• Journal of Astronomy and Space Sciences
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• v.36 no.4
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• pp.235-248
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• 2019

This paper suggests a relative orbit control strategy for the CubeSat Astronomy by NASA and Yonsei using Virtual Telescope Alignment eXperiment (CANYVAL-X) mission whose main goal is to demonstrate an essential technique, which is an arrangement among two satellites and a specific celestial object, referred to as inertial alignment, for a next-generation virtual space telescope. The inertial alignment system is a relative orbit control system and has requirements for the relative state. Through the proposed orbit control strategy, consisting of separation, proximity keeping, and reconfiguration, the requirements will be satisfied. The separation direction of the two CubeSats with respect to the orbital plane is decided to provide advantageous initial condition to the orbit controller. Proximity keeping is accomplished by differential atmospheric drag control (DADC), which generates acceleration by changing the spacecraft's effective cross section via attitude control rather than consuming propellant. Reconfiguration is performed to meet the requirements after proximity keeping. Numerical simulations show that the requirements can be satisfied by the relative orbit control strategy. Furthermore, through numerical simulations, it is demonstrated that the inertial alignment can be achieved. A beacon signal had been received for several months after the launch; however, we have lost the signal at present.

• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.387-393
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• 2015

This study presents a precise relative navigation algorithm using both laser and Global Positioning System (GPS) measurements in real time. The measurement model of the navigation algorithm between two spacecraft is comprised of relative distances measured by laser instruments and single differences of GPS pseudo-range measurements in spherical coordinates. Based on the measurement model, the Extended Kalman Filter (EKF) is applied to smooth the pseudo-range measurements and to obtain the relative navigation solution. While the navigation algorithm using only laser measurements might become inaccurate because of the limited accuracy of spacecraft attitude estimation when the distance between spacecraft is rather large, the proposed approach is able to provide an accurate solution even in such cases by employing the smoothed GPS pseudo-range measurements. Numerical simulations demonstrate that the errors of the proposed algorithm are reduced by more than about 12% compared to those of an algorithm using only laser measurements, as the accuracy of angular measurements is greater than $0.001^{\circ}$ at relative distances greater than 30 km.

• East Asian Economic Review
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• v.24 no.3
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• pp.207-235
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• 2020

Acknowledging that individuals dislike having low relative income renders trade less attractive when seen as a technology that integrates two economies by merging separate social spheres into one. We define a "trembling trade" as a situation in which gains from trade are less than losses in relative income, with the result that global social welfare is reduced. We show that a "trembling trade" can arise even when trade is more gainful in four ways: through trade the absolute income of everyone increases, the income gap in both economies is reduced, as is the income gap between the trading economies. However, trade brings populations, economies, or markets that were not previously connected closer together in social space. As a consequence, separate social spheres merge, and people's social space and their comparators are altered. Assuming that people like high (absolute) income and dislike low relative income, the aggregate increase in unhappiness caused by the trade-induced escalation in relative deprivation can result in a negative overall impact of trade on (utilitarian-measured) social welfare, if the absolute income gains are not large enough to mitigate the relative income losses.

• Journal of Astronomy and Space Sciences
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• v.26 no.1
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• pp.59-74
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• 2009

Relative navigation system is presented using GPS measurements from a single-channel global positioning system (GPS) simulator. The objective of this study is to provide the real-time inter-satellite relative positions as well as absolute positions for two formation flying satellites in low earth orbit. To improve the navigation performance, the absolute states are estimated using ion-free GRAPHIC (group and phase ionospheric correction) pseudo-ranges and the relative states are determined using double differential carrier-phase data and singled-differential C/A code data based on the extended Kalman filter and the unscented Kalman filter. Furthermore, pseudo-relative dynamic model and modified relative measurement model are developed. This modified EKF method prevents non-linearity of the measurement model from degrading precision by applying linearization about absolute navigation solutions not about the priori estimates. The LAMBDA method also has been used to improve the relative navigation performance by fixing ambiguities to integers for precise relative navigation. The software-based simulation has been performed and the steady state accuracies of 1 m and 6 mm ($1{\sigma}$ of 3-dimensional difference errors) are achieved for the absolute and relative navigation using EKF for a short baseline leader/follower formation. In addition, the navigation performances are compared for the EKF and the UKF for 10 hours simulation, and relative position errors are mm-level for the two filters showing the similar trends.

• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.315-326
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• 2007

Recently introduced, several explicit solutions of relative motion between neighboring elliptic satellite orbits are reviewed. The performance of these solutions is compared with an analytic solution of the general linearized equation of motion. The inversion solution by the Hill-Clohessy-Wiltshire equations is used to produce the initial condition of numerical results. Despite the difference of the reference orbit, the relative motion with the relatively small eccentricity shows the similar results on elliptic case and circular case. In case of the 'chief' satellite with the relatively large eccentricity, HCW equation with the circular reference orbit has relatively larger error than other elliptic equation of motion does.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.1
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• pp.77-88
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• 2015

The dynamics of relative motion in a perturbed orbital environment are exploited based on Gauss' and Cowell's variational equations. The inertial coordinate frame and relative coordinate frame (Hill frame) are used, and a linear high fidelity model is developed to describe the relative motion. This model takes into account the primary gravitational and atmospheric drag perturbations. Then, this model is used in the design of a navigation, guidance, and control system of a chaser vehicle to approach towards and to depart from a target vehicle in proximity operations. Relative navigation uses an extended Kalman filter based on this relative model to estimate the relative position/velocity of the chaser vehicle with respect to the target vehicle. This filter uses the range and angle measurements of the target relative to the chaser from a simulated LIDAR system. The corresponding measurement models, process noise matrix, and other filter parameters are provided. Numerical simulations are performed to assess the precision of this model with respect to the full nonlinear model. The analyses include the navigation errors and trajectory dispersions.

• Asian Journal of Turfgrass Science
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• v.15 no.3
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• pp.111-118
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• 2001

We observed air temperature and relative humidity in the green space why this research graspes effect of climate relax by coverage condition and height difference tree in green space of the 4ha scale. With this data, analyzed relationship of coverage and air temperature or relative humidity distribution, number of tree and climate relax by revolution analysis. In this result, higher zone formed barren area, lower zone did forest and surround grassland. Relative humidity have corresponding type of air temperature distribution. higher air temperature zone was lower humidity and lower zone was higher humidity. Coverage condition effect climate relax by increasing forest and grassland. and increasing number of tree effect climate relax no related hight of tree. This efficiency order of an arbor, subarbor.

• Journal of the Korean Institute of Rural Architecture
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• v.25 no.4
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• pp.37-44
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• 2023

As a basic study to analyze the relative importance of external space in urban development projects, this study selects evaluation indicators for external space planning and then analyzes systematic external space planning through expert surveys. The scope of the study is to examine the criteria of evaluation items for external space derived from existing studies and to suggest the importance and priority of evaluation items. As a research method, we reviewed the legal and research literature on landscape planning and external space-related guidelines, and conducted a primary review of external space planning evaluation items analyzed by questionnaire. The reviewed items were again reviewed and selected through expert group discussions (FGI). The selected evaluation items were surveyed by expert groups and analyzed in depth using the hierarchical analysis method (AHP). Looking at the relative importance of the calculated sub-items, among the 17 sub-items, 'planning open space' (.096) is the largest, followed by 'pedestrianization' (.082), 'linking with adjacent buildings, streets, parks, and green areas' (.077), 'securing public space through various planning techniques such as linking with pedestrian paths' (.066), 'Plan the placement, form, and scale of buildings in consideration of the identity of the destination' (.065), 'Plan buildings, streets, parks, and green spaces in an integrated and holistic manner' (.065), 'Harmonize with the surrounding environment (landscape)' (.063), 'Harmonize with surrounding buildings and apply landscape planning in urban planning' (.063), 'Entrances and lower floors of buildings are planned as parks for users and pedestrians' (.060), 'Preserve and expand green areas and establish maintenance plans for urban greening' (.054), 'Form the basis for a comfortable life for urban residents by providing long-term development directions' (.047), 'Activate community activities and plan pedestrian environments and streetscapes considering human scale' (.047), 'Establish and propose basic directions for urban greening' (.046), 'Plan buildings, streets, parks, and green areas considering the hierarchy and characteristics of the landscape structure' (.045), 'Plan for integrated land use' (.045), 'Create green axes in connection without cutting them due to development activities' (.044), and 'Apply barrier free design' (.034).

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.50 no.7
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• pp.350-353
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• 2001

In general, the Least Square Error method is used for signal classification to measure distance in the $l^2$ metric or the $L^2$ metric space. A defect of the Least Square Error method is that it does not classify properly some waveforms, which is due to the property of the Least Square Error method: the global analysis. This paper proposes a new linear operator, the Integra-Normalizer, that removes the problem. The Integra-Normalizer possesses excellent property that measures the degree of relative similarity between signals by expanding the functional space with removing the restriction on the functional space inherited by the Least Square Error method. The Integra-Normalizer shows superiority to the Least Square Error method in measuring the relative similarity among one dimensional waveforms.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.11
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• pp.1048-1052
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• 2013

Recently, many countries have attempted to protect their satellites from damage caused by space debris. To design these collision avoidance maneuvers, optimal algorithms based on numerical simulations are widely used due to their practicality. However, these algorithms often require a great expenditure of time in order to find solutions. Therefore, in this paper, a simple analytical strategy is suggested to find the initial prediction required to find these numerical solutions for collision avoidance maneuvers by using relative dynamics for the rendezvous and docking problems. For this analytical strategy, the simple dynamics on the CW (Clohessy-Wiltshire) frame is adopted as an attempt to introduce an analytical solution.