Mars Global Surveyor Mission Status
28 Jan 1999
(Source: Jet Propulsion Laboratory)
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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Mars Global Surveyor began the last portion of its second aerobraking phase, known as the "walk-out" phase, at 8:34 a.m. Pacific Standard Time today. During this final stage of aerobraking, the spacecraft will "walk out" of the Martian atmosphere in four steps. This morning, the spacecraft's orbit was raised from a closest approach of 100 kilometers (62.5 miles) to 103 kilometers (64.4 miles) above the planet's surface. As the closest approach, or periapsis, is adjusted, the spacecraft's apoapsis, or farthest point from Mars, will continue to diminish until Global Surveyor is in a two-hour orbit over the poles of the planet.
The flight team at the Jet Propulsion Laboratory in Pasadena and Lockheed Martin Astronautics in Denver will uplink aerobraking sequences twice a day over the next six days to adjust both the nearest and farthest points of the spacecraft's orbit. These sequences will allow the spacecraft to execute one propulsive maneuver each day. The flight team will track Global Surveyor's altitude over the Martian surface during each of 12 daily passes through the Martian atmosphere.
Aerobraking is expected to end on February 4, when Global Surveyor will be instructed to fire its main rocket engine and raise its orbit completely out of the Martian atmosphere. The burn will be executed when the flight team has determined that the spacecraft's apoapsis has dropped from the current 1,000 kilometers (625 miles) to the designated 450 kilometers (279 miles) over the Martian surface. Over the next two weeks, the spacecraft's closest approach over Mars will slowly drift south until it has moved into a Sun-synchronous orbit, in which the spacecraft will cross the equator at about 2 a.m. local solar time on Mars each orbit. 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).
Mars Global Surveyor remains in excellent health more than two years after its launch. The magnetometer, one of six scientific instruments onboard the spacecraft, was turned off today for completion of the aerobraking phase. It will be turned on again on February 10, and the rest of the science payload will be powered on for calibration tests beginning on February 25. A "pre-mapping phase" in which the spacecraft will acquire one complete global map of Mars will be conducted March 8-28.