The next time you see a US rocket launch from Cape Kennedy, think about this. A horse's ass made our solid rocket boosters (SRBs) smaller than we would have liked. The company that manufactured the SRBs had to ship them by rail and they had to pass through a rail tunnel in the Rockies. The designed size of the SRBs was limited by the tunnel size. The tunnel size was based upon the railroad; more specifically the rail gauge. This is the distance between the rails. The gauge in the US is 4' 8.5" just like the English gauge. The English started building the American rail system and used the same gauge as they had in England. The gauge in England was determined by the horse drawn cart. Trains in England were made with the same wheel base as horse drawn carts. All horse drawn carts in England had the same wheel base because most of the country roads had ruts with this same 4' 8.5" gauge. Carts just wouldn't work very well if they didn't have a wheel base to match the ruts in the dirt roads. The ruts in the dirt roads were made by the Roman settlers. The ruts were made by chariots. All chariots had the same wheel base - 4' 8.5". This size was determined by the width of a horse's ass and, thus, so is the size of our Solid Rocket Boosters.