• Journal of the Korean Chemical Society
• /
• v.28 no.4
• /
• pp.217-230
• /
• 1984

The MINDO/3 method was used in determination of transition states and activation barriers for various 1,2-, 1,3- and 1,5-sigmatropic hydrogen rearrangements involving systems with central carbon atom. It was found that, besides the consideration of orbital symmetry, steric effect, aromaticity, and orbital interactions were found to dictate the stability of the transition state. For systems with hetero atoms, lone pair orbitals tend to ease orbital distortion required at the transition state by participating in hydrogen transfer process and were found to lower the activation barrier accordingly. Comparison of the relative barrier heights with those obtained by using more sophisticated ab initio MO calculations showed that the MINDO/3 results give qualitatively the same tendency of the relative order of the activation barriers.

• Proceedings of the KIPE Conference
• /
• 2014.11a
• /
• pp.165-166
• /
• 2014

위성의 전력 시스템 초기 설계를 위해 고려해야 하는 중요한 설계 요소에는 위성 운용 기간 동안의 전력 소모량 예측 및 전이궤도와 운용궤도에서의 태양 전지판과 배터리의 운용 개념 설계이다. 이를 토대로 태양 전지판에서 생성되는 전력의 정류 개념과 배터리 충전/방전 토폴로지를 구현해야 한다. 본 논문에서는 2.5KW급 정지궤도 위성의 전력 시스템 초기 설계를 위해 고려해야 하는 설계 요소들을 나열하고, 이들에 대한 전반적인 검토 사항을 기술한다.

• Defense and Technology
• /
• no.1 s.131
• /
• pp.6-13
• /
• 1990

지상 수백km정도의 고도밖에는 왕복할수 없는 현재의 제한된 우주수송능력은 비교적 가까운 우주공간에서 화물을 운반하고 작업을 하는 궤도기동체(OMV)와 우주공간의 어느 곳, 어떤 궤도에도 왕래하는 우주전이비행체(STV)를 필요로 하고 있다. 이들은 재래식 화학로켓을 개량한 진보형 추진시스템을 1차적으로 활용하는 방향으로 개발이 진행되고 있다. 우주와 지구사이를 비교적 경제적으로 용이하게 왕래하고 우주공간에서 자유로이 기동작동하는 추진시스템이 완성되면, 인류의 우주개척은 본궤도에 오르게 되며, 생활권을 우주로 옮기는 날도 가까워질 것이다

• Journal of Astronomy and Space Sciences
• /
• v.15 no.1
• /
• pp.235-244
• /
• 1998

The solutions of orbital maneuver problem using the sliding mode control in the presence of the erath gravitational perturbations is obtained. Especially, the optimization of consuming fuel for maneuver is performed. The impulsive solution to Lambert's problem using the combined equation method to minimize total ${\Delta}V is used for the desired orbit and the maneuver times. Two-step sliding mode control method is introduced for satisfying the boundary conditions of finite-thrust rendezvous problem at the end of maneuver time. Using the new approach to the orbit maneuver problem, two-step sliding mode control, orbit maneuvers are processed. The solutions to a rendezvous using the optimal control are obtained, and they are compared to the results by two-step sliding control.According to the new approach for orbit maneuver, the thrust-coast-thrust type controller is obtained to make satellite to track desired Lambert's orbit, and the total ${\Delta}V$ required for maneuver is resonable in comparison with the impulsive solution to Lambert's problem. The final state variables, also are close to the boundary conditions at the end of maneuver times.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.807-808
• /
• 2010

To insert payload to the orbit over the 200km-altitude using launch vehicle which has 300sec the Isp, multi staging technique for launch is necessary. The range between the sea-level to the transfer orbit about 200~250km is for operation of 1st and 2nd rocket engines and the higher altitude is for propulsion system of the acceleration block and satellite. The upper stage rocket engine should have the high technology for entering the payload into the orbit precisely more than the performance for high thrust level. With this investigation of the upper stage rocket engines which have been used, we want to understand their development trend and prospect which is going to be references for the development of ours.

• Journal of Advanced Navigation Technology
• /
• v.18 no.5
• /
• pp.421-428
• /
• 2014

GPS satellite positions can be obtained from the navigation message transmitted from the GPS satellite. In this paper, the accuracy of broadcast orbit and clock are analyzed by comparing with the NGA precise ephemeris. For analyzing global and local orbit errors in 2004 to 2013, GPS satellite visibilities are calculated in Korea. Local RMS of 3D orbit error and SISRE are 4 cm and 3 cm less than global RMS of 3D orbit errors and SISRE. Orbit and clock errors are calculated for each GPS satellite Block for 10 years. SISRE of Block IIA satellites are 2.8 times greater than Block IIF satellites. The correlation between orbit errors and shadow condition is analyzed. The orbit errors in shadow is 2.1% higher than that in sunlight. Correlation analysis between the orbit errors and solar/geomagnetic index shows that orbit errors has a high correlation with from 2004 to 2008. However, the correlation became low since 2009.

• Journal of Korean Society of Disaster and Security
• /
• v.5 no.2
• /
• pp.71-79
• /
• 2012

Recently, in the total railroad construction field, the concrete slab track is adapted, not ballast track. Because the ballast track have the characteristics doing the ongoing maintenance and difficult to handle increasing maintenance costs, eventually the concrete slab track is selected as an alternative. However, owing to the hydration heat reactions and temperature affected shrinkage cracks related to concrete itself, a variety of studies to solve maintenance problems related to concrete slab track are underway. This study analysed characteristics of TQI values evaluating the track irregularity, searched the relationship between crack progress and TQI, and then evaluated of the correlation between the two values. Through this method, there is a need to complete the problems of the current method, only TQI is the main decision making tool in track maintenance, and also the need for the development of evaluation index considering the crack.

• Journal of the Korean Society for Railway
• /
• v.18 no.3
• /
• pp.232-240
• /
• 2015

Two types of track circuits are used in high speed railway car depots: one is High Voltage Impulse Track Circuit(HVITC); the other is AF track circuit. HVITC detects train occupation of blocks and broken rail; the AF track circuit is used for train onboard control system pretesting before departure. This testing is used to transmit train control information through the AF track circuit. The two systems are switched in turns for testing. We propose a system in which the AF track circuit is replaced by a loop cable that is installed on the inside rail; as such, engineers do not need to switch the systems. In cases in which the two systems run simultaneously, mutual interference may occur. In this paper, we identified this mutual interference by modeling of the two circuits.

• Current Industrial and Technological Trends in Aerospace
• /
• v.7 no.2
• /
• pp.121-130
• /
• 2009

In this paper, the attitude and orbit control subsystem technology of new GEO communication and observation satellite using Sun sensors are introduced and analyzed. COMS is new GEO communication and Earth observation satellite based on EUROSTAR 3000 space bus technology. The attitude and orbit control subsystem of COMS adopts a configuration using three BASS and three LIASS Sun sensors to acquire the attitude error information in the specific reference frames. These Sun sensors are used to acquire Sun direction and to control the spacecraft to keep the relative attitude with respect to a reference Sun direction in both transfer and operational orbits. In this paper, the mathematical models of BASS and LIASS are described as well as their operational implementation in the flight software.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.8
• /
• pp.747-752
• /
• 2007

Domestic satellite development programme is generally classified into two categories: COMS as GEO satellite and KOMPSAT as LEO one. Each satellite has the on-board propulsion system fulfilling its own mission requirements. The COMS propulsion system provides the thrust and torque required for the insertion into GEO, attitude and orbit control/adjustment of spacecraft. It is the well-known Chemical Propulsion System(CPS) using bipropellants. On the other hand, the monopropellant propulsion system is employed in KOMPSAT, and its main role is on-station attitude control excluding the orbit transfer function. In this study, these two representative propulsion systems are compared and analysed as well, in terms of essential differences and important characteristics.