Low Power Mode

Objectives

ArcticSat low power analysis was performed using the ArcticSat attitude simulator. The objectives of this analysis include:

1. Determining the best orientation to maintain when in low power mode (R-ARC-ADC-002) (R-ARC-ADC-004)

2. Investigate the transition to and from science mode (R-ARC-ADC-016).

3. Investigate sun vector determination (R-ARC-ADC-037) and how accurately ArcticSat can maintain sun pointing (R-ARC-ADC-039).

Simulation Setup

The simulation was set up to represent a worst-case scenario for the metrics we are investigating. ArcticSat will have the least power generation capability around the summer solstice, when it spends the most time in eclipse, so this deployment time was chosen to investigate. Time and orbit details can be found below.

• Epoch: 21 June 2025 12:00:00 UTC

• Altitude: 525 km

• Inclination: 97.5 deg

• RAAN: 180 deg

• Arg. Perigee: 0 deg

• True Anomaly: 30 deg

An initial error angle of 45 degrees with components in all body axes was chosen to test the control system's ability to handle three-axis control with an underactuated system.

Controllers

Low power mode uses a PID sun-pointing controller to align its main solar array with the sun. This mode will not use the reaction wheel, so control is exclusively magnetic. The sun sensors will be the primary attitude sensors used, however the sun's position can also be approximated using the time and the satellite's orbital position.

An error quaternion is calculated from the normal vector of ArcticSat's solar array and the sensed sun vector. This quaternion is converted to Euler angles before being input to the PID controller.

Simulation Results

The above plots show ArcticSat minimizing the 45 degree angle between the sun vector and the solar array in about 16 minutes. The vector components have quite different looking recoveries, likely due to the varying control authority between axes.

These plots also seem to tell the same story. The spacecraft will have the least authority in the direction of the magnetic field, which for most of the simulation is in the z axis. The output torque plot shows it is relatively much lower than the other axes.