|Country of origin||France|
|Designer||Société d'Etudes pour la Propulsion par Réaction|
|Application||Cryogenic Engine Testbed|
|Propellant||Liquid oxygen / Liquid hydrogen|
|Thrust||40 kN (8,992 lbf)|
|Isp (vac.)||412 s (4.04 km/s)|
|Dry weight||198 kg|
|Notes||Testbed engine, never flew|
The HM4 was a first non-American cryogenic rocket engine.[verification needed] Developed in France between 1967 and 1969 it never flew into space, was used purely as a testbed for new technologies. Technologies developed in HM4 become a base for HM7 engine used in Ariane.
HM4 evolved from a liquid fuel combustion chamber development projects H2 and H3 led by Société d'Etudes pour la Propulsion par Réaction (SERP) tested between 1961 and 1963 with an intention of using H2 as an upper stage to proposed Diamant Hydrogen variant with a turbopomp derived from Mirage IIIC. However, both projects were abandoned in 1964 and replaced by HM4 engine in 4-chamber configuration producing 40 kN (8,992 lbf) each for a total of 160 kN (35,970 lbf). First test of a new engine concluded in March 1967. In total 85 trials of HM4 took place with a combined burn time of 2300 seconds, including the longest tested burn time of 350 seconds. Engine was proposed by SERP to be used in ELDO-B project, an evolution of Europa rocket, in a single-chamber configuration to be developed by Rolls-Royce, however project was canceled in 1969 and instead development focused on HM7 which was later used in Ariane 1 upper stage.
- SnecMag (8 August 2012). "Snecma rocket engines and Ariane launchers: a powerful, winning combination". Archived from the original on 2014-08-12. Retrieved 16 December 2015.
At the same time, we had developed the HM7 engine, a descendent of the first non-American cryogenic engine (using liquid hydrogen as fuel): the HM4, developed in the 1960s by the Société d'Etudes et de Propulsion par Réaction (SEPR) in Villaroche, the other entity behind the creation of our division.
- Christophe Rothmund. "La cooperation franco-allemande dans le domaine des moteurs-fusées cryotechniques" (PDF) (in French). Snecma, Vernon. pp. 83–85. Retrieved 10 August 2014.
- Airbus Air and Defence. "HM-7 and HM-7B Rocket Engine - Thrust Chamber". Retrieved 16 December 2015.