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Could a spinning disk dropped from orbit survive speeds faster than conventional aircraft in our atmosphere? Does the rate of spin matter when dispersing heat? Does a spinning disk create stability from tumbling at hypersonic speeds?

Some hypersonic planes don't appear to have a blunt edge at the nose. I want to say a blunt edge is design either not to melt off and/or help slow the vehicle. I am on the fence if a blunt edge would be needed for a disk that glides in?

enter image description here Hypersonic Technology Vehicle 2 (HTV-2) is a crewless, experimental hypersonic glide vehicle rocket glider developed as part of the DARPA Falcon Project capable of flying at 13,000 mph (Mach 17.53, 21,000 km/h) https://en.wikipedia.org/wiki/DARPA_Falcon_Project

enter image description here This is a picture of the experimental HTV-2 sub-orbital hypersonic re-entry glider with a sharp profile but in the form of a disk to disperse heat away from the edge for a higher top speed. Could this wing profile be adapted to a disk?

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  • $\begingroup$ Related $\endgroup$ – Pondlife Nov 6 '17 at 13:51
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    $\begingroup$ If the idea of the question is for the disc to enter the atmosphere edgewise, consider why so many reentry vehicles are designed to present a blunt surface forward. $\endgroup$ – David K Jan 2 '18 at 21:37
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    $\begingroup$ Regarding the latest edit... hypersonic planes are designed for low drag, a re-entry vehicle is trying to crate drag to slow down. And it's better to ask new questions than edit them in to old ones. $\endgroup$ – fooot Mar 19 at 21:20
  • $\begingroup$ Also, huge difference in amount of heat created from even orbital re-entry (Mach 24) and hypersonic flight. The shock wave from the drag producing blunt end conveniently pushes the heated air away from the capsule AND it slows its descent. One could have a capsule re-enter nose first simply by shifting CG towards the nose, but it would not have the insulating effects of the larger blunt shock wave. The hypersonic craft has to manage sustained heating. The aluminum Concorde did that by not exceeding Mach 2. $\endgroup$ – Robert DiGiovanni Mar 20 at 19:49
  • $\begingroup$ @RobertDiGiovanni I think this design could achieve Mach 24? $\endgroup$ – user20435 Mar 20 at 22:28
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Actually, a slower, rotisserie like roll could be considered. But the Apollo missions solved re-entry from outer space (25,000 miles per hour), as compared with orbital re-entry (18,000 mph), and even slower sub-orbital speeds by shifting the weight in the capsule to actually glide through the atmosphere, keeping its re-entry angle at an acceptable level. Without this innovation not only would the capsule be subject to higher temperatures, the G forces on the human occupants would also be much higher. (This "gliding" was further improved on the Space Shuttle). Orbiting Mercury astronauts did not have it as easy.

Also, re-entering blunt end first creates a large shock wave in front of the capsule, keeping the highest temperatures away from it. The rounded bottom also contributes to stability. This is Keep It Simple and Stupid (KISS) at its finest. Something to think about today.

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  • $\begingroup$ I thought this was a good answer and have edited my question again. Sorry I'm trying to get the privilege to ask new questions again. $\endgroup$ – user20435 Mar 20 at 22:27
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This is the heat distribution during reentry for the Orion capsule:

enter image description here

So the leading edge is hotter than the trailing edge, even for very large angles of attack (almost perpendicular).

I assume a disk would have a similar heating profile. So spinning the disk would move the edge of the disk from a high-heating area to a less hot area. This suggests spinning the disk could reduce the peak temperature of the edge somewhat.

The cost to do this is high, though: you have to either spin the entire disk (unpleasant for the crew) or spin the outer shell relative to the innards (complex). Controlling the vehicle becomes more difficult. You can't deploy parachutes while the craft is spinning.

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  • $\begingroup$ I'm sorry for editing the question I am trying to make the few I have better to earn back the privilege to ask again. Know that I did up vote your answer first. $\endgroup$ – user20435 Mar 20 at 22:26
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it probably would not help with heat dispersion, for the following reason. The rate at which we could conveniently spin the disc (~several thousand RPM- assuming there are no people inside it!) yields a rim speed which is extremely slow compared to the speed with which the disc would be re-entering the atmosphere. so from the standpoint of the very rapidly evolving gas dynamics & heat transfer mechanisms taking place between the hypersonic shock wave in front of the disc and the body of the disc itself during re-entry, it is as if the disc were essentially not rotating.

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  • $\begingroup$ The idea is that the disk reenters edge-first. The question assumes the forward edge of the disk would be subject to more heating than the back edge, so rotating the disk (could be done fairly slowly) would allow the entire edge to heat up evenly and reach a lower maximum temperature than if the disk were stationary. $\endgroup$ – Hobbes Jan 2 '18 at 12:36
  • $\begingroup$ I see. I think your hypothesis is testable with a heat transfer simulation, but my intuition suggests it wouldn't be useful. If the re-entry vehicle has people in it, their capsule would have to be de-spun to keep from subjecting them to a very " interesting" ride. $\endgroup$ – niels nielsen Jan 2 '18 at 17:24
  • $\begingroup$ I'm sorry for editing the question I am trying to make the few I have better to earn back the privilege to ask again. Know that I did up vote your answer first. $\endgroup$ – user20435 Mar 20 at 22:25
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Apparently, the world records for flying discs (depending on which source you believe) are 144 km/hour and 152.9 km/hour. Achieving supersonic speeds would be quite the improvement above either of these records.

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  • $\begingroup$ That's slower than a plane! $\endgroup$ – Geocrafter Oct 12 '17 at 11:37
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    $\begingroup$ Relative to cosmic microwave background, frisbees can reach 368 km/sec. $\endgroup$ – qq jkztd Nov 5 '17 at 20:00
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    $\begingroup$ Do manhole covers count as "flying discs"? $\endgroup$ – dalearn Jan 4 '18 at 21:49
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    $\begingroup$ @RalphJ en.wikipedia.org/wiki/… $\endgroup$ – dalearn Jan 5 '18 at 20:56
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    $\begingroup$ @dalearn Okay, that one flew! Although it sounds like it was “flying plasma” or at least flying vapor very shortly after it became a “flying disc”. Cool find in any event! $\endgroup$ – Ralph J Jan 5 '18 at 21:02

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