STS-135 T-10 Days - Shuttle Program

Shuttle Liftof

As we move into the final ten days, it is time to talk about the Space Shuttle.  The Shuttle is comprised of 4 major components.  The Orbiter is the part that goes into space carrying the astronauts and the cargo.  It has three liquid fuel rocket engines that are reused on each flight.  The fuel for the engine comes from the huge orange External Fuel Tank, which is jettisoned and discarded into the ocean when the fuel is exhausted..  Mounted on each side of the External Tank are two Solid Rocket Boosters. which provide 83% of the thrust needed for liftoff.  After 2 minutes, they are burned out, get jettisoned, and are retrieved for reuse after splashing down in the Atlantic. The final component of the Shuttle is the orbiter add-on, that is carried in the Orbiter bay and varies among flights.  Atlantis will carry a Multi-Purpose Logistics Module to the space station on it's last flight.  It will be the final supply trip to the space station from the US.  The flexibility to carry and return cargo in the huge bay has been the hallmark of the shuttle program.

Orbiter Approaching Space Station

As I continue the countdown, perhaps a word about the countdown is in order.  The most frequently heard portion starts at ten.  When growing up we used the 10, 9, 8... countdown to kick off many activities.  The countdown is linked to a very long checklist of items that must be performed in a specific order and with specific timing in order for the launch to occur.

Shuttle Final Countdown

The shuttle countdown begins at T-72 hours with the team called to their stations.  As the time ticks down, the shuttle is fueled, the astronauts board, all the equipment is checked, and everything else that has to be done. T-0 is liftoff.  With the shuttle, the main engines on the orbiter are ignited at T-6.6 seconds.  Huge bolts hold the shuttle to the pad as the engines build power in preparation for liftoff.  At T-0, the solid rocket booster on each side, are started and immediately provide the thrust needed to take off.  The bolts are exploded and off it goes. 

The Saturn V was ignited at T-3 seconds.  I remember watching TV videos taken at the bottom of the launch pad that showed the rockets firing and the latches holding it down as it built up power.  Then at the zero count, the latches pulled back and the rocket would start to lift.

http://en.wikipedia.org/wiki/Space_shuttle_launch_countdown

http://science.ksc.nasa.gov/shuttle/countdown/count.html#T-06H00M