# Chase orbit questions

So my google-fu is failing me so I'm hoping someone can help out here.

I've been reading up on chase orbits and how things like the Shuttle, dragon, etc all approach the ISS and I understand the process, what I cannot find are the formulas to work out the distance between the chase spacecraft and the ISS or the per orbit catch up rate.

Can anyone help me find it?

• Can you be more specific? The distance can be calculated in the same way the distance between any two objects can be calculated. And what is the second parameter "per orbit catch up rate"? Units? Mar 7, 2020 at 14:09
• km, m it doesn't matter. I'm trying to work out how to time the rendezvous. SO, for example, if I'm closing at the rate of 100km per orbit and the ISS is 10,000km away I know it'll take 100 orbits. Mar 7, 2020 at 15:16
• So the unit on your "per orbit catch up rate" is "km per orbit"? Mar 7, 2020 at 15:18
• km per orbit would work for this question, yes. Mar 8, 2020 at 0:13
• slightly related: What is the “ISS's Keep Out Sphere” and what is its radius?
– uhoh
Mar 8, 2020 at 2:06