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Mars Global Surveyor's Orbit Raised While Solar Panel Is Analyzed

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Contact: Diane Ainsworth

FOR IMMEDIATE RELEASE                         October 14, 1997

GLOBAL SURVEYOR'S ORBIT RAISED WHILE SOLAR PANEL IS ANALYZED

     The lowest point of Mars Global Surveyor's aerobraking orbit 
has been raised temporarily and aerobraking has been suspended 
while the flight team analyzes data to understand why one of the 
spacecraft's two solar panels, which did not fully deploy, 
exhibited unexpected motion during a recent dip through the upper 
Martian atmosphere.

     The spacecraft's current 35-hour orbit around Mars, which 
was taking it down to 121 kilometers (75 miles) above the Martian 
surface during each of its closest passes over the planet, has 
been raised to 170 kilometers (105 miles). The orbit was raised 
Oct. 12 by the operations team at NASA's Jet Propulsion 
Laboratory, Pasadena, CA, and Lockheed Martin Astronautics, 
Denver, CO, by performing a brief, 2.3-meter-per-second (5.15-
mile-per-hour) propulsive burn at the farthest point of the 
spacecraft's orbit around Mars. The panel's performance has had 
no effect on spacecraft power. 

     "We're taking a hiatus from aerobraking for the next few 
weeks while we study data to try to model and understand the 
apparent deflection of the solar panel that never fully deployed 
and latched in place after launch," said Glenn E. Cunningham, 
Mars Global Surveyor project manager at JPL. "This delay in the 
aerobraking process will probably change the spacecraft's final 
mapping orbit from the originally planned 2 p.m. passage over the 
planet's equator in local Mars time to another time, and we are 
studying several other orbits that will give us nearly the same 
outstanding science results."

     Preliminary data from the panel indicate that it has moved 
past what would have been its fully deployed and latched 
position, Cunningham said. In addition, the panel has shown some 
movement rather than maintaining its rigid position during 
aerobraking. These changes occurred during the spacecraft's 
fifteenth closest approach over the Martian surface, on Oct. 6, 
when the density of the Martian atmosphere doubled unexpectedly.

     During the next few weeks, the Mars Global Surveyor flight 
team will leave the spacecraft's orbit in the current, 35-hour 
revolution around Mars, which will not take the spacecraft 
through the upper atmosphere of Mars, while they analyze data and 
simulate conditions in the Martian atmosphere to understand the 
behavior of the solar panel. This hiatus also means the 
spacecraft's solar panels will not be reconfigured for each close 
pass over Mars, but will remain in the normal cruise position.

     "We can't explain yet what has happened," Cunningham said. 
"We saw the unlatched panel move past the latched-up position, 
and it remains past that point now. By raising the spacecraft's 
orbit above the upper atmosphere, the panel should not shift 
further because it will not be exposed to the aerodynamic forces 
of the Martian atmosphere."

     Several other mapping orbits are available to Mars Global 
Surveyor to carry out its science objectives. The flight team 
will explore alternatives in the next few weeks to accomplish the 
lowest orbit possible and achieve a "sun synchronous" orbit that 
will allow Global Surveyor to fly over the Martian equator at the 
same local solar time each orbit. These sun synchronous orbits 
are designed so that the spacecraft's instruments always see Mars 
at the same lighting angle on every pass over the surface.

     "As we step back from aggressive aerobraking temporarily, we 
will have the opportunity to study the situation until we fully 
understand it," Cunningham said. "We will take advantage of this
opportunity to return some spectacular data from the camera and 
laser altimeter. The thermal emission spectrometer and 
magnetometer/electron reflectometer also will continue to collect 
data while we remain in this holding pattern."

     The Mars Global Surveyor atmospheric advisory group reported 
that the Martian atmosphere has more than doubled in thickness in 
the last week. Global Surveyor is designed to withstand more than 
a 50 percent increase in atmospheric density, but began showing 
movement in the solar panel last week, during the fifteenth 
periapsis on Oct. 6. 

     Additional information about the Mars Global Surveyor 
mission is available on the World Wide Web by accessing JPL's 
Mars news site at http://www.jpl.nasa.gov/marsnews or the Global 
Surveyor project home page at http://mars.jpl.nasa.gov .

     Mars Global Surveyor is part of a sustained program of Mars 
exploration, known as the Mars Surveyor Program. The mission is 
managed by the Jet Propulsion Laboratory for NASA's Office of 
Space Science, Washington, DC. JPL's industrial partner is 
Lockheed Martin Astronautics, Denver, CO, which developed and 
operates the spacecraft. JPL is a division of the California 
Institute of Technology, Pasadena, CA.

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