NASA's Mars Odyssey spacecraft completed two maneuvers this week, fine-tuning its orbit in preparation for the science mapping mission that will begin in late February.

At 2 p.m. Pacific Time, January 17, Odyssey reduced the farthest point in its orbit, called the apoapsis, from an altitude of 520 kilometers (323 miles) to an altitude of 450 kilometers (280 miles). The spacecraft fired its thrusters for 195 seconds, and decreased the velocity of the spacecraft by 27 meters per second (60 miles per hour). This maneuver also moved the closest point of the orbit, called the periapsis, under the south pole of the planet.

Earlier this week, on January 15, Odyssey fired its thrusters for 398 seconds, increasing its speed by 56 meters per second (125 miles per hour) and raising the closest point in its orbit from 186 kilometers (116 miles) to 419 kilometers (260 miles). Flight controllers also changed the inclination of the orbit, the angle between the orbit plane and the Mars equator, to 93.1 degrees.

"Aside from the orbit insertion burn in October, these are the largest maneuvers that we have executed and they help us circularize the orbit. They were also the most complex to design and implement," said Bob Mase, Odyssey's lead navigator at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "These burns had to be executed at specific times to achieve the desired results, so the flight team had a lot of work to do in a very short amount of time. The maneuver performance was excellent."

During the next few weeks, flight controllers will continue to refine the orbit to achieve a final mapping orbit with a periapsis altitude of 387 kilometers (240 miles) and apoapsis altitude of 450 kilometers (280 miles).

Also this week, engineers turned on the neutron spectrometer, the high-energy neutron detector and a portion of the gamma ray spectrometer subsystem. These science instruments are working as expected. The formal mapping mission will begin next month.

JPL manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. Principal investigators at Arizona State University in Tempe, the University of Arizona in Tucson, and NASA's Johnson Space Center, Houston, Texas, operate the science instruments. Additional science investigators are located at the Russian Space Research Institute and Los Alamos National Laboratories, N.M. Lockheed Martin Astronautics, Denver, Colo., is the prime contractor for the project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena. NASA's Langley Research Center in Hampton, Va., is providing aerobraking support to JPL's navigation team during mission operations.


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