Jonathan T. Black

Evaluation of Shear Compliant Borders for Wrinkle Reduction in Thin Film Membrane Structures

Many ultra-lightweight (Gossamer) space structure designs under consideration for future missions (e.g. solar sails, sun shields, reflectors) are comprised of thin film, flat membrane panels. Such structures must be maintained in a state of biaxial tension in order to suppress wrinkle formation. One such support method under consideration involves the incorporation of integrated, shear compliant borders along the top and bottom edges of the membrane. In this paper, finite element modeling is used to predict the effectiveness of various shear-compliant support geometries. The wrinkle configurations predicted (e.g. amplitude, angle) compare favorably with experimental surface measurements, made using photogrammetry, of membranes incorporating shear compliant borders.

Experimental and Numerical Correlation of Gravity Sag in Solar Sail Quality Membranes

family, due to their potential to provide propellantless propulsion. They are comprised of ultrathin membrane panels that, to date, have proven very difficult to experimentally characterize and numerically model, due to their reflectivity and flexibility and the effects of gravity sag and air damping. Numerical models must be correlated with experimental measurements of subscale solar sails as the first step in verifying that the models can be scaled up to represent full-sized solar sails. In this paper, the surface shapes of two horizontally-supported 25-m-thick aluminized Kapton membranes were measured to a 1.0-mm resolution using photogrammetry. Simple numerical models were developed and their output matched the corresponding experimental data in all cases with less than 33% error. This correlation between the numerical predictions and the experimental data is in line with similar resultsobtainedbyotherswhousedmorecomplexnumericalmodelstopredictthegravity-induced sagoflargersail panels. The results indicate that the largest source of discrepancy between predicted and measured data is membraneslack.Itispostulatedthatincorporationofgeometricslackintothenumericalmodelswouldlikelyreduce this discrepancy.

Measurement of In-Plane Motion of Thin-Film Structures Using Videogrammetry

the shaker. The presence of modally induced in-plane film deformation was confirmed by tracking the change in distance between points F1 and F2. The standard deviation of the value of the measured distance between these two points was found to be about 57 m. This value was well above the noise floor for this measurement, 11 m, experimentallydeterminedbycalculatingthestandarddeviationofthemeasureddistancebetweenpointsR1andR2 on the aluminum film holder, which was considered to be rigid and hence was not expected to undergo in-plane deformation.

Responsive Theater Maneuvers via Particle Swarm Optimization

This research investigates the performance of the particle swarm optimization algorithm in the solution of responsive theater maneuvers, introduced here for the first time. The responsive theater maneuver is designed to alter a spacecraft’s arrival position as it overflies a hazardous geographic region, while still meeting sensor range constraints. The maneuver places the satellite on an exclusion ellipse centered at the spacecraft’s expected arrival position at the expected time of entry into the hazardous region. A global particle swarm optimization algorithm is shown to generate optimal solutions for the single-pass responsive theater maneuver scenario in shorter time frames than local particle swarm variants, a genetic algorithm, and a parameter search. The global particle swarm algorithm is then shown to generate consistent performance in the solution of single-, double-, and triple-pass responsive theater maneuver scenarios for various size exclusion ellipses.

Texture-Based Photogrammetry Accuracy on Curved Surfaces

Photogrammetry is a preferred technique for noncontact measurement of flexible structures, such as large membranes and flapping-wing vehicles. Traditionally, discrete features are triangulated between photos. New techniques use the local texture of a surface to match random speckle among images. Texture-based photogrammetry allows for higher resolution surfaces, and this paper tests if the precision is similar to traditional photogrammetry. Test surfaces provide known, rounded profiles used to compare surface reconstructions. Many images are taken of an object with a projected texture, and the depth error is used to quantify the accuracy of the results. Results on surfacemeshes from800 to 2500 points show accuracy on the order of 1:2000, or nearly that of one pixel. Camera locations had a surprisingly minor effect on surface quality. There is a slight correlation of more parallel views tomore points on the surface. To show that the technique extends to practical use, results are shown for aflapping cycle of amembranewing.Dense surfacemeshes are important for higherfidelitymodels in computational fluid dynamics and finite element analysis.

Optical flow background subtraction for real-time PTZ camera object tracking

The use of pan/tilt/zoom (PTZ) camera systems with Computer Vision (CV) techniques is a burgeoning field. Utility is most commonly seen with security systems, robotics, navigation and for capturing sports events. This paper seeks to expand the use of PTZs in the area of measurement; specifically, the real-time tracking and measurement of Nano/Micro Unmanned Aircraft Systems (UAS). Empirical methods for developing various Nano/Micro UASs, typically ornithopter-related, show possibilities, but require theoretical development for continued understanding and advancements. The study of Nano/Micro UAS state characteristics would enable empirical development by providing supplementary model information for use in finite element and computational fluid dynamics analyses. One such advancement is to develop a metrology system using CV tracking coupled with videogrammetry techniques. The focus of this work is to provide a unique method for obtaining high-resolution, high frame-rate images of a UAS. A novel approach using a Graphics Processing Unit (GPU)-based pyramidal implementation of the Lucas-Kanade feature tracker (i.e. optical flow) to subtract PTZ movement is used to obtain motion measurements for directing the PTZ cameras.

Vibration interaction in a multiple flywheel system

Abstract This paper investigates vibration interaction in a multiple flywheel system. Flywheels can be used for kinetic energy storage in a satellite Integrated Power and Attitude Control System (IPACS). One hitherto unstudied problem with IPACS is vibration interaction between multiple unbalanced wheels. This paper uses a linear state-space dynamics model to study the impact of vibration interaction. Specifically, imbalance-induced vibration inputs in one flywheel rotor are used to cause a resonant whirling vibration in another rotor. Extra-synchronous resonant vibrations are shown to exist, but with damping modeled the effect is minimal. Vibration is most severe when both rotors are spinning in the same direction.

Prototype Development and Dynamic Characterization of Deployable CubeSat Booms

Abstract : The current barrier to CubeSat proliferation is their lack of utility depth. These small satellites are exceptionally well suited for specific space missions such as space weather observation and other scientific data gathering exploits, however, they are not suited for every mission. The 10cm-cube form factor that gives the CubeSat its unique advantage is also its greatest hindrance. A potential bridge over this gap is the successful integration of deployable booms onto the CubeSat structure. With this research, the Air Force Institute of Technology (AFIT) explored the parameters of deployable tapespring booms using the triangular retractable and collapsible (TRAC) cross-sectional geometry developed by Air Force Research Labs (AFRL) and used on NASAs CubeSat, Nanosail-D These booms were augmented with reflective membranes and specifically designed to deploy on orbit for the purpose of ground observation, observations that could later be used to determine the deployed dynamics of the booms from optical data gained passively by solar illumination.

Disaggregated Space System Concept Optimization: Model-Based Conceptual Design Methods

Optimal design techniques have proven to be an effective systems engineering tool. Using systems architecture as the foundation, this paper explores the use of mixed variable optimization models for synthesizing and evaluating disaggregated space system concepts. Model-based conceptual design MBCD techniques are used to identify and assess system architectures based upon estimated system cost and performance trades. The Disaggregated Integral System Concept Optimization DISCO methodology is introduced, and then applied to a space-based, fire detection mission. Several results are obtained that indicate potential cost effectiveness gains from the concept design optimization of a fire detection mission. The general methodology has broad applicability for MBCD of systems, but is particularly useful for dynamic, nonlinear disaggregated space systems.

Measuring and Modeling the Dynamics of Stiffened Thin-Film Polyimide Panels

Stiff, ultralightweight thermal-formed polyimide panels are examples of next-generation space structures that address some of the issues of membrane-dominated ultralightweight structures while maintaining their low mass and low stowage volume characteristics. The research presented here involved dynamically characterizing and modeling two of these panels, one 0.0625 m 2 with a mass of 38 g and the other 0.1875 m 2 with a mass of 81 g, to develop validated computer models that can be used to determine the effects of changing manufacturing parameters and scalability. Modal testing using an impact hammer and accelerometer extracted the first four structural natural frequencies, the first occurring at 71.9 Hz. These data were replicated by simple, coarsely meshed shell element finite element models that are significantly smaller than previous finite element models of similar structures.