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Aviation History
1985
1985 - 2125.PDF
continued from page 24 Development of a success ful dual-role powerplant is crucial to the success of the Hotol concept. Rolls-Royce is working on a hybrid engine which uses atmospheric oxygen and on-board liquid hydrogen to accelerate the craft in the lower, denser atmosphere, transitioning to pure rocket propulsion using the liquid hydrogen and a supply of on-board liquid oxygen. Conchie says that technical problems have hitherto prevented this ap proach, but that a "potential" propulsion breakthrough occurred concurrently with BAe's studies of an advanced launcher which renders the idea practical. Proof-of-con- cept work on the engine is ex pected to begin in the autumn. An important element of Hotol is the use of a ground trolley at take-off. The craft weighs five times as much at the beginning of a mission as it does at the end, which means that an excessively heavy undercarriage would have to be carried into orbit. Conchie says that the trolley "should be regarded simply as a second undercarriage" which is left behind. Other take-off ideas are being studied, but the trolley is at present seen as the best system. As now configured, Hotol's fuselage cross section is simi lar to that of Shuttle's, but optimised for satellites weigh ing around 7 tonnes "which is a popular size," says Conchie. The chosen Concorde-type wing planform combines the required lift/drag and stability characteristics with good structural efficiency. The wing is rear-mounted, since Hotol's e.g. is a long way aft owing to a "relatively heavy" powerplant and liquid oxygen storage, the latter accounting for over half of take-off mass. The liquid hydrogen tank is stored ahead of the payload bay and occupies considerable volume, since hydrogen is used in all phases of the climb to orbit. Because of the rearward e.g. and consequent short tail moment arm, Hotol will need actively controlled horizontal and vertical canards to main tain stability. These can also be used to trim aerodynamic moments during transonic flight, says BAe. A major advantage claimed for Hotol is the very good Payload bay (7 tonnes) Canard Hydrogen controls ——*f\ «0 Engines Re-entry thermal protection Intakes- Hotol's fuselage is largely taken up by liquid hydrogen and oxygen tanks. The dual-mode engine means that the oxygen tank can be much smaller than in conventional rockets crossrange ability conferred by a hypersonic lift-to-drag ratio "twice that of Shuttle's". This means that the craft would be able to return to a European base from an equa torial orbit, saving turnround time. For geostationary launches, with a perigee boost motor aboard, Hotol would fly a sub-orbital trajectory to a suitable airfield near the equator (Ascension Island would be one possibility, the Ariane launch centre at Kourou another), refuel, and climb to orbit. Apart from the engine, Hotol does not require dramatic technology ad vances, according to BAe. The vehicle is more lightly loaded than Shuttle on re-entry and temperatures are sufficiently low to use metallic thermal protection instead of ceramic tiles. Titanium would be the principal material used in construction, with composites where possible. One area in which there might be prob lems, however, is the insu lation of liquid hydrogen and oxygen tanks, which will form part of the outer structure. Technology input for Hotol is derived from Concorde, and from experience in rocket technology going back to the 1950s, when the UK worked on the Blue Streak ballistic missile. This eventually be came the first stage of a Euro pean civil launcher called Europa, which failed because of management problems and rising costs. The UK also shares in the Ariane pro gramme, with responsibility for guidance, launch release gear and, on Ariane 4, the satellite mounting capsule. British Aerospace claims that Hotol could reduce launch costs to low-earth orbit by a factor of five and halve the cost of launch to geostationary orbit, enabling it to compete realistically for about 75 per cent of the commercial market from the beginning of the next century. Development cost of Hotol is roughly estimated at £4,000 million, taking the project up to 1997 with a single oper ational vehicle. Funding is currently very limited, but the UK Government will be asked to contribute to the pro gramme later this year. BAe and Rolls-Royce would match Government contribution pound for pound. The UK avionics industry will not become involved until proof- of-concept trials are com pleted in two years time. Avionics would be derived from systems in civil airliner Secrecy surrounds the details ofHotol's engine. This diagram suggests that oxygen separation occurs in a device placed in front of the turbopump stage Liquid hydrogen i Liquid ^Hydrogen l^gen Air£> SPACEFLIGHT use in the 1990s, possibly making considerable use of fly-by-light control tech nology. In the long term, Hotol's future will rest on continued support from the UK Govern ment, which would have to agree to increased spending on launcher development, an area which is currently outside the UK frame of refer ence within ESA. Conchie promotes Hotol as a way of ensuring Europe's long-term competitiveness in the satellite launch business. He says that the French understand the eventual need for a single-stage to orbit vehicle, "but not within the Ariane timescale". He notes, however, that Ariane 5 has yet to win full ESA approval, and that Hermes remains a French-only project, with no ESA funding. SPACESHOTS Within its normal framework of scientific exchanges with the Soviet Union, ESA is discussing the flight of one or two experiments on the two Soviet Mars Orbiters due to be launched in 1988. One of these probes will rendezvous with the Martian moon Phobos. Nasa and the Chilean Government are discussing the use of Easter Island (Isla de Pascua) in the Pacific Ocean as an emergency land ing site for Shuttles launched from Vandenberg AFB. The island's Mataveri airfield could be used as a trans- Pacific landing site in the event of a launch abort and also as an additional con tingency landing site. If agree ment is reached, Nasa will pay Chile to increase the length of the present runway from 2,900m to 3,350m. Another Pacific abort site is at Hao, a French island which already has a 3,350m runway built to support France's nuclear test programme. Nasa has ordered a Honeywell-developed space vehicle guidance system from Orbital Sciences (OSC). The laser inertial navigation system using three ring laser gyros is being developed by Honeywell for OSC's private- venture transfer orbit stage, with space qualification scheduled for May 1986. The Nasa contract is worth almost $270,000. FLIGHT International, 29 June 1985 27
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