Docking ports ?

[1800mage]

I am trying to complete my first mun mission , and in my transfer burn my lander module swings around in it's docking port wildly, disrupting the burn. The two modules are not docked on launch, so struts will not work. Is there any way to fix this?

[Scotius]

A screenshot of your rocket would be useful. Anyway, try to place a separator between two ports - and then strut everything together.

[Plusck]

The junior docking port is pretty weak, so you have to be careful.

First things to do (without somewhat artificially reinforcing the joint):

- toggle off gimbal on your engine,
- toggle off the big reaction wheel - it's really excessively overpowered for a ship that size
- toggle off the reaction wheels in the lander.

That leaves you with the Mk1-2 pod's reaction wheels for control, which should be absolutely fine as long as the lander is balanced. If the lander isn't balanced, there's not much you can do other than throttle down (not good for the transfer burn) since the docking port is so weak.

You could also transfer the fuel out of the lander until you get into low Munar orbit., that would also help.
 

[bewing]

If you turn on Advanced Tweakables, you can still autostrut your craft together after you do the docking.

[magnemoe]

You might also turn on autostrut from the MK3 command pod and the service bay fuel tank, set to heaviest part, that would be the transfer stage fuel tank. 

[Superfluous J]

3 hours ago, Plusck said:

So for your case, you could autostrut the docking ports and it would be much stronger.

I personally like to - in the VAB (though you can in flight too if you forget - right click every docking port and set Autostrut to "Grandparent." Whenever you dock, one of the ports will be on the far side of the root part, so if they're all set to "Grandparent" then you're guaranteed to always get an autostrut connection between docking ports.

[Vanamonde]

This question about how to play the game has been moved to Gameplay Questions. 

[1800mage]

Here is the craft:

Do you mean to put a separator and then struts to keep it in place? Wouldn't it not be able to move forward to the opposite port?

Edited October 17, 2016 by 1800mage

[1800mage]

14 minutes ago, Vanamonde said:

This question about how to play the game has been moved to Gameplay Questions. 

Apologies, I did not know it existed

[1800mage]

thank you!

[1800mage]

What exactly is autostrut?

[Plusck]

1 hour ago, 1800mage said:

What exactly is autostrut?

New thing in 1.2. Optional.

It started with landing wheels - to get them to hold together they created an magic invisible strut that connects them to the body of the aircraft. Then it kinda morphed into an "advanced tweakable" so now you can autostrut anything together.

So for your case, you could autostrut the docking ports and it would be much stronger.

The problem is that it is kinda cheaty. Understandable for wings and landing gear, but less if you use it to make tiny parts support enormous amounts of torque.

[1800mage]

2 hours ago, Plusck said:

New thing in 1.2. Optional.

It started with landing wheels - to get them to hold together they created an magic invisible strut that connects them to the body of the aircraft. Then it kinda morphed into an "advanced tweakable" so now you can autostrut anything together.

So for your case, you could autostrut the docking ports and it would be much stronger.

The problem is that it is kinda cheaty. Understandable for wings and landing gear, but less if you use it to make tiny parts support enormous amounts of torque.

Thanks! quite new to ksp 

 

[radonek]

Autostrutting in midflight is a bug and will be probably removed with next update. Jr. port is meant for small probes and such, if you really want to use it, you will just have to live with it. I'd guess that one solution would be to pack lot of torque in transfer stage and just let it swing. Less thrust will also help. But I'd venture to say it is not a good idea to perform your first mun mission with such a overengineered and needlessly challenging vehicle.
 

[Snark]

On 10/16/2016 at 8:52 PM, 1800mage said:

Here is the craft:

Yah, the "junior" docking port is super weak and bendy-- you should use that only for tiny ships.  Using it to connect two massive ships like yours is just about guaranteed to have problems.

Ways to mitigate the problem:

• Use a bigger docking port!  The bigger the port, the stiffer the connection.
• You can use autostruts, as other folks have suggested.
• The worst-case scenario for getting stuff bending at a joint is when there's approximately equal moment of inertia (e.g. mass) on both sides of the joint.  You get less bending if it's as lopsided as possible (e.g. a lightweight thing connected to a heavy thing).  So, for example, while they're docked, transfer as much fuel as possible out of your lander and into the big tug.  Ideally you'd want your lander to be empty of fuel, so it's as lightweight as possible.  (You can transfer the fuel back again after you arrive and you're ready to undock.)
• Don't thrust at full power.  The more gently you thrust, the less problem you'll have with bending.
• As folks have suggested, turn off the gimbal on your engine and dial down the power of your reaction wheels.

[1800mage]

The craft does not swing around with the regular docking port.  Will have to remember not to use the junior version in future.

[Blaarkies]

12 hours ago, 1800mage said:

The craft does not swing around with the regular docking port.  Will have to remember not to use the junior version in future.

But still remember to put an extra Junior on space stations and the like...for those unforseen upgrades, like adding a newer stronger comm dish

[genericeventhandler]

Have you tried doing the burn from the lander, instead of the transfer craft ? I might be more stable that way around.

[1800mage]

1 hour ago, genericeventhandler said:

Have you tried doing the burn from the lander, instead of the transfer craft ? I might be more stable that way around.

I did try with the junior docking port, but the command module started swinging around again. The regular docking port works fine though.