A novel facility for reduced-gravity testing: A setup for studying low-velocity collisions into granular surfaces

Abstract

This work presents an experimental design for studying low-velocity collisions into granular surfaces in low-gravity. In the experiment apparatus, reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth's gravity. The acceleration of the surface is controlled through the use of an Atwood machine, or a system of pulleys and counterweights. The starting height of the surface container and the initial separation distance between the projectile and surface are variable and chosen to accommodate collision velocities up to 20 cm/s and effective accelerations of ∼0.1 to 1.0 m/s(2). Accelerometers, placed on the surface container and inside the projectile, provide acceleration data, while high-speed cameras capture the collision and act as secondary data sources. The experiment is built into an existing 5.5 m drop tower frame and requires the custom design of all components, including the projectile, surface sample container, release mechanism, and deceleration system. Data from calibration tests verify the efficiency of the experiment's deceleration system and provide a quantitative understanding of the performance of the Atwood system.

An experimental study of low-velocity impacts into granular material in reduced gravity

“…The reference markings for image post-processing can also be seen on the surface container. Images from (Sunday et al 2016).…”

“…This extended free-fall period increases the experiment duration, making it easier to use accelerometers and high-speed cameras for data collection. The experiment is built into an existing 5.5 m drop tower frame (originally built for aircraft and material drop-tests; Israr et al 2014) and has required the custom design of all components, including the projectile, surface sample container and release mechanism (Sunday et al 2016). The design of our experiment accommodates effective accelerations of ∼0.1-1.0 m/s 2 .…”

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In order to improve our understanding of landing on small bodies and of asteroid evolution, we use our novel drop tower facility (Sunday et al 2016) to perform lowvelocity (2 -40 cm/s), shallow impact experiments of a 10 cm diameter aluminum sphere into quartz sand in low effective gravities (∼ 0.2 − 1 m/s 2 ). Using in-situ accelerometers we measure the acceleration profile during the impacts and determine the peak accelerations, collision durations and maximum penetration depth.

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Small Solar System Bodies as granular media

“…Whereas in the case of finite element methods (FEM) (Hirabayashi et al 2016;Holsapple 2004), the specific geometry of the gravitational field is calculated from the specific shape of the studied body, with a given rheology and equation of state of the material. Experiments need to be carried out in droptowers (Sunday et al 2016), and in aeroplanes that perform a number of parabolic flights to emulate lower gravitational conditions (milli-g levels for tens of seconds are common) (Murdoch et al 2013a). In the best case scenario, experiments can be carried out in the International Space Station as this guarantees micro-gravity conditions for extended periods of time (Fries et al 2016;Fries et al 2018).…”

“…Low velocity impacts (2-40 cm/s) of larger (approx. 10cm) projectile on a granular surface have been tested using an Atwood machine installed in a small droptower (Sunday et al 2016). This system, which uses a system of pulleys and counterweights, allows the effective surface acceleration of the granular material to be varied from 0.2 − 1 m/s 2 (Murdoch et al 2017a).…”