Where the numbers come from

Five sources

NASA public telemetry, through Lightstreamer

163 readings — power, life support, thermal, attitude, communications, onboard computers — pushed to the browser over a WebSocket from push.lightstreamer.com, adapter set ISSLIVE. The same broadcast that NASA's ISSLive! site used and that Lightstreamer's reference client still reads. It comes and goes: the broadcast has been silent for days at a time, and the page says so rather than showing yesterday's numbers as today's.

Celestrak, orbital elements for NORAD object 25544

The station's position, speed, altitude and the solar beta angle are computed in the browser by SGP4 propagation of these elements. Checked once against an independent service that propagates its own elements, the position came within a kilometre on the ground — which is why the coordinates stop at two decimals, and why the map keeps working when the telemetry does not.

NASA 3D Resources

The 3D model is NASA's IGOAL build of the station, structured by module and by joint, prepared once into a compressed file. Its rotary joints and solar-wing gimbals are driven by the telemetry, so the wings on screen turn the way the real ones report turning.

NASA Image and Video Library

For 44 of the 62 parts, a photograph searched by title from NASA's public archive, with its credit and its date. The rest — the rotary joints, most stowage platforms, a few antennas — have no photograph that shows them and would be misrepresented by one that does not; they show none.

Natural Earth

The coastlines on the map, at 1:110,000,000, and the marine areas that name what the station is over — "the Coral Sea", "the Mozambique Channel" — by point-in-polygon against real outlines rather than a table of guesses.

Why every value has an age

The broadcast re-sends whatever it likes whenever it likes. A reading can arrive a second ago and carry a measurement taken weeks earlier — several sensors have done exactly that for a month. So the age shown beside a value is read from the station's own clock wherever the station provides one, never from when the packet landed. (Eight channels — the array drive currents, which publish nothing but zero — carry no timestamp at all; for those, arrival is all there is, and the page says they are not working.) The age means one of two things:

On a measurement

how long since the sensor last produced a number. Past a day, the reading is marked as stopped: it is a memory, not a measurement, and comparing it with a live one compares two moments rather than two sensors.

On a state

how long since it last changed. A computer that has reported the same mode for a month is working, and the page says "unchanged since", not "stale".

A zero from a channel that cannot physically read zero — cabin pressure, the station's mass — is a fault of the broadcast, not of the station, and is not shown.

The station itself

The twin names 62 parts. The station, module by module lists them all, and each of the six subsystem pages — power, life support, thermal, attitude and orbit, communications, command and data — explains every reading it publishes.

What settles what a symbol means

NASA's catalogue names its symbols — this site subscribes to 163 of them — but does not say how to read them. These documents do, and every explanation on this site can be traced to one of them.

The code

Everything is open: github.com/maximvs101/iss-live. The repository carries the reasoning behind each decision, the scripts that verify the readings against independent sources, and the record of what was measured rather than assumed.