Docking targetting problem

[THX1138]

I'm trying to dock two vessels. I set the docking port of one vessel to "control from here" and the other vessel as "set as target". I do that for both vessels. I set the SAS to target the target reticule and allow both vessels to equilibrate. I end up with something like this:

but I expect them to be properly aligned. Why won't the ports face each other?

[Beachernaut]

It only shows that you're pointing at the target, not that you're aligned with the port. There is no auto align tool in stock KSP to align your ship with a chosen port. It may take some practice, but it shouldn't be too difficult to align your ship properly when you get close.

However, if you prefer you can use Mechjeb to align or do all of the docking for you.

[THX1138]

They're not pointed at each other though.

[Beachernaut]

Can you post a screen shot?

[Starhawk]

Are you clicking on the docking port of the opposing vessel and setting that as the target?

[Sirrobert]

That should work. I did it all the time with Mechjeb ASS before .90 (which did basicly the same thing as a fully leveled pilot)

[Starwhip]

Yeah, a screen shot would be helpful, but I think I know what you're saying:

If you are pointing at your target, the ship level indicator (the one which shows which orientation your ship is in, looks like --.--) will be aligned with the purple target prograde marker. However, it cannot detect your rotation relative to the port, so even if you are 180 degrees from the front of the port it will say you're dead on target.

[THX1138]

Here's a screenshot. I am setting targets and control-from-here points on both craft and swapping back and forth. I put red and green overlays to emphasise that they are not both looking at each other.

[Sirrobert]

Well clearly the rocket is set correct. It's the fueling station that's wrong.

Here's a general question: Can SAS still rotate the ship if you are controlling a different ship?

So if you jump in the station and make it rotate, will the rocket rotate along with it?

[Sampa]

well, technically, it did line you up with your target, just not properly, you need to back off a bit and fine tune your approach to docking

[Starwhip]

Yep, the problem is as I described above: the "Target Prograde" marker only points to your target "center", and doesn't care about orientation. Now, if you set both to the automatic target hold, and set targets to the opposite docking port, they will attempt to face each other.

[THX1138]

Well clearly the rocket is set correct. It's the fueling station that's wrong.

Here's a general question: Can SAS still rotate the ship if you are controlling a different ship?

So if you jump in the station and make it rotate, will the rocket rotate along with it?

No, when you switch ships, the SAS switches to fixed-point. Hence me switching back and forth between ships to keep them both correct.

- - - Updated - - -

Yep, the problem is as I described above: the "Target Prograde" marker only points to your target "center", and doesn't care about orientation. Now, if you set both to the automatic target hold, and set targets to the opposite docking port, they will attempt to face each other.

That's precisely what I'm doing.

[Starhawk]

If I may suggest, it might be best to treat the fueling station as inert, and simply move your rocket over (using RCS) until it is along the axis line of the fuel station dock. Once that is accomplished and all relative velocity killed, it should be a fairly simple matter to rotate the rocket into alignment and then slowly move it along the axis of the target docking port. That assumes that the fuel station is not spinning, of course, but it should not be if it has SAS set.

[Beachernaut]

Hmmm... So apparently there were some features on .90 that I have not yet used.

[Starhawk]

My guess is that the vessel you switch out of doesn't actually hold to target, and as you rotate the vessel which has the focus so that it points to the target, the other docking port is no longer aligned as a result. That's why I suggest you just focus on the rocket and shepherd it around using RCS.

- - - Updated - - -

In more detail... These long craft have docking ports far from the centre of mass. When you rotate these vessels in order to change their orientation, you are rotating around the centre of mass. Since the docking ports are far out, they move a signifcant distance as you rotate the vessel, and this moves them out of the axis of opposing docking port. Switching back and forth is just a chicken and egg game which will go on forever until one or the other actually moves over by the correct amount to place it's centre of mass on the axis line of the target docking port, and then rotates it's own docking port into alignment on that same axis.

I hope this makes sense. And helps, of course.

Good luck!