David Kipping

It'd probably only cost you

few tens of thousands of dollars, maybe a hundred thousand dollars, but there's basically no one who flies out that far except for bespoke missions, such as like a mission that's going to Mars or something that would pass through that kind of space.

And they typically don't have a lot of leeway and excess payload that they're willing to strap on for radical experiments.

So that's been the problem with it.

In theory, it should work beautifully, but it's a very difficult idea to experimentally test.

Can you elaborate why the focal point is that far away?

So you get about half a degree bend from the Earth's atmosphere when you're looking at the Sun at the horizon, and you get that two times over if you're outside of the planet's atmosphere, because the star is half a bend to you still on the horizon and half a degree back out the other way.

So you get about a one degree bend.

You take the radius of the Earth, which is about 7,000 kilometers, and do your arctan function, you'll end up with a distance that's about... It's actually the inner focal point is about two-thirds the distance of the Earth-Moon system.

The problem with that inner focal point is not useful because that light ray path had to basically scrape the surface of the earth.

So it passes through the clouds.

It passes through all the thick atmosphere.

It gets a lot of extinction along the way.

If you go higher up in altitude, you get less extinction.

In fact, you can even go above the clouds.

And so that's even better because the clouds obviously are going to be a pain in the neck for doing anything optical.

But the problem with that is that the atmosphere, because it gets thinner at higher altitude, it bends light less.

And so that pushes the focal point out.

So the most useful focal point is actually about three or four times the distance of the Earth-Moon separation.

And so that's what we call one of the Lagrange points, essentially.