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From what I can imagine, using an autorotative maneuver as a re-entry control method would be a good idea because I believe very high lifts would be generated when relative air speed is high (first re-entry phases).

This would in-turn reduce the rate of descent, reducing g-forces, heat exchange and would make the whole experience more enjoyable, at the cost of making it substantially longer.

It would also bring many advantages relative to vehicle control, landing, reusability, and overall weight reduction.

Has anything like this ever been tested ? Does it sound like a good idea, and if not, why ? details of the physics are welcome.

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    $\begingroup$ Lift depends not only on speed, but also on the density of the air. I don't know where first reentry phase ends, but it starts in near vacuum and, at a relatively high Mach number. $\endgroup$ – Solomon Slow Nov 11 '18 at 16:07
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    $\begingroup$ Aerodynamics is a little bit different with cosmical speeds. The rotors would break or burn in the first moment. $\endgroup$ – peterh Nov 11 '18 at 16:07
  • $\begingroup$ Seeing how low the air density would be, I am not sure your affirmation is accurate @peterh $\endgroup$ – Magix Nov 11 '18 at 16:09
  • $\begingroup$ @Magix The Columbia was broken in little parts on the air. Essentially, it crashed on the atmosphere. The Soyuz re-entry capsule requires a huge shield which partially burns down on reentry. Its top temperature grows until 2000 C. $\endgroup$ – peterh Nov 11 '18 at 16:13
  • $\begingroup$ @Magix Mars entry occurs from 12,000-14,000 mph, with 10-12g deceleration, in an aerodynamically shaped vehicle. A rotor would not only be shredded, it would mostly likely cause the S/C to tumble, which is game over. Earth is even faster (up to 28,000 mph), but manned reentry pulls fewer g's (unless there's an anomaly, as there was last month). Also: I suspect the hypersonic modelers would have trouble modeling the flow around rotors. $\endgroup$ – JEB Nov 11 '18 at 16:41
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Looks like the idea was tested before (https://www.nasa.gov/centers/kennedy/news/rotocapsule.html ):"The design would give a capsule the stability and control of a helicopter, but would not be powered. Instead, the wind passing over the rotors as the capsule descends would make the blades turn, a process called auto-rotation that has been proven repeatedly on helicopters but never tried on spacecraft." However, it looks like this was only considered for the final stage of reentry.

EDIT (11/11/2018): There is another material dealing with earlier stages of reentry: "A theoretical analysis was conducted to determine the aerodynamic and performance characteristics of a capsule incorporating an autorotating rotor for recovery from earth orbit. The potential advantages of this combination include the reduction of landing speeds to improve the chances of successful emergency landings on water, uneven terrain, or during inclement weather. Since others have concentrated on the approach and landing phases, the aim herein was to determine the range, deceleration, and heating effects during the entire re-entry. Rotor-to-capsule diameter and rotor deployment time were varied along with type of recovery, i.e., capsule lifting or nonlifting. The addition of a rotor was found to provide a significant increase in lateral range capability while changing maximum deceleration only slightly; however, excessive aerodynamic rotor heating requires either delayed deployment (reducing the performance gains) or substitution/development of structural materials having higher heat resistance than those studied."

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    $\begingroup$ For planets with an atmosphere, it's called "(re)Entry Descent Landing", or EDL. (The "re" only applies to Earth return vehicles, so far). So this tech appears to be in the "Landing" phase, which in terms of engineering, has nothing to do with Entry. Entry ends when you don't need a heat shield. Descent end at the end of gravity turn, or when you're done flying and go into "constant velocity mode". Of course we all know when landing ends. $\endgroup$ – JEB Nov 11 '18 at 16:31

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