Demonstration of a Magnetic Locking Flux-Pinned Revolute Joint for Use on CubeSat-Standard Spacecraft

Abstract

Magnetic flux pinning is an interaction between strong magnets and certain superconductors that causes a damped, non-contacting equilibrium to form, connecting the flux-pinned objects. This interaction has been proposed for use in establishing a stable formation of spacecraft modules that is resistant to disturbances. Although flux pinning can exert forces in all six degrees of freedom, a flux-pinned interface can be designed to constrain only certain degrees of freedom so that it functions as a non-contacting kinematic joint. One such joint consists of a superconductor flux pinned to a cylindrical magnet and free to move around the magnet's axis of symmetry. Such an interface would serve as a revolute joint that allows two modular spacecraft to reconfigure. This paper explores the development of one such joint compatible with the CubeSat standard. We extend the functionality of the revolute joint by introducing electromagnets that create two stable equilibrium states in a system of two modules. The electromagnets also provide the means of reconfiguration between the two states, eliminating the need for reaction wheels, thrusters, or other conventional actuators for this maneuver. Finally, this paper discusses future testing for flux-pinned joints and ongoing work on an in-orbit demonstration. Nomenclature

An Air-Levitated Testbed for Flux Pinning Interactions at the Nanosatellite Scale

“…When such a magnetic field is generated by one spacecraft module and a superconductor flux-pinned to that field is mounted on another module, the FPI can function as a revolute joint. Previous work in this area 2,3,8 has confirmed that flux pinning can create joints and other mechanisms, some of which have been validated in both laboratory experiments and during microgravity testing. 9 These mechanisms, when deployed as links on a close formation of spacecraft modules, could allow the spacecraft to easily reconfigure via ground-based commands to electromagnets.…”

“…Air-powered levitation for previous flux pinning experiments was accomplished with the use of an air table which raised experimental vehicles above its surface for unconstrained motion. 8 The primary limitation of this arrangement was that a surface large enough for desirable maneuvers required a prohibitively high input pressure of gas to provide sufficient pressure over the entire surface to support the vehicles. In effect, most of the input gas was not used to support experimental vehicles but expended over empty surface area.…”

“…A previous experiment used this setup to demonstrate a flux-pinned revolute joint, shown in Figure 2. 8 This method had several drawbacks, however, including a low mass limit on floating vehicles and a large flow rate of high pressure gas to provide sufficient output over the entire table surface. These limitations provided incentive for us to design a new testbed and make it more robust to allow more complex maneuvers in equipment testing.…”

“…Standard laboratory experiments of spacecraft components (such as the flux-pinned mechanisms previously demonstrated 2,8,9 ) face the challenge of operating in a test environment that is dissimilar to the conditions present in a space environment, particularly with regards to gravity. High-precision systems found on satellite hardware that require a low-torque environment are often overcome by the typical forces encountered in an earth environment, making it difficult to validate their functionality.…”

Flux-Pinned Dynamics Model Parameterization and Sensitivity Study

“…Flux-pinned interfaces leverage the dynamics of magnetic flux pinning to control the relative orientation and position of close-proximity spacecraft without mechanical contact. These unique traits make flux-pinned interfaces a technology candidate for applications such as spacecraft capture and docking 1,2 , assembly of modular systems 3,4 , formation flying [5][6][7] , kinematic mechanisms 8,9 , and station-keeping 10,11 . However, for this technology to be mature enough for spaceflight applications, its physics must be represented in a high-fidelity predictive dynamics model that can inform design trade and analyses.…”