Power Saving in Magnetorquers by Operating in Cryogenic Environments

Satellites with cryogenic instrumentation have great potential for military, commercial, and scientific space missions due to the increased sensitivity of their sensors, even for Low Earth Orbit (LEO) missions. For these missions, magnetorquers are a common electromagnetic actuation solution for controlling the attitude and orientation of the satellite. As for any other component of a satellite, the optimization of power consumption and weight is always beneficial for the design. In this work, we propose a novel idea to reduce power consumption during magnetorquer operation: installing the magnetorquer in the cryogenic area of the satellite, instead of installing an actuator in the hot area. As the electric resistivity of the wire is greatly reduced, power consumption is also reduced. However, the heat generated in the magnetorquer, even if lower, must still be dissipated by the cryocooling system, which has an additional energetic cost. The cryogenic temperature range where this effect is beneficial, and the amount of power saved, was determined as a function of different cryocooler technologies' efficiency and the purity of the copper wire material. It is analytically demonstrated that the operation of the magnetorquer in a temperature range from 10 to 40 K could save energy with respect to operation at 300 K if the copper wires have a residual resistance ratio larger than 200 RRR. A prototype magnetorquer suitable for cryogenic temperatures was manufactured and tested at liquid nitrogen temperature, 77 K, to experimentally demonstrate the variation in the energy consumption. The magnetorquer comprised an iron core with copper wire winding that achieved 1.42 Am-2 by applying 0.565 W at 0.5 A. When operating submerged in liquid nitrogen at a temperature of 77 K, the power used by the magnetorquer was reduced by eight times due to the change in electrical resistivity.