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PostPosted: Fri May 26, 2017 12:27 pm 
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Suppose you want to set up a station in a flare star system, for Nefarious Evil ResearchTM purposes or the like. You'd want to make sure you didn't get cooked by a flare. I hear it's not any fun.

I'm wondering how well any of the following might work:
  • Someplace in the outer zone, on some icy frozen moon. For an M dwarf flare star, how far out is safe enough?
  • The dark side of a tide-locked world.
  • A station orbiting in the L-2 point behind a decent-sized world, such that the world was big enough to entirely occlude the star

That last one I'm definitely curious about. Would something at Mercury's L-2 point get any sunlight?


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PostPosted: Fri May 26, 2017 1:12 pm 
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Matt Wilson wrote:
Someplace in the outer zone, on some icy frozen moon. For an M dwarf flare star, how far out is safe enough?

It depends. Some flare stars get to be about as energetic as our Sun is normally when they flare; others can be considerably brighter. On a quick search, it looks as if the shielding needed for long-term protection from galactic cosmic rays (GCR) would probably be sufficient for all but the most extreme cases.

Quote:
The dark side of a tide-locked world.

This would definitely be sufficient, as well as cutting your GCR dose in half.

Quote:
A station orbiting in the L-2 point behind a decent-sized world, such that the world was big enough to entirely occlude the star

That last one I'm definitely curious about. Would something at Mercury's L-2 point get any sunlight?

This would work in theory, but would be hard to implement in practice. The three colinear Lagrange points (L1, L2, and L3) are inherently unstable: any perturbation tends to move an object away from them. In the case of a close-in planet (e.g., Mercury) there are relativistic forces that act as perturbations, making it effectively impossible to passively remain at the L2 point. The options are (1) constant thrust, which may not be a problem if your setting has reactionless or high-Isp thrusters, or (2) one of a class of periodic orbits around the L2 point. This latter option may not be very helpful, however, as the orbits tend to be wide (tens of thousands of kilometers). They might not fit in the umbral zone of a close-in planet unless it was Jupiter-sized.


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PostPosted: Fri May 26, 2017 3:23 pm 
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Cool. Thanks for the quick and thorough feedback.

I was in fact thinking about it in terms of a Traveller situation, so probably the L-2 station could be a thing, but really it sounds easier to just set up on the surface.


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PostPosted: Sat May 27, 2017 1:33 pm 
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Matt Wilson wrote:
[*]A station orbiting in the L-2 point behind a decent-sized world, such that the world was big enough to entirely occlude the star[/list]

That last one I'm definitely curious about. Would something at Mercury's L-2 point get any sunlight?

I found a page that answers your question.

Short answer: Mercury's L2 point is in penumbra — from there the apparent disc of Mercury is smaller than the apparent disc of the Sun, so sunlight reaches it around the edges of Mercury. The same is true for the L2 points of Venus and Earth. But Jupiter's L2 point is in umbra, and so are those of Saturn, Uranus, Neptune, and Pluto.

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