Analysis of GOES -13 Orbit and Attitude Determination

The Geostationary Operational Environmental Satellite (GOES) 13 is th e first in a new series of weather satellites. Compared to previous GOES satellites, GOES -13 has improved Image Navigation and Registration (INR) accuracy and can continue imaging during eclipse periods. Post launch testing showed that GOES -13 met all INR requirements, but systematic patterns appeared in differences between actual landmark and ra nge measurements and 24 hour measurement predictions based on estimated orbit and attitude parameters. Presence of t hese residual patterns implied that the models used in Orbit and Attitude Determination (OAD) did not accurately match reality. Thorough inv estigations were conducted to determine the modeling error source. It was concluded that an angular bias between star and landmark observations was the most likely modeling error, although small uncompensated range biases could also be present. Further ana lysis of on -orbit and test data eliminated numerous potential instrument, spacecraft and ground processing error sources. Although the cause of the landmark -star bias is still unknown, the bias causes no operational problems because OAD solution of a range bias compensates for the error. Even without range bias adjustment, GOES -13 met all INR requirements with margin.