Docking, speed, orbit generic question blah blah blah

[alexinblack]

I am orbiting Kerbin, I wish to dock with another ship. I have lined up the orbits so they are more-or-less perfectly aligned. The only issue I now face is catching up to the target ship without ruining my beautiful orbit. Help would be wonderful and greatly appreciated!

[Rocket In My Pocket]

The thing is that if your orbits are exactly matched you'll never catch up to him because accelerating will only take you higher, while slowing down will sink you lower. The way I like to think of it is: You gotta be wrong before you can be right.

What you need to do is have your orbit either smaller or larger than his but the same shape, and intersecting at one point. (Picture two hula hoops standing upright on the ground where one is larger than the other.)

Then when your ship has reached this common intersection point where the lines touch, you speed up/slow down in order to match the orbits.

If the guy who made this illustrated guide got a dollar for every time it got posted on these forums, he'd be a rich man lol.

Edited March 7, 2016 by Rocket In My Pocket

[Plusck]

As Mr Happy-to-see-you (happy2KU?) clearly said, you're going to have to ruin your perfectly synchronised orbits.

First of all, it's far easier to catch up than to rendezvous with something behind you.

To catch up, it's simple: slow down a touch. You'll fall into a tighter orbit, then as you start to approach you can speed up a touch to boost your orbit, catch up the last few kilometres and make your RDV.

If the target is behind, then it's more counter-intuitive. You speed up to raise your orbit and therefore slow down angularly-wise (which is, admittedly, just as counter-intuitive as the opposite case, above), but you've got to be much more careful about the final approach and leave the change in orbit much later. If your target is coming up behind a few kilometres away, and you try to accelerate towards it, you'll drop your orbit and after a very short time heading towards the target, you'll find yourself heading down to a lower orbit and accelerating away again.

For this reason, if the target is behind you (well, to be honest in all cases, but especially if the target is behind) it is best to rely completely on the map view. Select target, drop a node and set it to boost radially out / prograde (the exact combination will depend on how impatient you are and how much fuel you want to spend) until you get a very close approach (under 1 km). Then do what the map and burn indicator says and wait until you're extremely close to switch your attention to the navball and make small burns to push retrograde over anti-target.

[Plusck]

Finally, if the target is really far away and you don't mind warping a few orbits, set a first node with a prograde/retrograde burn that seems reasonable. Then set a second one a good distance after the next target approach marker. Then right click it and click on the orbit+ button until the target approach is very close. Then go back to your first node and correct it until the target intercept is perfect.

[Gojira1000]

And you can watch How to Dock advice right here, as well.

[Mjarf]

Scott Manley has a video on rendezvous and docking as well, it's the one I learned from from. Rendezvousing is something that's really difficult the first time, but then it "clicks in place" in your brain and it's much easier after that first successful attempt. I've found that those intersect nodes aren't very relevant, focus on the visual approach in the orbital map, and use the navball in regular mode once you get closer than 20km or so. The way I do it is I go into a higher or lower orbit (depending on the target being in front of or behind me) until the two ships are flying close to parallel, then I burn to the same orbit height as the target's orbit, then I use the navball for the close approach. Don't worry about the orbits at this point, just focus on carefully closing in on the target. Patience is key here, as in most things in KSP.

Edited March 9, 2016 by Mjarf

[RizzoTheRat]

I always aim get an orbit which touches the target orbit at one point, preferably the AP or PE but it doesn't matter that much.  This will give the orange (and purple if the orbits cross twice) closest approach marker,  then make a manoeuvre node just after the intersection point and increase or decrease velocity to get the target ship marker as close as possible on the next orbit.  I can easily get to within a couple of km like this, and then once that manoeuvre has been conducted a bit of experimentation will find where (usually about 1/2-2/3 of the orbit but depends on which direction the offset is) to put another node to bring the ships within a couple of hundred meters.

 

The breakthrough for me on docking was learning how to use the nav ball (keep the target on the nose and use RCS to keep the prograde vector on the target), and realising that switching camera mode (V key) to locked meant I could align the view I had with the directions the RCS work in, meaning I actually thrusted in the right directions to line up properly.