What was the main design parameter for the size of the booster rockets of the space shuttle? If you read the title and came at the grand assumption that it is indeed that, you are right. But NASA could afford a large truck. Right? Yes, again!
Is this a design problem? Indeed. The determining constraint beyond the obvious specification requirements (boost, weight etc.) is related to logistics.
The booster rockets were built in Utah. The only feasible mode of transportation for these rockets were on rail. The cargo had to pass the tunnel cut through the Rocky Mountains. The boosters had to fit within the tunnel and the Tunnel size was determined by the width of the railway tracks (Standard gauge = 4 feet, 8 and a half inches). And the standard gauge was determined by designs of the earliest railroads (designed by the English).
The English used standard tools and jigs for building wagons and all wagons had uniform wheel spacing determined by the design of the wheel ruts in the old European long distance roads, which were built by the Roman Empire to accommodate their chariots which were designed just to be wide enough to accommodate the width of the rear end two war horses side by side.
NASA had a logistics constraint (with deep historical roots) determining the design of the booster rockets of the Space Shuttle….