The Space Shuttle was both a spacecraft and an aircraft, which made its return to Earth one of the most demanding flights in aviation history. After leaving orbit, the orbiter entered the atmosphere at hypersonic speed and had no engines for powered flight. From that point on, it became a heavy glider that had to manage energy, heat, lift, and drag with extreme precision.
Its subtitle, The Flying Spacecraft, captures this unusual role: it flew in space, then flew home through the air.
Understanding Aviation: The Space Shuttle
Reentry was first an energy-management task. The orbiter arrived from orbit carrying enormous kinetic energy because it was moving so fast. It could not get rid of that energy all at once.
A rapid descent into dense air would create heating and forces beyond its limits. Instead, it entered thin upper air at a high angle, where the atmosphere slowed it gradually. Much of the heating came from air being compressed in front of the vehicle.
The compressed air became extremely hot. Thousands of silica tiles protected most of the orbiter, while stronger carbon-carbon panels protected the nose and the leading edges of the wings. Damage in these areas was especially dangerous because hot gas could enter the structure.
The shuttle did not simply point at the runway and descend. Flight controllers planned a path called the entry interface corridor. This was a narrow range of altitude, speed, and flight path angle.
Too shallow, and the orbiter could skip back toward space or travel too far. Too steep, and heating and deceleration could become excessive. During reentry, it made large banking turns called heading alignment maneuvers.
Banking changed the direction of lift. This let the shuttle control its range and shed energy while staying within safe heating limits. The delta wing worked well in this regime because it remained stable at high speed and at a high angle of attack.
Its control surfaces had unusual jobs. Elevons along the trailing edge of each wing acted like elevators and ailerons. They controlled pitch and roll.
A body flap at the rear helped balance the strong nose-up effect produced during atmospheric flight. The vertical tail had a rudder that could split open to act as a speed brake. These surfaces had to work across very different air densities.
In thin air, the orbiter needed large movements to produce useful control forces. Lower down, the same movements could produce much stronger forces. Pilots and computers constantly adjusted the vehicle to keep it on the planned path.
Near the runway, the shuttle had little margin for error. Its wings produced relatively little lift compared with the drag they created. This meant it descended much more steeply than an airliner and could not circle around for another attempt.
The commander aimed at a point well short of the runway, then raised the nose in a flare to reduce the descent rate. Landing gear, wheel brakes, and a drag chute helped slow the heavy vehicle after touchdown. Students learning this topic should connect speed, air density, lift, drag, heating, and control.
Each changes during descent. The shuttle shows that a successful landing begins far above the runway, with careful choices made while the vehicle is still moving through the edge of space.
Key Facts
- During landing, the Space Shuttle orbiter was unpowered and flew as a glider.
- Lift equation: L = 1/2 rho v^2 A CL, where rho is air density, v is speed, A is wing area, and CL is lift coefficient.
- Drag equation: D = 1/2 rho v^2 A CD, where CD is drag coefficient.
- The orbiter used a delta wing, which helped with stability and control at high speeds and high angles of attack.
- Typical landing speed was about 214 to 226 mph, much faster than many commercial airliners at touchdown.
- The final approach was very steep, about 18 to 20 degrees at first, compared with about 3 degrees for a typical airliner.
Vocabulary
- Orbiter
- The winged Space Shuttle vehicle that carried astronauts to space and returned to Earth as a glider.
- Hypersonic
- A speed regime faster than Mach 5, or more than five times the speed of sound.
- Delta wing
- A triangular wing shape that can handle high speed flight and provide useful lift and control during reentry.
- Angle of attack
- The angle between the direction of airflow and the reference line of a wing or vehicle.
- Glide ratio
- The distance an aircraft travels forward divided by the altitude it loses during unpowered flight.
Common Mistakes to Avoid
- Thinking the Shuttle used jet engines to land is wrong because the orbiter had no air-breathing engines and made its approach entirely unpowered.
- Treating the Shuttle like a normal airplane is wrong because it had a much steeper descent, higher landing speed, and lower glide performance than typical aircraft.
- Assuming reentry was just falling straight down is wrong because the orbiter used lift, banking turns, and drag to control its path and reduce speed.
- Ignoring air density in lift and drag calculations is wrong because both lift and drag depend on rho, so the forces change greatly as the orbiter descends into thicker air.
Practice Questions
- 1 A Shuttle-like glider has a glide ratio of 4.5:1. If it loses 8 km of altitude, how far forward can it travel in still air?
- 2 During final approach, suppose the orbiter descends at an 18 degree angle. If it travels 12 km horizontally, about how much altitude does it lose? Use altitude loss = horizontal distance times tan(18 degrees).
- 3 Explain why the Space Shuttle needed a steep approach and careful energy management during landing, even though it had wings like an airplane.