Tracking satellites can be fun (where is the ISS now?) … and complicated. Fortunately there are some algorithms that can help like the SGP4.
I’ve used an available php implementation of the SGP4 algorithm and made a simple satellite tracker application showing the ISS, but really it can show any satellite as long I feed the proper Two Line Element from CelesTrack.
Check the link and you’ll see where the ISS is hovering now: www.spacemig.com/satellite-tracker
And you can check how accurate this is by going to this link:
References
- http://en.wikipedia.org/wiki/Simplified_perturbations_models
- http://en.wikipedia.org/wiki/Two-line_element_set
- http://www.celestrak.com/NORAD/elements/