It’s a cube truncated to preserve three adjacent faces. Both the solid prism and hollow (just mirror surfaces) work as practical retroreflectors. You can’t bui

It’s a cube truncated to preserve three adjacent faces. Both the solid prism and hollow (just mirror surfaces) work as practical retroreflectors. You can’t build machine tools, semiconductor processing tools, or accurately tighten the bolts that hold on a 777’s wing without them. If you have an array of them on the moon, you can measure the distance to the moon, at one instant, to an accuracy of a millimeter.