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Mars Global Surveyor Update - September 23, 1997

Mars Global Surveyor
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