Theoretical engineering OFLAMERON - An interesting area of development could be increasing the energy capabilities of solid-propellant rockets. A variant of the combined propulsion system could be investigated. Use a solid fuel with a large combustion area and a liquid oxidizer, which is injected into the combustion area by a special system. You can get the ability to control the thrust of the engine as in liquid propellant rockets, a more compact fuel unit, and you can use more energy efficient fuels. For example, metal compositions.