The turbojet, turboramjet, and turborocket are air-breathing engines. The minimum mass (for 1-ton cargo) is about 10 tons.
M. Minoda, K. Sakata, T. Tamaki, T. Saitoh, and A. Yasuda, "Feasibility Study of Air-Breathing Turboengines for Horizontal Takeoff and Landing Space Planes," Journal of Propulsion and Power, Vol. 7, No. 5, September-October 1991, pp. 821-827.
Giuseppe Bussi, Guido Colasurdo, and Dario Pastrone, "Analysis of Air-Turborocket Performance," Journal of Propulsion and Power, Vol. 11, No. 5, September-October 1995, pp. 950-954.
A continuous stream of air is compressed by a turbocompressor, mixed with fuel, ignited, and expanded through a turbine. The turbocompressor and the turbine are on the same shaft. Thrust-to-weight ratio is less than about 10. Their maximum speed is limited by maximum temperature the engine can withstand. The fastest turbojet plane, SR-71 (also known as Blackbird) flew at 1.1 km/s. Turbojet was invented by Frank Whittle of Great Britain in 1928.
The steamjet engine is described in U.S. patent 6,202,404. Its most practicable implementation, called mass injection precompressor cooling (MIPCC) is a turbojet cooled with copious amounts of water and liquid oxygen. The cooling enables the turbojet to generate thrust up to the altitude of about 30 km, and reach the maximum altitude of about 60 km.
The ramjet is one of the best air-breathing engines, but it cannot generate thrust at takeoff. A turbojet is placed inside the ramjet to accelerate the ramjet to operating speed (about 1 km/s). The contraption is called turboramjet.
The turborocket is heavier than the turbojet but performs better at high velocity. The turborocket turbine is powered by a gas generator exhaust. A heat exchanger in the combustion chamber heats up hydrogen fuel before it reaches the gas generator. The turborocket is sometimes called "air-turborocket" or "gas generator cycle air-turboramjet."
