Ultra-lightweight Space Structures Research Articles

A reference architecture for orbiting solar reflectors to enhance terrestrial solar power plant output

Orbiting reflectors offer the possibility of illuminating large terrestrial solar power plants to enhance their output, particularly at dawn and dusk when their output is low but energy spot prices can be high. While the concept of orbiting solar reflectors has been considered in various forms in the past, there is now a timely overlap of rapidly growing global demand for clean energy services, falling launch costs through reusability and the emergence of in-orbit manufacturing technologies to enable the fabrication of large, ultra-lightweight space structures. This paper provides an end-to-end analysis of a possible minimum initial architecture to deliver such global clean energy services. The analysis will cover orbit selection, attitude control requirements, structural analysis and economical viability, followed by a discussion on regulatory issues, future improvements and further applications.

Electro-Active Papers for Remotely-Driven Smart Actuators

This paper introduces the concept of remotely-driven smart actuator utilized by electro-active paper (EAPap). The feature of remotely-driven smart actuator offers unique performance and application capabilities and exploit many of these unique capabilities. Since the microwave-driven actuator does not require carry-on-battery, ultra-lightweight, and distributed micro size actuators can be made. A dipole rectifying antenna (rectenna) array receives the microwave and converts it into a DC power. Recently, cellulose based paper has been came across as an lectroactive paper (EAPap) material so as to be used as artificial muscles for biomimetic insects. Since the power requirement of EAPap is less than the safety limit of microwave power in air, the EAPap actuators can be driven by wireless microwave power. This idea is useful for specific applications that require multifunctional capabilities such as smart skin, ultra-lightweight space structures, micro robots, flapping wing for insect-like flying objects and smart wall paper as well. Current research status along with its issues is addressed including a hybrid actuator of EAPap and conducting polymers that will enhance the performance of the actuator.

A Comparison between SISO and MIMO Modal Analysis Techniques on a Membrane Mirror Satellite

The future of space satellite technology lies in the development of ultra-large, ultra-lightweight space structures, orders of magnitude greater in size than the current satellites. Such large crafts will increase communication and imaging capabilities from orbits. Many such proposed ultra-flexible satellites are inflated structures. To get these ultra-large structures in space, they will have to be stored within the Space Shuttle cargo bay and then inflated on-orbit. However, the highly flexible and pressurized nature of these ultra-large spacecraft poses several daunting vibration and control problems. Disturbances (i.e., on-orbit maneuvering, guidance and attitude control, and the harsh environment of space) wreck havoc with the on-orbit stability, pointing accuracy, and surface resolution capability of the inflated satellite. Fortunately, recent advances in integrated smart material systems promise to provide solutions to these problems. Recent research into the use of Macro-Fiber Composite (MFC®) devices integrated into the dynamic measurement and vibration control of inflated structures has had promising results (Wilkie et al., 2000). These piezoelectric-based devices possess a superior electro-mechanical coupling coefficient making them superb actuators and decent sensors in dynamic analysis applications. Initially, research was performed on an inflated torus using single-input, single-output (SISO) testing techniques. Since then, steps have been taken to outline a new, multiple-input, multiple-output (MIMO) testing technique for these ultra-large structures. This study applies these results to an inflated torus with bonded membrane mirror to extract modal parameters, such as the damped natural frequencies, associated damping, and mode shapes within the frequency bandwidth of interest for these structures (5–200 Hz). Further, the nonlinear dynamic behavior of the inflated torus and membrane mirror is accentuated through a comparison of SISO and MIMO modal analysis techniques, and a discussion of the nonlinear results follows. The purpose of this work is to apply the results from prior works to an inflated torus with bonded membrane mirror to accomplish the following three goals: (1) to establish a baseline dynamic characterization of the test structure using SISO modal analysis techniques;(2) to perform a MIMO modal analysis of the test structure to identify natural frequencies, mode shapes, and damping ratios, and compare these MIMO results to the SISO analysis; and(3) to use the discrepancies between the two testing technique results as a platform for discussing the nonlinear nature of the test structure. In the future, the results of this work may form the premise for an autonomous, self-contained system that can both identify the vibratory characteristics of an ultra-large, inflated space craft and apply an appropriate control algorithm to suppress any unwanted vibration – all while on-orbit.

Transparent, flexible, conductive carbon nanotube coatings for electrostatic charge mitigation

Low color, space environmentally durable polymeric films with sufficient electrical conductivity to mitigate electrostatic charge (ESC) build-up are needed for applications on advanced spacecraft, particularly on large, ultra-light weight space structures. For these applications, the films must exhibit electrical conductivity that can survive the folding and unfolding required for packaging and deployment. The work described herein consists of coating the surface of polymer films with a thin layer of single-walled carbon nanotubes (SWNTs). Surface resistivities in the range sufficient for ESC mitigation were achieved with minimal effects on the optical and thermo-optical properties of the films. Bending, folding or crumpling did not affect the surface resistivity of the coated films. The preparation and characterization of SWNT coated space durable polymer films are discussed.

Laser-Induced Fluorescence Photogrammetry for Dynamic Characterization of Membrane Structures

Photogrammetry has proven to be a valuable tool for static and dynamic profiling of membrane-based inflatable and ultralightweight space structures. However, the traditional photogrammetric targeting techniques used for solid structures, such as attached retroreflective targets and white-light dot projection, have some disadvantages and are not ideally suited for measuring highly transparent or reflective membrane structures. In this paper, we describe a new laser-induced-fluorescence-based target generation technique that is more suitable for these types of structures. We also present several examples of noncontact noninvasive photogrammetric measurements of laser-dye doped polymer membranes, including the dynamic measurement and modal analysis of a 1 m X 1 m aluminized membrane.

Microwave power for smart material actuators

The concept of microwave-driven smart material actuators was envisioned anddeveloped as the best option to alleviate the complexity and weight associatedwith a hard-wire-networked power and control system for smart actuator arrays.The patch rectenna array was initially designed for high current output, but hasundergone further development for high voltage output devices used in shape controlapplications. Test results show that more than 200 V of output were obtained from a6 × 6 array at a far-field exposure (1.8 m away) with an X-band input power of 18 W. The6 × 6 array patch rectenna was designed to theoretically generate voltages up to 540 V,but practically it has generated voltages in the range between 200 and 300 V.Testing was also performed with a thin layer composite unimorph ferroelectricdriver and sensor and electro-active paper as smart actuators attached to the6 × 6 array. Flexible dipole rectenna arrays built on thin-film-based flexible membranes are mostapplicable for NASA’s various missions, such as microwave-driven shape controls foraircraft morphing and large, ultra-lightweight space structures. An array of dipolerectennas was designed for high voltage output by densely populating Schottky barrierdiodes to drive piezoelectric or electrostrictive actuators. The dipole rectenna array willeventually be integrated with a power allocation and distribution logic circuit andmicrobatteries for storage of excessive power. The roadmap for the development of wirelesspower drivers based on the rectenna array for shape control requires the development ofnew membrane materials with proper dielectric constants that are suitable for dipolerectenna arrays.

PHOTOGRAMMETRY OF A 5M INFLATABLE SPACE ANTENNA WITH CONSUMER-GRADE DIGITAL CAMERAS

This paper discusses photogrammetric measurements of a 5m-diameter inflatable space antenna using four Kodak DC290 (2.1 megapixel) digital cameras. The study had two objectives: 1) Determine the photogrammetric measurement precision obtained using multiple consumer-grade digital cameras and 2) Gain experience with new commercial photogrammetry software packages, specifically PhotoModeler Pro from Eos Systems, Inc. The paper covers the eight steps required using this hardware/software combination. The baseline data set contained four images of the structure taken from various viewing directions. Each image came from a separate camera. This approach simulated the situation of using multiple time-synchronized cameras, which will be required in future tests of vibrating or deploying ultra-lightweight space structures. With four images, the average measurement precision for more than 500 points on the antenna surface was less than 0.020 inches in-plane and approximately 0.050 inches out-of-plane.