Rendezvous and docking. Again.

[Skorpychan]

So, I've been messing around with trying to figure out how to dock things, since my heavy lifters keep exploding when I try to add more oomph. And I have questions.

I can get encounters of a few km between the craft and the station I'm docking with. Should I set maneuver nodes up at this encounter to synchronise orbits and match speed?

Should I try and set up this encounter at periapsis or apoapsis to save having to do radial burns?

Also, I got frustrated and resorted to mechjeb to do it for me, but couldn't get the mechjeb part to stick onto the rocket. Then I couldn't exit the VAB because the button wouldn't work. Am I doing it wrong?

Edited August 14, 2013 by Skorpychan

[Richy teh space man]

When you get to within a few km of the other ship, match velocities manually at the closest point, (target the ship and use the navball) until relative velocity is 0, then burn towards the other ship directly and match velocities at the closest point. Rinse and repeat as necessary.

Also, make sure your using mechjeb 2, as the first version is a little outdated now, the console itself should just fasten onto the side of your ship.

[Thomas Cook]

I'm not using Mechjeb just yet, as I would like to fully get the hang of docking.

Once I think the job gets tedious, I'll install it.

But as Richy teh space man said I fully agree.

Within a few kilometers, I set the navball to "Target" and burn down the distance using the retrograde to zero.

Then I use the pink prograde to set my velocity towards the target.

Then see the distance get smaller. However after a while the distance closure gets lesser and lesser.

At that time repeat the maneuver and get closer every time. I mostly repeat it two to three times.

Once you're very close look at the map screen. Both orbits's should match very well.

[DChurchill]

Here's my how-to, for whatever it's worth: http://forum.kerbalspaceprogram.com/showthread.php/45379-Someone-Needs-to-Create-an-Easy-Mode-Mod?p=583313&viewfull=1#post583313

I have no problems docking using this method, MJ or no MJ, either way. People say higher is easier, and I'm sure it is, but to me it doesn't make that much difference. 95% of the stuff I do is between 95 - 105 km.

[RoboRay]

Higher technically is easier, as the gravitational gradient is shallower and craft will drift more slowly relative to one another based on their orbit deviations. That said, you have to double your distance from Kerbin's center to halve the gradient. So, going from 100km orbit to 200km orbit does essentially nothing. With the planet's radius of 600km, you have to go from 100km to 800km to cut the drift rate in half. To reduce the drift to 25% of the LKO amount, you need a 2200km orbit.

Considering that still only makes docking marginally easier (the rate of drift isn't usually the problem), it's simply not worth doing.

[HeadHunter67]

Well, that's a lot of food for thought, thank you. I want to practice rendezvous at an altitude of at least 120km (as that seems the lowest sensible altitude at which to establish a station), but if 300km isn't going to have any noticeable difference, I'll stick to the lower orbits.

[RoboRay]

Actually, now that I think about it, there can be a situation where higher orbits are easier, but it's very easy to make that situation irrelevant...

If your docking axis is anything other then the Normal axis of your orbit, the two craft will appear to be rotating relative to each other due to the curved trajectory they follow. Being in a higher orbit mitigates this effect because the circumference of the circular orbit is greater (the apparent rotation slows because of the shallower curvature).

However, you can completely eliminate this effect at any orbital altitude by aligning your docking ports to the orbit Normal (90 degrees left or right of prograde and on the NavBall horizon, or, North/South if you are in a standard equatorial orbit), so it's still not a great reason to seek higher orbits for docking practice.

Edited August 14, 2013 by RoboRay

[Skorpychan]

I'm somewhat limited, mainly because of where my LKO station ended up after a lifter malfunction. I aborted to orbit, but it's a rather eccentric orbit.

What do the relative velocity markers look like?

And can I set up maneuver nodes according to them, so I have a dV meter to show progress?

[Somerled]

What do the relative velocity markers look like?

On the nav-ball, they look just like the prograde and retrograde markers. In fact, they replace the prograde and retrograde markers. If you click on the speed display just above the nav-ball, you switch between orbit, surface, and target (relative) speed readouts and it changes the markers on the nav-ball as well. If you have a target set, this should switch to target mode automatically around, I think, 75km away from the target, but you can always do it manually if you need to.

And can I set up maneuver nodes according to them, so I have a dV meter to show progress?

Yes and no. You can't set up a maneuver node that will take into account target velocities. But, if you set up a maneuver node at or very near the intersection point between you and the target, then adjust the maneuver until the two orbits match as close as possible, that gives you a pretty close estimate on the dV meter, plus burn time and burn direction.