On Sat, 15 Feb 2003 [EMAIL PROTECTED] wrote:
> If one assumes that that vertical takeoff, base-first reentry, and vertical
> landing is the simplest and lightest way to make an SSTO...
Note a fine point: you can use separate landing engines. While using the
same engines seems attractive, the thrust requirement is very much lower,
feed arrangements might want to be different if you've got separate tanks
for landing fuel, and the mass penalty for separate engines is not large.
> 1) Let the nozzles project a bit beyond the heat shield and just come in that
> way; they're made for more heat going up than they'll see coming down.
> (Problems: engines radiate a lot of heat; nice to have that outside the
> spaceship.)
And as already noted, sharp edges sticking forward get awfully hot,
especially if they're long enough to project beyond the main bow shock.
> 2) 2-part clamshell heat shield. (Problems: complexity, seam in shield,
> failure mode)
Back when X-34 was an air-launched TSTO, for configuration reasons one
version of it reentered upside-down, to avoid hot-surface doors. When
someone in the Space Access audience asked if such doors were that big a
deal, given that the shuttle has them, somebody else in the audience stood
up and said: "I designed the shuttle's landing-gear doors, and I think
the X-34 is doing the right thing".
Any scheme which involves major mechanical movement to go from takeoff
configuration to landing configuration may have trouble with abort cases.
> 4) vertically retractable engines and doors. (Problems: structural
> engineering, moving parts, failure modes).
Assorted variations exist -- think aircraft landing gear. Notably,
engines can retract by pivoting, more-or-less around the gimbal bearing
(or where a gimbal bearing would be, if the engines aren't gimbaled),
which eases the structural problems considerably.
You can eliminate the retraction part by having the engine exit plane
roughly flush with the lower surface, although it may make the door
design harder.
> 7) inject water into engines, which will turn to steam as they get hot and
> protect them. (Problems: corrosion, mass, complexity)
Phil Bono liked to run LH2 through the base of his aerospike to cool it
during reentry, and dump the resulting GH2 through the engines. If you
are using transpiration cooling for the vehicle base, that may keep the
engines cool enough without any special arrangements, if they don't stick
out much.
Henry Spencer
[EMAIL PROTECTED]
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