http://www.lamonitor.com/articles/2007/04/14/headline_news/news01.txt
GRaND instrument primed for voyage ROGER SNODGRASS Monitor Assistant Editor The Dawn spacecraft, carrying an instrument package from Los Alamos, reached another milestone this week on a journey to the asteroids. NASA announced that Dawn arrived at Astrotech Space Operations in Titusville, Fla., at 9 a.m. Tuesday for final preparations. Countdown is now 76 days until June 30, when Dawn is set to go up like thunder on a heavy-lifting version of a Delta II rocket. "It's particularly sweet for us, in that we had quite a few ups and downs getting to the point where we are ready to launch," said Tom Prettyman, the lead scientist for the Los Alamos instrument and a mission co-investigator. The next step is a 15-mile jaunt down the road to the launch pad, followed by a 3.2 billion-mile expedition to the asteroid belt that lies between Mars and Jupiter. The spacecraft will be powered by a pioneering new ion propulsion system that uses electric fields instead of chemical reactions to achieve a thrust. Dawn's job is to visit and circle around two contrasting space objects - first, the asteroid Vesta and second, the dwarf planet Ceres. Vesta is dry and volcanic. Ceres may harbor ice or water. Vesta is melted, evolved and shaped like the top of a skull. Ceres is rough and crude, but round. Vesta, Prettyman said, is an inner-belt body, closer to the sun than Ceres, which is larger and more in the middle of the asteroid belt. The difference between them is one of the main points of the mission and partly why they were chosen as destinations. "We want to understand how solar nebulae varied with the distance from the sun and how the planets formed," he said. Both objects are thought to be very old relics, among the first-formed bodies in the solar system 4.5 billion years ago. Because they have probably always been among the biggest chunks of matter in the region, they were the least likely to be perturbed or swept up by the gas-giant Jupiter. The smallest pieces were knocked around, broken into pieces and expelled, until only a fraction of the original main belt asteroid material remains. An old hypothesis held that asteroids were the remains of a destroyed planet named Phaeton, but now the main line of inquiry is why the pieces went through a building and accreting process up to a point but failed to form a planet. After Dawn gets a gravity boost in a fly-by of Mars in March 2009, it will reach Vesta in late 2011 and Ceres in early 2015. In both cases, the spacecraft will survey the situation before beginning a polar orbit and bearing down for closer inspection. The spacecraft will circle both poles, while the body rotates to reveal its entire surface. The LANL instrument, the Gamma Ray and Neutron Detector (GRaND), one of three science instruments Dawn carries in its payload, comes from a long line of space instruments the lab has built for NASA missions. It will map the surface of each asteroid for ratios of rock-forming elements and the telltale hydrogen atoms that indicate ice or water. Another goal is to try to pin down Vesta's tantalizing relationship to a class of meteorites known as HEDs (howardite, eucrite and diogenite) and to try to determine if any meteorites come from Ceres. "These are places we've never been before," said Prettyman. "They are intriguing because they are representatives of planetary embryos." The mission is managed by the Jet Propulsion Laboratory in Pasadena and involves scientific partnerships with the German Aerospace Center, the Max Planck Institute for Solar System Research and the Italian National Institute of Astrophysics. Three groups in the labs International Space and Response Division have been involved in developing and engineering the GRaND and integrating it with the spacecraft. ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://six.pairlist.net/mailman/listinfo/meteorite-list
