Flight Results of GPS Receiver for Geosynchronous Satellites

Abstract

This paper presents the latest GPS receiver (GPSR) developed by JAXA and NEC/NEC Space Technologies, Ltd. for satellites in geosynchronous orbit (GEO). The flight results are also presented. This is the first time a Japanese GPS receiver has used GPS signals above the GPS constellation of satellites. GPS was originally designed for ground users; thus, there are difficulties in receiving signals from GPS in GEO. GEO satellites fly above the GPS constellation orbit. Therefore, they can receive signals from GPS satellites positioned on the other side of the earth. The expected signal strength is weaker in GEO than observed in low Earth orbit (LEO) since the distance from GPS satellites to the receiver is farther than from LEO satellites. With improved sensitivity, the new GPSR was developed to receive these weak signals and determine satellite position using a highly directional antenna optimized for GEO. This receiver was mounted on an optical data relay satellite launched in late 2020. The GPSR successfully activated and determined the satellite's position. This paper introduces the flight results and evaluates the receiver performance in orbit. The results indicated that the GEO GPSR could determine its position within 100 m. This accuracy is far beyond the conventional range and range rate (R&RR) method for determining a satellite's orbit.