I don't mean to interrupt you guys' interesting discussion on algorithms, but I think an equally important discussion to have isn't can we build on moving ships, but should we be able to build on moving ships?
Just off the top of my head I can think of several balance issues with this, specifically when it comes to combat. What's to stop people from running around on extra-large ships and replacing/adding weapons mid fight? Or adding armor, shields, thrusters, etc? Even if you disable building while engaged in combat, there's the ability to quickly re-design your ship as soon as you anticipate a fight, which I suppose would depend on the range you can see people, but still. Then you have to worry about transport ships re-tooling for combat right before the pirates show up and start killing them. On the one hand, that could be very interesting gameplay... but how on earth do you manage to balance something like that?
Additionally, imagine the economic impact of being able to edit fully functional ships. Why would you ever buy more than 1 ship (or why would there be more than one type of ship on the market) if you can just re-tool them to your specific situation? Without knowing any of the specifics on how ships will work exactly, if you could edit ships at any time, why not just carry around a ton of parts and replace them when you need them? I'd just fly around in my combat ship until I found some nice resources worth mining, and then I'd replace the guns with mining equipment or whatever. Same goes for any specialized ship equipment. If people can do such things, then there stops being a need for ship types that have specific capabilities. Everyone would just buy the most efficiently customizable ship possible and swap things around as needed.
Needless to say, I don't like the idea of being able to do this, as it sacrifices a lot in terms of game depth.