Chase orbit questions

Question

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? — Organic Marble, Mar 07 '20 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. — Gary Williams, Mar 07 '20 at 15:16
So the unit on your "per orbit catch up rate" is "km per orbit"? — Organic Marble, Mar 07 '20 at 15:18
slightly related: What is the “ISS's Keep Out Sphere” and what is its radius? — uhoh, Mar 08 '20 at 02:06
If you assume circular orbits for both the target and the chaser, the catch up rate expressed in angular units is the most simple case. To calculate a distance between points on concentric circles is much harder. — Uwe, Mar 08 '20 at 14:26

Uwe · Answer 1 · 2020-03-08T17:33:12.017

1

A circular orbit at 400 km height has a period of 1 hour, 32 minutes and 24 seconds. At 302 km it is 1:30:24, only two minutes faster.

If the chaser at 302 km was launched 20 seconds too late, it will need 1/6 of a full orbit to keep up to the target at 400 km, or 15 minutes and 4 seconds. But the target and the chaser are now above the same point on Earth only, the height difference is still 98 km.

edited Mar 08 '20 at 17:33

answered Mar 08 '20 at 17:09

Uwe

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Chase orbit questions

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