PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Diane Ainsworth
FOR IMMEDIATE RELEASEOctober 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
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.