Figure 10.3.3 Retrodirective Cell Architecture. Subsystem assessment Structure The structure of the SGD-1 (Space to Ground Demonstrator -1) satellite will not be describe in detail because of design decisions yet to be made. The general structure is illustrated in Figures 10.3.4 and 10.3.5. Platform: The structure makes maximum use of light-weight carbon fiber/honeycomb technology. A modular design simplifies satellite assembly and integration activities. A central tube in carbon fiber provides the necessary rigidity for both, and houses the tanks for the propulsion systems. Solar Array: The solar array is composed of two wings. Each wing has a surface of 500 m2. The solar array is deployed by a Deployment Mechanism that is composed of three main parts: driver mechanism, a boom and an interface plate, which connects the deployment mechanism. Thermal Control The thermal control subsystem is important in the design phase because of the harsh thermal environment of the spacecraft in space: • Extremely cold space (4K) • Intense solar illumination (1350 W/m2 in low Earth orbit) • Eclipses (even in sun-synchronous orbit, none at 1500 km) • Vacuum: absence of convective heat transfer The narrow temperatures ranges for spacecraft components, the limited thermal gradients allowed and the thermal stability required makes the thermal mathematical model essential for the validation of the global mathematical model of the spacecraft. The SGD-1 thermal control subsystem goals are globally to keep the temperature of the spacecraft components within allowable ranges for all mission phases by controlling the following parameters: • Net thermal energy exchange with space environment (by selecting coatings and finishes and by heating) • Heat exchange between interior and external surfaces • Heat exchanges between internal satellite components mutually • Local time constants (temperature excursions, selection of materials and their masses)
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