The NASA Mission Information Page by Jeffry J. Brickley
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Last Updated: 11/14/99.
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Aerobraking

Aerobraking is a process of slowing a space vehicle down by "brushing" the upper atmosphere of a planet. Once an object enters a 'stable' orbit around a gravitational body (like a planet) it will remain in the same orbit with very little change over a period of years. However to change that orbit requires a great deal of fuel and manuevering thrusters or very slight use of manuevering thrusters and a good use of the planet's atmosphere which causes the vehicle to "drag" along the upper atmosphere, thus slowing the vehicle down. To start this procedure, the vehicle adjust from a stable orbit to an orbit that heads closer to the planet until it will contact the atmosphere, then it waits until it has passed through the upper edge of the to 'readjust' to a stable orbit (if necessary). The deeper an object goes into the upper atmosphere, the more the object will slow down. A good example of this is the recent developements with the Mars Global Surveyor. The MGS had a failure with one of the solar panels, making NASA opt for a slower aerobraking procedure that goes through more orbits and less into the atmosphere of MARS. The result is a 'gentler' treatment of the broken solar panel and less risk to the vehicle.

As a cost-saving measure, the option of aerobraking was chosen for the Mars Global Surveyor. The main problem with aerobraking is that it is VERY time consuming. However, during the near orbit, NASA has planed several "fly-by" shots of mars. These pictures will give scientists some early data prior to the full mapping mission and allow the MGS to "stretch it's legs" in showing what it's later capabilities will be.