Platform for Controlled Ultra Low Gravity Profiles

After conducting our own experiments, we propose the platform we developed as a tool for other users. Designed for ultra low velocity impacts in granular beds simulating asteroid surfaces [1], the main requirement in platform design was a clean partial gravity generation without any coriolis forces. This is achieved by using a two stage approach: First, earth gravity is reduced to microgravity using the ZARM drop tower at Bremen. Second, microgravity is converted to the desired level of partial gravity. This is done by using a linear stage, driven at a constant acceleration inside of the drop tower capsule. The acceleration imposed by the moving experiment volume onto the drop tower capsule is supposed to be neglected, because of the vastly different inertial masses of approximately 2-3 kg for the experiment and several hundred kg for the drop tower capsule. As required for its original purpose, our platform is optimized for providing accelerations in the milligravity regime, but not limited to that. Partial gravities in the cm/s^2 regime were succesfully tested and our platform has also proven to be able to induce oscillations to agitate the experiment. Arbitrary trajectories are possible, respecting available microgravity time and the maximum travel of 30 cm.

In detail, we evaluate our platforms capabilities, performance and compliance. The drop tower provides 9.3 s of microgravity in catapult mode. Because of an initial equilibration time and the necessity to return our system to a safe resting position, our platform can forward a usable duration of approximately 7 s to the experiment. Expected values g-jitter, meaning the unwanted residual acceleration, lie in the range of 10^-6 g. Vacuum supply, power and remote control are supplied by ZARM until just before launch. The experiment can be made accessible after a delay after each launch. The capsules are compatible, so our system may be used in the Gravitower Bremen Pro as well.

[1] Joeris, K., Schönau, L., Keulen, M., Born, P., & Kollmer, J. E. (2022). The influence of Interparticle cohesion on rebounding slow impacts on rubble pile asteroids. npj Microgravity, 8(1), 36.

[2] Von Kampen, P., Kaczmarczik, U., & Rath, H. J. (2006). The new drop tower catapult system. Acta Astronautica, 59(1-5), 278-283.