George H. Diller October 19, 1992 Kennedy Space Center 407/867-2468 KSC Release No. 145-92 COUNTDOWN FOR STS-52 LAUNCH OF COLUMBIA BEGINS TODAY The countdown clock for the STS-52 flight of the Space Shuttle Columbia is scheduled to begin at 4 p.m. (EDT) today at the T-43 hour mark. The countdown includes 24 hours and 16 minutes of built-in hold time leading up to the opening of the launch window at 11:16 a.m. (EDT) on Thursday, October 22. The launch window extends until 2:21 p.m. that day. At the start of the countdown, the launch team in firing room 3 of the Launch Control Center verifies the Shuttle vehicle is powered up and that the data processing system and backup flight control system are operating. Flight software stored in the orbiter's twin memory banks will be reviewed, computer con- trolled display systems will be activated, and the backup flight system general purpose computer will be loaded. Preparations also start at the liquid oxygen and liquid hydrogen storage farms for loading the external tank with super cold, or cryogenic, propellants. The main propulsion system and shuttle main engines are prepared for cryogenic loading, orbiter navigation aids are turned on and tested, and the inertial measurement units are activated. In parallel with these activities, the launch team prepares for loading Columbia's onboard fuel cell storage tanks with liq- uid oxygen and liquid hydrogen reactants. Also performed at the start of the countdown is the final stowage, microbial sampling and water level adjustment of the crew waste management system. At T-27 hours, the countdown will enter its first built-in hold. This is a 4-hour hold which extends from 8 a.m. to 12 noon on Tuesday, October 20. When the countdown resumes, the launch pad will be cleared of all personnel in preparation for loading the fuel cell storage tanks. Servicing of the liquid oxygen and liquid hydrogen fuel cell supply tanks is scheduled to start at the T-25 hour mark. Servic- ing activities take approximately five hours. When servicing of the fuel cell tanks has been completed, the pad will be reopened for normal work, and the countdown will enter the second planned hold. During this four-hour hold at the T-19 hour mark, the orbiter mid-body umbilical unit used to load the super cold fuel cell reactants into the orbiter will be demated. This hold will extend from 8 p.m. to 12 midnight on Tuesday. When the countdown resumes, technicians will complete final vehicle and facility closeouts and begin activating the orbiter's communications systems and configuring Columbia's cockpit for flight. The orbiter's flight control system navigation aids and com- munications systems will be activated, and switches in the cock- pit will be configured for loading of the external tank. The stowable mission specialist seats will be installed in the flight and mid-decks. The countdown will enter the next built-in hold at T-11 hours at 8 a.m. on Wednesday. During the hold, time critical equipment will be installed in the orbiter's cockpit and the in- ertial measurement units will be activated and warmed up. At about 11 a.m., the rotating service structure will be moved away from the vehicle to the launch position. This hold is scheduled to last 12 hours, 56 minutes, or until 8:56 p.m. on Wednesday. At T-9 hours, the onboard fuel cells will be activated, and the launch team will begin evacuating the blast danger area at T- 8 hours, or about 11:56 p.m. Wednesday. At T-7 hours, 45 minutes, conditioned air that is flowing through the orbiter's payload bay and other areas will be switched to gaseous nitrogen in prepara- tion for loading the external tank with super-cold liquid propel- lants. The inertial measurement units will transition from the warm up stage to the operate/attitude determination mode at T-6 hours and 45 minutes. The countdown will enter another planned built-in hold at the T-6 hour mark at approximately 1:56 a.m. Thursday. During this one-hour hold, final preparations for loading the external tank will be completed and a pre-tanking weather briefing will be conducted. Chilldown of the lines that carry the cryogenic propellants to the external tank will begin at the T-6 hour and counting mark, at 2:56 a.m. Thursday. Filling and topping of the external tank should be complete at the beginning of the planned hold at T-3 hours which will start at 5:56 a.m. Thursday. This hold is two hours in duration. During this time, the ice inspection team will perform a survey of the tank's outer in- sulation, and the closeout crew will begin configuring the crew module and white room for the flight crew's arrival. Liquid oxygen and liquid hydrogen will be in a stable replenish mode during this time to replace the propellant that "boils" off. The STS-52 flight crew is scheduled to be awakened at 6:21 a.m. Thursday and have breakfast. Their breakfast is scheduled at 6:51 a.m. After eating, the crew will receive a briefing on weather conditions around the world via satellite from Mission Control- Houston. The flight crew will suit up in their partial pressure suits, then leave the Operations and Checkout Building at about 8:01 a.m., at T-3 hours. They will arrive at the pad white room at about 8:31 a.m. where they will be assisted by white room per- sonnel in getting into the crew cabin. Just prior to the T-1 hour mark, the test team and the flight crew will get another weather update, including observa- tions from an astronaut flying in a Shuttle Training Aircraft in the KSC area. The last two built-in holds will be 10 minutes in duration and will occur at the T-20 minute mark or at 10:36 a.m. and at the T-9 minute mark or at 10:57 a.m. During the final hold, the flight crew and ground team receive the NASA Launch Director's and the Mission Management Team's final "go" for launch. Milestones after the T-9 minute mark include start of the ground launch sequencer; retraction of the orbiter access arm at T-7 minutes, 30 seconds; start of the orbiter's auxiliary power units at T-5 minutes; pressurization of the liquid oxygen tank at T-2 minutes, 55 seconds; pressurization of the liquid hydrogen tank at T-1 minute, 57 seconds; and the electronic "go" to Endeavour's onboard computers to start their own terminal countdown sequence at T-31 seconds. The orbiter's three main en- gines will start at T-6.6 seconds. COUNTDOWN MILESTONES Launch - 3 Days (Monday, October 19) Perform the call-to-stations at T-43 hours. Begin check out of the backup flight system and review flight software stored in mass memory units and display systems. Astronauts arrive. Load backup flight system software into Columbia's fifth general purpose computer. Begin stowage of flight crew equipment. Inspect the orbiter's mid and flight decks and remove crew module platforms. Start external tank loading preparations. Close payload bay doors. Launch - 2 Days (Tuesday, October 20) Enter first planned built-in hold at T-27 hours for a dura- tion of 4 hours. Resume countdown. Start preparations for servicing fuel cell storage tanks and begin final vehicle and facility closeouts for launch. Clear launch pad of all personnel and load liquid oxygen and liquid hydrogen reactants into Columbia's fuel cell storage tanks. Enter second planned built-in hold at T-19 hours for four hours. After the loading operation, the pad will be reopened for normal work and orbiter and ground support equipment closeouts will resume. Demate orbiter mid-body umbilical unit used during fuel cell loading. Resume countdown. Retract rotating service struc- ture. Launch - 1 Day (Wednesday, October 21) Activate orbiter communications systems, flight control and navigation systems. Install mission and payload specialist seats in crew cabin. The tail service masts on the mobile launcher platform will be closed out for launch. Pepare Shuttle main en- gines for propellant tanking and flight. Enter planned hold at T-11 hours (8 a.m.) for a duration of 12 hours and 56 minutes. Perform orbiter ascent switch list in crew cabin. During this hold, the orbiter's inertial measurement units will be ac- tivated and kept in the "warm up" mode and film will be installed in the numerous cameras on the launch pad. In addition, safety personnel will conduct a debris walkdown and the pad sound sup- pression system water tank will be filled. The rotating service structure will be moved to the park position during this hold at 11 a.m. Resume countdown at 8:56 p.m. Install time critical flight crew equipment and perform the pre-ingress switch list. Start fuel cell flow-through purge. Activate orbiter fuel cells. Configure communications at Mission Control Houston for launch. Clear the blast danger area of all non-essential personnel and switch Columbia's purge air to gaseous nitrogen. Launch Day (Thursday, October 22) Enter one-hour planned built-in hold at T-6 hours (1:56 a.m.). Resume countdown. Launch team verifies there are no viola- tions of launch commit criteria prior to cryogenic loading of the external tank. Start loading the external tank with cryogenic propellants. Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants. Perform open loop test with Range Safety and conduct gimbal profile checks of orbi- tal maneuvering system engines. Perform inertial measurement unit preflight calibration and align Merritt Island Launch Area (MILA) tracking antennas. Enter 2 hour hold at T-3 hours. Closeout crew and ice in- spection team proceeds to launch pad 39-B. Resume countdown at T-3 hours (7:56 a.m.) Complete closeout preparations in the white room and cockpit switch configurations. Crew departs astronaut quarters at Operations and Checkout Build- ing for the pad. Flight crew enters orbiter. Astronauts perform air-to-ground voice checks with Mission Control Houston. Close Columbia's crew hatch. Begin Range Safety final network open loop command check, perform hatch seal and cabin leak checks, begin the inertial measurement unit preflight alignment and range safety closed loop test. The white room is closed out and the closeout crew moves to fallback area. Primary ascent guidance data is transferred to the backup flight system. Enter planned 10-minute hold at T-20 minutes. Resume countdown. Transition orbiter onboard computers to launch configuration and start fuel cell thermal conditioning. Close orbiter cabin vent valves. Backup flight system transitions to launch configuration. Enter planned 10 minute hold at T-9 minutes. Resume countdown. Start automatic ground launch sequencer (T-9 minutes). Retract orbiter crew access arm (T-7:30). Start mission recorders (T-5:30). Start APU's. Arm SRB and ET range safety safe and arm devices (T- 5). Start liquid oxygen drainback (T-4:55). Start orbiter aerosurface profile test (T-3:55). Orbiter transfers to internal power (T-3:30). Start MPS gimbal profile test (T-3:30). Pressurize liquid oxygen (LO2) tank/retract gaseous oxygen vent arm (T-2:55). Fuel cells to internal reactants (T-2:35). Pressurize liquid hydrogen (LH2) tank (T-1:57). Deactivate SRB joint heaters (T-1:00). LPS go for start of orbiter automatic sequence (T-0:31 seconds). Start SRB gimbal profile test (T-0:6.6). SRB ignition and liftoff (T-0).