Reflector Structural Design The following guidelines were employed in selecting a preferred structural concept: • High specific stiffness and strength • Statistically determinate design • Easy to erect, deploy or assemble • Can accommodate imperfections without increasing stresses • Passive damping through damped joint design • Active damping through memory metals and adaptive structure • Ability to operate at very low fundamental frequencies • Veiy low to zero coefficient of thermal expansion • Low volume for packaging Loading and design conditions include solar radiation pressure, microwave radiation pressure, thermal cycling, ultra-violet and ionizing space environment radiation, gravity gradient loads, maneuvering and pointing control loads, deployment and erection loads, and launch loads. An erectable structural concept requires the least amount of new technology development. It will be of low mass, could be developed in the near future, and deployed with a limited number of launches. Deployable tetrahedral and cubic truss structures have been developed and proven in support of several space programs. The Kapton film-type reflector was selected for use with this structure. A completely deployable reflector would require significant new technology development. Several concepts for large diameter up to 1 km. dia., reflector spacecraft have been proposed in the past. One of the concepts uses a deployable truss rim structure made of composite tubular members. The reflector materials proposed for this concept are either a Kapton film or a compliant mesh type. Mechanical deployment has been one of the most failure-prone aspects of spacecraft operations. Many missions have failed or been severely degraded by deployment failures. This disadvantage can be overcome by selecting a deployable design, incorporating motor-powered deployment involving jack-screw mechanisms of the type often used in jet aircraft for flap deployment. This is a proven and robust method that is highly reliable in aircraft service. Previous spacecraft deployment failures have been associated with spring-deployed systems in which the deployment force must be reduced to prevent build-up of the deployment velocity to prevent causing structural damage when the deployment motion encounters limit stops. Rendezvous and berthing are routine operations. Rendezvous has never failed in the history of U.S. space operations. Berthing or docking has never failed in the U.S. program except for one Gemini mission in which the target vehicle nose cone failed to separate properly and the docking port was not usable. Several missions to retrieve satellites not designed for retrieval, have been performed by the space shuttle.
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