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Mars Global Surveyor may be at mission's end
NASA's Mars Global Surveyor has likely finished its operating career.
The spacecraft has served the longest and been the most productive of
any mission ever sent to the red planet.
"Mars Global Surveyor has surpassed all expectations," said
Michael Meyer, NASA's lead scientist for Mars exploration at NASA Headquarters,
Washington. "It has already been the most productive science mission
to Mars, and it will yield more discoveries as the treasury of observations
it has made continues to be analyzed for years to come." Its camera
has returned more than 240,000 images to Earth.
The orbiter has not communicated with Earth since Nov. 2. Preliminary
indications are that a solar panel became difficult to pivot, raising
the possibility that the spacecraft may no longer be able to generate
enough power to communicate. Engineers are also exploring other possible
explanations for the radio silence.
"Realistically, we have run through the most likely possibilities
for re-establishing communication, and we are facing the likelihood that
the amazing flow of scientific observations from Mars Global Surveyor
is over," said Fuk Li, Mars Exploration Program manager at NASA's
Jet Propulsion Laboratory (JPL), Pasadena, Calif. "We are not giving
up hope, though."
Efforts to regain contact with the spacecraft and determine what has
happened to it will continue. NASA's newest Mars spacecraft, the Mars
Reconnaissance Orbiter, pointed its cameras towards Mars Global Surveyor
on Monday. "We have looked for Mars Global Surveyor with the star
tracker, the context camera and the high-resolution camera on Mars Reconnaissance
Orbiter," said Doug McCuistion, Mars Exploration Program director
at NASA Headquarters. "Preliminary analysis of the images did not
show any definitive sightings of a spacecraft."
The next possibility for learning more about Mars Global Surveyor's status
is a plan to send it a command to use a transmitter that could be heard
by one of NASA's Mars Exploration Rovers later this week.
Mars Global Surveyor launched on Nov. 7, 1996, and began orbiting Mars
on Sept. 11, 1997. It pioneered the use of aerobraking at Mars, using
careful dips into the atmosphere for friction to shrink a long elliptical
orbit into a nearly circular one. The mission then started its primary
mapping phase in April 1999. The original plan was to examine the planet
for one Mars year, nearly two Earth years. Based on the value of the science
returned by the spacecraft, NASA extended its mission four times.
"It is an extraordinary machine that has done things the designers
never envisioned despite a broken wing, a failed gyro and a worn-out reaction
wheel. The builders and operating staff can be proud of their legacy of
scientific discoveries and key support for subsequent missions,"
said Tom Thorpe, project manager for Mars Global Surveyor at JPL.
The spacecraft evaluated landing sites for the twin NASA rovers that
landed in 2004 and sites for future landings of the Phoenix and Mars Science
Laboratory missions. It monitored atmospheric conditions during aerobraking
by newer orbiters. It served as a relay link for the rovers and provided
mapping information about their surroundings.
"When we watched the launch 10 years ago, we wondered if we would
make the specified mission length. We certainly were not thinking of a
10-year operating life," said JPL retiree Glenn Cunningham, who managed
the Global Surveyor project through development and launch.
A few of the mission's many important discoveries about Mars include:
• The spacecraft's camera found gullies cut into many slopes that have
few, if any, impact craters. This indicates the gullies are geologically
young. Scientists interpret this as evidence of action by liquid water,
essentially in modern times.
• The mineral-mapping infrared spectrometer found concentrations of
a mineral that often forms under wet conditions, fine-grained hematite.
This discovery led to selection of a hematite-rich region as the landing
site for NASA's Mars Exploration Rover Opportunity.
• Laser altimeter measurements have produced an unprecedented global
topographic map of Mars. The instrument revealed a multitude of highly
eroded or buried craters too subtle for previous observation, and mapped
canyons within the polar ice caps.
• The magnetometer found localized remnant magnetic fields, indicating
that Mars once had a global magnetic field like Earth's, shielding the
surface from deadly cosmic rays.
• The camera found a fan-shaped area of interweaving, curved ridges
interpreted as evidence of an ancient river delta resulting from persistent
flow of water over an extended period in the planet's ancient past.
• A long life allowed Global Surveyor to track changes through repeated
annual cycles. For three Martian summers in a row, deposits of carbon-dioxide
ice near Mars' South Pole shrunk from the previous year's size, suggesting
a climate change in progress.
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