• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.5
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• pp.197-203
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• 2016

In this paper, the dipole antenna that can control a beam steering were designed for attaching on LEO(Low Earth Orbit) small satellite. The proposed antenna was based on Yagi-Uda antenna. The parasitic element was proposed as a T-shape. Depending on the state of open or short at the end of a vertical element, we can choose a characteristic of the parasitic element with fixing a vertical element length of the parasitic element. Using this characteristic, we designed the director element and reflector element. The proposed antenna was designed to receive UHF 436.5 MHz. Antenna gain was chosen by link budget between one satellite and the other satellite or between the satellite and the ground station. By changing a vertical element length which is the largest variable that chooses an antenna characteristic, we confirmed that ${\lambda}/2$ length transformer has a result that improve 0.5 dB in comparison ${\lambda}/4$ length transformer from maximum gain direction. In production, we made an on/off switch composed of a diode, capacitor, and inductor control an open and short at the end of the parasitic element. As a result, the gain of antenna used in a link between one satellite and the other satellite had average 5.92 dBi. And the gain of antenna used in a link between the satellite and the ground station had average 0.99 dBi.

• Journal of Satellite, Information and Communications
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• v.2 no.1
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• pp.35-40
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• 2007

COSPAS-SARSAT is the search and rescue system for providing a distress alarm and a position identification using an international satellite and ground facilities. Aviators, mariners and land users worldwide are equipped with COSPAS-SARSAT distress beacons, which could help save their in emergency situations anywhere in the world. As the existing COSPAS-SARSAT system is generally operated by LEO(Low-altitude Earth Orbit) Satellite System, the time from the distress beacon to the rescue is more than 1 hour with average and the accuracy of the distress location is about 5 Km. Therefore, in order to overcome this problem, the development for the next generation SAR(search and rescue) system which uses the MEO(middle-altitude Earth Orbit) satellites is going on the Galileo project. EU is developing this project for the full operation capability in 2011, and this project will have SAR payloads and support to the Search and Rescue service-herein called SAR/Galileo. SAR/Galileo will have the performance of a few meter accuracy, within 10 minutes to rescue from reception of distress messages, and Return Link Service(from the SAR operator to the distress emitting beacon), thereby facilitating more efficient rescue operations and helping to reduce the rate of false alerts. As the disaster is larger every year, the ground station, MEOLUT for next generation ASR/Galileo is urgently needed for the lifesaving for the larger disaster, the research for beacon and the ground station such as MEOLUT for introducing the next generation SAR/Galileo in Korea is very timely and is important. This paper presents the procedures and the strategies for the participation, the area to develop reasonably, and the propulsion organization for developing the SAR/Galileo ground system in Korea.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.669-677
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• 2009

In general, the pitch momentum biased system that induces inherently nutational motion in roll/yaw plane, has been adapted for geosynchronous communications satellites. This paper discusses the method of roll attitude control using yaw axis momentum management method for a low earth orbit(LEO) satellite which is a pitch momentum biased system equipped with only two reaction wheels. The robustness of wheel momentum management method with PI-controller is investigated comparing with wheel torque control method. The transfer function of roll/yaw axis momentum management system that is useful for attitude controller design is derived. The disturbance effect of roll/yaw axis momentum management system for attitude control is investigated to identify design parameters such as magnitude of momentum bias and to get the insight for controller design. As an example, the PID controller design result of momentum management system for roll/yaw axis control is provided and the simulation results are presented to provide further physical insight into the momentum management system.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.67-71
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• 2017

A solar array is main electrical energy source for Low-Earth-Orbit(LEO) satellite. The solar array cannot generate electrical energy during eclipse period, a battery supply electrical energy to the satellite. The electrical power of the solar array is changed in accordance with operating voltage and the solar array has the maximum power point. The solar array regulator makes the solar array supply electrical energy to the satellite and charge the battery. The solar array is connected to the solar array regulator input and the battery is connected to the solar array regulator output. The solar array regulator consists 2 of 3 hot redundant. One solar array regulator contains 3 DC-DC converters, and the solar array regulator operates stably even if the failure occur in one DC-DC converter. In this paper, the solar array regulator, the battery and the solar array operation is analyzed when the failure occur in one DC-DC converter.

• Journal of Astronomy and Space Sciences
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• v.34 no.4
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• pp.303-314
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• 2017

With increased human activity in space, the risk of re-entry and collision between space objects is constantly increasing. Hence, the need for space situational awareness (SSA) programs has been acknowledged by many experienced space agencies. Optical and radar sensors, which enable the surveillance and tracking of space objects, are the most important technical components of SSA systems. In particular, combinations of radar systems and optical sensor networks play an outstanding role in SSA programs. At present, Korea operates the optical wide field patrol network (OWL-Net), the only optical system for tracking space objects. However, due to their dependence on weather conditions and observation time, it is not reasonable to use optical systems alone for SSA initiatives, as they have limited operational availability. Therefore, the strategies for developing radar systems should be considered for an efficient SSA system using currently available technology. The purpose of this paper is to analyze the performance of a radar system in detecting and tracking space objects. With the radar system investigated, the minimum sensitivity is defined as detection of a $1-m^2$ radar cross section (RCS) at an altitude of 2,000 km, with operating frequencies in the L, S, C, X or Ku-band. The results of power budget analysis showed that the maximum detection range of 2,000 km, which includes the low earth orbit (LEO) environment, can be achieved with a transmission power of 900 kW, transmit and receive antenna gains of 40 dB and 43 dB, respectively, a pulse width of 2 ms, and a signal processing gain of 13.3 dB, at a frequency of 1.3 GHz. We defined the key parameters of the radar following a performance analysis of the system. This research can thus provide guidelines for the conceptual design of radar systems for national SSA initiatives.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.330-339
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• 2008

Ground-based interceptors(GBI) comprise a major element of the strategic defense against hostile targets like Intercontinental Ballistic Missiles(ICBM) and reentry vehicles(RV) dispersed from them. An optimum design of the subsystems is required to increase the performance and reliability of these GBI. Propulsion subsystem design and optimization is the motivation for this effort. This paper describes an effort in which an entire GBI missile system, including a multi-stage solid rocket booster, is considered simultaneously in a Genetic Algorithm(GA) performance optimization process. Single goal, constrained optimization is performed. For specified payload and miss distance, time of flight, the most important component in the optimization process is the booster, for its takeoff weight, time of flight, or a combination of the two. The GBI is assumed to be a multistage missile that uses target location data provided by two ground based RF radar sensors and two low earth orbit(LEO) IR sensors. 3Dimensional model is developed for a multistage target with a boost phase acceleration profile that depends on total mass, propellant mass and the specific impulse in the gravity field. The monostatic radar cross section (RCS) data of a three stage ICBM is used. For preliminary design, GBI is assumed to have a fixed initial position from the target launch point and zero launch delay. GBI carries the Kill Vehicle(KV) to an optimal position in space to allow it to complete the intercept. The objective is to design and optimize the propulsion system for the GBI that will fulfill mission requirements and objectives. The KV weight and volume requirements are specified in the problem definition before the optimization is computed. We have considered only continuous design variables, while considering discrete variables as input. Though the number of stages should also be one of the design variables, however, in this paper it is fixed as three. The elite solution from GA is passed on to(Sequential Quadratic Programming) SQP as near optimal guess. The SQP then performs local convergence to identify the minimum mass of the GBI. The performance of the three staged GBI is validated using a ballistic missile intercept scenario modeled in Matlab/SIMULINK.

• Journal of Space Technology and Applications
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• v.2 no.1
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• pp.1-12
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• 2022

In this paper, we described the development of a drag augmentation device for nanosatellite. Recently, space industry has entered the New Space era, and barriers to entry into Low Earth Orbit (LEO) for artificial objects such as small rockets and nanosatellite mega constellations have been significantly lowered. As a result, the number of space debris is increasing exponentially, and it is approaching as a major threat to satellite currently in operation as well as satellites to be launched in near future. To prevent this, international organizations like Inter-Agency Space Debris Coordination Committee (IADC) have been proposed space debris mitigation guidelines. The Korea Aerospace Research Institute (KARI) conducted KARI Rendezvous & Docking demonstration SATellite (KARDSAT) project, the first nanosatellites for rendezvous and docking technology demonstration in Korea, and we also developed drag augmentation device for KARDSAT Target nanosatellite that complied with the international guideline of post-mission disposal.

• Journal of the Korea Society of Computer and Information
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• v.29 no.1
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• pp.121-130
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• 2024

In this paper, we propose an installation approach for Naval Combat Management System(CMS) software that identifies potential data anomalies during installation. With the popularization of wireless communication methods, such as Low Earth Orbit(LEO) satellite communications, various utilization methods using wireless networks are being discussed in CMS. One of these methods includes the use of wireless network communications for installation, which is expected to enhance the real-time performance of the CMS. However, wireless networks are relatively more vulnerable to security threats compared to wired networks, necessitating additional security measures. This paper presents a method where files are transmitted to multiple nodes using encryption, and after the installation of the files, a validity check is performed to determine if there has been any tampering or alteration during transmission, ensuring proper installation. The feasibility of applying the proposed method to Naval Combat Systems is demonstrated by evaluating transmission performance, security, and stability, and based on these evaluations, results sufficient for application to CMS have been derived.

• Journal of Space Technology and Applications
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• v.4 no.1
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• pp.62-73
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• 2024

This study analyzed the effectiveness of orbital change through attitude change in nano-satellites operating in low Earth orbit (LEO) without thrusters, focusing on collision avoidance maneuvers. The results revealed that changes in the satellite's cross-sectional area significantly impact its in-track direction, influenced by the aspect ratio of cross-sectional area change and mission altitude. Notably, satellites at lower altitudes demonstrated significant reduction in collision risks with a small amount of attitude change. Through this study, it is judged that the changing the cross-sectional area through attitude maneuver is a sufficiently suitable method in the operation of nano-satellites without thrusters, and is expected to contribute to improving the safety of satellite operations in the New Space era.

• Composites Research
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• v.30 no.6
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• pp.379-383
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• 2017

A study on the low Earth orbit (LEO) space environment have been conducted as a use of composites have increased. Among the LEO environmental factors, atomic oxygen is one of the most critical factors because atomic oxygen can react and erode a surface of polymer-based composite materials. POSS (Polyhedral Oligomeric Silsesquioxane) materials have been widely studied as an atomic oxygen-resistant nanomaterial. In this study, nanocomposites, which are composed of OG (Octaglycidyldimethylsilyl) POSS nanomaterials and DGEBA/DDM epoxy, were fabricated to find out its thermal and mechanical properties. FT-IR results showed that the nanocomposites were fully cured and contained OG POSS enough. Thermogravimetric analysis and differential scanning calorimetry were performed to measure the thermal properties of the nanocomposites. The initial mass loss temperature and char yield were increased through the filling of OG POSS. As the content of OG POSS increased, glass transition temperature tended to increase to 5 wt.% of OG POSS, but the temperature decreased significantly at 10 wt.% of OG POSS. The tensile test results showed that the content of OG POSS did not affect tensile strength and tensile stiffness.