Kepler

Kepler is a flight training program disguised as a puzzle game. Two controls — thrust and brake — and real gravitational physics powered by a Velocity Verlet N-body integrator.

The first five missions teach the basics: what thrust is, how momentum works in a vacuum, what gravity does to a trajectory, and how multiple bodies combine forces. Then the history begins.

Twenty missions recreate real moments in spaceflight: Apollo 13's free-return trajectory, Voyager's Jupiter slingshot, Cassini threading Saturn's rings, DART's kinetic impact on Dimorphos. Each level's briefing card tells the story of the real mission. Each fun-fact on the win screen teaches something the player didn't know before.

Bodies have independent mass and radius — a gas giant is enormous but gravitationally modest; a black hole is tiny but pulls hard. The gravity-well mesh warps the background grid to show where spacetime bends, making Einstein's rubber-sheet analogy playable.

Built as a single HTML file with a Velocity Verlet integrator, wrapped in Capacitor for iOS distribution. Every level was simulation-verified for solvability before shipping. The entire game — engine, levels, HUD, audio — is under 600 lines of JavaScript.