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MESSENGER's Gamma-Ray Spectrometer Gears up for Mercury Flyby
MESSENGER's Gamma-Ray Spectrometer Gears up for Mercury Flyby
22 Sep 2008
(Source: Johns Hopkins University Applied Physics Laboratory)

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 degrees Celsius for a period of time before lowering it to an operating temperature of -183 degrees Celsius. 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.

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."

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 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.

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.

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Last Updated: 22 Sep 2008