Tuesday, September 21, 2010
We Fly The Space Shuttle (Simulator, That Is)
What’s it like to reenter the atmosphere from Earth’s orbit?
At two minutes, the Shuttle is passing through Mach 4 and is already climbing through 150,000 feet. At this point, the spacecraft is burning about 60,000 gallons of fuel a minute. Looking out the side windows, you’ll see the flash of the SRBs shutting down and separating from the stack. The SRBs parachute down and land in the Atlantic where they’re retrieved for use on a future launch. Now, the Shuttle is flying on its three main engines, still burning fuel from the giant external tank.
At five minutes, I glance out the small, left window to see what I’m told is the outline of the Chesapeake Bay drifting by below. The simulator’s depictions of Earth aren’t very realistic, but they don’t need to be, as astronaut trainees have little use for the outside display. Considerations of IFR and VFR become irrelevant in an aircraft designed to operate outside the atmosphere.
At just under nine minutes after launch and 75 miles altitude (roughly 400,000 feet), the main engines shut down and the orange tank is ejected at the equivalent of Mach 25, typically 75 miles up, and the Shuttle continues to coast uphill at 500 feet per second to orbit. In total, the Shuttle’s climb to altitude requires some 45 minutes, and all but the first nine minutes is without power. Once established in orbit, the Shuttle circles the Earth every hour-and-a-half in a typical orbit at 180 miles.
Return To Earth
At the conclusion of the orbital flight, the Shuttle begins the reentry process in what most pilots would consider an unusual manner. For several good reasons, the spacecraft typically flies in space upside down and backward with reference to the Earth.
The most important reason is that flying backward with the engines in the rear provides the crew with maximum protection from micrometeorites and space debris. Second, all the windows on the Shuttle are on the top of the fuselage, and since there’s no up or down in space, it’s logical to fly inverted to orient the windows toward Earth. Third, those 34,000 heat-shielding silica tiles on the belly of the aircraft help protect the crew from the heat of the sun, no longer filtered through the atmosphere. In the direct light of the sun in orbit, OAT in space can rise to 121 degrees C (250 degrees F).
The deorbit process begins with a three-minute burn of the orbital maneuvering system (OMS) engines, slowing orbital velocity by about 200 mph. This slows orbital velocity to a mere 17,000 mph, not enough to keep the spacecraft in orbit, and the Shuttle slowly begins to descend. To manage the reentry, the computer maneuvers the spacecraft through a half somersault to fly belly down, nose forward, the equivalent of straight and level. (The commander or pilot can fly the full reentry if necessary, but most of the time, the computer will do a more accurate job.)
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