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Laboratory for Atmospheric and Space Physics

Attitude Determination and Control Subsystem

CSSWE uses a Passive Magnetic Attitude Control (PMAC) system that aligns the CubeSat to the Earth’s local magnetic field line at all points in the orbit. The system is composed of two primary elements. The first is a bar magnet, which provides a restoring torque towards the local magnetic field of the Earth. The second is an array of soft-magnetic hysteresis rods mounted orthogonal to the bar magnet, which are magnetized by the local earth field. As the satellite rotates, the relative orientation between the hysteresis rods and the local earth magnetic field changes, which changes the polarity of the rods. Energy is lost to heat as the magnetic domains within the hysteresis rods change direction. This energy loss serves to dampen the satellite rotation until the satellite bar magnet axis is roughly aligned with the local earth field direction. Thus, the satellite will settle to tracking the local magnetic field at each point in its orbit.

The CSSWE team has developed a passive magnetic attitude control simulation to determine the angular motion of the CubeSat. The exact magnitude of the torque due to the hysteresis rods is of paramount importance to such a model. Thus, a Helmholtz cage test setup was built to measure the rod magnetization vs. the magnetizing field applied parallel to the rod. This measurement method seeks to provide accurate inputs to the simulation.

A calibrated magnetometer is located onboard to provide two axis attitude knowledge during operations. Two-axis attitude knowledge (relative to the Earth’s magnetic field) is expected within ±3°. Photodiodes on each of the solar arrays have also been installed to provide three-axis attitude knowledge when the spacecraft is insolated.