this post was submitted on 03 Sep 2024
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If photon hitting a surface can impart momentum, does generating photons also impart momentum? Like, if you put a solar powered laser pointer in space, would it move?
Yes, it's called radiation pressure by emmision
The formula for it is Irradiance^1 of the emission/speed of light.
1: irradiance is basically how much power per unit area is emmited by the object, it's units are watt/m^2
As for the lasers thing, I'm not a 100% sure how effective that will be and TBH lasers are pretty complicated and I don't really get them
Yes, but that would be a lot less efficient. With a dielectric mirror you can get easily 99.9% of the maximum momentum gain from the light, while with a solar powered laser you would get for the emission the compounded efficiency of the solar panel + storage + laser, so way below 10%. So you would gain around 10 times more impulse from your solar panel absorbing light than from the actual laser.
The final momentum gain is a bit different as the maximum you can gain from a photon is double its momentum (because you can reflect it back with opposite direction).
aww so people are pushed away from me because of my brightness and not because I'm dumb??
Sure, but it would be less efficient than a sail, and since the incoming radiation would impart inertia on the solar panels, you would still be limited on where you could steer.
Sail absorbs power while also acting as a sail, and you can use the lasers to steer?
It would also be like steering a boat more or less no?
The solar sail reflects light instead of absorbing it so you get to double dip on photon momentum.
And sure, you can steer with the laser I suppose, but with that kind of super weak deltaV, you’re not going to be exactly doing donuts in the solar system.
Even the massive solar sail only imparts a super small amount of force. It’s only useful because it does so for free over a long period of time with no air resistance.
You’d be better off using a conventional thruster to do whatever steering you needed to do before letting the sail take over. It’s not like you need to steer around any obstacles.