Alan Bond, Managing Director of Reaction Engines Ltd, spoke at the Institute of Engineering and Technology in London on 8 May with his customary clarity of explanation and humour.

Alan Bond

Much of what he said is also covered in an interview recorded in late 2011 and posted in April 2012 on YouTube by DeltaVeeMedia. This interview gives clear descriptions of both the technical problems of single-stage to orbit, and the broader strategy issues. The London lecture brought in some additional points, as follows.

Alan began with praise for the expendable rocket, but pointed out its high cost. We are up a blind alley, he said, and it is now very difficult for us to back out of it.

The key characteristics required for a practical commercial transport system to low Earth orbit are:

Reusability: in Skylon’s case, 200 flights is the target which Reaction Engines is aiming for, but an in-house study of the use of Skylon to orbit components of a solar power satellite system thought this might be extended to more like 500 flights in the case of the engines, and to at least 1000 flights for each airframe.

Single-stage: because that minimises ground operations between flights.

Unpiloted, which reduces development cost. (Interestingly, in his book Spaceflight Revolution David Ashford argued the opposite, that having a human pilot on board reduces the development cost, so there is scope for some interesting discussion here.)

Abort capability at all stages of flight. There is an economic limit to the reliability achievable in a throw-away rocket, and that limit has been reached. Clearly, only a reusable vehicle can return to base and try again another day, and only a comprehensive abort capability can save the payload.

User-friendly operations, which again comes back to the simplicity of operation of the system.

Re-entry cross-range capability of plus/minus 1600 miles needed to return a vehicle from orbit to the landing-site of choice without having to wait for the orbital track to pass closely over that point on the ground.

The key to the Skylon spaceplane is the innovative jet-rocket Sabre engine, and the key to the engine is the pre-cooler, currently undergoing tests at Culham. One gets an idea of the technological challenge of the pre-cooler when one realises that each complete engine must contain some 2000 km of extremely fine (1 mm diameter) tubing. Manufacturing this tubing has been a major development focus: its object is to cool the incoming rush of air at Mach 5 from 1000 degrees C to minus 140 degrees C in just one hundredth of a second. At the same time it has to avoid frosting up as the moisture in the air cools to ice, threatening the clog the piping.

Fortunately the pre-cooler can be built in modular sections, and a module has been being tested at Culham recently. Tests so far have investigated the airflow around and through the unit, and these have gone completely satisfactorily. The next stage is to demonstrate its actual function in cooling hot incoming air, and this stage will take up the rest of the current year.

After that, there needs to be a three-year Phase 3 development programme with the following objectives:

Raise engine TRL (technology readiness level) to level 6.

Complete the design of the latest iteration of the engine, Sabre 4, to manufacturing drawings.

Ensure vehicle requirements and Sabre 4 design are compatible.

Flight-test the design for the engine nacelles. The engine nacelle is not just a box that encloses the engine! It has to manage air capture and bypass excess air. Reaction Engines would like to demonstrate the airflow characteristics with a flying test vehicle which is 9 metres long, weighs about 1 tonne, and is driven by a rocket or ramjet engine to Mach 5.

Alan concluded with a number of key points:

The major technology problems of an airbreathing/rocket SSTO have been solved.

Yet around the world a new range of expendable rockets is being advocated and assigned large amounts of development money.

The UK has the lead in reusable access to space, and at the same time it needs new technology programmes to develop its economy. (Here, Alan is in full agreement with what David Ashford has been saying.)

In recent years the UK government has been immensely supportive. The UK Space Agency knows that the Skylon project is valid and promising.

Reaction Engines has also achieved a breakthrough by demonstrating that public/private partnership works in a technology development programme. The work so far has been done on a mixture of about 15% institutional (government) funding, 85% from private investors such as high net worth individuals.

The outlook for Skylon is extremely good. The company are planning to display the pre-cooler at the Farnborough Air Show later this year.

During the question and answer session that followed, some more interesting points emerged.

Reaction Engines envisage Skylon entering service around 2020. A total of 30 vehicles sold to operators worldwide would recover the development cost. However, each individual operator would own only one or two Skylons. The cost per launch should be around $5 million once the system is up and running. (The costs per launch given by Alan for the Shuttle and Ariane were $700 million and $180 million respectively; however, elsewhere I have seen an estimate of Shuttle costs double that.)

In its current (D1) design, with a 15-tonne payload to equatorial 300 km orbit, Skylon can carry a passenger module with 20 to 30 people on board, including researchers and tourists visiting orbital space stations. Surprisingly (to me), the economics of operating Skylon as a publicly accessible passenger vehicle have not been investigated. Alan thought that a dedicated passenger-carrying derivative of Skylon would be better suited to the task, presumably meaning one in which the passenger module is integrated into the vehicle rather than just being an optional plug-in payload.

However, the potential for growth is a highly contentious issue. If you drop the transport cost by an order of magnitude, how much more traffic do you attract? Alan regretted that the tachyon chip in his crystal ball was not working; nevertheless, he concluded here with a vision of a growing space infrastructure of orbital stations, propellant depots and reusable, space-based upper stages.

Full-scale development and manufacture of Skylon would create some 18,000 high-tech jobs in the UK and Europe, plus another 45,000 jobs associated less directly with the programme, Alan stated. More new work is created when one considers the payloads which might be flown, up to and including manned Mars missions (at, needless to say, much lower cost than on traditional giant launch vehicles). The UK needs this sort of economic stimulus.

In fact (though Alan did not refer to him) this is exactly the point made by Patrick Collins for many years: that as lower-grade jobs migrate out of the most highly developed economies to developing countries, new technologies and markets are needed to maintain the growth of the rich countries, and developing a space infrastructure is the ideal arena for this new burst of growth.

A public offering of shares in Reaction Engines is on the cards in the near future.

Having endured the coach trip from Oxford to London and back in order to attend the lecture, I can only add that I hope an equally thorough development effort will go towards fitting Skylon with comfortable seating...

Reaction Engines have an informative and nicely designed website, including images by artist Adrian Mann available for download in a variety of sizes.