ABOUT HM7B
The HM7B is a cryogenic upper stage engine developed by ArianeGroup (originally SEP) for the Ariane launch vehicle family. Burning liquid hydrogen and liquid oxygen in a gas generator cycle, it powered the upper stages of Ariane 2, 3, 4, and 5 ECA. The HM7B served as Europe’s primary upper stage engine for four decades before being succeeded by Vinci.
Image: ESA
PERFORMANCE
| Thrust (Sea Level) | N/A (upper stage) kN |
| Thrust (Vacuum) | 64.8 kN (14,570 lbf) kN |
| ISP (Sea Level) | N/A s |
| ISP (Vacuum) | 446 s s |
| Chamber Pressure | 3.5 MPa (508 psi) bar |
| Mass | 165 kg |
| Thrust-to-Weight | 40 |
| Throttle Range | Not throttleable |
| Restart Capable | No |
THRUST CONVERSIONS (VACUUM)
| Kilonewtons | 64.8 kN |
| Pounds-force | 14,568 lbf |
ENGINE CYCLE
Gas Generator
A gas generator cycle taps off a small portion of propellants to drive turbopumps via a separate combustion chamber. The turbine exhaust is dumped overboard, making it less efficient but simpler and more reliable. Used by the Merlin, F-1, and RS-27.
PROPULSION
| Propellant | Liquid Hydrogen (LH₂) |
| Oxidizer | LOX |
| Engine Cycle | Gas Generator |
| Mixture Ratio | 5.15:1 |
| Flow Rate | ~15 kg/s kg/s |
PHYSICAL
| Dimensions | 1.0 m diameter × 1.8 m length |
| Combustion Chambers | 1 |
| Nozzle Expansion Ratio | 83.1:1:1 |
GENERAL
| Manufacturer | ArianeGroup (SEP/Snecma) |
| Country | France / Europe |
| Status | Retired |
| First Flight | April 16, 1979 |
VARIANTS (2)
- HM7
- HM7B
VEHICLES USING HM7B (4)
- Ariane 2
- Ariane 3
- Ariane 4
- Ariane 5 ECA
ENGINE LINEAGE
⚖ PROPELLANTS
