Propulsion from combustion of solid propellant pellet-projectiles for providing a useful propulsion that has the advantages of both solid and liquid propulsion engines, and also can make use of either solid chemical propellants or fissionable nuclear material as the fuel. Preferred methods and systems can include a storage chamber for storing solid propellant pellets, a feeding system having a pellet feeding channel and a pellet feeding mechanism connected to the storage chamber and to a gun assembly, which is positioned along a longitudinal axis to eject the pellets at a certain velocity. A triggering system positioned between gun assembly and thrust chamber can initiate the propellant pellet-projectile, and a thrust chamber having a combustion chamber for combustion of propellant pellet-projectile with an exhaust nozzle. Additionally, an auxiliary power system can be used to power the components and various electrical and electronic systems that may be present in the invention for controlling the engine components. The gun assembly may include an ejector mechanism for ejecting the propellant pellets through at least one barrel. The triggering system can produce a medium creating an ambience for the initiation of propellant pellet-projectiles. Methods and systems can be used for space and rocket crafts, turbojets and ramjets.