Atmospheric reentry

Atmospheric reentry is the passage of a spacecraft or other object from space into a planet’s atmosphere. It involves intense aerodynamic heating and forces as the object encounters denser air.

Aerodynamic heating: Heating of an object caused by its motion through a fluid, especially at high speed. Compression and viscous effects heat a vehicle as it enters denser atmospheric layers.
Orbital velocity: The speed an object needs to remain in orbit at a given distance from a celestial body. Vehicles returning from orbit carry much of this speed into the atmosphere.
Crewed spacecraft: A spacecraft designed to carry people. Crewed vehicles must control entry loads and temperatures to return astronauts safely.
Reentry corridor: The range of trajectories that permit a vehicle to enter an atmosphere while meeting flight constraints. The corridor captures the narrow balance between skipping out of the atmosphere and descending too steeply.
Apollo 11: The 1969 Apollo mission that first landed humans on the Moon and returned them to Earth. Its command module used a heat shield and guided entry to bring the crew home.
Shock wave: A propagating disturbance in a fluid that produces abrupt changes in pressure, temperature, and density. A bow shock forms ahead of a fast reentry vehicle and contributes to its thermal environment.
Specific orbital energy: The orbital energy of a body per unit mass, determined by its speed and gravitational position. It helps describe how much energy a returning vehicle must shed before landing.
Space capsule: A compact spacecraft with a blunt, usually nonlifting shape, commonly used for crew or cargo return. Capsules use robust heat shields and parachutes for atmospheric return.
Skip reentry: A trajectory that briefly enters an atmosphere, gains altitude through aerodynamic lift, and later reenters more deeply. Skipping can extend range or reduce peak heating compared with a direct entry.
Apollo 13: The 1970 Apollo mission whose crew returned safely after an in-flight spacecraft emergency. The mission’s trajectory and power constraints made its Earth entry a demanding part of the rescue.

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