Slide 1
Reentry must remove much of the spacecraft’s kinetic energy
A returning spacecraft must shed much of its orbital kinetic energy. Atmospheric entry transfers energy into the surrounding gas and the vehicle’s thermal environment.
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A parachute cannot safely replace the first part of this process at orbital speed. The craft must slow through earlier entry phases before parachutes can operate within their designed conditions.
Slide 2
A shock heats the gas ahead of the vehicle
At hypersonic speed, a shock forms ahead of an entering vehicle. Strong compression and other flow processes create a very hot layer of gas.
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Describing entry heating only as surface rubbing misses much of the physics. Chemical changes, ionization and radiation can matter in the heated flow, especially at high entry speeds.
Slide 3
A blunt shield holds the strongest shock away
A blunt heat shield can hold the strongest shock away from the vehicle. Its geometry influences both aerodynamic braking and the heat reaching the surface.
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A shape that looks streamlined for ordinary flight may be unsuitable for entry. The design objective includes controlling heat transfer, not merely minimizing aerodynamic drag.
Slide 4
Thermal protection changes or insulates to manage the heat
Ablative materials protect a spacecraft partly by undergoing controlled physical and chemical changes. Other systems use insulating materials designed to remain in place.
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Ablation consumes material and carries away energy, while insulation limits transfer toward the structure. These approaches involve different mass, inspection and reuse considerations.
Slide 5
Entry angle and speed determine the heating history
Entry angle, speed and vehicle control determine the heating and deceleration history. Engineers test protection systems against the conditions their trajectory will produce.
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Peak heating and total absorbed heat are different design measures. A brief intense event and a longer milder event can challenge materials in different ways even if one number appears similar.
Sources
- Core Area of Expertise: Entry Systems
NASA Ames Research Center
- Heat Shield Testing Recycles Waste on Earth
NASA
- Orion: Testing
NASA
- Ames Contributions to Apollo
NASA