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Aviation History
1981
1981 - 3338.PDF
Improving Ariane 4 EUROPE'S Ariane 4 is unlikely to have larger solid-propellant boosters, according to the latest study made by French space agency CNES. The work showed that liquid-propellant boosters were a better way of increasing per formance to cope with heavier satel lites. The European Space Agency's (ESA's) Ariane programme board has the final say, however, and a prelimin ary decision is expected by the end of the month. CNES manages Ariane on behalf of ESA, and reexamined Ariane 4 plans because of a trend toward heavier satellites. Intelsat has already speci fied room for growth in its proposed Intelsat VI communications satellite. Intelsat VI is now roughly 3,500kg in weight, and a 20 per cent increase would put it in the 4,000kg class. Two options for achieving this performance were studied. The first envisaged solid-propellant strap-on boosters, and the second liquid-fuelled units. Both options had to be low-risk, in line with Ariane development philosophy. The solid-propellant option was forced to include a fifth engine in the first stage—because of the solid- propellant technology available in Europe, and the need to limit stresses. This option also demanded a slightly larger first stage extension than the 6m one planned, which increases first stage propellants from the 140 tonnes of Ariane 3 to 210 tonnes. The liquid-propellant option as sumed use of the existing first stage engine for each booster, and that they be independent of the first stage. It also allowed use of the small solid- propellant boosters being developed for Ariane 3. CNES used six criteria to compare the two options, and reached the fol lowing conclusions: Development timetable Liquids turned out to be less critical, calling for a programme start in early 1982. Technical aspects The weight of reinforcement needed by solids was felt to balance the extra launch pad complexity of liquids, and their more complex dynamics. Development cost Liquids were preferred because of their lower risk —the estimated cost of each option being comparable. Unit cost Solids proved to be slightly cheaper than liquids. Performance Four liquid boosters give Ariane 4 a payload of 4,300kg, while four solids allow 3,900kg. Continuity with Ariane 3 Liquids are better because Ariane 4's first stage is virtually identical to that of Ariane 3. The liquid-propellant option LIQUID BOOSTER DATA Length 16m Diameter 2 3m Thrust 67 tonnes Propellant mass 40 tonnes Burn time 140sec. was thus preferable overall. ESA estimates that Ariane 4 will cost 200 million accounting units to develop (1 accounting unit is worth $1-2). The Ariane 4 option with four liquid-propellant boosters would have a maximum launch weight of 460 tonnes, of which 415 tonnes are pro pellant. ESA has yet to reach a decision on the 4m-diameter fairing proposed for Ariane 4, which would complement the current 3 • 2m-diameter unit. The 4m-diameter fairing would be avail able in several different heights, and for double satellite launches the aft part would act as support for the top craft. • Ariane engine manufacturer Societe Europeenne de Propulsion (SEP) has successfully demonstrated combustion pressures of 58 bar in tests of the Viking engine, which powers the first and second stage. This pressure is higher than that of the basic Ariane, and will be stan dard for Ariane 2, 3 and 4. SEP diluted the unsymmetrical di methyl hydrazine fuel with 25 per cent of a hydrazine hydrate in these trials, to avoid recurrence of the type of in stability which caused the loss of the second Ariane. This dilution causes a Spaceflight slight shortfall in performance, but is likely to be adopted from Ariane 2 onward. • Work on the second Ariane launch pad at Kourou, French Guiana, has now reached the stage where concrete pouring is about to begin. The second pad is only a few hundred metres away from the first, and is now simply a large hole in the ground. Ariane 4 demands a new launch pad because of its longer first stage, but the facility will also allow a higher overall launch rate and act as a back up. ESA plans to have an Ariane 4 test flight in the third quarter of 1985, followed by a first operational launch in early 1986. The contractors for the Ariane 4 liquid-propellant boosters have yet to be chosen, but testing of them is likely to be at DFVLR's range at Hard- thausen, West Germany. ARIANE 4 PERFORMANCE A40 A4ZP A44P Payload (kg) 2,000 2,700 3,100 Notes (a) Payloads are to geostationary transter orbit. (b) Ariane 3 single-satellite payload is 2,460kg. A42L 3,300 A44LP 3,800 A44L 4,300 Ariane 4 can be tailored to a wide variety of payloads by the use of two types of strap-on booster. The small solid-propeilant boosters are already being developed for Ariane 3, but the larger, liquid-propellant units would be a new venture. From left to right are the Ariane 4 versions with the following strap-on boosters; none, two solids, four solids, two liquids, two liquids and two solids, and four liquids m a a a A40 A42P A44P A42L m \ •a a A A44LP A44L 1246 FLIGHT International, 24 October 198/
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