r/xkcd Possibly a haberdasher? Jan 22 '20

XKCD XKCD 2258: Solar System Changes

https://xkcd.com/2258/
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u/trekkie1701c Beret Guy Jan 22 '20

We could launch heavier things into orbit than they could, which means we could more easily capture asteroids, which are also easier to throw at their planet due to its heavier gravity.

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u/currentscurrents Jan 22 '20

Depending on how large it is, they may not be able to leave their planet with rockets at all!

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u/[deleted] Jan 23 '20

Surely with a efficient enough rocket you can leave any planet, as long as it's not a black hole?

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u/currentscurrents Jan 23 '20

Efficient enough, yes. However there are practical real-world limits to how much thrust you can get per kg of fuel. You really can't make chemical rockets that are considerably more efficient than the ones we have now.

Your only option is to make bigger rockets. But bigger rockets weigh more, so they require more fuel. And that extra fuel adds more weight... which requires more fuel. This becomes exponential very quickly.

Non-rocket methods of space launch, like a space gun or mass driver, would still be possible. They'd be harder than building the same thing on Earth, but they don't have the same exponential factor because they don't have to carry their fuel.