An artist's concept of Mars Odyssey at the Red Planet. Photo: NASA/JPL

NASA's 2001 Mars Odyssey spacecraft performed its third trajectory correction maneuver Sunday night to fine-tune its flight path for arrival at Mars next month.

At 4:06 a.m. Universal time on Monday, Sept. 17 (9:06 p.m. Pacific time, Sunday, Sept. 16), Odyssey fired its small thrusters for 12 seconds, which changed the speed and direction of the spacecraft by .45 meters per second (1 mile per hour). Odyssey will arrive at Mars at 0230 Universal time Oct. 24 (7:30 p.m. Pacific time Oct. 23).

"This was the first maneuver to target our final aim point for Mars orbit insertion. Early indications are that the maneuver was right on the money," said David A. Spencer, Odyssey's mission manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

During the past several weeks, the flight team has been troubleshooting occasional problems with its star camera. Flight controllers use the star camera to determine Odyssey's orientation in space. During most of cruise, the star camera has been shaded from the sun by the high gain antenna. When the spacecraft has been rotated so that the star camera is no longer shaded, the images from the star camera have been saturated by sunlight. An internal shade within the star camera is supposed to prevent image saturation. Engineers determined that part of the problem was reflected light from the open door of the gamma ray spectrometer instrument. The door was closed on August 31. A subsequent checkout of the planned spacecraft orientations for the rest of the mission showed that the star camera should provide valid images during these critical periods.

Also on August 31, the flight team transitioned the spacecraft to a new orientation for the remainder of its cruise. The new orientation is designed to limit the number of times Odyssey needs to fire its small thrusters to de-spin the reaction wheels as they build up momentum.

On September 6, the flight team performed a checkout of the spacecraft telecommunications subsystem for Mars orbit insertion. During the checkout, the spacecraft was turned to the planned orientation for the large burn, and the radio signal from the spacecraft was monitored. All systems performed as expected.

Odyssey is 10.8 million kilometers (6.7 million miles) from Mars, traveling at a speed of 24 kilometers per second (52,700 miles per hour) relative to the Sun.

The 2001 Mars Odyssey mission is managed by JPL for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. The Odyssey spacecraft was built by Lockheed Martin Astronautics, Denver. The thermal emission imaging system is managed by Arizona State University, Tempe, and the gamma ray spectrometer is managed by the University of Arizona, Tucson. NASA's Johnson Space Center, Houston, built and manages the Martian radiation environment experiment. The thermal emission imaging system is managed by Arizona State University, Tempe, and the gamma ray spectrometer is managed by the University of Arizona, Tucson.