Douglas Isbell               November 27, 1996
Headquarters, Washington, DC
(Phone:  202/358-1753)

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

RELEASE:  96-250

MARS GLOBAL SURVEYOR SOLAR PANEL WILL NOT HINDER MISSION GOALS

     Mission engineers studying a solar array on NASA's Mars
Global Surveyor that did not fully deploy during the
spacecraft's first day in space have concluded that the
situation will not significantly impair Surveyor's ability to
aerobrake into its mapping orbit, or affect its performance
during the cruise and science portions of the mission.

     The solar panel under analysis is one of two 11-foot
(3.5-meter) wings that were unfolded shortly after the Nov. 7
launch and are used to power Global Surveyor. Currently, the
so-called -Y direction array is tilted 20.5 degrees away from
its fully deployed and latched position.

    "After extensive investigation with our industry
partner, Lockheed Martin Astronautics, using a variety of
computer-simulated models and engineering tests, we believe
the tilted array poses no extreme threat to the mission,"
said Glenn Cunningham, Mars Global Surveyor project manager
at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.  "We
plan to carry out some activities in the next couple of
months using the spacecraft's electrically driven solar array
positioning actuators to try to gently manipulate the array
so that it drops into place.  Even if we are not able to
fully deploy the array, we can orient it during aerobraking
so that the panel will not be a significant problem."

    Diagnosis of the solar array position emerged from two
weeks of spacecraft telemetry and Global Surveyor's picture-
perfect performance during the first trajectory maneuver,
which was conducted on Nov. 21.  The 43-second burn achieved
a change in spacecraft velocity of about 60 miles per hour
(27 meters per second), just as expected. The burn was
performed to move the spacecraft on a track more directly
aimed toward Mars, since it was launched at a slight angle to
prevent its Delta third-stage booster from following a
trajectory that would collide with the planet.

     Both the telemetry data and ground-based computer models
indicate that a piece of metal called the "damper arm," which
is part of the solar array deployment mechanism at the joint
where the entire panel is attached to the spacecraft,
probably broke during the panel's initial rotation and was
trapped in the two inch space between the shoulder joint and
the edge of the solar panel, Cunningham said.

    Engineers at JPL and Lockheed Martin Astronautics,
Denver, CO, are working to develop a process to clear the
obstruction by gently moving the solar panel.  The damper arm
connects the panel to a device called the "rate damper,"
which functions in much the same way as the hydraulic closer
on a screen door acts to limit the speed at which the door
closes.  In Global Surveyor's case, the rate damper was used
to slow the motion of the solar panel as it unfolded from its
stowed position.

     Engineers have been re-evaluating the aerobraking phase
of the Global Surveyor mission, which begins in September
1997 after the spacecraft is captured into an elongated orbit
around the planet using its on-board rocket engine.  The
solar arrays are essential to the aerobraking technique and
will be used to drag the spacecraft into its final, circular
mapping orbit.  First tested on the Magellan spacecraft at
Venus, aerobraking allows the spacecraft to carry less fuel
to a planet and take advantage of its atmospheric drag to
gradually lower itself into the correct orbit.

     "Since we launched early in our window of opportunity,
we will not have to aerobrake as fast to reach the mapping
orbit, and this reduces the amount of heating that the solar
panels are exposed to," Cunningham said.  "In the event that
our efforts to latch the solar array properly in place are
not successful, this reduced heating should allow us to tilt
the array in such a way to prevent it from folding up and yet
still provide enough useful aerobraking force."  Additional
analysis and testing will be performed over the next several
months to verify this hypothesis.

      Meanwhile, Mars Global Surveyor continues to perform
very well as it completes its first two weeks in space, with
on-going science instrument calibrations being performed this
week.  At the same time, the Mars Relay radio transmitter has
been turned on for a post-launch checkout.  Radio amateurs
around the world are gearing up to participate in a radio
tracking experiment in which they will become receiving
stations for the low-power beacon signal transmitted by the
Mars Relay radio system.

      Mars Global Surveyor is approximately 3.4 million miles
(5.5 million kilometers) from Earth today, traveling at a
speed of about 74,000 miles per hour (119,000 kilometers per
hour) with respect to the Sun.

      Mars Global Surveyor is the first mission in a sustained
program of robotic exploration of Mars, managed by JPL for
NASA's Office of Space Science, Washington, DC.

                          -end-

Note to Editors:  A line-drawing of Mars Global Surveyor
showing the current position of the solar panel in its fully
deployed position, including a blow-up which shows the area
in which the broken deployment mechanism is located, can be
found under "News Flashes" on JPL's World Wide Web home page
using the following URL: http://www.jpl.nasa.gov