Ejecta Production in Microgravity from Low Velocity Impacts in Regolith

Abstract:

We report on the results of the third PRIME (Physics of Regolith Impacts in Microgravity Experiment) campaign on-board the NASA C-9 airplane in August 2014. The objective of PRIME is to study low-velocity impacts of cm-scale particles into planetary regolith under reduced gravity and microgravity conditions, measuring how dust on the surfaces of planetary ring particles, planetesimals and asteroids dissipates energy in the collision and the mass-velocity distribution of any ejecta produced in the impact.

PRIME can perform impacts into granular materials at speeds of ~5-50 cm/s in microgravity. Impacts are performed in vacuum and projectiles are spherical particles launched by a spring designed to provide the desired impact energy. The target materials studied are quartz sand and JSC-1 lunar regolith simulant, filled to a depth of 2 cm in the target tray. Projectile materials are quartz, brass, and stainless steel to provide a range of impact energies at constant impact velocity. Impacts are performed in isolated chambers and up to 8 experiments can be performed per flight. The data collected consists of video recordings of the impacts, taken with a high resolution video camera at 120 frames per second.

The impacts observed during the PRIME-3 campaign resulted in 9 marble rebounds and 15 impacts with ejecta. Seven of these 15 were at accelerations of ~0.05 g while the remaining impacts were performed in free fall. For each rebound observed, the coefficient of restitution of the impact was measured and for each collision that produced ejecta, the ejected particles were tracked to determine their initial velocities. The PRIME-3 campaign successfully extended the region of the parameter field explored by investigating impacts at velocities lower than observed during previous campaigns while collecting new data on impacts at asteroid gravity levels. We present our new results and combine them with results from previous similar experiments and discuss applications to planetary ring systems, planetesimal accretion, and in situ exploration of asteroids and small planetary satellites.