Reusable spaceplanes are spacecraft with wings that return from space by flying through the atmosphere and landing on a runway. They combine features of rockets, aircraft, and heat shield systems, which makes them important examples of applied physics and engineering. The Space Shuttle was the most famous operational spaceplane, and newer designs explore lower-cost access to orbit, rapid turnaround, and flexible mission profiles.
Their main promise is reuse, because recovering major vehicle parts can reduce the cost and waste of spaceflight.
Key Facts
- Orbital speed near low Earth orbit is about v = 7.8 km/s.
- Kinetic energy is KE = 1/2 mv^2, so re-entry from orbit involves enormous energy dissipation.
- Lift is approximately L = 1/2 rho v^2 C_L A, where rho is air density, v is speed, C_L is lift coefficient, and A is wing area.
- Drag is approximately D = 1/2 rho v^2 C_D A, and it helps slow the vehicle during re-entry.
- A spaceplane changes from spacecraft behavior in near vacuum to aircraft behavior as atmospheric density increases.
- Thermal protection systems protect the structure because re-entry heating can raise surface temperatures above 1000 degrees Celsius.
Vocabulary
- Spaceplane
- A spaceplane is a spacecraft with wings or lifting surfaces that can return through the atmosphere and land like an aircraft.
- Re-entry
- Re-entry is the phase when a spacecraft enters the atmosphere at high speed and converts much of its kinetic energy into heat and drag.
- Thermal protection system
- A thermal protection system is a set of heat resistant tiles, blankets, panels, or coatings that keeps a spacecraft from overheating during re-entry.
- Glide ratio
- Glide ratio is the horizontal distance traveled divided by altitude lost during unpowered flight.
- Crossrange
- Crossrange is the sideways distance a returning spacecraft can travel from its original ground track during re-entry and glide.
Common Mistakes to Avoid
- Thinking a spaceplane lands because its engines keep running, which is wrong because many spaceplanes glide unpowered after re-entry and use stored energy and lift to reach the runway.
- Ignoring re-entry heating, which is wrong because orbital kinetic energy must be removed and much of it becomes heat in the surrounding air and vehicle surfaces.
- Assuming wings work well in space, which is wrong because lift requires air density and wings become useful only when the vehicle enters the atmosphere.
- Confusing suborbital and orbital spaceplanes, which is wrong because an orbital vehicle must reach much higher speed and faces much greater re-entry energy than a suborbital vehicle.
Practice Questions
- 1 A 9000 kg spaceplane is moving at 7800 m/s in low Earth orbit. Estimate its kinetic energy using KE = 1/2 mv^2.
- 2 A returning spaceplane has a glide ratio of 4.5. If it begins its final glide 12 km above the runway, how far horizontally can it travel before landing, assuming the glide ratio stays constant?
- 3 Explain why a reusable spaceplane needs both a thermal protection system and wings, even though those systems are most useful during different parts of the mission.