Eli5 how solar sails work?
In: 5
Light carries momentum, just like moving air does. A solar sail bounces light off of it to generate momentum, just like a regular sail bounces air off of it to generate momentum. The thrust of a solar sail is tiny, but they take no power and can run for as long as you like.
It seems weird because it’s completely alien to our lived experience, but light can push things.
It’s a phenomenon called “radiation pressure” and it happens because light, despite being massless, still has some momentum that it can transfer to other things.
This amount is very very small, but if there is nothing else pushing against your sail, you can use the ambient light of a nearby star to push you.
Light has no *rest* mass, that’s true, but since we can’t ever find it at rest, it’s also completely irrelevant in our everyday lives. While in motion (as it always is) it has *potential* mass, and that’s the part if the energy equation that allows it to drive a solar sail
So, all of these “light has momentum but no mass” answers are correct, but I’ve never found them very satisfying. It’s much nicer to just think of light in terms of electromagnetic waves. Then you don’t have to wrestle with the concept of massless particles that have momentum.
When light travels, it’s the electric and magnetic fields wiggling back and forth.
When light hits something that has electric charge, say the protons in an atom, the wiggling electric field makes those charged particles bob up and down.
That electric field is accompanied by a magnetic field too. One of the basics of electromagnetism is that charged particles moving in a magnetic field will get pushed perpendicular to their movement.
So, you have charged particles bobbing up and down in a magnetic field. That up and down bobbing in a magnetic field pushes them forwards. It just so happens that the direction they get pushed is exactly the same direction the light was moving.
These charged particles bobbing up and down cause their own electromagnetic waves (any wiggling charge will make an electromagnetic wave).
The electromagnetic waves caused by the particles bobbing up and down cancel out the original light, and travel back in the opposite direction, essentially “reflecting” the original light.
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All together this means:
– Light hits solar sail
– Solar sail particles start wiggling up and down
– Up and down wiggling + magnetic field from light makes sail travel forwards
– Up and down wiggling reflects the light back in the direction it came from.
Here’s a question: How long realistically would a solar sail like the one in DS9 take to get up to speed? I’m not looking for exact numbers just if it’s useable or if it would take longer than a human lifetime to get anywhere.
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