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For Release: Sept. 5, 1997

Catherine E. Watson
(757) 864-6122

Release No. 97-109

Global Surveyor Spacecraft Arrives at Mars Sept. 11


As the Mars Global Surveyor (MGS) repeatedly dips into the Martian atmosphere to slow itself down, graduate students from the George Washington University Joint Institute for Advancement of Flight Sciences (JIAFS) at NASA Langley will gather unique data on the vertical structure of the planet's upper atmosphere.

The JIAFS graduate students will monitor near real-time data coming from one of Surveyor's accelerometers. The accelerometer will measure changes in the speed of the Surveyor spacecraft caused by changes in the density of the Martian atmosphere. The JIAFS students will use these measurements to determine the vertical structure of Mars' upper atmosphere. Dr. Gerald Keating, the principal investigator of the JIAFS project said, "The [Surveyor] accelerometer experiment will provide the first orbiter accelerometer measurements of any planetary atmosphere. Hundreds of vertical structure measurements will be obtained compared to only three in the past (two from the Viking missions and one from the recent Pathfinder mission - all planetary probes)."

Less than a week after Surveyor reaches Mars, the spacecraft will begin to use the Martian atmosphere to slow down in a process called "aerobraking" (using the friction of the atmosphere flowing past a spacecraft to slow the craft down). The aerobraking (deceleration) phase of the Surveyor spacecraft will lower it into a nearly circular mapping orbit over the poles of Mars.

The aerobraking technique is an innovative method of braking which allows a spacecraft to carry less fuel to a planet and take advantage of a planet's atmospheric drag to descend into a low-altitude orbit. Carrying less fuel also enables a spacecraft to carry more scientific instrumentation.

In addition to the atmospheric studies, Surveyor mission engineers will use results from the accelerometer data analyzed by the JIAFS students to determine how well the aerobraking is working and to make adjustments to the spacecraft's aerobraking orbit. Because the Surveyor spacecraft will be near its aerodynamic heating limits throughout much of the four-month aerobraking procedure, the accelerometer data is crucial.

Interviews, images, video b-roll (including animation) and on-site tours of the JIAFS facility at NASA Langley are available.

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