Chair Force Engineer

Friday, February 05, 2010

A Capsule of Knowledge

Rob Coppinger has an excellent piece about the demise of the Orion spacecraft, complete with pics of the Boeing/Bigelow spacecraft that's being dubbed "Orion-Lite." (Ironically, the cancellation comes just a week after a good friend suggested I should apply for a LockMart job in Denver working on Orion.) He makes a lot of good points about the distinctons between a capsule designed for missions to low-earth orbit versus a lunar-capable capsule. A beefier heatshield, more consumables and radiation shielding, and bigger parachutes are just some of the differences which necessitate a nontrivial redesign for a "Block II" spacecraft that can return from the moon.

But is it necessary to lug the capsule and reentry systems with you on voyages to the moon, Mars or asteroids? Some of Mr. Coppinger's commenters make this point as well. The parachute deployment pyros and heat shields might not hold up well when exposed to the cold vacuum and intense radiation of the space environment for extended-duration missions. If we follow some of Buzz Aldrin's old advice, we'd be flying reusable "cycler" spacecraft to Mars. Such a cycler would presumably aerobrake into orbit around Earth, where a capsule could be launched from Earth to recover the crew. A similar strategy could be followed for a lunar transportation architecture.

The jury is still out on how you'd recover a crew at the end of a round-trip Mars mission. Would they aerobrake into orbit around earth and spend a quarantine at a space station before being allowed to return to Earth? Or is it possible to spread out the deceleration forces from re-entry so that the stresses would not kill a crew that had been weakened by 900 days of minimal gravity? Boeing's 1968 IMIS proposal for sending humans to Mars posited a biconic "Earth Entry Module" to give astronauts a low-G, lifting re-entry. Other plans have ended with retrieval from the space station.

In many ways, Orion was a design tailored for the lunar mission. It was heavier than necessary for space station missions, yet probably not robust enough for a trip to Mars and back without some major modifications. I don't lose too much sleep about its cancellation, and I hope that its commercially-designed replacements benefit from Orion "lessons learned." Regardless, the traditional paradigm of "carry all your reentry systems with you" has its limitations, and it should be rigorously challenged as America feels its way along the "flexible path."