Sensing Technologies for Formation‐Flying Spacecraft in LEO using CDGPS and an Interspacecraft Communications System

This paper describes research on sensing technologies for formation‐flying spacecraft in low earth orbit. The approach is based on a combination of carrier‐phase differential GPS (CDGPS) sensors and GPS‐like transceivers that are combined with the interspacecraft communications system. By providing additional inter‐spacecraft range and Doppler measurements to the navigation solution, these on‐board transmitters could facilitate the use of CDGPS for orbits in which adequate visibility/geometry to the NAVSTAR constellation is not available. In addition, the carrier‐phase cycle ambiguity can be rapidly initialized using relative vehicle motions. The paper discusses this augmentation concept in detail and presents a new algorithm that significantly improves the bias initialization process. The paper also addresses some key measurement errors associated with formation‐flying spacecraft separated by long baselines (10–100 km). Experimental results on a new terrestrial testbed are presented to show the vehicle formation undergoing short path initialization and formation maneuvers.