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Mars Global Surveyor Update - July 17, 1998

Note the reference to upcoming observations of Phobos, one of the
moons of Mars.  Phobos is suspected to be a captured asteroid.

Ron Baalke

Mars Global Surveyor
Flight Status Report 
Friday, 17 July 1998

     As of today, the Mars Global Surveyor spacecraft has completed 
nearly seven weeks of science collection operations since the end of 
solar conjunction in late May. During that month, the flight team 
suspended science operations because Mars passed behind the Sun as viewed 
from the Earth. This geometry physically blocked radio communications 
with the spacecraft.

     Since the end of conjunction, Surveyor has completed over 100 
revolutions around the red planet and has transmitted almost two 
gigabytes of scientific information back to Earth. Some of the latest 
images released from this summer's science observations include pictures 
of a crater that may have contained a lake long ago in Martian history. 
Other highlights include laser topography measurements of the North Pole, 
and analysis of radio signals sent from the spacecraft to aid the 
understanding of the gravity field in the northern hemisphere.

     Over the remainder of this summer's science operations, 
investigators on Earth will receive their data in less time after 
transmission as the Earth to Mars distance decreases from its June 22nd 
maximum of 234 million miles (377 million kilometers). At that distance, 
2.5 times greater than Earth's distance to the Sun, radio signals from 
the spacecraft took 21 minutes to reach Earth. This time delay will 
gradually decrease to just under five minutes by next May.

     Currently, members of the flight team are preparing for upcoming 
activities in the late summer and fall months. In late August and early 
September, Surveyor will pass within a thousand miles of the Martian moon 
Phobos. This satellite orbits the red planet once every 7.7 hours and is 
a potato-shaped rock about the size of Manhattan. During the close 
approaches, several of the science instruments are scheduled to make 
observations of the moon.

     During August, the flight team will also begin training for the 
next phase of aerobraking. This phase will begin in mid-September and 
last until February 1999. Over the course of those four months, Surveyor 
will repeatedly fly through the upper Martian atmosphere and use air 
resistance to gradually shrink the size of the orbit. The goal is to 
reduce the  period from its current value of 11.6 hours to just under two 
hours. Global mapping operations from this two-hour orbit will begin in 
March or April of next year.

     After a mission elapsed time of 617 days from launch, Surveyor is 
232.68 million miles (374.46 million kilometers) from the Earth and in an 
orbit around Mars with a high point of  11,111 miles (17,881km), a low 
point of 109.6 miles (176.4 km), and a period of 11.6 hours. The 
spacecraft is currently executing the P430 command sequence, and all 
systems continue to perform as expected. The next status report will be 
released sometime in August.

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

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