The European Space Agency commissioned a study on European nuclear thermal propulsion that would allow for faster missions to the Moon and Mars than currently possible. The Alumni study was carried out by the French Atomic Energy and Alternative Energies Agency (CEA), ArianeGroup, and Framatome Space, together with ESA. The Alumni study concluded on the merits of nuclear propulsion in space and proposed a new nuclear thermal propulsion design and a development roadmap.[...]Even though nuclear propulsion holds great promise, the study looked at many scenarios and concluded that it is ideal for heavy spacecraft that need massive acceleration and braking, with changes in velocity of a minimum of 25 000 km/h – values typically needed for missions to the Moon or Mars.Hydrogen was pinpointed as the ideal propellant to be used in nuclear thermal engines as it offers maximum efficiency, but the Alumni study noted that other propellants such as ammonia are possible, which can offer advantages in some mission scenarios as it is easier to store, and decreases the dry mass of the engine and the propellant tank.
