# Solar sail acceleration

Rob060870
if you had two spacecraft which had a solar sail as its means of Propulsion A & B, and were both identical.

Spaceship A has light from the sun to push it along its way.

Spaceship B has only gamma rays to push it along.(both craft have the whole of their sail surface covered with their respective radiation)

now would spaceship A accelerate slower, faster or the same as spaceship B? and why?

i know that both forms of radiation of course travel at the speed of light but does the higher energies that gamma rays possesses hit the solar sail harder and make it accelerate quicker?

if any readers could enlighten me on this matter i would be most grateful.

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Mentor
The impulse provided per photon would be greater for the higher energy (and higher momentum) gamma rays, but the overall pressure also depends on the number of photons reflected per second. So the radiation source that provides the greater intensity (power per unit area) will produce the most pressure.

Rob060870
The impulse provided per photon would be greater for the higher energy (and higher momentum) gamma rays, but the overall pressure also depends on the number of photons reflected per second. So the radiation source that provides the greater intensity (power per unit area) will produce the most pressure.

thankyou,
so then. . photon for photon the radiation with the higher energy will exert more pressure than the photon with lower energy.

meaning spaceship B will accelerate quicker, but does that mean that when both spacecraft max out, it will attain a faster total speed?. i would think that it does?

Mentor
so then. . photon for photon the radiation with the higher energy will exert more pressure than the photon with lower energy.
Right.

meaning spaceship B will accelerate quicker,
Not necessarily. (That would be true if each radiation source produced the same number of photons per second.)
but does that mean that when both spacecraft max out, it will attain a faster total speed?. i would think that it does?
Why would you think that?

Rob060870
i think that because if you had the same number of photons hitting the solar sails on craft A and craft B then the photons with the higher energy, ie. . B would hit the sail harder and eventually because of that attain a higher speed in the end?

what would be the reason for the spacecraft maxing out and attaining their top speed be?

it can't be friction of course as we are in a vacuum!,so as they both accelerate the energy pushing both craft are converted into mass so the craft with more energy pushing it will attain a faster speed. I am proberly barking up the wrong tree here but I am having a go lol!

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willem2
As the craft moves further away from the source of the photons, it will catch less and less light.
The amount of energy it can catch is finite.

Rob060870
Thats a very good point willem2!.

people are talking about using solar sails to travel to the outer reachies of our solar system, one problem with that one is-

How do you slow down when you arrive at your destination?
thanks

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