Shuttle Launch Countdown starts on Wednesday

From NASA:

MEDIA ADVISORY: M06-106

NASA Space Shuttle Discovery's Launch Countdown Begins June 28

NASA will begin the countdown for the launch of Space Shuttle Discovery at 5 p.m. EDT June 28. The countdown includes nearly 28 hours of built-in hold time leading to a scheduled launch at about 3:49 p.m. on July 1. The launch window extends for nearly five minutes. The launch team at NASA's Kennedy Space Center, Fla., will conduct the countdown from the newly renovated Firing Room 4 of the Launch Control Center.

This mission is designated STS-121. It is the 115th shuttle flight and the 18th U.S. flight to the International Space Station. Discovery's mission is scheduled to last about 12 days and end with 10:45 a.m. landing at Kennedy on July 13. The crew will test new equipment and procedures to improve shuttle safety, as well as deliver supplies and make repairs to the International Space Station.

COUNTDOWN MILESTONES (TIMES SUBJECT TO CHANGE)

Launch-3 Days (Wednesday, June 28): Countdown begins at the T-43 hour mark (5 p.m.)

Launch-2 Days (Thursday, June 29)
Remove mid-deck and flight-deck platforms (1 a.m.);
Complete preparation to load power reactant storage and distribution system (4 a.m.)
Activate and test navigational systems (6 a.m.);
Flight deck preliminary inspections complete (9 a.m.)
Enter first built-in hold at T-27 hours for duration of 4 hours (9 a.m.); Clear launch pad of all non-essential personnel; Perform test of the vehicle's pyrotechnic initiator controllers
Resume countdown (1 p.m.) Begin operations to load cryogenic reactants into Discovery's fuel cell storage tanks (2:30 p.m.)
Enter 4-hour built-in hold at T-19 hours (9 p.m.); Demate orbiter mid-body umbilical unit (9:30 p.m.) Resume orbiter and ground support equipment closeouts

Launch-1 Day (Friday, June 30)
Resume countdown (1 a.m.); Final preparations of shuttle's three main engines for main propellant tanking and flight (1 a.m.); Begin filling pad sound suppression system water tank (2 a.m.); Pad sound suppression system water tank filling complete (5 a.m.); Close out the tail service masts on the mobile launcher platform

Enter planned hold at T-11 hours for 13 hours, 53 minutes (9 a.m.);
Begin star tracker functional checks (9:50 a.m.); Activate orbiter's inertial measurement units; Activate the orbiter's communications systems; Install film in numerous cameras on the launch pad (10:55 a.m.); Flight crew equipment late stow (2:50 p.m.); Move Rotating Service Structure (RSS) to the park position (6:30 p.m.); Perform ascent switch list; Fuel cell flow-through purge complete Resume countdown at T-11 hours (10:53 p.m.)

Launch Day (Saturday, July 1)
Activate the orbiter's fuel cells (12:02 a.m.); Clear the blast danger area of all non-essential personnel; Switch Discovery's purge air to gaseous nitrogen (12:53 a.m.)
Enter planned 2-hour built-in hold at the T-6 hour mark (3:53 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 (5:53 a.m.); Chill down of propellant transfer lines (5:53 a.m.); Begin loading the external tank with about 500,000 gallons of cryogenic propellants (about 6:03 a.m.); Complete filling the external tank with its flight load of liquid hydrogen and liquid oxygen propellants (about 8:53 a.m.); Final Inspection Team proceed to launch pad
Enter planned 3-hour built-in hold at T-3 hours (8:53 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 (11:53 a.m.); Crew departs Operations and Checkout Building for the pad (11:58 a.m.); Complete closeout preparations in the white room
Check cockpit switch configurations; Flight crew begins entry into the orbiter (about 12:28 p.m.); Astronauts perform air-to-ground voice checks with Launch and Mission Control. Begin to close Discovery's crew hatch (about 1:38 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 (2:33 p.m.); NASA test director conducts final launch team briefings; Complete inertial measurement unit preflight alignments
Resume countdown at T-20 minutes (2:43 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 40-minute hold at T-9 minutes (2:54 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 3:40 p.m.); Start automatic ground launch sequencer; 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 bi-pod heaters (T-1:52); Deactivate SRB joint heaters (T-0:60 seconds); 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)

STS-121 CREW & LAUNCH DAY ACTIVITIES
Commander Steve Lindsey; Pilot Mark Kelly; mission specialists Michael Fossum, Lisa Nowak, Stephanie Wilson, Piers Sellers and Thomas Reiter of the European Space Agency

# 5:15 a.m. Crew wakes up
# 10:10 a.m. Breakfast
# 10:48 a.m. Weather briefing for STS-121 commander and two crew members
# 11:30 a.m. Astronauts put on flight suits
# 11:58 a.m. Depart for launch pad
# 12:28 p.m. Arrive at white room and begin to enter Discovery
# 1:43 p.m. Close crew hatch
# 3:49 p.m. Launch