ABOUT RS-25
The RS-25, also known as the Space Shuttle Main Engine (SSME), is a liquid-fuel cryogenic staged combustion cycle engine built by Aerojet Rocketdyne. Originally developed for the Space Shuttle program, it is now adapted for the core stage of NASA’s Space Launch System (SLS). It is one of the most tested and reliable large rocket engines ever built, known for its exceptional performance and reusability heritage.
Image: NASA
PERFORMANCE
| Thrust (Sea Level) | 1,860 kN (418,000 lbf) at 109% kN |
| Thrust (Vacuum) | 2,279 kN (512,300 lbf) at 109% kN |
| ISP (Sea Level) | 366 s s |
| ISP (Vacuum) | 452 s s |
| Chamber Pressure | 20.6 MPa (2,994 psi) bar |
| Mass | 3 kg |
| Thrust-to-Weight | 73 |
| Throttle Range | 67–109% |
| Restart Capable | No (in SLS config) |
THRUST CONVERSIONS (VACUUM)
| Kilonewtons | 2.0 kN |
| Pounds-force | 450 lbf |
ENGINE CYCLE
Staged Combustion
In staged combustion, one propellant is burned with the turbopump exhaust, then all products are injected into the main chamber for complete combustion. This achieves higher chamber pressures and efficiency. Used by the RS-25 (SSME) and RD-180.
PROPULSION
| Propellant | Liquid Hydrogen (LH₂) |
| Oxidizer | LOX |
| Engine Cycle | Staged Combustion |
| Mixture Ratio | 6:1 |
| Flow Rate | ~500 kg/s kg/s |
PHYSICAL
| Dimensions | 2.4 m diameter × 4.3 m length |
| Combustion Chambers | 1 |
| Nozzle Expansion Ratio | 77.5:1:1 |
GENERAL
| Manufacturer | Aerojet Rocketdyne |
| Country | United States |
| Status | Active (SLS) |
| First Flight | January 1, 1970 |
VARIANTS (4)
- Block I
- Block II
- RS-25D
- RS-25E
VEHICLES USING RS-25 (3)
- Space Shuttle
- SLS Block 1
- SLS Block 2
ENGINE LINEAGE
⚖ PROPELLANTS
