Thursday, December 3, 1998 - 6:30 a.m. CST

The first International Space Station assembly mission was postponed for 24 hours when the brief 5-minute launch window ran out before flight controllers could fully analyze the cause of a master alarm that sounded inside the Space Shuttle Endeavour's crew cabin.

The next launch attempt is tentatively scheduled for 2:36 a.m. CST Friday.

With the countdown clock at T-minus 4 minutes, STS-88 Commander Bob Cabana reported the alarm, forcing the countdown to be placed on hold. At a briefing following the launch attempt, Shuttle Launch Integration Manager Don McMonagle, said the alarm turned out to have been triggered by a sudden, brief dip in pressure that had never been seen before in one of the shuttle's three hydraulic systems.

The pressure change occurred when the auxiliary power units that provide pressure to the hydraulic lines shifted from low to high pressure after startup, McMonagle said, but then the pressure readings returned to normal and held steady. As hydraulic and instrumenta-ion engineers analyzed the data to identify what had caused the master alarm to sound and to assure that the systems were safe for flight, time ran out on Endeavour's ability to reach the Zarya control module, orbiting 240 statute miles above the Earth.

Once the launch had been postponed, support teams safed all of Endeavour's systems, drained the liquid hydrogen and liquid oxygen from the external tank and began recycling the shuttle for Friday's launch attempt. Engineers will review all of the data from today's launch attempt to ensure that all systems are functioning well.

Commander Bob Cabana, Pilot Rick Sturckow and Mission Specialists Nancy Currie, Jerry Ross, Jim Newman and Russian Cosmonaut Sergei Krikalev exited the shuttle and returned to crew quarters to rest for tomorrow's launch opportunity. The astronauts will awaken at mid-afternoon today and will sit down for the traditional prelaunch meal at 9:30 p.m. CST.

The countdown will resume at the T-11 hour mark at 10:46 a.m. CST, and. NASA Television coverage will begin at 9 p.m. CST tonight.

The next Mission Control Center Status Report will be issued following launch.