>> I'd love to know exactly what legacy of the olden days makes 12ft the right diameter<<
Transport of stages, I think. Some will claim this is all due to pork-barrel politics and creation of jobs in various parts of the country; e.g. if you want congresscritter Smith to vote to allocate 'n' billion $ to NASA this vote will cost having facility 'x' in his/her district source the making of [insert subassembly.] On the other hand if a manufacturer already has expertise in [insert subassembly technology] and has a trained workforce already in place in say Utah then this is where the [subassembly] will need to be made unless you're willing to guarantee very very long term contracts. i.e. expedience, not necessarily pork barrels.
Biting the hand that feeds IT
