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Contact: Mary Hardin (818) 354-0344

FOR IMMEDIATE RELEASE February 4, 1999

MARS GLOBAL SURVEYOR SUCCESSFULLY COMPLETES AEROBRAKING

       NASA's Mars Global Surveyor spacecraft will soon begin its primary mapping mission after it successfully fired its main rocket engine early this morning and raised its orbit completely out of the Martian atmosphere to end the aerobraking phase of the mission.

       The burn was executed at 12:11 a.m. Pacific time when the flight team determined that the farthest point in the spacecraft's orbit had dropped to 450 kilometers (279 miles) above the Martian surface. During the next two weeks, the spacecraft's closest approach to Mars will slowly drift south until it has moved into a circular Sun-synchronous orbit, in which the spacecraft will cross the Martian equator at about 2 a.m. local solar time.

       "The use of aerobraking has been a pioneering operation for a spacecraft at Mars, and we now know that we can use this technique with confidence for future Mars missions," said Glenn E. Cunningham, deputy director of the Mars Exploration Program at NASA's Jet Propulsion Laboratory. "It has been a long and arduous task that has turned into a valuable learning experience for all of us - engineer and scientist alike. The flight team has done a superb job and we're really glad the aerobraking phase of the mission is now successfully behind us. We're looking forward to beginning the primary mapping mission within the next few weeks."

       The start of the primary mapping mission has been delayed by about a year due to a structural problem with the spacecraft's solar panel that required the flight team to take a more cautious approach to aerobraking to ensure that the weakened panel was not overstressed.

       In addition to making a photographic map of the entire planet during one full Martian year (687 Earth days), Mars Global Surveyor will study the planet's topography, magnetic field, mineral composition and atmosphere.

       "Global Surveyor will become our first weather satellite at Mars. During the extended aerobraking phase, the spacecraft was able to acquire some "bonus" science data that has yielded some spectacular new findings about Mars. We now have a profile of the planet's northern polar cap and information about the unique nature of its remnant magnetic fields," Cunningham said.

       During the aerobraking technique, the spacecraft uses frictional drag as it skims through the planet's thin upper atmosphere to alter the shape of its orbit around the planet. First tested in the final days of the Magellan mission to Venus in 1994, the technique is an innovative way of changing the spacecraft's orbit while carrying less onboard fuel.

       When Global Surveyor arrived at Mars in September 1997, it initially entered a looping, elliptical orbit around the planet that has been gradually circularized through aerobraking. Its winged solar panels -- which feature a Kapton flap at the tip of each wing for added drag -- supply most of the surface area that slowed the spacecraft by a total of more than 1,200 meters per second (about 2,700 miles per hour) during the entire aerobraking phase. Since the start of aerobraking, Surveyor's orbit around Mars has shrunk from an initial elliptical orbit of 45 hours to the now nearly circular orbit taking less than two hours to complete.

       Flight controllers will again fire the spacecraft's main engine on February 18 and perform a final "transfer to mapping orbit" burn, which will lower Global Surveyor's closest approach over Mars from 405 kilometers (253 miles) to approximately 379 kilometers (237 miles). After a short period of calibrating the science instruments, mapping will begin in early March.

       Mars Global Surveyor is the first mission in a long-term program of Mars exploration known as the Mars Surveyor Program that is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft. JPL is a division of the California Institute of Technology, Pasadena, CA.

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