A novel laser ranging method is described that uses a two-mode laser source, and detection of the phase of the return beam. The design eliminates the cyclic error usually associated with phase measurements and provides unambiguous, absolute distance determination. Measurements of an 8m path are obtained at a beat frequency of 13 GHz. We analyse the 1µm stability of the data obtained with this preliminary implementation, and expect that an improved version will allow accuracies well below 1 µm, for the kilometer-scale distances involved in satellite formation flight
