This page describes a high-level overview of the Attitude Determination and Control Systems (ADCS) sub-team’s goals and how it intends to achieve them. Contained in this page is the ADCS block diagram and its explanation, as well as a brief discussion of the engineering decisions that lead to its creation.
The figure below shows the most recent revision of the ADCS block diagram.
ADCS Block Diagram - 2nd iteration
As can be seen in the figure above, ADCS takes in readings from three types of sensors: its sun sensors, its gyroscopes, and its magnetometers.
These readings are then paired with orbital information supplied by NORAD and information regarding the Earth’s magnetic field which are then processed by a Kalman Filter to eliminate noise.
Using the processed data and the desired attitude of the satellite, ADCS can then calculate the necessary magnetic torque and slew rate to bring the satellite from its current orientation to its desired one.
It does so by controlling its two actuators: its magnetic torque rods (magnetorquers) and its reaction wheels.
The ADCS block diagram in full can be found here:
Flowchart Maker & Online Diagram Software
The Canadian Satellite Design Competition (CSDC) specifies that the satellite must achieve a pointing precision between 1-1.5 degrees. The satellite’s secondary payload, operated by QEYNet requires that the satellite must achieve a pointing precision of 0.1-0.2 degrees.
With these tight tolerances in mind, magnetometers and sun sensors were chosen to aid with the CSDC specifications as they provide up to 3 degrees of accuracy. The gyroscopes were therefore chosen to achieve the QEYNet requirements as they could maintain steady pointing of as low as 0.003 deg/hr.
On the actuator side, the magnetorquers were chosen to achieve the CSDC specifications with their ~1 degree of accuracy. Meanwhile the reaction wheels, with ~0.01 degrees of accuracy, were selected to meet the QEYNet requirements.
Since organizations like NORAD already track satellite positions in-orbit, it was decided to outsource that responsibility to them rather than attempt to create the ground infrastructure required to do so from scratch.
It should be noted that NORAD provides updates on satellite position once every 24 hrs. However, the provided data can be used to create a propagation of the orbit using a Universal Orbit Propagator algorithm, with which the satellite position can be determined with reasonable accuracy. However, the propagated position will eventually deviate from the true position of the satellite, at which point a new NORAD reading can be used to update the orbit propagation.