Attitude Determination & Control System (ADCS) is responsible for determining and controlling AcubeSAT’s attitude and orbit at any point during our mission in a safe and orderly fashion. The main designed ADCS modes include: after-launch stabilizing (detumbling mode), and achieving nadir-pointing orientation while in orbit (nominal mode). Our nanosatellite shall be able to maintain this specific orientation so that the patch antenna faces the earth, ensuring required mission data transmission to the ground station installed on earth. The design phase has been successfully concluded. Furthermore, the physical architecture, determination and control strategies and algorithms have been decided upon.

Sensors:

  • Gyroscope
  • Two magnetometers
  • Fine sun sensor
  • GNSS

These sensors are deemed sufficient to cover our mission’s needs as we can fully define our orientation and angular velocity using the magnetometers, fine sun sensor measurements and gyroscope. We have opted for dual redundancy in our magnetometers, due to their being cost-efficient, reliable, and with minimal restrictions. GPS data is used periodically to initialize and update on-board orbital elements.

Determination Strategies & Algorithms

An Extended Kalman Filter combining gyroscope, magnetometer and fine sun sensor measurements while also taking into account our dynamic and kinematic model has been developed. Because a Kalman Filter requires an initial state estimation, we also developed SVD algorithms solving Wahba’s problem, combining both sun sensor and magnetometer measurements. These strategies are simulated based on our already defined control cycle.

Actuators:

  • 3 magnetorquers (1 per axis)
  • Reaction Wheel

We opt for magnetic actuation, an inexpensive and efficient way to control small satellites, combined with a reaction wheel, constituting a robust solution to satellite control.

Control Strategies & Algorithms

To control the satellite at any time we are developing controllers to calculate the optimal applied torques. For the detumbling mode, a B-dot controller is currently being developed. For the nominal mode, we are developing a PD controller. The calculated required torques are then translated to desired voltage to our actuators.

Orbit Propagation Strategies & Algorithms

An on-board orbit propagator is used to determine AcubeSAT’s position and velocity at any point during the mission. The propagator’s on-board orbital elements will be initialized using TLE files or GNSS measurements.