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Comment by RobertoG | Hacker News Reader

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RobertoG·

From the moon, the 'traditional' idea is a mass driver:

https://en.wikipedia.org/wiki/Mass_driver

First time I heard about it was in:

https://en.wikipedia.org/wiki/The_High_Frontier:_Human_Colon...

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Anybody interested in this should play Policenauts. It is an amazing game by Hideo Kojima of Metal Gear fame. It features lots of details like that about life in space, very fleshed out, and is just altogether one of the best games ever made.

There is also an amazing English translation, and a blog on how it was done: https://lparchive.org/Policenauts/Update%2042/

The big advantage of the rotating launcher is that you can aim it towards other targets, not only the Earth. You can take your shuttle from LEO to the Moon and then board the big spaceliner in her maiden voyage (because that's the last time it'll be on a planetary surface) towards Mars.

Where you aim the ground launcher (given you're aiming "over the horizon" at least) doesn't have a lot to do with where you wind up in orbit.

Would it not take more dV to cirularize if we fired it straight up?

The better aligned to the desired trajectory you launch, the less delta-V you need to get where you want to be. If we launch a payload and, in order to get to where you want it'll need to do a u-turn, our launcher isn't helping.

Precisely. Therefore a 45 or 30 degree launch angle gets more of the velocity in the orbital vector.

Unless you are talking about launching it at lunar escape velocity directly at earth orbit.

We were discussing the installation of these on the Moon as a way to launch spacecraft. A straight rail would be aimed at a fixed point, but a centrifugal launcher could release its payload at any point and send it in any direction (as most interesting destinations in the solar system are on a single plane).

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