posted 08-05-2007 10:47 PM               

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Official Countdown Began Sunday Night
08.05.07 - 8 p.m. EDT

In Firing Room 4 of the launch control center at NASA’s Kennedy Space Center, the countdown clock began ticking backward on schedule for a launch at 6:36 p.m. on Wednesday.

All countdown preparations are proceeding as planned at Launch Pad 39-A to meet an on-time launch of Space Shuttle Endeavour.

The weather forecast for launch day looks promising. Currently, there's only a 30% chance that isolated showers or anvil clouds could prevent launch. This prediction remains the same in the event of a 24-hour delay.

During the 11-day mission to the International Space Station, Endeavour's crew will add another truss segment to the expanding station, install a new gyroscope and add a spare parts platform. The flight will have at least three spacewalks. It also will debut a new system that enables docked shuttles to draw electrical power from the station to extend visits to the outpost.

This mission is the 119th space shuttle flight, the 20th flight for Endeavour and the 22nd U.S. flight to the International Space Station. The mission will be Endeavour's first flight in more than four years. The shuttle has undergone extensive modifications, including the addition of safety upgrades already added to shuttles Discovery and Atlantis.

STS-118 Launch Countdown Milestones and Times
(All times Eastern)

Launch-3 Days (Sunday, Aug. 5)

• Prepare for the start of the STS-118 launch countdown
  
• Perform the call to stations (7:30 p.m.)
  
• Countdown begins at the T-43 hour mark (8 p.m.)
  
• Begin final vehicle and facility closeouts for launch
  
• Check out backup flight systems

Launch-2 Days (Monday, Aug. 6)

• Review flight software stored in mass memory units and display systems
  
• Load backup flight system software into Endeavour's general purpose computers
  
• Remove flight-deck platforms (2 a.m.)
  
• Activate and test navigational systems (9 a.m.)
  
• Complete preparation to load power reactant storage and distribution system (11 a.m.)
  
• Flight deck preliminary inspections complete (12 p.m.)

Enter first built-in hold at T-27 hours for duration of 4 hours (12 p.m.)

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

Resume countdown (4 p.m.)

Launch-1 Day (Tuesday, Aug. 7)

Enter 4-hour built-in hold at T-19 hours (12 a.m.)

• Demate orbiter mid-body umbilical unit (12:30 a.m.)
  
• Resume orbiter and ground support equipment closeouts
  
• Begin operations to load cryogenic reactants into Endeavour's fuel cell storage tanks (2 a.m.)

Resume countdown (4 a.m.)

• Final preparations of the shuttle's three main engines for main propellant tanking and flight (4 a.m.)
  
• Begin filling pad sound suppression system water tank (6 a.m.)
  
• Pad sound suppression system water tank filling complete (9 a.m.)
  
• Close out the tail service masts on the mobile launcher platform
  
• Begin star tracker functional checks (11:50 p.m.)

Enter planned hold at T-11 hours for 13 hours, 7 minutes (12 p.m.)

• Activate orbiter's inertial measurement units
  
• Activate the orbiter's communications systems
  
• Install film in numerous cameras on the launch pad (12:55 p.m.)
  
• Flight crew equipment late stow (5:10 p.m.)
  
• Move Rotating Service Structure to the park position (9 p.m.)
  
• Perform ascent switch list
  
• Fuel cell flow-through purge complete

Launch Day (Wednesday, Aug. 8)

Resume countdown at T-11 hours (1:41 a.m.)

• Activate the orbiter's fuel cells (2:51 a.m.)
  
• Clear the blast danger area of all non-essential personnel
  
• Switch Endeavour's purge air to gaseous nitrogen (3:26 a.m.)

Enter planned 2-hour built-in hold at the T-6 hour mark (6:41 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 (8:41 a.m.)

• Chill down propellant transfer lines (8:41 a.m.)
  
• Begin loading the external fuel tank with about 500,000 gallons of cryogenic propellants (about 8:51 a.m.)
  
• Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants (about 11:41 a.m.)
  
• Final Inspection Team proceeds to launch pad

Enter planned 3-hour built-in hold at T-3 hours (11:41 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 (2:41 p.m.)

• Crew departs Operations and Checkout Building for the pad (2:46 p.m.)
  
• Complete closeout preparations in the White Room
  
• Check cockpit switch configurations
  
• Flight crew begins entry into the orbiter (about 3:16 p.m.)
  
• Astronauts perform air-to-ground voice checks with Launch and Mission Control
  
• Begin to close Endeavour's crew hatch (4:31 p.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 (5:21 p.m.)

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

Resume countdown at T-20 minutes (5:31 p.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 46-minute hold at T-9 minutes (5:42 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 (about 6:27 p.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-1)
  
• 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)

Summary of STS-118 Launch Day Crew Activities
Televised events (times may vary slightly)
All times Eastern

Wednesday, Aug. 8
8:04 a.m. --- Crew wake up
12:29 p.m. --- Television coverage from crew quarters
2:06 p.m. --- Weather briefing
2:16 p.m. --- Don flight suits
2:46 p.m. --- Depart for launch pad
3:16 p.m. --- Arrive at White Room and begin ingress
4:31 p.m. --- Close crew hatch
6:36 p.m. --- Launch

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