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NASA's Solar, Anomalous and Magnetosphere Particle Explorer (SAMPEX) satellite, an international collaboration with Germany, will contribute new information on the composition of energetic particles arriving at Earth from the solar atmosphere and interstellar space.
Most of the particles SAMPEX will observe will be atoms stripped of some or all of their electrons and accelerated to speeds between approximately 3,400 miles per second (5,470 km) and 140,000 miles per second (225,302 km), or 2 percent and 75 percent of the speed of light. Determining the abundance of each element and the abundance of isotopes for many of the elements will enable scientists to learn more about the Sun, our interplanetary environment, and the interstellar environment. SAMPEX also will measure the number of relativistic electrons (at speeds just below the speed of light) that enter our atmosphere and contribute to the destruction of ozone.
The satellite, which is scheduled for launch on a four-stage, Scout expendable launch vehicle from Vandenberg Air Force Base, CA, in June 1992, was developed by the Small Explorer (SMEX) project at NASA's Goddard Space Flight Center, Greenbelt, MD, in just three years since the mission was initiated. SAMPEX is designed to support a minimum mission duration of one year, with a mission goal of three or more years.
Dr. Glenn M. Mason, University of Maryland, College Park, is principal investigator for SAMPEX, and there are 10 co- investigators from American and German institutions. Gilberto Colon is mission manager, Dr. Daniel Baker is mission scientist, and Roberto Aleman is the SAMPEX instrument manager. All three are from the Goddard Space Flight Center, as is Orlando Figueroa, project manager for SMEX.
While SAMPEX, with its four instruments, is expected to provide unprecedented detail about the composition of energetic particles from our galaxy (galactic cosmic rays) and from the Sun (solar energetic particles), the most dramatic, new results are expected to come from measuring the composition of "anomalous" cosmic rays. Anomalous cosmic rays are thought to be atoms of the local, interstellar gas that enter the solar system, are ionized and then accelerated to cosmic ray energies at the boundary of the magnetically-defined region of space called the heliosphere.
At low latitudes, the Earth's magnetic field can turn back most charged, energetic particles before they reach the 342 mile (550 km) to 419 mile (675 km) altitude of SAMPEX's orbit. Nonetheless, SAMPEX's instruments are so sensitive that during the time spent near the Earth's north and south magnetic poles, SAMPEX will obtain 10 to 100 times more anomalous cosmic rays and solar energetic particles than any previous mission.
More importantly, SAMPEX will be able to use the shielding power of the Earth's magnetic field at somewhat lower latitudes to discriminate energetic particles coming from the Sun and the galaxy from anomalous cosmic rays. If the theory of anomalous cosmic rays is confirmed by SAMPEX, the atoms should only be partially ionized and therefore better able to penetrate the Earth's magnetic field. The possibility of directly measuring the composition of a sample of local interstellar matter in this way has very high scientific value.
The SAMPEX mission will carry four scientific instruments: the Low Energy Ion Composition Analyzer (LEICA), the Heavy Ion Large Telescope (HILT), the Mass Spectrometer Telescope (MAST) and the Proton/ Electron Telescope (PET). A brief description of the four instruments follows:
The LEICA instrument identifies the element, isotope, and energy by simultaneously measuring the speed, direction, mass, and energy of lower energy (2 percent to 23 percent of the speed of light) particles that enter the telescope and stop in one of four silicon, solid-state detectors. An earlier model of this instrument flew on the Space Shuttle in 1989 as a Get Away Special (GAS) experiment. LEICA is provided by the University of Maryland, College Park.
Like all the instruments, HILT will measure galactic cosmic rays and solar energetic particles when it is near the Earth's magnetic poles. In addition, this instrument is designed to determine the energy and elemental composition of "anomalous" cosmic rays at energies where they are most abundant. HILT will measure the direction, energy and nuclear charge of each nucleus from helium to nickel. HILT is provided by the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. An earlier version of HILT also flew as a GAS experiment in 1989.
MAST will determine the direction, energy, element, and isotope of atoms from all elements up to nickel entering the instrument with velocities between about 12 percent and 75 percent of the speed of light. MAST is provided by the California Institute of Technology, Pasadena, CA.
The PET system is designed to complement MAST by measuring the energy of electrons, protons, and helium nuclei coming from the Earth's radiation belts, the Sun, interplanetary space, and interstellar space. The electrons will be moving very close to the speed of light (186,000 miles [299,338 km] per second) and could have a significant effect on the destruction of ozone high in the Earth's atmosphere. PET is provided by the California Institute of Technology and is housed in the same instrument box as MAST.
These four instruments were constructed at the separate institutions and integrated with their Data Processing Unit (DPU) provided by the Aerospace Corporation of Redondo Beach, CA. The DPU is responsible for overall control of the science payload and controls instrument housekeeping functions.
The SAMPEX control and data handling functions are performed by the Small Explorer Data System (SEDS). The SEDS provides onboard computers that can be programmed to perform mission unique functions as required and provides autonomous operation of the spacecraft when it is not in contact with the ground. The data system uses computer memory instead of more conventional tape recorders to record spacecraft telemetry data.
The Cooperative Satellite Learning Project (CSLP) is a unique educational partnership between Laurel High School, Laurel, MD, Bendix Field Engineering Corporation, Seabrook, MD, Falcon Microsystems, Landover, MD and Goddard that involves high school students in the process of developing and operating SAMPEX. This pilot program provides students with an understanding of the overall "end-to-end" system used to support SAMPEX and will demonstrate how NASA implements a specific mission for a given scientific endeavor. It also introduces the students to careers in space.
A Mission Monitor System in the high school will receive and process SAMPEX satellite data and provide computer-assisted tutoring. In this way, students will participate directly in SAMPEX tests, simulations and orbital operations.
SAMPEX is the first of the Small Explorer missions. Two other SMEX missions currently are approved, they are: the Fast Auroral Snapshot Explorer, (FAST), scheduled for launch in September 1994; and the Submillimeter Wave Astronomy Satellite, (SWAS), scheduled for launch in 1995. The Small Explorer program is managed by NASA Headquarters Office of Space Science and Applications. The program manager is Dr. David A. Gilman.