Science: Into orbit in a plane made of balsawood: Aeroplanes could be low-cost, simpler and safer successors to the shuttle, reports Tom Wilkie
Monday 18 July 1994
It sounds bizarre, but David Ashford's Microsonic spaceplane is a serious proposition. Mr Ashford, a former project manager with British Aerospace in Bristol, has just completed a feasibility study of the technology of spaceplanes under contract to the European Space Agency (ESA).
'In the Fifties the expectation was that the first men in space would get there by aeroplane,' says Mr Ashford. 'The rocket- powered experimental X-planes were flying ever higher and faster. Then came Sputnik in 1957. The race to put men in space then became an overriding national priority. Since spaceplanes were still several years off, ballistic missiles were converted to provide transportation as a temporary expedient, and the habit has stuck.'
The space shuttle uses large throwaway components derived from ballistic missile technology and, mainly for this reason, costs some 20,000 times more per flight than a Boeing 747. Yet, Mr Ashford maintains, 'aeroplanes are far more suitable for passenger and cargo transport than ballistic missiles. They are far less expensive, safer and more practicable.'
Microsonic, the balsawood spaceplane, would be the forerunner of a larger craft known as Spacecab that would carry a crew of six into orbit at very low cost using existing, proven technology.
Microsonic would be a single- seater aeroplane designed to zoom- climb to space, with a maximum altitude of 50 miles. It would be the smallest supersonic aeroplane yet built and would be aero-towed, like a glider, to 40,000ft behind a Canberra (the most suitable aircraft available in the UK). The pilot then casts off the tow line, starts the battery of small rocket motors and pulls up into a steep climb. Two minutes later, the rocket fuel is used up. Microsonic is then flying almost vertically at a height of 32 miles and a speed of Mach 2.5 (Mach 1 is the speed of sound), from which it coasts to 50 miles before running out of speed. The pilot then dives vertically, re- enters the atmosphere, pulls up to level flight and glides back to base.
The aeroplane needs a very light structure and could be made mainly of thin sheets of balsawood. This is only possible because Microsonic uses its rocket motors to fly high to thin air - it would be impossible to use this construction on an aeroplane designed to fly supersonic near to sea level because the air loads would pull it apart.
Microsonic would require only a very thin layer of surface insulation to prevent burn-up on re- entry, partly because the velocities would not be anything like those of the space shuttle, for example, and also because balsawood itself is a very good thermal insulator.
Aeroplanes capable of flying into orbit are feasible with existing technology, and they could enter service at a development cost far lower than generally estimated, Mr Ashford maintains. 'There were numerous projects in the Sixties for small orbital aeroplanes. My first job was in a team designing one. They were considered feasible, but expensive to develop because they needed very advanced technology.'
He is so convinced of the practicality of spaceplanes that he has set up his own company, Bristol Spaceplanes Ltd, to promote the Spacecab project - in effect an updated version of plans developed in the Sixties but designed to use the technology of the Nineties. Spacecab has two stages - a carrier aeroplane and an orbiter - so that it can use existing engines and proven materials. Spacecab would be a piloted, fully re-useable, winged craft, carrying six people.
A key feature of Spacecab is that the upper stage reaches orbit avoiding high air loads. It is partially buried in the carrier aeroplane, and separates at great height, almost in space, where the air is very thin. The lower stage would have both jet and rocket engines to allow it to reach Mach 4.
A 'ski-jump' separation at such supersonic speed enables the second stage to accelerate to satellite speed before gravity has time to pull it back to dense air. Low air loads make it easier to use conventional aircraft aluminium alloy as the main structural material, thereby avoiding the cost and time of an advanced materials development programme. The total development cost would be about half that of a large new airliner and could be afforded easily by Europe.
Spacecab would greatly reduce the cost and improve the safety of transport to orbit. Enlarged versions could have a cost per person to orbit as low as about pounds 7,500 - about 1,000 times cheaper than the shuttle. But, Mr Ashford says, 'the idea of low-cost spaceplanes is not yet widely accepted. We have become used to the cost, risk and glamour of throwaway launchers.' His cheap and cheerful balsawood Microsonic is intended to provide direct evidence for the aeroplane way to space. With the due caution of an engineer, however, he adds that 'it should be remembered that a brief zoom-climb to space is easier than acceleration to satellite speed'.
The main problem is getting Spacecab taken seriously, so powerful are the interests vested in throwaway launchers. The official ESA proposal for transporting crews to and from space stations is called the 'crew transfer vehicle' (CTV). This will be carried to orbit on top of an expendable Ariane 5, at present under development. Spacecab would do much the same job and would cost much the same to develop, but, when the technology is mature, would cost about 1,000 times less per flight - simply because aeroplanes are far safer and cheaper to fly than ballistic missiles. Even though these claims are explained in a study report which it paid for, the ESA is planning to spend several hundred million pounds studying CTV and nothing on Spacecab.
To be fair, ESA has started a programme to study spaceplanes. The problem here is that the British government plans no more than observer status in the programme, which makes it difficult for ESA to place contracts in the UK. There is no British programme that makes even seedcorn funding available for spaceplanes, even though these are about to become the largest aerospace growth area.
Microsonic is intended mainly to encourage the space authorities in the UK and Europe to take the possibility of low-cost spaceplane development seriously. UK industry could then hope to gain a large share of the business. Otherwise the United States or Japan will be first, and a major opportunity will have been lost.
Mr Ashford says: 'Microsonic could be afforded by industry as a private venture project, or even by corporate sponsorship. My design files are open for inspection, and I would welcome the challenge of making it work.'
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