MESSENGER's Gamma-Ray Spectrometer Gears up for Mercury Flyby
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MESSENGER Mission News
September 22, 2008
MESSENGER's Gamma-Ray Spectrometer Gears up for Mercury Flyby
Two weeks from today, the MESSENGER spacecraft will fly by Mercury for
the second time. As part of the final preparations for this encounter,
the Gamma-Ray Spectrometer (GRS) was placed in an "anneal mode" to
prepare its detector for optimal performance during the flyby.
"The detector material itself is a high-purity crystal made of the
element germanium,' explains GRS Instrument Engineer John O. Goldsten.
"In space, the crystal develops defects - atoms knocked out of place -
when
bombarded by high-energy cosmic radiation, and this degrades the
instrument's performance. Heating the detector to high temperatures
promotes realignment in the crystal, a process called annealing.'
This annealing process increases the detector temperature to 84°C for
a
period of time before lowering it to an operating temperature of
-183°C.
The annealing will last for two weeks in preparation for Mercury flyby
2
to improve energy resolution and signal-to-background ratio. The GRS
detector will be annealed once again prior to the third flyby of
Mercury
in September 2009, and once every Mercury year (88 Earth days) during
the orbital phase of the mission.
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MESSENGER Team Receives NASA Group Achievement Awards
Although MESSENGER has two and one-half years remaining before it
begins
its primary mission of orbiting Mercury, NASA acknowledged the
successful development, launch, and operation of the spacecraft
through
Mercury flyby 1 by giving the MESSENGER Team a Group Achievement
Award.
Many team members from the Johns Hopkins University Applied Physics
Laboratory (APL) in Laurel, Md., were on hand on September 11, 2008,
to
receive awards from the director of NASA's Planetary Science Division,
James Green. The awards going to non-APL recipients are in the process
of being distributed.
Many members of the group receiving the award are now shepherding the
spacecraft to its second encounter with Mercury in less than a year
and
will ultimately guide MESSENGER to its final destination: Mercury's
orbit.
In accepting the award on behalf of the team, MESSENGER Principal
Investigator Sean Solomon said: "This is indeed an honor for the
entire
team, and I am proud of the hundreds of engineers, scientists,
managers,
and educators from institutions across the country who are helping us
send the first spacecraft to orbit Mercury."
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Seeing Another Side of Mercury
The last image that the Mercury Dual Imaging System (MDIS) took of
Mercury during MESSENGER's first flyby of the planet on January 14,
2008, before the spacecraft turned its antennas to begin transmitting
the flyby data to Earth, can be seen online at
http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=204.
The geometry of the second Mercury flyby is different from the first
encounter - the point of closest approach will be nearly on the
opposite
side of the planet. So, MESSENGER will view about 30% of Mercury's
surface never before seen by spacecraft. This new territory is located
just to the left of the day/night terminator in this image.
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MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and
Ranging) is a NASA-sponsored scientific investigation of the planet
Mercury and the first space mission designed to orbit the planet
closest
to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and
after flybys of Earth, Venus, and Mercury will start a yearlong study
of
its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie
Institution of Washington, leads the mission as principal
investigator.
The Johns Hopkins University Applied Physics Laboratory built and
operates the MESSENGER spacecraft and manages this Discovery -class
mission for NASA.