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{{short description|UK spaceplane design of the 1980s}}
{{For|the generic concept of horizontal takeoff and landing|
{{Use British English|date=March 2015}}
{{Use dmy dates|date=December 2014}}
{|{{Infobox aircraft begin
[[File:HOTOL.JPG|thumb|An artist's depiction of HOTOL]]▼
|name = HOTOL
'''HOTOL''', for '''Horizontal Take-Off and Landing''', was a 1980s [[United Kingdom|British]] design for a [[single-stage-to-orbit]] (SSTO) [[spaceplane]] that was to be powered by an [[airbreathing jet engine]]. Development was being conducted by a consortium led by [[Rolls-Royce plc|Rolls-Royce]] and [[British Aerospace]] (BAe).▼
|image = HOTOL.JPG
}}{{Infobox aircraft type
|type = [[Spaceplane]]
|national origin = United Kingdom
|developed into = [[Skylon (spacecraft)|Skylon]]
}}
|}
▲'''HOTOL''', for '''Horizontal Take-Off and Landing''', was a 1980s
Designed as a [[single-stage-to-orbit]] (SSTO) reusable winged launch vehicle, HOTOL was to be fitted with a unique air-breathing engine, the RB545 or Swallow, that was under development by British engine manufacturer Rolls-Royce. The propellant for the engine technically consisted of a combination of liquid [[hydrogen]]/liquid [[oxygen]]; however, it was to employ a new means of dramatically reducing the amount of oxidizer needed to be carried on board by utilising atmospheric oxygen as the spacecraft climbed through the lower atmosphere. Since the oxidizer typically represents the majority of the takeoff weight of a rocket, HOTOL was to be considerably smaller than normal pure-rocket designs, roughly the size of a medium-haul airliner such as the [[McDonnell Douglas DC-9]]/[[McDonnell Douglas MD-80|MD-80]].
While HOTOL's [[proof-of-concept]] design study was being carried out, attempts were made by both industry and the British government to establish international cooperation to develop, produce, and deploy the spacecraft. In spite of American interest in the programme, there was little appetite amongst the members of the [[European Space Agency]] (ESA), and the British government was not prepared to depart from ESA cooperation. Additionally, technical issues were encountered, and there were allegations that comparisons with alternative launch systems such as conventional rocket vehicle using similar construction techniques failed to show much advantage to HOTOL. In 1989, funding for the project ended. The termination of development work on HOTOL led to the formation of [[Reaction Engines|Reaction Engines Limited]] (REL) to develop and produce [[Skylon (spacecraft)|Skylon]], a proposed spacecraft based on HOTOL technologies, including its air-breathing engine.
==Development==
===Origins===
The ideas behind HOTOL originated from work done by British
Thus, the project had soon
In December 1984, a [[Department of Trade and Industry (United Kingdom)|Department of Trade and Industry]] (DTI) memorandum noted that [[West Germany]] was interested in the
===American interest and design study===
In March 1985, there were claims that Rolls-Royce was in the process of conducting [[Licensed production|licensing]] talks for HOTOL engine technology with American propulsion company [[Rocketdyne]].<ref name
In July 1985, Rolls-Royce's technical director [[Gordon Lewis (engineer)|Gordon Lewis]] stated that the firm sought the involvement of the [[Royal Aircraft Establishment]]'s (RAE) propulsion group, and that Rolls-Royce was not prepared to invest its own funds into engine development for HOTOL.<ref name
By November 1985, DTI and RAE discussions noted that Rolls-Royce were seeking American data on [[ramjet]] technology to support their work on the engine, which it referred to by the name ''Swallow''.<ref name
According to British government files, neither BAe nor the MoD were enthusiastic for the prospects of American involvement in the programme, expressing reluctance out of a belief that the outcome of such a move could result in the UK becoming a junior member in a project that it once led.<ref name
===Problems and criticism===
In December 1984, project management consultant David Andrews issued an eight-page critique of the programme, noting that the design was optimised for the ascent while exposing itself to extended thermal loads during descent due to a low level of [[Aerodynamic drag|drag]]. He also claimed that the vehicle offered no capability that was not already available; BAe responded that the criticisms made had been answered.<ref name
In November 1985, the RAE issued an assessment of HOTOL's study proposal; the organisation
During development, it was found that the comparatively heavy rear-mounted engine moved the centre of mass of the vehicle rearwards. This meant that the vehicle had to be designed to push the centre of drag as far rearward as possible to ensure stability during the entire flight regime. Redesign of the vehicle to do this required a large mass of hydraulic systems, which cost a significant proportion of the payload, and made the economics unclear.<ref>{{cite
===Shutdown===
By 1989, the outlook for HOTOL had become bleak; from the onset of the project, support between the British government and industrial partners had been uneven, while the United States had emerged as the only foreign nation that showed willingness to contribute to the programme,<ref name
===Successors===
A cheaper redesign, '''Interim HOTOL''' or '''HOTOL 2''', which was to be launched from the back of a [[Antonov An-325|modified]] [[Antonov An-225 Mriya|Antonov An-225
In 1989, HOTOL co-creator
==Design==
===Overview===
HOTOL was envisioned as an unmanned, fully
During its high-altitude phase, its [[flight control system]] would have been linked to ground stations and to space-based [[Global Positioning System|global navigation system]] navigation, while [[radar]] would have been used during the take-off and landing phases. In
As designed, HOTOL would have been 62 metres long, 12.8 metres high, a fuselage diameter of 5.7
===Engine===▼
{{Infobox rocket engine
|name = Rolls-Royce RB545 "Swallow"
|image =
|image_size =
|caption =
|
|
▲ |designer = [[Rolls-Royce Limited|Rolls-Royce]]
|purpose = [[Single-stage-to-orbit]]
|associated = HOTOL
▲ |status = [[Project cancellation|Cancelled]]
|predecessor = SATAN
|status = Cancelled
|type = liquid
|
|
|cycle = Combined cycle [[precooled jet engine]] and [[closed cycle rocket engine]]
|
|
|thrust(SL) =
|
|specific_impulse_vacuum = {{convert|4500|Ns/kg|isp}}
|specific_impulse_sea_level = {{convert|14780|Ns/kg|isp}}
|
|references = <ref name="
}}
The RB545, which was given the name "Swallow" by its manufacturer, British engine maker
▲===Engine===
▲The RB545, which was given the name "Swallow" by its manufacturer, British engine maker [[Rolls-Royce plc|Rolls-Royce]], was an air-breathing rocket engine.<ref name = "secret 2009"/> It would have functioned as an integrated dual-role powerplant, having been capable of air-breathing while operating within the [[atmosphere]] and operating in a similar manner to that of a [[rocket]] when having attained close to and within LEO.<ref name = "moxon 38 40">Moxon 1986, pp. 38, 40.</ref> This engine would have also been capable of powering the spacecraft to [[hypersonic]] speeds. It was a crucial element of the programme, having been publicly attributed as "the heart of Hotol's very low launch costs".<ref name = "moxon 40"/>
The exact details of this engine were covered by the [[Official Secrets Act]] of the United Kingdom; consequently, there is relatively little public information about its development and on its operation. However, material was later declassified when government policy changed to prevent the keeping of secret patents without an attributed justification.<ref>
Within the atmosphere, air is taken in through two vertically mounted [[
To prevent the pre-coolers from icing up, the first pre-cooler cooled the air to around 10 degrees above freezing point, to liquefy the water vapour in the air. Then liquid oxygen (LOX) would have been injected into the airflow to drop the temperature to {{cvt|-
When it was no longer possible to use the atmosphere for combustion, the RB545 would switch to using on-board
==See also==
{{portal|Spaceflight}}
* [[Rockwell X-30
* [[Reaction Engines
* [[Liquid air cycle engine]] – a related engine cycle that liquifies the air
* [[Saenger (spacecraft)]]
{{notelist}}▼
==References==
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===Bibliography===
{{refbegin}}
*{{cite
*
{{refend}}
▲===Notes===
▲{{notelist}}
== External links ==
{{Commons category}}
* {{webarchive |date=30 January 2013 |title=Cutaway drawing of the HOTOL |url=https://web.archive.org/web/20130130095436/http://www.flightglobal.com/airspace/media/missilespacesystemscutaways/images/10296/bae-hotol-cutaway.jpg
* [
{{Reaction Engines}}
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[[Category:British Aerospace aircraft|HOTOL]]
[[Category:Spaceplanes]]▼
[[Category:Cancelled spacecraft]]
[[Category:Single-stage-to-orbit]]▼
[[Category:Former proposed space launch system concepts]]
▲[[Category:Single-stage-to-orbit]]
[[Category:Space programme of the United Kingdom]]
▲[[Category:Spaceplanes]]
[[Category:Tailless delta-wing aircraft]]
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