# Thread: Spinning round planets, using planets as slingshots and crashing into a planet...

1. Established Member
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Dec 2007
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349

## Orbiting around planets, and using planets as slingshots.

How do scientists know how far from a planet they send their space craft, so the planet will be used as a slingshot, or for their craft to orbit it, so it doesn't miss the planet completely or crash into it?

And how do they know which position it should be in when sent further into place so it works out? And how do they make it do this? Do all spacecraft have little thrusters that are radio controlled or something?

Thanks.

2. Originally Posted by Ross PK81
How do scientists know how far from a planet they send their space craft, so the planet will be used as a slingshot, or for their craft to orbit it, so it doesn't miss the planet completely or crash into it?
A lot of complicated math that I don't know. But; the range of error is known, and they only need to be as far away from that planet as the range of error indicates.

Originally Posted by Ross PK81
Do all spacecraft have little thrusters that are radio controlled or something?
Yes; some for actual maneuvering, some just for attitude control. Although the attitude controlled ones can use sensors instead of radio control.

3. Established Member
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Thanks.

Keep an eye out for porkchop plots, like these described for a simpler Mars mission: NASA feature: "Porkchop" is the First Menu Item on a Trip to Mars

5. The performing of the calculations is a beastly job, and modern computers make it doable in a reasonable amount of time. In theory, Newton or Leibniz could have done it with pen and paper, but it might have taken a lifetime to get even a rough result.

6. So how does our trajectory calculations now stack up to the ones done for e.g. Voyager in the 1970's? Could the tricks performed with Cassini have been done back then? (I'm thinking of the Titan encounter where Cassini's trajectory had to go into Plan B because it could not extract the datastream from Huygens otherwise).

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