Precise accelerometry onboard the GRACE gravity field satellite mission

Abstract The twin satellites of the GRACE (Gravity field recovery and climate experiment) mission are equipped with three-axes capacitive accelerometers measuring the non-gravitational surface forces acting on the satellites with a sensitivity which is unprecedented for low earth orbiters. In this paper, we study 10 Hz raw accelerometer observations from both GRACE satellites. We identify and analyse numerous acceleration spikes related to switching activity in the circuits of onboard heaters. These spikes are very well observed, but their source is not yet understood. Based on various indications, we suggest the presence of mechanical forces due to electrical current changes. The acceleration spikes demonstrate the difficulty to create a quiet environment on a low earth orbiter platform. We use spike-free data from time spans without heater activity to show that the accelerometers indeed achieve the expected sensitivity, with a noise level slightly below 10 - 10 m/s 2 / Hz for the along track and radial axes. We derive average models for the switching spikes and use them to construct a synthetic spike time series. Based on preliminary modeling results, we expect at most a slight influence of the acceleration spikes on the GRACE gravity field determination. However, the acceleration spikes are not negligible for the investigation of satellite aeronomy and of the sources of non-gravitational forces.

[1]  Victor Zlotnicki,et al.  Time‐variable gravity from GRACE: First results , 2004 .

[2]  Hermann Lühr,et al.  Zonal winds in the equatorial upper thermosphere: Decomposing the solar flux, geomagnetic activity, and seasonal dependencies , 2006 .

[3]  J. B. Thomas.  An Analysis of Gravity-Field Estimation Based on Intersatellite Dual-1-Way Biased Ranging , 1999 .

[4]  C. Reigber,et al.  CHAMP mission status , 2002 .

[5]  R. Nerem,et al.  Thermosphere density response to the 20-21 November 2003 solar and geomagnetic storm from CHAMP and GRACE accelerometer data , 2006 .

[6]  Pierre Touboul,et al.  Flight experience on CHAMP and GRACE with ultra-sensitive accelerometers and return for LISA , 2003 .

[7]  M. Cheng,et al.  GGM02 – An improved Earth gravity field model from GRACE , 2005 .

[8]  P. Touboul,et al.  In orbit nano-g measurements, lessons for future space missions , 2004 .

[9]  Frank Flechtner,et al.  GRACE Performance Study and Sensor Analysis , 2005 .

[10]  B. Frommknecht,et al.  Integrated Sensor Analysis of the GRACE Mission , 2007 .

[11]  Jeongrae Kim,et al.  Simulation study of a low-low satellite-to-satellite tracking mission , 2000 .

[12]  U. Meyer,et al.  Static and Time-Variable Gravity from GRACE Mission Data , 2006 .

[13]  Jeongrae Kim,et al.  Error Analysis of a Low-Low Satellite-to-Satellite Tracking Mission , 2002 .

[14]  M. Watkins,et al.  GRACE Measurements of Mass Variability in the Earth System , 2004, Science.

[15]  Roland Schmidt,et al.  Zur Bestimmung des cm-Geoids und dessen zeitlicher Variationen mit GRACE , 2007 .

[16]  M. Schelkle.  The GRACE Cold Gas Attitude and Orbit Control System , 2000 .

[17]  Jakob Flury,et al.  Integrated Sensor Analysis GRACE , 2003 .

[18]  S. Swenson,et al.  Accuracy of GRACE mass estimates , 2006 .

[19]  Hermann Lühr,et al.  Global distribution of the thermospheric total mass density derived from CHAMP , 2004 .

[20]  G. Balmino,et al.  Dedicated gravity field missions—principles and aims , 2002 .

[21]  Markus Rothacher,et al.  Observation of the Earth system from space , 2006 .

[22]  J. Forbes,et al.  Thermosphere density variations due to the 15–24 April 2002 solar events from CHAMP/STAR accelerometer measurements , 2005 .

[23]  Jeffrey M. Forbes,et al.  Global thermospheric neutral density and wind response to the severe 2003 geomagnetic storms from CHAMP accelerometer data , 2005 .

[24]  John C. Ries,et al.  Precise orbit determination for GRACE using accelerometer data , 2006 .

[25]  E. Sutton,et al.  Neutral density response to the solar flares of October and November, 2003 , 2006 .

[26]  Sean Bruinsma,et al.  Solar Rotation Effects on the Thermospheres of Mars and Earth , 2006, Science.