HISTORIC SHUTTLE LAUNCH ABORTED.

Byline: Marcia Dunn Associated Press 

An indication of a dangerous buildup of hydrogen gas in space shuttle Columbia's engine compartment stopped the countdown early today just 6-1/2 seconds before launch.

Eileen Collins, the first female space shuttle commander, and the four other astronauts were safe but rushed nonetheless to turn off all shuttle systems and get out of the rocket filled with more than 500,000 gallons of liquid hydrogen fuel and liquid oxygen.

Columbia was to have blasted off at 12:36 a.m. EDT carrying the world's most powerful X-ray telescope.

The reading of excess hydrogen - which NASA suspects may have been faulty - was detected by on-board computers an instant before the three main engines were to ignite.

``Cutoff!'' a launch controller shouted. ``Cutoff was given,'' another replied.

NASA launch commentator Bruce Buckingham said depending on the problem another launch attempt might be made Thursday.

It was the first time in years that trouble struck so late in the countdown. At first, engineers considered the reading to be accurate but as they checked their data began to suspect there was no hydrogen buildup.

``Engineers in the firing room will continue to monitor the situation and strive to understand exactly what happened that caused this abort,'' Buckingham said.

It was a huge disappointment for the female notables on hand - and also for the astronauts.

The U.S. women's soccer team, as well as first lady Hillary Rodham Clinton, her daughter, Chelsea, and Sally Ride, America's first woman in space, had gathered to cheer Collins on. A sign held by a female space worker summed up the mood on the 30th anniversary of the first manned moon landing, by Apollo 11: ``Eileen - You go girl''

``This really is the last barrier to be broken,'' observed Ride. She had called Collins earlier to wish her good luck.

The lengthy VIP list also included Health and Human Services Secretary Donna Shalala; 15 members of Congress, 13 of them women; and Judy Collins, who wrote a song for the occasion.

Columbia's five crew members were scheduled to eject the $1.5 billion Chandra X-ray Observatory from the shuttle. For five years, it will scrutinize stars, galaxies and quasars, search for black holes and study the so-called black matter that fills the cosmos.

Collins, 42, an Air Force colonel and a former test pilot, has flown before as a shuttle co-pilot. This week's flight would have been her third.

Collins has said that she is honored to be the first woman to command a mission in 38 years of U.S. human spaceflight, and that a female commander is long overdue.

But she said she sometimes wonders: ``Why would anyone be interested in hearing about me when the science and the exploration part of our mission, to me, is so exciting?''

The 45-foot Chandra is the biggest X-ray telescope ever built and the heaviest payload ever put aboard a space shuttle. With its attached rocket motor and support gear, Chandra weighs 50,000 pounds.

Columbia is the only shuttle big enough to hold it. NASA ran extra engineering studies to make sure the shuttle could sustain the weight if, because of some problem, it had to return to Earth with the telescope still on board.

NASA's top managers granted permission for the shuttle to carry the observatory after the space agency stripped 7,000 pounds from Columbia by using lighter engines and discarding unnecessary gear.

After decades of working on the program, dozens of scientists gathered at the launch site in anticipation. The telescope should have flown last August but was grounded first by software problems, then bad circuit boards, then a suspect rocket motor.

Martin Weisskopf, a National Aeronautics and Space Administration astrophysicist in charge of the project, said he hasn't been so nervous since the day he got married. ``There are hundreds of things you can worry about if you want to,'' he said, ``but I think we've done everything we can do.''

NASA's top space scientist, Ed Weiler, noted that like the Hubble Space Telescope, Chandra has 1 million parts. Hubble was launched in 1990 with a flawed mirror that wasn't discovered until the telescope was in orbit.

The entire Chandra project, including the shuttle ride and five years of orbital operations, comes in at $2.8 billion.

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Photo

PHOTO Eileen Collins waves to family members Monday, hours before the first female shuttle commander and her crew boarded Columbia.

George Sheldon/NASA