Reentry capsule
Because a capsule shape has little aerodynamic lift, the final descent is via parachute, either coming to rest on land, at sea, or by active capture by an aircraft.
Reentry capsules have typically been smaller than 5 meters (16 feet) in diameter due to launch vehicle aerodynamic requirements.
The Orion Multi-Purpose Crew Vehicle appears likely, as of December 2005, to use a ten-times reusable capsule with a replaceable heat shield.
Materials for the capsule are designed in different ways, like the Apollo command module’s aluminum honeycomb structure.
The early spacecraft had a coating of glass embedded with synthetic resin and put in very high temperatures.
The space capsule must be strong enough to withstand reentry forces such as drag, and must reenter at a precise angle of attack to prevent a skip off the surface of the atmosphere or destructively high accelerations.
Parachutes are used for the final descent, sometimes augmented by braking rockets if the capsule is designed to land on the Earth's surface.
Whereas delta-wing gliders such as the Space Shuttle can reenter from Low Earth Orbit, and lifting bodies are capable of entry from as far away as the Moon, it is rare to find designs for reentry vehicles from Mars that are not capsules.
The capsule must be strong enough to slow down quickly, must endure extremely high or low temperatures, and must survive the landing.
Capsules reenter aft-end first with the occupants lying down, as this is the optimum position for the human body to withstand the decelerative g-force.
Rotational thrusters were used to steer the capsule under either automatic or manual control by changing the lift vector.
When the capsule comes through the atmosphere, it compresses the air in front of it which heats up to very high temperatures (contrary to popular belief friction is not significant).
A shooting star, which is usually tiny, creates so much heat coming through the atmosphere that the air around the meteorite glows white hot.
The new Soyuz TMA spacecraft, now used solely for International Space Station flights, had its couches modified to allow for taller crewmembers to fly, and features "glass cockpit" technology similar to that found on the Space Shuttle and newer commercial and military aircraft.
Soyuz 1 ended in disaster when the parachutes failed to deploy and the capsule smashed into the earth at speeds over 300 mph (483 km/h), killing cosmonaut Vladimir Komarov.
Soyuz 5 almost ended in disaster, when the reentry capsule entered the atmosphere nose first – attributed to a failure of the service module to separate similar to that on the Vostok 1 flight.
