The bus is the platform: solar panels and batteries, attitude control (which way it points), a computer, a radio for control (TT&C) and often a small engine to adjust the orbit. The payload is the useful load: a telescope, a radar, a receiver or a transmitter. Many satellites use a standard bus with a varying payload — the military Starshield satellites, for example, use the Starlink bus.
| Size | Mass | Example |
|---|---|---|
| Cubesat / nanosatellite | 1–10 kg | Experimental satellites, such as the Dutch BRIK-II |
| Small satellite | 10–500 kg | Commercial radar satellites, Starlink-type constellations |
| Large satellite | 500 kg – several tonnes | Geostationary communications and warning satellites |
Fuel is lifetime
A satellite that manoeuvres often — to avoid debris, to get a better look or to approach another satellite — uses fuel. Unusual manoeuvres are therefore an important clue for analysts (see 10.3).