October 2, 1995

KSC Release No. 99-95

SPACE SHUTTLE MISSION STS-73 LAUNCH COUNTDOWN AGAIN UNDERWAY

	The countdown for launch of the Space Shuttle Columbia on
mission STS-73 began today at 4 a.m. EDT, at the T-43 hour mark. This
is the second launch attempt of Columbia on mission STS-73. It
follows last week’s launch scrub during tanking operations due to a
leaking main fuel valve on main engine no. 1. The valve was
successfully replaced at the pad, tested and checked for leaks over
the weekend.

	The KSC launch team will conduct the countdown from Firing
Room 3 of the Launch Control Center. The countdown includes 34 hours
and 40 minutes of built-in hold time leading to the opening of the
launch window at 9:40 a.m. (EDT) on Oct. 5. The launch window extends
for 2 1/2 hours.

	STS-73 is the sixth Space Shuttle mission for 1995. It will
be the 18th flight of the Shuttle Columbia and the 72nd flight
overall in NASA’s Space Shuttle program.

	The primary objective of mission STS-73 is to successfully
perform the planned operations of the second U.S. Microgravity
Laboratory. USML-2 experiments cover a variety of scientific
disciplines including fluid physics, materials science, biotechnology
and combustion science.

	Columbia was rolled out of Orbiter Processing Facility bay 3
on Aug. 21 and mated with the external tank and solid rocket boosters
in the Vehicle Assembly Building. The Shuttle stack was then
transported to Pad 39-B on Aug. 28.

	This mission will be Columbia’s first in over a year.
Columbia was sent to Palmdale, Calif., for about six months where it
underwent various structural inspections and modifications. It was
returned to KSC on April 14. Columbia last flew in July 1994.

	The STS-73 crew are: Commander Ken Bowersox, Pilot Kent
Rominger, Mission Specialists Kathryn Thornton, Catherine Coleman and
Michael Lopez-Alegria, and Payload Specialists Fred Leslie and Albert
Sacco.

	The crew will arrive at KSC later this afternoon and tonight
in two waves. The Red Team (Bowersox, Rominger, Thornton and Sacco)
is scheduled to arrive at 4 p.m. The Blue Team (Coleman,
Lopez-Alegria and Leslie) is scheduled to arrive at about 10:30 p.m.
Their activities at KSC prior to launch will include equipment fit
checks, medical examinations and opportunities to fly in the Shuttle
Training Aircraft.


COUNTDOWN MILESTONES

All times Eastern
Launch - 3 Days (Monday, Oct. 2)

* Prepare for the start of the STS-73 launch countdown
* Perform the call-to-stations. All Firing Room console operators
  report on station.
* All members of the launch team report to their respective consoles
  in Firing Room 3 in the Launch Control Center for the start of the
  countdown.
* Countdown begins at 4 a.m. EDT at the T-43 hour mark
* Start preparations for servicing fuel cell storage tanks
* Begin final vehicle and facility close-outs for launch
* Begin stowage of flight crew equipment
* Load backup flight system software into Columbia's general purpose computers
* Check out back-up flight systems
* Inspect the orbiter's mid-deck and flight-deck and remove crew
  module platforms
* Review flight software stored in mass memory units and display systems

Enter first planned built-in hold at T-27 hours for duration of four hours (8 p.m.)

* Clear launch pad of all personnel
* Perform test of the vehicle's pyrotechnic initiator controllers

Resume countdown (12 midnight)

Launch - 2 Days (Tuesday, Oct. 3)

* Begin the 12-hour operation to load cryogenic reactants into
  Columbia's fuel cell storage tanks and Extended Duration Orbiter
  storage tanks.

Enter eight-hour built-in hold at T-19 hours (8 a.m.)

* After cryogenic loading operations, re-open the pad
* Resume orbiter and ground support equipment close-outs
* Begin installation of mission specialists' seats in crew cabin

Resume countdown (4 p.m.)

* Activate spacelab and begin late stowage of spacelab equipment and
  experiments
* Demate orbiter mid-body umbilical unit and retract into fixed
  service structure
* Start final preparations of the Shuttle's three main engines for
  main propellant tanking and flight
* Activate flight controls and navigation systems
* Close-out the tail service masts on the mobile launcher platform
* Perform orbiter ascent switch list in crew cabin
* Install film in numerous cameras on the launch pad
* Activate the orbiter's communications systems
* Activate orbiter's inertial measurement units

Launch - 1 Day (Wednesday, Oct. 4)

Enter planned hold at T-11 hours for 19 hours, 20 minutes (12 midnight)

* Fill pad sound suppression system water tank
* Safety personnel conduct debris walkdown
* Move Rotating Service Structure (RSS) to the park position at about 2 p.m.
* Following the RSS move, continue final stowage of mid-deck
  experiments and flight crew equipment

Resume countdown (7:20 p.m.)

* Start fuel cell flow-through purge
* Install time critical flight crew equipment
* Perform pre-ingress switch list
* Activate the orbiter's fuel cells
* Configure communications at Mission Control in Houston for launch
* Activate the solid rocket booster’s joint heaters
* Clear the blast danger area of all non-essential personnel
* Switch Columbia's purge air to gaseous nitrogen
* Activate auxiliary power unit heaters

Launch Day (Thursday, Oct. 5)

Enter planned one-hour built-in hold at the T-6 hour mark (12:20 a.m.)

* Launch team verifies no violations of launch commit criteria prior
  to cryogenic loading of the external tank
* Verify pad is clear of all personnel

Resume countdown (1:20 a.m.)

* Begin loading the external tank with cryogenic propellants (1:20 a.m.)
* Perform inertial measurement unit preflight calibration
* Align Merritt Island Launch Area (MILA) tracking antennas
* Complete filling the external tank with its flight load of liquid
  hydrogen and liquid oxygen propellants (4:20 a.m.)

Enter two-hour hold at T-3 hours (4:20 a.m.)

* Perform open loop test with Eastern Range
* Conduct gimbal profile checks of orbital maneuvering system engines
* Close-out crew and Final Inspection Team proceeds to Launch Pad 39-B

Resume countdown at T-3 hours (6:20 a.m.)

* Crew departs Operations and Checkout Building for Launch Pad 39-B
  (6:25 a.m.)
* Complete close-out preparations in the white room
* Check cockpit switch configurations
* Flight crew enters orbiter
* Astronauts perform air-to-ground voice checks with Launch Control and
  Mission Control
* Close Columbia's crew hatch
* Begin Eastern Range final network open loop command checks
* Perform hatch seal and cabin leak checks
* Complete white room close-out
* Close-out 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 (9:00 a.m.)

* NASA Test Director conducts final launch team briefings

Resume countdown (9:10 a.m.)

* Transition the orbiter's onboard computers to launch configuration
* Start fuel cell thermal conditioning
* Close orbiter cabin vent valves
* Transition backup flight system to launch configuration

Enter final 10-minute hold at T-9 minutes (9:21 a.m.)

* Launch Director, Mission Management Team and NASA Test Director
  conduct final polls for go/no go to launch

Resume countdown at T-9 minutes (9:31 a.m.)

* 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)
* 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)
* Orbiter transfers from ground to internal power (T-0:50 seconds)
* Ground Launch Sequencer go for auto sequence start (T-0:31 seconds)
* Ignition of three Space Shuttle main engines (T-6.6 seconds)
* SRB ignition and liftoff (T-0)


CREW FOR MISSION STS-73

Ken Bowersox		Commander (CDR)		   Red Team
Kent Rominger 		Pilot (PLT)                Red Team
Catherine Coleman	Mission Specialist (MS1)   Blue Team
Michael Lopez-Alegria	Mission Specialist (MS2)   Blue Team
Kathryn Thornton	Mission Specialist (MS3)   Red Team
Fred Leslie		Payload Specialist (PS1)   Blue Team
Albert Sacco		Payload Specialist (PS2)   Red Team


SUMMARY OF STS-73 LAUNCH DAY CREW ACTIVITIES

Wednesday, Oct. 4

7:00 p.m.		Wake up (Blue Team)
7:30 p.m.		Breakfast (Blue Team)

Thursday, Oct. 5

  12:30 a.m. 		Lunch (Blue Team)
   4:00 a.m.		Wake up (Red Team)
*  5:15 a.m.		Breakfast/Dinner and Crew Photo
   5:45 a.m.            Weather briefing (CDR, PLT, MS2)
   5:45 a.m.		Don launch and entry suits (MS1, MS3, PS1, PS2)
   5:55 a.m.		Don launch and entry suits (CDR, PLT, MS2)
*  6:10 a.m.		Crew suiting photo
*  6:25 a.m.		Depart for Launch Pad 39B
*  6:55 a.m.		Arrive at white room and begin orbiter ingress
*  8:10 a.m.		Close crew hatch
*  9:40 a.m.		Launch

* Televised events (times may vary slightly)
All times Eastern