Re: Brute force re-entry

From: Jeff Findley (jeff.findley_at_ugs.nojunk.com)
Date: 08/25/04 

To: sci-space-tech@moderators.isc.org
Date: Wed, 25 Aug 2004 11:15:01 -0400

"Allen Meece" <navigaiter2002@aol.comSpamsuX.retro.com> wrote in message
news:20040822223359.28808.00001501@mb-m26.aol.com...
> <<I think the point that he was trying to make was that given the steep
> angle of re-entry that NASA always uses, you might as well be "running
> directly into the planet at full speed" instead of "skipping repeatedly
> off the top of the atmosphere to shed speed">>
> True. Flying into reentry is more elegant than plunging downward and
also
> cheaper and easier compared to heavy duty thermal tile systems. It's what
we'll
> need to do for CATS, cheap access to space.

It may appear to be more elegant, but it's much harder to do. This is
because you either need a great deal of L/D, or you need to burn fuel to get
back out of the atmosphere every time you "skip". Either way, this would
only be a net "win" if you could shead heat from your TPS quickly while out
of the atmosphere. This limits your TPS materials greatly (shuttle tiles
don't shead heat quickly). If your TPS can't shead the heat while out of
the atmosphere, the "skipping" trajectory will be worse in terms of total
heat load than a "traditional" re-entry.

> Critics wrongfully claim it'll take lots of braking fuel to get the
speed
> down but that's boar wash. The ship is nearly empty so short thrusting
will be
> enough to slow it down enough to start skipping into the outer atmosphere.

This is what the shuttle and capsules already do. The re-entry burn is only
big enough to make the orbit intersect the atmosphere. The reason they
don't typically skip is due to the L/D and materials issues.

Jeff 

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