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In this new generation of space race, where aerospace companies like SpaceX, Blue Origin, Virgin Galactic, etc. are vying to pioneer in the domain of spaceflight and satellite launch systems by each introducing its own state of the art launch technologies, Britain’s Reaction Engines Ltd. (REL) has proposed its own engine named SABRE (Synergetic Air-Breathing Rocket engine) based on a novel concept.

SABRE is a hypersonic precooled hybrid air-breathing engine which is a combination of precooled engine, ramjet and rocket engine cycles. It is assumed to become the world’s first air-breathing rocket engine. It is set to revolutionize the air travel as well as spaceflight due to its dual nature of the operation.

SABRE can be thought of like a cross between an air-breathing jet engine and a rocket engine. It is claimed to break the record of maximum speed achieved by a jet engine in an unassisted take-off and landing flight which is presently held by Pratt &Whitney’s J58 turbojet engine that powered Lockheed Martin’s SR-71 Blackbird to a speed of Mach 3.5 (1,200 m/s). In its jet-engine mode, SABRE is capable of achieving a maximum speed of Mach 5.4 (1,852 m/s), that is more than five times the speed of sound. In its jet mode, SABRE uses atmospheric air to burn the fuel and ascend higher in the altitude like any other air-breathing engine. At an altitude higher than 28 km (17.4 miles), it will transition from jet-engine to closed cycle rocket-engine mode. During its rocket engine mode at high speeds and higher altitude, it uses the onboard oxygen supplies to combust the fuel and produce thrust to attain a maximum speed of Mach 25. As it scoops up atmospheric air until it reaches Mach 5.4 and uses the onboard oxidizer for the operation thereafter, it would have to carry much less bulky onboard oxygen supplies, such a vehicle could deliver the same payload to orbit of a half the vehicle mass of current launchers, as well as potentially offering a large reduction in cost and higher launch rate.

To achieve the objective of attaining a flight with speed higher than Mach 5 using an air-breathing engine isn’t an easy task. It is accompanied by the numerous engineering problems that are encountered while operating at hypersonic speeds. One of them is a conventional one, the increase in speed leading to an increase in the thermodynamic effects and encountering temperatures which are way higher than the melting points of the materials of the engine components. In the past, this issue was tackled by developing scramjets/ramjets which lead to a heavier engine and reduced thrust to weight ratios. To overcome this issue, SABRE uses a novel and innovative technology of pre-cooler. SABRE uses pre-cooler to cool down the incoming air efficiently and swiftly, within a period of a second. Pre-cooler consists of an array of tightly packed tubes which is supplied with chilled helium that pulls out all the heat from the incoming air and further supplied for the combustion process.

SABRE is being designed to propel Skylon spaceplane, a single stage to orbit spaceplane proposed by REL. With two SABREs fitted on the tips of Skylon, the spaceplane will takeoff from the runway carrying the payload and would land back on the runway in an unassisted manner after the completion of the operation. The duality of SABRE makes Skylon capable to be used rapid air travel between two locations on earth as well as go out of earth’s atmosphere to deliver the payload and return back. Due to the ultra lightweight nature of SABRE, Skylon can carry 24% more weight than SpaceX’s Falcon 9 Delta-V. To gain upper hand over the current reusable launch systems, Skylon is believed to complete at least 200 orbital flights per vehicle as compared to Falcon-9’s 100 flights.

In the recent tests, ESA together with the UK Space Agency (UKSA) recently reviewed the preliminary design of the demonstrator engine core of the SABRE and gave a green light which is a major milestone. If all goes well as per the plan, then the first ground-based engine tests could happen in 2020, and SABRE engines could be performing unmanned test flights by 2025.

It is amazing to see the introduction of such innovations in this new-age of space race which could have been an unimaginable thing a few decades ago. In the ’60s, the timeline between two subsequent satellite launches used to be somewhere between a year or two and in the present day, it is just a matter of a few days. Without any doubt, I can say that it is the most thrilling and awe-inspiring time for every aerospace and astronomy fan to live in where the world of technology is everchanging.

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