What could allow a spacefaring civilization to actively construct and maintain ships, stations and weapons, but stop them from actually manufacturing the individual components?
First, let me try to define "components": I mostly mean more complex devices, like energy sources, advanced computers, space weapons, drives, artificial gravity, etc. They know how these things behave, but they can't replicate them. They are not incapable of building their own basic components, but they are highly inadequate (perhaps on the level we have today).
Perhaps, to make a few more clear example: they could know how to build a normal computer, but quantum computers can only be salvaged. They could build rocket-propelled ships, but can't build those fancy sub-light or even FTL drives. They can build a basic slug-thrower or rocket launcher as a weapon, but those don't even come close to the advanced weapons they find in wrecks. Essentially, they have lego bricks; they can stick them together in many creative ways, but can't make their own.
Going with the "lost knowledge" approach (like after an apocalypse), that wouldn't stop that civilization from quickly reverse-engineer those components and eventually manufacture their own; especially since they already know how to repair and maintain them on a superficial level.
All their components come from scavenging, from old shipwrecks and ruins (from some prior galactic civilization). Existing ships and structures are recycled. Scarcity isn't a bit issue either - there are plenty of these components lying around, like sand on a beach, to the point where they are considered completely expendable. At least for as long as they keep finding new ship graveyards.
I was thinking of a few approaches that might achieve this:
- All these parts come with some sort of advanced DRM that can't be cracked (yet) and perhaps even damages the part if attempted.
- Since a lot of this is military hardware, perhaps they are designed in a way that makes reverse-engineering almost impossible (but would that ever be possible to do?)
- Perhaps this DRM doesn't come as part of the component, but instead, as some external force ("call home" feature). Trying to duplicate or modify it results in some AI/drone incursion - that old civilization is gone, but their mechanical servants are still around and watching.
- The availability of these components makes manufacturing them pointless, and eventually over generations it just becomes normality. This could work on the surface, but I doubt that will stop anyone from trying to learn more.