Why couldn't the space shuttle slow down in space and eliminate the dangerous temps during reentry?
Using the braking of the atmosphere is really good value (weight for weight, compared with fuel).
Who'd want to test pilot such a re-entry system? Several 'déja vue' situations in a row and each one just as likely to involve frying.FWIW, I don't think any crewed craft have used this (Per '2010' ?), only some space probes doing Mars' atmospheric braking to save fuel...
You don't solve any problems if you just use fuel to try to avoid the heating. That way is a straight trade off of fuel against heating penalty as far as I can see.Also keep in mind that the earlier you try to decelerate to avoid the heat, the longer gravity pulls you and thus the more fuel you need to constantly stay below the velocity needed to avoid the heat.
Perhaps not "without using fuel" but with some intelligent refrigeration system. The temperature difference between the surface of a 'hot' craft and the effective temperature of surrounding space is actually quite large so the performance coefficient could be pretty good.dissipate it as effectively as possible without using fuel.
Downside, your heat-shield & structure must tolerate such 'short cycling', must not 'soak' cumulative heat and, yes, must dissipate one dip's heat before starting the next...
FWIW, I don't think any crewed craft have used this (Per '2010' ?), only some space probes doing Mars' atmospheric braking to save fuel...
The front is really hot, the side is still very hot, and the back is a vacuum where you only have radiation. Dumping the heat into stuff inside the spacecraft is the only reasonable option for things that need cooling.Perhaps not "without using fuel" but with some intelligent refrigeration system. The temperature difference between the surface of a 'hot' craft and the effective temperature of surrounding space is actually quite large so the performance coefficient could be pretty good.
Zond 6 and 7 made a full orbit after slowing in the atmosphere.As far as I know aero-capture (i.e. dropping from hyperbolic to elliptical speeds via aerodynamic drag alone - a more intense form of aero-breaking) has not been performed in practice yet.
Zond 6 and 7 made a full orbit after slowing in the atmosphere.
I wouldn't argue with that but refrigeration systems do not rely on external convection to shed heat in principle. I did use the term "intelligent refrigeration" and that would need to involve a very hot heat sink. Obvs a liquid based refrigeration cycle wouldn't work.The front is really hot, the side is still very hot, and the back is a vacuum where you only have radiation.
Everyone always says it flies like a brick
I don't find the orbit description any more that I read a while ago but you can check e.g. Beyond Earth. Page 81 describes the Zond 6 re-entry, the first skip reduced the velocity to 7.6 km/s, that is the velocity of a low Earth orbit. With a eccentricity that gives you nearly a full revolution before you enter the atmosphere again. You could call it a very long skip.Didn't knew about those probes, thanks.
You mention they did a full orbit after aero-breaking, so I assume the probes did a "simple" ballistic aero-capture followed by reentry at next perigee? The wikipedia article mentions they employed skip-entry, but as I understand skip-entry that is a maneuver for sub-orbital speeds where lift is used to turn the trajectory upwards to extend the range.
You are not in orbit in the situation considered here.In fact, if the orbit were elliptical
Well, Google tells me the shuttle has an L/D max (glide ratio) of 4.5 on approach, but a 747 is 15. A Cessna 172 is 9. Sure, the method is the same - pitch for the glide airspeed - but it's a lot steeper.Yep. Shuttle was the result of the lifting body tests combined with the X15.
But her gliding is on par with a 747.
Just keep her at <370KIAS and she flies well enough
It's counter-intuitive, but glide ratio is pretty much independent of load:Is that an empty 747?
I usually fly the 747 full, and the shuttle empty.
Yes - I agree but in order to avoid too have a net gain of heat into the core of the craft during the process, you have two choices. You can let the surface get extremely hot and then cooling it down in the atmosphere before the core gets too hot or getting it less hot and losing the heat by another mechanism (based on some sort of refrigeration cycle / heat pumping ) but still avoiding the core getting too hot. Time is a factor because of the limited insulation available.you get maximum heat emission if you let the surface stay hot.
Google tells me the shuttle has an L/D max (glide ratio) of 4.5 on approach
I couldn't object to that statement - it's a general principle that applies everywhere. All I am suggesting is that a heat pumping system (perhaps made of unobtanium, of course) could increase the temperatures of parts of the surface that are cooler than the front and so increase the radiant heat loss. A re-entry that takes a long time has more of a problem with keeping the core cool because there is no atmosphere to provide last-minute fast cooling before the heat has diffused into the core.Well, there is simply no useful mechanism to get rid of heat by anything apart from dumping it into some material (the heat protection itself or some cooling system), evaporating material (the heat protection material, or some cooling fluid) or thermal radiation from the hot surface.
Do you mean somewhere to dump the heat that gets through? How would that not imply a large mass would be required?Once the heat is in the cooling system you are good, you don't need that much cooling fluid.
Any cooling system could only shed heat by radiation (from the back end, I imagine).
That's interesting but the amount of heat to be dealt with would be much more if water spray were used for re-entry. Latent Heat of water is pretty good but would it be enough? It's like other ablative systems in that you have to carry it with you all the way. A heat pump feeding a radiator would also require fuel mass. Would . could that be comparable with the mass of water needed for the same effect? I think the sums are beyond me and appropriate heat pump technology is probably not there yet, in any case.or the Shuttle, https://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/wsp/index.html was used both at lift-off and at reentry for normal cooling of internal systems (e.g. APU's and hydraulics), and these vent water steam overboard