Contract - Rescue Mission (intercept points)

[Nullpointer]

I have completed the contract Rescue Mission (retrieving a lost Kerbal from orbit). I have done this contract twice successfully. I was interested in a little bit more background or if someone can direct me to literature to read up on that would be great too.

My question is I have only been able to complete this mission if I launch ahead of <said Kerbal), if <said Kerbal> has already passed above me and I launch, I find it impossible to maneuver to match up intercepts. However if I launch ahead of <said Kerbal> I can usually obtain intercept points, get them close enough and successfully complete the mission.

My question is general around intercept points. What is a good algorithm (approach) to organizing intercept approaches such that I can get them whether I launch in advance or after a target? I guess I am just not understanding some of the math and theory behind it and would like to get more information so that I can succeed on the latter approach where the target is ahead of me. I would assume this knowledge will help me on all other aspects of the game where an intercept is required. Thank you in advance

Edited October 5, 2014 by Nullpointer

[Taki117]

the basic concept is that objects in a lower orbit move faster. Basically this gives you two options.

Option A: you are in a higher orbit and moving slower allowing your target to catch up to you.

Option B: You are in a lower orbit and moving faster causing you to catch up with your target.

Both are viable rendezvous options, but if you are ahead of your target I would move to a higher orbit and let it catch up. sounds like you have the rendezvous part down so I won't go into that.

[Nullpointer]

Thanks Taki, so in short if I am behind the target drop to a lower orbit and catch up to the target. If I am ahead of the target rise to a higher orbit and let the target catch up to me. Thanks again for the speedy answer.

[Taki117]

Thanks Taki, so in short if I am behind the target drop to a lower orbit and catch up to the target. If I am ahead of the target rise to a higher orbit and let the target catch up to me. Thanks again for the speedy answer.

Most welcome. Also note that you can have an eliptical orbit to achieve the same affect. If your orbit touches your targets orbit and you have an apoapsis higher than the orbit of your target your target will eventually catch up. The opposite is true if your orbit is inside the target orbit. Keep in mind though that this generally takes longer than simply circularizing at a higher altitude because only half of your orbit is spent slower than, or faster than, the target.

[Kryxal]

It may take longer, but it's also easier, I find ... you have intersect points AND a different orbital period, so can just drop a node on the intersect point, click "next orbit" until the marker crosses sides, and apply some thrust then to make the rendezvous REALLY close. If you feel like getting fancy, you can also add radial/normal so you have less target motion to deal with on intercept.