[polyfractal]

A minor note: the LightSail team says the perigee is lowering due to atmospheric drag not due to the sun slowing it down:

> The perigee, or low point of its orbit, has dropped by a similar amount, which is consistent with pre-flight expectations for the effects of atmospheric drag on the spacecraft.

That's not to say the solar pressure isn't potentially slowing it down too, but it sounds like the main driver is drag in this case.

[e12e]

I wonder if it'd be feasible to just have the sail be a one way mirror? Transparent on the "front".

[doctorphil]

There are no known materials that act as a one way mirror. We don't expect to find any such material. With a one way mirror it would be easy to lower global entropy.