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Flight Status Report

Sunday, 21 September 1997

Surveyor's third aerobraking pass occurred early this morning at 3:07 PDT. For a time period of about five minutes centered around the low point and start of the sixth orbit, the spacecraft flew through the upper Martian atmosphere at an altitude of 75.4 miles (121.4 km).

According to navigator Dan Johnston, today's pass through the atmosphere slowed Surveyor by 1.45 m.p.h. (0.65 meters per second). This reduction in velocity lowered the altitude of the orbit's high point by 161.5 miles (260 km) and resulted in a new high point of 33,302 miles (53,595 km). The slow down also caused the orbit period to shrink by 17.5 minutes.

As with the previous aerobrake pass two days ago, the thickness of the atmosphere on today's pass exceeded the expected value as predicted by current models. Consequently, the flight team has decided to fly through the atmosphere at the same altitude on the next pass which will occur late Monday night.

This additional pass at the same altitude will allow the navigation team to gather more data before deciding to drop lower into the atmosphere on subsequent passes. Eventually, the low point of the orbit will be dropped to an altitude where the atmospheric thickness will cause an average slow down of about 11 m.p.h. (5 meters per second) per orbit.

After a mission elapsed time of 318 days from launch, Surveyor is 162.66 million miles (261.77 million kilometers) from the Earth and in an orbit around Mars with a period of 44.36 hours. The spacecraft is currently executing the P6 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