[seabass-labrax]

I used to think that if it were only slightly off, the return beam might end up intersecting the Earth at somewhere inconvenient, or even missing it entirely. Even more impressively, it took only five minutes to deploy, which is faster than most bathroom mirrors are installed :)

The reason why this isn't a problem is that the device wasn't 'just' a mirror, but rather a retroreflector. This reflects any light back at its source, regardless of which direction the light came from.

If you were really lost in deep space, perhaps you could flash a very bright light (not a laser) momentarily, then look for the return flash from the retroreflector moments later - or at least, hopefully that soon, otherwise you are very far away indeed! A few strategically-placed retroreflectors around the solar system could make an effective triangulation-based location tracker. I wonder if this already exists in some form.