Serious problems with interception/docking

[tjsnh]

So, I've got rocket design down and am decent at interplanetary navigation - but I stink at docking.

Running stock, no mods;

I've only managed to successfully dock once, two small capsules, and it took several real-time hours. Typically what happens is that I end up getting "kindof close" , within a few KM, but can't get under 1km to my target. A couple of times I've gotten under 1km but what always happens is that I end up spending all my fuel trying to make corrections and ending up just circling my target.

I'm not sure what I'm doing wrong. Should I be chasing the pink dot? Is it "normal" for docking to take 3+ hours?

Edited April 22, 2014 by tjsnh

[Flight]

Once you get to less than 10km and a reasonable speed in relation to your target, it should take just a few more minutes to dock.

You should chase the pink circle, but don't just burn to its direction. You have to bring your prograde (yellow circle) to it. For example, if your prograde is to the left of your pink target, burn to the right of your target to bring the prograde closer.

When both prograde and target are together at your navball, wait until the distance is short enough, and burn retrograde to slow down. Bring your speed to 0 (in relation to target) when you are at about 100 meters from it, and then go on with RCS.

There are other ways to approach, and there are many videos on youtube better showing how to do it.

[tjsnh]

Thanks for the quick reply. :-)

I've watched at least a dozen vids on youtube about this, and none of the methods they showed worked very well for me. I'll give it another shot this evening and post results, it's been a few days since I've tried.

[diomedea]

I believe your problems starts with the "kind of close" rendezvous. Getting within a few Km leaves enough distance for the orbits of the two crafts to be different enough, and orbital mechanics then bring to increase distance again.

I would start with a good rendezvous. First, making sure the two orbits are in the same plane (inclination difference = 0), then changing altitude of the peri/apoapsis of the maneuvering ship so to match the altitude of the other ship at the same location, and in the end finely changing the other apside altitude so to achieve the closest possible distance at intercept. It is quite possible (without any help from mods) to achieve minimum intercept distance of 200-300 metres.

When approaching the intercept point, I prepare to match speed with the target, therefore orient the ship towards the relative speed minus marker (Navball set on Target mode). It may help to set a node at the intercept point so to burn in the direction needed to have the two orbits match, so the blue marker of the node is giving the correct orientation and Delta-V required much sooner than the relative speed marker.

At the intercept point, cancel almost entirely the speed difference (burn towards the relative speed marker until the relative speed goes close to 0).

Once stable in the same orbit (relative speed 0), point towards the target and close at a slow speed. Once close enough (around 200 mt.) you can target the docking port, and then you need to bring your ship on the axis coming out of that port. The target ship must not rotate. There are different styles for approaching the axis to the docking port, one is to rotate your ship parallel to the axis and use only traslation to move towards the axis, another is to move the ship to a point along that axis, stop it there and then rotate it towards the docking port. In both cases, you should now be at some distance from the docking port, aligned with its axis and pointing the port. The navball (in Target mode) provides relative speed markers and you need to bring them aligned with the purple marker (target), translation mode is essential now. Close slowly, keeping relative speed aligned with the target (while your ship must remain on the axis). Apply retroburn just enough to have a very slow speed at contact (0.1 - 0.2 mt/s).

EDIT: it is useful to me to change the camera to "chase" mode and align it with the ship, while docking. That way, the translation keys (I-K-J-L) match the orientation of the ship.

Edited April 8, 2014 by diomedea
more info

[radonek]

Less complicated (and a bit less fuel efficient) way I learned from wiki:

Make sure you are int target mode. Turn to pink circle. Burn a bit. See target closing. Turn retrograde (yellow cross) and wait until target is closest possible. Burn until your relative velocity is zero.

Rinse, repeat.

Every cycle should bring you a bit closer to your target, once you have it in hand you will se how and why Flight's method works.

[Kasuha]

Less complicated (and a bit less fuel efficient) way I learned from wiki:

Make sure you are int target mode. Turn to pink circle. Burn a bit. See target closing. Turn retrograde (yellow cross) and wait until target is closest possible. Burn until your relative velocity is zero.

Rinse, repeat.

Every cycle should bring you a bit closer to your target, once you have it in hand you will se how and why Flight's method works.

^ I recommend to start with this.

When you get better at it, try not burning exactly at the retrograde marker but slightly to its side instead. It will "repel" it from that point. That way you can keep it on the target retrograde marker while gradually reducing your speed. Watch out to not crash into your target, though!

My rule of thumb for beginners is speed (in m/s) = 1% of distance (in m). 1 km distance -> 10 m/s; 100 m distance -> 1 m/s.

[Starwhip]

Tutorial in signature. Check it out.

(I've had to have said that at least three times today...)

[Aphobius]

If the dozens methods from the youtube didn't worked very well, try THIS method.

[JiWint]

I have a tutorial

It isn't perfect but I hope it helps you

[Voculus]

The first thing to do, once you're close, is to kill all of your speed in relation to your target, by burning retrograde to it. Your navball should read "Target"' not Surface or Orbit. When that's done, you burn toward the pink target marker on the navball to get closer, and then kill your speed again. Repeat as often as necessary, and when you're quite close, with relatively little or no speed difference between you and your target, you'll find yourself in an identical orbit. Then it should be easy to RCS your way into a docked state.

After a few tries, you'll get better at judging speeds at which to burn, and maneuvering with greater efficiency.

Edited April 8, 2014 by Voculus

[tjsnh]

Well, it took about an hour (mainly due to the fact that I was basically flying a huge frickin' gas tank with nothing but RCS but I _FINALLY_ managed to dock my first module into my station core!

The docking part only took about 5-10 minutes. The intercept/rendezvous is the part that took forever. Once I got within 1KM it took most of the hour to get close enough without any velocity... ugh.

In the pic below, the module on the right is the one I was 'flying'. Behind it was the "control module" with some RCS thrusters+tanks, a gas tank, and a poodle motor.

[ArmchairGravy]

I have a text/pictures tutorial in my signature that may help.

[cantab]

The Basic maneuvers page on the wiki taught me how to rendezvous. It took a couple of goes, but now I find it pretty straightforward.

I also made my first docking with two parts of the ship I'd just undocked, making things a bit simpler.

And if you're using main engines, to align the yellow-green prograde/retrograde markers with the magneta target direction markers, remember "Pull prograde, repel retrograde".

[RW-1]

The first thing to do, once you're close, is to kill all of your speed in relation to your target, by burning retrograde to it. Your navball should read "Target"' not Surface or Orbit. When that's done, you burn toward the pink target marker on the navball to get closer, and then kill your speed again. Repeat as often as necessary, and when you're quite close, with relatively little or no speed difference between you and your target, you'll find yourself in an identical orbit. Then it should be easy to RCS your way into a docked state.

After a few tries, you'll get better at judging speeds at which to burn, and maneuvering with greater efficiency.

This is a great way to start, and I second it for beginners.

Just make sure you have selected the other ship as the target, and than set your navball to target as well.

As voculus says, then you get better at it you can begin trying a curved approach to the target, knowing where to place the prograde marker relative to the target as you close in.

Doing this procedure, you also have to have patience, after you have killed relative motion and burned towards the other ship (prograde on the circle), depending on your relative orbits, the prograde marker will drift a bit, you can correct using docking and linear mode RCS for that. Thing is, depending on the initial distance, keep the closure at 10 m/s or under and warp a little bit, this way you dont either hit it if you were that good, or shoot by if you were not that good.

Don't rush it and you'll get there.

[Kerba Fett]

One important thing to remember with all the talk about burning prograde or retrograde to dock is that you're actually not. While the navball uses the same icons, when you're in target mode they indicate relative velocity between you and your target NOT orbital direction.

If you don't understand the difference in what the navball is telling you it's much harder to understand how to dock

[tjsnh]

I've had some better luck trying the tips here, thanks guys.

I also learned the hard way that the whole process is a L O T easier if you have RCS distributed on BOTH ends of your module and the thrusters are aligned in a + relative to the Z axis, as opposed to an X if that makes sense.

[TheD007]

one method that worked for me when i was learning how to dock was to take a small probe (1.25m) with some rcs (one medium sized tank) add solar panels to both and a small tank of fuel with small engine have an identical probe docked to it on the pad. launch and get to orbit then separate them by undocking and using RCS to thrust away. practice again and again from greater separations and different alignments until you gain a sense of direction about it. if the docking becomes second nature you can easily design ships that you know that you will be able to dock easily.

hope this can help

[Redshift OTF]

Are you trying to close to the target with just RCS? Most people use engines for that.

[radonek]

I also learned the hard way that the whole process is a L O T easier if you have RCS distributed on BOTH ends of your module and the thrusters are aligned in a + relative to the Z axis, as opposed to an X if that makes sense.

RCS ports placement is art in itself. This is why you really should do your first docking with small, maneuvrable ship. Yours is quite heavy and ports does not seem to be well placed. For more complicated designs, RCS Build Aid mod is a must.

[Skorpychan]

I recently cracked this myself, from watching mechjeb do it. Once you're close and at the same speed, you turn directly towards the target and make a short burn, then flip your craft around. When you're close, about 100m or so, burn again to slow to a near-standstill. After that, switch to RCS. Get yourself aligned with a docking port, and burn towards that. Slow as you close, make final adjustments, then go in for final approach.

I recently had to take over docking from mechjeb, because it was so terrible at it.

[Doozler]

...you really should do your first docking with small, maneuvrable ship.

First time I practice docking was with two purpose built craft - simple, cylindrical, perfectly placed RCS, docking port on the front, and it was relatively easy. Since then when I try it with "real" craft with fuel sloshing everywhere, solar panels at all angles, Kerbals wiggling about etc, it's been much harder. I'd agree with the suggestion to try using special "practice craft".

I second the simple approach for the first few times (Remember to shift naval to target!):

1) Towards the green cross until velocity is 0, then

2) Towards the pink circle for a bit, wait until target is closer, then

3) repeat

[Othuyeg]

With a little bit of practice docking becomes one of the most enjoyable things in this game. Or atleast it did for me. It is just somehow thrilling to do.

Today I went big and docked something with a bit more mass.

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[O-Doc]

First time I practice docking was with two purpose built craft - simple, cylindrical, perfectly placed RCS, docking port on the front, and it was relatively easy. Since then when I try it with "real" craft with fuel sloshing everywhere, solar panels at all angles, Kerbals wiggling about etc, it's been much harder. I'd agree with the suggestion to try using special "practice craft".

If you can't have perfect RCS alignment then add in reaction wheels. This will counter balance any rotational forces that result in lopsided RCS placement. The most obvious example is station building using a tug. So, a decent amount of reaction wheels are good to have when you are learning to dock.

[Sirine]

KSP Extreme fast rendezvous and docking (100% Stock)

[O-Doc]

KSP Extreme fast rendezvous and docking (100% Stock)

You can improve this docking by having a high apoapsis on your first craft. Your second will catchup within minutes and you can match the target orbit by burning between prograde and radial out. Also, when you are slowing down, push your target retrograde into the target anti-direction. It's more efficient and faster than trying to match orbital velocities before you are inside RCS range. If you are trying adjust your approach direction without changing your approach speed then burn halfway between target retrograde and target pro-direction.

If you follow these techniques you can get a dock after about 1/4 the 1/3 the orbit. Or, about 30min after first lift-off.