HOTOL Credit - Mark Lindroos

This single-stage-to-orbit winged horizontal takeoff/horizontal landing launch vehicle concept was powered by the unique Rolls-Royce RB545 air / liquid hydrogen / liquid oxygen rocket engine. HOTOL development was conducted from 1982 to 1986 before the British government withdrew funding. It was superseded by the Interim HOTOL design which sought to reduce development cost through use of existing Lox/LH2 engines.

HOTOL development was begun in 1982 by a Rolls-Royce / British Aerospace team led by John Scott and Dr Bob Parkinson. The project was reasonably well advanced (engine detailed design and mockup) by the time the British government withdrew further funding in the mid-1980's. HOTOL would have taken off horizontally from a runway, from a purpose made, rocket propelled trolley. It would transition to pure rocket propulsion at Mach 5.0 - Mach 6.0 and ascend to orbit. A moderate re-entry profile would decrease the thermal loading constraints. HOTOL would return via a glide landing, to a landing on gear on a conventional runway.

The original HOTOL airframe design was derived from conventional vertical takeoff rockets with the engines mounted at the rear of a blunt based fuselage. Since such a vehicle’s empty centre of gravity was dominated by the engine location, the wings and the tank for the dense liquid oxygen also had to be at the rear. The payload bay and hydrogen tankage were placed in a projecting forebody.

The resulting configuration suffered from a severe centre of pressure / centre of gravity mismatch during the air breathing ascent. The centre of pressure shifted 10 m forward, due to the wide Mach range, the large fuselage cross section to wing area ratio, and the long overhang of the forward fuselage. Various alterations were made to the design to handle these problems, all of which eroded the payload.

Conventional landing gear were replaced by a specially designed takeoff trolley in order to improve the marginal payload fraction. The final design had serious operational disadvantages and a small payload. The only way the designers could continue to claim to put a reasonable payload into orbit was by specifying untried and speculative structural materials.

Manufacturer: British Aerospace. Liftoff Thrust: 3,152.200 kN (708,643 lbf). Total Mass: 250,000 kg (550,000 lb). Core Diameter: 7.00 m (22.90 ft). Total Length: 75.00 m (246.00 ft). Flyaway Unit Cost $: 10.000 million. in: 1985 unit dollars.

• Stage Number: 1. 1 x Stage: HOTOL. Gross Mass: 250,000 kg (550,000 lb). Empty Mass: 50,000 kg (110,000 lb). Thrust (vac): 1,103.200 kN (248,009 lbf). Isp: 700 sec. Burn time: 730 sec. Isp(sl): 2,000 sec. Diameter: 7.00 m (22.90 ft). Span: 28.30 m (92.80 ft). Length: 62.80 m (206.00 ft). Propellants: Liquid Air/Lox/LH2. No Engines: 3. Engine: RB545. Other designations: Horizontal Takeoff and Landing. Status: Development ended 1985.

1982 - Launch Vehicle: HOTOL.

• HOTOL development begun by a Rolls-Royce / British Aerospace team Nation: UK. The project was reasonably well advanced (engine detailed design and mockup) by the time the British government withdrew further funding in the mid-1980's. HOTOL would have taken off horizontally, transition to pure rocket propulsion at Mach 5.0 - Mach 6.0. and ascend to orbit. A moderate re-entry profile would decrease the thermal loading constraints. HOTOL would return via a glide landing, to a landing on gear on a conventional runway.

• Aviation Week and Space Technology, "Britain Urges ESA Members to Join HOTOL Development Project", 1985-06-17, page 91.