Here is an interview, by Sander Olson, with Richard Varvill, the Technical Director and Chief Designer at Reaction Engines Limited. Reaction Engines Limited is a UK company that is developing a fully reusable launch system called skylon. Skylon is an unpiloted reusable spaceplane that will have a hybrid jet/rocket engine and take off from an airport to achieve orbit. Mr. Varvill believes that Skylon could begin flight testing by 2020, and may eventually reduce launch costs to as low as $5 million per flight. [Videos and more pictures are below]
Question 1: Tell us about the Skylon rocket project. How much will it cost to develop, and to what extent could it bring down launch costs?
Answer: Skylon is a reusable single stage to orbit launch vehicle and is intended to replace current expendable launch vehicles. It is designed to last 200 flights and is intended to reduce the cost (to about 1/10th), increase the reliability (about 400fold) and reduce turnaround times (from about 2 months to 2 days). Skylon will cost about €10.5Billion to develop at current (2009) prices. The amount it brings down prices is heavily dependant on the launch rate (since the recurring costs are low). At current worldwide launch rates (approx 100 per year) the launch cost with full development and production cost amortization and without any hidden subsidies will be about €30M. However at say 1000 flights/year the cost falls to €4.5M.
LAPCAT (Long-Term Advanced Propulsion Concepts and Technologies) is a 36 month European FP6 project to examine ways to produce engines for a Mach 4-8 Hypersonic aircraft. The project is funded by the EUROPA general R&D fund rather than ESA.
One possible supersonic transport aircraft being researched as part of this project is the A2 by Reaction Engines Limited. The researchers are looking at an aircraft capable of flying from Brussels (Belgium) to Sydney (Australia) in 2-4 hours, significantly reducing journey times across the globe.
To attain and maintain such high speeds, Reaction Engines Limited would need to develop its newly designed concept engine called the Scimitar, which exploits the thermodynamic properties of liquid hydrogen. The engine is theoretically capable of powering the A2 to a sustained Mach 5 throughout flight with an effective exhaust velocity of 40,900 m/s (4170 s).
“Results so far show [the Mach 5 vehicle from Reaction Engines] can avoid later [technology] pitfalls and could travel from Brussels to Sydney,” says ESA’s LAPCAT project coordinator Johan Steelant.
Question 2: The Sabre engine is essentially a hybrid rocket. Is this approach unequivocally superior to having separate and simpler jet and rocket engines?
Answer: The Sabre engine is designed to capitalize on the best aspects of airbreathing propulsion (low fuel consumption) without adding too much hardware mass whilst also increasing the practical airbreathing Mach range by precooling. By combining the airbreathing and rocket modes into a single engine we save a lot of mass compared to separate jet and rocket engines.
Skylon Mission Animation Video
Question 3: The Sabre engine will necessarily be quite complex. Will it be able to operate reliably? Will it require extensive and frequent maintenance?
Answer: The Sabre engine is certainly more complex than current jet or rocket engines in terms of parts count. However, reliability is only loosely related to the number of parts. Reliability is mainly related to factors such as component stress levels, fatigue, creep, wear, vibration, production quality control etc and also importantly how much money is spent during the engine development program. The engine on a reusable launch vehicle has to be more reliable than current expendable engines to meet the overall program objectives, which places emphasis on rocket thrust chamber life, turbopump bearings and seals and the precooler.
Question 4: Your company estimates launch costs as low as $5 million per flight. and per-passenger costs to orbit of $100,000. How much confidence do you have in these estimates?
Answer: As discussed above the costs are dependant on the vehicle operational scenario. Our development and production costs are empirically derived from previous aircraft and rocket projects and are estimated to have a standard deviation of about 15%.
Question 5: The Skylon’s airframe will be only .5 mm thick, yet will need to withstand the intense heat of re-entry. What material could meet these criteria? Has this material been fabricated?
Answer: Skylon’s reentry trajectory is less severe than STS due to its lower ballistic coefficient (resulting in lower skin temperatures). The aeroshell is currently specified in a fiber reinforced glass ceramic which can withstand temperatures up to 1400K. We have been testing coupons of this material in a specially designed test rig at Reaction Engines to verify its ability to survive chemical attack by the reentry plasma. Sections of corrugated aeroshell have already been made.
Question 6: What sort of avionics will be required for the Skylon? Will flight be completely automatic?
Answer: The flight will be completely automatic but with flight data fed back to a ground monitoring center (it is not really a flight control center in a traditional space sense of the word). It is expected that SKYLON operations will be incorporated into existing Air Traffic Control.
The ability to completely conduct a flight of this type as a UAV was proven in the 1980s by the Russian Buran. However we are currently re-looking at the SKYLON avionics incorporating integrated architectures, high capacity data-buses and other features of modern aircraft avionics.
Power is provided by fuel cells fed from the orbital cryogenic propellant supply
Question 7: When is the earliest that the Skylon could be operating? How confident are you of meeting development schedules?
Answer: Earliest possible Entry Into Service is 2020 assuming that system development starts soon. Program delay is more likely to be caused by political wrangling than technical difficulties.
Question 8: Reaction Engines Long-Term Advanced Concepts and Technologies (LAPCAT) aims to reintroduce supersonic commercial flights. How extensively has your company researched this concept?
Answer: LAPCAT is an EU Framework program managed by the European Space Agency and includes 14 partners of which we are one. Our A2 vehicle design aims to capitalize on the technology of Skylon and its Sabre engines. LAPCAT 1 was a feasibility study which showed that the A2 had promise and was able to meet the payload/range requirement under practical operational constraints. In LAPCAT 2 we are now studying some of the technical aspects in more detail.
Question 9: Could you foresee a factory mass-producing Skylon and LAPCAT vehicles within a few decades? Could you see the production cost being reduced to the cost of a jumbo jet?
Answer: Skylon is much more likely to be developed than LAPCAT since it is such a large improvement (in every sense) over current launch vehicles. The initial production run is probably going to be smaller than civil jets due to the current low worldwide flight rate compared to Skylon’s capability. Our initial estimate for the Mk1 machine is for total worldwide sales of only 30 vehicles. For this limited run the production cost will be about 2.5 times a jumbo jet. However, increased production would reduce the cost correspondingly.
Question 10: Reaction Engines has done extensive testing on the benefits of contra-rotating turbines. What are the preliminary results from that research?
Answer: The research proved that contra-rotating turbines have no aerodynamic anomalies and can be designed by similar methods to conventional turbines. They are lighter than conventional turbines (with fewer stages) when the turbine drive gas has a high speed of sound compared to the compressor.
Question 11: Your company has designed an orbital base station. How difficult would such a station be to develop and launch? What logistics/maintenance would be involved in operating such a station?
Answer: The Orbital Base Station on the website was designed as part of Project Troy and is sized to provide an assembly facility for the human mission to Mars. This is a conceptual study which is part of the process of checking what future missions SKYLON can support, which, it turns out, is all of them. We have also looked at supporting Solar Power Satellites, nuclear waste disposal, human lunar missions again all looking good. This OBS will not be the first station to be built when SKYLON becomes operational and the details of the cost and logistics flow have only been looked at superficially. We are looking in more detail at smaller and more imminent space stations and the results of that study – which will answers the questions of cost and maintenance flow, will be ready in about a year.
Question 12: Describe the concepts of Reaction Engines space-based orbital transfer vehicle.
Answer: On the Website we have outlined the Fluyt stage which is a large orbital transfer vehicle, which would be based at a space base (like the OBS). Like the OBS it is a conceptual study intended to test the ability of SKYLON to undertake the most ambitious of future missions. There is also a much smaller SKYLON Upper Stage (SUS) with a propellant load of 7 tons, which is ground based and will be available at the start of SKYLON operations. The details of this stage should be made public in the next few weeks.
Question 13: How much funding has the British Government provided? Is Reaction Engines seeking any venture financing?
Answer: The UK government has contributed €1million into our current Technology Demonstration Program (split between the GSTP and TRP budgets). The balance of the funding (about 75%) has been raised through private investment.
Question 14: Assuming sufficient funding, how do you foresee these projects opening up space access in the next twenty years?
Answer: By reducing launch cost and increasing launch reliability space access will be transformed forever. Hopefully this will initiate a new space age where the economic returns from space based activities far exceed the initial investment.
The Orbital Base Station is a design for an orbital assembly complex in low Earth orbit, functioning as an integral part of a space transportation system and enabling the construction and maintenance of vehicles for the exploration of the Moon and Mars. Orbital Base StationHome > Current Projects > Orbital Base StationAssembly Dock Structure
Construction of the OBS would be highly modular, with the outer shell made from 10m^2 panels, covered with a skin of aluminised Mylar. The structure would also provide tank farms for liquid oxygen and hydrogen propellants, accommodation for construction crews, and fuel cells to provide the base load power. Large doors at either end provide access for vehicles, while payload loading doors along the side enable cargo from docked SKYLON vehicles to be transferred using manipulator arms.