The Spacecraft Autonomous Navigation System using GPS for Earth Orbiters (SANS-GEO) computer program is designed to perform the navigation calculations that will enable the New Millennium Program's Earth Orbiter-1 (EO-1) spacecraft to fly in formation with the Landsat-7 (LS-7) satellite in orbit around the Earth. Scheduled to be launched in May 1999, the EO-1 will be required to follow 450±50 km behind the LS-7, and to keep its ground track within 3 km of the LS-7 ground track. Using data from an onboard Global Positioning System (GPS) receiver and empirical (purely kinematic) GPS navigation algorithms, SANS-GEO would compute parameters of the EO-1 orbit; these parameters would include rates of atmospheric-drag-induced decay. SANS-GEO would then utilize these parameters, along with the corresponding parameters and with maneuver plans generated remotely for the LS-7, to determine EO-1 velocity-change maneuvers needed to satisfy absolute orbital constraints (e.g., ground-track-repeat requirements) and/or relative orbital constraints (formation-flying requirements). The computed velocity-change maneuvers would be converted into commands for the EO-1 attitude-control system and thrusters.

The Spacecraft Autonomous Navigation System depicts the extent of the onboard processing.

This program was written by Joseph Guinn of Caltech for NASA's Jet Propulsion Laboratory.

This software is available for commercial licensing. Please contact Don Hart of the California Institute of Technology at (818) 393-3425. Refer to NPO-20190.


This Brief includes a Technical Support Package (TSP).
Software for navigation of a spacecraft flying in formation

(reference NPO20190) is currently available for download from the TSP library.

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This article first appeared in the July, 1998 issue of NASA Tech Briefs Magazine.

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