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January 30, 2009

Progress to the Skylon Single Stage to Orbit Spaceplane for 2019


The last time this site had looked at the work of Reaction Engines, the designers of the Skylon Single-stage to Orbit vehicle proposal, they had designed the Mach 5 - A2 commercial Concorde replacement.

Reaction Engines has gotten tens of millions of dollars in funding for various engine and cooler subsystem development and testing. They have also released a report that details the progress that has been made.

Funding Tens of Millions to Develop sub-systems, Prove and Develop Concepts
The Skylon single stage to orbit spaceplane will cost $10-30 billion to develop.

LAPCAT II is a follow-on to the successful LAPCAT I program aimed at technology development for long range hypersonic civil flight. Two vehicle concepts (the precooled turbojet powered Mach 5 and scramjet powered Mach 8) are retained in the new program. LAPCAT II will be completed over a 4 year period and involves 16 partners. The total budget is €10.4M with the EU contributing €7.4M. Reaction Engines is managing the Mach 5 A2 work package which will include intake, nozzle, combustion chamber and vehicle structure studies.


The Skylon reduces the required mass ratio by improving the engine specific impulse by operating in an airbreathing mode in the early stages of the flight – up to around Mach 5.5 and an altitude of 25 kilometres before the engine switches to a pure rocket mode to complete the ascent to orbit. This makes a very significant difference; a pure rocket needs to achieve an equivalent velocity of around 9200 m/sec (7700 m/sec orbital speed and 1500 m/sec in various trajectory losses) whereas the airbreathing absorbs about 1500 m/sec of the orbital speed and 1200 m/sec of the trajectory losses so the pure rocket phases needs to provide only 6500 m/sec and this increases the minimum mass ratio from 0.13 to 0.21. Even with the extra engine mass required for the airbreathing operation this is a far more achievable target.




Pyrosic, from Pyromeral Systems in France, is the leading candidate material for the skin of the vehicle. PyroSic is aStructural High Temperature Composite, which retains good mechanical strength at temperatures as high as 1000°C (1800°F). The material is incombustible and does not release smoke or gas when exposed to heat or fire.

The Skylon development is estimated to take 9.5 years and cost 9518 M (2004 prices). The development program will produce a vehicle with a life of 200 flights, a launch abort probability of 1% and a vehicle loss probability of 0.005%. Assuming a production run of 30 vehicles each vehicle would cost about €565 M. In operation it should be capable of achieving a recurring launch cost of €6.9 M per flight or less.


Reaction Engines has gotten tens of millions of dollars in funding for various engine and cooler subsystem development and testing. There is an immediate and funded technology demonstration programme for the next two years. This will then lead in to a full development programme which will probably take a further 8 years.



Precooler Heat Exchanger
The basis of the Reaction Engines manufacturing expertise was a research project conducted by the University of Bristol (completed in 2000) leading to successful
testing of a heat exchanger with a heat transfer of nearly 1 gigawatt per m**3, well within the required performance of the Sabre precooler. This work has been extended with the successful manufacture of tubes in Inconel 718 which have 0.88 mm bore and
40 m wall thickness which ensures good heat exchange properties without compromising physical strength. The tubes have been successfully creep tested at 200 bar and 720 °C and also for oxidation for 1800 hours. The other key technology is the method of brazing the fine tubes into the feeder headers which has also been successfully demonstrated. The Precooler is designed to cool the engine airflow (about 400kg/s) from intake recovered conditions (up to 1000°C at Mach 5) down to about -140°C prior to compression.

STERN Engine Tests

Project STERN (Static Test Expansion deflection Rocket Nozzle) also received funding.

The objective of the test programme was to explore the flow stability and behaviour in an unusual rocket nozzle known as an Expansion Deflection Nozzle. In theory these should allow very large expansion nozzles suitable for operating in the vacuum of space to also perform stably and efficiently within an atmosphere. If so, then the performance of single stage to orbit launch vehicles like Skylon could be significantly improved.

Dr Taylor said: “Test programmes like this usually take years and costs hundreds of thousands of pounds, but we’ve done this in 18 months and on a relative shoestring, the whole team has done a really good job but the guys from Airborne Engineering who designed, manufactured and assembled the test rig have worked near miracles.

The STERN engine burns hydrogen and air, the same as Skylon’s Sabre engines when in air breathing mode. To maximise the engine’s life the test firings were held below the engine design values with measured thrust between 1500 and 2000 Newtons (1/5 tonne). Each firing was restricted to less than a second, as any longer and the (un-cooled) chamber walls could start to melt. This still provided sufficient time for the flow to stabilise, and all the required data to be obtained.

The initial results have confirmed that the flow within Expansion Deflection nozzles is stable across a very wide range of pressure ratios. In addition, broad agreement with computer simulations of their behaviour has also been achieved.


Static Test Rocket Incorporating Cooled Thrust Chamber (STRICT)

Project STRICT is the follow on to Project STERN. This engine will be water cooled so that it can be run continuously - The STERN engine can only be fired for short durations. The objective of Project STRICT is to explore the stability of the exhaust flow and the heat input to the engine walls. Formal planning for Project STRICT started in the latter half of 2008.

The STRICT engine's design features are still being established, but its propellants and thrust level are likely to be similar to the STERN engine. The nozzle type is also the subject of a series of cold flow tests before a decision is made on whether to have an ED nozzle or a dual bell nozzle.


Contra-rotating Turbine for the Scimitar Precooled Mach 5 Cruise Engine

Design and Testing of the Contra-rotating Turbine for the Scimitar Precooled Mach 5 Cruise Engine



Contra rotating turbines can reduce mass and increase efficiency when the speed of sound in the turbine working fluid is significantly greater than the compressor. A four stage contra rotating turbine has been designed for the Scimitar Mach 5 cruise engine which employs high pressure helium in the power loop. The turbine aerodynamics were optimised by a genetic algorithm supported by CFD and FEM analysis. A full linear scale contra-rotating turbine rig has been designed and built which operates with reduced inlet temperature and pressure and a high molecular weight working fluid (argon). The rig generates 0.5% of the full scale turbine power whilst the flow Reynolds numbers are about 30% of full scale. The Reaction Engines B9 test facility has been modified to supply up to 12kg/s of gaseous argon at 5 bar and 350K to enable blowdown runs of about 5 minutes duration. Turbine testing was scheduled to start in September 2008.


Old C Design Specs and New D Design

The technology programs carried out over the last two decades have shown that the technology assumptions in the HOTOL/Skylon projects are achievable. In many cases experimental investigation has led to further development in new areas so that greater performance may be available when the final design for Skylon is undertaken.

This extra performance can be used to both increase the system margins reducing the technical risk and increase the performance, with consequent reduction in the specific launch costs.


Skylon C specs are above

The next stage is a final set of research projects with substantiall increased funding and a wider range of industrial partners. This will give high confidence in the technology assumptions used in the final design. Skylon configuration C1 is a relatively old design and work is underway to incorporate various improvements into a new baseline; configuration D.

An update on the 8th of December, 2008 revealed that the Skylon concept design is being reworked to take it from the configuration C1 to configuration D1.

The new D1 vehicle will be slightly bigger, with a 25% increase in payload mass (from 12 tons to 15 tons to LEO). The payload bay is being resized and there is a revision to the mounting provisions and other payload support features. The new configuration will include the result of a number of technology development programmes almost certainly including an Expansion Deflection Nozzle in the Sabre Engine following the successful STERN Engine test programme.

A follow on project called STRICT (Static Test Rocket Incorporating Cooled Thrust-chamber) will be started in early 2009. This engine will be water cooled allowing extended firing runs (STERN is limited to half a second) and explore heat transfer within the nozzle.

A competitive advantage lies with the Sabre airbreathing engine technology combined with the Skylon optimised airframe. A Hybrid Airbreathing / Rocket Engine, Sabre Represents a Huge Advance over LACE Technology. The design of Sabre evolved from liquid-air cycle engines (LACE) which have a single rocket combustion chamber with associated pumps, preburner and nozzle which are utilised in both modes. LACE engines employ the cooling capacity of the cryogenic liquid hydrogen fuel to liquefy incoming air prior to pumping. Unfortunately, this type of cycle necessitates very high fuel flow.


Cost to Orbit

The Skylon vehicle has been designed with the aim of achieving not less than 200 flights per vehicle. This seems a reasonable target for a first generation machine. Various scenarios have been examined but the uncertainty lies with assumptions on traffic growth.

At present the true launch cost of a typical 2-3 tonne spacecraft is about $150 million. Actual costs paid by customers vary from about one-third to one half of this due to the hidden subsidies on vehicle development, range maintenance, range activity and support infrastructure. For Skylon, if no growth occurred and all operators flew equal numbers of the current approximately 100 satellites per year using 30 in-service spaceplanes from 3 spaceports, the true launch cost would be about $40 million per flight [$1200/lb to LEO].

They expect mission costs to fall to about $10 million per launch for high product value cargo (e.g. communications satellites) $2-5 million for low product value cargo (e.g. science satellites) and for costs per passenger to fall below $100k, for tourists when orbital facilities exist to accommodate them.

As high volume flights are performed the 15 ton payload to LEO orbit would be $2-10 million per launch which would be $66/lb to $330/lb.


Efficient Hydrogen fuel with the Skylon design could achieve 2000-3000 ISP. 4 to 7 times better than most chemical rockets.

Rotovator tether systems or laser arrays could make the Mach 8+ segment of getting into orbit more efficient and cheaper.



High Volume Mission: A Lot of Solar Space Power

Reaction Engines (REL) has revised, updated and completed a new business plan for 2009. The tube for the Micro-Defect Detector has also arrived for commissioning.

REL has also recently completed an internally funded study into the launch aspects of Solar Power Satellites using Skylon. A solar power satellite (SPS) collects sunlight and transforms it into electrical energy. This is electromagnetically beamed back to Earth where it is collected by a large array of receivers for conversion to electricity.

Unlike conventional renewable energy (wind, wave) SPS is scalable to very high power levels (>5Gw) and can provide baseload power (load factor >90%). Although first proposed in 1968 the idea has not been implemented due mainly to the very high cost of current expendable launchers. However the report shows that the low cost, high reliability and rapid turnaround characteristics of Skylon would overcome this problem. The launch cost would be reduced by a factor of 50-100 compared to today's expendable launchers and about 5 compared to reusable TSTO rockets.


FURTHER READING
Analysis by Rocketeers UK
Reaction Engines is making encouraging progress in e.g, heat exchanger development, but they are still some way away from an "all-up" engine test. I have some significant fear that Reaction Engines will reach a critical point in their development where they have a more-or-less working test engine, and will say "we need x billion to develop a flying vehicle" and the funding agencies will turn round and say "no". Development of the Skylon as proposed is an "all or nothing" proposition... the existence of intermediate products which can themselves make commercial profits is... unclear at the moment.

Development of the Skylon is fighting entrenched interests in ESA for support of Arianespace and existing expendable launchers.

I have concerns that companies purely reliant on a succession of research grant funding from a small number of agencies are inherently vulnerable to changes in bureaucratic climate. The primary "product" of Reaction Engines is test data and engineering R&D reports. The primary product of XCOR and Armadillo is fully working propulsion systems that customers can install and use in their own vehicles. UK NewSpace companies need tangible product that they can sell to paying customers NOW (not in ten years' time), and then reinvest the sales profits in developing new systems.

In some ways, the Bristol Spaceplanes/David Ashford solution of a two-stage winged RLV is "better" in that it affords more intermediate stages which can be monetized before developing a full-scale orbital RLV. The operability and performance may be somewhat lower, but the technical hurdles are also significantly lower (some questions remain about e.g. vehicle separation at supersonic/hypersonic speeds). However, Bristol Spaceplanes doesn't even have the resources to cross the first hurdle (the Ascender suborbital spaceplane) which IMO is desperately sad.

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