Rendezvous - on same orbit, about 40km ahead, what do I do?

[EricT43]

I'm doing my first rescue mission. There's a Kerbonaut stuck in orbit in her capsule. During the last 1.5 hours I've managed to get into orbit, close a considerable distance, and get "slightly" ahead so that I can go back and push to slow her down for re-entry. Problem is, I've got everything lined up, but I'm still about 40km in front of her. Anything I do to try to close the distance is going to throw off my orbit and make things worse instead of better?

What do I do now?

Edited May 5, 2015 by EricT43

[Reddeyfish]

if you have the building upgrade that allows you to do this, set the other kerbal as a target, then get yourself in a higher orbit and wait/timewarp until you have a close enough encounter. (higher orbits move slower than lower orbits, so you can close that 40km gap)

(you can use maneuver nodes with the close encounters to plan more exactly)

EDIT: you mention slowing her down for re-entry; the craft that the kerbal spawns in cannot survive re-entry (it doesn't have parachutes). You'll need to have an extra crew space in your craft so you can transfer the kerbal over to your craft for a safe re-entry.

Edited May 3, 2015 by Reddeyfish

[EricT43]

EDIT: you mention slowing her down for re-entry; the craft that the kerbal spawns in cannot survive re-entry (it doesn't have parachutes). You'll need to have an extra crew space in your craft so you can transfer the kerbal over to your craft for a safe re-entry.

DOH! Guess I'll need to go home and get another cockpit.

[RexKramer]

DOH! Guess I'll need to go home and get another cockpit.

Yes, but while you are up there, might as well practice your orbital rendezvous maneuvering.

40km is pretty close. If your orbits are closely matched (nearly identical), burn prograde a little, to make your orbit slightly larger than your target's. Key word is slightly. Be patient while the target catches up to you.

When you get within about 2km, you can set the ship as a target even if you haven't upgraded your TS (tracking station). You can do that by double-clicking the vessel once it's within visual range.

You can switch to the other ship when you are within 2.5km, by using the [ or ] keys. However, I really recommend getting within 100m, and zeroing your relative velocity before switching to the stranded kerbal, especially if you are new to EVA, and working with the jet pack. Because that's next.

As Reddeyfish mentioned, you will need to EVA the stranded kerbal, and maneuver him/her with the jet pack to the rescue ship. EVA controls can be tricky if you haven't done it before. Be patient and go slow.

Good luck!

[CorBlimey]

welcome to the world of rendezvous I still remember my first one with horror. It gets so easy after a couple you can do it without thinking.

Another alternative to the proper approach mentioned above, when 40km away is, if you have oodles of dV, just burn straight towards your target to get about 50m/s in their direction. You will cover the distance in a few minutes so your changed orbit wont matter much (a bit like how to do EVA).

Now, docking...that is another kettle of fish and still a PITA for me.

[Chruschtschow]

Point at the other ship and accelerate. That's at least what NASA did with Gemini IV. Then strange stuff happened. Then probably someone remembered that guy named Kepler.

And to add something useful:

You can see your relative speed to the target, if you click the speed display above the artifical horizon. Prograde and retrograde markers as well as the speed are now shown in relation to the target instead of orbit.

[TheXRuler]

Oh god yes, welcome to one of the hardest things in KSP. When I did my first rendezvous there were no contracts, so it was with the purpose of docking. I remember taking about two hours to even get close. And I was like yay, almost done. Three hours later I was finally docked xD

What the others have said is completely correct. By going higher you will increase your orbital period (the time you need for one full orbit) and hence your target will start catching up. If you need to catch up to your target you need to shorten your orbital period by making your orbit smaller. For a full rendezvous and docking tutorial take a look here, it is by scott manley who is something of a KSP-guru for me ^^ I have learnt a lot from watching all his videos.

[Chaos_Klaus]

And that means: Burn away from the target ship, to make your orbital period longer. after one complete orbit, the target will have caught up with you a little. on the last orbit before your target overtakes you, you have to do another burn to put you exactly ontop of your target after completing one more orbit.

Then it's just a matter of arresting all relative velocity when you meet the other craft. After that, start your direct approach by burning towards your target.

[EricT43]

Thanks all. Successfully rescued on attempt #2. Got within 50m!

[Meithan]

Thanks all. Successfully rescued on attempt #2. Got within 50m!

Congrats! I still remember my first rendezvous. Boy was that exciting, seeing another spaceship just out there, at arm's reach, both free falling at ludicrous speeds in perfect synchrony. Now you have to try docking. Rendezvous is half the work, so you're almost there.

Here's what Wally Schirra, the Gemini 6 astronaut who accomplished the first successful orbital rendezvous in 1965 (although the spacecraft did not dock), had to say about rendezvous:

"Somebody said ... when you come to within three miles (5 km), you've rendezvoused. If anybody thinks they've pulled a rendezvous off at three miles (5 km), have fun! This is when we started doing our work. I don't think rendezvous is over until you are stopped  completely stopped  with no relative motion between the two vehicles, at a range of approximately 120 feet (37 m). That's rendezvous! From there on, it's stationkeeping. That's when you can go back and play the game of driving a car or driving an airplane or pushing a skateboard  it's about that simple."

Happy flying!