Press Release

NASA Set to Begin Space Shuttle Discovery Countdown Oct. 20

By SpaceRef Editor
October 19, 2007
Filed under , , ,
NASA Set to Begin Space Shuttle Discovery Countdown Oct. 20

CAPE CANAVERAL, Fla. — NASA will start the launch countdown for space shuttle Discovery’s STS-120 mission at 2 p.m. EDT Saturday, Oct. 20, at T-43 hours. The countdown includes 26 hours and 38 minutes of built-in hold time leading to a preferred launch time of approximately 11:38 a.m. on Tuesday, Oct. 23. The launch window extends an additional five minutes.

During the 14-day mission to the International Space Station, Discovery’s crew will add the Node 2 module to the expanding station. Node 2, known as Harmony, will provide attachment points for European and Japanese laboratory modules to be installed later this year and early in 2008, respectively. The Discovery crew also will move the station’s Port 6 segment of the station’s backbone, or truss, and its solar arrays to a permanent position at the very end of the left side of the truss. The flight will include five spacewalks.

A detailed list of launch countdown milestones and times is available at:

This mission is the 120th space shuttle flight, the 34th flight for Discovery and the 23rd U.S. flight to the International Space Station. This mission includes the most number of spacewalks ever conducted while the shuttle is docked to the station.

For more information about the STS-120 crew and the mission to the space station, visit:



(All times Eastern)

Launch-3 Days (Saturday, Oct. 20)

  • Prepare for the start of the STS-120 launch countdown
  • Perform the call to stations (1:30 p.m.)
  • Countdown begins at the T-43 hour mark (2 p.m.)
  • Begin final vehicle and facility closeouts for launch
  • Check out backup flight systems
  • Review flight software stored in mass memory units and display systems

  • Load backup flight system software into Discovery’s general purpose computers
  • Mid-deck and flight-deck platform removal complete (10 p.m.)

Launch-2 Days (Sunday, Oct. 21)

  • Activate and test navigational systems (3 a.m.)
  • Complete preparations to load power reactant storage and distribution system (5 a.m.)
  • Flight deck preliminary inspections complete (6 a.m.)

Enter first built-in hold at T-27 hours for duration of 4 hours (6 a.m.)

Clear launch pad of all non-essential personnel Perform test of the vehicle’s pyrotechnic initiator controllers

Resume countdown (10 a.m.)

Enter 4-hour built-in hold at T-19 hours (6 p.m.)

  • Begin operations to load cryogenic reactants into Discovery’s fuel cell storage tanks (6 p.m.)
  • Demate orbiter mid-body umbilical unit (6:30 p.m.)
  • Resume orbiter and ground support equipment closeouts

Resume countdown (10 p.m.)

  • Final preparations of the shuttle’s three main engines for main
  • propellant tanking (10 p.m.)

Launch-1 Day (Monday, Oct. 22)

  • Begin filling pad sound suppression system water tank (3 a.m.)
  • Close out the tail service masts on the mobile launcher platform
  • Begin star tracker functional checks (5:50 a.m.)
  • Pad sound suppression system water tank filling complete (6 a.m.)

Enter planned hold at T-11 hours for 13 hours, 13 minutes (6 a.m.)

  • Activate orbiter’s inertial measurement units
  • Activate the orbiter’s communications systems
  • Install film in numerous cameras on the launch pad (6:55 a.m.)
  • Flight crew equipment late stow (11:10 a.m.)
  • Move Rotating Service Structure to the park position (3 p.m.)
  • Perform ascent switch list
  • Fuel cell flow-through purge complete

Resume countdown at T-11 hours (7:13 p.m.)

  • Activate the orbiter’s fuel cells (8:23 p.m.)
  • Clear the blast danger area of all non-essential personnel
  • Switch Discovery’s purge air to gaseous nitrogen (8:58 p.m.)

Launch Day (Tuesday, Oct. 23)

  • Enter planned 2-hour built-in hold at the T-6 hour mark (12:13 a.m.)
  • Launch team verifies no violations of launch commit criteria prior to
  • cryogenic loading of the external tank
  • Clear pad of all personnel

Resume countdown (2:13 a.m.)

  • Chill down propellant transfer lines (2:13 a.m.)
  • Begin loading the external fuel tank with about 500,000 gallons of cryogenic propellants (about 2:23 a.m.)
  • Complete filling the external tank with its flight load of liquid
  • hydrogen and liquid oxygen propellants (about 5:13 a.m.)
  • Final Inspection Team proceeds to launch pad

Enter planned 2-hour, 30 minute built-in hold at T-3 hours (5:13 a.m.)

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

Resume countdown at T-3 hours (7:43 a.m.)

  • Crew departs Operations and Checkout Building for the pad (7:48 a.m.)
  • Complete closeout preparations in the White Room
  • Check cockpit switch configurations
  • Flight crew begins entry into the orbiter (about 8:18 a.m.)
  • Astronauts perform air-to-ground voice checks with Launch and Mission Control
  • Begin to close Discovery’s crew hatch (9:23 a.m.)
  • Begin Eastern Range final network open loop command checks
  • Perform hatch seal and cabin leak checks
  • Complete White Room closeout
  • 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 (10:23 a.m.)

  • NASA test director conducts final launch team briefings
  • Complete inertial measurement unit preflight alignments

Resume countdown at T-20 minutes (10:33 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 estimated 45-minute hold at T-9 minutes (10:44 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 (about 11:29 a.m.)

  • Start automatic ground launch sequencer (T-9 minutes)
  • Retract orbiter crew access arm (T-7:30)
  • Start mission recorders (T-6:15)
  • Start Auxiliary Power Units (T-5)
  • Arm solid rocket booster and external tank range safety safe and arm devices (T-5)
  • 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 bi-pod heaters (T-1:52)
  • Deactivate solid rocket booster joint heaters (T-0:50)
  • Orbiter transfers from ground to internal power (T-0:50 seconds)
  • Ground Launch Sequencer go for auto sequence start (T-0:31 seconds)
  • Booster gimbal profile (T-0:21 seconds)
  • Ignition of three space shuttle main engines (T-6.6 seconds)
  • Booster ignition and liftoff (T-0)


  • Commander: Pam Melroy
  • Pilot: George Zamka
  • Mission Specialist: Scott Parazynski
  • Mission Specialist: Doug Wheelock
  • Mission Specialist: Stephanie Wilson
  • Mission Specialist: Paolo Nespoli
  • Mission Specialist: Daniel Tani


Televised events (times may vary slightly) All times Eastern

Tuesday, Oct. 23

  • 1:30 a.m. — Crew wakes up
  • 7:08 a.m. — Weather briefing
  • 7:18 a.m. — Don flight suits
  • 7:48 a.m. — Depart for launch pad
  • 8:18 a.m. — Arrive at White Room and begin ingress
  • 9:33 a.m. — Close crew hatch
  • 11:38 a.m. — Launch

SpaceRef staff editor.