GNC Debugging Lab

This lab is designed as an interactive engineering exercise. Instead of only reading a solved problem, the student tests an incorrect model, observes what fails, applies the correct fix, and checks the result.

The lab follows a simplified 2D spacecraft GNC workflow: rotational-state propagation, SatelliteBus consistency, attitude control, chaser guidance, mode switching, and disturbance comparison.

Try → Observe → Diagnose → Fix → Validate → Learn

Stage 1 — Rotational Dynamics Debugger

Problem

A spacecraft has an applied moment that produces angular acceleration \( \dot{\omega} \). The task is to decide how the attitude state should be propagated before it is sent to the controller.

Choose a model:

Model A: \( d\omega \rightarrow \int \rightarrow \theta \) Model B: \( d\omega \rightarrow \int \rightarrow \omega \rightarrow \int \rightarrow \theta \)

Choose a model and click Run Simulation.

What to notice

The incorrect model sends angular acceleration directly into orientation. That skips angular velocity, so the attitude state is incomplete.

Correct rotational chain:

\( \dot{\omega} = \alpha \)
\( \dot{\theta} = \omega \)

Stage 2 — SatelliteBus Checker

Problem

A controller can only use the states that are exposed to it. If the bus is missing a key variable, the controller may fail even if the internal dynamics are correct.

Select bus fields and validate the spacecraft state.

Engineering lesson

For attitude control, orientation alone is not enough. A PD controller also needs angular velocity so the derivative term can damp the response.

Required attitude state:

\( \text{state}_{attitude} = [\theta,\ \omega] \)

Stage 3 — Attitude Control PD Tuning

Problem

After fixing the rotational state, the spacecraft can now be controlled. Tune a PD controller so the spacecraft tracks a target attitude.

\( \tau = K_p(\theta_{target} - \theta) - K_d\omega \)

Kp: 5

Kd: 2

Tune Kp and Kd, then run the controller.

Stage 4 — Chaser–Target Relative Navigation

Problem

Satellite 2 acts as the chaser and must reduce its distance from Satellite 1. The controller uses relative position and velocity feedback.

Initial Distance: 50

Kp: 2

Kd: 5

Use wrong controller sign

Try the wrong sign first, then correct it.

Stage 5 — State-Machine Threshold Test

Problem

A chaser spacecraft changes behaviour depending on its distance from the target. This test shows how APPROACH, RENDEZVOUS, and STATION_KEEP modes change as thresholds are adjusted.

Approach threshold: 49.8

Rendezvous threshold: 49.4

Adjust thresholds and observe mode transitions.

Stage 6 — Disturbance On/Off Comparison

Problem

Disturbances such as drag, solar pressure, and noise may change the chaser response. This simplified comparison shows whether the controller remains stable when small disturbances are enabled.

Enable disturbance comparison

Enable or disable disturbances, then compare the response.