Design of the Geosat Exact Repeat Mission

The GEOSA T spacecraft was launched into a retrograde orbit from the Western Test Range in March 1985. The first 18 months were dedicated to completing the high-resolution mapping of the marine geoid undertaken by the Seasat mission in 1978 and interrupted by its early demise. In September 1986, the spacecraft was maneuvered into an orbit more suited for oceanography. That phase of the mission is referred to as .the .GEOSA T Exact Repeat Mission. In order to minimize the effect of geoid uncertainty on the determmation of ocean variability derived from GEOSA T altimetry, the ground tracks from each repeat cycle should deviate by no more than 1 kilometer from the mean ground tracks in all other repeat cycles. The origin and planning for the Exact Repeat Mission are described here, together with a discussion of the feasibility of maneuvering and maintaining the spacecraft in an exact repeat orbit.