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Abstract:
We performed impact experiments into ice-silicate surfaces using the plasmadynamic accelerator and the electrothermal accelerator of the Fachbereich Raumfahrt of the Technische Universitat Munchen. Projectile velocities varied between 0.9 and 11.4 km/s, and masses between 1.7 . 10(-11) kg and 7.2 . 10(-10) kg at the plasma accelerator and between 1.1 and 3.3 km/s and 6 . 10(-6) kg to 3 . 10(-5) kg at the electrothermal accelerator. Projectile materials were glass at the plasma accelerator, and nylon at the electrothermal accelerator. The kinetic energies ranged over 6 orders of magnitude, from 8.8 . 10(-5) J to 70 J. The target temperature was 250 K 5 K. Witness films were used to determine the size and the position of ejecta particles. The ejecta velocities were determined by piezo detectors. The maximum velocities of the ejecta particles observed were in the order of several 100 m/s, independent on the projectile velocity. At about 60degrees to 65degrees ejection angle to the target surface, velocities were highest (about 700 to 800 m/s), at lower and higher angles, the maximum velocity decreased. The cumulative ejecta mass smaller than a given size follows power laws. Three distinct slopes were observed. For particle sizes smaller than about 10 mum, the average slope was 2.2, for ca. 10 mum to 20 mum, the average slope was 12, and for particles larger than about 20 mum, the average slope was 1.4. The high slope between 10 and 20 mum indicates a comparably high number of particles in this size regime. This is a result of only partially or nondestroyed silicate particles, which originally had a size in this range. The total mass ejected at a given angle can be approximated by a Gaussian distribution with a maximum at approximate to70degrees to the target surface. We combined the empirically found distributions into a formula which allows the calculation of the mass ejected in a given ejection angle range with a given size range as a function of the projectile and target properties. (C) 2001 Elsevier Science (USA).
