Scaling Effects in Miniaturization of Reaction Spheres

This paper investigates the performance of miniaturized reaction spheres. Currently, a majority of existing reaction spheres are at a technology readiness level of 3 to 4 and prototypes are developed for 50 kg-class spacecraft. Since the motivation of replacing reaction wheels with reaction spheres stems from the limited volume and power budgets of small spacecraft such as nanosatellites, miniaturization of reaction spheres is of relevance. In this paper, reaction spheres with two different types of driving units are miniaturized such that they can be used for CubeSats. Based on the published models and experimental data of prototypes, performances of the miniaturized reaction spheres are estimated. Relations between the estimated performances, such as output torque per power, and scaling factors are investigated. Through comparisons of the scaling characteristics of studied prototypes, reaction spheres with a PM (permanent magnet) based driving unit demonstrate great advantages in the miniaturization. Based on the reference of the Delfi-n3xt CubeSat, performance requirements of a single reaction sphere are derived. By comparing the required and estimated performances of the scaled reaction sphere, it is found that generating required outputs with the limited power budget is the main challenge for electromagnetic induction based small actuators. To improve their efficiency, advances in superconducting and manufacturing technologies are needed. Reaction spheres with a PM based driving unit require advanced sensors and control algorithms to make their applications to small spacecraft feasible.