What’s the most difficult docking you’ve ever done (or at least attempted)?

[MythicalHeFF]

Not sure if a threat about this already exists somewhere, but as I’m sure you’re aware, docking in KSP can be pretty hard to do sometimes, especially if you’ve got docking ports at awkward angles or are docking two large craft, which tends to bring down frame rates. But what’s the most difficult docking maneuver you’ve ever done successfully (or at least attempted)? Share your stories here!

As for me, the most difficult docking I’ve ever tried (and what gave me the idea for this thread to begin with), was just last night when I was attempting to attach a several hundred-ton booster to my 1,100-part mothership, the Kilonova, in low Mesbin orbit. Due to the combined part count of over 1300, I was experiencing frame rates of 2-3 FPS, and because the booster was so heavy, even trying to orient it the correct way took minutes, at which point the mothership would just start moving out of alignment again.

This was about as close as I got before giving up and destroying the booster with Whack-A-Kerbal to ease my frustration (I’d already been trying for 20+ minutes)

 

I don’t really remember what my most difficult successful docking was, but it was probably something pretty similar in scope, just actually made possible by me using a better computer.

Edited September 28, 2022 by Jack Joseph Kerman

[Aerodynamic Kerbal]

Its definitely my one and only shuttle docking. I mounted the docking port on the back (the entire spaceplane was Dreamchaser-ish.

It was also carrying a compact telescopic solar panel module. It barely even ran out of fuel too.

So, I somehow docked the shuttle. Cool!

[Beamer]

In my experience docking is only difficult if you are impatient. My 'docking rules' are that I go no faster than 1 m/s when within 200 meter and no faster than 0.12 m/s (since the prograde marker on the nav ball disappears < 0.10 m/s) when within 20 meter or so. Never had a problem even docking stations with well over 1000 parts, but it takes its sweet time at those speeds.

I find the Docking Alignment Indicator invaluable though, base KSP lacks a proper docking readout. What also helps with some of my larger structures is that I tend to keep them in a fixed orientation w.r.t. either the body they are orbiting or Kerbol (using Smart A.S.S.) which means I can typically lock the docking vessel with Smart A.S.S. in the same frame of reference and thus only have to worry about translation.

That said, my hardest dock was long ago, when I first tried to dock to an inflatable airlock. Took me a long time to realize those things are Jr sized

 

[king of nowhere]

this attempted docking

what? it looks nothing special? well, do you see that green smidgen on the tip of the farther ship? here's the same part magnified

now, as this may still be lacking in scale; that extreme tip on the right is a cupola. it's attached over a Mk3 crew cabin. the antenna dishes you see are RA-100, the biggest available.

now go back and see again how that tip compared to the rest of the ship.

that was an attempt to attach a cylinder of six 4000-tons fuel tanks to a 200 thousand tons ship.

I got a lot of mods with bigger parts, still got 1300 parts. well, that's not the first 1300 parts ship I used, but it does lag worse than others. and rotation was slooooow, even though i had several modded reaction wheels each equivalent to many dozens regular wheels (and with a mass equally upscaled, I may add). and after half an hour to wait for everything to align, the fuel tank cracked in two parts. that was when I gave up on the whole Ringrazer concept.

______________________________________________

the most difficult docking I did succeed in making - indeed, I perform it on a semi-regular basis - is not the one on multiple Ringrazer subunits; I did perform a docking between two 100 thousand tons subunits, but it went well enough.

For a while I thought of the docking of the FU Eve...

The FU Eve, my first Eve lander at over 400 tons. It's quite suboptimal in many of its design choices. I can only say I got better later.

... with the DREAM BIG, my first major mothership. At 3000 tons it seemed gigantic at the time.

This was quite the tricky docking because I was using a small docking port. The alignment had to be really perfect, and there was the lag... but then I remembered, the DREAM BIG actually had an RCS system. Which is something I don't do anymore; I don't want to move my expensive, fuel-hungry mothership to dock, it's more effective to move the other ship around the mothership. Indeed, I had no more occasions to use that RCS system during the mission. But it did enable that first docking, so it wasn't too hard.

_____________________________________________

no, the most difficult docking I successfully perform is to mate the two subunits of A'Twin

A'Twin is the mothership I'm using for my kerbalism + rss grand tour. it must carry over 700 tons of mining equipment to make new fuel, because mining in kerbalism is much harder than in stock. It has a mass of 7000 tons when full, yielding roughly 7 km/s; enough for anything around kerbol. but in the real solar system everything is a lot more expensive, and there are several missions where 7 km/s are nowhere near enough for a round trip. So I designed the ship to be split in two, with all the heavy machinery remaining behind while a lighter exploration module can reach 11 km/s.

The shape is a sort of box to protect from solar radiations (another feature of kerbalism). You can protect from solar radiation just by putting a heavy fuel tank between the crew pods and the sun, but when the ship is landed and refueling, it will be forced to stand still while the sun moves in the sky; so I have to put fuel tanks all around the ship for protection.

As a result, docking entails inserting a huge ship inside the gap of another huge ship, and there is a very tight fitting on the edges. generally the two subunits get stuck a few meters before the docking port touch, and I have to give a gentle push with the engines - or several not-so-gentle pushes - to get them moving again.

As an aside, docking a Dolphin escape pod in Cylinder after use is also quite difficult.

Yes, it's called an escape pod, it's supposed to be a one-use feature. You're not supposed to dock it back in place. But, well, as those ships have excellent long-term life support and a long range xenon propulsion, I keep finding improvised ways to use them.

 

[vossiewulf]

The fact is that docking isn't that hard, or at least shouldn't be, if you have the right amount of RCS. Too little or too much, and your vehicle is tough to control and accuracy becomes impossible. The trick is knowing how much is enough and where to place the RCS units, and that only comes with trying to dock lots of different things of different sizes.

That said, I got a little out of control building Icarus Orbital Station, and the docking of the fuel arms in particular was tricky because they had a huge mass and had to be lined up and rotated perfectly.

The launches of the fuel arms were plenty tricky also

[miklkit]

All of the attempts.  Never actually did it.

[sturmhauke]

I was testing out this SSTO...

when the kraken attacked.

I broke the port section off by ramming it into the ground...

...and then later tried to dock with a station in LKO...

...but the RCS system was damaged after the kraken attack, and I couldn't control the ship accurately enough. I had to send out the station's space tug to bring the SSTO in.

And then I decided to send up a bunch of upgraded modules for the station, because why not?

[Superfluous J]

For sure, landing on a docking port from orbit. I used to do it all the time. The first time took an hour, probably. The second time took minutes. After that I could pretty much do it at will.

Of course this was all done on Minmus because no way am I going to try it anywhere heavier. And Gilly doesn't count because you're basically in free-fall anyway.

[vossiewulf]

14 hours ago, miklkit said:

All of the attempts.  Never actually did it.

Did you try having the two vehicles target each other and then use SAS on each to point toward their targets? With anything not huge that will line you up perfectly. Then switch to linear docking mode and hit the shift key until you're moving at around .3m/s toward the target. Then use the up/down/left/right keys to get your prograde marker centered on the target also. That guarantees you're moving directly at the target. Wait until contact, you should be docked. No need for mods or anything fancy.

[Dinlink]

I don't know if the hardest... But the most stressful docking I have ever performed was an emergency docking to save a Kerbal that went out of fuel trying to reach low orbit from the surface of the Mun...

The Kerbal was on a small exploration wheeled rocket... And I miss calculated the DV needed to reach low orbit and got stuck on a suborbital trajectory without fuel with an AP of 14km...

Luckily I had an automated (probe-controlled) fuel delivery rocket in a close orbit... I had to rush for an intercept trajectory 40km or more off target, get into a rendez-vous in suborbital trajectory with both rockets falling towards the surface of the Mun...

I made a quick nose to nose docking (No RCS) and transfered all the fuel to the Kerbal ship ... Then I completed the burn to get into the low orbit with the Kerbal ship at about 8km altitude... Letting the empty automated refueling rocket to crash into the surface of the Mun few moments later... Saving the Kerbal in the process 

Edited October 5, 2022 by Dinlink

[miklkit]

10 hours ago, vossiewulf said:

Did you try having the two vehicles target each other and then use SAS on each to point toward their targets? With anything not huge that will line you up perfectly. Then switch to linear docking mode and hit the shift key until you're moving at around .3m/s toward the target. Then use the up/down/left/right keys to get your prograde marker centered on the target also. That guarantees you're moving directly at the target. Wait until contact, you should be docked. No need for mods or anything fancy.

Kept running out of fuel and/or falling back into the atmosphere.  Even tried it with a Mun rocket, thinking that would have enough fuel.  Nope.

[vossiewulf]

6 hours ago, miklkit said:

Kept running out of fuel and/or falling back into the atmosphere.  Even tried it with a Mun rocket, thinking that would have enough fuel.  Nope.

That sounds like you are having problems making a rendezvous, not docking. So here are the instructions for the easy way to orbital rendezvous:

1. Install Mechjeb.
2. Launch your two ships, one the docker and the other the dockee. Put the docker at 200k orbit, the dockee down at 100k.
3. Go to your docker ship. Go to the map, left click on the dockee ship in the map view, and click on Select as Target.
4. Exit map view and click on the Mechjeb button on the top of the screen. A list of Mechjeb tools will be displayed. Click on Maneuver Planner. If you don't see Maneuver Planner listed, you don't aren't far enough down the tech tree yet.
5. Clicking on Maneuver Planner will display a Mechjeb window. Click on the drop-down button at the top of the Mechjeb window. Select Match Planes with Target.
6. The Mechjeb window will reconfigure with new buttons. Click on Create Node. Then click on Execute Next Node. Sit back and watch your ship match orbital planes with the dockee ship.
7. Click on the drop-down button at the top of the Mechjeb window and select Bi-Impulsive Hohmann Transfer to Target. Click on Create Node. Click on Execute Next Node. Depending on the relative positions of the docker and dockee ships, it may be a few hours before the node.
8. As soon as the Hohmann Transfer burn is complete, SAVE THE GAME. Important. Mechjeb's biggest problem with rendezvous is that it can be TOO accurate, and your two ships run into each other at closest approach. So you want to save at this point in case they do end up playing orbital demolition derby.
9. Click on the drop-down button again in the Mechjeb window. This time select Match Velocities with Target. Click on Create Node. Click on Execute Next Node.
10. If your ships don't spearfish each other, you're done, you'll find the two ships in close proximity at zero relative speed compared to each other.
11. If they do wreck, go back to your save. Make the tiniest burn you can-.1m/sec is plenty for this purpose. Then go through matching velocities with the target again. You'll find they're farther apart now. 

[jimmymcgoochie]

I’m not sure this is “docking” as such, but I once spent a good 15 minutes chasing after a Kerbal who let go of her capsule and then discovered that her EVA jetpack didn’t work- moments after drifting out of grabbing range and starting a slow tumble. Cue a long and awkward series of manoeuvres with a craft that had unbalanced RCS, of which only some were working, to get close enough for the drifting Kerbal to grab on again.

The Kerbal was saved eventually and the cause of failure found (using RO and RP-1 in KSP 1.11 when it was only meant to be used in 1.10 and the jetpacks weren’t properly configured) and eventually rectified (hacky hack deployed in this save, eventually RO/RP-1 were updated for 1.12 and the problems were solved for good). Being RP-1, there are no reaction wheels on the capsule so all attitude control had to be done with RCS on the service module (far right on the craft above), but that resulted in lateral drift which the translation thrusters (centre) had to compensate for, but the reverse thrusters didn’t work; eventually I turned on the capsule’s re-entry RCS and used that to get a bit more control to shimmy close enough for the drifting astronaut to grab hold of the door and hoik herself in.

Edited October 6, 2022 by jimmymcgoochie

[DiomedesDK]

Well in the beginning of my career i had a few instances, where i had to dock without RCS or enough battery for SAS. That was quite a challenge (especially when combined with inexperience with docking in general). I do however believe that the most challenging docking i ever did was when my space station was moving around like a boat in high seas. It kinda reminded me of air-to-air refueling in DCS  Fortunately i managed to catch it on video :) The challenge