Esa Bulletin March 1999 [antikvár]

flSesa bulletin 97 march 1999The Ariane-5 Evolution Programme: Three Years after ToulouseD. CoulonDirectorate for Launchers, ESA, ParisIntroductionThe primary objective in embarking on the development of Ariane-5 Evolution back in 1995 was to increase the vehicle's payload performance from 5970 to 7400 kg in Geostationary Transfer Orbit (GTO), and to maintain Europe's already solid Industrial base In the launcher field, especially in propulsion technology.To consolidate its success, Europe's Ariane launch vehicle must be continually adapted to meet the demands of the commercial markets that it serves. In the case of Ariane-5, a first increment to the basic launcher's capabilities was sanctioned by the ESA Council, meeting at Ministerial Level, in Granada in 1992. Preliminary studies were conducted to establish a basis for the so-called 'Ariane-5 Evolution Programme', followed by an appropriate Preparatory Programme. The Ariane-5 Evolution Programme was subsequently formally accepted at the Council Meeting at Ministerial Level in Toulouse in October 1995.In April 1998, the decision was taken to accelerate the Ariane-5 Evolution Programme whilst still maintaining schedule compatibility with the development of the cryogenic upper stage, in response to the pressing needs of the satellite launch market. The first flight of this new, more performant member of the Ariane launcher family is scheduled for May 2002.Since the uprated vehicle was to be a close derivative of the original Ariane-5, the changes envisaged were the following:-On the cryogenic stage, the common bulkhead between the oxygen and hydrogen tanks is being lowered by about 65 cm, enabling the mass of oxygen carried to be increased by 16 tonnes to cope with the increased mixing ratio of the Mark-2 version of the Vulcaln engine.-A Vulcain Mark-2 engine is being derived from the current Vulcaln, with the thrust Increased from 1145 to 1350 kN by Increasing the oxygen flow rate. The mixing ratio is raised from 5.3 to 6.2. The oxygen turbopump is the subsystem undergoing the most significant changes. The combustion chamber Is being adapted to accommodatethe new flow rates. Finally, the expansion ratio of the divergent Is being increased by 30% with the turbine exhaust gases reintroduced.-The Ariane-5E solid boosters are being enhanced by the Introduction of welded joints between the cylindrical sections that make up the booster segments, replacing the original seals. This modification produces a significant mass saving, an increase in reliability and lower production costs.-A new dual-launch system, known as Sylda-5, is proposed for Arlane-5E. This structure lies entirely within the fairing and can accommodate a satellite with a diameter of 4 m in the lower position. Sylda-5 provides a mass saving of 350 kg compared with the current Speltra.The programme approachThe programme content began with the launch-system activities, including a set of general studies leading to an updating of system specifications and preliminary definition of electrical-system adaptations presented at the System Design Review.For the cryogenic main stage, this activity consisted of layout studies and mechanical and functional studies, including the updating of the relevant specifications. The Integrated Equipped Tanks preliminary design effort is proceeding, with tank-pressure optimisation being performed to balance propulsion needs against tank panel welding-technology limitations. The Preliminary Design Review took place in November 1998.The Vulcain-2 studies have covered the engine system, the oxygen and hydrogen turbopumps, the combustion chamber, the divergent and other equipment items. Preliminary Design Reviews were held throughout 1997 as the various activities were completed.