Some thoughts about structural rigidity (like autostruts - but in smart and realistic way)

[Alchemist]

Yeah, we all can agree that autostruts going across half the vessel aren't always realistic and might be not the greatest option to counter wobbly rockets. But there are certain scenarios when in real-life assembly there would be extra structural integrity added between parts even without attaching external structural beams or notable extra mass.

 

Reasonable limitations to effect:

1. Same rigid element - no auto-connections going across decouplers or docking ports or (as future possibility) movable hinges - anything supposed to come apart at some point would still require specially placed struts if more rigidity is needed before that.
2. Direct proximity - the maximum distance (as placed in the VAB) between collider surfaces should be no more than a certain value (maybe certain percentage of the larger part's size). This will only ever need to be evaluated in VAB, no crazy in-flight collider calculations needed.
3. Contact length matters - side-by-side across full length should be stronger than barely touching near the ends. This, actually, should apply to directly surface-attaching parts as well (could be as extra connections along the contact line).

 

Some options when it could come into play:

1. Parallel stacks (with no decoupler in-between). For example, some tanks surface-attached to center stack and then longer tank stacks built off them. Or 1 to multiple stacks splitters/adapters. These stacks, running within touching distance of each other are 100% logical to be welded together without need for additional struts.
2. Stack-attaching through several thin parts. The most common scenario is when under the decoupler (or a docking port) there are several parts like probe core, reaction wheel, battery - and only then go the fuel tanks. The decoupler should have some connection directly to the tanks through the thin parts. And, while auto-strutting shouldn't go across the decoupler, the decoupler placed below a shrouded engine should transfer most force not to the engine but to the part above it.
3. Landing gear, legs, wheels. Should auto-connect to any parts within a certain range (could be larger range than in other cases) of the attachment point. Like landing gear right next to where a wing is attached to the fuselage should transfer the force to both the wing and the fuselage, no matter which of them it's placed on.