93-161

Evaluation Of Landsat-4 Orbit Determination Accuracy Using Batch Least-Squares And Sequential Methods *

D. H. Oza**, T. L. Jones***, R. Feiertag****, M. V. Samii*****, C. E. Doll******, G. D. Mistretta****** and R. C. Hart*******

Abstract

The Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) commissioned Applied Technology Associates, Incorporated, to devebp the Real-Time Orbit DeterminationlEnhanced (RTOD/E) system on a Disk Operating System (DOS)-based personal computer (PC) as a prototype system for sequential orbit determination of spacecraR. This paper presents the results of a study to compare the orbit determination accuracy for a Tracking and Data Relay Satellite (TDRS) System (TDRSS) user spacecraft, Landsat-4, obtained using RTOD/E, operating on a PC, with the accuracy of an established batch least-squares system, the Goddard Trajectory Determination System (GTDS), operating on a mainframe computer. The results of Landsat-4 orbit determination will provide useful experience for the Earth Observing System (EOS) series of satellites. The Landsat-4 ephemerides were estimated for the May 18-24, 1992, timeframe, during which intensive TDRSS tracking data for Landsat-4 were available. During this period, there were two separate orbit-adjust maneuvers on one of the TDRSS spacecraft (TDRS-East) and one small orbit-adjust maneuver for Landsat-4. Independent assessments were made of the consistencies (overlap comparisons for the batch case and covariances and the first measurement residuals for the sequential case) of solutions produced by the batch and sequential methods. The forward-filtered RTOD/E orbit solutions were compared with the definitive GTDS orbit solutions for Landsat-4; the solution differences were generally less than 30 meters after the filter had reached steady state. 

* This work was supported by the National Aeronautics and Space Administration (NASA)/Goddard Space Flight Center (GSFC). Greenbelt. Maryland, under Contract NAS 5-31500. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

**  Principal Engineer. Computer Sciences Corporation (CSC), Green Tec ll Building, 10110 Aerospace Road, Lanham-Seabrook, Maryland 20706. Member AIAA.

***   Computer Scientist. Computer Sciences Corporation (CSC), Green Tec ll Building, 10110 Aerospace Road, Lanham-Seabrook, Maryland 20706.

****Member of the Technical Staff. Computer Sciences Corporation (CSC), Green Tec ll Building, 10110 Aerospace Road. Lanham-Seabrook. Maryland 20706.

*****Department Manager, Computer Sciences Corporation (CSC), Green Tec ll Building, 10110 Aerospace Road, Lanham-Seabrook, Maryland 20706. Member AIAA

******Aerospace Engineer, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771. Member AIAA.

*******Aerospace Engineer, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771.