Artist concept of Jason

In an experiment that could change the way satellites are flown in Earth orbit, the U.S./French TOPEX/Poseidon satellite has successfully completed the first-ever NASA autonomous navigational maneuver.

The experiment, which was designed to help validate technology that allows Earth-orbiting satellites to autonomously adjust their orbits, was conducted in early December from the TOPEX/Poseidon mission control room at the Jet Propulsion Laboratory.

"The importance of this maneuver lies in the fact that it provides confidence that autonomous satellite actions can be affordably developed and executed at an acceptable level of risk. It is the first step in demonstrating a complete autonomous navigation system for Earth-orbiting satellites," said Charles Yamarone, program manager of JPL's Earth Science Flight Projects Office.

In the experiment, flight controllers uplinked software to TOPEX/Poseidon that autonomously planned the satellite's actions and generated a series of commands to steer it. The software required minimal input from ground controllers, consisting only of changes in velocity and the time to execute the maneuver. The software then computed the changes in satellite orientation and the amount and timing of satellite thruster burns with no further input from ground controllers.

TOPEX/Poseidon was selected for this experiment because it is an operational satellite that needs to precisely maintain its ground track. It also has an onboard computer that could be used for the experiment without interrupting or jeopardizing satellite normal operations. This computer is part of the experimental Global Positioning System receiver that is normally used for precision orbit determination.

NASA's first mission planned to test completely autonomous navigation is the New Millenium Program's Earth Orbiter 1 planned for launch in late 1999 or early 2000.

The TOPEX/Poseidon mission is managed by JPL for NASA's Office of Earth Science, Washington, DC. JPL is a division of the California Institute of Technology.

For more information, please visit the TOPEX/Poseidon web site at

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