Figure IV-B-1-c-9b shows a modified inflatable concept in which an essentially parabolically patterned system is inflated and subsequently distorted with tension wires attached to a mainframe to fine-tune the system toward a more perfect paraboloidal shape. The top half of the system is transparent, and the bottom half is coated with a reflective substance. Advantages of this system include a higher concentration ratio than the inflatable spherical system with less overall complexity. Problems exist, however, with orientation of the overall structure and inflation gas leakage. Also, some losses are involved due to reflection of incident solar energy off the transparent surface. Figure IV-B-l-c-9c shows a parabolically patterned reflector system which is rigidized in space. Unless an extremely lightweight foam or other rigidizing material is used, the weight of the rigidizing material would cause the large-area collector system to be excessively heavy. Figure IV-B-1-c-9d shows a petal-type reflector which is a fairly high-precision system requiring a rigid mainframe support structure. The petal-type system was not seriously considered due to the extremely large weight penalty associated with providing a structure rigid enough to insure adequate solar concentration. Figure IV-B-l-c-9e shows a faceted collector of paraboloidal approximation. This is the Boeing concept. Each flat-plate facet is approximately one fourth of an acre in area and is individually steered providing a high degree of system redundancy. Figure IV-B-1-c-9f is essentially the same concept, except that all the facets are mounted in a common plane. Although this concept was first considered for simplicity of construction, it is judged to be inferior to the concept of Figure IV-B-1-c-9e due to shadowing effects as well as its lack of structural rigidity. Figure IV-B-1-c-9g shows a drum configuration with a pair of tensioned nets approximating a paraboloid of revolution. The aluminized thin-film facets would be mounted on the concave side of one of the tensioned nets. This system may or may not need individual facet steering provisions, but in any case is expected to save a considerable amount of weight in reduced mainframe structure. 2.7 Heat Rejection Subsystems The dissipation of waste heat from any space system requires rejection to the space environment. Intermediate devices such as heat pipes may be used to transfer the waste heat with a minimum temperature drop to the radiator system, but the radiating surface itself cannot be eliminated. For this reason it is essential to design into the radiator system the highest possible effectiveness. The effectiveness of a space radiator is the ratio of the amount of heat actually rejected from the radiator to the amount of heat which could be rejected from a fin or plate radiating isothermally to space at the inlet fluid temperature (i.e., no temperature gradients exist in the plate). A high effectiveness is important since the radiator is the heaviest single component of the thermal engine system. Many parameters are involved in the design of a fin-tube radiator system, such as fluid temperature levels, the nature of the space environment (dictated by orbital attitude, surrounding
RkJQdWJsaXNoZXIy MTU5NjU0Mg==