yee@trident.arc.nasa.gov (Peter E. Yee) (09/16/90)
Mark Hess/Ed Campion Headquarters, Washington, D.C. September 12, 1990 (Phone: 202/453-8536) Lisa Malone Kennedy Space Center, Fla. (Phone: 407/867-2468) LAUNCH ADVISORY FOR SHUTTLE MISSIONS STS-35 AND STS-41 NASA managers today set Tuesday, Sept. 18, 1990 as the launch date for Space Shuttle Columbia and the STS-35 Astro-1 mission. The decision on the new launch date follows the removal, replacement and testing of the liquid hydrogen recirculation pump package in Columbia's main propulsion system. Launch of Columbia and the STS-35 mission was scrubbed on Sept. 5 when high concentrations of liquid hydrogen were detected in the aft compartment of the orbiter. Subsequent tests showed the leak came from the vicinity of the recirculation pump package. During leak check operations following installation of the new recirculation pump package, technicians found a crushed seal on the prevalve of the main propulsion system. The seal is part of a detent cover. The prevalve is the main hydrogen valve which supplies hydrogen to Space Shuttle Main Engine #3. The detent holds the prevalve in place in the open position. Helium leak checks indicated the seal was within specification, however, this particular detent cover had an order of magnitude greater leak than other detent covers. Alert technicians and engineers decided to investigate further and discovered the damaged seal. Engineers believe the location of the seal and the nature of the damage to the seal make it a prime suspect as the cause of the hydrogen concentrations seen in the aft of Columbia during tanking operations. The seal in question was replaced following Columbia's last flight, STS-32 in January 1990, when an inspection for possible corundum contamination of the main propulsion system was conducted. Engineers believe the seal was damaged during the post- inspection installation and remained undiscovered until yesterday. Countdown for the launch of Columbia is scheduled to begin on Saturday, Sept. 15 at 1:00 a.m. EDT at the T minus 43 hour mark. The 1 hour, 39 minute launch window on Sept. 18 opens at 1:28 a.m. EDT and closes at 3:07 a.m. Space Shuttle Discovery and the STS-41 mission will be launched as early in the launch window (Oct. 5-23, 1990) as possible. Current scheduling indicates a likelihood of launching on Oct. 8 or 9, but a few days either side are possible, depending on actual test and preparation times needed. The actual launch date for Shuttle mission STS-41 will be set at the flight readiness review, currently scheduled for Sept. 24-25. Discovery's freon cooling loop #1, which has given indications of a small leak since leaving the Orbiter Processing Facility, has undergone special testing. After review of the test data, Shuttle managers have determined that this condition can be safely flown in its present state. Launch preparations will include topping off the freon system of Discovery a few days before launch which will keep the freon level well above the amount needed to support Shuttle operations during the 4-day mission.