NLSI Lunar Science Conference (2008)
MICROMETEORITE ACCELERATOR FOR LUNAR IMPACT STUDIES: NEEDS AND CAPABILITIES. T. Munsat1, E. Grün2,3, M. Horányi3, S. Robertson1, R. Srama2, Z. Sternovsky3, X. Wang1, 1Center for Integrated Plasma Studies, Univ. Colorado (Boulder, CO 80309-0390, USA, firstname.lastname@example.org), 2Max-Planck-Institut für Kernphysik, Heidelberg Germany, 3Laboratory for Atmospheric and Space Physics, Univ. Colorado, USA. Introduction: The lunar surface is continually bombarded with micrometeorites of a variety of sizes (masses) and energies, the bulk of which lie in the 0.11 µm and < 100 km/s range. The impacts of such particles at the lunar surface introduce significant potential hazards to humans and instruments. Upon impact into the lunar regolith, cratering and micro-plasma creation can lead to liberation of volatile materials into the charged lunar dust population. Dust detectors aboard GALILEO and ULYSSES have provided unprecedented knowledge of the mass distribution and origin of interplanetary dust particles, and advanced dust detectors are planned for future satellite and lunar studies. A key component to the success of such instruments is detailed calibration with known sources of hypervelocity microparticles. Lastly, the origin, composition, and properties of such micrometeorites arriving at the lunar surface are interesting as a basis for which to infer the behavior of the interplanetary dust environment, with potential consequences for future human space activities. To address the many scientific and technical questions surrounding the hypervelocity micrometeorites at the lunar surface, a proposed accelerator facility based on nuclear accelerator techniques is described. The primary design is based on an existing facility at the Max-Planck Institute in Heidelberg, Germany, which is presently a center of such studies within the international community. Here we describe a proposed domestic facility, including the technical basis and a list of scientific questions which can be addressed. Existing Technology and Capabilities: The present state-of-the-art is the Heidelberg dust accelerator. This is a facility based on a 2 MV Van de Graaff ion accelerator, adapted for a novel charged particle source . A variety of microparticle charging methods (including ion/electron beam bombardment) have been attempted by various groups over the years, and indeed the maximum particle charge is the major limiting factor for the achievable energies in a microparticle accelerator. The most successful strategy has been direct electrostatic charging, embodied in the particle source at the Heidelberg facility, which has achieved surface electric field levels of ~3×109 V/m for both Iron and latex particles (compared to the theoretical ion fieldemission limit of 1010 V/m). Accelerated through the 2 MV Van de Graaff, this has led to velocities of up to 7 km/s and 13 km/s for 1 µm Iron and latex particles, respectively, and up to 20 km/s for smaller particles of both materials. A proposed facility, based on a 3 MV Pelletron accelerator, would incrementally improve the achievable velocities even with no additional development in the charging technology of the dust source, would modernize the handling and accelerator operation, and, significantly, would enable current and future micrometeorite studies at a U.S. facility. The advantages of a facility based on electrostatic acceleration, rather than alternative techniques such as electron-beam or plasma acceleration, include 1) higher achievable charge and mass, up to realistic micrometeorite parameters, 2) precise selection of particle size and velocity for high experimental control, 3) high repetition and data acquisition rates. Additionally, such a device could be designed to also house a 3 MV ion accelerator, which may have applications for auxiliary lunar/space studies such as material characterization (PIXE, ion channelling, etc.). Outstanding Questions: In addition to the critically important need to calibrate future dust detectors for use in lunar and satellite missions, a hypervelocity micrometeorite accelerator facility can directly address a number of scientific questions relevant to the lunar surface and human activity on the moon: § What are the characteristics of the micro-plasma created upon micrometeorite impact? § What is the size, charge, and chemical composition of the liberated debris following a micrometeorite impact on realistic lunar regolith material? § How are micrometeorite impacts affected by, and how do they affect, local magnetic anomalies at the lunar surface? § How are micrometeorite impacts affected by, and how do they affect, the charged lunar dust atmosphere? § What is the effect (single and accumulated) of micrometeorite bombardment of instrumentation and equipment (optics, structures, space suits, etc.)? § Can we develop techniques or select materials to mitigate such effects? § What is the accumulated effect of micrometeorite bombardment on the material structure of the lunar regolith itself? 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