A Satellite Laser Interferometry Gravity Mission Study

Yun-Kau Lau
Institute of Appl. Maths., Chinese Academy of Sciences, Beijing, China.
On behalf of the Space Advanced Gravity Measurements (SAGM) working group. Current member institutes:
Academy of Mathematics and System Sciences, CAS,
CAS Nanocenter, Beijing,
Dong Fang Hong Satellite Company,
Huazhong University of Science and Technology,
Institute of Atmospheric Physics, CAS,
Institute of Mechanics, CAS,
Institute of Physics, CAS,
Shanghai Engineering Center for MicroSatellites, CAS,
Wuhan Institute of Geodesy and Geophysics, CAS,
Wuhan Institute of Physics and mathematics, CAS.

This presentation outlines an ongoing, informal feasibility study of a low-low satellite-to-satellite laser interferometry tracking scientific satellite mission to map the Earth’s temporal gravity field within the Chinese microgravity community. This prospective mission is planned to be launched after the NASA/DLR Gravity Recovery and Climate Experiment (GRACE), or concurrent with or after the scheduled NASA GRACE Follow on mission. Unlike the current GRACE mission, we intend to use two co-orbiting drag-free satellites with laser ranging in place of microwave ranging to enhance the precision of satellite-to-satellite tracking measurement, to infer and to measure variations of the Earth’s gravity field. The scientific justification of the satellite mission includes but not limited to, quantification of the Asian continent and global hydrology, co-seismic and post-seismic deformations resulting from earthquakes and continental geodynamics, and observables driving or resulting from global climate change. At present, the preliminary baseline design parameters under consideration include: (1) the distance between the two co-orbiting spacecrafts: 50–100 km, (2) the precision of the laser interferometric measurement: 1–10 nm, (3) the altitude with drag-free control: 300–350 km, (4) the residual acceleration: 10-10 to 10-12 ms-2(Hz)-1 at around 0.1 Hz, and (5) nominal mission time: four to five years. In-depth instrument error analysis being conducted includes laser metrology, pointing stability and development of reference sensors. Sensitivity analysis is ongoing and one of the critical issues being addressed is the temporal aliasing of signals from errors from background forward models (for example, barotropic atmosphere and ocean responses and tides) as well as the desired signals to be measured. With potential international collaborative partners, collectively one could address of feasibility of formation flights or optimal constellations involving two or even three pairs of GRACE-type satellites to significantly minimize observability, temporal or spatial aliasing problems.