This image of the NASA mission control shows the world map screen at the centre. I'm probably wrong about this (feel free to shoot me down) but the map up there appears to render what look like 3 different orbit tracks.

Why are there 3 orbit tracks? Does Mission control track multiple craft in adjacent orbit? Are these something like an nominal, sub-nominal, and supra-nominal orbit? What is the typical margin between these orbits?


1 Answer 1


As @David said, those are the current and the two next orbits of the same spacecraft. On this photo you can see the ISS superimposed on one of the orbits, and the orbit numbers (4, 5, 6) to the left.
Mission control screen

As @Gerrit said, if the spacecraft isn't doing any maneuvering, the next orbit can be predicted with 100% accuracy. The only information you need is the orbit's period. As the Earth rotates beneath the spacecraft, the orbit's period determines the distance between the ground tracks.

(edited because my initial answer was incorrect)

  • $\begingroup$ I can understand previous, and current. How far in advance can variations to the next orbit be made? What guides that decision? Does mission control just (for want of a better phrase) play it by the ear? $\endgroup$
    – Everyone
    Apr 30, 2014 at 14:35
  • 2
    $\begingroup$ I believe it's the current and next two orbits rather than previous, current, and next. $\endgroup$ Apr 30, 2014 at 15:59
  • 1
    $\begingroup$ @Hobbes with 100% accuracy is a little misleading. We are good, but not that good. For example we can predict where it'll be to the nearest meter, centimetre, maybe even millimetre, but not micrometer. We also can't 100% guarantee it wont be knocked off course by a collision of some sort. This is mostly semantics, but it's misleading to say any exact future prediction is 100% accurate. $\endgroup$
    – ThePlanMan
    Apr 30, 2014 at 19:30
  • 1
    $\begingroup$ @MichaelKjörling of course predicting to the nearest micrometer wouldn't make you 100% accurate, I was making a point. Predicting to the nearest 1.61619926 × 10^-35m would be 100% accurate though! $\endgroup$
    – ThePlanMan
    Apr 30, 2014 at 21:43
  • 2
    $\begingroup$ @FraserOfSmeg But by then, which spacecraft atom is it that you are tracking? :) $\endgroup$
    – user
    Apr 30, 2014 at 21:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.