The countdown for launch of the Space Shuttle Discovery on mission STS-51 began as scheduled today at 8 a.m. EDT, at the T-43 hour mark.
This marks the beginning of the fourth launch attempt of the orbiter Discovery since launch was scrubbed on July 17 and 24 due to technical problems and again, most recently, on August 12. Additionally, launch was postponed from August 4 until August 12 due to concerns regarding the Perseid meteor shower and from September 10 to 12 due to concerns with the Advanced Communications Technology Satellite (ACTS) payload.
The countdown includes 28 hours and 45 minutes of built-in hold time leading to the opening of the launch window at 7:45 a.m. (EDT) on Sunday, September 12. The 1 hour, 55 minute window extends until 9:40 a.m.
A primary objective of this mission is the deployment of the ACTS and its Transfer Orbit Stage (TOS). ACTS/TOS is the latest in NASA's series of advanced communication satellites and a test-bed for technology which will be used in future operational satellites. Also, the Orbiting Retrievable Far and Extreme Ultraviolet Spectrometer-Shuttle Pallet Satellite (ORFEUS-SPAS) payload will be deployed and retrieved during this mission.
Also on board is the Commercial Protein Crystal Growth (CPCG) experiment, the Chromosome and Plant Cell Division in Space (CHROMEX) experiment, and the IMAX camera.
In addition, astronauts Jim Newman and Carl Walz are scheduled to perform a six hour spacewalk on the fifth day of the mission as a continuation of a series of test spacewalks to increase experience and refine training methods. They will work with several tools that may be used during the servicing of the Hubble Space Telescope mission later this year.
Today in Firing Room 1 of the Launch Control Center, the KSC launch team is verifying systems to assure that the Shuttle is powered up and that the data processing and backup flight control systems are operating trouble free.
Verifications will be conducted throughout the count to ensure reviews are being made of the flight software which is stored in the orbiter's twin memory banks. Computer controlled display systems will be activated and the backup flight system general purpose computer will be loaded.
Operations are also underway to prepare the orbiter for on- board cryogenic loading. Later, orbiter navigation aids will be turned on and tested and the inertial measurement units will be activated.
Also today, ground crews are making the final storage of mid- deck and flight deck supplies and payloads. They will perform microbial samplings of the flight crew's drinking water and check water levels in the crew waste management system.
The STS-51 crew is scheduled to arrive at KSC at about 1 p.m. today.
At T-27 hours, the countdown will enter its first built-in hold. This is an eight hour hold lasting from 12 midnight to 8 a.m. Friday.
When the countdown resumes, the launch pad will be cleared of all personnel in preparation for cryogenic fuel loading of the power reactant and storage distribution system tanks located under the payload bay lining. These tanks hold the super-cold liquid hydrogen and liquid oxygen reactants used by the fuel cells to provide electricity to the orbiter and drinking water for the crew.
Cryogenic flow is scheduled to start at about 10 a.m. Friday and continue for about five hours.
As servicing of the cryogenic tanks concludes, the clock will enter another built-in hold at the T-19 hour mark. This hold will last from 4 to 8 p.m. on Tuesday.
Following cryogenic loading operations, the pad will be re- opened for normal work and the orbiter mid-body umbilical unit used to load the super-cold reactants in the orbiter's fuel cell tanks will be demated and retracted into the launch structure.
When the countdown resumes, technicians will complete final vehicle and facility closeouts and begin activating the orbiter's communications systems and configuring Discovery's cockpit for flight. The orbiter's flight control system and navigation aids will be activated. The stowable crew seats will be installed in the flight and mid-decks.
The countdown will enter a built-in hold at the T-11 hour mark at 4 a.m. Saturday. This 13 hour, 25 minute hold will last until 5:25 p.m. Saturday. During this hold, time critical equipment will be installed in the orbiter's cockpit and the inertial measurement units will be activated and warmed up.
At about 11 a.m. Saturday, the Rotating Service Structure is scheduled to be moved away from the vehicle and placed in launch position.
At T-9 hours, about 7:25 p.m. Saturday the onboard fuel cells will be activated. At T-8 hours, the launch team will begin evacuating the blast danger area and clear the pad for loading the external tank with the super-cold cryogenic fuels. At T-7 hours, 30 minutes, conditioned air that is flowing through the orbiter's payload bay and other areas on the orbiter will be switched to gaseous nitrogen in preparation for fueling the external tank. The inertial measurement units will transition from the warm up stage to the operate/attitude determination mode at T-6 hours, 45 minutes.
The countdown will enter another planned built-in hold at the T-6 hour mark at 10:25 p.m. Saturday. 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 begins when the clock starts counting again at 11:25 p.m. Saturday. Filling and topping off the external tank should be complete at the beginning of the next planned hold at T- 3 hours, or 2:25 a.m. Sunday.
During the two-hour hold at T-3 hours, an ice inspection team will conduct a survey of the external tank's outer insulation and other Shuttle components. Also, the closeout crew will be dispatched to the pad and 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 any propellant that "boils" off.
During the hold at T-3 hours, the five-member STS-51 crew will be awakened at about 2:50 a.m. Sunday.
Following breakfast, the crew will receive a briefing on weather conditions both at KSC and 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 during the T-3 hour hold, or at about 4:30 a.m. They will arrive at the pad's white room at about 5 a.m. where they will be assisted by white room personnel 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 observations from astronaut Robert "Hoot" Gibson 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 (7:05 a.m.) and at the T-9 minute mark (7:26 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 inside the external tank at T-2 minutes, 55 seconds; pressurization of the liquid hydrogen tank at T-1 minute, 57 seconds; and the electronic "go" to Discovery's onboard computers to start their own terminal countdown sequence at T-31 seconds. The orbiter's three main engines will start at T-6.6 seconds.
Prepare for the start of the STS-51 launch countdown and perform the call-to-stations at the T-43 hour mark. Countdown began at 8 a.m. All members of the launch team reported to their respective consoles in Firing Room 1 in the Launch Control Center for the start of the countdown.
The payload bay doors are scheduled to be closed for flight at about 4 p.m.
Enter the first planned built-in hold at T-27 hours for a duration of eight hours.
Check out back-up flight system and review flight software stored in mass memory units and display systems. Load backup flight system software into Discovery's general purpose computers.
Begin stowage of flight crew equipment. Inspect the orbiter's mid-deck and flight-deck and remove crew module platforms. Start external tank loading preparations and prepare the Shuttle's main engines for main propellant tanking and flight.
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 begin loading liquid oxygen and liquid hydrogen reactants into Discovery's fuel cell storage tanks.
After loading operations, the pad will be reopened for normal work. Orbiter and ground support equipment closeouts will resume.
Enter planned built-in hold at T-19 hours for a duration of 4 hours.
Demate orbiter mid-body umbilical unit.
Resume countdown.
Activate orbiter communications systems, flight control and navigation systems. Install mission specialists' seats in crew cabin. The tail service masts on the mobile launcher platform will be closed out for launch.
Enter planned hold at T-11 hours for a duration of 13 hours, 25 minutes.
Perform orbiter ascent switch list in crew cabin. During this hold at T-11 hours, the orbiter's inertial measurement units will be activated 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 suppression system water tank will be filled.
The Rotating Service Structure will be moved to the park position during this hold at about 11 a.m.
Final stowage of mid-deck experiments and flight crew equipment stowage will begin.
Resume countdown. Install time critical flight crew equipment and perform the pre-ingress switch list. Start fuel cell flow- through purge.
Activate the orbiter's fuel cells. Configure communications at Mission Control, Houston, for launch. Clear the blast danger area of all non-essential personnel and switch Discovery's purge air to gaseous nitrogen.
Enter planned one-hour built-in hold at the T-6 hour mark.
Launch team verifies there are no violations of launch commit criteria prior to cryogenic loading of the external tank. Clear pad of all personnel.
Resume countdown. Loading the external tank with cryogenic propellants is scheduled to begin at 11:25 p.m.
Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants. Perform open loop test with Eastern Space and Missile Center and conduct gimbal profile checks of orbital maneuvering system engines.
Perform inertial measurement unit preflight calibration and align Merritt Island Launch Area tracking antennas.
Enter two-hour hold at T-3 hours. Wake flight crew at 2:50 a.m.
Closeout crew and ice inspection team proceeds to Launch Pad 39-B. Crew departs Operations and Checkout Building for the pad at 4:30 a.m.
Resume countdown at T-3 hours. Complete closeout preparations in the white room and cockpit switch configurations.
Flight crew enters orbiter. Astronauts perform air-to-ground voice checks with Mission Control, Houston. Close Discovery's crew hatch. Begin Eastern Space and Missile Center final network open loop command checks.
Perform hatch seal and cabin leak checks. 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.
NASA Shuttle Test Director conducts final briefing.
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 last planned hold at T-9 minutes.
Launch Director and Mission Management Team complete final polls for launch. Resume countdown.
Start automatic ground launch sequencer (T-9:00 minutes)
Retract orbiter crew access arm (T-7:30)
Start mission recorders (T-5:30)
Start Auxiliary Power Units (T-5:00)
Arm SRB and ET range safety safe and arm devices (T-5:00)
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 tank (T-2:55)
Begin retraction of the gaseous oxygen vent arm (T-2:55)
Fuel cells to internal reactants (T-2:35)
Pressurize liquid hydrogen tank (T-1:57)
Deactivate SRB joint heaters (T-1:00)
LPS go for start of orbiter automatic sequence (T-0:31 seconds)
Ignition of Shuttle's three main engines (T-6.6 seconds)
SRB ignition and liftoff (T-0)
T-TIME LENGTH OF HOLD HOLD BEGINS HOLD ENDS T-27 hours 8 hours 12:00 am Fri. 8:00 am Fri. T-19 hours 4 hours 4:00 pm Fri. 8:00 pm Fri. T-11 hours 13 hrs., 25 mins. 4:00 am Sat. 5:25 pm Sat. T-6 hours 1 hour 10:25 pm Sat. 11:25 pm Sat. T-3 hours 2 hours 2:25 am Sun. 4:25 am Sun. T-20 minutes 10 minutes 7:05 am Sun. 7:15 am Sun. T-9 minutes 10 minutes 7:26 am Sun. 7:36 am Sun.
Commander (CDR): Frank Culbertson
Pilot (PLT): Bill Readdy
Mission Specialist (MS1): Jim Newman
Mission Specialist (MS2): Dan Bursch
Mission Specialist (MS3): Carl Walz
Sunday, September 12, 1993 2:50 a.m. Wake up 3:20 a.m. Breakfast 3:50 a.m. Weather briefing (CDR, PLT, MS2) 3:50 a.m. Don flight equipment (MS1, MS3) 4:00 a.m. Don flight equipment (CDR, PLT, MS2) 4:30 a.m. Depart for launch pad 39-B 5:00 a.m. Arrive at white room and begin ingress 6:15 a.m. Close crew hatch 7:45 a.m. Launch