Shuttle Team Hopes for Liftoff Next Week : Space: The hydrogen leak that scrubbed Tuesday’s launch could ground Columbia much longer. NASA’s schedule may be in jeopardy.

The launch of the space shuttle Columbia with the Astro observatory will be delayed until at least the middle of next week, and perhaps much longer, as engineers search for the hydrogen leak that caused the postponement of Tuesday evening’s planned launch.

NASA officials did not know the precise site of the leak Wednesday evening and did not expect to know until this morning, at the earliest, but engineers believe they have identified two potential sites:

One is in the external equipment that is used for fueling the craft. Columbia could have launched if this were the only leak present, according to launch director Robert Sieck.

The second, and more important, leak is thought to be in a 17-inch-diameter line connecting the external fuel tank to the shuttle’s engines.

NASA held out some hope that the leak would be found in some readily repairable component of the fuel system, but that possibility grew seemingly more remote with the passage of time. “With the work we’ve laid out near-term, the middle of next week would probably be the earliest” that Columbia could be launched even if they find a simple-to-fix source of the leak, Sieck said.

In a worst-case scenario, engineers would have to return the shuttle to the mammoth vehicle assembly building here for repair, a process that would delay the launch by at least three weeks. “We may have to do some shuffling (of shuttle launches) in September and October,” Sieck said.

The launch had already been delayed for two weeks as a result of a broken valve in Columbia’s cooling system, and the new delay threatened to play havoc with NASA’s launch schedule for the rest of the year.

Columbia was slated to carry the Astro observatory--a $150-million collection of four telescopes--into space at 9:38 p.m. PDT Tuesday night, beginning a 9- or 10-day mission in which the seven-man crew would conduct astronomy around the clock.

Workers had just begun loading half a million pounds of liquid hydrogen and helium into the shuttle’s rust-colored external fuel tank when sensors in the engine compartment detected unusually high concentrations of highly flammable hydrogen--about five times the maximum acceptable limit. Sieck said the amount of hydrogen present suggested a “pinhole-sized leak.”

NASA officials emphasized that the shuttle was never in danger of exploding, however. The engine compartment is normally flooded with inert gas to prevent an explosion, and the hydrogen level was still only about 1/13 the concentration necessary for an explosion.

The launch was scrubbed about six hours before the scheduled launch, and the disappointed Columbia crew returned to Houston Wednesday morning.

Engineers spent Tuesday night and most of Wednesday removing all of the hydrogen from the fuel tanks so that they could work on the shuttle safely. They then began pressurizing the fuel system with inert helium to assist them in finding the leak.

Technicians were expected to gain access to the engine compartment late Wednesday night to begin trying to pinpoint the leak.

Officials held out hope that the leak was not in the line connecting the fuel tank to the engines because it had previously checked out as being leak-free. But if that is the site--or if technicians cannot quickly find the leak--the shuttle will have to be moved back to the vehicle assembly building for repair, and that will present NASA with a problem.

Both shuttle stalls in the building are currently occupied. One contains the assembled external fuel tank and solid rocket boosters that will be attached to Atlantis for a planned launch in July. The second contains the partially assembled booster rockets to be attached to Columbia for a scheduled September launch.

If Columbia is returned to the assembly building, NASA will be forced either to move the already-assembled booster vehicle to a launch pad temporarily or to disassemble the boosters for Columbia’s next flight. Either option would be a major impediment to NASA’s already tight flight schedule.