• Journal of Astronomy and Space Sciences
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• 제34권4호
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• pp.331-342
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• 2017

To ensure the successful launch of the Korea pathfinder lunar orbiter (KPLO) mission, the Korea Aerospace Research Institute (KARI) is now performing extensive trajectory design and analysis studies. From the trajectory design perspective, it is crucial to prepare contingency trajectory options for the failure of the first lunar brake or the failure of the first lunar orbit insertion (LOI) maneuver. As part of the early phase trajectory design and analysis activities, the required time of flight (TOF) and associated delta-V magnitudes for each recovery maneuver (RM) to recover the KPLO mission trajectory are analyzed. There are two typical trajectory recovery options, direct recovery and low energy recovery. The current work is focused on the direct recovery option. Results indicate that a quicker execution of the first RM after the failure of the first LOI plays a significant role in saving the magnitudes of the RMs. Under the conditions of the extremely tight delta-V budget that is currently allocated for the KPLO mission, it is found that the recovery of the KPLO without altering the originally planned mission orbit (a 100 km circular orbit) cannot be achieved via direct recovery options. However, feasible recovery options are suggested within the boundaries of the currently planned delta-V budget. By changing the shape and orientation of the recovered final mission orbit, it is expected that the KPLO mission may partially pursue its scientific mission after successful recovery, though it will be limited.

• Journal of Astronomy and Space Sciences
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• 제33권4호
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• pp.323-333
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• 2016

In this study, the uncertainty requirements for orbit, attitude, and burn performance were estimated and analyzed for the execution of the $1^{st}$ lunar orbit insertion (LOI) maneuver of the Korea Pathfinder Lunar Orbiter (KPLO) mission. During the early design phase of the system, associate analysis is an essential design factor as the $1^{st}$ LOI maneuver is the largest burn that utilizes the onboard propulsion system; the success of the lunar capture is directly affected by the performance achieved. For the analysis, the spacecraft is assumed to have already approached the periselene with a hyperbolic arrival trajectory around the moon. In addition, diverse arrival conditions and mission constraints were considered, such as varying periselene approach velocity, altitude, and orbital period of the capture orbit after execution of the $1^{st}$ LOI maneuver. The current analysis assumed an impulsive LOI maneuver, and two-body equations of motion were adapted to simplify the problem for a preliminary analysis. Monte Carlo simulations were performed for the statistical analysis to analyze diverse uncertainties that might arise at the moment when the maneuver is executed. As a result, three major requirements were analyzed and estimated for the early design phase. First, the minimum requirements were estimated for the burn performance to be captured around the moon. Second, the requirements for orbit, attitude, and maneuver burn performances were simultaneously estimated and analyzed to maintain the $1^{st}$ elliptical orbit achieved around the moon within the specified orbital period. Finally, the dispersion requirements on the B-plane aiming at target points to meet the target insertion goal were analyzed and can be utilized as reference target guidelines for a mid-course correction (MCC) maneuver during the transfer. More detailed system requirements for the KPLO mission, particularly for the spacecraft bus itself and for the flight dynamics subsystem at the ground control center, are expected to be prepared and established based on the current results, including a contingency trajectory design plan.

• International Journal of Aeronautical and Space Sciences
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• 제10권1호
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• pp.67-74
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• 2009

In general, the lunar landing stage can be divided into two distinct phases: de-orbit and descent, and the descent phase usually comprises two sub-phases: braking and approach. And many optimization problems of minimal energy are usually focused on descent phases. In these approaches, the energy of de-orbit burning is not considered. Therefore, a possible low perilune altitude can be chosen to save fuel for the descent phase. Perilune altitude is typically specified between 10 and 15km because of the mountainous lunar terrain and possible guidance errors. However, it requires more de-orbit burning energy for the lower perilune altitude. Therefore, in this paper, the perilune altitude of the intermediate orbit is also considered with optimal thrust programming for minimal energy. Furthermore, the perilune altitude and optimal thrust programming can be expressed by a function of the radius of a parking orbit by using continuation method and co-state estimator.

• 한국항공우주학회지
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• 제45권8호
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• pp.662-670
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• 2017

본 논문에서는 한국형 달 착륙 임무를 위한 아폴로 유도 법칙의 파라미터 선정을 위한 최적화 기반의 절차를 제안하였다. 달 착륙 문제를 연료 소모량을 최소화하기 위한 궤적 최적화 문제로 공식화하였으며 비행 이전 단계에서 본 문제를 풀어 착륙선의 기준 궤적을 획득할 수 있다. 아폴로 유도의 파라미터들은 유도 명령을 정의하기 위해 사용되는 다항식의 계수들이며, 비행 이전 단계에서 구해진 기준 궤적을 기반으로 선정된다. 제안된 절차의 효과를 입증하기 위해, 본 절차를 사용한 한국형 달 착륙 임무의 착륙 유도 사례연구를 수행하였다.

• Journal of Astronomy and Space Sciences
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• 제35권4호
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• pp.295-308
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• 2018

In this study, orbit determination (OD) simulation for the Korea Pathfinder Lunar Orbiter (KPLO) was accomplished for investigation of the observational arc-length effect using a sequential estimation algorithm. A lunar polar orbit located at 100 km altitude and $90^{\circ}$ inclination was mainly considered for the KPLO mission operation phase. For measurement simulation and OD for KPLO, the Analytical Graphics Inc. Systems Tool Kit 11 and Orbit Determination Tool Kit 6 software were utilized. Three deep-space ground stations, including two deep space network (DSN) antennas and the Korea Deep Space Antenna, were configured for the OD simulation. To investigate the arc-length effect on OD, 60-hr, 48-hr, 24-hr, and 12-hr tracking data were prepared. Position uncertainty by error covariance and orbit overlap precision were used for OD performance evaluation. Additionally, orbit prediction (OP) accuracy was also assessed by the position difference between the estimated and true orbits. Finally, we concluded that the 48-hr-based OD strategy is suitable for effective flight dynamics operation of KPLO. This work suggests a useful guideline for the OD strategy of KPLO mission planning and operation during the nominal lunar orbits phase.

• 한국항공우주학회지
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• 제46권4호
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• pp.324-331
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• 2018

달 탐사를 위한 착륙선이 운용되는 열환경은 태양에 대한 달의 자전주기가 약 28일인 것에 기인하여 낮 시간과 밤 시간이 지구에 비하여 매우 장기간 지속 되는 등 지표나 지구 저궤도 환경에 비해 더욱 극단적이다. 달 착륙선의 초기 설계 단계에서는 착륙지 선정을 위해 각각의 후보 지역에서의 착륙선으로의 열 유입량 분석이 중요하다. 본 논문에서는 달 착륙선의 후보 착륙지에 따른 열적특성을 분석하고자 달의 표면온도를 모사할 수 있는 표토층의 열모델을 구축하였다. 그리고 상기 표토층에 착륙선을 적용하여 착륙지가 달의 적도, 중위도, 극지방에 위치한 경우, 바다 및 고지대에 위치한 조건에서의 열 유입량을 분석하였다. 또한 언덕의 경사진 지형조건이 착륙선의 열 유입량에 미치는 영향성 분석을 수행하였다.

• 우주기술과 응용
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• 제3권3호
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• pp.199-212
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• 2023

과거 1970년대까지의 달 표면탐사에서는 단기간 달에서의 임무 특성을 가지는 것에 비해 최근 달 표면탐사는 달에서의 장기체류와 이를 기반으로 궁극적으로 화성까지 탐사 범위를 확장하는 방향으로 진행되고 있다. 인간의 달표면 장기체류를 실현하기 위해서는 탐사 현지 자원을 활용하여 체류에 필요한 소비재나 연료 등의 현지 생산 및 사용이 중요한 전제가 된다. 국제우주탐사협의체(ISECG, International Space Exploration Coordination Group)에서 각국의 우주탐사 계획을 반영하여 제시하는 글로벌 우주탐사 로드맵에는 달표면 탐사로부터 화성탐사로 이어지는 발전 단계가 제시되며 각 단계에서 현지자원활용은 중요한 요소가 되고 있다. 본 논문에서는 국제우주탐사협의체의 현지자원활용(ISRU) 격차분석 보고서를 기반으로 현지자원활용의 기술 분야를 현지 연료 및 소비재 생산, 현지 건설, 우주상 제조, 그리고 생성 결과물의 보관 및 활용, 자원활용에 필요한 전력시스템 등과 같은 연관 분야로 분류하여 주요 분야에서의 기술 개발 및 검증 현황을 분석한다. 다수의 국가는 달 자원 중 극 지역 영구음영지역의 얼음물 이용 그리고 표토에서 산소 등의 추출에 우선 순위를 부여하고, 무인 착륙임무를 통하여 달 남극 영구음영지역 근처에서 물질 및 물 분포 확인을 준비하고 있다. 자원 활용을 위하여 수전해를 이용한 수소, 산소 등 연료 생산, 모사토를 이용한 달 표토에서 산소의 추출 등의 기술을 개발하고 있다. 자원활용 기술의 개발을 위하여 지상에 달표면 모사환경을 구현하고 기술의 개발, 시나리오의 시연 등을 통한 효율적 현지자원활용 구현 방법 등을 모색하고 있다. 지속 가능한 달 표면 탐사를 위하여 각국은 달 표면 도달, 자원의 조사, 물질의 추출 등에 서비스 구매 등 민간 영역의 능력을 활용하고 발전시키는 노력을 병행하고 있다.

• 한국발생생물학회지:발생과생식
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• 제14권1호
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• pp.21-25
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• 2010

Nile tilapia (Oreochromis niloticus) are mouth-brooders so that the females holding eggs in their mouth sacrifice their somatic growth for reproduction. For this reason, artificial control of reproduction for the culture of this species has been of interest. Manipulation of photoperiod is an emerging technique for such purpose, but little information is available to establish appropriate photoperiod regime. To obtain necessary basic information, sexually mature females were individually accommodated to glass aquarium, and the spawning activity of these females were monitored for two years under natural photoperiod regime. Female tilapia spawned most frequently on March, April and May when the day length gradually increased from 11 hours to 14 hours and least frequently on September, October, November and December when the day length gradually decreased from 13 hours to less than 10 hours in the first year. The decrease of spawning frequency as day length decreased was also observed in the second year, although the increase of spawning frequency as day length increased was less clear. Spawning of female tilapia was less active when the night was dark due to the disappearance of moonlight (Dark Phase), compared to the Phase of Getting Lighter, Light Phase and Phase of Getting Darker. Results from this study suggest that long day length, particularly increasing phase, is favoured for active spawning of Nile tilapia, and that this species, as a tropical fish species, may utilize changing lunar phases as a secondary environmental cue for reproduction.

• 한국항공우주학회지
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• 제44권3호
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• pp.218-227
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• 2016

대한민국 정부는 2020년까지 달에 궤도선과 착륙선 발사를 계획하고 있다. 두 가지 탐사선을 발사하기 이전에 탐사선의 핵심기술 확보 및 달의 과학 데이터를 획득하기 위해 시험용 궤도선을 2018년까지 발사할 계획이다. 궤도선의 탑재체는 달 표면 촬영 및 과학 데이터를 획득한 후 지상으로 전송한다. 또한 궤도선이 지상국과 교신이 가능하면 S-band 대역으로 원격명령 및 원격 측정 데이터를 전송하고, X-band 대역으로 과학 데이터를 전송한다. 한국형 심우주 네트워크는 궤도선과 주로 S 및 X-band 통신을 수행한다. 지구-달 전이 단계에서 한국형 심우주 네트워크가 가용할지 않을 경우 Deep Space Network 또는 Universal Space Network를 이용하며, 임무 궤도에서는 예비로 이 네트워크들이 사용된다. 본 논문은 임무 시나리오에 따른 궤도선의 일별 교신 횟수를 예측하고 운영 시나리오를 작성하기 위해 다양한 안테나 및 마스크 각도에 따른 가시성 조건을 분석하였다.

• 대한원격탐사학회지
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• 제37권1호
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• pp.69-84
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• 2021

Awareness of boats is a main issue in areas of fishery management, illegal fishing, and maritime traffic, etc. For the awareness, Automatic Identification System (AIS) and Vessel-Pass System (V-PASS) have been widely used to collect the boat-related information. However, only using these systems makes it difficult to collect the accurate information. Recently, satellite-based data has been increasingly used as a cooperative system. In 2015, U.S. National Oceanic and Atmospheric Administration (NOAA) developed a boat detection algorithm using Visible Infrared Imaging Radiometer Suite (VIIRS) Day & Night Band (DNB) data. Although the detections have been widely utilized in many publications, it is difficult to estimate the night-time fishing boats immediately. Particularly, it is difficult to estimate the threshold due to the lunar irradiation effect. This effect must be corrected to apply a single specific threshold. In this study, the moon phase was considered as the main frequency of this effect. Considering the moon phase, relational expressions are derived and then used as offsets for relative correction. After the correction, it shows a significant reduction in the standard deviation of the threshold compared to the threshold of NOAA. Through the correction, this study can set a constant threshold every day without determination of different thresholds. In conclusion, this study can achieve the detection applying the single specific threshold regardless of the moon phase.