Creating a SpaceX Crew Dragon simulator autopilot in Clojure

In preparation for the SpaceX Crew Dragon’s first crewed mission Demo-2 in late May, SpaceX released a pretty cool little WebGL docking simulator, featuring the Dragon spacecraft. After getting the docking done successfully a few times, I realised this is a perfect opportunity to write a docking autopilot! How does one even approach a problem like this?

In preparation for the SpaceX Crew Dragon’s first crewed mission Demo-2 in late May, SpaceX released a pretty cool little WebGL docking simulator, featuring the Dragon spacecraft. After getting the docking done successfully a few times, I realised this is a perfect opportunity to write a docking autopilot! How does one even approach a problem like this?

An orbital spacecraft is a bit different from what you would consider a normal vehicle, like a car or an airplane. In space, you have all 6 Degrees of Freedom (DoF), meaning you can go up-down, left-right, roll clockwise-anti-clockwise etc.

That is great, but how do we actually dock?

In the context of the simulator, a successful docking means that:

• We are perfectly aligned with the docking port on the ISS
• Our final approach rate on contact is below a certain value
• We don’t want to crash our multi-million dollar spaceship into anything along the way

If you break it down, the problem simply consists of aligning the Dragon how it should be (aligned with the ISS docking port), and flying it to where it should be (at the docking port) slowly.

For the language, I am using Clojure, a Lisp-like *functional programming *language that runs on the JVM. It is highly extensible, simple, with lots of libraries and powerful concurrency abstractions, which we will absolutely need later.

The first step is to obviously figure out how to *control *the simulator. The best way to drive the browser these days is using WebDriver, and some API or client library to send commands to and from it. On our side, all we have to do is create a control interface in our code. In the entire project I am using Etaoin, which is a fantastic pure Clojure implementation of the WebDriver protocol.

clojure dragon automation functional-programming spacex

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