Hybrid Self-deployable Tubular CFRP Booms for Deployable Membrane

Transcription

1 Hybrid Self-deployable Tubular CFRP Booms for Deployable Membrane By Takaomi CHUBACHI 1) Hiroshi FURUYA 1) and Akihito WATANABE 2) 1) Tokyo Institute of Technology, Yokohama, Japan 2) Sakase Adtech Co. Ltd., Fukui, Japan This paper presents the hybrid self-deployable tubular CFRP boom to improve the performance of deployment torque by extending the self-deployable tubular CFRP booms we have developed and the properties of storing and deployment torque experimentally. We propose the hybrid self-deployable tubular CFRP boom by installing a metal convex tape in the conventional self-deployable tubular CFRP boom so as to keep the foldability with higher deployment torque and to reduce the decrement rate of deployment torque due to a long term stored state. To investigate the performance of the hybrid selfdeployable tubular CFRP boom, the detailed properties of storing and deployment torques are experimentally examined. Because the self-deployable tubular CFRP boom which consists of two half cylindrical CFRP bound with elastomer film has attractive features with wrapping foldability and high torsional stiffness due to the closed cross-section, however the storing and deployment torque properties are quit complex. The measurements have been performed by measuring the bending angle of the self-deployable tubular CFRP boom for the given bending torque. Experimental results show the detailed properties of storing and deployment torque quantitatively as well as the effects of the fixation conditions. Also, the decrement properties of deployment torque are examined for the self-deployable tubular CFRP boom and hybrid one. Key Words: Self-deployable, CFRP boom, tape, Buckling Nomenclature θ : bending angle of boom from the initial condition φ : bending angle of boom from horizontal line ψ : initial inclination angle L : boom length M : weight l : length of the center of gravity from loot m : boom mass T : torque H : height of boom fix end h : height of boom tip 1. Introduction Solar Sail, deployment thickness membrane stored on the ground in space and generating electricity by thickness solar cell on the deployed membrane, has been considered before. Deployment mechanism for membrane in space are divided into two types roughly, spin type and deployable boom type. Spin type use centrifugal force to deploy membrane. This type is suitable for increasing in size of satellite, however operation of the satellite is troublesome. For operational experience in real, exists experimental spacecraft IKAROS 1). IKAROS deployed 14[m] square thickness membrane in two stages by using centrifugal force. Also, using this experience, development of 5[m] square solar sail is considered 2). On the other hand, deployable boom type is advantageous for use of small satellite. In particular deployment of SAR antenna (16[m] 4.5[m]) DLR (25) has lightweight deployable boom which the cross-section is Ω-shape 3). This type is extending and deploying high torsional boom from stored state by feed mechanism. Though Ω-shape boom is high stiffness for closed cross-section, it is hard to manufacture and use easily. For deployable boom using feed mechanism, STEM (Storable Tubular Extendible Member) exists 4). Moreover, bi-stem, arranged double in antiphase and connected with aperture at the top of STEM, has higher stiffness than STEM 5). Main feature for every boom is deforming cross-section largely and having high storability in storing process. However, conventional deployable boom type is hard to use for microsatellite in terms of weight and size because of the fees mechanism and the stored state, deployment using not feed mechanism but restoring force of boom (self-deployable boom) is considered, recently 6). Additionally, BCON boom, consists of two convex tape covered with braid, is deployable boom using elastic energy too 7). This boom has lower stiffness because of opened cross-section than CFRP boom proposed in 6). However, the construction of boom makes the boom easily to store 7). Furthermore, there is cylindrical shell structure having hinge which consists of three transversally curved strips of material as convex tape 8). Additionally, as developing and using microsatellite, there is needed de-orbit for satellite expired the operation 9). Then, mounting small and lightweight deployment mechanism using self-deployable boom and deploying membrane, decelerate the revolution velocity of satellite at the end of operation, and fulfill de-orbit. For deployment membrane using self-deployable boom, the deployment force influence the success of deployment. Though 1

2 the deployment torque is evaluated analytically 8), is not evaluated experimentally. Torque is only measured within the range of minute bending angle on reference 7). Then, selfdeployable boom is still the stage of deployment. Hence, propose of boom more suitable for deployment and evaluate about the stowing and deployment torque of boom, quantitatively. 2. Self-deployable tubular CFRP boom 2.1. The boom consists of CFRP tube and elastomer as Fig. 1. Two CFRP tube places face-to-face so that the cross-section is circle, and it is covered with elastomer. We can deform the cross-section as hinge of joint between tubes as Fig. 2. This boom is high torsional stiffness due to the closed cross-section and so, withstands lateral buckling in the deployment process. Local deformation Elastomer film Fig. 1. Cross-section of tubular CFRP boom. Store Deploy Fig. 1. Deformation of cross-section. Half cylindrical CFRP torsional stiffness due to its open section configuration with respect to the CFRP booms. To examine the mechanical properties of hybrid selfdeployable tubular CFRP booms, three types of configurations are investigated as shown in Fig. 4. Figure 4 (a)-(c) are cross-section of hybrid self-deployable tubular CFRP booms used in the experiments. Where, Fig. 4 (a) and (b) are single convex model, which outer and inner convex models which is installed in the CFRP boom so that the convex tape becomes the outside and the inside when the bending load is applied, respectively, and Fig. 4(c) is the bi-convex model. (a) Outer single convex (b) Inner single convex 3. Fixation condition (c) Bi-convex Outer side convex Inner side convex Fig. 4. Configurations of hybrid tubular CFRP boom As the properties of storing and the deployment torque for the CFRP booms depend on the fixation condition, two types of fixation conditions are considered in the experiments. Note that, as referred in section 2.1, it is hard to measure the torque by three-point bending test and four-point bending test because of large deformation of boom cross-section. Thus, consider the properties of torque by experiment based on cantilever. Complete fixation is the one to confirm the properties of boom torque originally by fixing well away from buckling point. On the other hand, main feature by one side fixation is that boom is fixed by only one side and buckling point is near the fixed point. Each feature has an effect on the deformation of boom cross-section. This type is the fixation on microsatellite ORIGAMI-SAT1, this comparison shows the effect by limited condition aimed at small storing. Length for buckling Fig. 3. Deformation of cross-section and tubular CFRP boom 2.2. Hybrid tubular CFRP boom The decrement of deployment torque due to a long term stored state before deployment is critical technical issue to apply the self-deployable CFRP booms into the space missions as deployment of deorbiting membrane for satellites. To overcome the technical issue, a hybrid self-deployable tubular CFRP boom where a metal convex tape is installed is proposed to improve the deployment torque and to reduce the decrement rate of deployment torque without disturbing the foldability, because the metal convex tape has higher durability for bending torque in a long term storing state although low Round bar for bend (a) Complete fixation Fig. 5. Length for buckling (b) One side fixation Fixation for tubular CFRP boom 2

3 At first, we consider the relation between torque and bending angle for boom by complete fixation, then one side fixation. Fig. 5 and Fig. 6 shows the side-view respectively, two types of fixation and for hybrid tubular CFRP boom by one side fixation. Hub Boom Bi-convex (a) Outside single convex (b) Inner single convex Fig. 8. (a) Storing process Example of wrap fold. Bending angle of boom is approximately π/2 [rad] on every time Torque properties by complete fixation Experiment setup and measurement Figure 9 shows the experiment setup in this work. Boom is inclined and fixed the root by the exclusive parts. The boom is loaded and unloaded by some washers as weight at the tip. Boom (b) Stored boom Bi-convex Weight Fig. 6. (c) Bi-convex Hybrid tubular CFRP boom by one side fixation Fig. 9. Experiment setup (complete fixation) (outer) (a) Outer single convex Bi-convex (c) Bi-convex The boom is loaded gradually from no load condition to the deformed condition around buckling point largely, then unload. Figure 1 represents the process. Note that when cross-section deforms largely, shift slowly the boom becoming a state of equilibrium. Additionally, the measuring range of bending angle is -1/2π [rad]. Where, loading and unloading process is the storing and deployment process, respectively. Fig. 7. End processing of convex tape 4. Properties of torque for self-deployable tubular CFRP boom 4.1. Purpose of experiment Self-deployable tubular CFRP boom adopted as the method for deploying membrane in space is, stored with membrane in the state of deformed cross-section. Where boom is bent at the corner of central hub as Fig. 8, repeatedly. Deployment result depends strongly on boom torque in the deployment process. Torque of self-deployable boom is however still not evaluated and studied. Thus, the purpose of experiment is to evaluate the properties of boom torque in the storing and deployment process by bending and restoring initial straight boom. (a) No load condition (b) Loading process (c) After local deformation (d) Unloading process Fig.1. Loading and unloading process 3

4 Analysis model Figure 11 implies the analysis model on this experiment. θ is bending angle of boom from initial condition and T is torque. By measuring, L, H, h on each weight, bending angle from initial condition, θ and torque, T is obtained. Geometric relationship implies Properties of torque for tubular CFRP boom by complete fixation in storing and deployment process Performing experiment by the setup as Fig. 9 makes the result as Fig. 13. In the storing and deployment process, when bending angle, θ varies largely snap-through occurs by occurrence or recovery of local deformation. Fig. 13 shows the value of boom torque is different largely depending on the configuration of the cross-section..4 Round bar for bend H l L ψ φ mg Horizontal line Boom Mg h Fig.1(b) Fig.1(a) Fig.1(d) Fig.1(c) Fig. 11. Analysis model Base line Initial inclination angle Angle between horizontal line and inclination of initial condition for boom, ψ on this work is approximately 1/6π [rad]. This value is derived from error assessment to restrain torque fluctuation by measuring error on measurement range, θ = - 1/2π [rad]. Evaluating the error, δh about measurement height, h lead to the following Eq. (4). Fig. 12 shows comparison between Eq. (5) and bending angle from the horizontal line, φ. This figure implies error ratio, dt/t is less than.1(=1 [%]) when the error, δh is.5 [mm] and bending angle from horizontal line, φ is less than 1/3π [rad], so when inclination angle, ψ is 1/6π [rad], torque fluctuation by measuring error is restrained on measurement range, θ = - 1/2π [rad]. Fig. 13. condition 1/6π 1/3π 1/2π 2/3π Torque history for tubular CFRP boom with complete fixation 4.3. Properties of torque by one side fixation condition In this section boom torque by one side fixation implies the influence by the fixation. By one side fixation, we can see the difference for buckling point as Fig δh=.5[mm] δh=1.[mm] Error ratio, δt/t (a) Complete fixation.4.2 1/12π 1/6π 1/4π 1/3π 5/12π Bending angle, φ[rad] Fig. 12. Relation between error ratio, dt/t and bending angle, φ [rad]. As increasing bending angle, error ratio increase drastically. Fig. 14. (b) one side fixation on each fixation 4

5 Experiment under the condition as Fig. 14-(b) showed the result as Fig. 15. The buckling torque is different behavior and the deployment torque corresponds to each other in Fig. 15. That is the behavior before boom local deformation is affected strongly by the fixation condition and the behavior after boom local deformation is not. absence of convex tape on the side applied compressive stress makes the storing stiffness. The storing stiffness is, thus, affected strongly by the condition of inner side of boom. Note that, the boom and hybrid boom with bi-convex is made in Sakase Adtech Co. Ltd, then the outer and inner model are installed in our laboratory Tokyo Tech to investigate the property..4 Complete One side Fig /6π 1/3π 1/2π 2/3π Torque histories by complete fixation and one side one 1/6π 1/3π 1/2π 2/3π Fig. 17. Torque histories for boom only and boom with bi-convex 4.4. Properties of torque in the storing and deployment for hybrid tubular CFRP boom In Fig. 16 each boom deformed around buckling point and occurred snap-through in loading process. Also in unloading process, convex tape makes boom torque increase. On the other hand, there is a different behavior for boom with outer single convex on snap-through. Thus, combination with boom and metal convex tape makes snap-through complicated /6π 1/3π 1/2π 2/3π Fig. 16. Torque histories for boom only and boom with outer single In Fig. 17, boom with bi-convex occurred snap-through in loading and unloading process. Where, bending and observing the boom, new snap-through for hybrid boom is occurred by the condition inner side of boom buckled and outer side didn't. Additionally the increment of deployment torque is larger than single one. Figure 18 shows outer convex makes boom torque more increase than inner convex. Moreover, in the behavior from no load to just before local deformation as Fig. 19, the presence or With inner convex 1/6π 1/3π 1/2π 2/3π Fig.18. Torque histories with outer single convex and inner one With inner convex 1/12π 1/6π Fig. 19. Torque histories (before local deformation) 5

6 4.5. Experiment about the decrement of deployment torque Purpose of experiment and measurement We have performed deployment experiment under microgravity environment in airplane on Feb Although the boom stored with membrane in central hub as Fig. 8 deployed successfully on the ground, the deployment under microgravity was end in failure. This is because a long term stored state before deployment. We need to evaluate fluctuation of torque for boom in a long term stored sate before deployment because it will pass in some months or years as it is stored before deployed in space. Therefor in adaption of deployment structure using CFRP boom, this phenomenon requires the design taken into account the decrement of deployment torque. In this experiment, deformed boom which bending angle θ is approximately 11/18 [rad] (weight is approximately 7[g]) is loaded for some hours, then unloaded. That is, evaluate the relation between deployment torque and loading time for boom Properties of torque for tubular CFRP boom in a long term stored state Figure 2 is the result behavior when unloaded immediately after the load for boom and unloaded after 168[hour]. Torque and stiffness decrease in the deployment process in Fig No loading time 168[hour] Fig [hours] /6π 1/3π 1/2π Torque history for each boom only on no loading time and The time history of torque for boom in a long term stored state We need to estimate torque after some months, some years from the relationship between loading time and the decrement of deployment torque. Thus, find out the torque on bending angle, θ = 9, 8, 7[degree] by comparing with each torque in unloading process after loading, t [hours]. Then obtain the relationship between boom torque and loading time on each bending angle. The approximation line in Fig. 22 is power approximation represented on Eq. (6). The value of variation, a, b is listed in Table. 1. Table. 1. Variation, a, b for tubular CFRP boom on each bending angle 9[deg] 8[deg] 7[deg] a Fig. 2. 1/6π 1/3π 1/2π Torque history for boom only on no loading time and 168[hour] Properties of torque for hybrid tubular CFRP boom in a long term stored state In section the decrement of deployment torque of boom in a long term stored state is disclosed, then observe the properties of torque for hybrid tubular CFRP boom in a long term stored state in this section. Figure 21 is the result on same experiment for hybrid boom with outer single convex and with bi-convex. The result implies the decrement of deployment torque occurs for every type. C[Nm] [deg] 8[deg] 7[deg] approximation Loading time, t[h] Fig. 22. Relation between torque and loading time for tubular CFRP boom on 9,8,7[degree] 6

7 Time history of torque for hybrid boom in a long term stored state By the same experiment for hybrid boom, consider the properties of torque for hybrid boom loaded t[hour]. Figure 23 implies torque of hybrid boom (with bi-convex) decreases as with Fig. 21, and Table. 3 is concrete parameter about the approximation for torque decreasing. Figure 24 is the relation between exponent, a and bending angle, θ. The relation shows hybrid boom reduces the decrement rate of deployment torque [deg] 8[deg] 7[deg] Approximation 5. Conclusion The mechanical properties of the hybrid self-deployable tubular CFRP booms were experimentally investigated. To measure the storing and deployment torque in the course of deformation process the measurement system based on the bending method for cantilevered beam was developed, and the storing and deployment torque histories were obtained. The experimental results shown the following properties; 1) The fixation condition strongly affected the storing stiffness and the maximum buckling torque and therefore the performance of storing performance. 2) The deployment stiffness and the deployment torque were not affected by the fixation condition. 3) The hybrid self-deployable tubular CFRP boom installed a metal convex tape in the boom was improved for the deployment torque and the storing stiffness. 4) The decrement rate of deployment torque for long term store state was characterized by the power of the stored time, and it was depended on the stored bending angle. Acknowledgments Fig. 23. Loading time, t[h] Relation between torque and loading time for hybrid tubular CFRP boom (with bi-convex) on 9,8,7[degree] Table. 2. on each bending angle Exponent, a Variation, a, b for hybrid tubular CFRP boom (with bi-convex) 9[deg] 8[deg] 7[deg] a C[Nm] Fig /3π 1/2π Relation between exponent and bending angle The authors appreciate IKAROS project members for valuable suggestions on this study and significant assistance for the experiments. This study has been supported by Japan Society for the Promotion of Science (JSPS), Grant-in-Aid for Scientific Research (B), No , and ORIGAMI Project (ORganizatIon of research Group on Advanced deployable Membrane structures for Innovative space science) granted by Aerospace science and technology promotion program by The Ministry of Education, Culture, Sports, Science and Technology, Japan. References 1) Tanaka, K. et al.: Development of Thin Film Solar Array for Small Solar Power Demonstrator IKAROS, Proceedings of the 61st International Astronautical Congress, Czech Republic, 21, IAC- 1.C3.4.3, pp ) Mori, O. et al.: Jovian Trojan Exploration by Solar Power Sail-craft, International Symposium on Space Technology and Science, Japan, 215, 215-k-14, pp ) Leipold, M. et al.: Large Membrane Antennas with Lightweight Deployable Booms, 28th ESA Antenna Workshop on Space Antenna Systems and Technologies, The Netherlands, 25, pp ) Rimrott, F.P.J, Fritzsche, G.: Fundamental of STEM Mechanics, IUTAM-IASS Symposium on Deployable Structures Theory and Applications, Kluwer Academic Publishers, Eds. Pellegrino, S. and Guest, S.D., 2, pp ) J.D. MacNaughton, et al.: The Bi-STEM -A new Technique in Unfurlable Structures, Second Aerospace Mechanisms Symposium, Santa Clara, 1967, pp ) Furuya, H., et al.: Deployment Dynamics of Membrane-Boom Wrapped Structures, 65th International Astronautical Congress, Canada, 213, IAC-14-C2.3.1, pp ) Okuizumi, N., et al.: Stepwise Deployments of Membrane Structure with Braided CFRP Bi- Booms, 3th International Symposium on Space Technology and Science, Japan, 215, 215- C-28, pp ) Soykasap, Ö.: Deployment analysis of a self-deployable composite boom, Composite Structures 89, 29, pp ) Kuwahara, T., et al: A Sail Deployment Mechanism for Active Prevention and Reduction of Space Debris, Proceedings of the 62st International Astronautical Congress, South Africa, 211, IAC-11- A6.4.7, pp