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The Space Shuttle is a true aerospace vehicle:
Watch as astronaut, Paul "Paco" Lockhart, describes the orbiter's final landing sequence, as shuttle crew members practice their landings in the Vertical Motion Simulator. The video can be watched by downloading Real Player on to your computer. The video is approximately 80 minutes long.
To examine this phase, let's begin the de-orbit process. The shuttle orbits the earth at a velocity of 27,000 km/hr. (That's over 17,000 mph! Race cars in the Daytona 500 speed race travel at "only" 230 mph.) Because the orbiter is traveling so fast, several things must be done in order to slow its descent and guide the orbiter safely back to earth.
One of things the orbiter does to slow itself down is to position the orbiter with its nose up at a high angle of attack and its travel-path at a glide slope between 28 to 38 degrees for reentry into the atmosphere. Because this brings the orbiter in belly-first, it increases drag as a wider surface is passing through all those air molecules. Imagine if you tried to sink a "boogie-board" (Styrofoam toy that floats on water) to the bottom of a swimming pool. It is much more difficult to sink the board if you tried to push it down belly-first, than if you tried to sink it on its side edge. This is the same concept that keeps the orbiter from landing at such a high speed.
Secondly, the orbiter is designed with a double-delta wing configuration in which the forward placed delta wing creates vortices that flow smoothly over the main delta wing which creates greater lift and reduces drag. Its purpose is to optimize hypersonic flight and still obtain a good lift-to-drag ratio for landing. With this lift-to-drag capability, the orbiter is able to maneuver from side-to-side at a range of 2000 km (1240mi ). In a typical reentry, the orbiter is 2000 km away from the path of the runway and must fly, to its right, at its capacity range in order to position itself in line with the runway. This maneuver occurs 52 minutes before landing, with the shuttle at its maximum bank angle of 71 degrees.
The orbiter also performs a maneuver called a roll reversal, or S-turn. When the orbiter is 16 minutes away from touchdown, it begins its first of four S-turns which slows it down, just like a skier can slow down by making turns when coming downhill.
The rudder, which is on the tail of the orbiter, controls the yaw of the vehicle. The orbiter has a unique split-design rudder which allows it to also act as a speed brake. By pressing on both rudder pedals with both feet, the rudder "splits" open in a flat position just like a birthday card opens up. The rudder is opened to a full-out position ten minutes before the orbiter lands, but is soon adjusted to another position to provide assistance in directing pitch, as well as help reduce its speed.
The shuttle is flying on auto-pilot for much of the descent, because the air is not thick enough for the orbiter's controls to be effective. But at 4 minutes before landing, the shuttle commander takes manual flight control of the spacecraft and keeps the orbiter in line with the center of the runway. The commander takes the orbiter out of the steep, 22 degree, glide slope by sharply pulling the nose up. This, flare maneuver, reduces the glide slope to 1.5 degrees (which is nearly parallel with the runway) with the nose pointed up. The pilot then lowers the landing gear at 27 meters (90 feet) off the runway. The landing gear creates a lot of drag and slows the orbiter down from 530 km/hr (330 mph) to 340 km/hr (215 mph). At this speed, the commander can land the orbiter at a safe speed. The speed at which the shuttle lands is almost 2x as fast as commercial airplanes that you and I would fly on a vacation. Commercial airplanes normally land at a speed between 120-130 mph.
On touchdown, the orbiter activates its rudder once again to its full open position, and finally, the orbiter deploys a parachute to slow to a stop.
The accuracy of the landing is crucial because the orbiter lands like a glider does. It is not equipped with engines to give it thrust while flying in the Earth's atmosphere. Because it does not have engines like regular airplanes, the commander cannot abort a landing, give full thrust to the (non-existent) engines and circle the runway for another attempt. It has only one chance to land. Amazingly enough, the orbiter, which is traveling at such a high velocity, reenters the atmosphere at a point halfway around the world from its landing site. From this distant reentry, it is committed to its landing site.
Angle of Attack The picture shows the wing
of an aircraft
as it travels in a straight path parallel to the ground. The angle of
attack refers to the angle between the wing and its flight direction.
Angle of attack can change in two ways:
Glide Slope The picture shows the shuttle as it approaches the runway for landing. Glide slope of the shuttle refers to the angle between the flight direction of the shuttle with respect to the ground. To understand glide slope, read this scenario: Imagine you are on a 3-meter high diving board (This is the typical size diving board found at local pools). Let's say you were to dive, head-first, body completely straight, and with your arms out in front of your body. If someone were to take a picture of you the moment your hands hit the water, the angle your body makes with the water, would be the glide slope. In competition, divers try to enter the water at a 90 degree glide slope.
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