Reaction Engines (RE), a UK-based company, receives $37.4 million strategic investment “boost” from aerospace giants Boeing and Rolls-Royce to develop a novel class of engines combining jet and rocket technologies.
Supersonic flight: An introduction
Short definition: Supersonic flight is being able to fly faster than the speed of sound.
For vehicles travelling in conditions of 68° Fahrenheit (20° Celsius) at sea level, this is about 768 mph, or 1,236 km/h. Supersonic speeds are also classified in terms of Mach numbers. The Mach number is the ratio of the speed of the vehicle to the speed of sound. So, a vehicle travelling at exactly the speed of sound is travelling at Mach 1. Mach numbers are also used to define various high speeds:
- Supersonic: Speed that is faster than Mach 1.
- Subsonic: Speed that is slower than Mach 1.
- Transonic: Speed that is between Mach 0.8-1.2
All modern passenger aircraft are subsonic and most modern fighter jets are supersonic. The only supersonic passenger aircraft to ever take flight were Concorde and Tupolev Tu-144. Since the grounding of Tupolev Tu-144 in 1978 and the retirement of Concorde in 2003, there have been no other supersonic passenger aircraft in the commercial airline market or service.
Need for speed: Hypersonic flight
Unlike supersonic speed, which has a clear definition of being faster than the speed of sound (>Mach 1), there is no perfect definition for hypersonic speed. A loose criterion defines hypersonic travel as speeds at which the air molecules surrounding the aircraft start to chemically disintegrate and become an electrically-charged field. This phenomena typically occurs at Mach 5 (five times greater than the speed of sound), equal to 3,836 mph (6,200 km/h) at sea level.
There are both defense and commercial interests in developing hypersonic vehicles. A hypersonic missile system has ultra-fast target reaching and attacking capabilities, making it a weapon with significant strategic advantage. Commercial interests in hypersonic vehicles revolve around reducing long flights/around-the-world travel, deploying satellites in orbit, and space tourism.
The challenge
Hypersonic speeds have been attained before, not surprisingly as a part of military experiments. In 1967, NASA’s North American X-15 was piloted at Mach 6.72 (4,520 mph) at an altitude of 31,120 meters. In 2004, the unmanned NASA’s X-43A reached a record speed at Mach 9.6 (7,310 mph) at a height of about 33,500 meters. These test runs were all rocket-powered. This simply means that a missile is “tied up” an airplane, or a similarly designed flying vehicle, and flown until it runs out of power and crashes. Consequently, this also means that these prototypes are extremely risky for manned travel.
A revolutionary new propulsion system
To overcome the risk of hypersonic prototypes and bring hypersonic flight application to reality, the engineers at RE are designing a novel propulsion system called Synergistic Air-Breathing Rocket Engine (SABRE). Defined in simple terms, SABRE is a dual mode (functioning) engine:
- Air-breathing mode: the engine utilizes atmospheric oxygen as a source (as in a typical jet engine) to burn with its liquid hydrogen fuel in the rocket combustion chamber. This occurs at low speeds (sub, trans, and supersonic).
- Rocket mode: the engine transitions to using the on-board liquid oxygen (as in conventional rockets). This switch occurs at high speeds (hypersonic).
Thus, the SABRE can operate similar to a commercial aircraft at low speeds and then is able to transition to rocket mode at high speeds. Reaction Engines’ speed estimates for the SABRE are up to Mach 5 in the air-breathing mode and can reach as far as Mach 25 in the rocket mode.
Investment to drive development
Boeing’s $37.4 million funding round alongside Rolls Royce will allow these aerospace companies to have access to this hybrid engine much sooner, although neither of them stated how they intend to use SABRE in their vehicles. According to RE, this state-of-the-art engine could be used in several ways, including hypersonic commercial passenger airliners, reusable space vehicles, and launching satellites into orbit. Reaction Engines estimates they will run a series of test flights on SABRE by 2020 and will have hypersonic flights operational by 2030.
What’s next?
Hypersonic technology would disrupt commercial airline, aerospace, and defense industries. For example, a 3460 mile (5571 kilometer) trip from London to New York could take just 35 minutes, or a trip from Sydney to London (a 10,500 mile or 17,000 km flight) could be done in two hours. However, any nascent technology, such as SABRE, could very well be expensive and uneconomical for airline companies. It remains to be seen how hypersonic passenger airlines can become profitable when it finds a market willing to pay for ultrafast flights that save time.
Military hypersonic applications, such as fighter planes and cruise missiles, if developed, could penetrate any defenses currently available while delivering destructive force. This is because the current defense systems and military technologies operate at less than Mach 5 (supersonic) speeds. Hypersonic weaponry would have a considerable impact on international and national security, and as well as nuclear deterrent strategies.
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