ISS Docking Controller

A PD controller that automatically docks in the SpaceX ISS Docking Simulator.

docking.mp4

Default 200 m approach, shown at 1.5× speed.

How it works

The controller corrects position and orientation every simulation frame:

• Proportional (P): pushes the craft toward the docking position and orientation.
• Derivative (D): damps linear and angular motion to reduce overshoot.

A distance-based speed limit slows the approach near the port. An alignment check brakes forward motion while the craft is off-center or poorly oriented.

Python and Playwright launch Chromium, load the simulator, set starting conditions, and record results. The JavaScript controller runs inside the page and uses the simulator's own thruster controls and physics. Three.js and GSAP come from the simulator; FFmpeg is optional for exporting videos.

Run

Requires Python 3.10+.

python3 -m venv .venv
.venv/bin/python -m pip install -r requirements.txt
.venv/bin/python -m playwright install chromium
.venv/bin/python -m scripts.dock --headed

The default start is fixed. Add --seed 42 for a repeatable random start, or --near --seed 42 for a start near the port. Change the seed to try another starting state.

Random starts and validation

The controller docked successfully from 94 distinct starting positions:

• 53 full-distance starts: 120–250 m along the approach axis, with varied lateral offsets and orientations.
• 41 near-port starts: 6–10 m along the approach axis, with small position and orientation errors.
• 20 of the full-distance starts also include initial linear and angular motion.

The suite contains two fixed starts and 92 seeded starts. Each pass must meet the simulator's docking tolerances and time/frame budgets. Separate checks cover recovery from disturbances, timeouts, and exact action replay.

.venv/bin/python -m scripts.evaluate --suite all
.venv/bin/python -m scripts.check_controller
.venv/bin/python -m unittest discover -s tests
.venv/bin/python -m scripts.replay --fast --fast-start

Validation results · Recorded actions · Control details

An independent browser-simulator experiment.