MEDIA RELATIONS 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: Mary Hardin (818) 354-0344
FOR IMMEDIATE RELEASE
February 22, 1999
MARS GLOBAL SURVEYOR READY TO BEGIN FULL MAPPING MISSION
NASA's Mars Global Surveyor spacecraft will begin its
primary mapping mission within the next two weeks, following a
successful firing of its main engine at 2:20 p.m. Pacific time on
Feb. 19 to fine-tune its path around the red planet into a nearly
circular, Sun-synchronous orbit.
The final "transfer to mapping orbit" burn lowered Global
Surveyor's closest approach over Mars from 405 kilometers (253
miles) to approximately 367 kilometers (229 miles). Later this
week, the flight team will turn on, focus and calibrate the
spacecraft's camera and power up several other science
instruments, including the thermal emission spectrometer and
laser altimeter.
"Reaching our mapping orbit has been a long time coming for
all involved. We are delighted to finally be able to do this
mission as it was designed, in the proper mapping orbit with all
the instruments working at their full potential," said Dr. Arden
Albee, the Mars Global Surveyor project scientist at the
California Institute of Technology, Pasadena, CA.
The mapping orbit was designed so that Surveyor passes over
a given part of Mars at the same local time each orbit. At about
2 p.m. local Mars time, the spacecraft will cross the equator
flying northward on the daytime side and about 2 a.m., it will
cross the equator flying southward on the nighttime side. This
timing is essential for effective interpretation of atmospheric
and surface measurements, because it allows scientists to
separate local daily variations from longer-term seasonal and
annual trends.
"We still have a few minor adjustments to fine-tune the
orbit during the next few weeks. Our plan at this point is to
conduct the first three one-week mapping cycles with Surveyor's
high-gain communication antenna in the stowed position. After we
have these first mapping cycles completed, we plan to deploy the
antenna and continue mapping in that configuration," said Glenn
E. Cunningham, deputy director of the Mars Exploration Program at
NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
Launched in November 1996 and in Mars orbit since September
1997, Mars Global Surveyor carries a dish-shaped high-gain
antenna that will be deployed on a 2-meter-long (6.6-foot) boom.
The antenna was stowed during launch and the early orbital phase
at Mars to reduce the chances of it being contaminated by the
exhaust plume from the spacecraft's main engine.
During deployment, the boom is pushed outward by a powerful
spring. A damper mechanism cushions the force of the spring and
limits the speed of the deployment, somewhat like an automobile
shock absorber or the piston-like automatic closer on a screen
door. Last year, engineers became aware of problems with similar
damper devices on deployable structures such as solar panels on
other spacecraft.
"Until we deploy the antenna, we must turn the entire
spacecraft periodically to transmit data to Earth," Cunningham
explained. "This means that we have to stop acquiring science
data. The advantage of deploying the high-gain antenna is that
we can then use its gimbals to point the antenna at Earth and
send science data back at the same time the instruments are
pointed at Mars."
The first phase of the primary mapping mission is scheduled
to begin on March 8. The deployment of high gain antenna is
currently scheduled for March 29, pending approval by NASA
Headquarters officials in mid-March.
Mars Global Surveyor is the first mission in a long-term
program of Mars exploration known as the Mars Surveyor Program
that 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.
Further information about the mission, including a link to
the "Top 10" images of Mars returned by Global Surveyor so far,
is available on the Internet at: http://mars.jpl.nasa.gov/mgs/
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