Is it possible to dock two large stations without Mechjeb?

[Shiv]

I have two large (well not huge, but large) stations I'm trying to dock together. So far it's been an exercise in frustration. Closest I've gotten was 100 m but then they just shot right by one another due to the amount of speed needed to get them close enough. I can't seem to get the exactitude necessary to get them to meet, but the orbits are pretty damn close. Is this doomed to failure or is it possible? Any suggestions for docking craft that aren't tiny demonstration ships (the ones they use in the tutorial videos)?

[Taki117]

It's possible, but I would try to minimize approach speed. A good rule of thumb is to not exeed a speed that is 1/100th distance to target. (i.e if you are 5km away don't approach faster than 50m/s)

[Tortoise]

Well first I should ask...Did you even learn how to manually dock before installing mechjeb to do it all for you?

[Dave Kerbin]

It sounds like the intercept rather then the docking is where you are having the issue and that isn't something related to size. You may need to scale back and brush up on your approach and docking before you try it with a large station. If the ships are shooting by each other then you are going way too fast which again sounds like you haven't learned basic docking before trying it on a more advanced scale.

The approach is just 3 simple steps repeated until you get as close enough to dock using RCS thrusters

1. Within about 5km point toward the target indicator on the navball. Burn to add a small amount of speed - the closer you are the less speed you want to pile on.

At more advanced levels you'll learn that you really want to manipulate your velocity so that your prograde indicator overlaps the target indicator.

2. Coast toward your target. The map screen will show you the closest you're going to get with your current direction and velocity. Wait until you are there.

3. Cancel out your relative velocity by checking that the navball says 'Target' and then burning in the direction marked retrograde until velocity is at or near 0 m/s.

If you are close enough to dock with RCS do it, otherwise go back to step 1.

[Kasuha]

It is definitely possible. Whatever MechJeb does is possible to be done manually.

Rendezvous and docking is not just about bringing the two stations together, it is also about matching their speeds. And to match their speeds when they are close you need to perform the approach correctly.

My rule of thumb for newbies is, when getting ships together, keep relative speed at about 1% of distance (e.g. at 1 km distance, keep relative speed 10 m/s) and keep the relative prograde marker on the target. It may take long but it leaves sufficient room for error in most cases.

[xtremespino]

Its definitely possible, its just just technique. Don't try to slow down at the last minute. Once within a few kilometres, just to target speed mode and burn in the retrograde half of the nav ball at a angle which lines up the retrograde marker and target marker that is on this side. Keep doing this, correcting your course, but don't burn to close to the retrograde marker, as you will slow do completely. Eventually you will be heading straight towards the target at a relatively slow speed. This is how I do all my docking now, after I found that burning at your closest approach when my relative speed was 100 m/s was uncontrollable. This method allows for more control.

[MarvinKitFox]

Rendezvous between two large ships/stations and small ships works exactly the same.

Practice manual docking with a smaller craft until you are comfortable with it, then go back to your big un's.

If you are unable to guide them with sufficient precision, then the problem is likely with your design, not with your piloting skill. And most certainly not in basic concept. Large vehicles follow the same orbital laws as small ones.

When it comes to the actual *docking*, large vehicles are much more difficult.

Simply put, the docking port requires the same level of accuracy in alignment, and exerts the same level of force, regardless of your ship size. But the ship "fights back" against the docking port's forces more strongly.

Double the mass, and your torque forces on the poor port is about 5 times as much.

It is expected that the actual docking maneuver (as in the last 2 meters) will be harder when using large and/or heavy vehicles.

But approach should be exactly as easy/difficult as with smaller ships.

P.S.

I rather sux at docking, myself.

But with patience, planning and more patience, I have docked the Power Module (835 tons) to the Fuel Bowser(2377 tons) in my mega-space-city.

It only took about 25 tries.

And yes, it was done by hand. Mechjeb, although present, failed miserably.

Edited June 15, 2014 by MarvinKitFox

[Claw]

...

P.S.

I rather sux at docking, myself.

But with patience, planning and more patience, I have docked the Power Module (835 tons) to the Fuel Bowser(2377 tons) in my mega-space-city.

It only took about 25 tries.

And yes, it was done by hand. Mechjeb, although present, failed miserably.

Heh. And I was all proud of myself for assembling a 600ish ton station (1300t wet).

I never have MJ do docking for me, but I did let it try on one of the modules for that job. I too found it did a bit sub-standard. It practically dumped all the mono overboard as it crashed my lab into the power module. Perhpas it's because I don't know how to use MJ to dock.

Personally I find that approaching a little faster works better for me. I find if my orbits are really misaligned and I approach slowly, I end up spending a lot of time reorienting the craft to burn and keep the approach path (prograde) on the target indicator. I keep my speed up around 40-50 m/s at 1km, keep the engines pointed toward the target, and do very light burns to keep the retrograde marker lined up on target. Then there's no need to flip the ship to stop. Just a nice steady but expedient approach.

Once down to 200ish m apart, I make sure the vellocity is down below 2 m/s. Much less than that if the module is bigger and takes time to flip.

Although I should say that I do most large rendezvous without monopro, and pick up docking tugs when I arrive. But then again, I haven't docked an 800t module yet.

[Pecan]

And to think I was sweating today docking a couple of 200-tonners ;-0 I think my computer would melt if I had that sort of mass within render distance. What are the part-counts?

[cantab]

For rendezvous, if you have a low TWR you'll want to enter a phasing orbit that's not too far from your target orbit, so your initial relative velocity at the intercept isn't too fast to stop in time. This may mean waiting more orbits before you get your close encounter.

For docking, you do need to be more precise on your approach with a bigger ship, as the magnetism in the docking ports won't be as able to pull the ships into position. Try and get your big things to handle well, so give them plenty of RCS thrusters and torque, and make sure everything's well-balanced. Imbalanced RCS will make docking a nightmare, as will incomplete RCS (ie not able to thrust in every direction). If you plan on leaving the ship permanently docked during its service life (eg if it's a station module) and you're worried about part count, mount the RCS thrusters on jetissonable blocks.

You may also want a mod to give your more instrumentation. I've used http://forum.kerbalspaceprogram.com/threads/54303-0-23-5-Navball-docking-alignment-indicator-v3 , which is very simple but suffices to ensure your ship's docking port is parallel to the target's. Other more sophisticated docking aids are available.

[FleshJeb]

One basic technique I have't seen mentioned here is to orient your ships north-south. That way, when you're docking/fine-tuning your rendezvous, you're not perturbing your matched orbit as much.

I'm not sure if this is in fact true mathematically, but I saw someone do it on youtube, and it seems easier.

EDIT: Silly me, the BEST part about this method is that the ship orientations don't shift as they orbit around the planet.

Edited June 16, 2014 by FleshJeb

[Claw]

One basic technique I have't seen mentioned here is to orient your ships north-south.

...

EDIT: Silly me, the BEST part about this method is that the ship orientations don't shift as they orbit around the planet.

This is a pretty good technique too, although I haven't used it as much. The orbits and orientations are still moving in the same way, it's just that all that movement is being translated into roll instead of yaw/pitch, which is often easier to deal with. It also depends on where the docking ports are.

[allmhuran]

In order to get the rendezvous part right using large ships, check out the more advanced techniques dicussed in this thread http://forum.kerbalspaceprogram.com/threads/81747-Rendezvous-for-dummies-who-inexplicably-don-t-get-it?p=1189576#post1189576

As you've experienced, the "normal" method people use for rendezvous doesn't work very well when the ship has relatively low thrust and turning speed.

[asheft]

I would recommend this mod http://forum.kerbalspaceprogram.com/threads/43901-0-23-5-Docking-Port-Alignment-Indicator-%28Version-3-1-Updated-05-08-14%29 it adds everything the mod mentioned earlier in the thread does, and then some.

[Pecan]

One basic technique I have't seen mentioned here is to orient your ships north-south.

I've never actually understood that advice since the vehicles aren't rotating at all. Any appearance of rotation is only relative to the horizon, and there's no point in looking at that at all.

I would recommend this mod...

That's Navyfish's docking alignment mod. The navball indicator is based on it so works in exactly the same way. The main difference is whether you want the big window on-screen as well or just the indicator on the navball.

[Claw]

I've never actually understood that advice since the vehicles aren't rotating at all. Any appearance of rotation is only relative to the horizon, and there's no point in looking at that at all.

It's like you said, they appear to rotate in relation to the horizon. If you orient north/south with an equitorial orbit, the station appears to roll instead of pitching/yawing. The assumption here is that most stations are symmetric around the roll axis. So if you approach it from an equitorial orbit, it will always appear as if you are approaching from the side of the station no matter where in the orbit you meet up.

As opposed to if it's oriented east/west, it may "appear" as if you are approaching from the top, or bottom, or one of the sides depending on where in the orbit your ship meets the target station/craft.

This doesn't really solve the "how to dock really big craft" problem though.

[Kasuha]

I've never actually understood that advice since the vehicles aren't rotating at all. Any appearance of rotation is only relative to the horizon, and there's no point in looking at that at all.

They are not rotating but they are getting misaligned over time since they follow each its own orbit. Aligning them along the axis perpendicular to the orbit plane minimizes this effect.

[asheft]

That's Navyfish's docking alignment mod. The navball indicator is based on it so works in exactly the same way. The main difference is whether you want the big window on-screen as well or just the indicator on the navball.

It also adds the markers to show whether you are exactly aligned with the docking port, distance from the docking port, and closure rate down to (if I am interpreting the readout right) one hundredth of a meter per second, all of which the original mod (as far as I can tell) does not have, and all of which, IMO, are very useful when docking.

[technion]

It also adds the markers to show whether you are exactly aligned with the docking port, distance from the docking port, and closure rate down to (if I am interpreting the readout right) one hundredth of a meter per second, all of which the original mod (as far as I can tell) does not have, and all of which, IMO, are very useful when docking.

Once a space station hits a certain size, the built in alignment indicators seem to bug out. It's a documented issue - but while people report it "rarely" occurring, I seem to have to deal with it on nearly everything I built, where you get up close and find pointing directly the pink target marker has you pointing right at an engine or something nowhere near the docking port.

I don't like mods that try to make things easy, but to me, Navyfish is a workaround for a buggy system.

[Oafman]

Go very slowly and use plenty of time warping. This applies to both RV and docking.

I've seen videos where people lean on the gas towards the target, then slam on the brakes when they're really close. MJ does this for RVs, but then MJ is a computer who needs a lower margin for error. Instead of gunning it towards their target they could just edge slowly towards it, time warp, slow time to make a tiny correction (eg just a single tap of RCS), time warp again etc etc. You have much more margin for error doing it this way, and much more opportunity to make corrections. And you'll use less fuel & monoprop

[Red Iron Crown]

I'm a MechJeb addict, but I do almost all of my docking manually. IME, for non-trivial ships MJ seems to use more monopropellant to get docked, I'm not really sure why or how the docking algorithm works and it may have improved. I do use MechJeb to dock when the part count of the two ships makes it a lagfest; it's difficult to do well when there's noticeable time between making your inputs and seeing the results of them.

Mostly, though, I dock manually because I find it to be one of the most satisfying piloting tasks in the game, there are few things quite like that magic moment when the magnets capture and the ships pull together.

[Kasuha]

Once a space station hits a certain size, the built in alignment indicators seem to bug out. It's a documented issue - but while people report it "rarely" occurring, I seem to have to deal with it on nearly everything I built, where you get up close and find pointing directly the pink target marker has you pointing right at an engine or something nowhere near the docking port.

I don't like mods that try to make things easy, but to me, Navyfish is a workaround for a buggy system.

As far as I know that does not come from the station size but from position of the root part relative to the used docking port. On stations with multiple docking ports, the root part is rarely aligned with each docking port it provides. But you can achieve the same effect even on very simple ship.

[Shiv]

Alright I'm still struggling with this. I can get so freaking close (50m going 1 m/s being closest so far) but I might as well be miles away because they just shoot past one another on one plane or another.

This is what I'm currently working with. No matter how much I thrust towards or around that target prograde vector to center my own prograde vector over it, I always end up with entirely too much speed and overshoot it. RCS can't make changes fast enough (due to the size of the ship) to be much use.

This is just leagues harder than the tiny practice ships I used. I think the big fuel cans used to get it up here are part of it but none of the smaller engines will have enough thrust to push it.

[Oafman]

Alright I'm still struggling with this. I can get so freaking close (50m going 1 m/s being closest so far) but I might as well be miles away because they just shoot past one another on one plane or another.

http://imgur.com/ccaI7hp.jpg

This is what I'm currently working with. No matter how much I thrust towards or around that target prograde vector to center my own prograde vector over it, I always end up with entirely too much speed and overshoot it. RCS can't make changes fast enough (due to the size of the ship) to be much use.

This is just leagues harder than the tiny practice ships I used. I think the big fuel cans used to get it up here are part of it but none of the smaller engines will have enough thrust to push it.

Have you been able to get your prograde vector on top of the target vector on your navball? If you can do that at a decent distance (which I accept will not be easy with a craft which is hard to control) then you can just edge in slowly, keeping the prograde vector on top of the target vector.

When the prograde vector starts to move off the target vector, aim to the opposite side of the target vector and accelerate very slowly (maybe just RCS, depends on distance). This will drag your prograde vector back onto the target vector. If you've turned around to slow down, then you need to 'push' your retrograde vector onto that of the target, which means you have to be on the opposite side of the retrograde vector from the target's retrograde vector.

So you 'pull' a prograde vector onto a target, and you 'push' a retrograde vector. I realise I'm not explaining this very clearly. Someone in another thread made a good diagram which explains this, but I cant remember which thread.

And you might already know all this. But the fact that your image makes it look like you're just burning towards the target vector, without considering your actual direction of travel, suggests this might be the problem.

Edited June 16, 2014 by Oafman

[Red Iron Crown]

Add more RCS thrusters to bigger ships, they can be made almost as responsive as smaller ones. I usually put 8 RCS quads on smaller ships, but I might have 24 or more on something more massive.

(This is the docking equivalent to the "Moar Boosters!" advice for making launchers work.)