Electromagnetic Formation Flight
Using electromagnetics for relative spacecraft formation flight
Electromagnetic Formation Flight (EMFF) investigates the concept of using electromagnets coupled with reaction wheels in place of more traditional propulsion systems to control the positions and attitudes of a number of spacecraft in close proximity. Unlike traditional propulsion systems, which use exhaustible propellants that often limit lifetime, the EMFF system uses solar power to energize a magnetic field. The Space Systems Laboratory is exploring this concept by developing dynamics and control models as well as an experimental testbed for their validation. The magnetic fields for EMFF are generated by sending current through coils of wire. The interaction between the magnetic dipoles created is easily understood with a far-field approximation where the separation distance between two vehicles is large compared to the physical size of the dipole. By controlling the dipoles on various vehicles, attraction, repulsion, and sheer forces can be created. Combined with reaction wheels, any desired maneuver can be performed as long as the formationís center of mass is not required to change. The MIT-SSL has constructed two EMFF testbed vehicles for demonstrating controllability of 2-D formations on a large flat floor. Vehicles are suspended on a frictionless air carriage and are completely self-contained using RF communications, microprocessors, and a metrology system. Liquid Nitrogen maintains cryogenic temperatures and batteries provide the power to the HTS coils. The testbed has demonstrated control of the relative DOFs in open loop and closed loop control using linearized controllers and a nonlinear sliding mode controller. Future tests planned include spin up, steady-state spin and spin down states. Logical follow-on efforts consist of flight tests of EMFF hardware in low Earth orbit.