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Aviation History
1964
1964 - 1760.PDF
FLIGHT International, 11 June 1964 975 Third-stage combustion chamber under test medium-energy fuels in designing the power unit. Further dis- cussions and studies within ELDO have led up to the present project. The propulsion unit of the third stage consists of a central main engine producing a thrust of 4,9501b, and two small control engines, of 1101b thrust each, with a large transverse angle. By cutting off the main engine the acceleration is reduced from 131ft/sec2 to 3.3ft/sec2. The low thrust of the control engines then permits a precise control of the propellant cut-off. Objections were raised against the thrust power of 2 x 17.61b in respect of control engines for very long combustion periods given in the optimal calculations, because of the difficulty of solving the cooling problems in such extremely small engines within the short development period. For this reason, it was decided to carry out the flight of the third stage in three phases; thrust; coast; thrust; thereby permitting the increase of the thrust of the control engines. Moreover, studies within ELDO on trajectory optimization led to substantial modifications of basic data. The originally projected diameter of the third stage was increased from 70.9in to 78.7in (the length of 137.8in remaining unaltered), and the thrust of the main engine from 4,410 to 4,9501b. Initial weight of the stage (including satellite) was increased to 7,7001b for high orbits and to 9,9201b for low orbits. The fuel (Aerozine 50) is a mixture of 50 per cent UDMH (un- symmetrical dimethyl hydrazine) and 50 per cent hydrazine; the oxidizer is nitrogen tetroxide. The spherical fuel container made of titanium has a diameter of 66.9in, and is fabricated by explosion forming. To avoid the expensive pump development, the fuel is fed by means of a gas pressure system. Since the stage operates only under vacuum conditions, a very low combustion pressure (about 1281b/sq in) can still produce the high expansion ratio necessary for a high specific impulse. For this reason, and because of the rela- tively small size of the third stage, the performance is only slightly lower than when using a pump system. Guidance is accomplished by an advanced electronic open and closed-loop system in a small section of the structure above the main bulkhead. The system consists of modules assembled for certain functions. Before launch, for example, a flight programme is stored, determining the succession of all necessary operations. During the flight, corrective signals can be transmitted by radio to achieve high path accuracy. Attitude stabilization is effected by a rate-gyro and computer which transforms the data into appropriate control signals travers- ing the engines. Telecommunication equipment includes the radio control receiver, a tracking transponder and a telemetry unit. The development and construction of the third stage is conducted in the German Federal Republic by the Arbeitsgemeinschaft Satellitentrager (ASAT), which is held jointly by Bolkow-Entwick- lungen KG. and Entwicklungsring Nord (ERNO). The drawing gives a general view of the construction of the third stage. The tank has an inside diameter of 67.7in, and is made of titan- ium. It is divided into two parts, upper for the fuel at 2771b/sq in and lower containing the oxidizer at 2631b/sq in. The container is suspended by means of diagonal titanium ribs (cross section 0.0078in x 1.18in) which are bonded or brazed to the container and spot-welded to the main bulkhead. For reasons of safety, the fuel suction line is not led through the oxidizer tank. The satellite support is a tubular framework with a satellite plat- form. It can be detached from the main bulkhead. The engine framework connects the spars, in which the engines are mounted, with the bulkhead by means of screws. It also accommodates the two pressure gas containers. The latter are oval glass-fibre rein- forced plastic tanks containing helium at 4,2671b/sq in. The main engine is mounted on gimbals permitting transverse corrections to a maximum of 6°. Under vacuum conditions the expansion ratio is 1,000 :1. Investigations have shown that the combustion chamber pressure can be increased, thus permitting a thrust increase up to 7,7181b without changing the measurements. Function of the control engines is twofold: regulation of flight attitude, and propulsion for missions in high orbit owing to their long combustion period. Under vacuum conditions the pressure is 71.11b/sq in, and the expansion ratio 1,000 :1. At the suggestion of ELDO, a 661b engine is being developed (by Bolkow) simul- taneously with the 1101b engine (ERNO). This appeared to be necessary in view of the great technical difficulties still involved in the construction of extremely small engines. The main bulkhead is the supporting element of the units des- cribed above. It takes up the forces of the engine supports and satellite supports as well as those of the fuel containers, and is attached to the fairing by spot-welding. In view of the variety of loads acting upon the fairing, the follow- ing construction was selected: corrugated sheet titanium is spot- welded on to the surface of a cylindrical inner shell. Internal rein- forcement is achieved by U-shaped circular frames arranged 3.94in apart from each other. All three structural parts are made of titan- ium (thickness 0.0039 to 0.0078in). Eight flaps arranged in opposite pairs are located in the upper section to accommodate the guidance and control electronics. Assembly rings to attach the satellite fairing or the middle section mark the upper and lower limits of the upper section fairing. Twelve explosive bolts will be provided on the cir- cumference between the middle and lower section (stage adaptor). After separation of the third from the second stage, the lower sec- tion remains firmly attached to the second stage. At a given moment during the thrust flight of the third stage, the middle section of the fairing is dropped, too, and only the upper section with the elec- tronic devices remains an integral part of the third stage. Following cut-off of the second stage, either the three engines or only the control engines of the third stage are fired at full thrust. This provides the necessary additional pressure between the stages, which can either be limited by h-p valves located in the stage adaptor or decreased by the stage separation itself. The explosive bolts in- stalled at the separation point are triggered, and the pressure in the stage adaptor, caused by the thrust of the third stage, together with the thrust of the retro-rockets, separates the stages. The test stands necessary for the development and construction of the third stage will be built in addition to those already existing at Trauen (Deutsche Forschungsanstalt fur Luft- und Raumfahrt e.V.) and Lampoldshausen (Deutsche Versuchsanstalt fur Luft- und Raumfahrt e.V.). At Trauen the engines are ground-tested with all their components. At Lampoldshausen the engines so tested are then subjected to altitude conditions and thereupon checked for compatibility with the structure, container and fuel system. This third stage enables the launcher to bring a satellite of more than one ton into polar orbit at an altitude of 311 miles, while the payload capacity for high orbits is about 4411b. By using a third stage with high-energy propellants, the payload can be considerably increased. Comparative studies are currently being made within the ELDO future programmes. 4: SATELLITE TEST VEHICLES By Ministero degli Affari Esteri, Delegazione Italiana ELDO THE SATELLITE TEST VEHICLE (STV) is being developed under the authority of the Italian Government as part of the Italian technical contribution to the ELDO initial programme. In order to study, develop and implement the system, the Italian Government en- trusted Consiglio Nazionale delle Ricerche (CNR) with supervising the programme. It was decided to establish at the Centro Ricerche Aerospaziali—a laboratory of the Aerospace Engineering School of Rome, under the sponsorship of Rome University and the Italian Air Force—an ELDO Integrated Staff to plan that portion of the programme entrusted to Italy by the London Convention. Members of the Integrated Staff are qualified experts from the CRA and experts made available by Italian industries. The Staff is assisted by a Project Review Group whose main task is to transfer experience acquired in other Italian space programmes, such as the San MarCO Project. Continued overleaf
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