ILC Dover, Inc. has developed the wire brake Controlled Deployment Mechanism (CDM) for use in the Inflatable Sunshield In Space (ISIS) Shuttle flight experiment. The ISIS experiment is a 1/3-scale sunshield demonstration unit precursor to the Next Generation Space Telescope (NGST). The NGST sunshield is a 35 × 15 meter diamond-shaped multi-membrane sunshield that will be used to passively protect the telescope from thermal radiation and stray light. The ISIS requirements call for a smooth and predictable deployment of the sunshield by inflatable booms that are governed by the wire brake CDM. To deploy the sunshield, inflation gas is introduced into the inflatable booms, which gives them rigidity and causes them to unroll from the stowed position. As the boom is inflated, the torsional resistance of the wire brake device causes the pressure in the booms to increase until the point where it overcomes the torsional resistance of the wire brake and the boom unrolls. The wire brake operates by converting mechanical energy to heat through the plastic deformation of a ductile metal wire. Associated mechanisms react the torque from the wire brake to the inflated portion of the boom. Through use of the CDM, the boom maintains a constant internal pressure during deployment to provide sufficient structural stiffness. The wire brake governs the internal pressure of the tube such that the boom provides the required force to deploy the sunshade plus any contingency load. Technical information detailing the development, design, analysis, and testing of the CDM are described in this paper.
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