Docking Difficulties

[Rithaniel]

Hi, I'm having a bit of difficulty docking two objects in orbit. I'm unable to upload screenshots, so I'll do my best to explain the situation in detail. The two vessels are pretty much exactly the same, with a lab above a fuel tank of the same size as the lab, and a poodle engine below that. Each one also has three docking ports put up with symmetry around the mid-point of the lab with one of these three docking ports occupied by a Mk1 lander can that was originally positioned on top of the vessel, before being decoupled and shifted to the side.

Now, here's where I believe I began screwing up: On one, I placed the RCS jets only around the lander can. On the other, I placed them around the lander can, and the lab, but not the fuel tank. So neither one has perfect translation. On top of this, when I shifted the lander can from the top to the side on the first ship (the one with jets only around the can) I also chose to "control from here" on a docking port, so now the navball is all insane, and, without a docking port on top of the ship, I can't reorient it correctly.

These two are going to be the base for a huge ship, so I really need them to be docked with their engines pointed the correct way, and I've managed to get them in just about perfectly synchronized orbits within 10m of each other, but I can't get them in parallel orientations, and, even if I'm close, when I try to translate, they rotate. What can I do?

Also, in case it's useful, this is a career mode game, I'm about halfway up the tech tree, and I have the following mods: KAS, KIS, KW Rocketry, Ferram, Infernal Robotics, Chatterer, MechJeb (There is a MechJeb module on each ship).

Edited June 16, 2015 by Rithaniel
A solution was found.

[Signo]

Easiest solution would be to ask MJ to do the job for you this time and then go back to the VAB to design a new project incorporating what you learnt.

To overcome the navball frenzy add a "friendly" pod in a reachable place to set it as the control part whenever needed.

[Rithaniel]

I plan to have future additions to this ship to include forward-facing docking ports to fix the navball issue, so that's not a long-term issue. As to getting MJ to get it to do the work for me, I've been fooling around with it for a while to just get the ships aligned, and I'm not sure how to utilize it to autodock.

[FlipNascar]

This won't help you with the current situation, but for the future... Seeing as you're already okay with mods, and from the description it seems to be thruster imbalance mucking you up in the design, may I deign to suggest you look at RCS Build Aid?

If your MJ module can't do Docking, then I suggest you make small inputs with the RCS and then correct the rotation using your reaction wheels - or leave SAS on and watch all your monoprop disappear...

Edit:

To get MJ's autodock find Docking Autopilot in the command menu and just hit the buttons - if you can't see if, probably not unlocked.

[kurja]

A solution to your problem with rotation: align the docking port on the larger craft (or whichever for any reason is less maneuverable) along the normal vector (north/south if you're on an equatorial orbit). Now the port will remain pointing in one direction. Then just approach as usual for docking, I do this pretty much every time I dock, it just makes things a lot easier without the unwanted rotation.

If your navball is 'misoriented' you can ofc click any docking port or command pod or core and just choose 'control form here'.

[Rithaniel]

This won't help you with the current situation, but for the future... Seeing as you're already okay with mods, and from the description it seems to be thruster imbalance mucking you up in the design, may I deign to suggest you look at RCS Build Aid?

If your MJ module can't do Docking, then I suggest you make small inputs with the RCS and then correct the rotation using your reaction wheels - or leave SAS on and watch all your monoprop disappear...

Edit:

To get MJ's autodock find Docking Autopilot in the command menu and just hit the buttons - if you can't see if, probably not unlocked.

I need to download that immediately.

Also, I just looked it up, and Docking Autopilot is unlocked at the 550 science floor, and I'm only about halfway through the 160 science floor, so MJ won't be there anytime soon.

A solution to your problem with rotation: align the docking port on the larger craft (or whichever for any reason is less maneuverable) along the normal vector (north/south if you're on an equatorial orbit). Now the port will remain pointing in one direction. Then just approach as usual for docking, I do this pretty much every time I dock, it just makes things a lot easier without the unwanted rotation.

If your navball is 'misoriented' you can ofc click any docking port or command pod or core and just choose 'control form here'.

Yeah, I've been trying to get the problematic ship aligned first, but using MJ puts it crooked every time, and, even if I manage to wrestle it into appropriate alignment manually, it just wanders out of that alignment of it's own accord as soon as I switch to the other ship.

Also, all docking ports are radially attached, so each one results in a misaligned navball.

[DancesWithSquirrels]

Ouch - that means your local vertical is from docked lander cans or one of the docking ports, with somewhat arbitrary orientations for the lander cans. Don't dock relative to the lander cans!

First, put the module with fewer RCS units as the fixed (not moving) module, and get the inclination of the orbit to 0.0 or as close as you can. If you don't have Kerbal Engineer or the like, set the Mun as the target and adjust your inclination to be identical as a reference (your ascending/descending nodes should start to swap). We'll call this Module A.

Set the orientation of your Module A docking port so that it points directly at one of the primary directions (prograde or retrograde for these directions, although radial/antiradial work too - just not the normal/antinormal purple triangles), and rotate around that orientation(Q/E) until your marker in the nav ball is perpendicular to the horizon line. You're now oriented with your lab either N or S. The 90-270 line is your reference - stay on and parallel to it, and you're pointing N/S.

Leave that one alone, rendezvous with Module B, orient until you're pointing roughly the same way, then maintain alignment by keeping the marker in the nav ball directly on and parallel to the 90-270 line. Dock as desired, and you should be good, with both engines pointing parallel.

Edit: If your docking port is rotated 90 degrees, somehow, and the alignment above doesn't get your module/engine pointing N/S, use the 0-180 line as a reference instead.

---

For your next module, add a docking port or pod on the end where your lander pod is/was, and control from there!

[Jason Patterson]

It's not what you want to hear, but two new launches with redesigned vessels will solve the problem fairly quickly. It only takes 10-15 minutes to get them into orbit and docked.

I'm not sure if this would be helpful or not, based on your description, but you really only need one vessel that moves correctly to fix your situation. Could you undock the lander can and get something maneuverable out of the parts that are left over?

[kurja]

Yeah, I've been trying to get the problematic ship aligned first, but using MJ puts it crooked every time, and, even if I manage to wrestle it into appropriate alignment manually, it just wanders out of that alignment of it's own accord as soon as I switch to the other ship.

Also, all docking ports are radially attached, so each one results in a misaligned navball.

Well don't use MJ if it doesn't work, just rotate your craft and align the port on the normal vector. It's not going to rotate out of that alignment on it's own, either turn on sas or kill rotation with time warp and it stays where you left it. Normal/Antinormal vector works like that, it doesn't change over time like radial and pro/retrograde do unless you use engines to change the orbit.

Okay all ports are radial, but is there no crew capsule or probe core that you could control from for correct alignment?

[Rithaniel]

Ouch - that means your local vertical is from docked lander cans or one of the docking ports, with somewhat arbitrary orientations for the lander cans. Don't dock relative to the lander cans!

First, put the module with fewer RCS units as the fixed (not moving) module, and get the inclination of the orbit to 0.0 or as close as you can. If you don't have Kerbal Engineer or the like, set the Mun as the target and adjust your inclination to be identical as a reference (your ascending/descending nodes should start to swap). We'll call this Module A.

Set the orientation of your Module A docking port so that it points directly at one of the primary directions (prograde or retrograde for these directions, although radial/antiradial work too - just not the normal/antinormal purple triangles), and rotate around that orientation(Q/E) until your marker in the nav ball is perpendicular to the horizon line. You're now oriented with your lab either N or S. The 90-270 line is your reference - stay on and parallel to it, and you're pointing N/S.

Leave that one alone, rendezvous with Module B, orient until you're pointing roughly the same way, then maintain alignment by keeping the marker in the nav ball directly on and parallel to the 90-270 line. Dock as desired, and you should be good, with both engines pointing parallel.

Edit: If your docking port is rotated 90 degrees, somehow, and the alignment above doesn't get your module/engine pointing N/S, use the 0-180 line as a reference instead.

---

For your next module, add a docking port or pod on the end where your lander pod is/was, and control from there!

Thank you very much for the exact instructions. They were a huge help, and now Primary 1 is beginning to take shape.

It's not what you want to hear, but two new launches with redesigned vessels will solve the problem fairly quickly. It only takes 10-15 minutes to get them into orbit and docked.

I'm not sure if this would be helpful or not, based on your description, but you really only need one vessel that moves correctly to fix your situation. Could you undock the lander can and get something maneuverable out of the parts that are left over?

Unfortunately, no, as I placed the vast majority of jets directly on the lander can, so it would wind up being the part with maneuverability. Also, I had considered launching new and larger parts to see about getting the docking to work through them, but that seemed like way too complex of an effort, if docking was still possible in the meantime.

Well don't use MJ if it doesn't work, just rotate your craft and align the port on the normal vector. It's not going to rotate out of that alignment on it's own, either turn on sas or kill rotation with time warp and it stays where you left it. Normal/Antinormal vector works like that, it doesn't change over time like radial and pro/retrograde do unless you use engines to change the orbit.

Okay all ports are radial, but is there no crew capsule or probe core that you could control from for correct alignment?

Yeah, there was the lander can, which was originally placed on top, with a port on top of it, but, for aesthetic reasons, it was decoupled, rotated, and attached to one of the radial ports, making it a radial can.

That all being said, docking has been achieved. Thank you all for the help.

[DancesWithSquirrels]

You could add some additional (small) modules - pilothouses!

Send up a couple of lander cans with RCS and a docking ports on the side, not the top/bottom. Dock with one of your module ports using the instructions I gave above (maneuver relative to the side docking port of the lander can), and once you're linked up you can control from the lander can itself, at the correct orientation to the engines.

Personally I find it almost impossible to run a main engine with a misaligned control location...

---

For your RCS woes; a module with, say, an OCTO, batteries, FL-R25 RCS tank, a LF-T800 (for length), a docking port on both sides near the top (so it can act as a pass-through), and clusters of 4 RCS thrusters at both the top and bottom. Dock it to one of your module side ports (reference from a docking port) with the long end towards the engines (the end without RCS thrusters), and you should now have more balanced control. And the probe core can be your new pilothouse!

Edited June 16, 2015 by DancesWithSquirrels
Added ideas

[ExaltedDuck]

One thing that can help immensely (and I didn't see this tip quickly skimming through the thread. If it has been mentioned, apologies for the redundancy) is the fact that obital time acceleration changes how physics are applied. Most notably, it makes each ship a stable and solid body. Any bending, spinning, rotation, vibration, porpoising, etc. will be killed off if time acceleration is applied even for the briefest instant. Some might consider exploiting this aspect as cheesing. But it might help you manage alignment by stoppung unwanted rotation. Otherwise, all I can suggest is trying to manage all 6 degrees of freedom with hands on wasdqe and ijklhn. It's difficult but as long the undesired rotation isn't too severe, you should be able to counter rotate against (wasd) it as it is induced by your translational control (ijkl) input.

Edited June 16, 2015 by ExaltedDuck
Typos for days