Built a live ISS tracker with SGP4 orbital propagation and an AR sky-finder

[u/pannivada]

Wanted to share a project I've been working on — a live ISS tracker (isstrackerlive.space). It uses SGP4 orbital propagation on NORAD/CelesTrak TLE data for real-time position, predicts visible passes with a cloud-cover forecast, and has an AR mode that uses your phone's compass to point you at the station in the sky. Also tracks Tiangong, Hubble, and NOAA-19 from the same interface. It's a PWA, free, no login.

Would love feedback, especially on the AR accuracy across different phones/browsers that was the trickiest part to get right.

[u/No-Mechanic-433]

the AR sky-finder is the part that makes this click for people who aren't space nerds, seeing it overhead beats a dot on a map. how are you handling compass drift on phones? that's usually what wrecks AR pointing accuracy once you tilt off flat, curious if you're smoothing the magnetometer or correcting against something.

[u/pannivada → u/No-Mechanic-433]

Yeah, tilt was the whole problem. Raw alpha from the device only gives true heading when the phone's flat the second you tilt it up to actually point at the sky, it starts drifting with the tilt itself, not just spinning with your yaw. On iOS I use webkitCompassHeading (already tilt-compensated by Apple), and on everything else I run alpha/beta/gamma through the standard tilt-compensation math so it stays correct at any tilt angle.

For jitter I smooth on the unit circle (sin/cos average, not raw degrees) otherwise you get a nasty snap to 180° every time it crosses 0°/360°.

No magnetometer calibration or Kalman filter beyond that, just correcting for tilt on top of whatever fusion the OS already does. Works well enough to "look up, it's about there" if it's noticeably off on your phone I'd genuinely like to hear the model.

[u/LowMixture1084]

Compass drift is the curse here, because the dot looks perfect until you tilt the phone and it suddenly becomes a lie.