Su-Hyeon Jeon

Experimental feasibility study for micro-jitter attenuation of stepper-actuated X-band antenna-pointing mechanism by using pseudoelastic SMA mesh washer

A stepper motor mechanism activates the azimuth and elevation direction of an X-band downlink antenna-pointing mechanism for effective data transfer from a satellite to a ground station. The stepper motor activation, and an imperfect intermeshed teeth harmonic-drive-gear configuration of the antenna mechanism may induce micro-jitter in the system, which can seriously affect the image quality of high-resolution observation satellites. In this study, to confirm the feasibility of on-orbit micro-jitter isolation of a whole-antenna mechanism assembly, a new type of passive vibration isolation system was proposed and investigated. This proposed system uses a pseudoelastic shape memory alloy compressed mesh washer isolator. The basic characteristics of the isolator were measured by performing static test on the isolator. The effectiveness of the design was also demonstrated via a micro-jitter measurement test, with and without the isolation system.

Structural Design and Analysis of 1U Standardized STEP Cube Lab for On-Orbit Verification of Fundamental Space Technologies

The STEP Cube Lab (Cube Laboratory for Space Technology Experimental Projects) is a 1U cube satellite developed by the Space Technology Synthesis Laboratory of Chosun University to be launched in 2015. Its mission objective is twofold: to determine which of the fundamental space technologies researched at domestic universities, will be potential candidates for use in future space missions and to verify the effectiveness of the technologies by investigating mission data obtained from on-orbit operation of the cube satellite. In this paper, a structural design concept based on the 1U standard to achieve the mission objective is introduced. The validity of the design has been demonstrated by quasi-static analysis and modal analysis. In addition, a non-explosive separation device triggered by burn wire heating, which is one of the main mission payloads is introduced.

Performance investigation of a novel pseudoelastic SMA mesh washer gear wheel with micro-jitter attenuation capability

A stepper-actuated mechanism, such as a gimbal type antenna, is a major source of micro-jitters that affect the image quality of a high-resolution observation satellite. Attenuating micro-jitter disturbances induced by a stepper motor activation is one method of enhancing image quality of an observation satellite. In this study, we propose a novel gear with micro-jitter attenuation capability for stepper-actuated mechanism. This can be achieved by implementing a pseudoelastic shape memory alloy mesh washer on the gear wheel. This application makes it possible to achieve the gear with lower torsional stiffness and higher damping in the torsional direction of the gear, whose characteristics will assist in resolving the micro-jitter attenuation issues of a gear. The effectiveness of the gear proposed in this study was demonstrated by numerical simulation and jitter measurement tests using the gimbal type antenna mechanism actuated by the stepper motor.

Functional Verification of Engineering Model of Non-explosive Shockless Holding and Release Mechanism Using Heating Wire Cutting Method

Non-explosive shockless holding and release mechanism for a nano class small satellite application has been proposed and investigated. The great advantages of the mechanism are a much lower shock level and larger constraint force than the conventional mechanism using pyro and the heating wire cutting mechanism which has been generally applied to the cube satellite program. To investigate the effectiveness of the mechanism design, EM mechanism was developed and tested to verify the basic function of the mechanism. The test results indicate that the proposed mechanism is well functioning as the mechanism design intends.

Enhancement of Microjitter Attenuation Capability for a Stepper-Actuated Two-Axis Gimbal-Type Antenna by Using a Spring-Blade Isolator

AbstractA two-axis gimbal-type X-band antenna used to transmit real-time image data from a satellite to a ground station is a potential source of microjitter, which can degrade image quality from h...

Micro-vibration Isolation Performance of X-band Antenna Using Blade Gear

ABSTRACT A 2-axis gimbal-type X-band antenna has been widely used to effectively transmit the high reso-lution image data from the observation satellite to the desired ground station. However, a dis-continuous stepper motor activation for rotating the pointing mechanism in azimuth and elevation di-rections induces undesirable micro-vibration disturbances which can result in the image quality degra-dation of a high-resolution observation satellite. To enhance the image quality of the observation sat-ellite, attenuating the micro-vibration induced by an activation of the stepper motor for rotational movements of the antenna is important task. In this study, we proposed a low-rotational-stiffness blade gear applied to the output shaft of the stepper motor to obtain the micro-vibration isolation performance. The design of the blade gear was performed through the structure analysis such that this gear is satisfied with the margin of safety rule under the derived torque budget. In addition, the micro-vibration isolation performance of the blade gear was verified through the micro-vibration measurement test using the dedicated micro-vibration measurement device proposed in this study.

Experimental Investigation of Complex System for Electrical Energy Harvesting and Vibration Isolation

Micro-vibration induced by on-board appendages that have mechanical moving parts has always been treated as an useless objective that has to be isolated, in order to comply with a high-resolution mission requirement of the observation satellite. In this study, we proposed a tuned mass damper energy harvester combined with a conventional passive vibration isolator for exhibiting dual functions of both electrical energy harvesting and micro-vibration isolation. The feasibility of the proposed dual-function complex system has been demonstrated through the comparison with numerical simulations, based on the results of basic characteristic tests, and experiments of the harvested power and micro-vibration.

Experimental Validation of Fatigue Life of CCGA 624 Package with Initial Contact Pressure of Thermal Gap Pads under Random Vibration Excitation

Thermal gap pads are widely used for effective heat transfer from high-heat-dissipating components to a heat sink. The initial contact pressure of thermal pads is an important parameter for enhancing the heat transfer capability of thermal design during the assembly process of the heat sink. However, this causes stress on the solder joint of the component as a result of the pad’s inherent resistance to deformation. In this study, we investigated the effect of thermal pad on the fatigue life of the solder joint of CCGA 624 package for space usage. A random vibration fatigue test for several specimen assembly sets with various pressurization levels of thermal gap pads was performed, and their fatigue lives were compared with that of the package without the initial pressure of thermal gap pads.

Life Prediction of Failure Mechanisms of the CubeSat Mission Board using Sherlock of Reliability and Life Prediction Tools

A cubesat classified as a pico-satellite typically uses commercial-grade components that satisfy the vibration and thermal environmental specifications and goes into mission orbit even after undergoing minimum environment tests due to their lower cost and short development period. However, its reliability exposed to the physical environment such as on-orbit thermal vacuum for long periods cannot be assured under minimum tests criterion. In this paper, we have analysed the reliability and life prediction of the failure mechanisms of the cubesat mission board during its service life under the launch and on-orbit environment by using the sherlock software which has been widely used in automobile fields to predict the reliability of electronic devices.

Verification of Micro-vibration Isolation Performance by using Low Rotational Stiffness Isolator under Elevation Direction Operation of the X-band Antenna

ABSTRACT A stepping motor is widely used to operate the elevation and azimuth stage of the X-band anten-na with 2-axis gimbal system for effective image data transmission from a satellite to a ground station. However, such stepping motor also generates an undesirable micro-vibration which is one of the main disturbance sources affecting image quality of the high-resolution observation satellite. In order to improve the image quality, the micro-vibration isolation of the X-band antenna system is essential. In this study, the low rotational stiffness isolator has been proposed to reduce the micro-vi-bration disturbance induced by elevation direction operation of the X-band antenna. In addition, its structural safety was confirmed by the structure analysis based on the derived torque budget. The ef-fectiveness of the design was also verified through the micro-vibration measurement test. * 1. 서 론 위성의 자세제어용 반작용 휠, 자세정보 제공을 위한 기계식 자이로, 임무장비의 극저온 구현을 위한 냉각기, 지향 조정 장치로 사용되는 2축 짐발 시스템, 태양전지판의 태양추적 구동기 등과 같이 기계적 구동부를 갖는 탑재장비는 궤도 운용 시 목적하는 기능을 구현함과 동시에 미소진동을 유발한다 . 상기의 탑재장비로부터 발생되는 진동외란의 크기는 극히 미소함에도 불구하고 정밀 지향성능이 요구되는 관측위성의 영상품질을 저하시키는 주요 원인 중 하나이며, 이를 해결하기 위해 탑재장비로부터 발생하는 미소진동을 주요 임무장비로 전달되지 않도록 추가적인 절연설계가 요구된다