Analyses

Simulator Model

The LI Bus simulator model is a Simulink model representing the attitude dynamics of the satellite in an orbit environment. 

Some features of the simulator model include:

• Gravity gradient and dynamic residual dipole disturbances: These model some of the disturbance torques LI Bus will experience in orbit. The residual dipole is modeled with a square wave to represent the current loop increasing during times like payload imaging.

• LI Bus sensor suite: LI Bus's sensors are modeled to replicate their data rates and resolution.

• NanoAvionics 4RW cluster model: This aims to model the reaction wheel cluster procured for LI Bus. The cluster's orientation means that each wheel has some authority in two axes, and it would be preferable to cold spare one of the four wheels to conserve power, so momentum management is an important factor in designing attitude maneuvers.

Simulation: Deorbit Mode

Simulation: Detumble Mode

Simulation: Science Mode

Simulation: Sun Pointing Mode

Simulation: Maneuver Mode

This simulation used a PID ram-pointing controller to point the +z axis in the anti-ram direction, with the thrust vector being parallel with the z axis. The thrust was considered to be 1.8 N initially and decreasing linearly to represent the pressure decreasing over time. The total simulation time was 180 seconds, during which the thruster fires twice for intervals of 1 second and 1.5 seconds. The two burns combined would total 0.5 m/s of delta-V.

Simulation: Science Mode

Science mode's normal pointing is controlled using two controllers working in parallel. In the results below, the payload is assumed to point in the -y direction, and the solar panels in the +x direction. First, the PID anti-ram pointing controller aligns the payload with the negative ram direction utilizing torques in the x and z axes. At the same time, a sun pointing controller uses torques about the y axis to maximize solar panel illumination.  The results of these controllers are shown below.

The spacecraft will also be able to receive commands to point elsewhere given an inertial quaternion, or Euler angles given the predictable orientation it is normally in. If this is commanded, the spacecraft will use a rate controller to perform the necessary slew, and a fine pointing controller to point at the target.

The first set of results are for a simulation lasting 120 seconds, showing the anti-ram controller responding to an initial pointing error around 500 arcminutes.

The simulation results below show the spacecraft in anti-ram pointing mode over one orbit.

Magnetorquer Sensitivity Analysis for Mounting Accuracy

Below is a sensitivity analysis performed at York University to verify geometric derivation compliance  for the Iris mission. LI Bus will be using the same magnetorquers and mounting them similarly, so similar results can be expected.

AODC Board Power Budget

Embedded below shows a preliminary power budget for the AODC board. It includes the components which connect to the board for power, and assumes they are drawing maximum power, an unlikely scenario during mission operations.