Discovery update

After a successful twelve days in space, shuttle Discovery is set to return to earth on Monday morning. NASA gave the shuttle the final thumbs up, as a final round of tests and checks were run testing everything from the external heat shield, to internal storage tanks. The crew will now prepare to start the process of re-entry. It is a process that is so fascinating to me that I had to share it (my thanks to NASA for the information that I am about to share with you all).

TIG-4 hours-Crew members begin preparations for landing. The orbiter's onboard computers are configured for entry, as is the hydraulic system that powers the orbiter's aerosurfaces -- its rudder speed brake and wing elevons.

TIG-3 hours-The payload bay doors are closed. Mission Control gives the commander the "go" for Ops 3, the portion of the orbiter's flight control software that manages entry and landing.

TIG-2 hours-Starting with the commander and pilot, the flight crew members don their orange launch and entry suits and strap into their seats.

TIG-1 hour-Mission Control gives the "go" for deorbit burn.

DEORBIT BURN-The orbiter and crew are officially on their way home.During reentry and landing, the orbiter is not powered by engines. Instead, it flies like a high-tech glider, relying first on its steering jets and then its aerosurfaces to control the airflow around it.
This is by far the most fascinating step, the shuttle is actually upside down and backwards as it heads back into the atmosphere. At this point the Shuttle is traveling at an extraordinary speed of over 16,000 mph.

Landing-30 minutes-Roughly half an hour after the deorbit burn, the orbiter will begin to encounter the effects of the atmosphere. Called entry interface, this point usually takes place at an altitude of about 80 miles, and more than 5,000 statute miles from the landing site.Early in reentry, the orbiter's orientation is controlled by the aft steering jets, part of the reaction control system. But during descent, the vehicle flies less like a spacecraft and more like an aircraft. Its aerosurfaces -- the wing flaps and rudder -- gradually become active as air pressure builds. As those surfaces become usable, the steering jets turn off automatically.To use up excess energy, the orbiter performs a series of four steep banks, rolling over as much as 80 degrees to one side or the other, to slow down. The series of banks gives the shuttle's track toward landing an appearance similar to an elongated letter "S."As the orbiter slices through the atmosphere faster than the speed of sound, the sonic boom -- really, two distinct claps less than a second apart -- can be heard across parts of Florida, depending on the flight path.

Landing-5 minutes-The orbiter's velocity eases below the speed of sound about 25 statute miles from the runway. As the orbiter nears the Shuttle Landing Facility, the commander takes manual control, piloting the vehicle to touchdown on one of two ends of the SLF.As it aligns with the runway, the orbiter begins a steep descent with the nose angled as much as 19 degrees down from horizontal. This glide slope is seven times steeper than the average commercial airliner landing. During the final approach, the vehicle drops toward the runway 20 times faster than a commercial airliner as its rate of descent and airspeed increase. At less than 2,000 feet above the ground, the commander raises the nose and slows the rate of descent in preparation for touchdown.

Landing-15 seconds-The main and nose landing gear are deployed and locked in place.

Touchdown! The orbiter's main landing gear touches down on the runway at 214 to 226 miles per hour, followed by the nose gear. The drag chute is deployed, and the orbiter coasts to a stop.

Discovery is set to land at Kennedy Space Center on runway 33 at 8:14 am Central time tomorrow morning. The weather at KSC has been suspect all day with rain and heavy cloud cover expected to last into tomorrow. There is an alternate landing time at KSC for 9:50 am CST. There is also the possibility of the shuttle landing at Edwards Air Force Base in California if needed (which is where Discovery landed last year on STS-114). The shuttle has enough resources and fuel to stay in space until Wednesday if needed.