown is well underway at Cape Canaveral Air Force Station's Complex 36 today as Lockheed Martin prepares to launch the first Atlas 3A rocket and the Eutelsat W4 communications satellite. Liftoff remains scheduled for 5:38 p.m. EDT, the opening of a 139-minute window.

0401 GMT (12:01 a.m. EDT)

Hoping the fourth time is the charm, Lockheed Martin will try again Saturday afternoon to launch its inaugural Atlas 3A rocket -- the first American booster to be powered by a Russian-made engine. Liftoff is scheduled for 5:38 p.m. EDT (2138 GMT) from pad 36B at Cape Canaveral Air Force Station in Florida. The available launch window extends to 7:57 p.m. EDT (2357 GMT).

Weather forecasters are calling for better than a 90 percent chance of acceptable conditions. Launch Weather Officer Jim Sardonia gave this overview on Friday:

"Strong high pressure will continue to dominate the local area bringing ideal conditions for launch on Saturday afternoon/evening. Since surface winds are expected to be more southeasterly, the 29 knot wind constraint will apply on Saturday. Peak winds may reach 22 knots during the afternoon hours. The only slight concern is for isolated enhanced cumulus clouds moving within 10 nautical miles of SLC 36 on Saturday. These clouds, however, will be short-lived and move rapidly through the Cape if they form. Conditions gradually deteriorate each day in the event of a 24 or 48 hour delay."

The launch time forecast on Saturday calls for scattered cumulus clouds at 3,000 feet, visibility of 7 miles, southeast winds 10 gusting to 20 knots at the pad, a temperature of 76 to 78 degrees F and relative humidity of 70 percent.

Should the launch be delayed for some reason, there is a 70 percent chance of good conditions on Sunday with the concern being thunderstorm anvil clouds moving within 10 miles of the pad from the west. On Monday, there is just a 30 percent of acceptable weather due to rainshowers and thunderstorms.

Countdown clocks will begin ticking on Saturday morning at 8:48 a.m. EDT as the launch team beginning readying the rocket for flight. The vehicle will be powered up and three hours of electrical and mechanical checks should get underway.

The Integrated Launch Operations -- the final portion of the countdown in which all members of the launch team participate -- will start at 2:23 p.m. EDT (1823 GMT). Retraction of the mobile service tower from around the rocket is slated for 2:38 p.m. EDT.

Fueling operations will commence at 3:52 p.m. EDT (1952 GMT) with super-cold liquid oxygen flowing into the Centaur upper stage. Loading of liquid oxygen into the Atlas booster stage should start at 4:13 p.m. EDT (2013 GMT). The final segment of fueling will begin at 4:32 p.m. EDT (2032 GMT) when liquid hydrogen is pumped into the Centaur. The Atlas stage was previously fueled with its supply of RP-1 kerosene.

The computer timing error experienced during the most recent launch attempt on Wednesday has been fixed, officials reported Friday. The problem occurred because the timing was off between the hardware-driven countdown sequencer and the software of the launch-controlling computer. Sensing the timing error, the launch computer aborted the countdown at T-minus 29 seconds.

The glitch was recreated during software testing on Thursday and a procedural change was put into place to ensure the problem does not reoccur on Saturday. The fix was successfully tested in Lockheed Martin's software verification lab.

"We are absolutely ready to go," said Julie Andrews, spokeswoman for International Launch Services, the joint U.S.-Russian venture that markets the Atlas and Proton rocket fleets. "We are pumped."

Monday's launch attempt was called off due to a faulty Range tracking radar in Bermuda and Tuesday saw unacceptable high altitude winds.

The Atlas 3A rocket will place Eutelsat's W4 communications satellite into orbit during its debut launch.

FRIDAY, MAY 19, 2000
1030 GMT (6:30 a.m. EDT)

With space shuttle Atlantis safely launched this morning, the Eastern Range at the Cape is clear for the maiden flight of Lockheed Martin's Atlas 3A rocket on Saturday.

Officials say the technical problem that scrubbed Wednesday's Atlas 3 countdown at T-minus 29 seconds has been corrected.

The Atlas launch team will have two-hours and 19 minutes to get the rocket airborne Saturday during a window running from 5:38 to 7:57 p.m. EDT (2138-2357 GMT). The weather forecast is promising.

THURSDAY, MAY 18, 2000

29 seconds. That is how close Lockheed Martin got to its debut launch of the Atlas 3A rocket from Cape Canaveral last night. But officials are optimistic the technical glitch that halted the countdown at T-minus 29 seconds is nearing resolution, clearing the way for another launch attempt on Saturday during an available window of 5:38 to 7:57 p.m. EDT (2138-2357 GMT).

However, a Saturday liftoff is dependent upon Friday's sunrise launch of space shuttle Atlantis from nearby Kennedy Space Center.

Both the Atlas and Atlantis require safety, communications and tracking services from the Air Force-run Eastern Range at the Cape. The Range can only support one launch ever 24 hours, needing the time between to rest its systems.

If Atlantis launches as planned on Friday at 6:12 a.m. EDT, then the Atlas 3A will receive Range support on Saturday evening. But if the shuttle is delayed for some reason, NASA has reserved the Range for backup launch attempts on Saturday and Sunday morning.

"We will be ready to launch as soon as the shuttle goes," said Julie Andrews, spokeswoman for International Launch Services, the joint U.S.-Russian venture that markets the Atlas and Proton rocket fleets.

Engineers troubleshooting last night's problem believe a timing error between the countdown sequencer and launch computer was to blame, officials report. A change in procedures has been ordered and testing is underway today in a Lockheed Martin software verification laboratory to ensure the fix will work, and not create a different problem. The testing is expected to be completed later today.

The handful of other problems experienced during yesterday's rather bumpy and dramatic countdown were put to rest, including a troublesome liquid oxygen valve at the launch pad and sensor-related glitches with the rocket.

Once launched, the Atlas 3A rocket will become the first American booster to be powered to space by a Russian-made engine -- the RD-180.

Designated AC-201, the first Atlas 3A shall place the W4 communications satellite into orbit for the European Telecommunications Satellite Organization, or Eutelsat. It will be parked in geostationary orbit 22,300 miles above Earth's equator at 36 degrees East, covering Russia and parts of Africa as part of Eutelsat's ongoing expansion effort. The craft was built by Alcatel Space to provide TV, business communications and Internet services via 31 Ku-band transponders, with 19 dedicated to Russian coverage and 12 to Africa.

WEDNESDAY, MAY 17, 2000
2350 GMT (7:50 p.m. EDT)

SCRUB! Lockheed Martin Launch Director Adrian Laffitte has scrubbed tonight's launch of the inaugural Atlas 3A rocket. The problem with the Master Inhibitor Bus electrical system on the rocket could not be resolved before the close of the available window.

This was the third consecutive postponement for maiden flight of Atlas 3A with the Eutelsat W4 communications satellite. Monday's attempt was called off due to a faulty tracking radar in Bermuda; then by unacceptable wind shear at high altitudes above the launch site on Tuesday.

When the next attempt will be made is not yet known. Today was Lockheed Martin's last shot at flying the Atlas 3A before giving way to NASA's efforts to launch space shuttle Atlantis on Friday from nearby Kennedy Space Center. Both launches need support from the U.S. Air Force-run Eastern Range, which provides required safety, communications and tracking services to all Cape rocket flights. The Range needs 24 hours between launches of different vehicles to reset its equipment.

If the shuttle is launched on time Friday, the Atlas 3 could be rescheduled for as early as Saturday night. However, that has not been confirmed.

The Atlas rocket and its Centaur upper stage will now be drained of its liquid oxygen and liquid hydrogen supplies, the RP-1 fuel injected into the RD-180 engine will be spit out and the vehicle systems safed.

A new nine-hour countdown will be conducted for the Atlas 3A when the launch is rescheduled.

2349 GMT (7:49 p.m. EDT)

Launch Conductor Ed Christiansen has just polled his launch team. "No go" was the consensus of the team.

2347 GMT (7:47 p.m. EDT)

There are 10 minutes left into tonight's window and five minutes before the countdown must be resumed from its current position at T-minus 5 minutes. There is still no resolution to the problem seen with the Master Inhibitor Bus that stopped the countdown at T-minus 29 seconds. Engineers are racing to understand the situation.

2343 GMT (7:43 p.m. EDT)

Computer data has been saved from the cutoff and countdown clocks are being recycled back to T-minus 5 minutes. Engineers are still investigating the problem seen a short time ago that stopped the count at T-minus 29 seconds. At this point, the cause of the glitch is not yet known.

2341 GMT (7:41 p.m. EDT)

The launch team has about 10 minutes to resolve the problem that tripped the "red-line" monitor at T-minus 29 seconds in the countdown. The count will be recycled back to T-minus 5 minutes and the whole timeline reperformed to prepare the rocket for liftoff. Officials have until 7:57 p.m. EDT tonight to get the rocket airborne.

2339 GMT (7:39 p.m. EDT)

NEW LAUNCH TIME. Liftoff has been rescheduled for 7:56 p.m. EDT, one minute before the end of the window, if the problem can be resolved.

2338 GMT (7:38 p.m. EDT)

A post-cutoff poll of the launch team has been completed by Launch Conductor Ed Christiansen. All parties reported safe conditions. Countdown clocks are being recycled to T-minus 5 minutes. There is still the chance liftoff could occur tonight by the end of the window at 7:57 p.m. EDT.

2336 GMT (7:36 p.m. EDT)

The countdown clock was stopped at T-minus 29 seconds due to a problem with the Master Inhibitor Bus. Tonight's window extends to 7:57 p.m. EDT. It is unclear if the launch team can recycle and still make another try tonight, provided the problem can be corrected in time.

2335 GMT (7:35 p.m. EDT)

CUTOFF! COUNTDOWN STOPPED!

2335 GMT (7:35 p.m. EDT)

T-minus 31 seconds. Launch Sequence Start. The Atlas 3A rocket's onboard computer is now controlling the countdown.

In the next few seconds the inertial navigation unit's countdown will be started, the liquid hydrogen and liquid oxygen vent valves will be locked for flight and the flight data recorders will be readied.

2335 GMT (7:35 p.m. EDT)

T-minus 1 minute. The RD-180 engine is being verified ready for flight and final status checks are under way. Engine ignition will occur at T-minus 2.73 seconds and the Russian-made powerplant will build up to 74 percent thrust. A check of eight engine parameters will performed by the rocket's onboard computer a half-second before liftoff. If no problems are detected, the rocket will be allowed to launch at T-0.

In the past minute, the inertial navigation unit was launch enabled, Centaur liquid hydrogen and liquid oxygen tanking was secured, fuel tank pressures stable and the ignition enable switch was closed.

2334 GMT (7:34 p.m. EDT)

T-minus 2 minutes. Pressurization of the Atlas and Centaur stages has started. Tanks now being brought to proper pressure levels for flight.

Shortly, the rocket's inadventant separation destruct safety system will be armed, the Centaur upper stage will go to internal power and the flight termination system will be armed.

2333 GMT (7:33 p.m. EDT)

T-minus 3 minutes. RP-1 kerosene fuel is now flowing into the RD-180 engine -- the first Russian-made engine to power an American rocket to space. The water system is being readied for activation at launch pad 36B.

2332 GMT (7:32 p.m. EDT)

T-minus 4 minutes. The Atlas booster stage and Flight Termination System are going on internal power.

2331 GMT (7:31 p.m. EDT)

T-minus 5 minutes and counting. The countdown has picked up for launch of the inaugural Lockheed Martin Atlas 3A rocket with the Eutelsat W4 communications satellite this evening from Cape Canaveral Air Force Station, Florida. There are no problems standing in the way of liftoff at 7:36 p.m. EDT.

2328 GMT (7:28 p.m. EDT)

Launch Conductor Ed Christiansen has completed another readiness poll of the launch team ensure all systems are "go" to pick up the countdown at 7:31 p.m. EDT. No problems were reported and liftoff remains scheduled for 7:36 p.m. EDT.

2326 GMT (7:26 p.m. EDT)

The Eutelsat W4 satellite confirmed on internal power. Liftoff still expected at 7:36 p.m. EDT (2336 GMT).

2325 GMT (7:25 p.m. EDT)

The fuel-fill sequence is starting to prepare the Russian-made RD-180 engine for launch.

2323 GMT (7:23 p.m. EDT)

Eutelsat's W4 communications satellite sitting atop the Atlas 3A rocket is now switching back to internal power for launch. The spacecraft will be relying on internal battery power until the solar arrays can begin recharging the power system once in space.

2321 GMT (7:21 p.m. EDT)

Now 10 minutes remaining in this hold at T-minus 5 minutes. Liftoff remains scheduled for 7:36 p.m. EDT (2336 GMT).

2315 GMT (7:15 p.m. EDT)

ANOTHER NEW LAUNCH TIME. The Air Force just reported the earliest the Range can support liftoff tonight is 7:36 p.m. EDT. So that is the new launch time. Countdown clocks will resume from T-minus 5 minutes at 7:31 p.m. EDT. The Range did say it can support through the remainder of the window to 7:57 p.m. EDT.

2310 GMT (7:10 p.m. EDT)

NEW LAUNCH TIME. Officials have established a new launch time of 7:33 p.m. EDT (2333 GMT) tonight for the first Atlas 3A rocket. This will be after the COLA, or collision avoidance period, with an ojbect orbiting in space.

The Range is redeploying the air-scan planes to ensure there are no boats in the danger area off the coast of Cape Canaveral, below the rocket's flight path. There was never confirmation on what the Range problem was earlier.

2307 GMT (7:07 p.m. EDT)

Lockheed Martin reports the Atlas liquid oxygen temperature measurement problem that stopped the countdown earlier has been put to rest. Officials are assessing options for a new launch time -- before or after the collision avoidance period.

2306 GMT (7:06 p.m. EDT)

The launch team just reported the Atlas and Centaur liquid oxygen tanks and Centaur liquid hydrogen tanks are topped off to flight level. The countdown remains holding at T-minus 5 minutes while engineers troubleshoot a temperature measurement from the Atlas stage that was detected out of limits.

2300 GMT (7:00 p.m. EDT)

There are number issues the launch team is working with at this time. First is the problem that caused the countdown to be stopped: a red-line indication from the Atlas rocket's liquid oxygen temperature.

Meanwhile, the RD-180 engine fuel-fill has stopped and the Eutelsat W4 satellite has gone back to external power. Those two countdown steps will have to be redone before liftoff can occur, giving the launch time a few items to deal with once the temperature problem is fixed.

Also, there is a collision avoidance period, or COLA, during tonight's window. The COLA will prohibit liftoff from 7:28:04 to 7:32:25 p.m. EDT.

Liftoff is currently set for no sooner than 7:22 p.m. EDT. The available launch window extends to 7:57 p.m. EDT.

2258 GMT (6:58 p.m. EDT)

Countdown is back to T-minus 5 minutes and holding. Launch Conductor Ed Christiansen has asked for a 20-minute hold at this point in the count. Tonight's window extends to 7:57 p.m. EDT.

2258 GMT (6:58 p.m. EDT)

A launch team member reported seeing a system measurement pass its "red-line" limit, a constraint to flight. The fuel-filling sequence to the RD-180 engine has stopped.

2257 GMT (6:57 p.m. EDT)

HOLD! Countdown has stopped due to a problem. Clocks are recycling back to T-minus 5 minutes.

2257 GMT (6:57 p.m. EDT)

T-minus 5 minutes and counting. The countdown has picked up for launch of the inaugural Lockheed Martin Atlas 3A rocket with the Eutelsat W4 communications satellite this evening from Cape Canaveral Air Force Station, Florida. There are no problems standing in the way of liftoff at 7:02 p.m. EDT.

2255 GMT (6:55 p.m. EDT)

A second readiness poll of the launch team by Launch Conductor Ed Christiansen has been completed and all systems are "go" for liftoff at 7:02 p.m. EDT.

2253 GMT (6:53 p.m. EDT)

The Range is expected to be again ready for launch momentarily. Standing by to resume the countdown at 6:57 p.m. EDT for liftoff at 7:02 p.m. EDT.

2251 GMT (6:51 p.m. EDT)

The fuel-fill sequence has started at pad 36B to ready the RD-180 engine for flight tonight. The sequence takes several minutes to complete as RP-1 fuel is dropped from the rocket's propellant tank into the engine.

The sensor problems with the rocket have been resolved and now only the Range issue stands in the way of liftoff at 7:02 p.m. EDT.

2250 GMT (6:50 p.m. EDT)

Lockheed Martin commentator Don Spencer says engineers troubleshooting the sensor problems with the rocket is nearing resolution.

2249 GMT (6:49 p.m. EDT)

The Air Force reports the Range is now "red." No details yet on the problem.

2243 GMT (6:43 p.m. EDT)

The launch team is working to understand two "anomalous" sensor readings coming from the Atlas rocket. Launch is currently scheduled for 7:02 p.m. EDT, however, officials may elect to slip the liftoff a bit further into tonight's window.

2237 GMT (6:37 p.m. EDT)

It appears the problem being discussed is an improper measurement coming from a sensor inside Atlas. Details were not provided of which tank of the rocket the sensor is connected. The current launch time is no sooner than 7:02 p.m. EDT. Tonight's launch window extends to 7:57 p.m. EDT.

2235 GMT (6:35 p.m. EDT)

Another 15 minutes has been added to this extended hold at T-minus 5 minutes. Still no details from Lockheed Martin on the problem.

Meanwhile, the Eutelsat W4 satellite atop the Atlas 3 rocket remains on internal power for launch.

2234 GMT (6:34 p.m. EDT)

The fuel-filling sequence to the RD-180 engine has been stopped. It will take several minutes to resume that before the countdown can be restarted. This sequence is unique to the Atlas 3A rocket as RP-1 fuel, a highly refined kerosene, is dropped down to the RD-180 engine in preparation for ignition at T-minus 2.73 seconds.

2233 GMT (6:33 p.m. EDT)

No word yet on what the problem is. However, the hold at T-minus 5 minutes has been extended an additional 10 minutes. So liftoff will now occur no sooner than 6:47 p.m. EDT (2247 GMT).

2232 GMT (6:32 p.m. EDT)

HOLD EXTENDED. A problem has cropped up. Countdown clocks remain holding at T-minus 5 minutes and liftoff will not occur at 6:37 p.m. EDT.

2230 GMT (6:30 p.m. EDT)

Lockheed Martin Launch Conductor Ed Christiansen's final readiness poll of the entire launch team was just conducted with all parties reporting a "go" for launch. Lockheed Martin Launch Director Adrian Laffitte then gave his approval for liftoff. Standing by the resume the countdown in two minutes for launch at 6:37 p.m. EDT from Cape Canaveral.

2222 GMT (6:22 p.m. EDT)

Now 15 minutes from liftoff. There are no problems being worked by the launch team and activities remain on track for liftoff at 6:37 p.m. EDT.

2217 GMT (6:17 p.m. EDT)

T-minus 5 minutes and holding. The countdown has entered the planned built-in hold at T-minus 5 minutes. 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.

2212 GMT (6:12 p.m. EDT)

T-minus 10 minutes and counting. Now five minutes away from entering the built-in hold at T-minus 5 minutes, and 25 minutes away from liftoff.

The loading of the Atlas booster and Centaur upper stage with super-cold cryogenic propellant is now completed. Given the cold nature of the liquid oxygen and liquid hydrogen, however, the cryogenics naturally boil away during the countdown. As a result, the tanks will be topped off until just minutes prior to liftoff. RP-1 fuel, a highly refined kerosene, was loaded aboard the Atlas stage earlier during a countdown dress rehearsal.

2207 GMT (6:07 p.m. EDT)

Now 30 minutes away from today's launch of the first Atlas 3A rocket. Liftoff will occur from pad 36B at Cape Canaveral Air Force Station in Florida.

2203 GMT (6:03 p.m. EDT)

A weather briefing was just given to launch managers by Air Force Launch Weather Officer Jim Sardonia. All launch weather rules are currently "green" and predicted to remain "go" today. At pad 36B, there is a easterly wind 10 to 18 knots, a temperature of 77 degrees F and a two layers of thin clouds. Upper levels are also acceptable.

2202 GMT (6:02 p.m. EDT)

T-minus 20 minutes and counting. The countdown is heading to T-minus 5 minutes where a 15-minute hold is planned. Liftoff remains scheduled for 6:37 p.m. EDT (2237 GMT). At this time there are no problems being discussed by the launch team.

2159 GMT (5:59 p.m. EDT)

The Flight Termination System self-test check was recently completed. The FTS would be used to destroy the Atlas rocket should problem occur during the launch. Also, the pogo suppression system at pad 36A has been readied. The system will be used to dampen the "bounce" of the rocket during engine ignition.

2153 GMT (5:53 p.m. EDT)

A steering check of the RD-180 engine's two bell-shaped nozzles is underway.

2151 GMT (5:51 p.m. EDT)

The Atlas liquid oxygen tank is now 98 percent full as the countdown continues toward the planned 6:37 p.m. EDT (2237 GMT) today. The Centaur liquid oxygen tank will filled earlier this afternoon before the countdown was stopped. The final step in fueling is loading liquid hydrogen in the Centaur.

2137 GMT (5:37 p.m. EDT)

The countdown clocks are running again toward liftoff at 6:37 p.m. EDT (2237 GMT).

Liquid oxygen tanking for the Atlas stage has started and liquid hydrogen fueling for the Centaur is expected to begin shortly.

2135 GMT (5:35 p.m. EDT)

The report is the main transfer vent valve for the Atlas liquid oxygen system has been fixed and the valve is working properly. Liquid oxygen is now flowing toward the Atlas stage. The rocket's shiny exterior has turned a frosty white as a thin layer of ice forms from the super-cold liquid oxygen.

2132 GMT (5:32 p.m. EDT)

T-minus 50 minutes and counting. The countdown has just resumed. One additional hold is planned at T-minus 5 minute for 15 minutes in duration. Liftoff is now set for 6:37 p.m. EDT. There is no update on how the valve problem was resolved at pad 36B. The Lockheed Martin has removed the launch team's communications loops from its broadcast. The press is awaiting a report on the status of the problem.

2131 GMT (5:31 p.m. EDT)

There is no update on the valve problem to pass along. The Lockheed Martin public affair commentator is now on console but has not reported anything on the valve recently.

2121 GMT (5:21 p.m. EDT)

NEW LAUNCH TIME! Liftoff has been pushed back to no sooner than 6:37 p.m. EDT (2237 GMT), one hour later than planned while troubleshooting of the liquid oxygen main transfer vent valve continues for the Atlas booster stage.

Otherwise, the weather conditions are acceptable and upper level winds are within limits today at Cape Canaveral. Tonight's launch window extends to 7:57 p.m. EDT (2357 GMT).

2112 GMT (5:12 p.m. EDT)

One engineer and one technician will be heading into launch pad 36B to further troubleshoot a liquid oxygen main transfer vent that is not closing properly.

2100 GMT (5:00 p.m. EDT)

Launch Conductor Ed Christiansen says a team of technicians may be dispatched to pad 36B for hands-on troubleshooting of the liquid oxygen main transfer vent valve cycling problem.

The countdown remains holding at T-minus 50 minutes and liftoff is not expected before 6:27 p.m. EDT (2227 GMT) today.

2059 GMT (4:59 p.m. EDT)

Another 20 minutes will be added to this unplanned hold at T-minus 50 minus minutes. This hold will now last a total duration of 50 minutes. Still no good news on the valve troubleshooting.

2051 GMT (4:51 p.m. EDT)

Another plan of attack is being put in place to attempt to cycle the liquid oxygen main transfer vent valve at pad 36B.

2048 GMT (4:48 p.m. EDT)

The launch team will extend this unplanned hold another 10 minutes. Launch Conductor Ed Christiansen says "fruitful troubleshooting" is continuing.

2041 GMT (4:41 p.m. EDT)

The launch team will now try to command the liquid oxygen valve while closely monitoring the voltage going to the valve.

2034 GMT (4:34 p.m. EDT)

The latest try to correct a liquid oxygen valve problem has not worked.

At this point, all countdown activities have stopped while the countdown holds at T-minus 50 minutes. This is planned to be a 20-minute hold, likely pushing back liftoff to 5:57 p.m. EDT. However, a change in the launch time has not been confirmed.

The Centaur liquid oxygen tank is 95 percent full and maintaining that level, liquid hydrogen chilldown is complete but tanking has not started and liquid oxygen loading operations for the Atlas stage are on hold.

2032 GMT (4:32 p.m. EDT)

T-minus 50 minutes and holding. The countdown has been stopped for an unplanned hold to allow engineers time to examine a liquid oxygen valve at pad 36B that is not closing when commanded to do so. At this time, the Anomaly Team is recommending changing the configuration of valves onboard the rocket to further troubleshoot the problem.

2028 GMT (4:28 p.m. EDT)

Another effort by the launch team to close a liquid oxygen valve at pad 36B has been unsuccessful. Officials have decided to hold the countdown at T-minus 50 minutes beginning at 4:32 p.m. EDT to further troubleshoot the problem. This unplanned hold is expected to last 20 minutes.

2019 GMT (4:19 p.m. EDT)

Chilldown of the liquid hydrogen propellant system at launch pad 36B has been completed. However, loading liquid hydrogen into the Centaur upper stage is on hold while troubleshooting continues with the problematic liquid oxygen main transfer vent valve at the pad. The launch team has been told to keep the hydrogen system conditioned for tanking, but to hold off fueling until the LOX valve problem can be fixed.

The countdown activities had been running a few minutes ahead of schedule this afternoon but this valve problem now has delayed the timeline. If needed, Lockheed Martin has two hours and 20 minutes to get the first Atlas 3A rocket off the ground: 5:37 to 7:57 p.m. EDT (2137-2357 GMT).

2012 GMT (4:12 p.m. EDT)

A problem has developed that will delay loading liquid oxygen into the Atlas booster stage. The main transfer vent valve for the liquid oxygen system at the launch pad is not closing when commanded by engineers in the Complex 36 Blockhouse. Launch Conductor Ed Christiansen has asked the Anomaly Team to begin working this problem and form a recommendation.

2008 GMT (4:08 p.m. EDT)

The final alignment of the Atlas 3A rocket's inertial navigation unit guidance computer has been completed. Final pre-launch preparations of the rocket's control system now begins.

We are now further into the countdown than achieved during the first two launch attempts on Monday and Tuesday.

2007 GMT (4:07 p.m. EDT)

T-minus 75 minutes and counting. The countdown remains on schedule toward today's launch time of 5:37 p.m. EDT (2137 GMT). The Centaur liquid oxygen tank has reached 95 percent full where it is being held. The launch team has now been given the approval to start pumping liquid oxygen into the Atlas booster stage.

2001 GMT (4:01 p.m. EDT)

The "chilldown" conditioning of liquid hydrogen propellant feed lines at pad 36B is now starting. This is done to thermally prepare the plumbing before the super-cold cryogenic flows through the pipes and into the rocket.

Also at this time, the Complex 36 Blockhouse doors are being sealed, protecting the 120-plus-member launch team. The Blockhouse is located just 1,400 feet away from the Atlas 3A rocket at pad 36B, and serves as the control center for the countdown to launch.

Last Friday, Spaceflight Now toured the historic Complex 36 Blockhouse. Now you can step inside through the eyes of our virtual reality camera. (286k QuickTime file).

1958 GMT (3:58 p.m. EDT)

The Centaur liquid oxygen tank is now 50 percent full as fueling operations continue without incident at Cape Canaveral's pad 36B.

1952 GMT (3:52 p.m. EDT)

Ten percent of the Centaur liquid oxygen tank has been filled. The super-cold liquid oxygen will be consumed along with liquid hydrogen by the stage's single RL-10 main engine built by Pratt & Whitney. Hydrogen will loaded aboard the stage in about 35 minutes.

1950 GMT (3:50 p.m. EDT)

Upper level winds continue to improve dramatically compared to yesterday's conditions that forced Lockheed Martin to scrub the inaugural launch of the Atlas 3A rocket. The latest wind data shows a much straighter curve in the wind speeds as the altitude rises, unlike the spikes seen earlier.

1946 GMT (3:46 p.m. EDT)

Chilldown condition of the liquid oxygen transfer lines at pad 36B has been completed and the launch team is now filling the Centaur upper stage with its its supply of liquid oxygen for launch today at 5:37 p.m. EDT.

1943 GMT (3:43 p.m. EDT)

The latest steering program is being loaded into the rocket's guidance computer based upon the upper level wind conditions, which are reported within limits at this time.

1938 GMT (3:38 p.m. EDT)

A "chilldown" procedure has started to thermally condition the liquid oxygen propellants lines at pad 36B in advance of loading the Centaur upper stage. Chilldown is a process in which a small amount of the super-cold liquid oxygen is released from the pad's storage tank into the feed lines that lead to the rocket.

1937 GMT (3:37 p.m. EDT)

T-minus 105 minutes and counting. Now two hours away from the scheduled launch of the Atlas 3A rocket and its history-making flight to space with the first Russian-made engine for an American booster. Today's countdown is continuing much smoother than the past two days.

1934 GMT (3:34 p.m. EDT)

The launch team has been polled by Launch Conductor Ed Christiansen to verify readiness to begin fueling the Atlas/Centaur rocket shortly. All systems were reported "go" and launch pad 36B is being cleared of all workers. The mobile service tower is fully retracted and secured for today's 5:37 p.m. EDT (2137 GMT) launch.

Countdown clocks are scheduled to resume in about three minutes.

1926 GMT (3:26 p.m. EDT)

Launch officials have reported that the camera problem at the launch pad, which is currently being troubleshooted, would not be a constraint to liftoff if remains broken. The camera is positioned to give the launch team a view of the rocket's RD-180 engine during ignition.

1907 GMT (3:07 p.m. EDT)

T-minus 105 minutes and holding. Clocks have entered a planned 30-minute hold period for the countdown this afternoon at Cape Canaveral Air Force Station for launch of the maiden Atlas 3A rocket.

Here is the latest on upper level winds. There are still shears being seen today. At 40,000 feet, winds are about 62 knots, at 43,000 feet they fall to 48 knots, then climb to 68 knots at 45,000, back down to 52 knots at at 48,000 feet and peaking at 82 knots at 52,000 feet before tailing off again.

Overall, the winds are better than yesterday and officials remain hopeful conditions will permit an on-time liftoff at 5:37 p.m. EDT (2137 GMT) today.

1905 GMT (3:05 p.m. EDT)

The Air Force has announced today's collision avoidance, or COLA, cutout of the launch window. Liftoff will be prohibited between 7:28:04 and 7:32:25 p.m. EDT to avoid passing too close to another orbiting object. Today's window extends to 5:37 to 7:57 p.m. EDT.

1901 GMT (3:01 p.m. EDT)

The final alignment test of the rocket's inertial navigation unit guidance computer has been completed and the pre-launch alignment is starting. Also, two technicians have been dispatched to pad 36B for an attempt to fix a broken video camera system needed to provide the launch team views of the rocket's RD-180 engine.

1847 GMT (2:47 p.m. EDT)

The mobile service tower is still rolling back from the Atlas 3A rocket on this warm Florida afternoon. Overall, weather conditions are looking good at pad 36B for liftoff at 5:37 p.m. EDT. The only concern being watched, like yesterday, is upper level wind shears above 40,000 feet.

1837 GMT (2:37 p.m. EDT)

Retraction of the mobile service tower from around the Atlas 3A rocket is starting at Cape Canaveral's launch pad 36B. The tower will be fully retracted to the "maintenance area" for launch.

The launch team reported preps for the Atlas and Centaur propulsion systems are complete, as were the hydraulic preps for Atlas.

1825 GMT (2:25 p.m. EDT)

A readiness poll of the launch team has been completed and all parties were "go" for retraction of the mobile service tower at 2:37 p.m. EDT.

1822 GMT (2:22 p.m. EDT)

T-minus 150 minutes and counting. Man stations for Integrated Launch Operations. The entire launch team is now reporting on console at Cape Canaveral's Complex 36. Two built-in holds -- one for 30 minutes at T-minus 105 and 15 minutes at T-minus 5 minutes -- remain in advance of today's planned 5:37 p.m. EDT (2137 GMT) launch. The mobile service tower is scheduled to be retracted from around the rocket in about 15 minutes at pad 36B.

High altitude winds are still being closely watched. Wind data displayed a short time ago indicates the wind shear may be easing.

1817 GMT (2:17 p.m. EDT)

Final preparations are underway at Complex 36 in advance of fueling the Atlas rocket and its Centaur upper stage with liquid oxygen and liquid hydrogen later in the afternoon. Meanwhile, the launch team will report on station for the Integrated Launch Operations for AC-201 in five minutes.

1800 GMT (2:00 p.m. EDT)

The countdown is continuing at Cape Canaveral Air Force Station for today's scheduled launch of the inaugural Atlas 3A rocket -- the American rocket to use a Russian-made engine. Launch remains scheduled for 5:37 p.m. EDT (2137 GMT), the opening of a two-hour, 20-minute window.

1720 GMT (1:20 p.m. EDT)

Upper altitude weather data received in the last hour is continuing to show varying wind speeds between 40,000 and 55,000 feet. Winds are being measured at 50 knots at 40,000 feet, then increasing to 72 knots at 45,000 feet, falling back to about 44 knots at 48,000 feet and back up to 76 knots at 52,000 feet.