HOTOL, for Horizontal Take-Off and Landing, was a 1980s 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 and British Aerospace (BAe).The ideas behind HOTOL originated from work done by British Engineer Alan Bond in the field of pre-cooled jet engines.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/MD-80.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.A Good description on Thumblegudget Youtube ChannelHOTOL - Spaceplane of the future
