This is an example of what's known as a Rocket Based Combined Cycle engine (RBCC), sometimes also referred to as Ducted Rockets or Air Augmented Rockets or Ejec

This is an example of what's known as a Rocket Based Combined Cycle engine (RBCC), sometimes also referred to as Ducted Rockets or Air Augmented Rockets or Ejector Ramjets. It's essentially the chemical analogue of a jet engine, using the thrust of a small rocket for compression instead of fan blades. While like a ramjet it doesn't have any moving parts in the airflow, the rocket engine lets it produce static thrust, so it can potentially take off from the ground. The pressure rise from the rocket exhaust can be much higher than what a mechanical system of the same weight could produce. The exhaust of the fuel rich rocket engine can be combusted further downstream with the entrained air, acting like an afterburner. The hot exhaust mixes with and heats the incoming air very quickly which is important at high speeds where the air has a short residency time in the engine. At higher altitudes where there isn't enough air to support combustion, the duct acts as a large and thus high-efficiency nozzle for the rocket engine. While not necessarily the best propulsion method at any one stage of the flight, RBCCs are unique in that they beat rocket performance at every point from ground to orbit. That all being said, RBCCs have some limitations. The ducts add significant weight and make the rocket more aerodynamically complex. For single stage to orbit orbit, most trajectories spend little time in the range where RBCCs provide their greatest advantage. For two stage to orbit, a Turbine Based Combined Cycle (TBCC) engine outperforms the RBCC for the first stage and the weight can't be justified over that of a pure rocket for the second stage. Finally with the advent of propulsive landing, the value of an airplane-like shuttle with a heavy structure has been called into question. While interesting and promising, it's hardly a new technology, it's been in development for decades. The Soviets were likely the first to seriously explore the concept in the form of their GNOM ICBM which reduced the size sufficiently for the ICBM to be transported easily on land[0], using Nasa explored an RBCC powered SSTO shuttle in the early 90s known as GTX[1]. Solid Propellant RBCCs have seen wide use in recent years for the latest generation of air-to-air missiles from several countries. [0] http://www.astronautix.com/g/gnom.html http://www.astronautix.com/g/gnom.html [1] https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990062726.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/199900...