About Apsis
Apsis is a small dashboard for near-Earth activity. It began as a way to stop opening five browser tabs every time something interesting was happening overhead, and it stayed useful enough to keep running.
Where the numbers come from
- Station position — Where the ISS at, refreshed every few seconds.
- Crew — Open Notify.
- Launch schedule — The Space Devs Launch Library, every ten minutes.
- Geomagnetic and X-ray data — NOAA SWPC, every five minutes.
- Orbital elements — Celestrak, every six hours.
- Coastlines — Natural Earth, public domain.
How it is built
Upstream sources are polled on a fixed schedule by background tasks, and every visitor is served from the resulting cache. Load on those public APIs stays constant no matter how busy the site gets — a courtesy worth extending to services that cost their operators money and charge nothing for access.
Passes are computed with SGP4 from current TLEs: positions are converted from TEME to an Earth-fixed frame, then into the observer's horizon coordinates. A coarse scan finds each visibility window, and its edges and peak are refined one second at a time.
No trackers, no analytics, no third-party scripts. Coordinates you enter stay in your browser and reach the server only as calculation parameters; they are never written down.
Accuracy
Passes are geometric: the spacecraft will be above your horizon, but whether you actually see it depends on sunlight, weather and light pollution. Launch times move constantly, and the schedule is only as current as its last refresh.