Though it may always have some role, particularly in surface transport applications, the days of the chemical rocket as a primary means of propulsion in space are numbered. By the time of Asgard a variety of alternative propulsion technologies may likely be in use, based primarily on a quest to increase ISP or ‘specific impulse’ while simplifying the handling and management of propellants. Today, the most likely of general purpose alternative rocket propulsion technologies is plasma propulsion, which evolved from the ion propulsion used for satellite attitude control and which will set down a path of evolution ultimately culminating in the anti-matter propulsion envisioned by Marshal Savage.