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.