A Multi-Satellite GRACE-like Mission Using Small Satellites

Measurement of global water variation provides information critical to climate change and water resource monitoring. The Gravity Recovery and Climate Experiment II (GRACE II) was chosen as a Tier III mission by National Research Council's decadal survey because of its unique ability to measure the global mass distributions and variations in the mass distribution caused primarily by water variation. We discuss a multi-satellite approach to a GRACE-like mission. Enhanced spatial resolution of mass variations over those provided by the current GRACE mission can be achieved by improving the ranging accuracy; an interferometric ranging concept that improves the ranging accuracy has been demonstrated[1]. However, recent calculations show that to obtain the full science improvement using interferometric ranging, temporal aliasing errors due to modeling and to undersampling of geophysical signals must be mitigated[2]. One approach is to improve the data analysis techniques and validation processes. Another approach is to fly two or more pairs of satellites, thereby sampling the Earth's gravitational field at shorter time intervals[3]. A multiple-pair mission is often dismissed as too expensive, but the mission costs of a multiple-pair GRACE-like mission could be greatly reduced by developing compact ranging systems so that the mass, power, and volume usage is consistent with small spacecraft buses. Such size reduction drastically reduces the launch costs by allowing the spacecraft to be launched as auxiliary payloads. We will discuss the technological challenges that are associated with a GRACE-like mission that uses smallsats to reduce costs of more than one pair of satellites, as well as the scientific benefits of the two or more satellite pairs. The technological challenges include reducing the size of the payload and developing a low-drag, low-pointing jitter spacecraft. [1]Pierce, R., J. Leitch, M. Stephens, P. Bender, and R. Nerem, “Intersatellite range monitoring using optical interferometry”, Appl. Opt. 47 (2008), 5007. [2]P. Visser and E. Pavlis in ”Report from the Workshop on The Future of Satellite Gravimetry”, edited by R. Koop and R. Rummel (ESTEC, Noordwijk, The Netherlands, 12-13 April, 2007), pg. 11. [3]Bender, P. L., D. N. Wiese, and R. S. Nerem, “A possible dual-GRACE mission with 90 degree and 63 degree inclination orbits, Proceedings of the 3rd International Symposium on Formation Flying, Missions and Technologies”, ESA Communication Production Office, ESA-SP-654, 2008.