Aerodynamic Heating - Reentry Vehicles

Reentry Vehicles

Aerodynamic heating is also a topic of concern in reentry vehicles. The heating induced by the very high speeds of reentry of greater than Mach 20 is sufficient to destroy the structure of the vehicle. The early space capsules such as those on Mercury, Gemini, and Apollo were given blunt shapes to produce a stand-off bow shock. As a result most of the heat is dissipated to surrounding air without transferring through the vehicle structure. Additionally, these vehicles had ablative material that sublimates into a gas at high temperature. The act of sublimation absorbs the thermal energy from the aerodynamic heating and erodes the material away as opposed to heating the capsule. The surface of the heat shield for the Mercury spacecraft had a coating of aluminum with glassfiber in many layers. As the temperature rose to 2,000 °F (1,100 °C) the layers would evaporate and take the heat with it. The spacecraft would become hot but not harmfully so. The Space Shuttle used insulating tiles on its lower surface to absorb and radiate heat while preventing conduction to the aluminum airframe. The compromise of the heat shield during liftoff of Space Shuttle Columbia contributed to its destruction upon reentry.