• 천문학논총
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• 제38권2호
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• pp.91-98
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• 2023

We present a novel method that can enhance the detection success rate of interstellar objects. Interstellar objects are objects that are not gravitationally bound to our solar system and thus are believed to have originated from other planetary systems. Since the finding of two interstellar objects, 1l/'Oumuamua in 2017 and 2l/Borisov in 2019, much attention has been paid to finding new interstellar objects. In this paper, we propose the use of Heliospheric Imagers (HIs) for the survey of interstellar objects. In particular, we show HI data taken from Solar TErrestrial RElation Observatory/Sun Earth Connection Coronal and Heliospheric Investigation and demonstrate their ability to detect 'Oumuamua-like interstellar objects. HIs are designed to monitor and study space weather by observing the solar wind traveling through interplanetary space. HIs provide the day-side observations and thus it can dramatically enlarge the observable sky range when combined with the traditional night-side observations. In this paper, we first review previous methods for detecting interstellar objects and demonstrate that HIs can be used for the survey of interstellar objects.

• Journal of Astronomy and Space Sciences
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• 제32권4호
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• pp.411-417
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• 2015

Several optical monitoring strategies by a ground-based telescope to protect a Geostationary Earth Orbit (GEO) satellite from collisions with close approaching objects were investigated. Geostationary Transfer Orbit (GTO) objects, Inclined GeoSynchronous Orbit (IGSO) objects, and drifted GEO objects forced by natural perturbations are hazardous to operational GEO satellites regarding issues related to close approaches. The status of these objects was analyzed on the basis of their orbital characteristics in Two-Line Element (TLE) data from the Joint Space Operation Center (JSpOC). We confirmed the conjunction probability with all catalogued objects for the domestic operational GEO satellite, Communication, Ocean and Meteorological Satellite (COMS) using the Conjunction Analysis Tools by Analytical Graphics, Inc (AGI). The longitudinal drift rates of GeoSynchronous Orbit (GSO) objects were calculated, with an analytic method and they were confirmed using the Systems Tool Kit by AGI. The required monitoring area was determined from the expected drift duration and inclination of the simulated target. The optical monitoring strategy for the target area was analyzed through the orbit determination accuracy. For this purpose, the close approach of Russian satellite Raduga 1-7 to Korean COMS in 2011 was selected.

• Journal of Astronomy and Space Sciences
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• 제34권4호
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• pp.289-302
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• 2017

The key risk analysis technologies for the re-entry of space objects into Earth's atmosphere are divided into four categories: cataloguing and databases of the re-entry of space objects, lifetime and re-entry trajectory predictions, break-up models after re-entry and multiple debris distribution predictions, and ground impact probability models. In this study, we focused on reentry prediction, including orbital lifetime assessments, for space situational awareness systems. Re-entry predictions are very difficult and are affected by various sources of uncertainty. In particular, during uncontrolled re-entry, large spacecraft may break into several pieces of debris, and the surviving fragments can be a significant hazard for persons and properties on the ground. In recent years, specific methods and procedures have been developed to provide clear information for predicting and analyzing the re-entry of space objects and for ground-risk assessments. Representative tools include object reentry survival analysis tool (ORSAT) and debris assessment software (DAS) developed by National Aeronautics and Space Administration (NASA), spacecraft atmospheric re-entry and aerothermal break-up (SCARAB) and debris risk assessment and mitigation analysis (DRAMA) developed by European Space Agency (ESA), and semi-analytic tool for end of life analysis (STELA) developed by Centre National d'Etudes Spatiales (CNES). In this study, various surveys of existing re-entry space objects are reviewed, and an efficient re-entry prediction technique is suggested based on STELA, the life-cycle analysis tool for satellites, and DRAMA, a re-entry analysis tool. To verify the proposed method, the re-entry of the Tiangong-1 Space Lab, which is expected to re-enter Earth's atmosphere shortly, was simulated. Eventually, these results will provide a basis for space situational awareness risk analyses of the re-entry of space objects.

• Journal of Astronomy and Space Sciences
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• 제23권4호
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• pp.435-444
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• 2006

인공우주물체는 출현 시간이 비교적 짧고 운동 특성이 고정적이지 않기 때문에 한 번의 관측으로 측광 및 분광 데이터를 획득하기 어렵다. 따라서 인공우주물체의 측광 및 분광 동시 관측을 위해서 경희대학교 인공위성 추적 및 관측시스템에 다중 광학계를 탑재할 수 있는 가대를 설계하였다. 이 연구에서는 구조해석을 통해 다중 광학계 탑재 시에 개조된 가대의 변형을 계산하고 인공 우주물체 추적 및 관측 시 발생할 수 있는 가대의 지향오차를 추론하여 관측시야에서 인공우주물체를 안정적으로 추적할 수 있음을 보였다. 또한 등가응력 해석을 수행하여 가대의 구조적 안전성을 확인하였다.

• Journal of Astronomy and Space Sciences
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• 제34권4호
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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.

• 항공우주기술
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• 제13권1호
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• pp.184-192
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• 2014

본 논문에서는 JSpOC에서 제공하는 TLE 데이터를 이용하여 지구 저궤도 상에 존재하는 인공적인 우주물체의 궤도수명을 예측하였다. 이를 위해 1957년부터 현재까지 우주파편 개체수의 변화를 관찰하여 우주파편 생성의 요인과 현재 남아있는 물체들의 현황을 파악하였으며, 현재 지구 저궤도 상에 존재하는 총 11,792개의 물체에 대해 2050년까지 궤도전파를 수행하여 궤도수명을 분석하였다. 효율적인 계산을 위해 STK/Lifetime Tool을 사용하였으며, 재진입 시 지상에 낙하할 가능성이 있는 폐위성이나 로켓동체와 같이 질량 대비 단면적이 큰 물체에 대해 연간 재진입 빈도를 분석하였다. 분석 결과 2050년까지 매해 위성과 로켓동체는 약 9개가 재진입하며, 지상에 피해를 줄 수 있는 규모는 약 2-3개로 나타났고, 전체 분석 대상의 약 40%이상은 200년 이상의 궤도수명을 가지는 것으로 나타났다.

• 천문학회보
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• 제46권2호
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• pp.62.1-62.1
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• 2021

Interstellar objects originate from other stellar systems. Thus, they contain information about the stellar systems that cannot be directly explored; the information includes the formation and evolution of the stellar systems and the possibility of life. The examples observed so far are 1l/Oumuamua in 2017 and 2l/Borisov in 2019. In this talk, we present the possibility of detecting interstellar objects using the Heliospheric Imagers designed for space weather research and forecasting by observing solar wind in interplanetary space between the Sun and Earth. Because interstellar objects are unpredictable events, the detection requires observations with wide coverage in spatial and long duration in temporal. The near-real time data availability is essential for follow-up observations to study their detailed properties and future rendezvous missions. Heliospheric Imagers provide day-side observations, inaccessible by traditional astronomical observations. This will dramatically increase the temporal and spatial coverage of observations and also the probability of detecting interstellar objects visiting our solar system, together with traditional astronomical observations. We demonstrate that this is the case. We have used data taken from Solar TErrestrial RElation Observatory (STEREO)/Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) HI-1. HI-1 is off-pointed from the Sun direction by 14 degrees with 20 degrees of the field of view. Using images observed from 2007 to 2019, we have found a total of 223 small objects other than stars, galaxies, or planets, indicative of the potential capability to detect interstellar objects. The same method can be applied to the currently operating missions such as the Parker Solar Probe and Solar Orbiter and also future L5 and L4 missions. Since the data can be analyzed in near-real time due to the space weather purposes, more detailed properties can be analyzed by follow-up observations in ground and space, and also future rendezvous missions. We discuss future possible rendezvous missions at the end of this talk.

• Spatial Information Research
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• 제16권3호
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• pp.291-301
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• 2008

대부분의 지리정보 시스템들은 유클리디안 공간을 기반으로 하고 있지만, 셀룰러 공간 역시 많은 지리정보 시스템 응용을 위한 기반 공간으로 사용될 수 있다. 셀룰러 공간에 존재하는 이동객체의 이동 형태를 분석하기 위해서는, 유클리디안 공간과 분명히 다른 특징을 갖는 셀룰러 공간상에 존재하는 이동객체들의 유사도에 대한 새로운 정의가 필요하다. 본 논문에서는 셀룰러 공간에 존재하는 이동객체의 특성에 대해 살펴보았다. 이에 따라, 셀룰러 공간에 존재하는 궤적들 간의 유사도를 정의할 수 있는 2가지의 비교지수를 제시하고, 실험을 통해 제시한 비교 지수들 간의 차이를 분석하였다.

• 천문학논총
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• 제21권2호
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• pp.75-79
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• 2006

An alt-azimuth type mount system, developed at the Space Science and Technology Laboratory, Kyung Hee University, has been found to experience some difficulties in monitoring of the artificial space objects. Since the telescope installed on the alt-azimuth mount does not rotate on the same axis as the earth does, this mount system needs an instrument rotator to correct the field rotation. Although there are some commercial instrument rotators already in the market, those are not suitable for our system due to their low interchangeability. In this study, we have designed a new high speed instrument rotator and calculated the deformation of new designed system using structural analyses.

• 한국항공우주학회지
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• 제42권3호
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• pp.270-278
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• 2014

본 논문에서는 우주물체 궤도예측의 개선 방안에 관하여 기술하였다. 운용위성과 우주물체와의 근접 가능성 여부를 확인하기 위해 이용되는 TLE(Two-Line Element)를 가관측으로 사용하였고, 비행역학시스템을 통해 궤도결정 및 예측을 수행하였다. 궤도를 결정함에 있어 일정기간 내 일련의 TLE를 이용하여 상태벡터를 가정하였고, 결정기간 및 가관측수(pseudo-observations)에 따른 예측결과 오차를 분석하였다. 또한, 제안된 방식을 적용할 경우 궤도예측 정밀도가 향상 되는지를 알아보기 위해 수 미터 수준의 정밀궤도 확인이 가능한 아리랑위성 2, 3호를 대상으로 먼저 적용하였으며, 동일한 조건으로 우주물체에 적용한 결과를 분석하였다. 우주물체 궤도예측의 RMS 오차 비교 결과, 7일 전파기준으로 궤도 예측 정밀도를 약 90% 향상시킬 수 있었다. 우주물체의 개선된 궤도예측은 매일 수행되는 충돌가능성 분석에 이용되어 위험성이 높은 근접 우주물체의 1차적인 선별에 활용가능 할 것이다.