this post was submitted on 13 Sep 2024
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Can a solar sail be used to put a craft into the sun?
That's an interesting question. A regular sail can sail into the wind, but they have a triangular sail, and a keel with water resistance. I don't think any of those things exist in space, so I'm going to guess no. Perhaps some sort of high efficiency propellant keel could make it possible?
My intuition would say no, but to be honest, I don't understand the physics of either solar or watercraft sails.
As a certified small keelboat skipper, I understand watercraft sails. I think I understand solar sails, but not nearly as well. I know Stephen Hawking wanted to send a bunch of micro drones to Alpha Centauri using solar sails powered by on-board lasers. That seems like the whole fan on a boat pointed at a sail situation, which doesn't work on earth, so maybe I don't actually understand solar sails. I'm definitely not going to say that Stephen Motherfucking Hawking was wrong about his area of expertise.
Edit: I got really curious about this after posting and looked into it more. The project was called The Breakthrough Starshot, and I misremembered the configuration. The lasers weren't onboard the spacecraft, they would have been earth or satellite based. So I guess I do understand how solar sails work. When photons hit the sail, they impart some of their momentum to the sail, and the attached spacecraft. Since billions of photons are hitting the sail every second, all those tiny little pushes provide forward momentum. I'm still not sure if you can use a high efficiency propellant keel to sail towards the light source or not, but I'm thinking probably "no".
This sounds incredibly legit, but question: Could you not gain a shit ton of momentum sailing directly with the wind in a regular boat, then drop your sails and steer into the direction of it to maintain some amount of velocity for an amount of time? Feels like the same principle could be applied here, especially because they would swap between photon momentum and gravitational momentum
You can do that with a sail boat because the keel prevents lateral movement. In space if you try to turn without trust then you just spin and keep heading into the original direction. You can definitely leverage gravity wells for additional thrust in a spaceship, but that's a whole other conversation. My idea was to try to tack into the light source with a solar sail, like you would tack into the wind with a sailboat, but use a propellant based keel to offset the lateral movement in the direction the photons are heading. But I suspect that it would be more efficient to just use the propellant as your thrust in the direction you want to go. Idk if using it as a keel is even possible. I feel like someone way smarter than me would have proposed it already if it was possible.
Yeah, in space there's nothing to push against so all turning the sail would do would be presenting a smaller surface to be pushed directly away from the sun
If it would work, it would be by stopping the angular momentum around the sun, then letting the sun’s gravity pull the object in.
Easily. You'd just have to use it to push your orbit in the right direction at the right time. If you are like Pluto, and way out there with a very eccentric orbit, unfurling the sail as you are heading into the galaxy might make your orbit path curve through the sun itself.
Yes, because of the way orbits work, you just need to add velocity horizontal to the orbit, which is just as easy going into the sun as out of it.
So a solar sail is just as good both in and out of the sun.