How stupid not to have thought of that (docking)

[Thanny]

Up to a couple days ago, whenever I wanted to dock two vessels together, I mentally designated one ship the docker, and one the dockee. The docker maneuvered around the dockee to line up the docking ports.

Then I had a ship dropping off a base at the Mun which had quite a bit more fuel than it needed for the return flight to Kerbin. As it happened, I also had another ship in orbit waiting to return a large rover back to Kerbin. It probably had enough fuel, but it certainly needed more than the other ship. So I decided to dock the two to transfer fuel, at which point I noticed that neither had any kind of RCS. After a very brief amount of time thinking about it, I figured I'd just arrest all relative velocity between the two ships after they were close enough, then point their docking ports towards each other, and give a short engine burst to get one of them moving (both ports were axial). It worked perfectly. So perfectly, in fact, that I sat there wondering why I hadn't been doing that all along with all docking operations.

Sure, not all ships have axial ports, and main engines are worthless for radial ports. But once you control from the docking port, RCS automatically thrusts in the correct direction based on translation controls. Get to zero relative velocity, control from the docking ports, aim towards the target (each ship targets the other), then close the gap. With especially large ships, you need to switch back and forth adjusting the aim, as the slow speeds you want to be using between two behemoths give time for the different orbital paths to change relative orientation.

In particular, it's shockingly better when docking a large tanker to a large fuel station (>1000t each). Previously, I'd burn up hundreds (if not thousands) of units of fuel maneuvering the tanker into position. Now I just burn at target retrograde until relative velocity is 0, then switch back and forth between station and tanker, pointing each to the other's targeted docking port, until the two docking ports are facing each other and square. A short burst of RCS to close the gap, a few minor adjustments back and forth, and they're docked, after using a miniscule amount of fuel. I could even get away with no RCS at all if need be, using just reaction wheels and main engines (with the latter tweaked to minimal output, of course).

So, am I the only one that did it the hard way until the easy way became the only way in a certain situation?

[Thomas988]

Huh. I've always heard of non-RCS docking always assumed it was next to impossible. However your technique of pointing the two spacecraft at each other certainly is something I haven't thought of before. I use RCS for my dockings, but very little since I've gotten very efficient with my maneuvering.

[Renegrade]

I've been doing such things for a while now, but it took me a while to figure it out too, so don't feel bad.

Also note that in some situations, just rolling the dockee a bit on it's long axis can make the approach a lot easier (works well if say you're approaching a long but narrow station, like a Babylon-5 type build -- most of my stations are like this, although that's mostly because they're just ships with big tanks and a research lab )...

And you CAN dock radially mounted ports with engine-only approaches (or low-RCS situations). Just roll the dockee so that the port is at right angles to the docker's heading, roll the docker so it's port is on a parallel axis to the other port, and then approach gently. Magnetism will take care of the rest

[Thanny]

And you CAN dock radially mounted ports with engine-only approaches (or low-RCS situations). Just roll the dockee so that the port is at right angles to the docker's heading, roll the docker so it's port is on a parallel axis to the other port, and then approach gently. Magnetism will take care of the rest

I meant when both ports are radial. On my fuel station, the big port is axial, but the standard and mini ports (and claws) are radial. My interplanetary ships, which I launch essentially empty, also have radial ports. It's hard to see how one could reliably dock two large vessels with both ports offset by 90 degrees from the only source of thrust. It would actually be not too bad if the port were at the ship's CoM, as you could thrust at the target then pitch the ship so the port rotated to the front. But none of my ships are like that.

[Norcalplanner]

If you use MechJeb, it's really easy to dock without using RCS. SmartASS on another ship will stay active as long as you're still in physics range, so just have each ship's docking port target the other and hold that heading with the target function of SmartASS. Small burst on the main engine to close at .3 m/s or so, and even if you're a bit off, the two ships will gracefully pirouette around each other and dock.

[Laie]

If you use MechJeb, it's really easy to dock without using RCS.

I hear that the new pilot/sas thingy will also be good enough in most cases. That said, I find that the "have both ships just point at each other" approach only really works for smallish ships / if the ports are close to the center of mass. Large ships tend to shake themselves out of alignment when the gap becomes really small.

[I_Killed_Jeb]

Indeed. I've stopped taking monoprop with me for basic docking altogether. Now it's only for very technical multi-port docking maneuvers

[Norpo]

Indeed. I've stopped taking monoprop with me for basic docking altogether. Now it's only for very technical multi-port docking maneuvers

This; it really depends what you're docking. A small probe, with plentiful SAS torque to an easy access space station? That could be done with rocket engines alone. Now, a slow, sluggish, mothership to a refueling station? RCS, for sure.

[Renegrade]

I meant when both ports are radial. On my fuel station, the big port is axial, but the standard and mini ports (and claws) are radial. My interplanetary ships, which I launch essentially empty, also have radial ports. It's hard to see how one could reliably dock two large vessels with both ports offset by 90 degrees from the only source of thrust. It would actually be not too bad if the port were at the ship's CoM, as you could thrust at the target then pitch the ship so the port rotated to the front. But none of my ships are like that.

Well, what you do is you aim for a point in front of the target's port, approach it at right angles, and roll your current ship so that your port is facing it. Visualize the target's docking port like it's main ring is making a plane - you basically want to have your current ship's port just outside of that plane, scraping along it's surface. I sometimes do that when changing out stations for improved models, or with specific types of vessels.

Update: Oh one thing that helps in this circumstance, if you're a bit fast while going past that docking port and/or a bit far, you can turn your ship towards the other ship to slow down the relative speed between the two docking ports and bring them closer (or farther apart, depending on the location of the port and the timing of the turn)

I hear that the new pilot/sas thingy will also be good enough in most cases. That said, I find that the "have both ships just point at each other" approach only really works for smallish ships / if the ports are close to the center of mass. Large ships tend to shake themselves out of alignment when the gap becomes really small.

Actually the old SAS could handle that too (well, the one that existed between 0.22 and 0.25 anyhow. I've noticed that really early KSPs have TERRIBLE SAS). The newest one is actually a bit worse, I find (and terrible like the ancient one if you tell it to hold a specific target).

If you take full control during the docking part (no SAS), you can often counteract the shake with the right movements (aim to dampen it). That sort of shimmying nonsense can happen even with nose-to-nose docking and such at times... countersteer

Indeed. I've stopped taking monoprop with me for basic docking altogether. Now it's only for very technical multi-port docking maneuvers

Meh don't stop taking monoprop, the reaction wheels are massively overpowered and #lolfake (which is my special term for things that are not just somewhat unrealistic, but massively so to the point of being 'unauthentic'.. like orbital turbojets). BTSM addresses this problem by ..pretty much removing RWs.. my Horrible Nerf just nerfs them (right in the face~ double cost for RWs and 10% effectiveness, plus massive nerfs to the cost of RCS parts), and even Squad's been looking at how silly they are.

[Jovus]

My proudest moment in KSP was when I docked some OKS parts together by lining them up, then undocking my maneuvering tug off the front and letting them glide together. (I'd forgotten the second docking port on the piece I wanted to add.)

So yes. I've done this. However, I don't usually feel it's worth the trouble. Delta V is so easy to come by in KSP.

[Rocket Farmer]

Actually I never bother with rcs at all and pretty much do exactly as you explain except I usually line up from 1-2km away and come in at 10m/s for the last 500m or so so I don't ever actually go completely to 0. With large units I will come in with the engines pointed at my target and flare down to 1m/s 50m out and then flip around and dock.

I am always fascinated at how much prep a lot of people take with rocking. I wouldn't say I'm good at it (my kerbals occasionally ram the ports together a couple of times to get it perfect) but most people seem to take a long time and a lot of rcs.

Try it without it. With the Nav ball just counter burn to get your crosshairs aligned in the target.

[r4pt0r]

once i figured out how to get my relative velocity to 0, docking became easy.

[katateochi]

If I have a small and really manoeuvrable craft I quite enjoy flying it around the larger ship that it's docking to, but in all other cases the way OP describes is basically the way I dock. If you use nothing but info from the nav-ball and this approach, then you can dock in the pitch black (for when you forget to install lights).

[problemecium]

Docking without RCS isn't so bad. Just imagine when you first learned to dock. It's about the same difficulty going from knowing how to dock to docking sans RCS, sort of like "docking level 2".

[KerikBalm]

This is pretty much how I do it...

Sometimes I use a little RCS... but not very much

[eddiew]

I find it easy to get a 'nearly there' with main engines, but usually it'll be a metre or two off to either side, and drifting somewhere between 0m/s and 0.1m/s in that murky realm where instruments are useless.

Still a bit of manoeuvring to get to that point will massively cut down the amount of monoprop needed to actually dock. Much more efficient than using MechJeb to do the job from 200m away on the wrong side!

[Rune]

Actually, with the new SAS modes you can just choose to point at target on both ships, and let that take care of your alignment. Myself, I usually roll my space stations so I don't have to go around them (they are usually radially symmetrical lately), then let myslef going towards the port at 1m/s at under 100m using the main engines alone (knowing how to herd your velocity vector wihtout nulling it completely makes for really fast an efficient dockings), then turn around and nullify that last m/s on RCS, with the forward component going first so I can drift laterally into proper alignment. Basically, I dock 95% by instruments, even when I don't use NavyFish's docking alignment indicator. The technique is great, because it allows you to dock in pitch-black situations without fear of bumping into anything. And if the stcok game finally learned to change your control point when you choose "control from here" (right now it only changes your control orientation, so relative position and distance reading are very wrong when you get close, especially for big ships).

Rune. The navball is so full of information, if you know how to find it.

[ShadowZone]

When I did my Apollo 11 recreation, I released the CM from the rest of the ship, turned around and jettisoned a decoupler that was still hanging on the back of the CM. The force of the decoupler propelled the CM into the bay where the LM waited and the two docked instantaneously

[Hcube]

i've always docked small ships this way, even with RCS... so much easier than to align the arriving ship !

Unless its a big station you can't move around of course