Attitude Determination and Control System  

A spacecraft's attitude is its orientation in space. Spacecraft attitude analysis is divided into two fields: attitude determination and attitude control.

Attitude Determination is concerned with computing the spacecraft attitude using sensory information. The USUsat attitude determination system consists of a three axis magnetometer and CMOS cameras. The attitude determination system uses Kalman filter and a detailed model of the Earth’s magnetosphere with the three axis magnetometer measurements to determine the satellite’s orientation. The magnetometer is assisted by the CMOS cameras, which are used as star cameras.

Attitude Control deals with controlling the spacecraft to a desired attitude. The USUsat bus uses torque coils as attitude control actuators, which use the forces created by their generated magnetic field interacting with the magnetic field of the Earth to rotate the satellite. The satellite regains control of its attitude via the B-dot control law.

 Sequence of operations for attitude initialization:

  • Satellite is released from the canister, power system will begin to charge up until there is sufficient power to turn on various systems
  • After an initial checkout, the satellite will begin the detumble process to stabilize any spin induced by the ejection phase (B-dot Law)
  • Once stable orientation attained, first contact communication takes place

The coils allow the USUsat bus to maintain an attitude accuracy of 5°. The new TOROID mission requires an attitude accuracy of ±1°. Future developments include using momentum biased attitude stabilization. Reaction wheel will be used in addition to the magnetic torque coils.



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