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Overview
Overview
Background and Context:
When CubeSats are first deployed into orbit, they often tumble or spin unpredictably. For missions like Pleiades-Atlas, where our payload includes a camera, the satellite must be able to maintain stability or point in a specific direction. Regardless of payload, satellites often require ADCS for many different possible reasons like the need to align its antennas with ground-based ones for Tracking Telemetry and Command (TTC) or to keep solar panels oriented toward the Sun for optimal light absorption.
MCCATS is the ground-based system we designed to test and validate the ADCS here on Earth. It uses a Merritt coil cage—a structure made of 12 large coils (4 per axis) that generates a controlled, uniform magnetic field around the satellite. The Merritt coil is a more effective version that is an extension of the more famous Helmholtz Coil which traditionally only has two coils per axis. The goal of the MCCATS testbed is to recreate the magnetic field found in Low Earth Orbit (LEO) and evaluate our attitude control system before launch.
Project Goals:
Simulate Earth’s magnetic field in a lab setting
Rotate the magnetic field to mimic satellite tumbling and test how our control algorithms respond
Measure the torque produced by our magnetorquers under realistic orbital conditions
Be able to fit up to a 12U-sized satellite within a uniform magnetic field area (original version of TeraLink was 12U, and the goal was to reuse this for as many satellites as possible)
Project Breakdown:
Mechanical: Cage and frame structure (I had fun learning to machine!)
Electrical: Parameter definitions and specifications
Electrical: Driver board design and bring up (Hand assembled)
Software: Algorithm that interfaces with the driver board to mimic the magnetic field perceived by a CubeSat tumbling in LEO
It's looking a bit chaotic here, but our goal was to test the driver boards here with a load equivalent to one full axis (4 coils in series). The white blocks are high power resistors!
Driver Mechanisms
Driver Mechanisms
Initially we looked into various topologies as outlined below in the slides. However, in the end we realized that the easiest solution was to implement a full bridge driver to drive the coils, similar to the typical construction of a stepper motor.
Looking Forward
Looking Forward
Due to logistical and financial constraints, we have decided to put this coil aside and are first making a smaller Merritt Cage to test our 1U satellite. However, the driver board designs can be mostly reused and kept the same because the gauge of the wire can be increased to adjust to make up for the smaller internal volume (which otherwise would result in a stronger central magnetic field)
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