Artist's concept of re-entry to Earth's atmosphere.
NASA has awarded the thermal protection system design and development contract to the Boeing Company; Fiber Materials Inc. (FMI) will be the principal subcontractor. The new TPS design will be used with the Orion crew exploration vehicle - the spacecraft that will take astronauts back to the moon.
NASA Ames Research Center has awarded the $14 million contract for the development of a phenolic impregnated carbon ablator (PICA) heat shield. The PICA shield was first used on the Stardust interplanetary spacecraft launched February 7, 1999 to study the composition of the Wild 2 comet. It successfully reentered Earth's atmosphere January 15, 2006. The capsule was traveling at 28,900 miles per hour (46,510 kilometer per second), the fastest reentry speed ever achieved by a man-made object. FMI fabricated the heat shield for the Stardust sample return capsule.
The ability to survive high speed reentry is an important consideration for the Orion spacecraft. Orion is intended to perform lunar-direct returns, which result in considerably higher speeds; the spacecraft will need to withstand about five times more heat than experienced by spacecraft returning from the International Space Station.
The best protection against high heat flux is an ablative heat shield. The extreme heat of reentry causes the material to pyrolize - the chemical decomposition of a material by heating in the absence of oxygen. As the PICA chars, melts and sublimates, it creates a cool boundary layer through blowing, protecting the spacecraft.
The first work on the technology of reentry was done in the early stages of the cold war. Intercontinental missile warheads would evaporate during reentry unless a protective technique could be found. Work that began at Douglas Aircraft Company's Project RAND in 1952 suggested that ablation cooling would be the best technique.
There is an interesting science fiction precursor to the idea of ablative cooling. In his 1934 novel Triplanetary, E.E. 'Doc' Smith wrote about a technique for jumping out of a supersonic plane traveling at 2,000 miles per hour in near vacuum.
...He rolled the ball out onto the hatch, where he opened
it: two hinged hemispheres, each heavily padded with molded composition
resembling sponge rubber...
...He curled up into one half of the ball; the other half closed over him and locked. The hatch opened. Ball and closely-prisoned man plummeted downward..
And as the ball bulleted downward on a screaming slant, it shrank!
...a synthetic which air-friction would erode away, molecule by molecule, so rapidly that no perceptible fragment of it would reach ground.
(Read more about Doc Smith's ablative heat shield)
Edward Elmer Smith had a doctorate in Chemical Engineering; that's a good place to start in writing hard science fiction.
(This Science Fiction in the News story used with permission from Technovelgy.com - where science meets fiction.)