A Smallsat Multi-pair GRACE-like Mission: Concept and Simulated Performance

Abstract:

The GRACE mission uses two spacecraft in near identical Earth orbits with a phase sensitive microwave ranging instrument that measures changes in spacecraft separation. High precision measurements of the spacecraft separation yield monthly Earth gravity field measurements. The GRACE FO mission adds the Laser Ranging Instrument (LRI) to demonstrate high resolution spacecraft separation measurements with phase-sensitive detection of a frequency-stabilized laser transponder. Previous studies show the improvements in mass change detection afforded by the higher sensitivity range change measurements.

The sparse spatial/temporal sampling and single gravity field component detection of a polar orbiting satellite pair leads to aliasing and artifacts in the gravity field data. These effects limit the mass change detection capability of a GRACE-like mission. Adding a second pair of satellites improves overall system performance by filling in data gaps and sampling the gravity field in different directions. The added expense of a second satellite pair has made this option for improved performance untenable.

A SmallSat GRACE-like mission addresses the cost concern for a multi-pair mission by reducing spacecraft expense and making common launch possible. Through use of a laser ranging sensor and other low-power subsystems and use of existing smallsat architectures, a complete spacecraft-instrument system is shown to meet measurement requirements and make the overall system expense comparable to existing single-pair missions. The resulting multi-pair space segment approach offers a viable option for a GRACE-like mission while improving the science through its better sampling of the gravity field. We show the system concept and simulated gravity field retrievals based on estimates of instrument and spacecraft performance.