[EMAIL PROTECTED] wrote:
Gentlefolk,Having them sticking out definitely moves them towards the shockwave boundary. It's like having a sharp nose on your reentry. You might get away with it if you make them of carbon-carbon I suppose, but it's somewhat problematical. Also it pushes up the hot gas surface area, the air under the vehicle stagnates and your nozzles sit right in it.
This is possibly an old topic, but I'd like to hear what people think.
If one assumes that that vertical takeoff, base-first reentry, and vertical landing is the simplest and lightest way to make an SSTO, what's the best way of dealing with the engines on reentry. Several possibilities present themselves.
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.)
It could work though.
2) 2-part clamshell heat shield. (Problems: complexity, seam in shield, failure mode)Yes, this could work too. The seam is probably less difficult than you think- if you maintain a positive pressure inside the clamshell you may avoid hot gas ingress. Also the shuttle has that kind of problem with it's wheels, and appears to have solved it 115/117 of the time anyway.
3) horizontally retractable engines on the sides (Problems: structural engineering, moving parts, engine-out dynamics, failure modes).
Well, the engines may well need thrust vectoring anyway...
4) vertically retractable engines and doors. (Problems: structural engineering, moving parts, failure modes).
Could work, don't like; looks heavy.
5) deployable mini-shield, or spike, to protect the engine cluster, annular shield farther back to protect everything else. (Problems, moving parts on the deployable shield, reentry dynamics)Probably nothing special about the engines; they need cooling too during reentry. They may survive with less cooling, but they still need it- a spike mainly moves the boundary away further I think, the heating is lowered a bit, but the air still stagnates under the vehicle, it's not enough on its own.
6) save enough fuel to fire the engines at low thrust during reentry (Problems: mass)
I'd imagine that would take a lot of fuel.
7) inject water into engines, which will turn to steam as they get hot and protect them. (Problems: corrosion, mass, complexity)I actually think that that works for protecting the inside of the engines. The outside surface is more difficult, and is about as big.
There are likely other ideas as well. I'd be interested in your thoughts.Inflatable reentry shield? That's got lots of theoretical advantages; the inflated cross-section area can be large (== lower thermal issues) and it can cover the whole base of the vehicle and then some. In theory you can control its diameter to minimise peak g-force. You could deploy it on orbit; make sure it was out before reentry and then reenter. One was tested by the Ruskies fairly recently; it worked. Not sure what the maximum vehicle size these inflatables can support is though.
--Best, Gerald
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