How to Read the Chart
- Across: the orbit plane. Every orbit crosses the equator heading north at one point on the sky, and this angle (the right ascension of the ascending node) says where. Satellites in the same plane share it.
- Up: where the satellite is along its orbit, counted from that northbound crossing (the argument of latitude). 90° is its most northerly point, 180° the southbound crossing.
- Columns: a finished plane is a column of evenly spaced dots, and gaps in it are empty slots. A plane that is still filling often leans, because satellites that reached their height later have drifted a little further round.
- Dots between the columns: satellites at a lower height. A lower orbit swings round faster, so they drift across the chart until they reach their plane.
- Height colours: at the shell's operational height (within 10 km), within 50 km below it, more than 50 km below it, or above it.
- Movement colours: each satellite's height now against its height a week earlier: climbing, coming down or holding.
What the Chart Shows Now
Starlink has 11,193 satellites in five shells, and 84% of them are at their shell’s operational height. The biggest shell is tilted 53.2° to the equator and flies at 463 km. Of the 1,495 Starlink satellites below their shell’s height, 748 are coming down and 83 are climbing.
Amazon Leo has 392 satellites in one shell at 630 km, with 97% at their shell’s operational height and 3 climbing.
Qianfan has 260 satellites in one shell at 1,066 km: 76% are at their shell’s operational height and 23 are climbing, with 18 too new to compare. Guowang has 230 in two shells at 1,150 and 1,165 km, with 89% at height and 17 climbing, plus 9 too new to compare.
Frequently Asked Questions
It is the flat sheet that an orbit lies in. A constellation spreads its satellites over many planes, each tilted at the same angle to the equator but turned to a different point round the Earth, so that between them they cover the globe. Within each plane the satellites follow one another round the same path.
Earth’s equatorial bulge slowly swings every orbit round, and the lower the orbit the faster it swings. A satellite waiting at a lower height drifts across the planes above it, so operators can move a satellite into a different plane with very little fuel, then raise it once it lines up. On the chart these satellites sit between the columns.
From the satellites themselves. For each shell we take the members whose height held steady over the past week and find the height where most of them sit. That is the shell’s operational height for the day. A shell is a group of satellites at the same tilt to the equator. Nothing is typed in by hand, so the heights follow the constellations when they move. Heights are measured above Earth’s equatorial radius, as on Satellites by Altitude, so they can differ by several kilometres from the round figures operators quote.
A satellite comes down when it is lowered to retire, so that air drag can pull it into the atmosphere, or when its operator moves it to a new, lower shell. The chart shows only the movement: a satellite counts as coming down when its height is lower than a week earlier by more than normal day-to-day variation.
Once a day. Every satellite is placed at the same moment from its latest orbit data, so the planes line up properly. Satellites without fresh orbit data in the three days before that moment are left out, so objects that have already re-entered never appear as ghosts.