Los Alamos Instruments to Capture the Sun
23 Jul 2001
(Source: Los Alamos National Laboratory)
Los Alamos National Laboratory
Shelley Thompson, firstname.lastname@example.org, (505) 665-7778
LOS ALAMOS, N.M. - Three instruments designed and built by researchers at the U.S. Department of Energy's Los Alamos National Laboratory will help scientists understand the origin of the solar system.
The instruments are aboard Genesis, a remote-controlled NASA space mission designed to capture particles from the sun and return them to Earth. The spacecraft is scheduled for launch on July 30 from Florida's Cape Canaveral Air Force Station.
Genesis will collect samples of the solar wind to reveal the makeup of the cloud that formed the solar system nearly five billion years ago.
Scientists believe the solar system possibly began with a dense cloud of gas and dust that collapsed in on itself. Most of this "solar nebula" condensed to form the sun, while outlying particles coalesced into the diverse planets, moons and comets that make up our solar system.
Although scientists have a general understanding of the formation of the solar system, the composition of the initial nebula remains relatively unknown. Fortunately, nature provides a record of the solar nebula; its pristine composition is preserved for the most part in the outer layers of the sun. The solar wind provides a continuous flow of this material into space.
"To understand how the planets were formed with their different compositions, we need to know the starting materials," explains Roger Wiens, who led the payload instrument development at Los Alamos.
Genesis' main goal is to determine isotopic ratios of different elements in solar matter, with a focus on oxygen - an element making up two thirds of everything found on earth. Oxygen isotope amounts vary among the different planets in the solar system and this puzzles scientists because all solar system bodies were supposedly formed from the same raw materials. An isotope is a variation of an element - it has more or fewer neutrons in its nucleus making it heavier or lighter than the standard form of the element.
Los Alamos designed and built a solar wind concentrator to collect a high concentration of oxygen and return the sample back to Earth for analysis. The concentrator takes solar wind and passes it through a series of electrically charged grids into a bowl-shaped mirror. The mirror reflects a filtered stream of elements heavier than hydrogen upward into a centrally poised collector tile, where oxygen and other elements embed themselves.
The several layers of charged grids are made of incredibly strong and durable wires one-fourth the diameter of a human hair. The wire grids possess different electrical charges to filter out the much more numerous hydrogen ions and direct other ions of interest to the collector tile.
The collector tile, a four inch disk, is made of four pie-shaped pieces of ultra-pure materials: one industrial diamond wedge, two silicon carbide wedges and one wedge of silicon topped with thin diamond. The entire interior of the concentrator is coated with a very thin layer of gold to keep all the surfaces free of oxygen.
The surface of the concentrator's bowl-shaped mirror was specially treated to reflect the sun's incoming light back out of the instrument to avoid damaging the collector tile with focused sunlight.
"We used a solar simulation, initially a spotlight purchased from Hollywood, to test how the concentrator will respond to sunlight in the vacuum of space," said Wiens. "During the test, we had to monitor the shapes of the fragile grids. If the grids get any damage, like wrinkles, this could change the path of the ions so that they don't reach the collector tile and this would give skewed results."
"The concentrator is the first solar instrument sent into space that we will ever see again," said Beth Nordholt, of the Neutron Science and Technology Group and one of the leaders on the concentrator instrument. "All other instruments aboard spacecrafts remain in space indefinitely, or, like Lunar Prospector, are intentionally crashed after their mission ends. This is the first mission in three decades, since the Apollo missions in the seventies, that will bring extraterrestrial samples back to Earth for analysis."
The other two Los Alamos instruments aboard Genesis are solar wind ion and electron monitors. Genesis' ion and electron monitors instantaneously determine which type of solar wind is passing the spacecraft at any time and translate that knowledge into actions for the solar wind concentrator and solar wind collector arrays - five meter-sized panels containing 55 coaster-sized tiles made of a variety of materials selected to trap specific elements in the solar wind.
The monitors will distinguish between three types of solar wind by recognizing their characteristic temperature, velocity, direction and composition. The onboard computer will use the information collected by the monitors to adjust the solar wind concentrator for optimum oxygen concentration and to select the appropriate collector arrays for exposure to the wind.
The ion monitor measures the density, temperature and energy of protons and alpha particles - helium atoms stripped of their electrons - in the solar wind. About 96 percent of the solar wind is composed of protons, 4 percent alpha particles and less than 1 percent minor ions, one being oxygen.
Genesis' electron monitor will determine the direction of travel of solar-wind-electrons. Located on the edge of Genesis' equipment deck, it can view the whole sky as the spacecraft rotates.
Genesis will collect just 10 to 20 micrograms of solar wind - or the equivalent of a few grains of salt. The extraterrestrial material will return to Earth in 2004 - in the spacecraft's specially designed sample return capsule - for analysis.
The instruments were built in clean rooms to avoid terrestrial contamination in order to guarantee the atoms analyzed are of pristine solar origin. They were designed and constructed by a team of scientists and engineers from Los Alamos' Space and Atmospheric Sciences and Space Instrumentation groups under the direction of Wiens, Nordholt, Bruce Barraclough, Donald Mietz, Eric Dors and Daniel Reisenfeld.
Genesis is the first spacecraft to have a completely robotically-controlled sample collection system in which data from science instruments is used to control sample collection. The software to control the payload was developed jointly by Los Alamos National Laboratory and the spacecraft builder, Lockheed Martin Astronautics in Denver.
The mission is led by Donald Burnett, a professor in the Geology and Planetary Science Division at California Institute of Technology, Pasadena, and is managed by NASA's Jet Propulsion Laboratory. The collector tile portion of the payload was also built at JPL.
During flight, the entire payload will be under the control of Los Alamos National Laboratory. Scientists will monitor the health of the payload instruments and will keep a history of all solar wind conditions and array exposure times. These data will be made available to the scientific community at large.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.
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