[ERPS] X-15 reusability, parachutes

[John Carmack]

A thought occurred to me today -- the X-15 is usually held up as the best example of reusable space transport actually fielded. The vehicle lands like an aircraft, but the lower fin is jettisoned before landing and recovered by parachute. A vehicles turnaround time is limited by the most difficult things to recover / refurbish, so parachutes didn't seem to critically harm the cycle time. Anyone know how many fins were lost? I know at least one was jettisoned very low.

A couple data points for parachute systems:

A military G-12 cargo chute is baselined for a 2000 lb load at 28 fps sink rate, and weighs 140lb. Butler parachutes has made a lightweight replacement for this that only weighed 44 lb, but it wasn't as robustly reusable. Even counting very heavy drogues, and a completely redundant system, it looks like our parachute system for the X-Prize vehicle is going to come in at 5% of vehicle dry mass. The crushable nose cone could be considered part of the recovery system, but we have to have it there for streamlining anyway, so it is sort of "free".

I'm still rather fond of rotors of some sort for landing, but they are going to take a bunch more work to develop.

John Carmack

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