Hydrogen Leak Delays Columbia Liftoff : Space: It’s the third time since May that such a problem has occurred. Officials say a launching in three or four days is possible but not ‘realistic.’

For the snake-bitten officials of NASA, the third time was not the charm.

For the third time since May, NASA engineers attempted to load liquid hydrogen fuel into a shuttle’s fuel tanks. And, for the third time, technicians discovered a hydrogen leak, forcing them to scrub the oft-delayed launching of the shuttle Columbia and the star-crossed Astro observatory.

At 2:38 p.m. PDT, less than an hour after fuel loading had begun and less than eight hours before Columbia’s scheduled launching at 10:20 p.m., launch director Robert Sieck decided that levels of potentially explosive hydrogen gas in the aft compartment of Columbia were too high for safety and ordered the launching aborted for the second time within a week.

At the time the mission was scrubbed, the level of hydrogen in the compartment was about 6,000 parts per million, about 10 times higher than the maximum level permissible for a launching.

By late evening Wednesday, engineers still had not identified the source of the leak, but space shuttle director Robert L. Crippen said it would be at least three or four days before another attempt at launching could be made. “But I don’t believe that’s realistic,” he added, indicating that such an attempt may be much further in the future.

Crippen said also that because of the leak he would probably order a fueling test of the shuttle Discovery, which is now on pad 39B awaiting its Oct. 5 launching with the Ulysses probe, which is to slingshot past Jupiter to go into a polar orbit around the sun. NASA has only an 18-day window in October during which to launch Ulysses. If it is not launched then, the agency must wait an additional 13 months before the planets are in the proper alignment once more.

Such a test would add at least five days to Discovery’s already tight prelaunching schedule, placing the flight in jeopardy. NASA officials had previously been worried by a loss of Freon coolant in Discovery, and the need for a test will further compound their problems.

Columbia was originally scheduled for launching on May 29, but officials scrubbed the liftoff when potentially explosive hydrogen gas was detected outside the shuttle and in its aft compartment. Officials ordered a test fueling of the shuttle Atlantis in July and found that it also was leaking.

Discovery of that leak caused NASA Administrator Richard H. Truly to ground the shuttle fleet until the cause of the leaks could be determined.

Studies of the 17-inch valve removed from Columbia after the first leak indicated it had been contaminated with submicroscopic glass beads that had prevented gaskets in the valve from making a tight seal. Although technicians have not yet disassembled the valve from Atlantis, it was from the same batch as the Columbia valve and Crippen had said earlier Wednesday that it most likely was also contaminated.

The newly installed 17-inch valve on Columbia was from a different batch and had shown a much lower leak rate during preliminary testing. Crippen said NASA was “very confident” that the leak problem had been solved.

NASA officials were so confidant, in fact, that they canceled a fueling test of Columbia because it would have added five days to their already tight schedule. That was a gamble that now appears not to have paid off.

Crippen noted Wednesday evening that engineers had run leak tests in Columbia’s aft compartment after the aborted May launching and had not found any leaks. Because of that, they assumed that the excess hydrogen in the aft compartment was a result of the leak on the 17-inch valve. That assumption, he conceded, was apparently wrong.

Because engineers have already unsuccessfully searched for a leak in the aft compartment, the probability of finding it quickly now seems small, he admitted. “That’s going to be tough,” he said.

The agency’s failure to find the leak in the previous tests, as well as Crippen’s decision not to run a fueling test on Columbia, is certain to bring fresh criticism to an agency that is already shell-shocked.

In addition to the summer-long grounding of the shuttle fleet, NASA suffered acute embarrassment from the discovery that the mirror on its showpiece Hubble Space Telescope has an imperfection that will greatly reduce the orbiting observatory’s scientific usefulness until it can be repaired by a shuttle mission in 1993.

In addition, engineers at NASA’s Jet Propulsion Laboratory have twice lost contact with the Magellan space probe, which is orbiting Venus.