What is "hotol"

HOTOL, for Horizontal Take-Off and Landing, was a British design for an airbreathing jet engine spaceplane by Rolls-Royce and British Aerospace.

Designed as a single-stage-to-orbit (SSTO) reusable winged launch vehicle, it was to be fitted with a unique air-breathing engine, the RB545 or Swallow, to be developed by the Rolls-Royce company. The engine was technically a liquid hydrogen/liquid oxygen design, but dramatically reduced the amount of oxidizer needed to be carried on board by utilising atmospheric oxygen as the spacecraft climbed through the lower atmosphere.

Since propellant 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. Ultimately, comparison with a rocket vehicle using similar construction techniques failed to show much advantage, and funding for the vehicle ceased.