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
November 27, 1996
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 3.5-meter (11-
foot) wings that were unfolded shortly after the Nov. 7 launch
are used to power Global Surveyor. Currently the so-called -Y
array is tilted 20.5 degrees away from its fully deployed and
latched position.
"After extensive investigation with our industrial 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. "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 27 meters per second (60 miles per
hour), 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 2-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 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 onboard 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 lower itself into the correct orbit.
"Because 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 if 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 ongoing
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 5.5 million kilometers
(3.4 million miles) from Earth today, traveling at a speed of
about 119,000 kilometers per hour (74,000 miles 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 the Jet
Propulsion Laboratory for NASA's Office of Space Science,
Washington, D.C.
#####
[Note to Editors: A line-drawing of Mars Global Surveyor, showing
the current position of the solar panel and its fully deployed
position, and 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 at:
http://www.jpl.nasa.gov/news]
11/22/96 DEA
#9690
