If the the photons approaching our sail at low energy can be given high energy when bouncing back we definitely shall gain more momentum.
Is my proposal feasible?
Raising the energy of a photon is equivalent to blue-shifting it. SInce sails extract energy from photons they can only red-shift them. Can you please explain more as to what you are proposing?
Are you proposing to increase photon energy by hitting them with a rotating propeller? If so, where is the energy for the rotation coming from? You would further need some kind of engine to turn the propeller, which is always a very bad thing in space (rotating axes are usually prohibitive, because they are maintenance heavy). Basically you would likely use solar energy to turn it into electrical energy and with that turn the propeller. That would need a ebtter efficiency than e.g. an electrical engine run by the same energy to be a better solution. Furthermore the hitting photons would always hit in the same direction, but with a propeller they would be reflected in a different one, how do you intend to make the impulse exchange in a beneficial direction? (Like it is done with solar sails).
Max,
This is, on the face of it, practical.
From the reflective blade's frame, the inbound photon is blue shifted. And thus carries more momentum. I think that there's something you've missed, as otherwise a circular array of reflective blades, rotating at high speed, would generate higher recoil forces than a static array.
Ah, yes. The blades are minutely slowed by the photon recoil - I suspect that the energy needed to maintain uniform rotational speed is exactly balanced by the gain in kinetic energy one experiences.
Not wrong, a novel form of photon drive.
At least that's my first take.
Turning it might be tricky.
I think that, in order to get any real momentum gain from this process, the propeller would have to move at a very substantial fraction of the speed of light relative to the propelled object. No material structure known could do this without disintegrating long before from internal inertial forces. Its rather like extracting the rest mass of matter as energy by dropping it into a black hole using a rope. If you do the calculations apparently you need a rope with the strength of a 'cosmic string' (whatever that is) in order to make the idea work. But it sounds interesting!
There is a concept called a heliogyro solar sail, developed in the late 70s at JPL for a proposed Halley's Comet rendezvous mission. The heliogyro deploys long flexible blades that are stabilized by centripetal acceleration. The heliogyro uses a control scheme similar to helicopters (collective or cyclic) to manage the heliogyro blades and keep them stable. In the case of the heliogyro, the blades are on the order of hundreds of meters to a few kilometers. The challenge is to keep them from twisting.
So in a sense there is already a proposal to have a bladed sail, which is not that dissimilar from a propeller. But I agree with the others...the rate at which you would have to spin the propeller makes it very impractical.
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