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      NanoRocks: Design and Performance of an Experiment Studying Planet Formation on the International Space Station

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          Abstract

          In an effort to better understand the early stages of planet formation, we have developed a 1.5U payload that flew on the International Space Station (ISS) in the NanoRacks NanoLab facility between September 2014 and March 2016. This payload, named NanoRocks, ran a particle collision experiment under long-term microgravity conditions. The objectives of the experiment were (a) to observe collisions between mm-sized particles at relative velocities of \(<\)1~cm/s, and (b) to study the formation and disruption of particle clusters for different particle types and collision velocities. Four types of particles were used: mm-sized acrylic, glass, and copper beads, and 0.75 mm-sized JSC-1 lunar regolith simulant grains. The particles were placed in sample cells carved out of an aluminum tray. This tray was attached to one side of the payload casing with three springs. Every 60~s, the tray was agitated and the resulting collisions between the particles in the sample cells were recorded by the experiment camera. During the 18 months the payload stayed on ISS, we obtained 158 videos, thus recording a great number of collisions. The average particle velocities in the sample cells after each shaking event were around 1 cm/s. After shaking stopped, the inter-particle collisions damped the particle kinetic energy in less than 20~s, reducing the average particle velocity to below 1 mm/s, and eventually slowing them to below our detection threshold. As the particle velocity decreased, we observed the transition from bouncing to sticking collisions. We recorded the formation of particle clusters at the end of each experiment run. This paper describes the design and performance of the NanoRocks ISS payload.

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          Free Collisions in a Microgravity Many-Particle Experiment III: The Collision Behavior of sub-Millimeter-Sized Dust Aggregates

          We conducted micro-gravity experiments to study the outcome of collisions between sub-mm-sized dust agglomerates consisting of \mu m-sized SiO2 monomer grains at velocities of several cm/s. Prior to the experiments, we used X-ray computer tomography (nano-CT) imaging to study the internal structure of these dust agglomerates and found no rim compaction so that their collision behavior is not governed by preparation-caused artefacts. We found that collisions between these dust aggregates can lead either to sticking or to bouncing, depending mostly on the impact velocity. While previous collision models derived the transition between both regimes from contact physics, we used the available empirical data from these and earlier experiments to derive a power law relation between dust-aggregate mass and impact velocity for the threshold between the two collision outcomes. In agreement with earlier experiments, we show that the transition between both regimes is not sharp, but follows a shallower power law than predicted by previous models (G\"uttler et al. 2010). Furthermore, we find that sticking between dust aggregates can lead to the formation of larger structures. Collisions between aggregates-of-aggregates can lead to growth at higher velocities than homogeneous dust agglomerates.
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            Author and article information

            Journal
            2017-06-26
            Article
            1706.08625
            8e0acfc1-38f4-4e72-95d8-42a593da6b6b

            http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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            Custom metadata
            8 pages, 8 figures
            astro-ph.EP

            Planetary astrophysics
            Planetary astrophysics

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