Seong-Cheol Kwon

Characteristics of spaceborne cooler passive vibration isolator by using a compressed shape memory alloy mesh washer

Cryogenic coolers produce undesirable micro-vibrations during on-orbit operation, which may seriously affect the image quality of high-resolution observation satellites. Micro-vibrations can be easily isolated by mounting the cooler on a vibration isolator with low stiffness to attenuate the vibration transmitted to the satellite structure. However, the structural safety of a cooler supported by an isolator with low stiffness cannot be guaranteed under the much more severe vibration condition of a launch environment. In this study, to guarantee vibration isolation performance in a launch environment while effectively isolating the micro-vibrations from the cooler on-orbit, a new type of passive vibration isolation system by using a compressed shape memory alloy mesh washer was proposed and investigated. The basic characteristics of the isolator were measured in static and free vibration tests of the isolator, and a simple equivalent model of the isolator was proposed. The effectiveness of the isolator design in a launch environment was demonstrated through sine vibration, random vibration, and shock tests.

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.

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...

Experimental Validation of Fly-Wheel Passive Launch and On-Orbit Vibration Isolation System by Using a Superelastic SMA Mesh Washer Isolator

On-board appendages with mechanical moving parts for satellites produce undesirable micro-jitters during their on-orbit operation. These micro-jitters may seriously affect the image quality from high-resolution observation satellites. A new application form of a passive vibration isolation system was proposed and investigated using a pseudoelastic SMA mesh washer. This system guarantees vibration isolation performance in a launch environment while effectively isolating the micro-disturbances from the on-orbit operation of jitter source. The main feature of the isolator proposed in this study is the use of a ring-type mesh washer as the main axis to support the micro-jitter source. This feature contrasts with conventional applications of the mesh washers where vibration damping is effective only in the thickness direction of the mesh washer. In this study, the basic characteristics of the SMA mesh washer isolator in each axis were measured in static tests. The effectiveness of the design for the new application form of the SMA mesh washer proposed in this study was demonstrated through both launch environment vibration test at qualification level and micro-jitter measurement test which corresponds to on-orbit condition.

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.

Characteristics of spaceborne cooler vibration isolator using a pseudoelastic shape memory alloy

Spaceborne cooler generates undesirable micro-vibration disturbances during its on-orbit operation and this may seriously affect the image quality of high resolution observation satellites. For the aim of assuring the high quality images of the observation satellite, most of studies have dealt with on-orbit micro-vibration isolation system with a low stiffness, but have not taken launch vibration environments into account. Hence, holding-and-release mechanisms should be considered for guaranteeing the structural safety of the cooler supported by a low stiffness isolator and isolator itself during harsh launch loads. However, this approach has increased the system complexity and lowered its reliability, in addition to increasing the total mass of the system. To overcome this drawback, in this study, a blade type passive vibration isolator employing the characteristics of a pseudoelastic shape memory alloy (SMA) was proposed. This isolator can guarantee structural safety of the cooler and the isolator itself under harsh launch vibration loads without requiring holding-and-release mechanism, while effectively isolating the cooler-induced micro-vibration in on-orbit conditions. The basic characteristics of the isolator were evaluated through a dynamic loading tests in accordance with temperature variations. Based on the measured characteristics, the effectiveness of the isolator design under launch and on-orbit environments was investigated.

Numerical Feasibility Study for a Spaceborne Cooler Dual-function Energy Harvesting System

Spaceborne cryocoolers produce undesirable micro-vibration disturbances during their on-orbit operation, which are a primary source of image-quality degradation for high-resolution observation satellites. Therefore, to comply with the strict mission requirement of high-quality image acquisition, micro-vibration disturbances induced by cooler operation have always been subjected to an isolation objective. However, in this study, we focused on the applicability of energy harvesting technology to generate electrical energy from micro-vibration energy of the cooler and investigated the feasibility of utilizing harvested energy as a power source to operate low-power-consumption devices such as micro-electromechanical system (MEMS) devices. A tuned mass damper (TMD)-type electromagnetic energy harvester combined with a conventional passive vibration isolator was proposed to achieve this objective. The system performs the dual functions of electrical energy generation and micro-vibration isolation. The effectiveness of the strategy was evaluated through numerical simulations.