Monday, July 13, 2015

SABRE's Secret Sauce

          By Brian Orlotti

Reaction Engines Limited, a UK-based firm developing a game-changing new type of rocket engine, has published a paper which sheds some light on one of the technology's key secrets.

Alan Bond, the founding director of Reaction Engines and the inventor of the SABRE engine, discusses the heat exchanger testing programme for the engine in this July, 2012 video. The SABRE concept derived from a 1980's British design for a single stage to orbit reusable winged launch vehicle, called the Horizontal Take-Off and Landing (HOTOL) concept, which Bond helped to develop. Bond was also involved with the development of the Blue Streak medium range ballistic missile and Project Daedalus, a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible unmanned interstellar spacecraft. Screen shot and video c/o Reaction Engines.

As outlined in the July 11th, 2015 Next Big Future article "Skylon spaceplane developers reveal the antifreeze method for the sabre hypersonic engine," the Oxfordshire based firm is developing a synergistic air-breathing rocket engine (SABRE). The engine is designed to propel the planned Skylon spaceplane at hypersonic (Mach 5.5+) speeds while in Earth's atmosphere, then switch to a purely rocket mode (around Mach 27+) in order to reach low Earth orbit.

The key to SABRE's ability to function as both an aircraft and rocket engine is a complex heat-exchanger system that allows oxygen to be drawn directly from Earth's atmosphere to oxidize the on-board hydrogen fuel.

The SABRE's heat-exchanger chills incoming air from more than 1,000C to -150C in less than 1/100th of a second before passing it through a turbo-compressor and into the rocket combustion chamber, where it's then burned with liquid hydrogen. Until recently, the means by which SABRE achieved this without ice-buildup in the pre-cooler was a closely guarded secret.

This April 27th, 2012 BBC News report on Skylon compared the space plane to traditional rockets. At the time, development was considered to be at a "critical" stage where development concepts needed to be validated before moving forward with the building of the full scale test vehicle. As outlined in the July 16th, 2013 Guardian article, "UK earmarks £60m for super-fast space rocket engine," the UK government has slowly begun to move forward since then. Graphic and video c/o BBC News.

But, according to the article at least, the SABRE engine uses simple methanol as an antifreeze.

According to Mark Thomas, a managing director at Reaction Engines, the company chose to go public with its frost control technology due to pending patent applications. He stated:
The trigger for patenting was the awareness that to execute this program we are going to have to involve other companies. You can’t keep trade secrets very long in that situation, so it is better to be protected formally and legally on the clever stuff...
Though the company is developing the SABRE engine primarily for the Skylon spaceplane, the propulsion system and its pre-cooler technology are attracting wider interest for use in future aircraft and two-stage space launch vehicles.

Perhaps the ultimate commercial application for the SABRE engine could be this 300 passenger aircraft. As outlined in the November 29th, 2012 Mail Online article, "One step closer to space travel: Engine breakthrough could see jets fly from London to Sydney in less than five hours," the real test of space technology is whether it can be commercialized to perform useful functions on Earth. Graphic c/o  Mail Online.

In 2011, Reaction Engines announced that they had secured $350Mln USD ($446.5Mln CDN) contingent on a successful test of the engine's precooler technology (which the company achieved in 2012). In July of 2013, the UK government pledged an additional £60 million GBP ($118.5Mln CDN) to the project, enabling a full-scale prototype of the SABRE engine to be built.

By 2015, the company had attracted the attention of the Americans. As outlined in the April 15th, 2015 Engineer.UK article, "ARFL confirms feasibility of Reaction Engines’ SABRE engine concept," various US based organizations, including the US Air Force Research Laboratory’s Aerospace Systems Directorate (AFRL) had concluded that there was something to the SABRE concept.

Skylon is single-stage-to-orbit spaceplane that will take off from a conventional runway, accelerating to Mach 5.4 at 26 kilometres altitude using the atmosphere's oxygen to oxidize its onboard hydrogen fuel before switching to the internal liquid oxygen supply for travel to Earth orbit.

Once in orbit, the craft would release its payload of up to 15 tonnes to a 300 km equatorial orbit, then reenter the atmosphere (protected by a ceramic composite skin) and land on a runway.

Skylon could also carry up to 11 tonnes to the International Space Station (ISS), almost 45% more capacity than the European Space Agency's (ESA) Automated Transfer Vehicle (ATV) spacecraft.

Portrait photograph from a ninth-plate daguerreotype of Henry David Thoreau by Calvin R. Greene. According to Thoreau, "In the long run, men hit only what they aim at. Therefore, they had better aim at something high." Photo c/o Wikipedia.

Reaction Engines' design goals for Skylon are a turnaround time of two days between flights and to be potentially reusable for 200 flights. Skylon will initially be unpiloted, but can also be certified to carry passengers.

Brian Orlotti.
The last time the UK stood on the cusp of such world-changing innovation was during the 1950's with the advent of the DeHaviland Comet commercial airliner. Although that aircraft was plagued by fatal flaws, Skylon seems poised to accomplish something far greater. 

Brian Orlotti is a network operations centre analyst at Shomi, a Canadian provider of on-demand internet streaming media and a regular contributor to the Commercial Space blog.

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