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STS-121 COUNTDOWN



SUBMITTED BY ARTHUR N1ORC - AMSAT A/C 31468


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

For information about the STS-121 crew and its mission to the 
International Space Station, visit:

http://www.nasa.gov/shuttle


For NASA TV downlink and scheduling information, visit:

http://www.nasa.gov/ntv
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