Joseph R. Blandino

Dot-Projection Photogrammetry and Videogrammetry of Gossamer Space Structures

This paper documents the technique of using hundreds or thousands of projected dots of light as targets for photogrammetry and videogrammetry of gossamer space structures. Photogrammetry calculates the three-dimensional coordinates of each target on the structure, and videogrammetry tracks the coordinates versus time. Gossamer structures characteristically contain large areas of delicate, thin-film membranes. Examples include solar sails, large antennas, inflatable solar arrays, solar power concentrators and transmitters, sun shields, and planetary balloons and habitats. Using projected-dot targets avoids the unwanted mass, stiffness, and installation costs of traditional retroreflective adhesive targets. Four laboratory applications are covered that demonstrate the practical effectiveness of white-light dot projection for both static-shape and dynamic measurement of reflective and diffuse surfaces, respectively. Comparisons are made between dot-projection videogrammetry and traditional laser vibrometry for membrane vibration measurements. The paper closes by introducing a promising extension of existing techniques using a novel laser-induced fluorescence approach.

Corner Wrinkling of a Square Membrane Due to Symmetric Mechanical Loads

Thin-e lm membrane structures are under consideration for use in many future gossamer spacecraft systems. Examples include sunshields for large-aperture telescopes, solar sails, and membrane optics. The development of capabilitiesfortesting and analyzing pretensioned,thin-e lm membranestructuresisanimportantand challenging aspectofgossamerspacecrafttechnologydevelopment.Resultsarepresentedfromexperimentalandcomputational studies performed to characterize the wrinkling behavior of thin-e lm membranes under mechanical loading. The test article is a 500-mm-square Kapton ® membrane subjected to symmetric corner loads. Data are presented for loads ranging from 0.49 to 4.91 N. The experimental resultsshow that as theload increases the number of wrinkles increases, while the wrinkle amplitude decreases. The computational model uses a e nite element implementation of Stein‐Hedgepeth membrane wrinkling theory to predict the behavior of the membrane. Comparisons were made with experimental results for the wrinkle angle and wrinkled region. There was reasonably good agreement between the measured wrinkle angle and the predicted directions of the major principle stresses. The shape of the wrinkled region predicted by the e nite element model matches that observed in the experiments; however, the size of the predicted region is smaller that that determined in the experiments.

Analytical and Experimental Characterization of Gravity Induced Deformations In Subscale Gossamer Structures

The development of gossamer space structures such as solar sails and sunshields presents many challenges due to their large size and extreme flexibility. The post-deployment structural geometry exhibited during ground testing may significantly depart from the in-space configuration due to the presence of gravity-induced deformations (gravity sag) of lightly preloaded membranes. This paper describes a study carried out to characterize gravity sag in two subscale gossamer structures: a single quadrant from a 2 m, 4 quadrant square solar sail and a 1.7 m membrane layer from a multi-layer sunshield The behavior of the test articles was studied over a range of preloads and in several orientations with respect to gravity. An experimental study was carried out to measure the global surface profiles using photogrammetry, and nonlinear finite element analysis was used to predict the behavior of the test articles. Comparison of measured and predicted surface profiles shows that the finite dement analysis qualitatively predicts deformed shapes comparable to those observed in the laboratory. Quantitatively, finite element analysis predictions for peak gravity-induced deformations in both test articles were within 10% of measured values. Results from this study provide increased insight into gravity sag behavior in gossamer structures, and demonstrates the potential to analytically predict gravity-induced deformations to within reasonable accuracy.

The Effect of Asymmetric Mechanical and Thermal Loading on Membrane Wrinkling

Effect of Asymmetric Mechanical and Thermal Loading on Membrane WrinklingJoseph R. Blandino*James Madison UniversityJohn D. Johnston**NASA Goddard Spaceflight CenterJonathan J. Miles*.**James Madison UniversityUrmil K. Dharamsi ....James Madison UniversityAbstractLarge, tensioned membranes are being considered forfuture gossamer spacecraft systems. Examples includesunshields, solar sails, and membrane optics. In manycases a relatively flat membrane with minimal _wrinkling is desired. Developing methods to predictand measure membrane wrinkling is important to thefuture development of gossamer spacecraft. Numericaland experimental data are presented for a 0.5 m square,tensioned membrane. The membrane is subjected tosymmetric and asymmetric mechanical loading. Dataare also presented for a symmetrically loadedmembrane subjected to spot heating in the center. Thenumerical model shows good agreement with theexperiment for wrinkle angle data. There is alsoreasonable agreement for the wrinkled area for bothisothermal and elevated temperature tests.IntroductionMembrane structures typically exhibit nonlinearbehavior when loaded. Since a membrane structurecannot support compressive stresses, local buckling orwrinkling often occurs. At ambient temperature thewrinkle pattern is dependent upon both the membraneand loading geometry. At elevated temperature thewrinkle pattem may also be a function of the materialproperties and the residual stress state of the membrane.The coefficient of thermal expansion will cause thematerial to expand, while heating may relieve any.residual stress from the membrane that was createdduring manufacturing. Quantifying the wrinklingbehavior of a membrane poses many challenges, bothexperimentally and analytically. Th e purpose of thispaper is to present both experimental and computationaldata quantifying the wrinkling behavior of a squaremembrane subjected to symmetric and asymmetricmechanical loading as well as non-uniform thermalloading.

Comparing Photogrammetry with a Conventional Displacement Measurement Technique on a 0.5m Square Kaptonì Membrane

A comparison between displacement measurements accomplished using photogrammetry and employing a conventional capacitance type displacement sensor is presented. The capacitance type sensor was designed to measure small amplitude displacement on metallic surfaces. Photogrammetry is a technique used by cartographers that has only recently been applied to studying the surface profile of membranes. Commercially available photogrammetry software provides precision estimates during the analysis but these numbers are often application specific and can be difficult to verify. This study compares measurements of the surface profile of an aluminized, 0.5m square Kapton ® membrane. The data shows good agreement between the two techniques provided there are a sufficient number of targets available for the photogrammetry analysis.

Use of High Spatial Resolution Fiber‐Optic Shape Sensors to Monitor the Shape of Deployable Space Structures

We report the use of a fiber‐optic distributed sensing system to monitor the shape of light‐weight deployable space structures. This technique involves using optical frequency domain reflectometry to demodulate the reflected signal from multiplexed Bragg gratings that have been photoetched in the core of an optical fiber. In this work, high‐resolution optical shape sensors were applied to the surface of isogrid booms and used to monitor the shape of the structure subjected to various static and dynamic loading conditions. Data from the fiber‐optic sensors correlates strongly with expected results.

Super Pressure Balloon Non -linear Structural Analysis and Correlation Using Photogrammetric Measurements

ठThe structural analysis of high altitude scientific balloons is studied with the introduction of innovative experimental techniques. A bi -axial material test apparatus is investigated in order to prov ide a more complete definition of fabric material elongation properties. This fabric test device has been under development and a recent balloon material study has provided an excellent opportunity to evaluate its performance. Photogrammetric 3D shape me asurements were conducted as part of a scale model balloon inflation test. Photogrammetry provides a full characterization of the 3D deformation under load so that a more rigorous evaluation of the Lagrangian strain tensor can be made. Pulling these two experimental efforts together, a finite element structural analysis of the balloon inflation test is presented. Material property inputs for the model were taken from both the uni -axial and bi -axial fabric testing. The 3D photogrammerty measurements were used to make detailed comparisons between the model response and that of the balloon experiment. The bi -axial test device was observed to under predict the actual stiffness at the initial points of the elastic modulus curve. At higher load states the bi -axial device provided fill direction modulus measurements that were in better agreement with the material stiffness observed during balloon inflation testing. A similar evaluation of the bi -axial warp modulus measurements was not possible with the range o f loads that were measured. The increase in rigor, made possible by the Photogrammetry data, enabled a valuable evaluation the bi -axial fabric testing device.

Optical Strain Measurement of an Inflated Cylinder using Photogrammetry with Application to Scientific Balloons

A study is presented using photogrammetry to measure the biaxial strain in an inflated cylinder. Two cylinders constructed from polyethylene and each approximately 222 mm in diameter and 930 mm in length were studied. The first had a 0.038 mm wall thickness while the second had a 0.02 mm wall thickness. The cylinders were inflated to a maximum pressure of 1379 Pa. The strain was determined from data collected from 60 retro-reflective targets arranged in a 12 x 5 grid. The uncertainty of the measurement system was determined to be 0.08, 0.04 and 0.06 mm in the x, y, and z directions respectively. The hoop and meridional strains determined from displacement data were compared to values obtained from a finite element analysis of a related proxy problem. The predicted hoop strains showed good agreement over the entire range of pressures while the meridional strains showed good agreement at the lower pressures.

Elevated Temperature Mechanical Characterization of Isogrid Booms

Structurally efficient isogrid booms, manufactured from rigidizable composite materials, are becoming an enabling technology for spacecraft structures because of their high packing efficiency. Selection of the materials used in the construction of rigidizable space structures is commonly driven by mechanical performance properties at elevated temperatures. Mechanical properties testing was performed on composite tow samples and on an isogrid boom at various temperatures. To characterize elevated temperature behavior, the isogrid booms, and its subelement composite tows were manufactured from ILC’s TP283E shape memory polymer (SMP) matrix resin and a carbon reinforcement. Both the flexural modulus and the tensile modulus of the composite tow samples were determined as a function of temperature. These values were compared to the calculated values for the composite based on rule of mixtures analysis. The predicted rule of mixtures composite modulus is used in ILC’s isogrid analytical code to predict the structural properties of the isogrid boom. A number of composite tow samples were fabricated by ILC and mechanically characterized by the Aerospace Corporation to gather independent performance data. An isogrid boom was fabricated by ILC and mechanically characterized at elevated temperatures by James Madison University (JMU). JMU tested this boom in tension, compression, and also performed preliminary creep testing at various temperatures. A similar isogrid boom was fabricated by ILC and tested by The Aerospace Corporation for composite CTE performance. This paper discusses the results of both the composite tow testing and the isogrid boom testing in preand post-packing conditions. A discussion of the correlation between the predicted values and the actual test values is also presented. Introduction NASA and DoD space missions in the near future will require much larger satellites, the sizes of which will be beyond the capabilities of current technologies. The types of Gossamer spacecraft that will be needed include antennas, solar arrays, sunshields, solar sails, and telescopes (Figs. 1-2). Some systems being considered are hundreds of meters in size to accomplish mission goals. Due to the increase in payload size required, innovative support structures, which can be packed into the faring of available launch vehicles, must be developed. In recent years, research and development work has been performed in this area. Of the available options, one of the most promising technological advancements is the rigidizable inflatable structure. A rigidizable inflatable structure is one that is fabricated on Earth, packed into the launch container, and inflated for deployment once on orbit. After deployment, the material is rigidized, or hardened, to form a stiff composite structure that no longer needs the inflation gas for support. This class of structures has unique benefits such as low packing volume, reduced mass, and in most cases, very high deployed structural efficiency. Several types of construction can be used in a rigidizable inflatable including monocoque, isogrid, IsoTruss, and truss-frame booms. Each composite structure can be fabricated into a varying geometric shapes utilizing any number of resin and fiber types. The fibrous reinforcement can be in tow or woven fabric form. In order to optimize the structure, the sizes of the tows and the weave styles of the fabrics can be varied. It is also possible to manufacture near-zero coefficient of thermal expansion (CTE) booms through the fiber and resin selection and by optimizing the volume fractions of each. However, key to all mechanical performance properties is the ability to fold and tightly pack the material. Member AIAA † Associate Fellow AIAA Undergraduate Research Assistant, Dept. of Int. Science and Tech. Associate Professor, Dept. of Int. Science and Tech. Senior Scientist, Materials Sciences Dept. Distinguished Scientist, Space Materials Lab Figure 2. ILC 3.2m Diameter TSU Hexapod Testbed Figure 1. 1⁄2 Scale Next Generation Space Telescope Sunshield

Evaluation of microbolometer-based thermography for gossamer space structures

In August 2003, NASAs In-Space Propulsion Program contracted with our team to develop a prototype on-board Optical Diagnostics System (ODS) for solar sail flight tests. The ODS is intended to monitor sail deployment as well as structural and thermal behavior, and to validate computational models for use in designing future solar sail missions. This paper focuses on the thermography aspects of the ODS. A thermal model was developed to predict local sail temperature variations as a function of sail tilt to the sun, billow depth, and spectral optical properties of front and back sail surfaces. Temperature variations as small as 0.5 oC can induce significant thermal strains that compare in magnitude to mechanical strains. These thermally induced strains may result in changes in shape and dynamics. The model also gave insight into the range and sensitivity required for in-flight thermal measurements and supported the development of an ABAQUS-coupled thermo-structural model. The paper also discusses three kinds of tests conducted to 1) determine the optical properties of candidate materials; 2) evaluate uncooled microbolometer-type infrared imagers; and 3) operate a prototype imager with the ODS baseline configuration. (Uncooled bolometers are less sensitive than cooled ones, but may be necessary because of restrictive ODS mass and power limits.) The team measured the spectral properties of several coated polymer samples at various angles of incidence. Two commercially available uncooled microbolometer imagers were compared, and it was found that reliable temperature measurements are feasible for both coated and uncoated sides of typical sail membrane materials.