This report describes a computational program, now in existence, for estimating the accuracy with which satellite positions can be calculated at any time on the basis of observations at various stations. The error in computed position is due to two main causes, at least if station location uncertainties are ignored. These are A observation errors, B fluctuations in the orbital decay rate due to drag. It is assumed here that uncertainties in the earths gravitational field have negligible effect on the satellite position. The treatment of A follows standard statistical practice Orbital parameters are adjusted to a least-squares fit to the observations. The covariances of the estimates of the orbit parameters are then obtainable quite easily from the variances of the observation errors, assuming that the different measurements are statistically independent with zero bias.