Covariance analysis of the performance of the Geoscience Laser Ranging System (GLRS) indicates that three-dimensional relative positions can be recovered to an accuracy of several millimeters over spatial scales from a few kilometers to several hundred kilometers and over temporal scales as short as several days. The key factors influencing the accuracy are range noise, number of targest and their locations, system pointing capability, dwell time on the targets, orbital geometry, and gravity field uncertainties. Based on the present trade-off studies. GLRS is designed to provide range measurements with 10 mm or better accuracy, fire at a rate of 40 pulses-per-second, point over a cone extending to 50¿ from nadir, and operate with a dwell time on individual targets of 2 s or less. Given a strain rate of 1014/s, estimated GLRS accuracy parameters suggest that the deformation can be detected in less than a month if it extends over 100 km and in less than 6 months if it extends over 10 km. ¿American Geophysical Union 1990