Sang-Cherl Lee

Collision Avoidance Maneuver Planning Using GA for LEO and GEO Satellite Maintained in Keeping Area

In this paper, a collision avoidance maneuver was sought for low Earth orbit (LEO) and geostationary Earth orbit (GEO) satellites maintained in a keeping area. A genetic algorithm was used to obtain both the maneuver start time and the delta-V to reduce the probability of collision with uncontrolled space objects or debris. Numerical simulations demonstrated the feasibility of the proposed algorithm for both LEO satellites and GEO satellites.

COMS Momentum Dumping Optimal Thruster Set Selection

This paper discusses wheel offloading approaches of the COMS which has a single solar array system for the accommodation of the optical payloads. First of all, in an effort to reduce fuel consumption and reflect practical implementation point of view, thruster sets for wheel offloading are proposed based on numerical analyses taking into account the COMS configuration. In this analysis, it is assumed that the wheel offloading is conducted twice a day. Secondly, in order to evaluate the effectiveness of the proposed thruster sets, orbit simulations are conducted for several wheel offloading approaches and compared.

Fuel Budget Analysis of the COMS Momentum Dumping

This paper analyzes the fuel consumption for the momentum dumping of the COMS which has a single solar array system. First, numerical analyses are conducted to find an optimal momentum dumping time considering the COMS configuration. It is assumed that the momentum dumping is conducted once a day and at a fixed time of a day. Secondly, in an effort to reduce the momentum dumping fuel consumption, this paper proposes a new approach which combines the momentum dumping and the ordinary north/south stationkeeping. Finally, to evaluate the proposed technique, the stationkeeping simulations are conducted and analyzed.

Analysis of Space debris collision risk using KARISMA for KOMPSAT Satellite series

Korea has successfully launched multipurpose satellites such as KOMPSAT (KOrea Multi Purpose SATellite) in low Earth orbit (LEO) since 1999. Thus far, KOMPSAT-2, KOMPSAT-3, and KOMPSAT-5 are in operation, and KOMPSAT-3A will be launched this year. Korea also successfully launched COMS (Communication, Ocean, and Meteorological Satellite), its first geostationary satellite, in 2006. The Korea Aerospace Research Institute (KARI) is therefore now concerned about the risk posed by space debris to these satellites. In fact, a preliminary analysis of the collision risk for KOMPSAT-1 (which was left out owing to a communication system malfunction in 2008) and KOMPSAT-2 was performed in light of Chinese’s Anti Satellite Test (ASAT) in 2007. The development of a full-scale analysis system for collision risk at KARI has been further encouraged by the satellite collision accident between the Iridium 33 satellite and the defunct Cosmos 2251 satellite at an altitude of 770 km, which significantly increased the amount of space debris in the LEO region of space. With this background in mind, the KARI Space debris collision risk MAnagement system (KARISMA) has been in development since 2011. KARISMA was finalized in July 2013 and then tested for the KOMPSAT satellite series. This paper presents the analysis results for the space collision risk of the KOMPSAT satellites using KARISMA as well as the collision avoidance (COLA) maneuver planning with various maneuver strategies for several conjunction events. The characteristics and architecture of KARISMA are also discussed with detailed operational views. Among the various features of KARISMA, the efficient process for both the analysis and the management of the collision risk and a user-friendly UI including various 2D and 3D displays for the results and conjunction geometry are the most remarkable. However, KARISMA has been developed as standalone software. Therefore, we plan to expand and modify it for various users in Korea by considering a server-client concept as a further work.

Comparison of Global Optimization Methods for Insertion Maneuver into Earth-Moon L2 Quasi-Halo Orbit Considering Collision Avoidance

A spacecraft placed in an Earth-Moon L2 quasi-halo orbit can maintain constant communication between the Earth and the far side of the Moon. This quasi-halo orbit could be used to establish a lunar space station and serve as a gateway to explore the solar system. For a mission in an Earth-Moon L2 quasi-halo orbit, a spacecraft would have to be transferred from the Earth to the vicinity of the Earth-Moon L2 point, then inserted into the Earth-Moon L2 quasi-halo orbit. Unlike the near Earth case, this orbit is essentially very unstable due to mutually perturbing gravitational attractions by the Earth, the Moon and the Sun. In this paper, an insertion maneuver of a spacecraft into an Earth-Moon L2 quasi-halo orbit was investigated using the global optimization algorithm, including simulated annealing, genetic algorithm and pattern search method with collision avoidance taken into consideration. The result shows that the spacecraft can maintain its own position in the Earth-Moon L2 quasi-halo orbit and avoid collisions with threatening objects.

Analytical Design of the Space Debris Collision Avoidance Maneuver based on Relative Dynamics

Abstract: 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. Keywords: space debris, collision avoidance maneuver, analytical solution, relative dynamics I. 서론 최초의 인공위성인 스푸트니크의 성공적인 발사 이후 50여년 동안 수많은 인공위성이 우주공간으로 발사되었다. 이러한 인공위성의 급격한 증가로 악화되기 시작한 우주환경으로 인해 최근 우주파편에 대한 관심이 고조되고 있다. 이러한 관심은 2009년 미국의 이리듐 33위성과 러시아의 코스모스 2251 통신 위성의 충돌사건[1] 이후 자국의 운영위성을 보호하기 위한 충돌위험 종합관리 시스템의 구축의 노력으로 이어졌다[2]. 우주파편으로부터 자국의 위성을 보호하기 위해서는 자국의 위성뿐만 아니라 접근해오는 우주파편에 대한 정밀한 궤도정보를 계산할 수 있어야 하며[3,4], 이를 바탕으로 충돌위험확률을 계산할 수 있어야 한다[5]. 이러한 과정을 통해 계산된 충돌확률이 높을 경우 이를 회피하기 위한 기동을 설계할 수 있어야 한다. 이러한 인공위성의 충돌회피 기동의 설계는 지상의 대상체에[6,7] 비해 상대적으로 빠른 속도로 움직이며, 실제 운영과 관련되기 때문에 높은 정밀도와 신뢰도를 바탕으로 하고 있다. 이러한 이유로 일반적으로 우주환경에 대한 정확한 모델링을 바탕으로 수치적인 방법으로 계산한다[8-10]. 이 단계에서 여러 운영요소들이 결합한 최적의 해를 찾기 위해 다양한 최적화 기법들이 도입 되었다. 하지만 이러한 수치 최적화 기법의 경우 방법에 따라서 상당한 시간이 소요될 수 있는 단점이 있다. 이러한 문제에도 불구하고 충돌회피 기동의 경우 실제 운영에 적용되는 문제이기 때문에 수치 최적화 기법을 배제할 수 없다. 따라서 본 논문에서는 이러한 충돌회피 기동을 설계하기 위한 수치 최적화 기법을 적용하기 전에 초기값에 대한 정보를 제공해줌으로써 보다 효율을 높이고자 한다. 이를 위해서 충돌회피 기동에 대한 해석적 방법의 설계전략을 제안하고자 한다. 일반적으로 우주파편에 대한 충돌회피 기동 설계 문제의 경우 랑데부-도킹 문제와 상당부분 유사점을 가지고 있는 점에 착안해서 이러한 랑데부-도킹 문제에서 사용하고 있는 여러 상대운동방정식을 이용해서 충돌회피 기동을 설계해보고자 하며, 그 시작으로 본 논문에서는 CW (Clohessy-Wiltshire) 좌표계에 대한 Hill’s 방정식을 이용한 가장 단순한 충돌회피 기동을 설계해보고자 한다. II. 상대운동 방정식 원형 궤도 주위를 돌고 있는 인공위성의 상대운동방정식의 경우 주로 CW 좌표계로 표현한다. CW 좌표계는 그림 1과 같이 임의의 기준 궤도를 따라 이동하는 비관성 이동 좌

New Method for Station Keeping of Geostationary Spacecraft Using Relative Orbital Motion and Optimization Technique

In this paper, a method of station keeping strategy using relative orbital motion and numerical optimization technique is presented for geostationary spacecraft. Relative position vector with respect to an ideal geostationary orbit is generated using high precision orbit propagation, and compressed in terms of polynomial and trigonometric function. Then this relative orbit model is combined with optimization scheme to propose a very efficient and flexible method of station keeping planning. Proper selection of objective and constraint functions for optimization can yield a variety of station keeping methods improved over the classical ones. Results from the nonlinear simulation have been shown to support such concept.

A Conceptual Study of Positioning System for the Geostationary Satellite Autonomous Operation

Even more than 240 commercial geostationary communication satellites currently on orbit at the higher location than the GPS orbit altitude perform their own missions only by the support of the ground segment because of weak visibility from GPS. In addition, the orbit determination accuracy is very low without using two or more dedicated ground tracking antennas in intercontinental ground segment, since the satellite hardly moves with respect to the ground station. In this paper, we propose the GSPS(Geostationary Satellite Positioning System) in circular orbits of two sidereal days period higher than the geosynchronous orbit for orbit determination and autonomous satellite operation. The GSPS is conceived as a ranging system in that unknown positions of a geostationary satellite can be acquired from the known positions of the GSPS satellites. Each GSPS satellite transmits navigation data, clock data, correction data, and geostationary satellite command to control a geostationary satellite.

A Study on the Station Relocation of the Koreasat

In general, station relocation for a geostationary orbit satellite is formulated as a request for moving the spacecraft from its present longitude to the target longitude within a given time interval. The station relocation maneuver is composed of drift orbit insertion maneuver and target orbit insertion maneuver. During station relocation, the satellite orbit is continually influenced by the non-spherical geo-potential. When we plan a maneuver, if we do not consider the influence, the satellite may not be relocate to desired longitude successfully. To solve this problem, we applied the linearised orbit transfer equation to acquire maneuver time and delta-V. Nonlinear simulation for the station relocation of multiple satellites is performed in order to verify the distance between two satellites.