A gravity simulator browser game with real physics

Apogee is an orbital mechanics simulator that runs entirely in your browser. Rather than reading about apoapsis, periapsis, and escape velocity, you feel them: drag a satellite off a tiny planet, let go, and its path is computed live, frame by frame, from inverse-square gravity. Nothing here is a pre-baked animation. Every launch is an actual physics outcome, so the same drag can crash, orbit, or escape depending on exactly how hard and in which direction you pull.

The integrator is semi-implicit (symplectic) Euler, which keeps orbital energy bounded over long runs. That is why a stable orbit here really stays stable instead of slowly spiraling in or out from rounding error, so you can watch a satellite loop for as long as you like. A live HUD reports velocity, altitude, apoapsis, periapsis, and orbital period as the satellite flies, and a gravity slider lets you retune the planet before the next launch.

Is this an online orbital mechanics simulator I can just open?

Yes. Apogee is a static web page, so it loads in any modern browser with no install, no account, and no download. Open it and drag from the planet to launch.

Is it a gravity simulator or a game?

Both. The simulation is a genuine two-body gravity model, and the three possible outcomes (crash, orbit, escape) turn it into a small game: aim for a clean orbit, or see how far past escape velocity you can push a launch.

How do I get a satellite into a stable orbit?

Drag roughly sideways relative to the planet, not straight out, and use a medium pull. Too little speed and the orbit dips into the surface for a crash; too much and it escapes. Hold a stable loop for two full periods and the orbit locks, adding to your orbit count.

Does it work on a phone?

Yes. Touch drag-to-launch works the same as mouse, the layout reflows for small screens, and reduced-motion preferences are respected.

View the source on GitHub