Remember Hotol? Years of hard work in the face of setbacks and lack of support could be about to pay off for the small team that never lost faith in the ’spaceplane’ concept.
Ten years ago all seemed lost for the UK’s involvement in ’spaceplanes’ – hypersonic vehicles that could use jet propulsion to reach the outer edge of the atmosphere, before switching to rockets to get into orbit. But, now at the beginning of the 21st century, a team of engineers believes those lofty goals of the 1980s might finally be realised.
In a small office at Culham Science Centre, home of the world’s biggest fusion research programme, sits Alan Bond, managing director of high-tech engineering company Reaction Engines, with his technical director Richard Varvill.
They are both veterans of British Aerospace’s Hotol project, the failed effort to create a viable UK space plane. Hotol would have been a horizontal take-off and landing, single-stage-to-orbit vehicle: the embodiment of the ideas of those who believe space exploration has taken the wrong trajectory in using ballistic missile technology (of a kind that propels the Space Shuttle) rather than more recognisable aircraft techniques.
But Hotol came to an end in 1988 with the stroke of a pen from the minister then responsible, Kenneth Clarke. For Bond and Varvill, the next 10 years was a time of hopes raised and dashed.
’We felt the technology was exciting enough to form Reaction Engines,’ says Bond. ’We formed it to rescue the concept and technology and tried to fund it ourselves.’
Bond and Varvill started the company with engineering director John Scott-Scott. It was the late 1980s and the nation was awash with money. They met wealthy businessman, Gerald Carroll, head of the Carroll Corporation construction company, who pointed out to the team that it did not have to keep knocking at the government’s door.
Private funding, explained Carroll, was actually a sensible option. So in 1990, Hotol became Skylon, named after the dart-like structure at the 1951 Festival of Britain. Reaction Engines’ focus then was on the banks and other financial institutions who might be persuaded of the commercial merits of Skylon as a satellite launcher.
But while that endeavour progressed, the small team needed money just to keep going. ’Our resources very quickly started to expire so we dragged in contract work and one thing led to another to prop up the project,’ says Bond.
Fortunately the contract engineering was in the high-tech arena and enabled them to keep up with engineering and materials developments required for their spaceplane dream.
The team continued to develop the spaceplane technology in their spare time. But they had to try to work out why the original Hotol had not quite ’got there’, either technically or commercially.
During Hotol’s development, problems had surfaced with its aerodynamics. Reaction Engines took the opportunity to make the necessary changes. ’We redesigned the whole thing, making it look more like an aeroplane. Basically, the centre of gravity was too far back. So we put the engines on the wing tips and moved everything forward, and split the main hydrogen tank so it wasn’t all at the front, creating a long spindly fuselage,’ says Bond.
Another change was the introduction of an undercarriage. Hotol was designed to be launched from a trolley. The theory was that the vehicle was too heavy for an undercarriage.
’If you use the normal calculations for an aircraft, you would need a 12.5 tonne undercarriage. But a spaceplane only weighs 20% of its take-off weight when it lands, so all sorts of things began to snap into place’, says Bond.
Skylon’s engines would operate as conventional rockets outside the atmosphere, but for altitudes of up to 26km and speeds of Mach 5, they would have a compressor to feed in atmospheric air, as in a gas turbine.
But at speeds of Mach 5, the air entering the engine is coming in at temperatures of up to 1000ºC. To compress this efficiently in order to burn it with the fuel, it first needs to be cooled to -130ºC. (The higher the temperature of the air, the more energy is needed to compress it, hence the requirement for a chiller.)
The one crucial piece of unproven technology in this is a heat exchanger to achieve this level of cooling without being enormously big and heavy.
Bond and his team believed they had cracked it, but needed to raise cash – around £850,000 – to build a prototype to demonstrate the technology.
They contacted everyone from insurance firms to banks to the British National Space Centre, engine companies, vehicle manufacturers, the European Space Agency and even rotary clubs. All to no avail.
’The problem we have has is that there is no government support,’ explains Bond.In the kind of high-risk project they wanted to launch, companies wanted government money backing it up. In 1997 Reaction Engines had what they thought was a lucky break. GEC/Marconi offered to put £400,000 into the project. The company then went to the BNSC and asked the government agency if it would match these funds. The BNSC’s response was, according to Bond: ’If you can find that much, why can’t you find the rest?’
And that was the end of that. After so many years of work, it would have seemed like the end for most people. But last year a wider interest in some of the post-Hotol technology emerged.
’People started to see that pre-cooled engines were a pre-requisite for getting jet engines to operate at the kind of hypersonic speeds we are talking about. Around the world there are now at least three pre-cooled engine projects on the go,’ says Bond.
Some funding has come in from a surprising source, in the form of backing from Paul Portelli, the owner of a London ceramics supplier, World’s End Tiles. Portelli, a space enthusiast, has even hung a model of Skylon in his showroom, and is understood to have contributed some tens of thousands of pounds to the project.
Obviously, more is needed, though the focus now is on building a small-scale laboratory bench demonstrator of the pre-cooler concept by next summer, which will cost around £60,000. Not that the team has given up on government support. While the UK government has yet to show an interest, Varvill and Bond are talking to other EU agencies about funding. They are also watching developments in Japan, which they say is ’making a hash’ of its pre-cooler technology. Japan’s heat exchanger, according to the Reaction Engines team, is ’positively agricultural’ compared to their own design. They are hoping that it is just a matter of time before Reaction Engines steps in to offer its design.
The US is also coming around to the technology. NASA has recently started a pre-cooled engine programme, using rockets and turbines in combination and hence requiring heat exchangers. And that, explains Bond, has given his company an ’in’: ’We have been talking to one of the engine companies since the end of last year.’Bond thinks his team is now ready to sell consulting services to thesevarious projects.
Hotol or Skylon may never be built as originally envisaged but, thanks to the efforts of the three Reaction Engines technologists, the UK could find itself guaranteed a role in developing whatever type of spaceplane is eventually built.
Sidebar: The Hotol story
Hotol was British Aerospace’s single-stage-to-orbit winged launch vehicle whose name was an approximate acronym of horizontal takeoff and horizontal landing. A Rolls-Royce/British Aerospace team began developing Hotol in 1982.
It was originally 62m long, its launch mass was 196 tonnes and it could carry a seven tonne payload. It would have taken off horizontally from a purpose-made, rocket-propelled trolley that ran down a runway. The vehicle would use jet engines until it reached Mach 5 or 6 and would then ascend to orbit using rocket engines.
The government decided to support the work and paid £2m from 1986 to 1988. In 1988 it decided not to fund any more work. Bond and his colleagues formed Reaction Engines, while Hotol was redesigned. British Aerospace removed the air-breathing engines, put on Russian rockets, reduced the hypersonic craft’s length to just 34m and designed the whole machine to be launched at 9km, with a payload of 4.5 tonnes, from a Russian transport aircraft.
But even that came to an end when safety issues regarding the launch from the back of the huge transport plane dogged its development. The official Hotol project was finally cancelled by British Aerospace in 1992.