For the purpose of simulating the surface alteration process called "space weathering", experiments of pulse laser irradiation, proton implantation, and laser irradiation to proton implanted samples were performed and reflectance spectra of altered materials were measured. To simulate the impact heating by micrometeorite bombardments, we made a new apparatus using a pulse laser whose pulse duration is 6-8 nanoseconds, comparable with a timescale of micrometeorite impacts. We find that the degree of space weathering, i.e., change of reflectance spectrum should depend on mineral composition. Laser irradiation onto olivine produces the largest reduction of albedo and the highest reddening of reflectance spectrum. In general, variation of olivine spectra is much larger than that of pyroxenes. Depths of absorption bands do not change in the scaled spectra. The olivine spectrum after the laser irradiation can match spectra of some olivine asteroids within a subtype of S-type asteroids. Comparison of Vesta spectrum with altered pyroxene spectra suggests that Vesta surface would be relatively older than olivine asteroids. We also investigate the influence of solar wind proton and pyroxene FeO content. The proton implantation causes small changes in olivine and enstatite spectra. Implanted protons do not influence spectral change by the laser irradiation: the laser irradiation and the proton implantation do not produce multiplicative but additive changes on the reflectance spectra. FeO content of pyroxenes does not relate to the degree of reflectance change.

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Abstract. Laboratory hypervelocity impact experiments were conducted to verify the performance of aerogel dust collectors used for gathering meteorolds and space debris in the near-Earth environment and to derive the relationships of various parameters characterizing the projectile with morphology of tracks left by t•he penetrating projectile in the aerogel collector pad. Silica aerogel collectors of 0.03 g/cm -• density were impacted at velocities ranging from 1 to 14 km/s with projectiles of aluminum oxide, olivine, or sodalime glass, with diameters ranging from 10 to 400/xm. At impact velocities below 6 km/s the projectiles were captured without fragmentation by the aerogel collector and, in many instances, without complete ablation even at 12 km/s. The shapes and dimensions of the penetration tracks left in the aerogel collector were correlated with the impact parameters, and the results permitted derivation of a series of equations relating the track dimensions to incoming projectile size, impact energy, and other projectile parameters. A simplified model, similar to meteor-entry phenomena, was used to predict the trends in experimental penetration track lengths and the diameters of captured projectiles. IntroductionSolid particles present in the near-Earth environment derive from either natural or artificial origin and are termed "meteoroids" and "space debris", respectively. Meteoroids are considered to be supplied from comets, asteroids, and planets, and some known as interstellar dust particles or interstellar grains are from outside the solar system [Griin et al., 1993]. Since meteoroids are thought to be closely related with the evolution of the solar system, study of these materials provides us with crucial information on the source materials for the solar system. In situ sampling of meteoroids in space can avoid contamination by terrestrial sources, which is unavoidable in sampling on Earth.Space debris is the product of normal satellite operations, the deterioration of satellites, and the fragmentation or breakup of satellites [Johnson and McKnight, 1991]. It is important to investigate micrometer-to-millimeter-sized debris, the range within which the majority of debris particles lie, because this changes the characteristics of the materials of spacecraft or of the on-board parts after colliding with them. The distribution and composition of small-sized debris are not well known, as these particles are too small to be observed with ground-based telescopes or radars. In situ sampling of dust particles is useful for getting material information on the de- The authors developed a dust collector made from silica aerogel to take the Manipulator Flight Demonstration (MFD) flight opportunity aboard the Space Shuttle (STS-85),