Radio communications apertures for spacecraft have long been implemented using deployable architectures in order to fit within the allowable launch vehicle volume. Apertures for optics missions have traditionally not been segmented because of the tight requirements on the deployed surface. By the nature of the problem, larger apertures are generally better, but complicate orbital delivery. While there are several reflectors commercially available, high packing ratios come at very high cost due to the extremely complex nature of the designs. Researchers at the Space Vehicles Directorate have been investigating ways to enable high packing ratios while reducing the design, integration, and testing complexity of deployable systems, thereby driving down cost and enabling greater mission capabilities. Recent advances in flexible composites have opened up the possibilities of packaging apertures using either distributed or concentrated strain. This paper offers an overview of recent work done to enable lower complexity deployable apertures. Several origami-inspired designs are presented including a flat spiral folding membrane, a parabolic antenna reflector, and a phased array structure.

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A folding concept has been developed which allows a precision membrane aperture to be elastically stowed with a very high compaction ratio without creasing. The lack of creasing is extremely important when the membrane is used in RF or diffractive optics applications because of its effect on the relative placement of surface features. This concept utilizes the spiral wrapped folding approach with a reduced thickness membrane in the folding hinge lines and through-hole strain relief at the intersecting folds. In application, it is intended that this packaging method will be used in an architecture where it is tensioned discretely from the outer edge. These developments allow for high compaction ratios previously only available through folding methods which caused plastic deformations in the membrane.

This work focuses on the analysis of wave propagation in rib-stiffened structures as it is related to Structural Health Monitoring (SHM) methods. Current satellite validation tests involve numerous procedures to qualify the satellite for the vibrations expected during launch, and for exposure to the space environment. SHM methods are being considered in an effort to truncate the number and duration of tests required for satellite checkout. The most promising of these SHM methods uses an active wave-based method in which an actuator propagates a Lamb wave through the structure, which is then received by a sensor. The received waves are evaluated over time to detect structural changes. Thus far, this method has proven effective in locating structural defects in a complex satellite panel; however, the attributes associated with the first wave arrival change significantly as the wave travels through ribs and joining features. Complex isogrid reinforcements within the satellite panel significantly affect any conclusions that can be made about the arriving waves. For this purpose, an experimental and numerical study of wave propagation within rib-reinforced plates has been undertaken. Wave propagation was modeled using finite element software. These results were analyzed for an understanding of dispersion within the structure, particularly how the group velocity and mode conversion are affected by the rib interaction. Experiments were carried out to validate the model and gain further insight into the wave propagation phenomena in the structure. The analysis indicates that mode conversion plays a significant role in the first wave arrival, although this can be accounted for through proper frequency selection, and signal analysis. A range of excitation frequencies which are most appropriate for the structure are presented.

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