• Journal of Astronomy and Space Sciences
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• 제40권4호
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• pp.199-215
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• 2023

The Korea Pathfinder Lunar Orbiter (KPLO), the first South Korea lunar exploration probe, successfully arrived at the Moon on December, 2022 (UTC), following a 4.5-month ballistic lunar transfer (BLT) trajectory. Since the launch (4 August, 2022), the KPLO magnetometer (KMAG) has carried out various observations during the trans-lunar cruise phase and a 100 km altitude lunar polar orbit. KMAG consists of three fluxgate magnetometers capable of measuring magnetic fields within a ± 1,000 nT range with a resolution of 0.2 nT. The sampling rate is 10 Hz. During the originally planned lifetime of one year, KMAG has been operating successfully while performing observations of lunar crustal magnetic fields, magnetic fields induced in the lunar interior, and various solar wind events. The calibration and offset processes were performed during the TLC phase. In addition, reliabilities of the KMAG lunar magnetic field observations have been verified by comparing them with the surface vector mapping (SVM) data. If the KPLO's mission orbit during the extended mission phase is close enough to the lunar surface, KMAG will contribute to updating the lunar surface magnetic field map and will provide insights into the lunar interior structure and lunar space environment.

• Journal of Astronomy and Space Sciences
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• 제31권1호
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• pp.51-61
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• 2014

In this work, the preliminary analysis on both the tracking schedule and measurements characteristics for the spacecraft on the phase of lunar transfer and capture is performed. To analyze both the tracking schedule and measurements characteristics, lunar transfer and capture phases' optimized trajectories are directly adapted from former research, and eleven ground tracking facilities (three Deep Space Network sties, seven Near Earth Network sites, one Daejeon site) are assumed to support the mission. Under these conceptual mission scenarios, detailed tracking schedules and expected measurement characteristics during critical maneuvers (Trans Lunar Injection, Lunar Orbit Insertion and Apoapsis Adjustment Maneuver), especially for the Deajeon station, are successfully analyzed. The orders of predicted measurements' variances during lunar capture phase according to critical maneuvers are found to be within the order of mm/s for the range and micro-deg/s for the angular measurements rates which are in good agreement with the recommended values of typical measurement modeling accuracies for Deep Space Networks. Although preliminary navigation accuracy guidelines are provided through this work, it is expected to give more practical insights into preparing the Korea's future lunar mission, especially for developing flight dynamics subsystem.

• 한국항공우주학회지
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• 제41권6호
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• pp.473-480
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• 2013

2020년 예정인 국내 달 탐사 프로그램을 위하여 달착륙선에 관한 다양한 연구가 진행되고 있다. 본 연구에서는 RCS jet을 고려한 달 착륙선의 Powered descent phase에서의 유도제어시스템을 구성하고 통합 시뮬레이션을 수행하였다. 달착륙선은 RCS 제트추력기를 이용하여 자세를 제어하므로 일반적인 비례제어기가 아닌 뱅뱅제어기를 사용하게 된다. 본 논문에서는 16개의 추력기를 이용하여 자세제어를 수행하고, 이를 위하여 phase-plane 스위칭 함수를 이용한 on/off 제어기와 추력기 선택 알고리즘을 적용하였다. 또한 Fuzzy logic을 이용한 유도 알고리즘을 이용하여 최적기법을 통해 생성된 기준경로에 따라 정확하고 안전하게 착륙 할 수 있음을 확인 하였다.

• 한국항공우주학회지
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• 제39권5호
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• pp.408-415
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• 2011

달착륙은 크게 궤도이탈 단계, 동력하강 단계로 구성되어지며, 동력하강단계는 Braking, Approach, Final landing phase의 세부 3단계로 나누어진다. 본 논문에서는 동력하강 세부 3단계의 최적경로를 통하여 달착륙선의 착륙 제어를 수행하기로 한다. 우선 Gauss pseudo-spectral 방법을 통하여 기준 궤적을 생성하였고, 고도와 각 방향의 속도오차를 이용하여 PID 제어기를 생성하였다. 마지막으로 Matlab의 Simulink를 이용하여 달착륙선의 착륙단계 시스템을 구성하고 이를 이용하여 시뮬레이션을 수행하였다.

• Journal of Astronomy and Space Sciences
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• 제36권4호
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• pp.293-306
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• 2019

In this study, the observational arc-length effect on orbit determination (OD) for the Korea Pathfinder Lunar Orbiter (KPLO) in the Earth-Moon Transfer phase was investigated. For the OD, we employed a sequential estimation using the extended Kalman filter and a fixed-point smoother. The mission periods, comprised between the perigee maneuvers (PM) and the lunar orbit insertion (LOI) maneuver in a 3.5 phasing loop of the KPLO, was the primary target. The total period was divided into three phases: launch-PM1, PM1-PM3, and PM3-LOI. The Doppler and range data obtained from three tracking stations [included in the deep space network (DSN) and Korea Deep Space Antenna (KDSA)] were utilized for the OD. Six arc-length cases (24 hrs, 48 hrs, 60 hrs, 3 days, 4 days, and 5 days) were considered for the arc-length effect investigation. In order to evaluate the OD accuracy, we analyzed the position uncertainties, the precision of orbit overlaps, and the position differences between true and estimated trajectories. The maximum performance of 3-day OD approach was observed in the case of stable flight dynamics operations and robust navigation capability. This study provides a guideline for the flight dynamics operations of the KPLO in the trans-lunar phase.

• 한국지구과학회지
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• 제39권1호
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• pp.103-116
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• 2018

이 연구의 목적은 초등학교 6학년 학생들의 달의 위상 변화에 대한 학습 발달과정을 천문학적 시스템 사고를 기반으로 탐색하는 것이다. 선행 연구 결과 분석을 통해 서답형 문항을 개발하고 가설적 학습 발달과정을 설정하였으며, 이를 토대로 문항 분석틀을 개발하였다. 달의 위상 변화에 대한 수업을 실시하기 전과 후에 서답형 문항을 이용한 검사 자료를 수집하였으며, 평가 결과를 이용하여 가설적 학습 발달과정의 타당성을 검증하였다. 이를 통하여, 상향식으로 지구-달 계에 대한 학습 발달과정을 탐색할 수 있었다. 연구 결과, 초등학생들은 지구 기반 관점과 우주 기반 관점 사이의 사고 전환에 어려움을 겪는 것으로 보인다. 또한, 달의 위상 변화에 대한 초등학생들의 학습 발달과정을 근거로 할 때, 달의 위상 변화의 개념은 교육과정 상에서 초등학교의 학습 내용으로 다소 높은 수준인 것으로 판단된다.

• 한국항공운항학회지
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• 제23권1호
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• pp.49-55
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• 2015

This paper deals with dynamic modeling and controller design of a future Korean lunar module planned to be launched 2020's in Korea. For dynamic modeling of the lunar module, we first assume the lunar module as a rigid body. And we derive equations of motion for the lunar module by considering allocation of main thrusters and reaction thrusters. With the equation of motion, we design the controller based on the quaternion. A Pulse Width Pulse Frequency modulator(PWPFM) is selected for generating on/off signal. Finally, we construct a 2-phase descent mode including initial guidance mode, terminal guidance mode. The MATLAB simulation is performed for evaluating the descent ability and final landing velocity. The dynamic modeling and descent simulation of the lunar module in this paper could be applied for developing the future work of the Korean lunar exploration program.

• Journal of Astronomy and Space Sciences
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• 제41권1호
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• pp.43-60
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• 2024

Korea Pathfinder Lunar Orbiter (KPLO) is South Korea's first space exploration mission, developed by the Korea Aerospace Research Institute. It aims to develop technologies for lunar exploration, explore lunar science, and test new technologies. KPLO was launched on August 5, 2022, by a Falcon-9 launch vehicle from cape canaveral space force station (CCSFS) in the United States and placed on a ballistic lunar transfer (BLT) trajectory. A total of four trajectory correction maneuvers were performed during the approximately 4.5-month trans-lunar cruise phase to reach the Moon. Starting with the first lunar orbit insertion (LOI) maneuver on December 16, the spacecraft performed a total of three maneuvers before arriving at the lunar mission orbit, at an altitude of 100 kilometers, on December 27, 2022. After entering lunar orbit, the commissioning phase validated the operation of the mission mode, in which the payload is oriented toward the center of the Moon. After completing about one month of commissioning, normal mission operations began, and each payload successfully performed its planned mission. All of the spacecraft operations that KPLO performs from launch to normal operations were designed through the system operations design process. This includes operations that are automatically initiated post-separation from the launch vehicle, as well as those in lunar transfer orbit and lunar mission orbit. Key operational procedures such as the spacecraft's initial checkout, trajectory correction maneuvers, LOI, and commissioning were developed during the early operation preparation phase. These procedures were executed effectively during both the early and normal operation phases. The successful execution of these operations confirms the robust verification of the system operation.

• 한국항공우주학회지
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• 제46권5호
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• pp.402-409
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• 2018

이 논문에서는 무인 달착륙 임무를 위해 고려하고 있는 달착륙 시나리오를 제안하고 제안된 시나리오를 기반으로 동력하강단계에서의 최적화 착륙궤적을 구현한다. 동력하강단계에서 달착륙선의 자세 변화는 사용 연료량뿐만 아니라 영상기반 항법의 센서 운용에도 영향을 주므로 자세 변화가 급격하게 이루어지지 않도록 자세각속도를 최적제어 가격함수에 포함하고 이때 자세각속도의 영향을 조절하는 가중치가 최적화 착륙궤적에 미치는 영향을 분석한다. 분석된 결과를 바탕으로 연료 사용을 최소화하고 안정된 자세 변화를 갖도록 최적화 착륙궤적을 설계할 수 있는 적절한 가중치를 제시한다.

• Journal of Astronomy and Space Sciences
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• 제27권4호
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• pp.377-382
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• 2010

In lunar explorer development program, computer simulator is necessary to provide virtual environments that vehicle confronts in lunar transfer, orbit, and landing missions, and to analyze dynamic behavior of the spacecraft under these environments. Objective of simulation differs depending on its application in spacecraft development cycle. Scope of use cases considered in this paper includes simulation of software based, processor and/or hardware in the loop, and support of ground-based flight test of developed vehicle. These use cases represent early phase in development cycle but reusability of modeling results in the next design phase is considered in defining requirements. A simulator architecture in which simulator platform is located in the middle and modules for modeling, analyzing, and three dimensional visualizing are connected to that platform is suggested. Baseline concepts and requirements for simulator development are described. Result of trade study for selecting simulation platform and approaches of defining other simulator components are summarized. Finally, characters of lunar elevation map data which is necessary for lunar terrain generation is described.