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Aviation History
1965
1965 - 0116.PDF
74 FLIGHT International, 14 January 1945 Ariel 2 prototype before and after dynamic spin-up and separation tests in 35ft vacuum chamber at Goddard Space Flight Center Spaceflight mechanical designers finalized the structural design, conducted stress analyses, and produced design specifications of all their sub- systems (basic structure, de-spin mechanism, separation system, reeling devices, experiment and inertia booms, and release mech- anisms). The size and approximate weights of all subsystems and experiments were determined to arrive at the spacecraft's physical configuration, total weight, and moments of inertia. Although spin-stabilized satellites have no active attitude control system, the mechanical group was concerned with attitude changes due to perturbations of the spacecraft while in orbit, caused by solar radiation pressure, magnetic torques and aerodynamic drag. To maintain a favourable orientation of the spin axis, the spacecraft system must be designed so that the ratio of the spin axis moment of inertia to the pitch or roll axis moment of inertia is always greater than unity. This is another reason for the constant monitor- ing of the spacecraft weight, which always seems to grow. The vehicle was also examined to determine the location of the spacecraft umbilical plug, the separation umbilical connector, the "turn-on" plug, the instrumentation plug, and the battery charging requirements. The overall spacecraft dimensions in a folded configuration were compared for physical compatibility with the inside dimensions of the Scout nose fairing, and the location of access doors for the payload plugs in the nose fairing was established. The mechanical and electronic designers work very closely in determining the optimum location of all subsystems within the spacecraft structure. The preliminary layouts are made with spin stability as the only concern. Power dissipation, noise, RF inter- ference and induced magnetism are all considered next in the detailed system design. The final design is a compromise, with no individual subsystem designer being completely satisfied. Many potential trouble areas are avoided through this mechanical and electrical integration interplay. The project management staff, assisted by electronic integration personnel, contributed to the over-all design of the spacecraft by virtue of their advisory responsibilities to the subsystem designers They exercised an influence on the selection of housekeeping functions and on the methods of telemetering them. They served a liaison function between the power system designer and subsystem designers, exercising some influence on the design of all subsystems. While the Ariel 2 system design was in progress, the project manager was required to prepare the project development plan which defined the major areas of responsibility for all project personnel and established a detailed project master schedule. Following completion of the project development plan, the system design specifications document was generated through joint consultation between project management and all the subsystem designers. Included in it were detailed values and limits of the major parameters of all the spacecraft subsystems and experiments. The chief parameters were: voltages, voltage regulation, power require- ments, impedance matching, weight and size, recording speed, playback rate, encoder format, appendage final location, perfor- mance parameters and programming sequence. This document was used as a reference for the major parameter values throughout the entire project. A detailed description of each experiment was included. Subsystem Design Specifications The major mechanical sub- systems are the structure, thermal control, separation device, attitude control, de-spin mechanism and parts of experiments. The major electronic subsystems are the RF portion (modulators, transmitters, aerials, and command receivers), spacecraft instru- mentation (performance parameters, housekeeping functions and attitude control), encoding, data handling, power (solar paddles, batteries, converters, regulators and power supplies), and the experiments. Except for the Ariel 2 experiments, all of these electronic subsystems were supplied by a spacecraft electronics branch, a flight data systems branch, and a space power technology branch of the Goddard Center, which also assisted in the detailed technical integration as required. An integral part of the structural design was the consideration of thermal control. This subsystem was the responsibility of a thermal systems branch. Since the thermal control was of a passive nature, the spacecraft outer surface was designed to accept the desired paints or coatings. The mechanical designers assisted the experi- menters and subsystem suppliers with any mechanical design problems they encountered. They designed special mechanisms and booms for the experimenters and pressurized containers for flight tape recorders. They assisted the power group by designing special cases and containers, heat sinks for converters, and solar paddle structures. The electrical designers contributed by designing circuits for supplying power to all the electro-meehanical areas, such as release mechanisms and erection systems. The electronic systems group for the project assisted the subsystem designers in the completion of their specifications, aad thereafter kept the experimenters informed en the system philosophy and physical design, alerting them to possible system problems. The subsystem design specifications for Ariel 2 were generated by the system engineers (project management staff with coatractor support) and subsystem design engineers. They were fallowed by detailed dimensional drawings, drawings, block diagrams, and
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