The Small SAR Technology Experimental Project (S-STEP) mission aims to develop a new (space-based 80 kg-class active X-band synthetic aperture radar (SAR)) satellite with a main imaging mode of 1 m resolution stripmap. In the S-STEP mission, to achieve the design goal of developing faster, cheaper, better, and lighter small SAR satellite systems, innovative thermo-mechanical design approaches have been proposed and investigated. The major design approaches are the bus-payload integrated flat plate-type structure, multifunctional transmit/receive (TR) module, and dedicated vibration-free orbit deployer (VFOD) with the function of whole spacecraft vibration isolation. To validate the feasibility of the innovative mechanical design of S-STEP, a structural analysis considering launch and on-orbit environments is performed. In addition, development test results are presented to confirm the effectiveness of the proposed design approach for VFOD.

Innovative Mechanical Design Strategy for Actualizing 80 kg-Class X-Band Active SAR Small Satellite of S-STEP

Effect of Ni substitution and annealing temperature on structural and magnetic properties of MnZn-Ferrites: Cytotoxicity study of ZnO and SiO2 coated core shell structures

Fundamentals of Multibody Dynamics: Theory and Applications F. Amirouche Birkhauser Verlag, Viaduktstrasse 42, CH- 4051 Basel, Switzerland. 2006. 684pp. Illustrated. £98.50. ISBN 0-8176-4236-6.

In this study, a passive truss-link mechanism applicable to large-scale deployable structures was designed to achieve successful deployment in space. First, we simplified the selected truss-link mechanisms to the two-dimensional geometry and calculated the degrees of freedom (DOF) to determine whether a kinematic over-constraint occurs. The dimensions of the truss-link structure were determined through a deployment kinematic analysis. Second, a deployment simulation with the truss-link was conducted using multibody dynamics (MBD) software. Finally, a deployment test was performed considering gravity compensation, and the results were compared with those of MBD simulation. The results of the deployment simulations were confirmed to be slightly faster than those of the deployment test due to friction effects existing in the joints and gravity compensation devices. To address this issue, inverse identification of the equivalent frictional torque (EFT) at the revolute joints in the deployment test was conducted through response surface methods (RSM) combined with the central composite design technique. As a result, we confirmed that the deployment angle history of the deployment simulation was similar to that of the deployment test.

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Modeling and Validation of a Passive Truss-Link Mechanism for Deployable Structures Considering Friction Compensation with Response Surface Methods

Reflector antennas systems use struts in order to support antenna structural parts such as feeders or sub-reflectors. Struts' presence generates scattered fields that affect the antenna performance. In this paper, a comparative study between different struts' materials and cross-sections is presented. For the analysis, a Cassegrain configuration was used, designed for X-band operation. Struts' analysis was conducted through simulations at 8.425 GHz. Two different struts' positions (setups) were also studied. Detailed discussion on performance results is presented.

Comparative Study of Struts' Geometry and Material in Reflector Antennas

To ensure high-resolution image acquisition for a spaceborne parabolic synthetic aperture radar (SAR) antenna, an appropriate thermal design is important to minimize the thermal distortion of the antenna reflector in severe on-orbit thermal environments. This paper describes the results of a preliminary thermal design and the analysis of a carbon fiber reinforced plastic skin-based unfurlable parabolic reflector for use in a spaceborne SAR antenna. The effectiveness of passive thermal designs for an antenna reflector using different thermal coatings was investigated with on-orbit thermal analyses according to the various antenna look angles to derive the most suitable design for minimizing the thermal gradient of the reflector. This contributes to minimize loss in antenna gain to ensure the SAR performance. In addition, the influence of the solar panel on the thermal gradient of the reflector was also analyzed because it is also important in affecting the thermal distortion.

Thermal Design and Analysis of Unfurlable CFRP Skin-Based Parabolic Reflector for Spaceborne SAR Antenna

Dynamic behaviors of the deployable composite reflector antenna are numerically and experimentally investigated. Equations of the motion are formalized using Kane’s equation by considering multibody systems with two degrees of freedom such as folding and twisting angles. To interpret structural deformations of the reflector antenna, the composite reflector is modeled using a beam model with the FSDT(First-order Shear Deformation Theory). To determine design parameters such as a torsional spring stiffness and a damping coefficient depending on deployment duration, an inverted pendulum model is simply applied. Based on the determined parameters, dynamic characteristics of the deployable reflector are investigated. In addition, its results are verified and compared through deployment tests using a gravity compensation device.

Flexible Multibody Dynamic Analysis of the Deployable Composite Reflector Antenna 전개형 복합재 반사판 안테나의 유연 다물체 동역학 해석

The pressure conductive silicone rubber socket (PCR) is one of the promising test socket devices in high-speed testing environments. In this study, we report highly dense PCR device channels comprised of high aspect-ratio flake-shaped Ni powders. The shape-controlled Ni powders are prepared by the high-energy milling process. The scanning electron microscopy (SEM) and particle size analyzer (PSA) results of the synthesized powder samples showed well-defined flake type Ni powder morphology, and the powder sizes are distributed in the range of ~24–49 μm. The cross-sectional SEM study of the fabricated PCR revealed that the channels consisting of flake Ni powder are uniformly, densely distributed, and connected as face-to-face contact. The resistance of the PCR channels comprised of flake-shaped Ni powders showed ~23% lower resistance values than the spherical-shaped Ni powders-based channels, which could be due to the face-to-face contact of the powders in the channels. The magnetic properties study for the flake-type Ni powder showed a high remanence (~2.2 emu/g) and coercivity (~5.24 mT), owing to the shape anisotropy factor. Finally, the fabricated highly dense and conductive channels of the silicone rubber socket device by shape-controlled Ni powder could be a potential test socket device.

/pdf/fabrication-of-pressure-conductive-silicone-rubber-socket-560xclex.pdf

Fabrication of Pressure Conductive Silicone Rubber Socket Device by Shape-Controlled Nickel Powders Produced by High-Energy Ball Milling

본 논문에서는 대형 메쉬 안테나 개발을 위한 모듈식 전개형 반사판 및 붐 구조의 전개 시 요구되는 구동력 및 전개 특성을 분석하고자 한다. 단위 전개 구조를 이용하여 모듈식 전개형 반사판 링과 붐 구조의 수납/전개된 형상을 분석하였다. Kane’s 방정식을 이용하여 전개 구조물의 다물체 동역학 방정식을 유도하고 PUTD(Pseudo Upper Triangular Decomposition) 방법을 적용하여 구속조건 문제를 해결하였다. 다물체동역학 시뮬레이션을 통해 설계된 모듈식 전개 반사판 링 그리고 붐 구조의 동적 특성을 살펴보고자 한다. 

Structural Dynamic Characteristics of Modular Deployable Reflectors and Booms for the Large Mesh Antennas

The performance of antenna reflectors crucially depends on the faceting error of the surface. The force density method (FDM) has been widely used for the form-finding analysis of the cable nets of reflectors. However, after performing form-finding of some cable nets, the effective reflective area will decrease. In addition, nonlinear deformations of the cable can not be achieved by using the FDM. Thus, an effective form-find methodology is proposed in this research. The whole parts of the cable networks are described by the absolute nodal coordinate formulation. The form-finding analysis of the reflector with standard configuration is performed to validate the proposed methodology. The influence of boundary condition changes on the configuration accuracy of the cable net is investigated.

Ji-Hyeon Yun

Papers

Thermal Design and Analysis of Unfurlable CFRP Skin-Based Parabolic Reflector for Spaceborne SAR Antenna

Flexible Multibody Dynamic Analysis of the Deployable Composite Reflector Antenna 전개형 복합재 반사판 안테나의 유연 다물체 동역학 해석

Fabrication of Pressure Conductive Silicone Rubber Socket Device by Shape-Controlled Nickel Powders Produced by High-Energy Ball Milling

Structural Dynamic Characteristics of Modular Deployable Reflectors and Booms for the Large Mesh Antennas

Form-finding and Deformation Analysis of the Cable Nets for Mesh Reflector Antennas