Could a rotary rocket entering the atmosphere collect enough energy in a super capacitor through the rotors (along with auto rotation) while descending to have a controlled landing in the last few second before touch down?

enter image description here https://commons.erau.edu/cgi/viewcontent.cgi?article=1283&context=discovery-day

related: Super Capacitor Stages

enter image description here

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    $\begingroup$ Whenever thinking of 'energy recovery on landing', check the energy density of your storage device. The supercapacitor energy density is around 15 Wh/kg, while fuel is 12,000 Wh/kg. That means you'll need to spend at the very least 800 times as much energy to put the capacitor in space as you recover upon landing. In other words, you'll spend more than \$800 extra to recover \$1. Forget all "solutions" that utilize storage of worse energy density than the fuel. $\endgroup$ – SF. Apr 21 '19 at 15:59
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    $\begingroup$ Rotary Rockets are not proven to work. $\endgroup$ – Organic Marble Apr 21 '19 at 17:12
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    $\begingroup$ On mars this is going to have the same problem as parachutes in the thin atmosphere, and is notable that probes to date seem to have got no slower than around 100kmh on parachutes alone. It is hard to come up with a lander design where parachutes+rockets or chutes+airbag does not produce a lower mass at launch than something that starts with 50-100 meter long blades and gets more complex from there. $\endgroup$ – GremlinWranger Apr 22 '19 at 0:19
  • $\begingroup$ If you make this more general, it might be more interesting. Any currently proposed Mars landing system for large (> 10 tons say) vehicles, seems to consist of aerobraking down to low supersonic speeds, followed by propulsive landing. Is there any way to capture any of the energy that would be dissipated during the aerobraking phase to usefully save fuel in the propulsive phase?" I could imagine storing heat in molten metal or salt, to heat a reaction mass or storing hot compressed atmosphere to use for propulsion. $\endgroup$ – Steve Linton Apr 22 '19 at 8:59

When a helicopter has an engine failure in flight, it goes into autorotation: as the helicopter loses altitude, the air moving up (relative to the rotor blades) drives the rotor blades to a usable speed. Just before hitting the ground, the pilot pulls up the collective pitch control to generate lift and slow the descent to a survivable landing. This must be done at the right time: the rotor slows down rapidly when you pull up. Do this too early and the rotor will stall and you'll crash.

With the right size rotor, you might be able to do this with a rocket stage. This really depends on how fast the stage descends.

  • $\begingroup$ Key element here in terms of the question is energy storage. Autoration stores energy kinetically in the blades, at close to 100% efficiency where question tries to store energy electrically at some lower efficiency and with added weight. $\endgroup$ – GremlinWranger Apr 22 '19 at 0:00
  • $\begingroup$ @GremlinWranger Along with autorotation. $\endgroup$ – Muze Apr 22 '19 at 1:11

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