Countdown Begins Today for the Second Launch Attempt of Shuttle Mission STS-99

On mission STS-99, Endeavour and crew will capture the most accurate elevation
measurements of the Earthís surface ever attained. Using a unique radar system dubbed
Shuttle Radar Topography Mission (SRTM), STS-99 will glean valuable 3-D mapping
images for application in fields ranging from military planning to back country recreation.

The STS-99 crew includes: Commander Kevin Kregel, Pilot Dom Gorie, Mission
Specialists Janet Kavandi, Janice Voss, Mamoru Mohri, and Gerhard Thiele.

The crew returned to KSC at about noon on Feb. 7. Their activities at KSC prior to
launch will include crew equipment fit checks, medical examinations and opportunities to fly
in the Shuttle Training Aircraft.

• Prepare for the start of the STS-99 launch countdown
• Perform the call-to-stations (5 p.m.)
• Countdown begins at the T-43 hour mark (5:30 p.m.)
• Begin final vehicle and facility close-outs for launch
• Check out back-up flight systems
• Review flight software stored in mass memory units and display systems
• Load backup flight system software into Endeavourís general purpose computers

• Remove mid-deck and flight-deck platforms (1:30 a.m.)
• Activate and test navigational systems
• Complete preparations for loading of power reactant storage and distribution system
• Middeck and flight deck preliminary inspections complete (9:30 a.m.)

Enter first built-in hold at T-27 hours for duration of 4 hours (9:30 a. m.)

• Clear launch pad of all non-essential personnel
• Perform test of the vehicle’s pyrotechnic initiator controllers (10:30 a.m.)

Resume countdown (1:30 p.m.)

• Begin operations to load cryogenic reactants into Endeavourís fuel cell storage tanks (1:30 ñ 9:30 p.m.)

Enter 4-hour built-in hold at T-19 hours (9:30 p.m.)

• Begin filling pad sound suppression system water tank
• Demate orbiter mid-body umbilical unit (10 p.m.)

• Resume orbiter and ground support equipment close-outs
• Pad sound suppression system water tank filled (1:30 a.m.)

Resume countdown (1:30 a.m.)

• Start final preparations of the Shuttle’s three main engines for main propellant tanking and flight
• Install mission specialists’ seats in crew cabin begins (3:30 a.m.)
• Close-out the tail service masts on the mobile launcher platform

Enter planned hold at T-11 hours for 12 hours, 40 minutes (9:30 a.m.)

• Begin startracker functional checks (10:30 a.m.)
• Activate orbiter’s inertial measurement units
• Activate the orbiter’s communications systems
• Install film in numerous cameras on the launch pad (1:30 p.m.)
• Flight crew equipment late stow (2 p.m.)
• Move Rotating Service Structure (RSS) to the park position (6:30 p.m.)
• Perform ascent switch list

Resume countdown (10:10 p.m.)

• Fuel cell flow-through purge complete
• Activate the orbiter’s fuel cells (11:20 p.m.)

• Clear the blast danger area of all non-essential personnel
• Switch Endeavourís purge air to gaseous nitrogen (12:25 a.m.)

Enter planned 1-hour built-in hold at the T-6 hour mark (3:10 a.m.)

• Launch team verifies no violations of launch commit criteria prior to cryogenic
  loading of the external tank (3:15 a.m.)
• Clear pad of all personnel
• Chilldown of propellant transfer lines
• Begin loading the external tank with about 500,000 gallons of cryogenic propellants (about 4:10 a.m.)

Resume countdown (4:10 a.m.)

• Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants (about 7:10 a.m.)
• Final Inspection Team proceed to launch pad

Enter planned 2-hour built-in hold at T-3 hours (7:10 a.m.)

• Perform inertial measurement unit preflight calibration
• Align Merritt Island Launch Area (MILA) tracking antennas
• Perform open loop test with Eastern Range

Resume countdown at T-3 hours (9:10 a.m.)

• Crew departs Operations and Checkout Building for the pad (9:15 a.m.)
• Complete close-out preparations in the white room
• Check cockpit switch configurations
• Flight crew begins entry into the orbiter (about 9:45 a.m.)
• Astronauts perform air-to-ground voice checks with Launch and Mission Control
• Close Endeavourís crew hatch (about 11 a.m.)
• 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 (11:50 a.m.)

• NASA Test Director conducts final launch team briefings
• Complete inertial measurement unit pre-flight alignments

Resume countdown (12 noon)

• 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 planned 10-minute hold at T-9 minutes (12:11 p.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 (12:21 p.m.)

• Start automatic ground launch sequencer (T-9:00 minutes)
• Retract orbiter crew access arm (T-7:30)
• Start mission recorders (T-6:15)
• 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 main engine 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)
• SRB gimbal profile (T-0:21 seconds)
• Ignition of three Space Shuttle main engines (T-6.6 seconds)
• SRB ignition and liftoff (T-0)