During the 1960's and early 1970's the UK embarked on a national space launch program which culminated in the launch of the Prospero scientific satellite by a Black Arrow launch vehicle on 28 October 1971. However, for many years further UK interests in launch vehicle development were transferred to ELDO and ESA programs. Finally, in 1982 British Aerospace engineers originated a concept for a single-stage, horizontal take-off and landing (HOTOL) space transportation system. For the next several years the design was refined and eventually presented to ESA for consideration; meanwhile a 2-year proof-of-concept study was initiated in 1985 among the UK government, British Aerospace, and Rolls Royce.
Firm support for HOTOL never materialized from the UK government or ESA, but the project managed to survive at a very low level of effort. The baseline HOTOL design in the late 1980's called for a 250 metric ton unmanned vehicle which could deliver a payload of up to seven metric tons to LEO on a typical mission lasting 50 hours. The vehicle would be similar in size to the Concorde supersonic aircraft with an overall length of 62 m and wing-span of 28 m. Propulsion would be provided by four RB545 dual-mode engines which would operate in an air-breathing mode up to an altitude of 26 km where a conversion would be made to a liquid oxygen/liquid hydrogen rocket propulsion mode. A 14-year development program was recommended before HOTOL would become operational. Despite some modest Government encouragement to industry, the current prospects for a full-sized HOTOL project in this decade are poor (References 485-487).
In 1991 British Aerospace joined with the USSR's Antonov Design Bureau to consider the possibility of developing a smaller version of HOTOL, dubbed Interim HOTOL, which could be air-launched by a modified An-225 aircraft. Interim HOTOL would be released at an altitude of about nine kilometers and would then use four Russian RD-0120, liquid oxygen/liquid hydrogen engines to carry a payload of 7-8 metric tons into LEO. Wind tunnel testing of the Interim HOTOL and engine Antonov carrier has been accomplished. The dimensions of Interim HOTOL are approximately 36 m length and 22 m wing-span. Despite considerable interest in the program, no full development plan has been approved and funded. The concept is still being evaluated and may be continued under ESA's FESTIP study activities (References 488-495).
In 1993 the British firm Reaction Engines, Ltd., revealed that it was developing an engine called SABRE which could propel a new spaceplane concept called Skylon. One of the founders of Reaction Engines was a principal in the design of HOTOL's unique power plant. Skylon would be 82 m in length with a wingspan of 27 m and could carry a payload of 10 metric tons to an orbit of 300 km at a 5 degree inclination (References 496-498).
485. HOTOL, brochure published by British Aerospace and Rolls Royce, undated.
486. M. Hempsell, "HOTOL's Secret Engines Revealed", Spaceflight, May 1993, pp. 168-172.
487. "New Hopes for UK Spaceplane Studies", Spaceflight, June 1993, p. 193.
488. C. A. Shifrin, "British Aerospace, Soviets to Study Launching HOTOL from AN-225", Aviation Week and Space Technology, 10 September 1992, p. 23.
489. S. Young, "Soviet Cooperation Gives Hotol a New Lease of Life, Spaceflight, October 1990, pp. 326-327.
490. P. B. de Selding, "Antonov-Hotol Project Passes Tests, Space News, 6-12 May 1991, P.26.
491. "Antonov Launched Hotol Moves Forward.", Spaceflight, August 1991, p. 259.
492. Izvestiya, 21 June 1991, p. 8.
493. J. M. Lenorovitz, "New Hotol Version Emerges Following British/Soviet Study", Aviation Week and Space Technology, 9 September 1991, PP.68-69.
494. S. W. Kandebo, "Soviets to Conduct Wind Tunnel Separation Tests on Hotol Launch System", Aviation Week and Space Technology, 6 January 1992, p. 58.
495. R. Parkinson, "Project 'Interim Hotol' Update", Space Technology International, 1992, pp. 127-128.
496. R. Varvill and A. Bond, "Skylon: A Key Element of a Future Space Transportation Systems", Spaceflight, May 1993, PP.162-166.
497. "Correspondence.", Spaceflight, July 1993, PP.240-242.
498. "Correspondence", Spaceflight, November 1993, P.388.