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Flight Status Report

Tuesday, 23 September 1997

After 12 days of orbital operations around the red planet, the Mars Global Surveyor spacecraft continues to perform its mission flawlessly. Late last night at 11:29 PDT, the spacecraft reached the low point of its seventh orbit and completed its fourth aerobraking pass through the upper Martian atmosphere. This pass occurred at an altitude of 75.1 miles (120.9 km).

Air resistance from the atmosphere slowed Surveyor and caused the altitude of the orbit's high point to drop from 33,302 miles (53,595 km) down to 33,143 miles (53,340 km). This amount is comparable to the drop that occurred from the previous pass which occurred on Sunday. The reason for this similarity is that the altitude of the atmospheric pass and the thickness of the atmosphere remained relatively constant between Sunday's aerobraking pass and yesterday's pass.

At 9:31 PDT tonight, the flight team will fire Surveyor's tiny rocket thrusters to lower the low point of the orbit deeper into the Martian atmosphere. As a result, the next aerobraking pass will occur on Wednesday night at an altitude of 72.1 miles (116 km). Eventually, the low point of the orbit will be dropped to an altitude where the atmospheric thickness will cause an average slow down of 11 m.p.h. (5 meters per second) per orbit. Currently, the amount of slow down per orbit is about 2.2 m.p.h. (1 meter per second).

After a mission elapsed time of 320 days from launch, Surveyor is 163.54 million miles (263.19 million kilometers) from the Earth and in an orbit around Mars with a period of 44.08 hours. The spacecraft is currently executing the P7 command sequence, and all systems continue to be in excellent condition.

Status report prepared by:

Office of the Flight Operations Manager
Mars Surveyor Operations Project
NASA Jet Propulsion Laboratory
California Institute of Technology
Pasadena, CA 91109