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Reply #5


Response to randome (Reply #4)

Wed Nov 7, 2012, 09:34 PM

5. They mean the Lagrange point "behind" the moon, relative to Earth

There's points in space where you can genuinely park something - where they'll be stationary relative to certain other nearby objects, so you don't need to expend fuel to keep them in a given location.

To really oversimplfy things, there's five Lagrange points with locations relative to the Earth and the moon, five relative to the Earth and the sun, and so on for most "one small object orbiting one bigger object" scenarios. The article's referring to the second Earth/Moon point. If you ran a straight line from the Earth through the moon, L2 would be 60,000 kilometers above the opposite side of the moon. The Earth/Sun L2 would be the same thing, only you'd draw the line from the sun through the Earth and the end point would be much further out. There'd be another set clustered around Mars or Venus, and so on and so forth.

They can be extremely useful places because of that - it makes keeping something there a lot cheaper, they're all far enough out of the gravity well to have other uses, and a few of them have extra bonuses beyond that. For example, you could put a space telescope at the Earth/Sun L2 point and it would always have Earth as a shade keeping the sun out of the telescope's eyes.

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