photogrammetry and videogrammetry methods for … · 2013-04-10 · photogrammetry are possible as...

-1-American Institute of Aeronautics and Astronautics

PHOTOGRAMMETRY AND VIDEOGRAMMETRY METHODS FOR SOLAR SAILS ANDOTHER GOSSAMER STRUCTURES

Jonathan T. Black, George Washington University, NASA Langley Research CenterRichard S. Pappa, NASA Langley Research Center

Abstract

Ultra-lightweight and inflatable gossamerspace structures are designed to be tightly packaged forlaunch, then deploy or inflate once in space. Theseproperties will allow for in-space construction of verylarge structures 10 to 1000 meters in size such as solarsails, inflatable antennae, and space solar powerstations using a single launch. Solar sails are ofparticular interest because of their potential forpropellantless propulsion. Gossamer structures do,however, have significant complications. Their lowmass and high flexibility make them very difficult totest on the ground. The added mass and stiffness ofattached measurement devices can significantly alterthe static and dynamic properties of the structure. Thiscomplication necessitates an alternative approach forcharacterization. This paper discusses the developmentand application of photogrammetry andvideogrammetry methods for the static and dynamiccharacterization of gossamer structures, as four specificsolar sail applications demonstrate. The applicationsprove that high-resolution, full-field, non-contact staticmeasurements of solar sails using dot projectionphotogrammetry are possible as well as full-field, non-contact, dynamic characterization using dot projectionvideogrammetry.

Introduction

The term gossamer is generally applied toultra-low-mass space structures. Frequently thesestructures are designed to be tightly packaged forlaunch, and then to deploy or inflate once in space.Most gossamer space structures rely on ultra-thinmembranes and inflatable tubes to achieve a reduction,compared to standard space hardware, in launch massby a factor of 10 and in launch volume by a factor of50. The technology has been adapted for possible usein a wide variety of applications, including deployableballutes for aerobraking on Mars, telescope sunshields,and membrane space solar arrays. [1 – 4]

Solar sails are studied because of their uniquepotential for providing propellantless propulsion.Through the momentum transfer of reflected photons ofsunlight (sail membranes have highly reflectivesurfaces), solar sails can generate a small butcontinuous acceleration on the order of 1.0 mm/s2. Thisconstant thrust allows travel in non-Keplerian orbits

enabling smaller versions less than 100 meters on a side(square sail) to hold an approximately stationarylocation relative to the Sun or the Earth, such as a polarobserving satellite. Larger sails, over 150 meters perside, will be able to reach Jupiter in only two years andPluto in just a decade [3 – 7].

Useful levels of continuous acceleration areonly achievable in solar sails with very low areal massdensities. The pressure provided by sunlight is just9.12x10-6 N/m2 at one AU, meaning that the spacecraftmust be very large and very lightweight – less thanapproximately 20 grams per square meter overall,including payload – to generate acceptable acceleration.Suitable membranes are less than 5 µm thick with arealdensities less than 7 g/m2 [4, 6, 7]. For comparison,standard 8.5 x 11 inch white paper is 100 µm thick witha density of 75 g/m2. While static and dynamiccharacterization of structures normally requires theattachment of accelerometers or other measurementdevices, the added mass and stiffness of potentiallyhundreds of these devices could drastically alter theproperties of the membrane structure. Therefore, atotally non-contact measurement method such as dotprojection photogrammetry is preferred. This paperdetails the development of dot projectionphotogrammetry and videogrammetry methods forstatic and dynamic characterization of solar sailstructures.

Photogrammetry

Photogrammetry is the science of makingprecise shape measurements from photographs. Togenerate these measurements, multiple images areloaded into the photogrammetry software andassociated with the appropriate calibration parameters.These parameters are calculated independently of themeasurement and allow the software to removedistortions in the images caused by lens curvature andimperfections, focus, aperture setting, and other camerafactors and aberrations.

Totally non-contact photogrammetry uses agrid of targets created by a projector on the test article.Multiple digital cameras then image these targets.After the images are loaded into the photogrammetrysoftware and assigned the calibration parameters, eachof the projected targets are marked to sub-pixelaccuracy using an automatic least squares matching(LSM) algorithm. The points, corresponding to the

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exact centers of the targets, are then matched across theimages and a bundle adjustment algorithm is run thatsimultaneously iterates on the camera and pointlocations, both in three-dimensional space. The finalresult of the process is a set of three-dimensional pointscalled a “point cloud” that is exported for measurement[7 – 11].

Static Application Examples

All three of the applications discussed in thissection were conducted for dual purposes: to developmeasurement methods suitable for use on actual solarsail spacecraft and to obtain measurements forvalidation of structural analytical models. Theexperiments used low-fidelity, generic solar sail testarticles currently at NASA Langley Research Center.These low-fidelity test articles are sub-scale modelsmanufactured from solar sail quality materials but arenot directly scalable to full size solar sails. Thedeveloped methods will be applied to other current andfuture high-fidelity gossamer test structures and spacemissions.

Low Density Full-field Two Meter Kapton Solar Sail

This experiment was designed to assess thefeasibility of using projected circular targets instead ofattached retro-reflective targets on highly reflectivemembrane surfaces. The two meter per side, square,aluminized Kapton solar sail test article shown inFigure 1 was selected for static shape measurementbecause of its continuity (other test articles are dividedinto four quadrants). A pattern of approximately 400dots was projected onto the membrane and imaged byfour consumer digital cameras. The cameras werepositioned at approximately 90o separation at thecorners of the sail and simultaneously photographed itto avoid possible membrane movement betweenimages, as shown in Figure 2.

Figure 3 shows an actual image used in thephotogrammetric processing, with the dot patternclearly visible on the surface of the sail. The image isunderexposed to create high-contrast targets optimal forphotogrammetric measurement.

Several trouble spots are evident in the imagein Figure 3. The long exposure time (30 seconds)required to obtain the images due to the reflectivenature of the membrane allowed ambient light to alsoimage on the sail, causing the background to appearmuch brighter than desired. In the image in Figure 3,ambient light imaging on the upper right corner of thesail drastically reduced the contrast between the dotsand the membrane in that area, leading to a loss oftarget information. Also, there are several “hot spots”in areas where the sail curled, reflecting much morelight into the camera than in the rest of image and

washing out all data (i.e. targets) in that particularregion. Two hot spots are visible in both bottomcorners of the image in Figure 3. The low density ofthe dot pattern creates a low resolution measurementcondition, meaning only the overall shape and not theintricate wrinkle pattern seen in Figure 1 can beadequately characterized from these images. While thelong exposure time, hot spots, and low resolution do notpreclude measurement, they detract from the achievableaccuracy and precision of the process.

Figure 2 shows an image of the point cloudand camera locations created from the 3-D Viewer inthe photogrammetry software, which can be studied toverify that the project processed correctly and that thesetup and result are as expected. The four camerastations (one in each corner of the sail) and the finalpoint cloud are positioned as expected. This resultdemonstrates that the camera positions have beencalculated successfully and that the point locationcalculations have produced a nearly planer three-dimensional cloud, expected when measuring apredominantly flat membrane.

Figure 4 demonstrates how the imperfectionsin the image in Figure 3 affect the photogrammetricprocessing of the project. It shows a close up view ofthe upper right corner of the sail in image in Figure 3after the processing was completed. As discussedearlier, the ambient light in the room led to a loss ofdata in this region of the membrane. Some targets inthe area are not visible and therefore could not bemarked (marked targets are identified by an asterisk).Several other targets do not have sufficient contrast tobe marked using the automatic LSM process andtherefore were marked by hand, reducing precision.The greatest amount of wrinkling occurs at the cornersof the membrane making them important in themeasurement. The ambient light, therefore, has causeda loss of accuracy and data in one of the most criticalareas of the sail.

The photogrammetry software estimatesprecision using error propagation techniques. Theaverage of all the precision values for all of the pointsin the project was calculated to be 0.16 mm, meaningthat overall for the two meter sail, the measurementswere precise to one part in 12,500 (1:12,500).

The three-dimensional point cloudcorresponding to centers (centriods) of the targets wasimported into a contour mapping program, which wasused to visualize the membrane shape. The first step inthe visualization involved the creation of a continuoussurface from the imported, discrete data; a processcalled gridding. Several different algorithms areavailable to the user during grid creation, depending onthe amount of smoothing and interpolation desired.Subsequently the grid was displayed as a shadedsurface representing the out of plane deflection of themembrane surface.


The results of the mapping for the gatheredphotogrammetry data are shown in Figure 5. Theshaded surface shows the overall low-resolution shapeof the membrane. This type of surface measurement isuseful for assessing the overall shape of the structure(e.g. is it warped or flat), but is of little value forcharacterizing wrinkle patterns, which requires high-resolution data. However this experiment doesdemonstrate the feasibility of using non-contact dotprojection photogrammetry to obtain surface shapemodels of highly reflective aluminized membranes. Atest to measure wrinkle pattern and amplitudes of thissame test article is detailed in the following section.

Wrinkle Test of Two Meter Kapton Solar Sail

The wrinkle test described here was performedto investigate if dot projection photogrammetry couldsuccessfully measure small amplitude surface featureson highly reflective solar sail membranes. Such dataare important for validation of structural models andwill lead to better prediction of the contribution ofwrinkling to loss in propulsive efficiency, to predictingand preventing localized hot spots, to understandingmembrane dynamics, and to providing an indication ofthe corresponding film stress. The two meteraluminized Kapton solar sail test article used for thepreviously described measurements (Figure 1) wasselected. The wrinkle pattern of the membrane shownin Figure 1 is a complex phenomena significantlyaffected by the seam running across the middle of themembrane, discrete corner loads, and gravity. Thepattern is marginally stable, changing somewhat withsmall external disturbances such as slight air currents.To obtain a consistent set of images, the four cameraswere again fired simultaneously, freezing the shape.Using attached retro-reflective targets in thisapplication is clearly inappropriate.

To increase contrast, a higher powered theaterprojector was used to create a grid of approximately5000 dots on a 0.9 x 0.5 meter area on the right side ofthe sail, as indicated by the box in Figure 1. The samefour consumer digital cameras used in the lowresolution test, arranged in the same configuration asbefore, simultaneously photographed the grid. Thereflectivity of the aluminized coating of the Kapton thatpreviously led to the use of long exposure times wasagain a complicating factor, but was compensated formuch more effectively. The higher powered projectorand smaller distances involved allowed exposure timesbelow 30 seconds, and the cameras were set to identicalexposure values instead of the identical shutter speedsused previously. An exposure value, which indicatesthe over- or under-exposure of the image, of –1.0 setdifferent shutter speeds in each camera ranging from 15to 30 seconds, resulting in images of similar contrast.

Two of the images used in the processing areshown in Figure 6. The images are nearly optimalwhite-on-black images. The effect of ambient roomlighting on the membrane has been eliminated andwhile a contrast gradient (inconsistent target contrastacross the image) is still present, each image containsuseful data out to the corners of the projected pattern.Note that while hot spots still caused a loss of data inthe image on the right, the nearly uniform contrast in allof the images enabled redundancy that minimized thenegative impact of the hot spots on the final outcome.In general the location of hot spots varies from oneimage to the next.

Figure 7 shows an image of the completedproject created with the 3-D Viewer in thephotogrammetry software. The graphic shows thecamera locations at 90o angles of separation, theirrelative orientations and fields of view, and the finalpoint cloud, all appearing as expected. Figure 8 is amagnified view of the upper left corner of the gridvisible in Figure 6, after the target marking wascompleted. Evident is a higher resolution comparedwith the previous application, indicating that the datapoints are sufficiently dense to measure the visiblewrinkles. The greater density, however, does have adrawback; it is highly computationally intensive tocalculate the positions of over 5000 points. Themeasurement in the low resolution case required hoursto process, while this measurement required almost oneweek. Also apparent in Figure 8 is the sufficientcontrast that allowed the computer to accurately markthe centers of almost all the targets using LSMcentroiding. Automatic centroiding minimized the needfor the human intervention necessary previously,thereby maximizing the accuracy of the markingprocess.

The average precision was calculated to be0.062 mm, yielding an overall precision on the areameasured of 1:32,300. These numbers, combined withthe high target density, allow for confidence in themeasurement of wrinkles less than one millimeter inamplitude. The increase in precision from the lowresolution test shows this measurement to be a markedimprovement, demonstrating that high quality, high-resolution measurements can be obtained for thesestructures using dot projection photogrammetry.Improvements in hardware and technique led to thegains, and further advances, detailed in the next section,will produce still better measurements.

The two views of the shaded surface shown inFigure 9 were created from the 3-D point cloudexported from the photogrammetry software. Thesemaps, normally used for displaying topographic landfeatures, clearly characterize the visible wrinkles in theKapton membrane and the seam cutting horizontallyacross the center. The wrinkle amplitude can also bedetermined in Figure 9. The smallest wrinkle


amplitude is approximately 0.25 mm and the averagewrinkle amplitude is approximately 5.0 mm. The seamand wrinkles visible in the shaded surface match thepattern seen in Figure 1. Note the amplitude in the Z-direction has been exaggerated for better viewing.

These results demonstrate that it is possibleusing careful experimental technique to make non-contact photogrammetric measurements of highlyreflective membranes that accurately characterize theirstatic shape, including wrinkling. These measurementsare the first of sufficient quality to validate analyticalmodels of this configuration. More powerful projectorswill allow high-resolution measurements such as theseon even large gossamer structures.

High Density Full-field Two Meter Kapton Solar Sail

The high density full-field test described herewas designed to generate measurements of comparableresolution to the results in the above high resolutionwrinkle test over the entire surface of the two meterKapton solar sail instead of on only a small section.The same test article was used once again, however, thesail was rotated slightly, as shown in Figure 10, tocreate a small gravity-induced billow in the bottom halfof the membrane. The billow will demonstrate theability of the method to simultaneously measure bothmedium-amplitude wrinkles and global non-planarshapes. Four professional digital cameras at 90o anglesof separation at the corners of the membranesimultaneously photographed a grid of approximately10,800 targets created by high power industrial flashprojector. The use of the professional cameras andturn-key projector signify a transition to professionalgrade hardware designed to yield full-field, high-resolution, high precision measurements the two metersolar sail structure.

One image used in the photogrammetricprocessing is shown in Figure 11. Ambient roomlighting was minimized, but data was still lost due tothe intensity of the flash projector. Because of thebillow in the sail and the angles involved, a percentageof the light reflected by the membrane fell onto thefloor. The high intensity of the projector meant a largeamount of light, when scattered in all directions by thefloor, imaged back onto the membrane. These imagesof the light on the floor were of sufficient intensity towash out the original points. Curling of the membraneand the large distances involved again led to hot spotsin the images; however all of the data loss wascompensated for again by the redundancy of fourcameras.

A three dimensional point cloud similar tothose seen in Figures 2 and 7 again resulted from thephotogrammetric processing. The time required togenerate the final project, however, was much greaterthan in the two previous examples (three weeks vs.

one). The current photogrammetry software was notdesigned to process such a large number of points, over10,000 in this measurement, or to handle such closepoint spacing. The loss of data caused by hot spots andthe image from the floor, shown in the top portion ofFigure 12, added to the overall complexity of theprocessing, making this an extremely demanding andcomplicated measurement. Also evident in Figure 12 isthe ability of the software to mark the projected dotsusing the LSM centroiding, as well as the trueresolution of the projected pattern (impossible to see inFigure 11). In this case, the number of dots per meter isnot quite as high as that used for the wrinkle applicationabove, but it is the highest currently achievable with theavailable hardware. Approximately 10,800 dots wereprojected onto the membrane, and with the small size ofthe targets and the distance from the test article to thecameras (approximately three meters), some dotsappeared as small as five pixels in diameter with aslittle as five pixels spacing. Higher pattern resolutionor larger dots are therefore impractical for thismeasurement given the current hardware configuration.The most important improvement of this measurementover the previous one is evident in the precisionnumbers. Over the four square meters of membranearea imaged, the professional system was precise to 59microns versus 62 microns over less than 0.5 squaremeters imaged previously, meaning that the overallprecision increased from 1:32,300 to 1:50,800.

The shaded surface shown in Figure 13 clearlycharacterizes all the medium-amplitude wrinkles, theseam, and the billow seen in Figure 10. This plotdetails the entire surface of the test article instead ofjust a small area as in the previous application. Thewrinkles are clearly evident, but in addition it ispossible to see the true size of the billow compared tothe wrinkles. The measured wrinkles are on averagefive millimeters in amplitude, matching themeasurement in the previous section, while the billowis almost ten times that size. Also apparent in Figure 13is the tendency of the membrane to curl at the edges.

The shape characterization produced here isunique. A realistic solar sail model has never beforebeen achieved in a full-field, totally non-contact mannerto this resolution. This surface model is of sufficientquality to be used for validation of analytical modelsand for supporting development of hardware andsoftware tools for future measurements and use inspace, achieving both of the stated goals.

Dynamic Analysis of a Two Meter Vellum Solar Sail

Structural dynamic characterization is alsoimportant for the development and validation ofanalytical models supporting future designs ofgossamer structures in general and solar sails inparticular. In the dynamic analysis of these structures,


as in the static characterization, non-contactmeasurement is necessary to avoid altering theresponses of the objects being measured.Videogrammetry expands the methods and techniquesof photogrammetry to multiple time steps yieldingdynamic data. While other non-contact dynamicmeasurement techniques exist, they are not full-field. Itwas hoped that the dynamic data generated would beuseful in simply tracking the overall shape of themembrane as a function of time. The accuracy of themeasurement of the resonant frequencies and operatingdeflection shapes that were extracted, however,surpassed all expectations. [11]

Figure 14 shows the two meter solar sail testarticle measured in this application. The test articlemembranes are 100 micron thick Vellum, a diffusewhite material ideal for dot projection since it scatterslight almost equally in all directions regardless of theangle of incidence. This property enables the Vellum toyield a grid of uniform contrast from any camera angle.The test article is not designed to approximate actualsolar sail material as is the test article used in the firstthree applications, but is designed as a research tool formeasurement method development. Figure 15 showsthe test setup used in the experiment. A grid of 49 dotswas created on the right quadrant of the four quadrantsolar sail by a digital projector and retro-reflectivetargets were attached to the booms. A long-strokeelectrodynamic shaker attached to the tip of the lowerright boom excited the structure with a pseudo-randomforcing function. A turn-key scanning laser vibrometermeasured the frequency response function of the sailquadrant and its corresponding operating deflectionshapes, and is used as a standard against which tocompare and determine the validity of thevideogrammetry results.

At high resolutions, the vibrometer measuresthousands of FFT lines at each point, 1600 in thisapplication, to produce detailed results. However thisform of data acquisition by scanning each pointindividually is slow at low frequencies, requiringseveral hours to run one test. Videogrammetry isattractive because of its ability to measure all of thepoints simultaneously. For the results presented below,the cameras recorded data for approximately tenseconds gathering a total of only 384 frames eachinstead of several sets of 3200 samples (twice thenumber of FFT lines) taken by the vibrometer at eachpoint. While the videogrammetric results shown beloware arguably not as clean as the vibrometer data, theyare full-field, simultaneous measurements taken in justa few seconds instead of hours.

The position versus time videogrammetry datawas loaded into modal analysis software forinterpretation where two different computationalmethods were used. The first involved overlaying thetime histories of individual points and calculating the

Fourier transform of the joint history. The softwarethen animated the Operating Deflection Shapes (ODS)at each peak in the frequency domain. The secondmethod of analysis calculated frequency responsefunctions (FRF). Here only one degree of freedom wasused, the out-of-plane displacement in the Z direction,identical to that used by the vibrometer. For thevideogrammetry experiment the input signal was notmeasured, so a non-node reference point on themembrane was specified enabling the software tocalculate the FRF’s and animate shapes again at thepeaks in the frequency domain. The combined resultsof both of these methods of analysis are comparedagainst the results of the laser vibrometer measurementsin Table 1 below. While neither the ODS or FRFmethod is currently considered to be entirely accurate,some combination of the two will likely capture alldynamics below 5 Hz. Note that the non-linear natureof the deflection shapes, their coupling, and theinability to compensate for atmospheric damping meanthat the shapes shown in Figures 16 through 20 are notactually mode shapes, and that the frequencies listed inTable 1 are not actually modal frequencies. These canalternatively be referred to as “structural resonances”and “resonant frequencies.” [12, 13]

Table 1 – Identified resonant frequencies of the 2 mVellum solar sail

Laser Vibrometer Videogrammetry1.75 Hz 1.77 Hz (ODS)

2.49 Hz (FRF, ODS)2.65 Hz

2.81 Hz (ODS)3.34 Hz 3.28 Hz (FRF)3.67 Hz 3.69 Hz (ODS, FRF)4.74 Hz 4.75 Hz (ODS, FRF)

Examination of Table 1 reveals goodcorrelation between the results found using laservibrometry and videogrammetry. While severalinconsistencies are evident, overall the resonantfrequencies were measured to within 0.2 Hz of eachother. The deflection shapes are shown in Figures 16through 20.

The first two shapes shown in Figures 16 and17 are basically boom driven modes. The firstdeflection shape shows that the booms are in phase, andthe second shows the booms to be out of phase with themembrane following in a first order fashion. Figure 18shows the third deflection shape of the system, with thebooms in phase and the membrane in a second orderconfiguration. The fourth deflection shape (Figure 19)shows the booms to be in phase with a large amplitudefirst order billow of the membrane. Finally, the fifthdeflection shape in Figure 20 shows a saddleconfiguration for the membrane. In all of the figuresvideogrammetry produced similar shapes at similarfrequencies as the vibrometer, demonstrating the


potential of the full-field non-contact dynamiccharacterization technique.

Videogrammetry can only measurefrequencies up to approximately one half the frame rateof the cameras without using stroboscopic flashes.This limitation will not generally be a hindrance for useon gossamer structures because the dominant modeswill occur below 5.0 Hz. Also, the displacement of thetest article must be large enough to be detected by thecameras, whereas the vibrometer is much moresensitive. The above results show videogrammetry tobe capable of achieving full-field non-contact dynamicmeasurements of solar sail structures.

Conclusions

Accurate static and dynamic characterizationof solar sail test articles is vital for creating andvalidating high-fidelity analytical models, developingspace quality hardware, and future advancement of thetechnology. Obtaining accurate static and dynamicmeasurements of the highly reflective ultra-thinmembranes, however, is not a trivial task. Dotprojection photogrammetry and videogrammetry wereused to avoid physically attaching any devices ortargets to the membranes that might alter their staticand dynamic properties. The described tests show aprogression from consumer hardware that produced lowresolution measurements to professional hardware thatproduced high resolution, full-field measurements oflocal wrinkles and global deformations. Dynamicmeasurements were performed using an adaptation ofphotogrammetry to time-dependant data calledvideogrammetry. The data yielded resonancefrequencies and deflection shapes which werecompared to data from a scanning laser vibrometer.The photogrammetry and videogrammetry methodsgenerated results of sufficient quality to be used in thevalidation of numerical models as well as futuredevelopment of solar sails.

Acknowledgements

The authors would like to thank Dr. KeithBelvin, Dr. Kara Slade, Mr. Tom Jones, Dr. AdrianDorrington, Dr. Paul Danehy, and all the members ofthe Ultra-lightweight and Inflatable Structures group atNASA Langley Research Center (LaRC), the membersof the Structural Dynamics Branch at LaRC, Dr. JackLeifer of the University of Kentucky, Dr. Joe Blandinoof James Madison University, and Dr. Paul Cooper, Dr.Robert Blanchard, and Dr. Robert Sandusky of GeorgeWashington University. This work was performed inpartial satisfaction of the Master of Science degreeunder a Graduate Research Scholar Assistantshipprovided by NASA Langley through the GeorgeWashington University.

References

[1] Jenkins, C. H. M. (editor), Gossamer Spacecraft:Membrane and Inflatable Structures Technology for SpaceApplications , Vol. 191, Progress in Astronautics andAeronautics, AIAA, Reston, VA, 2001.[2] Chmielewski, A. B., Moore, C., and Howard, R., “TheGossamer Initiative,” IEEE 0-7803-5846-5/00, 2000.[3] McInnes, C. R., Solar Sailing – Technology, Dynamicsand Mission Applications, Praxis Publishing Ltd, Chichester,UK, 1999.[4] West, J. L., and Derbes, B., “Solar Sail Vehicle SystemDesign for the GEOStorm Warning Mission,” AIAA 2000-5326, 2000.[5] McInnes, C. R., “Solar Sail Mission Opportunities,” RoyalAstronomical Society Discussion Meeting,10 May 2002.[6] Spieth, D. and Zubrin, R., “Ultra-Thin Solar Sails forInterstellar Travel – Phase I Final Report,” NASA Institute forAdvanced Concepts, Pioneer Astronautics Inc., December1999.[7] Pappa, R. S., Jones, T. W., Black, J. T., Walford, A.,Robson, S., and Shortis, M. R., “PhotogrammetryMethodology Development for Gossamer Space Structures,”Sound and Vibration, Vol. 36, No. 8, August 2002, pp. 12-21.[8] Mikhail, E. M., Bethel, J. S., and McGlone, J. C.,Introduction to Modern Photogrammetry, John Wiley &Sons, New York, NY, 2001.[9] Eos Systems, Inc., PhotoModeler Pro User’s Manual,Version 5, Vancouver, B.C., Canada, 2003.[10] Pappa, R. S., Black, J. T., Blandino, J. R., Jones, T. W.,Danehy, P. M., and Dorrington, A. A., “Dot ProjectionPhotogrammetry and Videogrammetry of Gossamer SpaceStructures,” to appear in the Journal of Spacecraft andRockets, NASA/TM-2003-212146, February 2003.[11] Black, J. T. and Pappa, R. S., “Videogrammetry UsingProjected Circular Targets: Proof-of-Concept Test,”NASA/TM-2003-212148, February 2003.[12] Blandino, J. R., Pappa, R. S., and Black J. T., “ModalIdentification of Membrane Structures with Videogrammetryand Laser Vibrometry,” AIAA Paper 2003-1745, April 2003.[13] Batel, M., “Operational Modal Analysis – Another Wayof Doing Modal Testing,” Sound and Vibration, Vol. 36, No.8, August 2002, pp. 22-27.


Figure 1 – Two meter Kapton single quadrant solar sail Figure 2 – Kapton two meter full field test setup

Figure 3 – Image used in photogrammetric Figure 4 – Marked points in upper right corner processing (1 of 4) of the solar sail test article

Figure 5 – Shaded surface for low density measurements of the solar sail test article (Z position amplified)

X Position (m)

Z Position (m)

Y Position (m)

Cameras

Projector

Point Cloud

WrinkleTest Area


Figure 6 – Images used in photogrammetric processing (2 of 4)

1 2

3 4

Figure 7 – Camera locations with fields of view Figure 8 – Marked points in upper left corner of the area imaged

Figure 9 - Two views of contour surface

X Position (m)Y Position (m)

Z P

osi

tio

n (

m)

Y Position (m)


Figure 10 – Two meter Kapton solar sail test article Figure 11 – Image used in photogrammetric rotated slightly with gravity-induced billow processing (1 of 4)

Figure 12 – Marked points in lower right 0.01 m2 of solar sail test article

Figure 13 – Two views of the contour surface generated


Figure 14 – Two meter four quadrant Vellum Figure 15 – Test setup for dynamic solar sail test article characterization

(a) 1.75 Hz Laser Vibrometer (b) 1.77 Hz Videogrammetry (ODS)

Figure 16 - First deflection shape comparison for Vellum solar sail test article

(a) 2.65 Hz Laser Vibrometer (b) 2.49 Hz Videogrammetry (FRF)

Figure 17 - Second deflection shape comparison for Vellum solar sail test article



Figure 18 – Third deflection shape comparison for Vellum solar sail test article


Figure 19 – Fourth deflection shape comparison for Vellum solar sail test article


Figure 20 – Fifth deflection shape comparison for Vellum solar sail test article

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