From the FAQ in the article: >Similar to laser or microwave beams, longer distances require larger dishes due to the effect of optical diffraction. However, s

From the FAQ in the article: >Similar to laser or microwave beams, longer distances require larger dishes due to the effect of optical diffraction. However, sunlight is only partially coherent (unlike lasers and masers), so regardless of the actual size of the reflector used, it behaves as if it was coherent light emitted from a reflector that is only 70 microns in diameter. It is possible to show that at a distance of 350 km, as would be needed for launching rockets to orbit, such a beam spreads out to a spot size that is 6 km in diameter. Although the distances might be smaller if the mirror was in space, I imagine they would still not be small enough.