Calculating Postition of ISS / Hubble in space How do I calculate the positions of above satellite in space ?
The orbit of the ISS does vary. Drag from the very thin atmosphere slowly causes the orbit to lower, and the speed to increase. So the ISS needs to be boosted about a couple of times a month.

Its position can be predicted, at least in the short term, and websites such as Heavens Above publish current position, predictions, and orbital information.