Attitude Determination & Control

The ELFIN ADCS (Attitude Determination and Control Subsystem) is responsible for designing, testing, and implementing the mechanisms which precisely acquire and control ELFIN’s attitude (i.e. orientation and spin vectors) in orbit.

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The torquer coils that actuate to give ELFIN attitude control

As the name implies, there are two major responsibilities ADCS must uphold: determining attitude and controlling it. Attitude determination uses onboard sensors and ground processing of telemetry data to acquire knowledge of ELFIN’s attitude at all given times. The onboard sensors include a pair of magnetoresistive magnetometers for in-flight ADCS activities. Further resolution can be gained using telemetry the fluxgate magnetometer. This telemetry is analyzed with various post-processing techniques. ADCS is responsible for developing and testing the various algorithms, in-house software, and instrumentation responsible for this telemetry in order to develop a full solution to ELFIN’s attitude.

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Helmholtz coil in a magnetically clean chamber, used to calibrate and test the magnetoresistive magnetometer.

The other major responsibility, attitude control, is the process of magnetic actuation in order to maintain specific orientation and spin vectors – i.e. nominal attitude conditions is spin-stabilized at ~20 RPM orbit-normal. Actuation involves two torquer coils aligned with ELFIN’s Y and Z axes. There are various major ADCS maneuvers throughout ELFIN’s lifespan that must be accomplished: spin-up/down and precession. Spin-up/down is used to adjust rotation speeds while precession is used to adjust the direction of the spin vector. ADCS is responsible for developing an algorithm for attitude control that complies with both science and engineering requirements. Testing is accomplished using several software simulations, such as MATLAB and STK, as well as several hardware tests. The algorithm will ultimately run on an on-board micro-controller, using sensor data as input and outputting current to drive torquer coils in response.