Garrett (HRE) (ARJ-1) Hypersonic Scramjet Research Engine

Type: Scramjet

Performance: 4,000 to 2,000 sec internal specific impulse (min.); 3,200 to 8,640 km/hr (2,000 to 5,400 mph)

Computerized analysis of supersonic combustion phenomena and ramjet cooling led to Garrett being awarded a 1965 contract by NASA for preliminary design of a Mach 3 to 8 research ramjet for flight-testing on the North American X-15. In that same year, a full-scale hydrogen fueled boiler-plate engine successfully demonstrated both subsonic and supersonic combustion.

In 1967, Garrett was awarded a follow-on contract to manufacture flightweight hypersonic research engines (HRE). This supersonic combustion ramjet (scramjet) was constructed during that program as a Mach 3 to 8 demonstrator. Utilizing hydrogen as both a fuel and a coolant was required because inlet temperatures exceeded 2,316 C (4,200 F) and exhaust temperatures exceeded 2,927 C (5,300 F).

After the 1968 retirement of the X-15 aircraft, the program was reoriented toward ground tests. Delivered in 1970, the engine ran in NASA Langley's Scramjet Test Facility at speeds up to Mach 7, 7,560 km/hr (4,725 mph), completing a major step toward hydrogen-fuel hypersonic propulsion systems.