• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.145-152
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• 2010

In this paper, we developed a local oscillator (LO) system of millimeter wave band receiver for radio astronomy observation. We measured the phase and amplitude drift stability of this LO system. The voltage control oscillator (VCO) of this LO system use the 3 mm band Gunn oscillator. We developed the digital phase locked loop (DPLL) module for the LO PLL function that can be computer-controlled. To verify the performance, we measured the output frequency/power and the phase/amplitude drift stability of the developed module and the commercial PLL module, respectively. We show the good performance of the LO system based on the developed PLL module from the measured data analysis. The test results and discussion will be useful tutorial reference to design the LO system for very long baseline interferometry (VLBI) receiver and single dish radio astronomy receiver at the 3 mm frequency band.

• Bulletin of the Korean Space Science Society
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• 2007.10a
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• pp.64-64
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• 2007

• International Journal of Aeronautical and Space Sciences
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• v.15 no.2
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• pp.153-162
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• 2014

A novel robust $H_{\infty}$ switching tracking control design method with disturbance observer is proposed for the near space interceptor (NSI) with aerodynamic fins and reaction jets. Initially, the flight envelop of the NSI is divided into small subregions, and a slow-fast loop polytopic linear parameter varying (LPV) model is proposed, to approximate the nonlinear dynamic of the NSI, based on the Jacobian linearization and Tensor-Product (T-P) model transformation approach. A disturbance observer is then constructed, to estimate the modeled disturbance. Subsequently, based on the descriptor system method, a robust switching controller is developed, to ensure that the closed-loop descriptor system is stable with a desired $H_{\infty}$ disturbance attenuation level. Furthermore, the outcome of the proposed switching tracking control problem is formulated as a set of linear matrix inequalities (LMIs). Finally, simulation results demonstrate the effectiveness of the proposed design method.

• Advances in aircraft and spacecraft science
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• v.4 no.6
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• pp.701-709
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• 2017

One of the components that used in the satellite thermal control subsystem is the Mechanically Pumped Fluid Loop (MPFL) system; this system mostly used in geosynchronous orbit (GEO) satellites, and can transfer heat from a hot point to a cold point using the fluid which circulated in a closed loop. Heat radiates to the deep space at the cold plate to cool down the fluid temperature. In this research, the radiative heatexchanger (RHX) for a MPFL system is optimized. The genetic algorithm has been used for minimizing the total mass and pressure drop by considering a constant transferred heat rate at the heat exchanger. The optimization has been done in two cases. In case I, two parameters are considered as a goal function, so optimization is performed using NSGA-II method. Results of optimization are shown in the pareto diagram. In case II, the diameter of pipe is considered constant, so the optimized value for distances of the parallel pipes is obtained by using the genetic algorithm, in which the system has the least total mass. Results show that in the RHX, by increasing the pipe diameter, pressure drop decreases and total mass increases. Also by considering a constant value for pipe diameter, an optimum distance between pipes and pipe length are obtained in which the system has a minimum mass.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.118-128
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• 2017

In this study, we propose a real time inertial navigation system/global positioning system (INS/GPS) integrated smoothing algorithm based on an extended Kalman filter (EKF) and a position damping loop (PDL) for synthetic aperture radar (SAR). Integrated navigation algorithms usually induce discontinuities due to error correction update by the Kalman filter, which are as detrimental to the performance of SAR as the relative position error. The proposed smoothing algorithm suppresses these discontinuities and also reduces the relative position error in real time. An EKF estimates the navigation errors and sensor biases, and all the errors except for the position error are corrected directly and instantly. A PDL activated during SAR operation period imposes damping effects on the position error estimates, where the estimated position error is corrected smoothly and gradually, which contributes to the real time smoothing and small relative position errors. The residual errors are re-estimated by the EKF to maintain the estimation performance and the stability of the overall loop. The performance improvements were confirmed by Monte Carlo simulations. The simulation results showed that the discontinuities were reduced by 99.8% and the relative position error by 48% compared with a conventional EKF without a smoothing loop, thereby satisfying the basic performance requirements for SAR operation. The proposed algorithm may be applicable to low cost SAR systems which use a conventional INS/GPS without changing their hardware configurations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.3
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• pp.391-398
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• 2012

Detecting races is important for debugging shared-memory parallel programs, because the races result in unintended non-deterministic executions of the programs. Previous on-the-fly techniques to detect races in parallel programs with general inter-thread coordination show serious space overhead which depends on the maximum parallelism of the program. Therefore, this paper presents a loop splitting technique for on-the-fly race detection of parallel programs which is more efficient in space complexity than previous techniques. This loop splitting technique is the debugged program which preserves semantics of the original program. Monitering loop splitting program in on-the-fly can detect first races.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.11
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• pp.1006-1012
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• 2007

In this paper, a suboptimal homing guidance law for the homing missiles with an impact angle constraint is presented. Unlike general LQ optimal control, the aided loop ensuring some degrees of freedom for the constraint is introduced. Then an optimal feedback loop in consideration of the aided loop is designed by using Schwartz inequality. The aided loop is synthesized with the optimal control to produce the guidance command. Furthermore, to investigate the characteristics of the guidance law we carry out the comparative studies with other guidance laws. The results of the various computer simulations show the good performance of the proposed law.

• The Mathematical Education
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• v.22 no.2
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• pp.5-12
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• 1984

Steenrod algebra $\alpha$$_{p}$(mod p) was generated for algebra on steenrod reduced powers p$^n$ and Bochstein coboudary operation $\beta$. We know the relation between them. In this thesis I have verified the theorem: (equation omitted)

• International Journal of Control, Automation, and Systems
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• v.5 no.2
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• pp.212-217
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• 2007

A new method of designing multi-loop PID controllers is presented in this paper. By using the generalized IMC-PID method for multi-loop systems, the optimization problem involved in finding the PID parameters is efficiently simplified to find the optimum closed-loop time constant in a reduced search space. A weighted sum Mp criterion is proposed as a performance cost function to cope with both the performance and robustness of a multi-loop control system. Several illustrative examples are included to demonstrate the improved performance of the multi-loop PID controllers obtained by the proposed design method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.2
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• pp.135-140
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• 2010

A new treatment is proposed to handle a deflection limit in the open-loop-onset-point (OLOP), which is commonly used in the prediction of pilot in-the-loop oscillation (PIO) due to a rate saturation. The new approach is motivated by the frequency response of a stand-alone actuator in that, unlike the suggestion by the original OLOP procedure, the rate limit onset is not delayed to a higher frequency by a deflection limit. Indeed, if a feedback control loop is closed, the rate limit onset can be shifted to a lower frequency since the controller tends to react with larger commands when deflection limited. The amplitude of the command at this onset frequency is combined with the deflection limit to estimate the associated gain reduction in the open-loop-onset-point in the final step of the OLOP process. The comparison of the new approach with the previous method reveals that an inaccurate optimism which can occur in the previous method is corrected by the proposed treatment.