Preliminary orbital error analysis for ERS-1

The accuracy with which the orbit of ERS-1 can be reconstituted from a short arc or a long arc of tracking data, and measurement and dynamic model error sources that contribute to orbital error, are discussed. For long arcs, the dominant error in the radial component is due to unknown gravitational forces. Solar radiation pressure also contributes. For arc lengths of more than one day, the error in the atmospheric drag perturbations becomes important. The addition of laser ranging data to the set of range rate data acquired at globally distributed Doppler tracking stations does not improve the radial orbital accuracy for arc lengths of one to three days. For arc lengths of 10 or 20 min, the major contributors to the radial orbital error are measurement, timing and station coordinate errors. Laser data improves short arc accuracy. If a radial rms error of 10 cm is required for short arcs, station positions must be known with an accuracy of five cm and the Doppler measurement noise should be 0.2 cm/sec.