wire used for that sole purpose. Two disadvantages of boron/aluminum use are its relative high cost and difficulty in fabricating non-tubular structural shapes. Nonstructural Materials TZ Solar Concentrator Materials Two materials are considered for use as the solar concentrators (reflectors), aluminized Mylar and aluminized Kapton. Both materials exhibit similar properties except that the Kapton (polyimide) is better for high temperature use than the Mylar (polyester). The concentrator temperature is expected to reach 300°K maximum, and either material should be satisfactory at that level. Both materials can be fabricated on earth in rolls, and transported to orbit for assembly on the SPS structure. One possible concern is the brittle low temperature properties of the materials, which might require special assembly procedures to insure that concentrators are "warm" enough to install without breakage. The use of Kapton favors lower temperature installation. Another consideration meriting additional study is the possibility of utilizing the space vacuum to vapor deposit the reflective aluminum on the Mylar or Kapton surfaces. All advantages/disadvantages of this approach have not been fully evaluated. 2. Coatings Thermal control coatings used in manned spacecraft systems are candidates, but they may not survive combined radiation and vacuum environment for extended periods of time required by the SPS. This class of materials will require testing and likely require development to find acceptably reliable coatings. Evaluation of coatings in use in current unmanned planetary spacecraft such as Mariner and Pioneer will provide significant insight into potential systems for the SPS applications. 3. Elastomers and Adhesives The need for seals and soft surfaces at low temperatures will require some development since few commercial materials will retain enough flexibility at temperatures below 116°K to perform satisfactorily. Silicones, Vitons, and fluoropolymers represent the best systems for immediate considerations. Thermal control systems may be needed for critical systems to prevent leakage or wear in these applications. It is anticipated that adhesive bonding will be a required joining/repair technique for much of the SPS. Structural adhesives are available for use from 127°K to 500°K. Joining of graphite composite members can be done with suitable adhesives, or by special fabrication techniques with graphite composite tapes. Specialized joints requiring multiple connection of several structural members might require reinforcement guide joints which are fabricated on earth and carried into orbit for assembly. 4. Other Nonstructural Materials The other major nonstructural materials proposed on SPS are the electrical conductors (EC Aluminum), solar cells (silicon), and antenna wave guides (aluminum). The wave guides are hollow rectangular tubes with close accuracy slots required on the microwave transmission face. The exact construction techniques required to produce the wave guides should be further evaluated to insure the feasibility of the proposed design. One area requiring additional study is the materials problems associated with the SPS power distribution system. The effective joining of the
RkJQdWJsaXNoZXIy MTU5NjU0Mg==