Rocket Decouples Shortly After Launch

[FusionNexus]

Heyo again! another question pretty soon after my spaceplane one, this one regarding decoupling issues. I use mechjeb fairly heavily, as my personal skills suck (slowly learning however, I've performed a couple launches and maneuvers manually)

I built a Payload rocket for the use of delivering space station parts into relatively low orbit (200km), and have built 2 segments of my space station. But I've noticed that when launching the power module and science module (power is connected, science one annoyed me), it had a tendency to instantly decouple the module part right after launching, I generally use mechjeb for these, and before this has never really been a problem. I'm wondering if it has to due with multiple command modules existing on the rocket (I have a guidance computer for my payload rocket, and the science module specifically has a manned command module (exists purely for the science experiment tied to it, plus lets me bring a ton of kerbals to the station in one shot, as I can carry up to 7 total with it and the science lab on board), and technically a guidance computer in the form of KSPIE's orbital assembly docking port, the ports I'm using to create the space station with).

the main control module is the payload rockets guidance computer. Could someone explain this to me why it possibly happens? I did notice that re-rooting the entire assembly to the manned control pod, then switching control to the guidance computer at the launch pad, stopped it from happening and it launched like normal, but I'm very confused. Is it a mechjeb issue? related to the command pods? root part? I have no idea what's causing it.

On a side note, what's the maximum distance for docking procedures? how close do I have to be to the craft to dock, its somewhat annoyed me at times that I cant set docking ports as targets, I read that the maximum distance is 200m?

[king of nowhere]

33 minutes ago, FusionNexus said:

Heyo again! another question pretty soon after my spaceplane one, this one regarding decoupling issues. I use mechjeb fairly heavily, as my personal skills suck (slowly learning however, I've performed a couple launches and maneuvers manually)

I built a Payload rocket for the use of delivering space station parts into relatively low orbit (200km), and have built 2 segments of my space station. But I've noticed that when launching the power module and science module (power is connected, science one annoyed me), it had a tendency to instantly decouple the module part right after launching,

 

the most likely option is staging. check if your staging sequence is such that it decouples the payload on launch.

alternatively, it may have a weak connection that breaks easily. in this case, autostruts may help

[FusionNexus]

25 minutes ago, king of nowhere said:

the most likely option is staging. check if your staging sequence is such that it decouples the payload on launch.

alternatively, it may have a weak connection that breaks easily. in this case, autostruts may help

both were solved pretty quickly after the first failure, my staging is pretty much set up so that every stage is 1 thing (this is a rocket that doesnt need multiple parts per stage, so the launch rockets thruster is the only thing in the first stage). the second part I did autostrut everything, i even added some actual struts to the rocket, the issue im honestly assuming is related to mechjeb in some way, as it happens upon launching after activating the ascent guidance autopilot. but the weird thing is that it kinda fixed itself by choosing a different root part, this issue strangely only happens if i have a manned module with kerbals inside, that arent the root controlling part.