RADCAL was an axially symmetric, gravity-gradient stabilized spacecraft launched into near-polar orbit at an alitude of 815 km by the U.S. Air Force for radar calibration studies. The spacecraft had a mass of 89.3 kg, a bus height of 40.6 cm, a diameter of 76.2 cm. The gravity gradient boom had a length of 6.069 meters. RADCAL was the first satellite to demonstrate attitude determination using the Global Positioning System (GPS), and carried a Trimble TANS Quadrex receiver. Four microstrip patch antenne were mounted on the top side of the spacecraft [Melvin et al., 1996; Lightsey et al., 1994].

RADCAL was tracked by the TRANET network, and data from March 1994 through August 1994 were included in EGM96. The data were processed in five day arcs, and 11 to 14 sites tracked the spacecraft in each arc. The a priori RMS of fit to the data was 0.3 to 0.4 cm/s.


Lightsey E. G., Cohen, C. E., Feess, W. A., and B. W. Parkinson, Analysis of spacecraft attitude measurements using onboard GPS, Paper No. 94-063, 17th annual Rocky Mountain Guidance and Control Conference, Keystone, Colorado, 1994.

Melvin, P. J., L. M. Ward, and P. Axelrad, The analysis of GPS attitude data from a slowly rotating, symmetrical gravity gradient satellite, J. Astronautical Sciences, 44(4), 515-539, October-December, 1996.

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Frank.G.Lemoine@nasa.gov or Nikolaos.Pavlis@raytheon.com
Last revised November 22, 2004 21:04 UTC