Kepler

Kepler is an orbital mechanics puzzle game. Every body in a mission pulls on the spacecraft at once, and the player has two controls: brake and accelerate. There’s no steering, because gravity does the turning, so every mission is a question of when to burn and how little fuel it takes. There’s one Daily mission, the same for everyone, and an archive of 121 missions to fly at your own pace, in five minutes or thirty.

Why we’re building it

Kepler started as a creative outlet for Tim: a way to see how far building with AI could go, and a chance to make the video game he wanted to make as a kid. It became something more when his daughter played it and loved it. Games as simple and safe as the ones he grew up with are hard to find for her now, so Kepler is free, with no ads, no tracking and no in-app purchases, and it works offline.

How it’s built

Swift and SwiftUI on iPhone and iPad, drawn with SwiftUI’s Canvas view rather than a game engine. The physics lives in its own package and simulates every body pulling on the ship at once, recalculated twenty times per second of mission time.

Before a mission ships, a harness flies thousands of attempts with varied burn timings to measure how forgiving it is, and a search finds the least fuel a perfect run needs, which is what the Daily score is measured against. Missions come out of a separate design tool that generates candidates, solves them, and keeps the ones worth playing.

Kepler is in final polish ahead of App Store submission. When making and maintaining software costs less, it can afford to be made for the people using it.