 For the perhaps simpler fission pulse units to be used by one Orion design, a 1964 source estimated a cost of $40000 or less each in mass production, which would be up to approximately $0.3 million each in modern-day dollars adjusted for inflation.Project Daedalus later proposed fusion explosives (deuterium or tritium pellets) detonated by electron beam inertial confinement.This is the same principle behind inertial confinement fusion.