Mission
Gravity Recovery and Climate Experiment (GRACE) was launched March 17, 2002. The primary objective of the GRACE mission is to obtain accurate global models for the mean and the time variable components of the Earth's gravity field. This objective is achieved by making measurements of inter-satellite range and its time derivative, for 2 co-planar, low altitude, near-polar orbiting satellites, using a microwave tracking system. In addition, each satellite carries Global Position System (GPS) receivers and high accuracy accelerometers to enable accurate orbit determination, spatial registration of gravity data and the estimation of gravity field models. (GRACE L1B Data Product User Handbook. K.Case, G. Kruizinga, S-C. Wu)

Products FTP / HEFT s/w 2-3 months x x - - seconds - Documentation: User Manual / Abstract / References Comments: Level 1B Products contain inter-satellite range variations and other science data, including all corrections, necessary to derive monthly time-variations in the Earth's gravity field. The data are correctly time-tagged, and the data sample rate is reduced from the high rate data of previous levels. FTP / HEFT s/w 3 months - x - x+ 30 days ~500km (depends on useage) Documentation: User Manual / Abstract / References Comments: Mean monthly estimates of spherical harmonic coefficients for the Earth gravitational potential. FTP / HEFT s/w 3 months x x - x 30 days ~500km (depends on useage) Documentation: User Manual / Abstract / References Comments: Mean monthly estimates of spherical harmonic coefficients for the Earth gravitational potential. FTP / HEFT s/w 3 months - - x x 30 days ~500km (depends on useage) Documentation: User Manual / Abstract / References Comments: Mean monthly estimates of spherical harmonic coefficients for the Earth gravitational potential. FTP / HEFT s/w 2-3 months - x x x 6 hours 1° (SH degree 180) Documentation: User Manual / Abstract / References Comments: Atmospheric and ocean de-aliasing product. Part of the L1B data. FTP / HEFT s/w 2-3 months - - - - 6 hours 1.875° Documentation: User Manual / Abstract / References Comments: Barotropic ocean model output (OCN1B). Part of the L1B data. Information related to OCN1B starts on Page 35 of the AODB1 User Manual.

Temporal resolution
Global and continuous with a temporal resolution of less than or equal to a month of non-repeating orbits at a 500 Km orbit which will decay over the 5 year (plus 2 year extended) life. Over a 30-day period a geographically dense data coverage is obtained.  See User Handbook for more information.

Spatial resolution
The twin GRACE satellites fly a polar orbit with an initial altitude of 500 km decaying to 300 km near the end of 5 year mission.

Documentation
GRACE Mission: http://podaac.jpl.nasa.gov/grace
GRACE Tellus: http://grace.jpl.nasa.gov/
GeoForschungsZenrum (GFZ) Potsdam Grace: http://www.gfz-potsdam.de/pb1/op/grace/index_GRACE.html
University of Texas Center For Space Research (UTCSR) Grace: http://www.csr.utexas.edu/grace/

http://podaac.jpl.nasa.gov/grace/documentation.html
http://grace.jpl.nasa.gov/   
http://www.csr.utexas.edu/grace/  
http://www.gfz-potsdam.de/pb1/op/grace/index_GRACE.html

Citations/References
http://gracetellus.jpl.nasa.gov/publications.html
http://podaac.jpl.nasa.gov/grace/