The orbits of most satellites are publicly known in the form of orbital elements (two-line elements, TLE), published by the US Space Force (Space-Track) and independent catalogues, among others. With that data you can calculate when a satellite passes over an area and how long it stays in view.
- As a user: you know when an image can be taken and how often (revisit). A single satellite in SSO passes over the same point about once a day or less; a constellation of hundreds of satellites several times a day.
- As a defender: the opponent can calculate the same for your satellites. Units therefore plan sensitive activities between passes, or camouflage just before one.
Note
Not all satellites are in public catalogues, and satellites can manoeuvre. A calculated pass is an expectation, not a certainty — especially for military satellites.
Try it yourself: N2YO “What's up?” and the Orbital Radar pass predictions calculate which satellites pass over a place, and when. Use a town name rather than the exact position of a barracks or training area (see 10.6).