SABRE (rocket engine)
SABRE (Synergetic Air Breathing Rocket Engine) is a concept under development by Reaction Engines Limited for a hypersonic precooled hybrid air-breathing rocket engine. The engine is being designed to achieve single-stage-to-orbit capability, propelling the proposed Skylon spaceplane to low Earth orbit. SABRE is an evolution of Alan Bond's series of LACE-like designs that started in the early/mid-1980s for the HOTOL project.
A version of the SABRE engine designed in the 1990s | |
| Country of origin | United Kingdom |
|---|---|
| Designer | Reaction Engines Limited |
| Application | Single-stage-to-orbit |
| Associated LV | Skylon |
| Predecessor | RB545 |
| Status | Research and development |
| Liquid-fuel engine | |
| Propellant | Air or liquid oxygen / liquid hydrogen |
| Cycle | Combined cycle precooled jet engine and closed cycle rocket engine |
| Performance | |
| Thrust, vacuum | Approx. 2,940 kN (660,000 lbf) |
| Thrust, sea-level | Approx. 1,960 kN (440,000 lbf) |
| Thrust-to-weight ratio | Up to 14 (atmospheric) |
| Specific impulse, vacuum | 460 seconds (4.5 km/s) |
| Specific impulse, sea-level | 3,600 seconds (1.0 lb/(lbf⋅h); 35 km/s) |
The design comprises a single combined cycle rocket engine with two modes of operation. The air-breathing mode combines a turbo-compressor with a lightweight air precooler positioned just behind the inlet cone. At high speeds this precooler cools the hot, ram-compressed air, which would otherwise reach a temperature that the engine could not withstand, leading to a very high pressure ratio within the engine. The compressed air is subsequently fed into the rocket combustion chamber where it is ignited along with stored liquid hydrogen. The high pressure ratio allows the engine to provide high thrust at very high speeds and altitudes. The low temperature of the air permits light alloy construction to be employed and allow a very lightweight engine—essential for reaching orbit. In addition, unlike the LACE concept, SABRE's precooler does not liquefy the air, letting it run more efficiently.
After shutting the inlet cone off at Mach 5.14, and at an altitude of 28.5 km, the system continues as a closed-cycle high-performance rocket engine burning liquid oxygen and liquid hydrogen from on-board fuel tanks, potentially allowing a hybrid spaceplane concept like Skylon to reach orbital velocity after leaving the atmosphere on a steep climb.
An engine derived from the SABRE concept called Scimitar has been designed for the company's A2 hypersonic passenger jet proposal for the European Union-funded LAPCAT study.