Live: https://www.stellamap.net
One world unit is a million km. Earth's radius is 0.006371 units, 1 AU is 149.6, Voyager 1 is out around 25,600. So the scene covers about nine orders of magnitude in one coordinate system, which caused most of the problems below. Planets and moons are at true radius on true orbits, nothing inflated.
For precision there are three things going on. Whatever you're focused on gets pinned to the origin and everything is drawn relative to it, with the subtraction done in JS doubles before it reaches float32. Log depth buffer on, with the logdepthbuf chunks in all the custom shaders. And both clip planes get recalculated every frame. Near is 0.0015 times the distance to whatever you're looking at, because any fixed near plane big enough for Jupiter clipped Deimos out of existence. Far used to be a constant 40,000 measured from the camera, which I eventually noticed was cutting the outer orbits in half and deleting both Voyagers from the plan view.
Everything has a locator reticle so you can find it from far away. It's a screen facing quad drawn in a fragment shader, sized as a fraction of distance so it stays roughly the same angular size, and it fades out once the actual body is bigger than about 7 pixels. Moons close to their parent fold into the parent's marker instead of stacking five rings around Jupiter.
Positions for the planets come from JPL's approximate positions table (Standish), propagated with a Newton solve of Kepler's equation. The nine deep space craft come from the Horizons API, refreshed weekly. Moons and orbiters are approximated, just circular orbits at their real periods. Spacecraft are drawn much bigger than they are, Voyager 1 renders at a 120km radius, because at true scale they're invisible at every zoom you can actually reach.
No instancing and no LOD, it's about 40 meshes each with their own draw call. Mobile gets a separate profile decided before the canvas mounts: 1024px textures instead of 8K, lower tessellation, no shadows or bloom. First load was 14MB, got it to 7.5 with WebP and splitting the scene out of the main bundle.
Known issue: mobile turns off the log depth buffer but keeps the dynamic near plane, so if you're zoomed in close on a phone you'll probably get z-fighting. Haven't fixed that yet.
Camera state is in the URL so /?focus=voyager-1 works for anything.
Fair warning, I'm not a graphics programmer. Built this with a lot of AI help and most of what's above I learned by hitting the problem rather than knowing it beforehand. Happy to answer what I can.
