# Slingshot thechnology in space travel

I have a huge ship in space with only nuclear power based electronics as my last reservoir. Can the ship be moved, if I shoot a ton of crap to a slingshot and it will bounce back (to whatever ther is rigid of my ship). I’m drunk as hell, but sort of need answer fast.

You just need the bolded part. Shoot a bunch of mass out the back, no need to bounce it back and strike your ship to impart motion. That’s all that rockets are doing, only they are using chemical reactions to shoot a bunch of mass out the back.

How are you shooting that ton of crap and what is the mass of the crap relative to your craft’s mass? If there are no external forces resisting your movement then projecting something away should move you per Newtonian physics.

I’m too drunk to see your point. But Chronos, or somebody, Can I move?

I think that the OP is asking about shooting things within the confines of the ship, so as to re-use the slingstones. If that’s the case, then no: Your hull will wiggle around a little to compensate for the stones moving around inside of it, but then it’ll wiggle right back when you bring the stones back to your slingshot.

If you instead shoot the stones away from the ship entirely, then yes, you’ll cause the ship to move. How fast the ship moves will depend on how much the stones mass compared to your ship, and how fast you’re able to launch them, but for typical values of things called “ships” and “slingshots”, it’ll be awfully darned slow. There’s a reason real rockets shoot hot gasses out the back instead of pebbles.

I’m not in space, really !

Everything’s in space, dude.

Short answer: If you shoot stuff out the back of your ship, you’ll move forward. If that stuff bounces back into your ship, it’ll pull you back to where you started from.

A portion of energy would be transferred to the spring energy. Would the total energy be a little forward?

I suspect that you’ve heard the phrase “slingshot” used in the context of space travel, but you never got a good explanation of it, and you are guessing that it works the way a slingshot works. Nope. A slingshot (to my mind) is a sort of handheld catapult, a way to get a projectile moving. In space travel, the slingshot effect is a way to increase the speed of a projectile that is already moving.

Specifically, suppose your vehicle is heading towards a planet or star. Well, not directly at it, because you don’t want to crash, but slightly off to the side. As you go, you are actually falling towards the planet, so you’re going to go faster and faster. But because you are not going straight down, it will be a near-miss. To someone standing on the planet, it will look like you were coming down, but then you leveled off and started going back up again. (This has nothing to do with Einstein’s relativity; just draw a circle, and a line near it but not touching, and it will make sense.)

Of course as you continue on your way, you are now going upwards, away from the planet. And of course, you’ll slow down in the process. Eventually, you’ll be so far from the planet that you’re not really losing much speed any more. If you do this right, you’ll now be traveling faster than you were when you started. Whipping past the planet, and gaining speed in the process, that’s the “slingshot effect”.

What I’ve described is a bit oversimplified. In reality, this trip will not be a straight line. As you approach the planet, you won’t go straight past it. Rather, you’ll swing around it for a bit, and then start to go up and away from it. I suspect that the shape of that curve is why it is called a “slingshot”.

You can use gravity slingshots to either speed up or slow down - you’re essentially stealing a bit of the planet’s orbital angular momentum (or in the case of slowing down, you’re dumping some of your own momentum into the planet)

A slingshot is not the same as a catapult; it is a much more primitive weapon. Take a length of leather or rope, with a pouch in the middle. Put a stone in the pouch and swing it round your head as fast as you can. At the right moment, let go one end of the rope and the stone will use all the angular momentum it has acquired to fly off in a straight line.

With no understanding of mathematics, ancient man learned by trial and error the optimum length of rope and the ideal weight of missile to get the best results.

Racing cars use the same system by gaining angular momentum on a bend to give them overtaking speed on the exit, and spaceships do it round planets.

This is what I mean - imagine a permanent magnet shot in a tube by an electromagnetic pulse. While the magnet speeds up the tube moves 180 degrees and the magnet returns for another shot. In order to keep the ship stable another tube with a magnet moves counter clockwise. So emission with no loss of mass.

The counter-rotating tube would cancel out any effect of the first tube. Consider a see-saw, where one end does move up while the other end moves down. No matter how many times you pump it your net change in position is zero.

No, it appears there is no motion imparted to your ship at all. Everything would balance and the ship would stay exactly where it was. The magnets are moving opposite each other, completely cancelling out the forces. Actually, each individual magnet cancels itself out since it has to travel down and back. Where do you see any forward forces in your model?

You can use flywheels and the like to alter your orientation in space (i.e. rotate around your centre of mass), but not to actually move from one position to another, without reacting against something external.

When ‘the magnet returns for another shot’, you undo what you did in the first place.

Well… it is possible to move without emitting any mass permanently. You can swim in relativistic space. However don’t count of getting anywhere fast. Or even before the sun goes cold.

I already admitted that I’m bad in mechanics - still I see an elastic collision and another not so elastic. I feel that the elastic collision(slingshot) reserves some energy and net movement would be forward. Still drunk, but I would feel the same if I was not.(Sorry to be drunk, though).

I meant sorry for mentioning, but OK for drinking all this time. You can choose your own favourite smiley.:eek:(mine)

Best not to worry about energy - just think momentum. Momentum is conserved. If your system is closed, no matter what you do within it, the momentum will always be the same. Even if your reaction mass is waving about on a length of elastic, if your whole system always remains the same bunch of stuff, the momentum remains the same. The only way to change momentum is to permanently throw some away. If you try to get the object with that momentum back, it will come back with that momentum still attached (in a very loose way of thinking) and you will be back with your original momentum again.