| Summary: | In-space manufacturing (ISM) of large structures with distributed actuators can enable radio frequency (RF) reflectors with previously inaccessible combinations of size and surface precision. A candidate approach for distributed actuation in large space structures is macroscale electrostatic actuation, which offers advantages in low power, high bandwidth, and low parasitic mass. Electrostatic actuation is commonly used in small-scale devices such as nano- and micro-electromechanical systems; however, its application in space structures, especially large structures fabricated via in-space manufacturing, presents novel challenges related to the exotic materials used in space, which must satisfy constraints from processability, environmental compatibility, and electro-thermo-mechanical structural performance. This thesis presents a detailed investigation on the design, processing, and performance of specialized electrodes compatible with an ISM technique termed Bend-Forming. A specific pair of electrodes is considered - a knitted metallic mesh electrode which serves as the RF reflector surface in a Bend-Formed antenna, and a deployable structural element which can be tiled to create a stiff command surface that manipulates the compliant mesh. The mechanical properties of the knitted mesh electrode are characterized via biaxial cyclic loading experiments, revealing anisotropic stiffness, lock-up at high strains, large hysteretic losses under cycling, and kinematic hardening. These insights are then used in a finite element simulation to determine a necessary pre-tension which result in uniform reaction forces at the attachments to a Bend-Formed support structure. The experiments and simulations are used together to determine the pretension for a 10 OPI mesh prototype, fabricated as part of this effort. This mesh also incorporates a specialized catenary system that mitigates wrinkling to maximize useful reflector area.
Next, structural elements that comprise the command surface electrode scheme are designed, manufactured, and tested. Each structural element is a flattenable fiber- reinforced composite boom which could then be coiled and used as feedstock during Bend-Forming. The design process considered two optimization criteria – minimizing transverse deflection under electrostatic pressure and maximizing breakdown voltage – subject to constraints on coilability, compatibility with Bend-Forming, and overall structural performance. A parametric finite element study is used to characterize the effects of different cross-sectional features, e.g. local curvature, opening angle, and flange intersections points, on transverse deflection, with a view towards determining optimally stiff designs that minimize deflection. Separately, experiments and simulations are used to determine a stacking of conductors and dielectrics that can be applied to the boom surface such that each boom is a robust, individually addressable electrode.
The thesis concludes with integration of this electrode pair in an electrostatically actuated mesh reflector. X-band RF testing on this reflector demonstrates in situ control over the reflector surface, enabling beam focusing through adjustment of the focal-length and beam steering by tuning the bias voltage on individual electrodes in the command surface. This work provides a framework for the design of macro- scale electrostatic actuators, with applications ranging from the Bend-Formed mesh reflectors of present interest to a novel class of deployable electrostatically actuated space structures.
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