• Bulletin of the Korean Space Science Society
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• 2004.04a
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• pp.61-61
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• 2004

과학기술위성 1호(STSAT-1)는 위성의 자세를 제어하기 위하여 Reaction Wheel Assembly(RWA)를 적용하였으며, 위성의 무게중심에 Wheel의 회전수에 비례하는 관성모멘트를 발생시켜 자세를 제어하였다. 과학기술위성 2호(STSAT-2)는 과학기술위성 1호에 적용하였던 반작용휠(RWA)과 펄스형태로 동작시켜 위성의 자세 및 궤도제어를 위하여 요구하는 추력을 얻을 수 있는 펄스형 전기 추진시스템(Pulsed Plasma Thruster: PPT)이 탑재된다. (중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.702-708
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• 2010

Reaction wheel assemblies(RWA) are expected to be one of the largest high frequency disturbance sources to the optical payload of satellites. To ensure the tight pointing-stability budget and high image quality of satellites, a vibration isolation device should be applied to the main disturbances. For developing the isolating system, the disturbances need to be identified and modeled accurately. In the present study, a modeling technique of RWA and its disturbance was described. The micro-vibration disturbances were generated numerically by using an analytical wheel and disturbance model. The parameter estimation scheme of the model was suggested, and the RWA and disturbance modeling technique was verified through the numerical example analysis. The analytical results show that the wheel and disturbance model can be accurately established by using the modeling technique proposed in the present study. The wheel and disturbance model is expected to be useful for development of the RWA isolator system.

• Journal of Aerospace System Engineering
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• v.12 no.6
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• pp.9-16
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• 2018

This paper describes how to find out the optimum position of the reaction wheel assembly (RWA) to minimize image quality degradation through the integrated system jitter prediction combining the micro-vibration test with finite element analysis considering optical coefficients. Micro-vibration generated from RWA that is widely used for satellite maneuver, is one of key factors that degrades the quality of satellite image. Due to varying vibration characteristics of each RWA, its accommodation position may affect image quality even though the same company manufactured them. To resolve this issue, an integrated system jitter prediction is conducted with all possible RWA accommodation location, and finally we determine optimal RWA position from the analysis results.

• Journal of Aerospace System Engineering
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• v.2 no.1
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• pp.13-16
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• 2008

The line of sight(LOS) is affected by the vibration of spacecraft. It is necessary to predict the effect of disturbance on LOS stability. Reaction wheel assembly is anticipated to be the largest disturbance source on spacecraft. The disturbance which is occurred mainly due to the mass imbalance is analyzed with harmonic numbers. The accuracy and stability are verified by probability density function with dynamic equation of the satellite motion.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.695-698
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• 2004

STSAT RWA (Reaction Wheel Assembly) micro-vibration is measured using KISTLER dynamic plate that can provide the time signals of three orthogonal forces and torques simultaneously up to 400Hz. In the post-processing, measured data are evaluated with respect to the wheel spin rate in both time and frequency domains, and the static/dynamic unbalances are evaluated from the extracted first harmonic component. Also the friction torque profile at each wheel speed is estimated from the measured data. Several higher order harmonic components are observed, that comes from its rotor shape as well as the wheel bearing characteristics. One of the most peculiar characteristics of this wheel is that the dynamic properties of two radial unbalance components are much different from each other as the RWA mounting configuration on a spacecraft is different from conventional RWA mounting configuration. Rocking mode is not appeared below 400Hz for all operating speed because the wheel size is very small. The post-processed results will be used for jitter analysis of STSAT due to RWA micro-vibration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.836-839
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• 2003

In this paper, we briefly introduce the test bench and test method of RWA micro-vibration. TAMAM RWA (Reaction Wheel Assembly) micro-vibration was measured on a KISTLER dynamic plate which can measure time signals of three orthogonal forces and torques simultaneously up to 400Hz, and test data was analyzed. Measured data were evaluated with respect to the wheel spin rate and the static/dynamic unbalances were estimated from the extracted first harmonic component. The estimated static and dynamic unbalances were 0.79gㆍcm and 17.4gㆍ$\textrm{cm}^2$ respectively. The resonance mode and two rocking modes were observed as a results of its frequency analysis. Several higher order harmonic components were observed, which comes from its rotor shape as well as the wheel bearing.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.18 no.4
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• pp.30-37
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• 2010

This paper deals with attitude determination and parameter estimation problems for a lunar module. For this we first derive equations of motion for the lunar module by considering allocation locations (configurations) of reaction thruster and a reaction wheel assembly. The lunar module is assumed as a rigid body. In order to include the effect of fuel sloshing on the dynamics of the lunar module, we model it as a spherical pendulum for a simple analysis. For estimating angular rates and moment of inertia of the module, we employ an extended Kalman filter and the least mean square algorithms, respectively. Finally we construct a dynamical model for the lunar module by combining all these elements.

• Aerospace Engineering and Technology
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• v.3 no.2
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• pp.25-33
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• 2004

In this paper, we briefly introduce the micro-vibration test bench of KARI and the test and analysis method of RWA(Reaction Wheel Assembly) micro-vibration. The micro-vibration of RWA is measured on a KISTLER dynamic plate which can measure the time signal of 6 DOF simultaneously up to 400Hz. Measured data are extensively evaluated with respect to the wheel spin rate to identify the complicate wheel dynamic characteristics, and the static/dynamic unbalances are estimated from the extracted first harmonic component as a part of evaluation process. The estimated static and dynamic unbalances. 0.79gcm and 17.4gcm² respectively. The structural resonance mode and two rocking modes observed as a results of its frequency analysis. Several higher order harmonic components observed, which come from its rotor shape as well as the wheel bearing characteristics.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.651-657
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• 2008

A new approach for maximizing torque capability of low efficient reaction wheel assembly is addressed in this paper. At first, to find out a solution in constrainted field, weighted pseudo-inverse and momentum minimized allocation are suggested instead of a general control allocation called pseudo-inverse. The second method is a structural manner to enlarge torque capability of specific axis by changing installed skew angle of wheels. Two proposed methods are applied to large angle maneuvers of satellite. Improvement of control performance and feasibility for applying to commercial satellite attitude control are demonstrated by numeric simulations.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.117-123
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• 2000

Using the modified DEM (Discrete Element Method), which we proposed in order to improve the accuracy of the simulation, soil behavior and reaction by lugs of rotating wheel and a soil cutting process by a high speed blade were calculated and compared with experimental data. The DEM is one of computational mechanics, where the object body is supposed as an assembly of small particles called elements and not a continuum as in the case of FEM. We can easily treat some discrete phenomena such as cracking, separating and sliding by the DEM. We had to modify the original mechanical model, which induced too free movement of elements, adding a tension spring, which would display the role of soil adhesion. The results of DEM simulations were successful from both the soil behavior and reaction points of view.