# Using orbital spin to accelerate an interstellar launch

• B
Ok, so I know I'm missing something here. But, you know how pool balls that rotate opposite direction increase the speed of one of them through kinetic transfer? Why don't we build a launch platform based on this approach and use the orbital spin of the Sun, Jupiter, and Saturn (gaining speed from their planetary rotation for your platform) and then transfer all that kinetic energy to a smaller object that is then launched from that platform? Like shooting a BB out of your spinning pool ball, to reach deep space?

Using a reversed electromagnetic field to produce the spin and the planetary object to increase the rate of spin. Using that method you should be able to launch an object going around 3 million km/h right? Or somewhere around that speed?

Simon Bridge
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Welcome to PF;
Why don't we build a launch platform based on this approach and use the orbital spin of the Sun, Jupiter, and Saturn (gaining speed from their planetary rotation for your platform) and then transfer all that kinetic energy to a smaller object that is then launched from that platform? Like shooting a BB out of your spinning pool ball, to reach deep space?
This is exactly what we do.

Using the earth's rotation, but I'm saying build an earth-like ceramic launch platform and use the sun's rotational energy. Wouldn't your escape velocity for your object be the combination of the sun's rotation and that of your rotating launch platform?

Simon Bridge
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What do you mean by "earth like ceramic launch platform"?
How were you expecting to couple the spacecraft to the Sun's angular momentum?
Have you tried looking up "gravitational slingshot" or "gravity assist"? Manouvers which couple a spacecraft to a planets angular momentum to assist it's travel are normal.

Well, it would have to be ceramic to resist the intense heat of the sun and you would want the platform to get as close as possible for greater kinetic transfer. You would also want your launch platform rotating in the opposite direction in relation to the spin of the sun. At the moment when optimal spin is achieved, you launch your interstellar object from your ceramic launch platform. Like launching a baseball at the batting cages, only your sun and your launch platform are the wheels. Wouldn't that produce near instant acceleration in excess of 3 million km/h?

I know we use gravity assist, but I'm imagining an object being launched from two objects in space rotating in opposite directions. When we use gravity assists, the spacecraft itself is not rotating and nothing is launching out of it. Imagine two pool balls spinning in opposite directions and then at the moment of impact, release a BB. Wouldn't the velocity of that BB be the combination of the kinetic energy of both rotating objects instead of just one?

Simon Bridge
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When we use gravity assists, the spacecraft itself is not rotating and nothing is launching out of it. Imagine two pool balls spinning in opposite directions and then at the moment of impact, release a BB. Wouldn't the velocity of that BB be the combination of the kinetic energy of both rotating objects instead of just one?
... a bit like how a tennis ball launcher works by shooting the ball through two wheels?

There is so much here it is hard to know where to start... ie. where would you find a ceramic capable of withstanding the heat of the Sun?
But assuming such a magic substance could be found - or you don't use the Sun - what do you mean "earth-like ceramic launcher"??

A bb may be launched between two balls if they were spinning at the same rate ... then the bb would have the velocity of the surface of the balls but not the sum of their velocities.. The bb would carry off some of the angular momentum of both balls. This is how an automatic pitcher works. But perhaps you are thinking that the launcher and the Sun/planet are spinning at different rates? In that case, how do you get the "bb" energy coupled to the launcher and the Sun but the launcher angular momentum is not coupled to the Sun? IF it spins at the same rate, then what holds the launcher together?

In the space version, you still need to give the platform it's initial angular momentum. If you have that much energy, why not just give it to the spacecraft and use gravity assist?

So: short answer is because what you are talking about requires large quantities of unobtainium.

Dale
Yes, exactly a tennis ball launcher.

I see what're you saying. You only gain the kinetic energy from one wheel. Whichever wheel is traveling faster.

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CWatters
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Gold Member
You then use existing propulsion methods to slingshot around Saturn and approach the Sun from Jupiter, which both spin in the same direction relative to the Sun.

Perhaps I'm wrong but I thought a gravitational sling shot slowed down the orbit of the planet around the sun not the planets rotation about it's own axis.

But I see another problem... You propose using Saturn to boost your speed in order to reach Jupiter which is fine, but once you reach Jupiter I think the only way to get closer to the sun is to slow down again which seems to defeat the purpose of going to Jupiter in the first place.

I see what what the problem is.

rcgldr
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You propose using Saturn to boost your speed in order to reach Jupiter which is fine, but once you reach Jupiter I think the only way to get closer to the sun is to slow down again which seems to defeat the purpose of going to Jupiter in the first place.
It's possible that using Jupiter to slow down the satellite could be used to setup a later slingshot off another planet. The sun could be used to change the path, but would not provide a gravity assist, since the sun is the frame of reference for velocity.

In the case of the Rosetta satellite, which eventually landed on an asteroid, a Mars gravity assist was used to slow down and adjust the orbit of the Rossetta to setup a second earth gravity assist. (The first earth gravity assist was made from the initial and slightly elliptical orbit). The third gravity assist from the earth was done after a second gravity assist from the earth without involving other planets, but this time earth made two orbits between the second and third assists.

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Simon Bridge
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Yes, exactly a tennis ball launcher.

I see what're you saying. You only gain the kinetic energy from one wheel. Whichever wheel is traveling faster.
Well sort of ... the ball interacts with both wheels: if the two wheels of the launcher were moving at different speeds, they would make the ball spin as it leaves the launcher.
Since there is a spin, the ball's linear speed would probably be smaller than the speed of the fast wheel.
You can see this easily if you imagine one wheel is stationary.

Simple run on grav assist:
http://www.schoolphysics.co.uk/age14-16/Astronomy/text/Slingshot_/index.html

Huh - Earth rotation can be used to assist a launch, isn't there a way to couple to another planets rotation?
Spacecraft are usually pretty fast though: V1 manages 17kmps for eg. and Apollo 10 managed 11kmps, while the surface of the earth manages about 0.5kmps though the orbit speed is more like 30kmps. Jupiter's rotation works out at an upper surface mean speed of 2kmps ... though that's probably misleading since there's no surface and there's the winds.