re: If all you want is to reflect light from space to the ground...
Thanks for the thoughtful reply. To maybe be more clear: 1) I thought suntracking solar arrays were somewhat more efficient than static ones, so it seemed if there was a way to add value to that it would make sense. 2) I'm not clear why the mirror would have to be large. with 99% reflectivity, wouldn't the mirror have to be just somewhat larger than the surface it was lighting? (to compensate for other losses and the sun/earth angle?)