HOTOL is a hypersonic space plane invented by British engineer Alan Bond in the early eighties. It stands for horizontal takeoff and landing. HOTOL was to be a single stage vehicle that could take off and land on a runway. It included a revolutionary dual-purpose engine that enabled it to take far less oxygen than a traditional spacecraft:
- During the initial stage of flight, it operated as a jet engine, taking in oxygen from the surrounding air of the earth's atmosphere. Other rockets take liquid oxygen to burn with fuel.
- When the air would become too thin, HOTOL would be converted into a rocket, burning liquid oxygen from an onboard supply. The unmanned spacecraft would reach velocities of Mach 7.
British Aerospace and Rolls-Royce developed the project, but fell flat for lack of capital in 1988. A government security order prevented the companies from showing plans to would-be overseas sponsors. Originally Bond (who closely worked with Dr Bob Parkinson later on) had patented his idea in 1982, naming the engine RB454. The Ministry of Defence classified the design as top secret. This was the reason that Bond could not ask foreign companies or governments to finance his project after the Thatcher government had pulled the plug. Members of the HOTOL team have now formed their own company (Reaction Engines Ltd.) and are working on a new but similar project called Skylon.
Some HOTOL engine statistics for you space buffs out there:
- Total mass: 250,000 kg.
- Core diameter: 7.0 m.
- Total length: 75.0 m.
- Flyaway unit cost: US$ 10 million
- Gross mass: 250,000 kg.
- Empty mass: 50,000 kg.
- Diameter: 7.0 m.
- Span: 28.3 m.
- Length: 62.8 m.