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LIVERMORE, Calif. — A team of scientists and engineers from the Lawrence Livermore National Laboratory, in collaboration with UC Berkeley's Space Science Laboratory and Johns Hopkins Applied Physics Laboratory, have designed and built a high resolution gamma-ray detector that will enable NASA's Mercury Messenger to measure the elemental composition of the planet's crust.
NASA's first trip to Mercury in 30 years — and the closest look ever at the innermost planet — is set for Aug. 2, with a predawn launch of the MESSENGER spacecraft from Cape Canaveral Air Force Station, Fla.
MESSENGER will conduct an in-depth study of Mercury, the least explored of the terrestrial planets that also include Venus, Earth and Mars. After a scheduled 2:16 a.m. EDT liftoff aboard a Delta II launch vehicle on Aug. 2, the first day of a 13-day launch period, MESSENGER's voyage includes three flybys of Mercury in 2008 and 2009 and a yearlong orbit of the planet starting in March 2011.
Livermore's role was critical in ensuring that the spacecraft's gamma-ray spectrometer could withstand the heat of the galaxy's closest planet to the sun. Livermore's Norm Madden and Monika Witte led a team that built a rugged, encapsulated germanium gamma-ray detector and mated it with a miniature cryocooler. The miniature cryocooler and a multi-layered thermal shield maintain the germanium detector at a temperature less than 90 degrees Kelvin, ensuring that the gamma-ray spectrometer operates correctly.
The Livermore team, which also worked with Lawrence Berkeley National Lab, consists of Doug Berger, Sue Bishop, Morgan Burks, Jerry Caulfield, Christopher Cork, Steve DeTeresa, Del Eckels, Mark Eli, Ross Eyre, Lorenzo Fabris, Mike Gerhard, Roger Gregory, Lisle Hagler, Wilthea Hibbard, Ethan Hull, Wayne Jensen, Mike Kennedy, Satish Kulkarni, Christopher Lee, Madden, Pete Meyer, Wayne Miller, Mitch Moffett, Jerry Moore, Marty Roeben, Bob Sanchez, Gordon Spellman, Carl Westrich and Witte.
The Laboratory also is working with The Johns Hopkins University Applied Physics Laboratory, which serves as the overseeing institution on the Mercury MESSENGER project.
Using the Livermore-built gamma ray-detector, MESSENGER will be able to trace gamma-ray emissions from the Mercurian crust as well as solar winds and cosmic rays as it orbits around the planet.
"This was truly a team effort," Witte said. "Everyone helped everyone else out."
Based on technology originally developed for Cryo 3, a mobile, handheld mechanically cooled germanium radiation detector that can detect gamma rays from radioactive material, the detector on board MESSENGER is also cooled mechanically by a low-power, compact micro cryocooler, eliminating the need for liquid nitrogen, yet attaining the same high level energy resolution.
"This is a direct spin off of Cyro 3," Madden said. "Now we're using similar technology in a geoscience and space science role."
Mercury's proximity to the sun makes it an unprecedented mission design challenge. The sun, viewed from the surface of Mercury, can appear up to 11 times brighter than what is seen on Earth, and Mercury's surface temperatures at its equator can reach 450 degrees Celsius (about 840 degrees Fahrenheit). However, MESSENGER will operate at room temperature behind a sunshade of heat-resistant ceramic fabric. The 1.2-ton spacecraft also features a heat-radiation system and will pass only briefly over Mercury's hottest regions, limiting exposure to the intense heat reflected back from the broiling surface.
"We have to maintain the heat at no higher than 90 degrees Kelvin (-297.67 degrees Fahrenheit)," Madden said. "The team has a good reputation for making this type of instrument and was glad to have this unique opportunity to put this superior detector on the MESSENGER spacecraft."
MESSENGER (short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is only the second spacecraft to set sights on Mercury. Mariner 10 flew past it three times in 1974 and 1975 and gathered detailed data on less than half the surface. Carrying seven scientific instruments on its compact and durable composite frame, MESSENGER will provide the first images of the entire planet. The mission will also collect detailed information on the composition and structure of Mercury's crust, its geologic history, the nature of its thin atmosphere and active magnetosphere, and the makeup of its core and polar materials.
On a 4.9-billion mile (7.9-billion kilometer) journey that includes 15 loops around the sun, the solar-powered MESSENGER will fly past Earth once, Venus twice and Mercury three times before orbiting around its target planet. The Earth flyby, a year after launch, and the Venus flybys, in October 2006 and June 2007, use the pull of the planets' gravity to guide MESSENGER toward Mercury's orbit. The Mercury flybys in January 2008, October 2008 and September 2009 fine-tune and slow MESSENGER's track while allowing the spacecraft to gather data critical to planning the mission's orbit phase.
For more information on MESSENGER, images and animation, go to http://messenger.jhuapl.edu.
Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.