This drawing demonstrates the original orbit of Mars Global Surveyor about Mars. The orbit is shown by the white line. One can see that the original orbit of MGS was far from circular! (This drawing is not to scale. It it merely meant to show the elliptical nature of MGS's original orbit)
Click on image for full size
Image from: NASA/JPL
MGS Original Orbit
Originally, the
Mars Global Surveyor entered a highly elliptical orbit around
Mars (as shown here). MGS's furthest point of orbit or its apoapsis was ~56,000 kilometers. Its periapsis or closest point was only ~150 kilometers above the surface. At this point, it took MGS 45 hours to complete one orbit of Mars.
To get into the near-circular, low-altitude orbit necessary to map the surface of Mars, MGS went through a series of aerobraking steps.
After aerobraking was completed, MGS's orbit looked more like a circle. In 2001, the spacecraft's altitude has ranged from about 310 km - 430 km (near-circular orbit) with an orbital period under 2 hours.
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