Re: SpaceShipOne and reentry heat

From: David Given (dg_at_cowlark.com)
Date: 06/25/04 

To: sci-space-tech@moderators.isc.org
Date: Fri, 25 Jun 2004 13:00:09 +0100

On Thu, 24 Jun 2004 09:18:51 -0700, Tony Rusi wrote:
[...]
> Interesting, for any spacecraft, if more fuel were used on orbit to
> bring the (actually tangental) velocity component closer to zero, then
> reentry heating shielding requirements are minimal like SS1. Maybe a
> heat tile damaged spaceshuttle could re-enter the same way? Maybe this
> last crew could have been saved with more fuel and/or less space shuttle
> mass and momentum. Maybe they could have taken an engine and tank off,
> performed a slowing burn, got into their emergency transfer beach balls
> and parachuted from 200k? Iknow probably not enough fuel, no way to pull
> an engine and tank off, no transfer beach balls on board, etc. etc.

There are people here with more technical knowledge than I, but I do know
that the shuttle's main engines aren't restartable. (Do they even have
on-board fuel tanks?) On-orbit, the shuttle manouvers using a completely
different set of engines, the OMS, that has a very small dV capacity. IIRC
it's about the most the OMS can do just to get the shuttle onto a reentry
trajectory.

*However*, it suddenly occurs to me that surviving reentry is actually
pretty simple in the appropriately designed vehicle: passive capsules like
the Soyuz and Apollo return vehicles are old, reliable technology.
(They're aerodynamically stable, and because they're only going to be used
once you can use ablative shielding rather than the TPS tiles.) They're
also small, in mass and volume.

How about fitting the shuttle out with a lifeboat? Stick it somewhere in
the cargo bay. If a shuttle gets sufficiently damaged that it can't
reenter, you use the capsule to get the crew down.

Depending on whether the capsule had its own thruster system, you would
get the choice of putting the shuttle onto a reentry trajectory and then
bailing out, or leaving the shuttle on orbit and just returning in the
capsule. The first option would almost certainly lose the shuttle, but if
you have to use the capsule the shuttle's probably not going to survive
reentry anyway. The second option would leave the shuttle intact in orbit,
where it could (possibly) be repaired, but would require the capsule to
have a fairly decent dV capacity. You'd also have to outfit the shuttle
with an automated station-keeping facility using the OMS; you wouldn't
want it to accidentally fall on someone.

(What's the lightest-weight way of getting a single human down from orbit?
Could you build something like an orbital parachute? If so, would that be
more appropriate than a combined capsule?) 

-- 
+- David Given --McQ-+ "Every planet is weird. I spent six weeks on a
|  dg@cowlark.com    | moon where the principal form of recreation was
| (dg@tao-group.com) | juggling geese. Baby geese. Goslings. They were
+- www.cowlark.com --+ juggled." --- Firefly, _Our Mrs. Reynolds_

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