[AR] supersonic retro (was Re: Re: Falcon 9 flight today)
- From: Henry Spencer <henry@xxxxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Wed, 2 Oct 2013 13:32:22 -0400 (EDT)
On Wed, 2 Oct 2013, Aplin Alexander T wrote:
> Musk pointed out during the post-flight Q&A that "I believe the first
> time that any rocket stage has attempted to do a supersonic
> retro-propulsion." Apparently it was successful (this was the 1st
> stage's initial 3-engine re-entry burn).
If you interpret "retro-propulsion" in the specific sense of firing main
engines forward while still in detectable atmosphere, yeah, I think
that's true. Kistler was going to do it, but they never flew. Nor did
the shuttle ever do an RTLS abort.
The Apollo LM did supersonic retro-propulsion down to landing, but that
was in vacuum. And many rocket stages have fired small solid-fuel retros
as part of stage separation, but that's not quite the same thing either.
> IIRC super-sonic retro-propulsion is one of the unknowns encountered in
> planning manned (and other large-payload) landings on Mars.
Yes, there's a problem with the Martian atmosphere just not being thick
enough to brake a big lander (with a lot of mass behind every square
meter of forward surface) adequately. Supersonic retro-propulsion seems
to be the current favorite answer to this.
(One caveat: I've never seen a detailed analysis of the problem with the
assumptions explicitly stated and justified. I have a faint suspicion
that possibly-feasible alternatives may have been neglected because
supersonic retro-propulsion was the pre-chosen winner.)
> I've always been surprised than no one's tried it before - is it
> something amateur rocketry could investigate here on earth?
If you mean doing tests that would actually be relevant to stage return
and/or Mars descent, I think it would be a considerable challenge, because
you have to start high up, in thin air, moving fast. Just getting to
those initial conditions isn't easy for amateurs.
Henry Spencer
henry@xxxxxxxxxxxxxxx
(hspencer@xxxxxxxxxxxxx)
(regexpguy@xxxxxxxxx)
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