 The expense of the fissionable materials required was thought to be high, until the physicist Ted Taylor showed that with the right designs for explosives, the amount of fissionables used on launch was close to constant for every size of Orion from 2,000 tons to 8,000,000 tons.The larger bombs used more explosives to super-compress the fissionables, increasing efficiency.The extra debris from the explosives also serves as additional propulsion mass.