The device comprises a primary heater (58) suitable for heating the propellant coming from the tank (16) prior to it being reintroduced into its tank. The primary heater uses the heat of combustion from the engine (10) and the device further comprises a secondary heater (66) having its source of heat independent from the operation of the engine, the secondary heater being arranged downstream from the primary heater (58) in order to heat the propellant between its outlet from the primary heater and being reintroduced into the tank. The device also has means (62) between the feed to the primary heater (58) and the return of the propellant to the tank for putting the propellant under pressure.