Differential Ranging Experiments with NASA's High-Gain Deep Space Network Antennas

Radar experiments are currently under way at the Goldstone Deep Space Communications Complex (GDSCC) to determine the range of cis-lunar objects using a single high-gain 34m antenna transmitting 20 kW at X-band wavelengths, and two 34m receivers located at the GDSCC. The 34m antennas of the Deep Space Network (DSN) have effective fields-of-view of approximately 1 milli-radians, hence predetermined pointing predicts with accuracies on the order of 1 milli-degree are required. The extremely accurate 1 nano-second timing distribution of the DSN network enables sub-meter level ranging in the radial direction, by measuring delays in phase-modulated pseudonoise (PN) echoes reflected from the target. In this paper we demonstrate initial experimental verification of the proposed techniques by post-processing radar reflections obtained from a decommissioned geo-synchronous satellite, GOES-8. The characteristics of correlation-based delay measurements obtained simultaneously with two different receiving antennas are described and analyzed for a single spacecraft and two co-located spacecrafts. These are the fundamental quantities used to form the “time difference of arrival” (TDOA) observables commonly used in GPS positioning algorithms, enabling hyperbolic position location as well as determining the differential range between co-located spacecraft, that could be utilized in the future to monitor spacecraft in cis-lunar space.