• Journal of Astronomy and Space Sciences
• /
• v.33 no.3
• /
• pp.211-219
• /
• 2016

Korea's lunar exploration project includes the launching of an orbiter, a lander (including a rover), and an experimental orbiter (referred to as a lunar pathfinder). Laser altimeters have played an important scientific role in lunar, planetary, and asteroid exploration missions since their first use in 1971 onboard the Apollo 15 mission to the Moon. In this study, a laser altimeter was proposed as a scientific instrument for the Korean lunar orbiter, which will be launched by 2020, to study the global topography of the surface of the Moon and its gravitational field and to support other payloads such as a terrain mapping camera or spectral imager. This study presents the baseline design and performance model for the proposed laser altimeter. Additionally, the study discusses the expected performance based on numerical simulation results. The simulation results indicate that the design of system parameters satisfies performance requirements with respect to detection probability and range error even under unfavorable conditions.

• Bulletin of the Korean Space Science Society
• /
• 2008.10a
• /
• pp.37.4-38
• /
• 2008

Recently, statement of Intent for ILN has been signed by 9 countries including Korea, initiated March of this year by NASA which invited countries having lunar exploration plans. Concept of ILN is placing several core set of instrumentation on the Moon, in order to maximize scientific return to all of the participants. Network measurements from various nodes on lunar surface is essential for understanding internal structure of the Moon and environment around the Moon. Currently, Core Instrument Working Group is discussing the scientific interests and instrumentation among participated countries. Korea also is looking over various ways to participate ILN. We will introduce the progress and possible lunar science of ILN and will discuss the science mission objectives.

• Journal of Astronomy and Space Sciences
• /
• v.27 no.2
• /
• pp.97-106
• /
• 2010

To prepare for a Korean lunar orbiter mission, a precise lunar orbit propagator; Yonsei precise lunar orbit propagator (YSPLOP) is developed. In the propagator, accelerations due to the Moon's non-spherical gravity, the point masses of the Earth, Moon, Sun, Mars, Jupiter and also, solar radiation pressures can be included. The developed propagator's performance is validated and propagation errors between YSPOLP and STK/Astrogator are found to have about maximum 4-m, in along-track direction during 30 days (Earth's time) of propagation. Also, it is found that the lifetime of a lunar polar orbiter is strongly affected by the different degrees and orders of the lunar gravity model, by a third body's gravitational attractions (especially the Earth), and by the different orbital inclinations. The reliable lifetime of circular lunar polar orbiter at about 100 km altitude is estimated to have about 160 days (Earth's time). However, to estimate the reasonable lifetime of circular lunar polar orbiter at about 100 km altitude, it is strongly recommended to consider at least $50\;{\times}\;50$ degrees and orders of the lunar gravity field. The results provided in this paper are expected to make further progress in the design fields of Korea's lunar orbiter missions.

• Journal of Astronomy and Space Sciences
• /
• v.34 no.3
• /
• pp.213-223
• /
• 2017

The deep space orbit determination software (DSODS) is a part of a flight dynamic subsystem (FDS) for the Korean Pathfinder Lunar Orbiter (KPLO), a lunar exploration mission expected to launch after 2018. The DSODS consists of several sub modules, of which the orbit determination (OD) module employs a weighted least squares algorithm for estimating the parameters related to the motion and the tracking system of the spacecraft, and subroutines for performance improvement and detailed analysis of the orbit solution. In this research, DSODS is demonstrated and validated at lunar orbit at an altitude of 100 km using actual Lunar Prospector tracking data. A set of a priori states are generated, and the robustness of DSODS to the a priori error is confirmed by the NASA planetary data system (PDS) orbit solutions. Furthermore, the accuracy of the orbit solutions is determined by solution comparison and overlap analysis as about tens of meters. Through these analyses, the ability of the DSODS to provide proper orbit solutions for the KPLO are proved.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.713-714
• /
• 2015

Indian astronomical texts have records of lunar astronomy since the Puranic age. In the Vednga Jyotia (1350 B CE), the algorithm for computing eclipses is not found. This phenomenon was interpreted in the Siddhntic texts as the occurrence of Vyatipati Yoga. This paper attempts to explain the computing and observational method found in astronomical texts of Siddhntic period.

• Journal of The Korean Astronomical Society
• /
• v.49 no.4
• /
• pp.163-173
• /
• 2016

In this paper, we study the lunar eclipse records in the Goryeosa (History of the Goryeo Dynasty), an official history book of the Goryeo dynasty (A.D. 918 - 1392). In the history book, a total of 228 lunar eclipse accounts are recorded, covering the period from 1009 to 1392. However, we find that two accounts are duplications and four accounts correspond to no known lunar eclipses around the dates. For the remaining lunar eclipses, we calculate the magnitude and the time of the eclipse at different phases using the DE406 ephemeris. Of the 222 lunar eclipse accounts, we find that the minimum penumbral magnitude was 0.5583. For eclipses which occurred after midnight, we find that some accounts were recorded on the day before the eclipse, like the astronomical records of the Joseonwangjosillok (Annals of the Joseon Dynasty), while others were on the day of the lunar eclipse. We also find that four accounts show a difference in the Julian dates between this study and that of Ahn et al., even though it is assumed that the Goryeo court did not change the dates in the accounts for lunar eclipses that occurred after midnight. With regard to the contents of the lunar eclipse accounts, we confirm that the accounts recorded as total eclipses are accurate, except for two accounts. However, both eclipses were very close to the total eclipse. We also confirm that all predicted lunar eclipses did occur, although one eclipse happened two days after the predicted date. In conclusion, we believe that this study is very helpful for investigating the lunar eclipse accounts of other periods in Korea, and furthermore, useful for verifying the calendar dates of the Goryeo dynasty.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.1
• /
• pp.65.1-65.1
• /
• 2014

달에 떨어지는 유성체(lunar meteoroid)는 그대로 표면에 충돌하여 섬광(flash)을 일으킨다. 이 현상은 매우 희미하고 순간적이지만 고감도 비디오카메라를 이용하면 지상 관측이 가능하다고 알려져 있다. 2013년 10월에 발사된 NASA의 Lunar Atmosphere and Dust Environment Explorer(LADEE)가 달 주위의 대기 및 먼지 환경을 측정하고 있는 동안 전 세계 지상관측 네트워크도 달 표면 충돌 감시 관측을 수행 중에 있다. 충남대학교에서도 LADEE 미션 시작인 10월부터 16인치 망원경에 고감도 비디오카메라를 장착한 시스템을 구성하여 매달 초승부터 상현까지 관측을 진행해왔다. 관측은 달 표면의 어두운 영역을 초당 30프레임으로 녹화하였으며, NASA에서 제공한 LunarScan 소프트웨어를 사용하여 섬광을 찾는 분석 작업을 수행하였다. 현재까지 약 70시간 동안 관측하고 분석하여 충돌 섬광 후보를 발견하였다. 본 발표에서 달 충돌 섬광 관측시스템에 대해 소개하고, 관측된 충돌 섬광 후보의 분석 결과를 제시할 것이다.

• Journal of Astronomy and Space Sciences
• /
• v.40 no.4
• /
• pp.199-215
• /
• 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
• /
• v.35 no.1
• /
• pp.47-54
• /
• 2018

Moon mineralogy mapper ($M^3$)'s work proved that the moon is not completely dry but has some hydroxyl/water. $M^{3{\prime}}s$ data confirmed that the amount of hydroxyl on the lunar surface is inversely related to the measured signal brightness, suggesting the lunar surface is sensitive to temperature by solar insolation. We tested the effect of solar insolation on the local distribution of hydroxyl by using $M^3$ data, and we found that most craters had more hydroxyl in shade areas than in sunlit areas. This means that the local distribution of hydroxyl is absolutely influenced by the amount of sunshine. We investigated the factors affecting differences in hydroxyl; we found that the higher the latitude, the larger the difference during daytime. We also measured the pyroxene content and found that pyroxene affects the amount of hydroxyl, but it does not affect the difference in hydroxyl between sunlit and shaded areas. Therefore, we confirmed that solar insolation plays a significant role in the local distribution of hydroxyl, regardless of surface composition.

• Journal of Astronomy and Space Sciences
• /
• v.31 no.4
• /
• pp.285-294
• /
• 2014

The uneven mass distribution of the Moon highly perturbs the lunar spacecrafts. This uneven mass distribution leads to peculiar dynamical features of the lunar orbiters. The critical inclination is the value of inclination which keeps the deviation of the argument of pericentre from the initial values to be zero. Considerable investigations have been performed for critical inclination when the gravity field is assumed to be symmetric around the equator, namely for oblate gravity field to which Earth's satellites are most likely to be subjected. But in the case of a lunar orbiter, the gravity field of mass distribution is rather asymmetric, that is, sectorial, and tesseral, harmonic coefficients are big enough so they can't be neglected. In the present work, the effects of the first sectorial and tesseral harmonic coefficients in addition to the first zonal harmonic coefficients on the critical inclination of a lunar artificial satellite are investigated. The study is carried out using the Hamiltonian framework. The Hamiltonian of the problem is cconstructed and the short periodic terms are eliminated using Delaunay canonical variables. Considering the above perturbations, numerical simulations for a hypothetical lunar orbiter are presented. Finally, this study reveals that the critical inclination is quite different from the critical inclination of traditional sense and/or even has multiple solutions. Consequently, different families of critical inclination are obtained and analyzed.