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Location: UFOUpDatesList.Com > 1997 > Oct > Oct 14

Global Surveyor's Orbit Raised While Solar Panel

From: NASANews@hq.nasa.gov
Date: Tue, 14 Oct 1997 16:18:30 -0400 (EDT)
Fwd Date: Tue, 14 Oct 1997 19:48:18 -0400
Subject: Global Surveyor's Orbit Raised While Solar Panel

Douglas Isbell
Headquarters, Washington, DC                  October 14, 1997
(Phone:  202/358-1753)

Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, CA
(Phone:  818/354-5011)

RELEASE:  97-232


     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 had not fully deployed,
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 75 miles (121 kilometers) above the Martian
surface during each of its closest passes over the planet, has
been raised to 105 miles (170 kilometers).  The orbit was raised
Oct. 12 by the operations team at NASA's Jet Propulsion Laboratory
(JPL), Pasadena, CA, and Lockheed Martin Astronautics, Denver, CO,
by performing a brief, 5.15-mile-per-hour (2.3-meter-per-second)
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. local Mars time
passage over the planet's equator to another time, and we are
studying several other orbits that will give us nearly the same
quality of 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 close
approach to Mars, 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 yet explain 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.  We will take advantage of this opportunity to
return some spectacular data from the camera and laser altimeter,"
Cunningham said.  "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 close
approach 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 URL:

or the Global Surveyor project home page at URL:


     Mars Global Surveyor is part of a sustained program of Mars
exploration, known as the Mars Surveyor Program.  The mission is
managed by JPL 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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