British Aerospace HOTOL
British Aerospace HOTOL
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British Aerospace HOTOL

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British Aerospace HOTOL

HOTOL, for Horizontal Take-Off and Landing, was a 1980s British design for a single-stage-to-orbit (SSTO) reusable spaceplane that was to be powered by an airbreathing jet engine. Development was being conducted by a consortium led by Rolls-Royce and British Aerospace (BAe).

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/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. Despite 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 Limited (REL) to develop and produce Skylon, a proposed spacecraft based on HOTOL technologies, including its air-breathing engine.

The ideas behind HOTOL originated from work done by British engineer Alan Bond in the field of pre-cooled jet engines. Bond had specifically performed this research with the intention of producing a viable engine for powering a space launch system. In 1982, British Aerospace (BAe), which was Europe's principal satellite-builder, began studying a prospective new launch system with the aim of providing launch costs that were 20 per cent of the American Space Shuttle operated by NASA. BAe became aware of work by British engine manufacturer Rolls-Royce on a suitable engine, and soon conceived of an uncrewed, fully reusable single-stage-to-orbit (SSTO) winged spaceplane as a launch vehicle.

Thus, the project had soon become a joint venture between BAe and Rolls-Royce, led by John Scott-Scott and Bob Parkinson. Early on, there was an ambition to 'Europeanise' the project and to involve other nations in its development and manufacture as it was recognised that an estimated £4 billion would be needed to fund full-scale development. In August 1984, BAe unveiled a public display of the HOTOL satellite launcher project and released details on its proposed operations.

In December 1984, a Department of Trade and Industry (DTI) memorandum noted that West Germany was interested in the programme, while France had adopted a critical attitude towards HOTOL, which the ministry viewed as potentially due to it being seen as a competitor to French-led projects. According to Minister of Trade and Industry Geoffrey Pattie, French diplomatic pressure to gather support for its own proposed Hermes space vehicle had inadvertently generated support and interest amongst European Space Agency (ESA) members in the HOTOL project. Despite this climate of tentative interest and possible European support, there was a general attitude of reluctance within the British government to take the lead on a new space launcher.

In March 1985, there were claims that Rolls-Royce was in the process of conducting licensing talks for HOTOL engine technology with American propulsion company Rocketdyne. In April 1985, Pattie wrote to Secretary of State for Defence Michael Heseltine to propose a two-year £3 million proof of concept study be performed under a public-private partnership arrangement, consisting of £1 million provided by the UK government and the remainder being financed by Rolls-Royce and BAe themselves. Pattie reasoned that the project would serve Britain's "strategic capability", and that tests of key technologies could foster international collaboration. According to aerospace publication Flight International, the support of the Ministry of Defense (MoD) was critical as the design of HOTOL's engine had been classified.

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