Heat Shield Shape Ablative Heat Shields Reusable Heat Shields

The simplest and cheapest type of heat shield is the ablative heat shield, which dissipates heat from the plasma by allowing its outer layers to vaporize.

All of the early spacecraft with the exception of the early Mercury capsules used ablative technologies to assist with the transition from high orbital speeds down to aerodynamic regimes where a spacecraft can be flown or parachuteApollo 15 capsule landed safely despite a parachute failure. A parachute is a device used to slow the descent of a falling body or load. The word parachute comes from the French words para, protect or shield, and chute, to fall. Therefore parachute actuald to safety.

Such heat shields are used on virtually all expendable spacecraft and on many ballistic missiles, since it doesn't matter whether they can withstand a second reentry.

3 Reusable Heat Shields

When the reusable Space Shuttle system was designed, it was decided that a non-reusable heat shield would not be an efficient approach. Instead the Space Shuttle's underside was coated with thousands of ceramic tiles that were intended to be able to survive multiple reentries with only minor repairs between missions. However, the original design proved to be somewhat less robust than intended; the Shuttle suffered from frequent lost and damaged tiles, and ultimately the Space Shuttle ColumbiaShuttle Orbiter Columbia (NASA Designation: OV-102 was the first space shuttle in NASA's orbital fleet, first flying mission STS-1 from April 12 to April 14, 1981. It was lost with all crew when it disintegrated during re-entry on its 28th mission, STS-10 was destroyedSTS-107 on launch day STS-107 was a space shuttle mission by NASA using the Space Shuttle Columbia''. The entire seven member crew was killed on February 1, 2003, when the shuttle disintegrated over Texas during reentry into the Earth's atmosphere. This w with all hands when a piece of insulating foamThe most general definition of foam is a substance that is formed by trapping many gas bubbles in a liquid or solid. It can also refer to anything that is analogous to such a phenomenon, such as quantum foam. Often people mean polyurethane foam, Styrofoam from its external fuel tank fell off and damaged the heat shield on its left wing.

4 Passive Cooling

In some ballistic missiles and the sub-orbitalFor other meanings of the term "orbit", see orbit (disambiguation In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. History Orbits were first analyse Mercury spacecraft, heat sinks were used to dissipate the plasma heat. However the technique required a considerable quantity of metal material, adding greatly to the mass. Consequently ablative or reusable shields are now far more common.

Some high-velocity aircraft, such as the SR-71 Blackbird and Concorde, have to deal with heating similar to that suffered by spacecraft but with lower intensity. Shockwaves can attach to the pointed nose and heat the aircraft through wave drag. Generally heat is conducted through the aluminium or titanium alloy, or occasionally stainless steel skins. In the case of Concorde the nose is permitted to reach a maximum operating temperature of 127 degrees C, typically 180 degrees warmer than the external air.

5 Active Cooling

Various advanced reusable spacecraft and hypersonic aircraft designs have been proposed recently that employ heat shields made from temperature-resistant metal alloys, some of them including active cooling systems in which water or cryogenic fuel is circulated over or through them.

6 Temperatures

The most violent reentry temperatures (14,000 degrees C) successfully survived by a spacecraft were those endured by the Jupiter atmospheric probe carried by the Galileo spacecraft, which entered the giant planet's atmosphere at 106,000 miles per hour (170,700 km per hour). The heat shield, made from carbon-phenolic, made up around 50% of the probe's mass prior to entry.

7 See Also

Conservation of energy for details of the conversion of kinetic energy into heat energy.

Spacecraft components

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1 Shape

2 Ablative Heat Shields