• Journal of Power Electronics
• /
• v.6 no.1
• /
• pp.18-28
• /
• 2006

The Electric Power Subsystem (EPS) is one of the most critical systems on any satellite because nearly every subsystem requires power. This makes the choice of power systems the most important task facing satellite designers. The main purpose of the Satellite EPS is to provide continuous, regulated and conditioned power to all the satellite subsystems. It has to withstand radiation, thermal cycling and vacuums in hostile space environments, as well as subsystem degradation over time. The EPS power characteristics are determined by both the parameters of the system itself and by the satellite orbit. After satellite separation from the launch vehicle (LV) to its orbit, in almost all situations, the satellite subsystems (attitude determination and control, communication and onboard computer and data handling (OBC&DH)), take their needed power from a storage battery (SB) and solar arrays (SA) besides the consumed power in the EPS management device. At this point (separation point, detumbling mode), the satellite's angular motion is high and the orientation of the solar arrays, with respect to the Sun, will change in a non-uniform way, so the amount of power generated by the solar arrays will be affected. The objective of this research is to select satellite EPS component types, to estimate solar array illumination parameters and to determine the efficiency of solar arrays during both detumbling and normal operation modes.

• Proceedings of the KSRS Conference
• /
• 2007.10a
• /
• pp.493-495
• /
• 2007

Future sub-meter resolution LEO missions require simultaneous dual-polarization downlink and/or multiple channel downlinks in single polarization. Especially, dual-polarization is needed to cope with bandwidth limitation due to high speed data transmission. Current KARI 13m X-Band antenna system needs to be upgraded to cope with such downlink schemes. This paper describes brief discussions on engineering work regarding how to meet the new requirements with minimum impact on current system as well as C&M (Control and Monitoring) software.

• Bulletin of the Korean Space Science Society
• /
• 2004.10b
• /
• pp.376-379
• /
• 2004

Operational orbit determination (OOD) depends on the capability of generating accurate prediction of spacecraft ephemeris in a short period. The predicted ephemeris is used in the operations such as instrument pointing and orbit maneuvers. In this study the orbit prediction problem consists of the estimating diverse arc length orbit using GPS navigation data, the predicted orbit for the next 48 hours, and the fitted 30-hour arc length orbits of double differenced GPS measurements for the predicted 48-hour period. For 24-hour orbit arc length, the predicted orbit difference from truth orbit was 205 meters due to the along-track error. The main error sources for the orbit prediction of the Low Earth Orbiter (LEO) satellite are solar pressure and atmosphere density.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.1
• /
• pp.82-87
• /
• 2002

The attitude determination in LEO Satellite like KOMPSAT is one of the most important issues for Sun-Acquisition. Particularly, in KOMPSAT, the roll axis direction can be determined since the sun sensor gives the information on the Euler angle for pitch and yaw axes in Sun-Acquisition mode. In other words, it is the problem to determine the two unknown axes direction with one axis knowledge. This paper proposes a new effective method for attitude determination of general LEO satellites when one axis information is avilable and proves its usefulness throughout the simulation.

• Journal of Astronomy and Space Sciences
• /
• v.33 no.2
• /
• pp.127-135
• /
• 2016

Inactive space objects are usually rotating and tumbling as a result of internal or external forces. KOREASAT 1 has been inactive since 2005, and its drift trajectory has been monitored with the optical wide-field patrol network (OWL-Net). However, a quantitative analysis of KOREASAT 1 in regard to the attitude evolution has never been performed. Here, two optical tracking systems were used to acquire raw measurements to analyze the rotation period of two inactive satellites. During the optical campaign in 2013, KOREASAT 1 was observed by a 0.6 m class optical telescope operated by the Korea Astronomy and Space Science Institute (KASI). The rotation period of KOREASAT 1 was analyzed with the light curves from the photometry results. The rotation periods of the low Earth orbit (LEO) satellite ASTRO-H after break-up were detected by OWL-Net on April 7, 2016. We analyzed the magnitude variation of each satellite by differential photometry and made comparisons with the star catalog. The illumination effect caused by the phase angle between the Sun and the target satellite was corrected with the system tool kit (STK) and two line element (TLE) technique. Finally, we determined the rotation period of two inactive satellites on LEO and geostationary Earth orbit (GEO) with light curves from the photometry. The main rotation periods were determined to be 5.2 sec for ASTRO-H and 74 sec for KOREASAT 1.

• International Journal of Aeronautical and Space Sciences
• /
• v.1 no.2
• /
• pp.43-49
• /
• 2000

The Global Positioning System (GPS) is becoming more attractive navigation means for LEO (Low Earth Orbit) spacecraft due to the data accuracy and convenience for utilization. The anomalies such as serious variations of Dilution-Of-Precision (DOP), loss of infrequent 3-dimensional position fix, and deterioration of instantaneous accuracy of position and velocity data could be observed, which have not been appeared during the ground testing. It may cause lots of difficulty for the processing of the orbit control algorithm using the GPS data. In this paper, the characteristics of the GPS data were analyzed according to the configuration of GPS receiver such as position fix algorithm and mask angle using GPS navigation data obtained from the first Korea Multi-Purpose Satellite (KOMPSAT). The problem in orbit tracking using GPS data, including the infrequent deterioration of the accuracy, and an efficient algorithm for its countermeasures has also been introduced. The reliability and efficiency of the modified algorithm were verified by analyzing the effect of the results between algorithm simulation using KOMPSAT flight data and ground simulator.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 2003.05a
• /
• pp.704-707
• /
• 2003

The Purpose of carrier tracking and tracing is to achieve more information over shipments via carrying in mobile business .At multimodes, especially consignor wants to be aware of the exact situation and position of goods. As an innovate business model, we present CGPS(Carrier Global Positioning System) scheme usiug LEO(Low Earth Orbital) satellite. The LEO collects the data periodically and sends to the web server, and eventually customer's PC or PDA. This provides shipping company or freight forwarder with more robust information such as door status, container inside condition, etc.

• Proceedings of the KSRS Conference
• /
• 2007.10a
• /
• pp.394-396
• /
• 2007

Radio occultation (RO) technique has been used in planetary science since 1960s. When signal goes through atmosphere, it is refracted due to the gradient of atmospheric refractivity. In 1995, the first low earth orbit (LEO) satellite, MicroLab-1, was launched to conduct RO mission. It receives the signal from global positioning system (GPS) satellites. After MicroLab-1, other RO missions, such as CHAMP, SAC-C, and GRACE, are executed in several years later. In 2006, Taiwan launched six LEO satellites for RO mission. The mission name is Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC). Under some abnormal situations, multipath and strong fluctuation in phase and amplitude of the signal appear in moist troposphere. Therefore, open loop (OL) technique has been applied to replace traditional phase lock loop (PLL) technique. In this paper, we will summarize the retrieval processing procedure and discuss the advantages and disadvantages of OL technique.

• Electronics and Telecommunications Trends
• /
• v.30 no.4
• /
• pp.162-173
• /
• 2015

약 20년 전 세상의 이목을 끌었다가 무너진 꿈으로 남아있는 위성벤처 1.0. 즉 텔레데식, 이리디움 등으로 대표되던 대규모 저궤도 위성군(Big LEO) 통신시스템이 다시 추진되고 있다. 이른바 위성벤처 2.0으로 불리우는 스페이스엑스(Space Exploration Technologies: SpaceX). 원웹(OneWeb), 리오셋(Leosat) 등의 저궤도 위성군 통신시스템의 경쟁적 재등장이다. 이 배경에는 인터넷 업체인 구글(Google)과 페이스북(Facebook)이 관련되어 있다. 이미 과거의 경험이 있는 상황이기 때문에 성공가능성에 대한 기대가 상당히 크지만 회의론도 만만치 않다. 이들의 등장배경과 각 시스템의 기술적 제안, 비지니스 모델, 그리고 네트워크 구축 및 운용경비 절감을 위한 각각의 전략적 접근에 대해서 간략히 알아본다. 기존 이리디움이나 글로벌스타도 1세대 위성수명이 다하여 이제 2세대 위성군으로 업그레이드된 상태이라 신구 시스템 간의 차별적 경쟁도 이제 피할 수 없게 되었다. 신규제안 시스템의 성공적 안착을 위한 고려사항과 이러한 흐름에 대한 우리나라의 대응도 살펴보았다.

• International journal of advanced smart convergence
• /
• v.13 no.2
• /
• pp.7-15
• /
• 2024

6G network technology represents the next generation of communications, supporting high-speed connectivity, ultra-low latency, and integration with cutting-edge technologies, such as the Internet of Things (IoT), virtual reality, and autonomous vehicles. These advancements promise to drive transformative changes in digital society. However, as technology progresses, the demand for efficient data transmission and energy management between smart devices and network equipment also intensifies. A significant challenge within 6G networks is the optimization of interactions between satellites and smart devices. This study addresses this issue by introducing a new game theory-based technique aimed at minimizing system-wide energy consumption and latency. The proposed technique reduces the processing load on smart devices and optimizes the offloading decision ratio to effectively utilize the resources of Low-Earth Orbit (LEO) satellites. Simulation results demonstrate that the proposed technique achieves a 30% reduction in energy consumption and a 40% improvement in latency compared to existing methods, thereby significantly enhancing performance.