Magnetic Cleanliness Verification of Miniature Satellites for High Precision Pointing

Fraunhofer EMI developed the ERNST (Experimental Spacecraft based on Nanosatellite Technology) mission which is a mid-wavelength infrared imaging satellite. The 12U nanosatellite is based on commercial off-the-shelf CubeSat components where appropriate parts were available. In particular, it is carrying a capable commercial infrared telescope for Earth observation. Like for other nanosatellite missions, a magnetic cleanliness verification was performed on the relevant components of the satellite to assure proper pointing performance. These magnetic cleanliness requirements tend to be proportional to the satellites' moment of inertia which scales approximately with the fifth power of the satellites cubic side length. On the other hand, the measured magnetic field strength drops with the third power of the distance to the magnetic dipole source. Thus, the signal to noise ratio of magnetic field measurements in the satellites far field decreases significantly with the satellites size. As a consequence, the robust identification of a multi dipole model of the magnetization for a miniaturized satellite becomes unfeasible in standard laboratory environments. To qualify the ERNST nanosatellite, Fraunhofer EMI and IPM developed a test setup for precise characterization of small residual dipole moments.