Development of the TigerSats ADCS Testbed: Novel Results in Hysteresis Rod Characterization for CubeSat Passive Attitude Stabilization

Abstract

Reduced CubeSat launch costs have enabled a larger range of science and engineering missions available to scientific researchers in the past decade. Attitude stabilization is key for many missions that involve remote sensing, astronomical observations, or direct ground-based communications. For budget-constrained research groups, a high confidence in stabilization performance prior to launch is crucial to a successful science mission, especially relevant to initial downlink acquisition–a common challenge for educational CubeSats. Hysteresis rods–a technique of achieving multi-axis passive magnetic stabilization via repeated demagnetization of ferromagnetic materials in Earth’s magnetic field–are currently used across a multitude of CubeSat missions for their low-budget and low-SWaP compared to alternative approaches. However, they take several days to stabilize CubeSats via torques that are just a few nanoNewtonmeters, which has previously limited the ability to ground-test hysteresis rods under laboratory conditions.

In this thesis, we present novel techniques to characterizing hysteresis rods in addition to developing the TigerSats attitude determination and control system (ADCS) testbed facility as an extension to the recently built homogeneity-optimized Helmholtz cage. We first develop the control electronics system and a Matlab software package to drive the Helmholtz coils to produce flightlike low-Earth orbit (LEO) magnetic fields. We then develop an air bearing module that mounts within the Helmholtz Cage, advancing the ground test ADCS capabilities within the TigerSats lab to being able to performance test a wide range of passive and attitude attitude actuators. Finally, we present a novel technique to measuring magnetization loops of hysteresis rods via their stray magnetic field as measured by a linear array of hall sensors. We show that the current state-of-the-art characterization of hysteresis rods in alternating magnetic fields under predicts the energy dissipation felt in flightlike ‘rotating’ magnetic fields. Furthermore, we characterize the dependence of the energy dissipated on the field intensity, compare these results to predictions by commonly-used numerical magnetic models, and provide potential reasons for their deviations. To increase the accessibility of ground-testing magnetic control and stabilization techniques for a wider range of small satellite student and research groups, we structure certain sections of this thesis as a “how-to” guide for low-budget replication of all our test apparatus.