(UTC, and also United Technologies Corp.) under a NASA contract, developed the rocket engine in the photograph with an ablative combustion chamber cooling system.

-The ablative cooling system comprises a double wall with a product or material that melts and vaporizes, making it an easy conductor of heat to the outside.

-A typical precedent could be the cooling system of certain piston engine valves with sodium inside.

"Test of the aforementioned rocket engine"

-Tests commissioned by NASA on hybrid propellant rocket engines were also conducted. The fuel was solid and the oxidizer was liquid.

"Test of a UTC Hybrid Engine"

-They required pyrotechnic, electric, or hypergolic ignition only for starting.