Shuttle Mission: STS-110
Orbiter: Atlantis
Date: April 8

Did You Know?

The liquid oxygen vent on the external tank has been opened to allow the super-cold liquid oxygen to boil off, thus preventing over pressurization while the tank remained near its full level. Now, with the vent closed, preparations are made to bring the tank to its flight pressure. This occurs at T minus 2 minutes, 55 seconds.

Once the Shuttle's on board computers start their terminal launch sequence any problem after that point will require calling a "hold" and the countdown recycled to T minus 20 minutes. Meanwhile, the Ground Launch Sequencer (GLS) continues to monitor several hundred launch commit functions and is able automatically to call a "hold" or a "cutoff" if a problem occurs.

The STS-110 crew patch is patterned after the cross section of the S0 truss, and encases the launch of the Shuttle Atlantis and a silhouette of the ISS as it will look following mission completion. The successfully installed S0 segment is highlighted in gold.

The S0 truss is 44 feet long and 15 feet wide, and weighs in at 27,000 pounds. That makes it about as long as a large charter bus, as wide as the interior cabin of a 767, and as heavy as two full-grown African elephants.

Despite the fact that three members are making their first space flight, the STS-110 crew has already totaled over 3000 hours in space on their previous flights with nearly 80 hours performing spacewalks.

T-09 minutes -- the Ground Launch Sequencer (GLS) is activated and the terminal countdown begins.  All countdown functions are now automatically controlled by the GLS computer located in the Firing Room Integration Console.

T-07 minutes, 30 seconds and counting -- the Orbiter Access Arm is retracted. Should an emergency occur requiring crew evacuation from the orbiter, the arm can be extended either manually or automatically in about 15 seconds.

T-05 minutes, 00 seconds and counting -- the crew activates the Auxiliary Power Units (APU) to provide pressure to the Shuttle's three hydraulic systems which move the main engine nozzles and the aero-surfaces.

T-04 minutes, 55 seconds and counting -- the liquid oxygen vent on the external tank is closed.

T-04 minutes, 00 seconds and counting -- the final helium purge of the Shuttle's three main engines is initiated in preparation for engine start.

T-02 minutes, 50 seconds and counting -- the external tank Gaseous Oxygen Vent Hood -- known as the beanie cap -- is raised and retracted. It had been in place during tanking operations to prevent ice buildup on the oxygen vents.

T-02 minutes, 00 seconds and counting -- STS-110 flight crew -- close and lock helmet visors.

T-01 minutes, 57 seconds and counting -- the external tank's liquid hydrogen is brought to flight pressure by closing the boil off vent, as was done earlier with the liquid oxygen vent.

T-00 minutes, 50 seconds and counting -- Orbiter transfers from ground to internal power.

T-00 minutes, 31 seconds and counting -- the Shuttle's onboard computers start their terminal launch sequence.

T-00 minutes, 16 seconds and counting -- the Sound Suppression System is activated and 400,000 gallons of water begins to pour onto the deck of the Mobile Launch Platform and Pad B to protect the Shuttle from acoustical damage at liftoff.

T-00 minutes, 10 seconds and counting -- the "go for main engine start" command is issued by the Ground Launch Sequencer. (The GLS retains the capability to command main engine stop until just before the Solid Rocket Boosters are ignited.) Concurrently, flares are ignited under the main engines to burn away any residual gaseous hydrogen that may have collected in the vicinity of the main engine nozzles. A half second later, the flight computers order the opening of valves which allow the liquid hydrogen and oxygen to flow into the engine's turbo pumps.