BY JUSTIN RAY

December 10, 1999 -- Follow the launch of the X-ray Multi-Mirror observatory aboard the Ariane 504 rocket. Reload this page for the very latest on the mission.

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

European Space Agency officials say the $700 million X-ray Multi-Mirror spacecraft is in good health following its successful launch today aboard the Ariane 504 rocket.

See our launch photo gallery for images of today's countdown and launch.

Within one hour of launch the European Space Operations Center at Darmstadt, Germany, confirmed XMM was under control with electrical power available from the solar arrays.

"XMM is the biggest and most innovative scientific spacecraft developed by ESA so far," said Roger Bonnet, ESA's director of science. "The world's space agencies now want the new technology that ESA and Europe's industries have put into XMM's amazingly sensitive X-ray telescopes. And the world's astronomers are queuing up to use XMM to explore the hottest places in the universe. We must ask them to be patient while we get XMM fully commissioned."

XMM's initial orbit following release from the Ariane 5 has a high point of 114,094 km, a low point of 825 km and inclination of 40 degrees to the equator.

XMM will later raise the orbit's low point to 7,000 kilometres by repeated firings of its onboard thrusters. Testing and checkout will follow to commission XMM's telescopes and science instruments. Full science operations should begin next spring.

According to ESA, the main scientific objectives for XMM are to find out exactly what goes on in the vicinity of black holes and to help to clear up the mystery of the stupendous explosions called gamma-ray bursts. Other hot topics for investigation include cannibalism among the stars, the release of newly made chemical elements from stellar explosions and the origin of the cosmic rays that rain on the Earth.

1511 GMT (10:11 a.m. EST)

Officials speaking to the guests gathered in Kourou say today's launch was a "moving" and an "emotional" experience. The XMM spacecraft, the most powerful X-ray telescope to be launched into space, was placed into an accurate orbit by the Ariane 504 rocket.

The next Arianespace launch will be an Ariane 4 rocket with the Galaxy 11 communications satellite on December 21. That will be the 10th and final Ariane launch of 1999. The next Ariane 5 launch is planned for the late February or early March. There could be as many as six Ariane 5 launches in 2000.

Check back later today for images and movies of the launch.

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

Plus 29 minutes. SPACECRAFT SEPARATION. The Ariane 5 rocket has successfully completed its first commercial launch. The European Space Agency's X-ray Multi-Mirror observatory has been released into space to seek out the invisible X-ray universe.

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

Plus 27 minutes. The upper stage cut off as planned. The stage will now orient the XMM spacecraft for separation in less than two minutes. Altitude is 1882 km, velocity is 9.07 km/sec.

1458 GMT (9:58 a.m. EST)

Plus 26 minutes. Coming up on completion of powered flight with the shutdown of the upper stage. Altitude is 1692 km, velocity is 9.01 km/sec.

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

Plus 25 minutes. Burnout of the storable propellant upper stage is expected at about Plus 26 minutes, 40 seconds. Altitude is 1515 km, velocity is 8.92 km/sec.

1456 GMT (9:56 a.m. EST)

Plus 24 minutes. Altitude is 1351 km, velocity is 8.83 km/sec.

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

Plus 23 minutes. Altitude is 1204 km, velocity is 8.74 km/sec.

1453 GMT (9:53 a.m. EST)

Plus 21 minutes, 30 seconds. Five minutes left in the upper stage burn. Altitude is 1002 km, velocity is 8.64 km/sec.

1452 GMT (9:52 a.m. EST)

Plus 20 minutes, 30 seconds. Altitude is 882 km, velocity is 8.57 km/sec.

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

Plus 19 minutes, 30 seconds. There are about seven minutes to go in the firing of the upper stage to complete today's powered flight. Altitude is 774 km, velocity is 8.5 km/sec.

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

Plus 18 minutes, 30 seconds. Altitude is 674 km, velocity is 8.4 km/sec.

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

Plus 17 minutes. Altitude is 543 km, velocity is 8.35 km/sec.

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

Plus 16 minutes. Altitude is 468 km, velocity is 8.29 km/sec. The Archachon tracking station in France has picked up the rocket's telemetry.

1446 GMT (9:46 a.m. EST)

Plus 14 minutes, 30 seconds. Still more than 12 minutes left in the planned firing of the storable propellant upper stage to place XMM into the desired orbit. No problems have been reported so far in the flight. Altitude is 366 km, velocity is 8.19 km/sec.

1443 GMT (9:43 a.m. EST)

Plus 11 minutes, 45 seconds. Altitude is 223 km, velocity is 8.0 km/sec.

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

Plus 10 minutes. The main cryogenic stage's Vulcain engine has cut off and the stage has separated. It will fall toward the Galapagos Islands in the Pacific Ocean. The upper stage, the storable propellant stage has ignited.

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

Plus 8 minutes, 30 seconds. Altitude is 128.8 km, velocity of 6.0 km/sec. All systems remain normal. The Monge down range tracking boat has acquired the rocket's signal.

1439 GMT (9:39 a.m. EST)

Plus 7 minutes, 30 seconds. Altitude is 135 km, velocity of 4.9 km/sec.

1438 GMT (9:38 a.m. EST)

Plus 6 minutes, 30 seconds. Now in the portion of flight in which the rocket gives up a bit of altitude to gain speed, sort of like a sling-shot.

1438 GMT (9:38 a.m. EST)

Plus 6 minutes. Altitude is 145 km, velocity of 3.7 km/sec.

1437 GMT (9:37 a.m. EST)

Plus 5 minutes. Altitude is 142 km, velocity of 3.1 km/sec.

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

Plus 4 minutes. The protective payload fairing has separated from the atop the Ariane 5. All systems reported normal.

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

Plus 2 minutes, 30 seconds. Solid rocket boosters have separted. Altitude is 75 km, velocity of 2.1 km/sec.

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

Plus 2 minutes. Incredible views of the Ariane 5 rocket as it accelerates into the clear sky over South America.

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

Plus 1 minute. No problems have been reported during the first 60 seconds of flight. Solid rocket boosters will be jettisoned at Plus+2 minutes, 23 seconds.

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

LIFTOFF. Liftoff of a new day in commercial space travel as Arianespace launches the first operational Ariane 5 rocket.

1431 GMT (9:31 a.m. EST)

Minus 1 minute. A fast-paced series of events leading to launch will begin at Minus 37 seconds when the automated ignition sequence is started. The water suppression system at the launch pad will start at Minus 30 seconds. At Minus 22 seconds, overall control will be given to the onboard computer. The Vulcain main engine will be readied for ignition with hydrogen chilldown starting at Minus 18 seconds. The residual hydrogen burn flares will fire beneath the Vulcain engine at Minus 7 seconds to burn away any hydrogen. At Minus 3 seconds, onboard systems take over and the two inertial guidance systems go to flight mode. Vulcain main engine ignition occurs at Minus 0 seconds with checkout between Plus+4 and 7 seconds. If there are no problems found, the solid rocket boosters are ignited at Plus+7.5 seconds.

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

Minus 2 minutes. Today's launch will be the 124th for an Ariane rocket, the 9th of 1999 and the fourth Ariane 5.

1428 GMT (9:28 a.m. EST)

Minus 4 minutes. Pressurization now under way for the main cryogenic stage's liquid oxygen and hydrogen tanks.

1425 GMT (9:25 a.m. EST)

Minus 6 minutes, 30 seconds. Synchronized launch sequence start. Computers are now in control of this final segment of the launch countdown to prepare the rocket and ground systems for liftoff.

There are two computers, one aboard the Ariane 5 and a redundant one at the ELA-3 launch complex, running the countdown.

1425 GMT (1425 EST)

Minus 7 minutes. The synchronized launch sequence will begin in 30 seconds. If a problem is detected after the sequence starts, the countdown would be stopped and clocks would recycle back to Minus-7 minutes and holding.

1422 GMT (1422 EST)

Minus 10 minutes. Countdown clocks are ticking along quietly for launch at 1432 GMT (9:32 a.m. EST). The launch team is not reporting any problems that would stop today's mission. Coming up in about 3 1/2 minutes, computers will take control for the synchronized launch sequence.

1412 GMT (9:12 a.m. EST)

Minus 20 minutes. The primary passenger aboard Arianespace Flight 119 is the European Space Agency's X-ray Multi-Mirror spacecraft. The observatory will orbit high above Earth to study the X-ray universe which is invisible to the human eye. Read an ESA release on XMM's science objectives.

1409 GMT (9:09 a.m. EST)

The next-to-last weather update continues to indicate favorable conditions for launch. All systems remain go for liftoff at 1432 GMT (9:32 a.m. EST).

1400 GMT (9:00 a.m. EST)

The launch campaign for Ariane 504 began on March 30 when workers removed the rocket's liquid-fueled main cryogenic stage from its shipping container in Kourou, French Guiana. During the following few days, the twin solid rocket boosters were connected to the main core stage. The Vehicle Equipment Bay, that contains the "brains" of the rocket, was added on April 9. The rocket came alive on April 19 when workers powered on to test its electrical and support systems. Engineers then performed a simulated 25-minute flight of the rocket on April 29. The Ariane 504's onboard guidance and attitude control system and telemetry system operated during the simulation. Actuation systems for the main cryogenic stage and the solid rocket motor also were operated, and the attitude control system for Ariane 5's upper stage.

On May 4, the rocket atop its mobile platform, was rolled from the Launcher Integration Building to the Final Assembly Building. Launch preparations were halted on May 5 to await the arrival of payloads in Kourou. Arianespace had planned an early July launch of the Indonesian Telkom-1 telecommunications satellite and the AsiaStar direct radio broadcasting spacecraft. But satellite delays prevented the pairing.

As a result, on August 13 Arianespace opted out of launching two commercial satellites proceeded to launch XMM in December on the first operational Ariane 5. XMM arrived in South America on September 23 after a 10-day ocean trip from Rotterdam in The Netherlands. On October 21, the launcher campaign resumed, and five days later, the new storable propellant upper stage was installed atop the rocket.

On November 17, the rocket was rolled to the launch zone for a launch rehearsal. The vehicle was returned to its hangar the following day. The XMM spacecraft was mated to the rocket on November 25. The fairing was installed on November 29.

The last major event coming into today's launch was to roll the rocket back to the pad. That occurred yesterday.

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

Weather conditions are currently sunny at the launch site. Forecasters are predicting some small rainshowers, however, they should be fast moving and clear quickly. At this point, all the launch weather rules are green.

1348 GMT (8:48 a.m. EST)

At this point in the countdown, the XMM X-ray observatory is scheduled to emerge from standby mode to open its venting doors and switch to onboard batteries.

1347 GMT (8:47 a.m. EST)

Now 45 minutes away from the opening of today's 36-minute launch window. The Ariane 5 rocket stands fully fueled and ready for liftoff today. The loading of liquid oxygen and liquid hydrogen into the cryogenic main stage was completed about two hours ago. The cryogenic tanks are being replenished continuously through the remained of the countdown to replace the fuel that naturally boils off.

1300 GMT (8 a.m. EST)

The countdown is well under way in Kourou today for launch of the Ariane 504 rocket. Liftoff is now about 90 minutes away. There are no technical problems reported and weather conditions are acceptable for liftoff.

THURSDAY, DECEMBER 9, 1999
2300 GMT (6 p.m. EST)

The first commercial launch of the Ariane 5 rocket is just hours away. The massive booster remains scheduled to lift off from Kourou, French Guiana on Friday at 1432 GMT (0932 EST), the opening of 36-minute window. Ariane 504 will place the European Space Agency's X-ray Multi-Mirror observatory in a highly elliptical orbit less than 29 minutes after launch. Weather forecasts are favorable.

Arianespace officials Wednesday conducted a readiness review and cleared the rocket and payload for flight. On Thursday, the rocket was rolled from its assembly building to the ELA-3 pad atop its mobile launch table.

On Friday, the final countdown will begin at 0532 GMT (0032 EST). Engineers will begin checking the electrical systems 90 minutes later. The connections between the rocket and the telemetry, tracking and command systems will be verified starting at 0832 GMT (0332 EST). Loading of super-cold propellant into the main cryogenic stage of the Ariane 5 will commence at 0912 GMT (0412 EST). Chilldown of the stage's Vulcain main engine will follow beginning at 1112 GMT (0612 EST).

The final computer-led countdown, call the synchronized sequence, will begin at Minus-6 minutes, 30 seconds. At zero seconds, the Vulcain main engine will be started and liftoff should follow 7.3 seconds later after the solid rocket boosters ignite.