Configuration Synthesis Of Deployable Rectangular Pyramid Unit And Mechanism Design For Modular Array Antenna

Satellite array synthetic aperture radar(SAR) has been widely applied in high-resolution earth observation. Deployable truss structures are the core components that ensure smooth deployment and high rigidity. Development trends, such as high resolution and large irradiating width, have resulted in a great SAR array size. A novelty module and expanded deployable truss structures are needed to meet the future requirements of satellite SAR. Meanwhile, a modular deployable truss structure is a complex spatial mechanism that is multi-looped and highly flexible and that has some special features. However, some common issues remain unsolved, such as the topological structure description and analysis method, over-constrained configuration synthetic approach, design variables and constrained correlation decoupling method, deployment process for accurate analysis and descriptive indexes, and others. All these issues restrict the performance evaluation and engineering application of deployable truss structures.To design novel configuration of pyramid deployable t russ structure(PDTS), a three-step topology structure analysis and design approach is proposed:(1) the conceptual configuration is synthesized;(2) topology structure is analyzed;(3) deployable truss structures are designed. Definition and classificatio n of the deployable truss structures are proposed according to the space application. A weighted graph and adjacency matrix are established to realize the topological description for PDTS. Algorithms A and B of the conceptual configuration for PDTS are then proposed. Topology graph is present to describe and analyze the relationship between the components of the deployable truss structures. Algorithm C is then established to construct topology graphs of the deployable truss structures. A kinematic pair of allocated principles of the deployable truss structures is given, and a design flow(algorithm D) is established. The topology of PDTSs are analyzed and designed systematically based on algorithms A, B, C, and D. All 11 rectangular PDTS(RPDTS) conceptual configurations, which can be folded on a plane, are discovered using the three-step method.The over-constrained RPDTS are synthesized systemically based on screw theory. The smooth deployment conditions of the deployable truss structures under an over-constrained situation are deduced based on a virtual work principle. A configuration synthesis flowchart for over-constrained deployable truss structures is raised(algorithm E). RPDTS is synthesized in detail under 12 common constraints of a screw coordinate system and redundancy constraints based on the front flowchart. Moreover, a series of RPDTSs, whose folded state is planar, is obtained. Dynamic simulation results predict that these RPDTSs can deploy swimmingly.Modular deployable truss structure unit schemes are presented based on the proposed deployable truss structure design and synthesis method. These schemes are then evaluated and optimized by fuzzy theory. A design scheme of modular deployable truss structure for large SAR antenna is presented. A dep loying kinematic model is built. The kinematic parameters and singularity of every loop for the deployable truss structure are analyzed and decoupled. A cubic polynomial is employed as the drive function, which can plan a smooth deployment path without singularity. The deploying kinematic model is verified by kinematics simulation.Considering flexibility, a desynchronized deployment phenomenon occurs during deployment, which is evident in the acceleration and deceleration phases. The dynamic equivalent model of the deployable truss structure is presented. This model simplifies solving procedures and predicts the required drive moment for deployment. A flexible deployment model with ground friction of the deployable truss structures is constructed to thoroughly investigate the process of deployment. Three indexes are identified to describe deployment: deployment synchronism, steady driving torque, and maximum strain energy. The surrogate models of the key parameters are modeled based on the response surface method. Three key parameters are set as the optimal object to solve the desynchrony phenomenon by designing and allocating a drive assistance spring. Thus, the synchronism of the optimal modular deployable truss structures has significantly improved.The launching state modal, operative state modal and on-orbit thermal deformation are analyzed by the finite element method. The effect for stiffness of each joint on fundamental frequency of deployable structure is investigated. The modular deployable truss structure of the array antenna is optimized for minimum thermal deformation, mass and fundamental frequency by allocating truss thickness and the coefficient of thermal expansion. Its achievable technical performance is described as follows: the deployment dimension is 15000 mm × 1400 mm, folded dimension is Φ2400 mm × 2250 mm, operative fundamental frequency is 2.89 Hz, launched fundamental frequency is 36 Hz, deploying process time is 4.2 min, repeated accuracy of the reduced-scale prototype is 2.658°, thermal deformation of the antenna at orbit is 0.86 mm, and total mass is 72 kg. A half scale prototype with two modules is finally developed. The rationality and effectiveness of the proposed design and analytical method are verified by the repeated deployme nt tests of the half scale prototype.