Skylon (spacecraft)

Skylon has its origins within a previous space development programme for an envisioned single-stage-to-orbit (SSTO) spaceplane, known as HOTOL.{{cite web |url=http://www.reactionengines.co.uk/bkgrnd.html |title=Reaction Engines Ltd : Company Background |publisher=Reaction Engines Ltd |access-date=25 September 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100808065903/http://www.reactionengines.co.uk/bkgrnd.html |archive-date=8 August 2010}} In 1982, when work commenced on the HOTOL by several British companies, there was significant international interest to develop and produce viable reusable launch systems, perhaps the most high-profile of these being the NASA-operated Space Shuttle. In conjunction with British Aerospace and Rolls-Royce, a promising design emerged to which the British government contributed £2 million towards its refinement; British engineer Alan Bond was amongst the engineers who worked on HOTOL. However, during 1988, the British government decided to withdraw further funding from the programme, resulting in development work being terminated. Aerospace publication Flight International observed that HOTOL and other competing spaceplane programmes were "over-ambitious" and that development on such launch systems would involve more research and slower progress than previously envisioned.{{cite web |url=https://www.flightglobal.com/news/articles/slow-road-to-reusability-60469/ |title=Slow road to reusability |work=Flight International |date=1 January 2000 |via=FlightGlobal.com}}

File:HOTOL.JPG project.]]

Following the setback of HOTOL's cancellation, in 1989 Alan Bond, along with John Scott-Scott and Richard Varvill decided to establish their own company, Reaction Engines Limited,{{cite web |title=Story so far |publisher=Reaction Engines Ltd |url=https://www.reactionengines.co.uk/aboutus/background/ |access-date=18 September 2017 |archive-url= https://web.archive.org/web/20170912055249/https://www.reactionengines.co.uk/aboutus/background/ |archive-date=12 September 2017 |url-status=dead}} to pursue the development of a viable spaceplane and associated technology using private funding. In 1993, Reaction publicly revealed its spaceplane proposal,{{sfn|Varvill|Bond|1993}} which it named Skylon after the Skylon structure that had inspired Alan Bond at the Festival of Britain exhibition. Skylon was a clean sheet redesign based on lessons learned during development of HOTOL, the new concept again utilised dual-mode propulsion system, using engines that could combust hydrogen with the external air during atmospheric flight.

Early on, Skylon was promoted by the company to the ESA for its Future European Space Transportation Investigations Programme (FESTIP) initiative, as well as seeking out both government or commercial investment in order to finance the vehicle's development. Reaction has also sought to form ties with other companies with the aim of producing an international consortium of interested firms to participate in the Skylon programme.{{cite web |title= Reusable Launch Vehicle Programs and Concepts. |publisher= Associate Administrator for Commercial Space Transportation (AST) |date= January 1998 |url= http://www.spacelaw.olemiss.edu/library/space/US/Executive/FAA/AST/1998rlv.pdf |access-date= 18 September 2017 |archive-url= https://web.archive.org/web/20170827062429/http://www.spacelaw.olemiss.edu/library/space/US/Executive/FAA/AST/1998rlv.pdf |archive-date= 27 August 2017 |url-status= dead}}

The Skylon design features several distinct differences when compared with the earlier HOTOL program.{{sfn|Hempsell|Longstaff|2009|p=4}} Whereas HOTOL would have launched from a rocket sled as a weight-saving measure, Skylon is to be equipped with conventional retractable undercarriage. The revised engine design, using the SABRE engine, is expected to offer higher performance than its predecessor.{{sfn|Hempsell|Longstaff|2009|p=4}} The rear mounted engine of HOTOL meant that the vehicle possessed intrinsically poor in-flight stability; early attempts to resolve this problem had ended up sacrificing much of HOTOL's payload potential, which in turn contributed to the failure of the overall project. Skylon's solution to the issue was to position its engines at the end of its wings, which located them further forward and much closer to the vehicle's longitudinal centre of mass, thereby resolving the instability problem.{{sfn|Hempsell|Longstaff|2009|p=11}}

File:Skylon climbing.jpg

Reaction intends ultimately to operate as a for-profit commercial enterprise which, upon the completion of development, shall manufacture Skylon vehicles for multiple international customers who shall operate their fleets directly, while being provided with support from Reaction. Skylon has been designed with the target of achieving no less than 200 flights per vehicle. According to the company, its business plan is to sell vehicles for $1 billion each, for which it has forecast a market for at least 30 Skylons, while recurring costs of just $10 million per flight are predicted to be incurred by operators. While the Reaction intends to manufacture some components directly, such as the engine precooler, other components have been designed by partner companies and a consortium of various aerospace firms is expected to handle full production of Skylon.{{cite interview |subject= Mark Hempsell |interviewer= Dr David M. Livingston |url= http://thespaceshow.com/show/06-aug-2009/broadcast-1203-special-edition |title=Broadcast 1203 |publisher=The Space Show |date=6 August 2009}}

In service, Skylon could potentially lower the cost of launching satellites which, according to evidence submitted to the UK parliament by Reaction, is forecast to be around £650/kg; as of 2011, the average launch cost using conventional methods was estimated to be roughly £15,000/kg. Amongst other prospective operations, Skylon would be capable of transporting payloads of up to 10-tonnes to the International Space Station.{{cite web |last=Thisdell |first=Dan |url=https://www.flightglobal.com/news/articles/skylon-concept-could-be-next-spaceplane-357546/ |title=Skylon concept could be next spaceplane |work=Flight International |date=14 June 2011 |via=FlightGlobal.com |archive-url=https://web.archive.org/web/20170119064916/https://www.flightglobal.com/news/articles/skylon-concept-could-be-next-spaceplane-357546/ |archive-date=19 January 2017}} Reaction has also completed internal studies into the use of Skylon as a launch platform for a network of space-based solar power satellites, which have been historically unfeasible due to high launch costs.

Speaking in June 2011, Reaction estimated that it would require ultimately $12 billion to achieve an operational configuration, which was then estimated to be achieved around 2020, dependent on funding. The obtaining of additional financing for the Skylon programme from the British government has often been difficult.{{sfn|House of Commons Science and Technology Committee|2007|p=262}} During 2000, Reaction issued an ultimately unsuccessful request for funding from the British government; according to the government, Reaction's proposal had involved an offer of a potentially large return on its investment.{{cite web |url=https://publications.parliament.uk/pa/cm199900/cmselect/cmtrdind/335/335ap32.htm |title=Memorandum submitted by the Association of Aerospace Universities |date=2000 |publisher=Parliament of the United Kingdom}} However, several officials have emerged as proponents and advocated for the official backing of the Skylon programme. Speaking in 2009, the former UK Minister for Science and Innovation, Lord Drayson, stated of Reaction: "This is an example of a British company developing world-beating technology with exciting consequences for the future of space."

During February 2009, following on from a series of extended discussions with the British National Space Centre (which later became the UK Space Agency), it was announced that a major funding agreement had been established between the British National Space Centre, ESA and Reaction, committing €1 million ($1.28 million) for the purpose of producing a demonstration engine for the Skylon programme by 2011.{{cite web |url=https://www.flightglobal.com/news/articles/skylon-spaceplane-engine-technology-gets-european-fu-322765/ |title=Skylon spaceplane engine technology gets European funding |date= 19 February 2009 |first= Rob |last= Coppinger |via=FlightGlobal.com |work=Flight International}}{{cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/7898434.stm |title=Skylon spaceplane gets cash boost |author=Jonathan Amos |work=BBC News |date=19 February 2009}}{{cite web |url=http://www.space.com/businesstechnology/090311-tw-space-plane.html |title=British Space Plane Concept Gets Boost |date=March 11, 2009 |author=Jeremy Hsu |work=Space.com}} The initiative, known as the Technology Demonstration Programme, was scheduled to last approximately 2.5 years, during which further financing in the form of €1 million was made available by ESA.{{cite web |url=http://www.rocketeers.co.uk/node/706 |title= Rockets and Skylon|date=2009 |work=20 Years Since HOTOL: Reaction Engines Ltd and SKYLON |publisher=UK Rocketeers |access-date=1 October 2010}} The 2009 agreement allowed Reaction to involve several external companies, including EADS-owned Astrium, the University of Bristol and the German Aerospace Center (DLR), in further development work. As a consequence of the enactment of the Technology Demonstration Programme, Reaction was able to transition from a Technology Readiness Level (TRL) of 2/3 up to 4/5 within a matter of months.{{cite web |url=http://www.parabolicarc.com/2009/08/26/reaction-engines-celebrates-20-years-success-skylon/ |title=Reaction Engines Celebrates 20 Years, Looks Forward to Success with Skylon |publisher=Parabolic Arc |date=26 August 2009}}

By 2012, according to the UK Space Agency, the funding required to develop and construct the entire craft has not yet been secured; as such, research and development work was at that point mainly focused on the engines alone, which was supported by an ESA grant of €1 million.{{cite web |title=The rocket that thinks it's a jet |date=February 19, 2009 |website=Phys.org |url=https://phys.org/news/2009-02-rocket-jet.html#:~:text=The%20SABRE%20is%20a%20unique,rocket%20engine%20when%20in%20space. |access-date=2020-11-13}} In January 2011, Reaction submitted a proposal to the British Government requesting additional funding for the Skylon project. On 13 April 2011, Reaction announced that the design of the Skylon had passed several rigorous independent reviews. On 24 May 2011, ESA publicly declared the design to be feasible, having found "no impediments or critical items" to be present in the proposal.{{cite web |last=Page |first=Lewis |title=ESA: British Skylon spaceplane seems perfectly possible |url=https://www.theregister.co.uk/2011/05/24/skylon_esa_report/ |work=The Register |date=24 May 2011}}Emspak, Jesse. [https://www.theverge.com/2016/3/8/11174670/rel-skylon-spaceplane-announced-jet-engine-rocket-propulsion "REL’s Skylon spaceplane aims to take on SpaceX with a reusable rocket design."] theverge.com, 8 March 2016. Speaking on the topic of Skylon in 2011, David Willetts, the UK Minister of State for Universities and Science, stated:

{{blockquote|The European Space Agency is funding proof of concept work for Skylon from UK contributions. This work is focusing on demonstrating the viability of the advanced British engine technology that would underpin the project. Initial work will be completed in mid 2011 and if the trial is successful, we will work with industry to consider next steps.}}

In June 2013, George Osborne, then Chancellor of the Exchequer, stated that the British government would be giving £60 million towards the further development of the SABRE engine.[https://twitter.com/George_Osborne/statuses/350253608115240961 "@George_Osborne"]. Twitter, 27 June 2013. The grant was contingent upon Reaction having an industrial partner. The first grant of £50 million was approved by the European Commission in August 2015.{{cite press release |date=14 August 2015 |url=http://europa.eu/rapid/press-release_IP-15-5495_en.htm |title=State aid: Commission approves £50 million UK support for the research and development of an innovative space launcher engine |publisher=European Commission}}

In October 2015, British defence conglomerate BAE Systems entered into an agreement with Reaction Engines, under which it would invest £20.6 million in Reaction to acquire 20% of its share capital, as well as to provide assistance in the development of the SABRE engine.{{cite news |url=http://aviationweek.com/technology/bae-takes-stake-reaction-engines-hypersonic-development |title=BAE Takes Stake in Reaction Engines Hypersonic Development |last1=Norris |first1=Guy |date=1 November 2015 |website=aviationweek.com |publisher=Aviation Week & Space Technology}}{{cite news |last1=Hollinger |first1=Peggy |last2=Cookson |first2=Clive |url=https://www.cnbc.com/2015/11/02/bae-systems-to-pay-206m-for-20-of-space-engine-group.html |title=BAE Systems to pay £20.6m for 20% of space engine group |work=CNBC |date=2 November 2015}}

In July 2016, the second grant of £10 million was approved by ESA.{{cite press release |author= |title= Reaction Engines secures funding to enable development of SABRE demonstrator engine |publisher= Reaction Engines Ltd |location= Cullham Science Centre, United Kingdom |url= https://www.reactionengines.co.uk/reaction-engines-secures-funding-to-enable-development-of-sabre-demonstrator-engine/ |access-date= 18 September 2017 |url-status= dead |archive-url= https://web.archive.org/web/20170320115534/https://www.reactionengines.co.uk/reaction-engines-secures-funding-to-enable-development-of-sabre-demonstrator-engine/ |archive-date= 20 March 2017}}

In September 2017, it was announced that the U.S. Defense Advanced Research Projects Agency (DARPA) had awarded a contract to Reaction Engines for an undisclosed amount to conduct high-temperature airflow testing at a Colorado, United States site of a Reaction Engines precooler called HTX. Testing work is scheduled to start in 2018.{{Cite web |url=https://www.reactionengines.co.uk/reaction-engines-awarded-darpa-contract-to-perform-high-temperature-testing-of-the-sabre-precooler/ |title=Reaction Engines Awarded DARPA Contract to Perform High-Temperature Testing of the SABRE Precooler |date=September 25, 2017 |publisher=Reaction Engines Ltd |access-date=30 January 2019 |url-status=dead |archive-url= https://web.archive.org/web/20170928232712/https://www.reactionengines.co.uk/reaction-engines-awarded-darpa-contract-to-perform-high-temperature-testing-of-the-sabre-precooler/ |archive-date=28 September 2017}}

In April 2018, Reaction Engines announced Boeing and Rolls-Royce would be joining BAE Systems as investors in the development of the SABRE engine. A total of $37.5 million of new funding is to be provided including contributions from Baillie Gifford Asset Management and Woodford Investment Management.{{cite web |title=Boeing, Rolls-Royce Back Reaction Hypersonic Engine Developer |date=April 11, 2018 |work=Aviation Week |url=http://aviationweek.com/defense/boeing-rolls-royce-back-reaction-hypersonic-engine-developer?NL=AW-05&Issue=AW-05_20180412_AW-05_974&sfvc4enews=42&cl=article_2&elq2=dec1a870a6ce48d088046561c44e0eac}}

File:Precooler Rig.jpg engine.]]

In 2000, the firm completed work with University of Bristol testing the precooler.Wang, Brian. [https://www.nextbigfuture.com/2009/01/progress-to-skylon-single-stage-to.html "Progress to the Skylon Single Stage to Orbit Spaceplane for 2019."] Next Big Future, 31 January 2009.

From 2007 to 2009 Reaction worked with University of Bristol and Airborne Engineering on Project STERN (Static Test Expansion/Deflection Rocket Nozzle), which tested Reaction's engine ignition system, a Reaction designed air breathing hydrogen rocket engine, and investigated the flow stability and behaviour of Dr Neil Taylor's expansion deflection nozzle design via multiple test-firings by Airborne Engineering. An expansion deflection nozzle is capable of compensating for the changing ambient pressure encountered while gaining altitude during atmospheric flight, thus generating greater thrust and thereby efficiency.{{cite web |url= http://www.projectstern.co.uk/projectstern.html |title= Project STERN |author= |publisher= Reaction Engines Ltd |url-status= dead |archive-url= https://web.archive.org/web/20120508133220/http://www.projectstern.co.uk/projectstern.html |archive-date= 8 May 2012}}

Work on STERN was continued in project STRICT (Static Test Rocket Incorporating Cooled Thrust-chamber), which investigated the stability of the engine's exhaust flow and the dissipation of the generated heat into the engine walls. The results and designs delivered by both the STRICT and STERN projects were subsequently declared by Reaction to have been "a great success".{{cite web |url=http://www.reactionengines.co.uk/sternstrict.html |title=Reaction Engines Ltd : Projects STERN and STRICT |publisher=Reaction Engines Ltd |access-date=25 September 2010 |archive-url= https://web.archive.org/web/20100814010821/http://www.reactionengines.co.uk/sternstrict.html |archive-date=14 August 2010 |url-status=dead}}

Static testing of the engine precooler began in June 2011, marking the start of Phase 3 in the Skylon development programme,{{cite web|title=Written evidence from Reaction Engines Limited|publisher=UK Parliament|work=Rebalancing the Economy: Trade and Investment – Business, Innovation and Skills Committee |url=https://publications.parliament.uk/pa/cm201011/cmselect/cmbis/writev/735/73522.htm |date=January 2011|access-date=27 January 2011 |url-status=dead |archive-url= https://web.archive.org/web/20160202045347/http://www.publications.parliament.uk/pa/cm201011/cmselect/cmbis/writev/735/73522.htm |archive-date=2 February 2016}}{{cite web |url=http://www.flightglobal.com/news/articles/spaceplane-engine-tests-under-way-361501/ |title=Spaceplane engine tests under way |first=Dan |last=Thisdell |date=1 September 2011 |work=Flight International |via=FlightGlobal.com}}{{cite web |url=http://www.space.com/11414-skylon-space-plane-british-engine-test.html |title=Big Test Looms for British Space Plane Concept |author=Mike Wall |date=April 18, 2011 |work=Space.com |access-date=18 April 2011}} In April 2012, Reaction announced that the first series of the precooler test programme had been successfully completed.{{cite news | url = https://www.bbc.co.uk/news/science-environment-17864782 | title = Key tests for Skylon spaceplane project | work=BBC News | date=27 April 2012}} On 10 July 2012, Reaction announced that the second of three series of tests has been completed successfully, and the final series of tests would begin the following month after the testing facilities had been upgraded to allow testing of {{convert|-150|C|F}} temperatures.{{cite press release |title=MAJOR ADVANCE TOWARDS THE NEXT JET ENGINE |url=http://www.reactionengines.co.uk/press_release/MAJOR%20ADVANCE%20TOWARDS%20THE%20NEXT%20JET%20ENGINE%20-%20PRESS%20RELEASE%20-%2010%20JULY%202012.pdf |publisher=Reaction Engines Ltd |date=10 July 2012 |archive-url=https://web.archive.org/web/20120813043006/https://www.reactionengines.co.uk/press_release/MAJOR%20ADVANCE%20TOWARDS%20THE%20NEXT%20JET%20ENGINE%20-%20PRESS%20RELEASE%20-%2010%20JULY%202012.pdf |archive-date=13 August 2012 |url-status=dead}}{{cite news |title=Move to open sky for Skylon spaceplane| url=https://www.bbc.co.uk/news/science-environment-18784866 |work=BBC News |date=11 July 2012}} ESA's propulsion division audited the precooler tests during mid-2012 and found the results satisfactory.{{cite news |date=28 November 2012 |title=Skylon spaceplane engine concept achieves key milestone |url=https://www.bbc.co.uk/news/science-environment-20510112 |access-date=28 November 2012 |work=BBC News}}{{cite web |first= Ian |last= Thomson |url=https://www.theregister.co.uk/2012/11/29/esa_sabre_clearance |title=European Space Agency clears SABRE orbital engines |website=The Register |date=29 November 2012}}

In 2011, Reaction stated that a preproduction prototype of the Skylon could be flying by 2016, and the proposed route would be a suborbital flight between the Guiana Space Centre near Kourou in French Guiana and the North European Aerospace Test Range, located in northern Sweden.{{cite web |url=http://www.rocketeers.co.uk/node/1375 |title=Skylon Phase 3 Development: Q&A |publisher=Rocketeers.co.uk |date=9 May 2011 |access-date=3 December 2012}} Pre-orders were expected in the 2011–2013 timeframe, coinciding with the formation of the manufacturing consortium. In December 2011, Alan Bond stated that Skylon would enter into service by 2021–2022 instead of 2020 as previously envisaged.{{sfn|Bond|2011}} In July 2012, ESA Director-General Jean-Jacques Dordain publicly stated that the ESA would be holding a series of talks with Reaction with the aim of developing a further "technical understanding".{{cite web |url=http://www.spacenews.com/launch/120713-europe-rocket-design-finalist.html |archive-url=https://archive.today/20130208191517/http://www.spacenews.com/launch/120713-europe-rocket-design-finalist.html |url-status=dead |archive-date=8 February 2013 |title=Europe's Next-gen Rocket Design Competition Had Surprise Bidder |publisher=Space News |date=13 July 2012}}

{{update after|2015}}

In November 2012, Reaction announced that it would commence work upon a three-and-a-half-year project to develop and build a test rig of the SABRE engine to prove its performance across both the air-breathing and rocket modes. Reaction's precooler was tested in 2022{{cite web |title=Reaction begins testing Mach 4 jet engine upgrades for US Air Force |url=https://newatlas.com/aircraft/reaction-engines-high-mach/ |website=NewAtlas |access-date=8 November 2022 |ref=July2022Test}} and 2024.{{Cite web |date=2024-08-15 |title=Reaction Engines achieves ground-breaking hypersonic propulsion system milestone |url=https://defence-industry.eu/reaction-engines-achieves-ground-breaking-hypersonic-propulsion-system-milestone/ |access-date=2025-02-28 |website=Defence Industry Europe |language=en}} Work ceased later in 2024, when the company entered administration.{{Cite web |last=Kleinman |first=Mark |date=31 October 2024 |title=British aviation pioneer Reaction Engines crashes into administration |url=https://news.sky.com/story/british-aviation-pioneer-reaction-engines-crashes-into-administration-13245418 |access-date=2025-02-28 |website=Sky News |language=en}}

{{See also|Single-stage-to-orbit}}

The Skylon is a fully reusable SSTO vehicle, able to achieve orbit without staging, which is intended to be used principally as a reusable launch system.{{sfn|Varvill|Bond|2003|p=108}} Proponents of the SSTO approach have often claimed that staging involves a number of inherent complications and problems due to complexity, such as being difficult or typically impossible to recover and reuse most elements, thus unavoidably incurring great expense to produce entirely new launch vehicles instead; therefore, they believe that SSTO designs hold the promise of providing a reduction to the high cost of space flights.{{sfn|Varvill|Bond|2003|p=108}} Operationally, it is envisioned for the non-crewed Skylon to take off from a specially strengthened runway, gain altitude in a fashion akin to a conventional aeroplane and perform an ascent at very high speeds, in excess of five times the speed of sound ({{cvt|3800|mph|order=flip|disp=or}}), to attain a peak air-breathing altitude of roughly {{convert|92,000|ft|km|order=flip}}, where payloads would typically be launched prior to the vehicle's re-entry into the atmosphere, upon which it will conduct a relatively gentle descent before performing a traditional landing upon a runway.{{sfn|Hempsell|Longstaff|2009|p=5}}

File:Skylon colour.svg is designed as a two-engine, "tailless" aircraft, which is fitted with a steerable canard.]]

The design of the Skylon D1 features a large cylindrical payload bay, {{convert|13|m|ftin|abbr=on}} long and {{convert|4.8|m|ftin|abbr=on}} in diameter.{{sfn|Hempsell|Longstaff|2014|p=13}} It is designed to be comparable with current payload dimensions, and able to support the containerisation of payloads that Reaction Engines envisions being produced in the future. To an equatorial orbit, Skylon could deliver {{convert|15|t|lb|abbr=on}} to a {{convert|300|km|nmi|abbr=on}} altitude or {{convert|11|t|lb|abbr=on}} to a {{convert|600|km|nmi|abbr=on}} altitude.{{sfn|Hempsell|Longstaff|2014|p=9}} Using interchangeable payload containers, Skylon could be fitted to carry satellites or fluid cargo into orbit, or, in a specialised habitation module, the latter being capable of housing a maximum of 30 astronauts during a single launch.{{cite web |url=http://www.reactionengines.co.uk/skylon_pax.html |title=Reaction Engines Ltd : Current Projects : SKYLON – Passenger Capability |publisher=Reaction Engines Ltd |access-date=25 September 2010 |archive-url= https://web.archive.org/web/20120615150211/http://www.reactionengines.co.uk/skylon_pax.html |archive-date=15 June 2012 |url-status=dead}}{{sfn|Scott-Scott|Harrison|Woodrow|2003}} Richard Varvill, technical director at Reaction, stated of Reaction's market: "we're competing with expendable rockets, a machine that is only used once".

Because the SABRE engine uses the atmosphere as reaction mass at low altitude, it will have a high specific impulse (around {{convert|40000|-|90000|Ns/kg|isp|order=flip}} for SABRE 4,{{sfn|Hempsell|Longstaff|2014|p=6}} or {{convert|35000|Ns/kg|isp|order=flip}} for SABRE 3,{{sfn|Hempsell|Longstaff|2009|p=3}}) and burn about one fifth of the propellant that would have been required by a conventional rocket. Therefore, Skylon would be able to take off with much less total propellant than conventional systems. The weight reduction enabled by the lower quantity of propellant needed meant that the vehicle would not require as much lift or thrust, which in turn permits the use of smaller engines and allows for the use of a conventional wing configuration. While flying within the atmosphere, the use of wings to counteract gravity drag is more fuel-efficient than simply expelling propellant (as in a rocket), which again serves to reduce the total amount of propellant needed. The payload fraction would be significantly greater than normal rockets and the vehicle should be fully reusable, capable of performing in excess of 200 launches.{{sfn|Varvill|Bond|2004|p=22}}

{{Main|SABRE (rocket engine)}}

File:SABRE engine designed for Skylon spaceplane, 1990s. (9660572897).jpg

One of the most significant features of the Skylon's design is its powerplant, known as Synergetic Air-Breathing Rocket Engine (SABRE).{{cite web |url=http://www.reactionengines.co.uk/techdemprog.html |title=Reaction Engines Limited : Technology Demonstration Programme |publisher=Reaction Engines Ltd |access-date=25 September 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100216153020/http://www.reactionengines.co.uk/techdemprog.html |archive-date=16 February 2010}} The design of the SABRE engine has drawn heavily upon the STRICT/STERN experimental engines, sharing many features such as the propellant and the adoption of the trialled Expansion Deflection Nozzle, as well as building upon the wider field of liquid air cycle engines (LACE).{{sfn|Hempsell|Longstaff|2009|p=4}} The engines are designed to operate much like a conventional jet engine to around {{convert|5.5|Mach|kph mph}},{{cite web | url =http://www.reactionengines.co.uk/sabre.html | title =SABRE engine | date = 2010| publisher =Reaction Engines Ltd}} {{convert|26|km|ft|0}} altitude, beyond which the air inlet closes and the engine operates as a highly efficient rocket to orbital speed. The proposed SABRE engine is not a scramjet, but a jet engine running combined cycles of a precooled jet engine, rocket engine and ramjet. Originally the key technology for this type of precooled jet engine did not exist, as it required a heat exchanger that was ten times lighter than the state of the art. Research conducted since then has achieved the necessary performance.{{sfn|Hempsell|Longstaff|2009|p=4}}{{cite news| url=https://www.bbc.co.uk/news/science-environment-17867586 | work=BBC News | title=Revolutionary space engine system for Skylon tested | date=27 April 2012}}

Operating an air-breathing jet engine at velocities of up to Mach 5.5 poses numerous engineering problems; several previous engines proposed by other designers have worked well as jet engines, but performed poorly as rockets. This engine design aims to be a good jet engine within the atmosphere, as well as being an excellent rocket engine outside; however, the conventional problem posed by operating at Mach 5.5 has been that the air coming into the engine rapidly heats up as it is compressed into the engine; due to certain thermodynamic effects, this greatly reduces the thrust that can be produced by burning fuel. Attempts to avoid these issues have typically resulted in the engine being much heavier (scramjets/ramjets) or has greatly reduced the thrust generated (conventional turbojets/ramjets); in either of these scenarios, the end result would be an engine that possesses a poor thrust to weight ratio at high speeds, which in turn would be too heavy to assist much in reaching orbit.

The SABRE engine design aims to avoid the historic weight-performance issue by using some of the liquid hydrogen fuel to cool helium within a closed-cycle precooler, which quickly reduces the temperature of the air at the inlet. The air is then used for combustion in a similar manner to a conventional jet engine. Once the helium has left the pre-cooler it is further heated by the products of the pre-burner giving it enough energy to drive the turbine and the liquid hydrogen pump. As a consequence of the air being cooled at all speeds, the jet can be built of light alloys and the weight is roughly halved. Additionally, more fuel can be burnt at high speeds. Beyond Mach 5.5, the air would normally become unusably hot despite the cooling; accordingly, the air inlet is closed upon attaining this speed and the engine instead is solely fed via on-board liquid oxygen and hydrogen fuel, as in a traditional rocket.

File:Skylon-réservoirs.png

The currently proposed Skylon model D1 is a large vehicle, possessing a length of {{convert|272|ft|9|in|m|order=flip}} and a diameter of {{convert|20|ft|8|in|m|order=flip}}.{{cite web |url=http://www.reactionengines.co.uk/skylon_vehicle.html |title=Reaction Engines Ltd : Current Projects : SKYLON – The Vehicle |publisher=Reaction Engines Ltd |access-date=25 September 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100715054918/http://www.reactionengines.co.uk/skylon_vehicle.html |archive-date=15 July 2010}} The fuselage of the Skylon is expected to be a silicon carbide reinforced titanium space frame;{{sfn|Davies|Hempsell|Varville|2015|p=8}} a light and strong structure that supports the weight of the aluminium fuel tanks and to which the ceramic skin is attached.{{sfn|Hempsell|Longstaff|2009|p=11}} Multiple layers of titanium foil thermal insulation are sandwiched between the skin and frame{{sfn|Hempsell|Longstaff|2009|p=15}} to protect the inside of Skylon from the heat of hypersonic flight and the intense heat of re-entry.

Due to the vehicle's use of a low-density fuel in the form of liquid hydrogen, a great volume is required to contain enough energy to reach orbit. The propellant is intended to be kept at low pressure to minimise stress; a vehicle that is both large and light has an advantage during atmospheric reentry compared to other vehicles due to a low ballistic coefficient.{{sfn|Hempsell|Longstaff|2009|p=7}} Because of the low ballistic coefficient, Skylon would be slowed at higher altitudes where the air is thinner; as a consequence, the skin of the vehicle would reach only {{cvt|1100|K|C F|order=out}}.{{sfn|Varvill|Bond|2004|p=25}}{{cite report |quote=During re-entry the temperature is kept down to {{cvt|1100|K|C F|-2}} by dynamically controlling the trajectory via active feedback of measured skin temperatures. This is possible by virtue of the low ballistic coefficient and the controllability of a lifting vehicle with active foreplanes. |title=Skylon Assessment Report |publisher=European Space Agency |year=2011 |url=http://knts.tsniimash.ru/ru/src/CenterInfRes/Skylon%20Assessment%20Report.pdf |archive-url= https://web.archive.org/web/20161026075919/http://knts.tsniimash.ru/ru/src/CenterInfRes/Skylon%20Assessment%20Report.pdf |archive-date=2016-10-26 |url-status=dead}} In contrast, the smaller Space Shuttle was heated to {{cvt|2,000|K|C F|order=out}} on its leading edge, and so employed an extremely heat-resistant but fragile silica thermal protection system. The Skylon design does not require such an approach, instead opting for using a far thinner yet durable reinforced ceramic skin; however, due to turbulent flow around the wings during re-entry, some sections of the vehicle shall need to be provided with active cooling systems.{{sfn|Hempsell|Longstaff|2009|p=15}}

The Skylon will possess a retractable undercarriage, equipped with high pressure tyres and water-cooled brakes; if any difficulties were to occur just before a take-off, the brakes would be applied to stop the vehicle, the water boiling away to dissipate the heat.{{sfn|Hempsell|Longstaff|2009|p=21}} During a normal landing, the empty vehicle would be far lighter, and hence the water would not be required,{{sfn|Hempsell|Longstaff|2009|p=21}} so upon a successful take-off, the {{convert|1410|kg|lb}} of water{{citation |contribution= SKYLON/SABRE Overview |title= presentation to the Northern Ireland Space Special Interest Group |date=5 March 2014}} would be jettisoned. When this feature was introduced in the C1 model of the design the weight of the brakes was reduced from around {{convert|3000|to|415|kg|lb|round=each}}.{{sfn|Varvill|Bond|2004}}

A special runway will be required for launch: it needs to be reinforced to tolerate the high equivalent single wheel load;{{cite web |url=http://www.reactionengines.co.uk/space_skylon_tech.html |title=Space Access: SKYLON – Technical |work=Reaction Engines |date=2014 |url-status=dead |archive-url= https://web.archive.org/web/20151217042713/http://www.reactionengines.co.uk/space_skylon_tech.html |archive-date=17 December 2015}} necessitated by the Skylon's 325 tonnes takeoff weight; it will need to have heat resistant sections{{citation needed|date=September 2017}} at the start of the take-off run and at the rotation zone;{{sfn|Hempsell|2014|p=15}} and it will have to be {{convert|5.9|km|mile}} long{{sfn|Hempsell|2014|p=15}} to allow the Skylon to accelerate to its {{convert|155|m/s|km/h knot|round=5|adj=on}} rotation speed,{{sfn|Hempsell|2014|p=5}} yet still have {{convert|1500|m|ft}} to abort the launch and brake to a standstill if required. At nearly 20,000 feet, this would be the longest paved runway in the world.{{cite web |url=https://www.worldatlas.com/articles/longest-runways-in-the-world.html |title=Longest Runways In The World |publisher=World Atlas |quote="Qamdo Bamda Airport in China has the longest paved runway in the world at 18,045 feet."}} The Skylon would be able to land on a {{convert|3.2|km|mile}} Code F civil runway.{{sfn|Hempsell|2014|p=15}}

When on the ground, it would undergo inspection and necessary maintenance, with a turnaround time of approximately two days, and be able to complete at least 200 orbital flights per vehicle.[https://web.archive.org/web/20160820132715/http://www.astronautix.com/s/skylon.html Skylon]. Mark Wade, Astronautix Encyclopedia.

File:Skylon.svg

File:Skylon diagram.jpg

{{Aircraft specs

|ref=the Skylon User Manual{{sfn|Hempsell|Longstaff|2014|p=}}

|prime units?=met

|crew=Zero

:: The proposed Skylon Personnel/Logistics Module (SPLM) has provision for a captain.{{sfn|Hempsell|Longstaff|2014|p=43}}

|capacity={{cvt|15000|kg}} of cargo

:: up to 24 passengers in the SPLM.{{sfn|Hempsell|Longstaff|2014|p=45}}

:: Potential for up to 30 passengers (in a special passenger module){{sfn|Scott-Scott|Harrison|Woodrow|2003}}

|length m=83.133

|length note={{sfn|Hempsell|Longstaff|2014|p=4}}

|span m=26.818

|span note={{sfn|Hempsell|Longstaff|2014|p=4}}

|height m=13.5

|height note={{sfn|Hempsell|Longstaff|2014|p=4}}

|empty weight kg=53,400

|empty weight note={{sfn|Hempsell|Longstaff|2014|p=6}}

|gross weight kg=325,000

|gross weight note={{sfn|Hempsell|Longstaff|2014|p=6}}

|eng1 number=2

|eng1 name=SABRE 4

|eng1 type=liquid air cycle engine

|eng1 kn=2000

|eng1 note={{sfn|Hempsell|Longstaff|2014|p=6}}

|more power=

• Specific impulse:

::{{convert|35000|Ns/kg|isp|order=flip|abbr=on}} air-breathing

::{{convert|4500|Ns/kg|isp|order=flip|abbr=on}} rocket{{sfn|Hempsell|Longstaff|2014|p=6}}

|max speed mach=5.5 air-breathing{{sfn|Hempsell|Longstaff|2014|p=6}}

|ceiling m=28500

|ceiling note=air-breathing

}}

• Reaction Engines A2, a Reaction design for an antipodal airliner using similar engine technology
• CFASTT-1, a similar design by University of Strathclyde
• Reusable launch system

{{Reflist |30em}}

{{refbegin}}

• {{cite conference |last= Bond |first= Alan |title= Progress on the SKYLON Reusable Spaceplane |conference= 7th Appleton Space Conference |date=8 December 2011 |url= https://www.ralspace.stfc.ac.uk/Pages/Presentation_13.pdf |access-date=3 December 2012 |archive-url= https://web.archive.org/web/20120712150558/http://www.stfc.ac.uk/RALSpace/resources/PDF/Presentation_13.pdf |archive-date=12 July 2012 |url-status=dead |publisher=Reaction Engines Ltd}}
• {{cite conference |first1= Philippa |last1= Davies |first2= Mark |last2= Hempsell |first3 = Richard |last3= Varville |title = Progress on SKYLON and SABRE |id=IAC-15-D2.1.8 |conference = 66th International Astronautical Congress |date= 2015 |url=https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36826.0;attach=1073534}} [https://iafastro.directory/iac/archive/browse/IAC-15/D2/1/31601/ IAC-15,D2,1,8,x31601]
• {{cite web|last1=Hempsell|first1=Mark|last2=Longstaff|first2=Roger|author-link1=Mark Hempsell |date=Sep 2009 |title=SKYLON Users' Manual – Rev 1 |publisher=Reaction Engines Ltd |url=http://www.reactionengines.co.uk:80/downloads/SKYLON_User_%20Manual_rev1%5b3%5d.pdf |archive-url= https://web.archive.org/web/20091219022940/http://www.reactionengines.co.uk/downloads/SKYLON_User_%20Manual_rev1%5b3%5d.pdf |archive-date=19 December 2009 |url-status=dead}}
• {{cite web |last1=Hempsell |first1=Mark |last2=Longstaff |first2=Roger |author-link1=Mark Hempsell |date=Jan 2010 |title=SKYLON Users' Manual – Rev 1.1 |publisher=Reaction Engines Ltd |url=http://www.reactionengines.co.uk/tech_docs/SKYLON_User_Manual_rev1-1.pdf|archive-url= https://web.archive.org/web/20160418035934/http://www.reactionengines.co.uk/tech_docs/SKYLON_User_Manual_rev1-1.pdf |archive-date=18 April 2016 |url-status=dead}}
• {{cite conference |first1= Mark |last1= Hempsell |first2= Alan |last2 = Bond |first3= R |last3= Bond |first4= Richard |last4= Varvill |title= Progress on the SKYLON and SABRE Development Programme |id=IAC-11.D 2.4.2, IAC-11.B3.2.6 |conference = 62nd International Astronautical Congress |place= Cape Town |date= October 2011}}
• {{cite web |last1=Hempsell |first1=Mark |last2=Longstaff |first2=Roger |author-link1=Mark Hempsell |date=June 2014 |title=SKYLON Users' Manual – Rev 2.1 |publisher=Reaction Engines Ltd |pages=1–52 |url=http://www.reactionengines.co.uk/tech_docs/SKYLON_Users_Manual_Rev_2.1.pdf |archive-url= https://web.archive.org/web/20151129034506/http://www.reactionengines.co.uk/tech_docs/SKYLON_Users_Manual_Rev_2.1.pdf |archive-date=29 November 2015 |url-status=dead}}
• {{cite conference |first= Mark |last= Hempsell |title=Progress on SKYLON and SABRE |id=IAC-13.D2.4.6 |conference= 64th International Astronautical Congress |place= Beijing, China |date= September 2013}}
• {{Cite conference |first=Mark |last=Hempsell |date=2014 |title=A Technical Overview of a SKYLON Based European Launch Service Operator |conference=65th International Astronautical Congress (IAC 2014): D2 Space Transportation Solutions and Innovations symposium |id=IAC-14.D2.4.5 |publisher=Reaction Engines Ltd}}
• {{cite book |author=House of Commons Science and Technology Committee |date=2007 |title=2007: A Space Policy – Seventh Report of Session 2006–08 |volume=II |url=https://books.google.com/books?id=nRdqigyj_RMC |publisher=Her Majesty's Stationery Office |isbn=978-0-215-03509-7}}
• {{cite journal |last1=Scott-Scott |first1=J.L. |last2=Harrison |first2=M. |last3=Woodrow |first3=A.D. |date=2003 |title=Considerations for Passenger Transport by Advanced Spaceplanes |journal=Journal of the British Interplanetary Society |volume=56 |pages=118–126 |url=http://www.reactionengines.co.uk/downloads/JBIS_v56_118-126.pdf |archive-url= https://web.archive.org/web/20090319105246/http://www.reactionengines.co.uk/downloads/JBIS_v56_118-126.pdf |archive-date=19 March 2009 |url-status=dead |bibcode=2003JBIS...56..118S}}
• {{cite magazine |first1= Richard |last1= Varvill |first2= Alan |last2= Bond |title= Skylon: A Key Element of a Future Space Transportation System |date= May 1993 |pages= 162–166 |issue= 5 |volume= 35 |magazine= Spaceflight |publisher= British Interplanetary Society |issn= 0038-6340 |place= London}}
• {{cite journal |last1=Varvill |first1=Richard |last2=Bond |first2=Alan |date=2003 |title=A Comparison of Propulsions Concepts for SSTO Reusable launchers |url=http://www.reactionengines.co.uk/downloads/JBIS_v56_108-117.pdf |journal=Journal of the British Interplanetary Society |volume=56 |pages=108–17 |bibcode=2003JBIS...56..108V |archive-url= https://web.archive.org/web/20120628231043/http://www.reactionengines.co.uk/downloads/JBIS_v56_108-117.pdf |archive-date=28 June 2012 |url-status=dead}}
• {{cite journal |last1=Varvill |first1=Richard |last2=Bond |first2=Alan |date=2004 |title=The SKYLON Spaceplane |journal=Journal of the British Interplanetary Society |volume=57 |pages=22–32 |bibcode= 2004JBIS...57...22V |url= http://www.reactionengines.co.uk/downloads/JBIS_v57_22-32.pdf |archive-url= https://web.archive.org/web/20110516165011/http://www.reactionengines.co.uk/downloads/JBIS_v57_22-32.pdf |archive-date= 16 May 2011 |url-status=dead}}
• {{cite journal |first1=Richard |last1=Varvill |first2=Alan |last2=Bond |title=The SKYLON Spaceplane - Progress to Realisation |journal=Journal of the British Interplanetary Society |volume=61 |pages=412–418 |year=2008 |bibcode= 2008JBIS...61..412V}}

{{refend}}

{{Commons}}

• [http://www.reactionengines.co.uk/ Reaction Engines Limited]
• [https://web.archive.org/web/20120219112920/http://www.thespaceshow.com/detail.asp?q=1203 Mark Hempsell from REL] on The Space Show talking about Skylon
• [http://www.smallspace.demon.co.uk/Model_Services/Skylon/skylon.htm World Tiles] {{Webarchive|url=https://web.archive.org/web/20190513063746/http://www.smallspace.demon.co.uk/Model_Services/Skylon/skylon.htm |date=13 May 2019 }} Skylon model
• [http://www.sworld.com.au/steven/space/lace.txt Liquid Air Cycle Engine (LACE) rocket equation reasonably well predicts the performance of Skylon]
• [https://www.youtube.com/watch?v=Uj45Au3KCRg Video animation TROY Mars Mission Concept]
• [http://vimeo.com/42682980 Video – SKYLON – Operations from Reaction Engines Ltd on Vimeo.]

{{Reaction Engines}}

{{Reusable launch systems}}

{{European launch systems}}

{{DEFAULTSORT:Skylon}}

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