• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.3
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• pp.233-239
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• 2013

A 100 W fuel cell system using chemical storage method has been applied for a propulsion system of the SUAV(Small Unmanned Aerial Vehicle). A fuel cell and battery have been combined for both the small/light hydrogen generation control system and the hybrid power supply system. A small hydrogen generation device was implemented to utilize NaBH4 aqueous solution and dead-end type PEMFC system, which were evaluated on the ground and by the flight tests. The system pressurized at a 45kpa stably operates and get higher fuel efficiency. The pressure inside of the hydrogen generation control system was maintained at between 45 kPa and 55 kPa. The 100W fuel cell system satisfies the required weight and power consumption rate as well as the propulsion system, and the fuel cell system performance was demonstrated through flight test.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4335-4349
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• 2023

Nuclear marine propulsion has been emerging as a next generation carbon-free power source, for which proper passive residual heat removal systems (PRHRSs) are needed for long-term safety. In particular, the characteristics of unlimited operation time and compact design are crucial in maritime applications due to the difficulties of safety aids and limited space. Accordingly, a compact and long-term-operable PRHRS has been proposed with the key design concept of using both air cooling and seawater cooling in tandem. To confirm its feasibility, this study conducted system design and a transient analysis in an accident scenario. Design results indicate that seawater cooling can considerably reduce the overall system size, and thus the compact and long-term-operable PRHRS can be realized. Regarding the transient analysis, the Multi-dimensional Analysis of Reactor Safety (MARS-KS) code was used to analyze the system behavior under a station blackout condition. Results show that the proposed design can satisfy the design requirements with a sufficient margin: the coolant temperature reached the safe shutdown condition within 36 h, and the maximum cooling rate did not exceed 40 ℃/h. Lastly, it was assessed that both air cooling and seawater cooling are necessary for achieving long-term operation and compact design.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.56-62
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• 2013

The system analysis and design program of the liquid rocket engine has been developed for preliminary conceptual design process. The program analyzes the engine system and obtains optimal design variables by optimization methods such as genetic algorithm for the higher specific impulse and thrust to weight ratio using given input parameters and requirements. For the users' convenience, the GUI has been offered. The 3-dimensional model for the visualization of results has been interconnected with the CATIA program. The results are expected to be applied to the design process of the space launch vehicle for the analysis and selection of the propulsion system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.7
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• pp.525-534
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• 2019

Water rocket is a pressurized liquid propellant rocket that shares the same basic principles of space launch vehicles. Water rockets can be used as an engineering educational material for the liquid rocket principles and the launch vehicle systems, far beyond the scope of K-12 level science education. In this paper, the principles and theories of water rocket propulsion and flight dynamics was investigated at the level of undergraduate rocket engineering classes. Also, the system level design and operation of water rocket is summarized by including the components of launch vehicle, launch pad, payload and recovery as well as altitude measurement methods.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.41-47
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• 2005

Conceptual design process is defined for the air-launching rocket by including analysis modules like mission analysis, staging, propulsion analysis, configuration, weight analysis, aerodynamics analysis and trajectory analysis. As a result of the conceptual design, the supersonic(M=1.5) air-launching rocket with hybrid engine for first stage propulsion system is designed. For the best system alternative selection, trade study for the 1st stage engine type and launching speeds using sequential optimization and confirming feasibility of baseline air-launching rocket has been performed. As a result of trade study, all alternatives are competitive in total weight and show only small difference in total weight per unit payload weight. Therefore, it is confirmed that the baseline air-launching rocket which has advantage in system safety especially in supersonic launching is feasible.

• Journal of Space Technology and Applications
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• v.3 no.2
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• pp.165-198
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• 2023

According to the studies recently published through advanced maui optical and space surveillance technologies (AMOS) Conference 2021, LEO conjunction assessment revolves around not on operating satellites but space debris such as rocket bodies and non-operational satellites, hence suggesting a solution through space traffic management. Against this backdrop, the issue of active debris removal (ADR) has emerged to the surface as an international challenge throughout the globe. In step with this, the United Nations General Assembly approved a resolution calling on nations to halt tests of direct-ascent anti-satellites, to which U.S. and twelve other nations included Republic of Korea were original signatories. ADR techniques are also actively being researched in the civil sector, and these commercial services, if successfully developed, could possibly be utilized for military use as well. As such, this paper will help readers' understanding for the current status of ADR techniques, space threat assessments, on-orbit rendezvous and proximity operations by looking at previous cases, reflecting on space-faring nations' ADR techniques and its development probability in relation to space weapons. As a conclusion, this study will propose the needs of developing space propulsion system by understanding Space Maneuver Warfare in preparation for the future space battlefield.

• Journal of Communications and Networks
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• v.7 no.4
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• pp.450-461
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• 2005

In this paper, we derive analytical expressions for the exact pairwise error probability (PEP) of a space-time coded system operating over spatially correlated fast (constant over the duration of a symbol) and slow (constant over the length of a code word) fad­ing channels using a moment-generating function-based approach. We discuss two analytical techniques that can be used to evaluate the exact-PEPs (and therefore, approximate the average bit error probability (BEP)) in closed form. These analytical expressions are more realistic than previously published PEP expressions as they fully account for antenna spacing, antenna geometries (uniform linear array, uniform grid array, uniform circular array, etc.) and scattering models (uniform, Gaussian, Laplacian, Von-mises, etc.). Inclusion of spatial information in these expressions provides valuable insights into the physical factors determining the performance of a space-time code. Using these new PEP expressions, we investigate the effect of antenna spacing, antenna geometries and azimuth power distribution parameters (angle of arrival/departure and angular spread) on the performance of a four-state QPSK space-time trellis code proposed by Tarokh et al. for two transmit antennas.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.6
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• pp.596-604
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• 2010

In order to investigate the operating conditions and major design parameters of a dual ramjet propulsion system, an theoretical analysis of ramjet and scramjet propulsion systems was performed. The performance characteristics of each engine are delivered by thermo-dynamical cycle analysis, considering loss effects in a real engine. The performance sensitivity analysis is conducted by investigating various performance parameters, such as an intake efficiency, combustor inlet Mach number, configuration of the combustor, fuel flow rate, and exhaust nozzle efficiency. Based on these analysis results, the processes of application to dual ramjet cycle engines are specified.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.154-164
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• 2017

This work conducts a validation study for the XH-59A helicopter using a rigid coaxial rotor system in order to establish the techniques of the conceptual design and performance analysis for the lift-offset compound rotorcraft. As a tool for conceptual design and performance analysis, NDARC (NASA Design and Analysis of Rotorcraft) is used for the present study. An assumed mission profile is considered for the conceptual design of the XH-59A. As a validation result of the design, the dimensions and weight of the XH-59A are appropriately designed when compared to the target values since the relative error is less than 0.5%. Then, performance analyses are conducted for the designed XH-59A model with and without auxiliary propulsion in hover and forward flight conditions. The present analyses show good validity since the prediction results compare well with both the flight test and previous analyses. Therefore, the techniques for the conceptual design and performance analysis of the lift-offset compound helicopter are overall considered to be appropriately established. In addition, this study investigates the influence of the lift-offset on the rotor effective lift-to-drag ratio of the XH-59A helicopter with auxiliary propulsion. As a result, the improvement of the rotor effective lift-to-drag ratio can be obtained by appropriately increasing the lift-offset in high-speed flight.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.246-249
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• 2009

Test and launch facilities which use oxygen as the propellant of a launch vehicle have hazards of fire and explosion by the leakage of oxygen. Also, the personnel operating the facilities, which use the high-pressured gases like nitrogen and helium in the closed room, is exposed to the hazard of death from suffocation. Consequently, we should keep out of the hazards and the accidents by monitoring the contents of oxygen in the air. The method and the system construction for monitoring oxygen contents in the air and the results from its application to Naro space center are described on this paper.