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The Wikipedia article lists several advantages relative to reflective solar sails, but there's also a major disadvantage not mentioned. A reflected photon impar
by mitthrowaway2 3y ago
The Wikipedia article lists several advantages relative to reflective solar sails, but there's also a major disadvantage not mentioned. A reflected photon imparts twice its momentum to the solar sail, whereas a diffracted photon imparts only a small portion of its momentum. The overall thrust would therefore be much lower than a reflective solar sail. The fact that "photons can be reused... by passing through a second diffraction grating for more thrust" is not an advantage but rather a testament to the lower efficiency of the diffractive sail.
Perhaps that's offset by the other advantages, but this is not clear.
- deleted 3y ago[deleted]
- monocasa 3y agoI'm not sure that's necessarily the case. A reflected photon can only impart half of its momentum before it's barreling off away from you. Several layers of diffractive sails would seem to be able to (at least theoretically) exceed that.
- AnimalMuppet 3y agoA reflected photon imparts twice its momentum.
- monocasa 3y agoMomentum was the wrong word, but it feels like layers of diffraction could red shift the light more, absorbing more energy out of each photon.
- jiggawatts 3y ago… which just heats up the sail. To move, you want to absorb momentum, not energy.
- woleium 3y agoCorrect as per Newtonian physics, bit shit gets weird when you go quantum :)
- monocasa 3y agoAt the scale of individual particles, heat is movement.
- ianburrell 3y agoHeat is random movement. Infrared photons go in random directions, not the direction wanting to go. Some go in the wrong direction. Reflection means solar sail goes in direction you want to go.
- mitthrowaway2 3y agoThe light reflected from a mirror is already red-shifted due to the velocity of the mirror.
- monocasa 3y agoWhich is why I said red shift more.
- deleted 3y ago[deleted]