## Photoelectric Solar Sail

Suppose you have a solar sail that was capable of perfect photoelectric conversion.

So this means that photons from the Sun are striking your solar sail, and also being photoelectrically converted to electrical current.

My question is - does the photoelectric conversion at all affect the momentum transfer of the photons to the solar sail?

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If conversion was PERFECT,all photon energy would be converted to electrical....this would include momentum....so it would appear some current momentum would be converted to electrical in a "PERFECT conversion.

 does the photoelectric conversion at all affect the momentum transfer of the photons to the solar sail?
via your established criteria, seems like it....whether that's practical or not is another question..such as solar cells getting warm in the sun....

Edit: Ignore the above...it seems the poster is addressing spacecraft solar SAILS....I wasn't paying attention....I missed photoELECTRIC instead of photoVOLTAIC....

 Quote by Naty1 If conversion was PERFECT,all photon energy would be converted to electrical....this would include momentum....so it would appear some current momentum would be converted to electrical in a "PERFECT conversion. via your established criteria, seems like it....whether that's practical or not is another question..such as solar cells getting warm in the sun....
So only SOME photon momentum would be converted into electrical energy, or ALL of it would?

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## Photoelectric Solar Sail

 Quote by Naty1 If conversion was PERFECT,all photon energy would be converted to electrical....this would include momentum....so it would appear some current momentum would be converted to electrical in a "PERFECT conversion.
No, momentum is still conserved in an inelastic collisions.

Normally solar sails are designed to be reflective, so you have an elastic collision between light and the sail. To make a photovoltaic sail, it would have to be absorptive, so you have an inelastic collision, with only half the momentum transfer.
 Why half?
 If the photon is absorbed, its momentum changes from p to 0, so the momentum of the sail increases by p. If the photon is reflected, the momentum changes from p to -p, so the momentum of the sail must increase by 2p. (actually it will be slightly different than this due to the fact that there is also energy transferred, resulting in a different wavelength.)
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