Korea Astronomy And Space Science Institute Research Articles

Long-Term Science Goals with In Situ Observations at the Sun-Earth Lagrange Point L4

The Korean heliospheric community, led by the Korea Astronomy and Space Science Institute (KASI), is currently assessing the viability of deploying a spacecraft at the Sun-Earth Lagrange Point L4 in collaboration with National Aeronautics and Space Administration (NASA). The aim of this mission is to utilize a combination of remote sensing and in situ instruments for comprehensive observations, complementing the capabilities of the L1 and L5 observatories. The paper outlines long-term scientific objectives, underscoring the significance of multi-point in-situ observations to better understand critical heliospheric phenomena. These include coronal mass ejections, magnetic flux ropes, heliospheric current sheets, kinetic waves and instabilities, suprathermal electrons and solar energetic particle events, as well as remote detection of solar radiation phenomena. Furthermore, the mission’s significance in advancing space weather prediction and space radiation exposure assessment models through the integration of L4 observations is discussed. This article is concluded with an emphasis on the potential of L4 observations to propel advancements in heliospheric science.

KOMPSAT-5 GNSS Radio Occultation Data Operations

The Korea Aerospace Research Institute launched KOMPSAT-5 on August 22, 2013, and has been operating for 10 years. KOMPSAT-5 has SAR (Synthetic Aperture Radar) for earth observation missions, and collects data necessary for earth atmosphere analysis through GNSS RO (Radio Occultation) receivers. RO data can be used for numerical weather forecast model based on temperature, pressure, and humidity by calculating the vertical distribution of atmospheric information. As a part of the Korea-US science and technology cooperation, KARI has been providing RO data of KOMPSAT-5 to the United States NOAA (National Oceanic and Atmospheric Administration) in near-real time since 2018. To this end, KARI receives telemetry data from the satellite about 12 times a day using 3 ground stations from Daejeon, Alaska in the U.S., and Sodankyla in Finland. The pre-processed data is being provided to both the UCAR (University Corporation for Atmospheric Research) in the U.S. and the KASI (Korea Astronomy and Space Science Institute). In this paper, radio occlusion data of KOMPSAT-5 is introduced, and system configuration, operation concepts for providing near-real time data and its application are also presented.

Feasibility Study of Communication Access via Iridium Constellation for Small-Scale Magnetospheric Ionospheric Plasma Experiment Mission

The small-scale magnetospheric and ionospheric plasma experiment (SNIPE) is a mission initiated by the Korea Astronomy and Space Science Institute (KASI) in 2017 and comprises four 6U-sized nano-satellites (Korea Astronomy and Space Science Institute Satellite-1, KASISat-1) flying in formations. The main goal of the SNIPE mission is to investigate the space environment in low Earth orbit at 500-km. Because Iridium & GPS Board (IGB) is installed on the KASISat-1, a communication simulation is required to analyze the contact number and the duration. In this study, communication simulations between the Iridium satellite network and KASISat-1 are performed using STK Pro (System Tool Kit Pro Ver 11.2) from the AGI (Analytical Graphics, Inc.). The contact number and durations were analyzed by each orbit and date. The analysis shows that the average access number per day is 38.714 times, with an average of 2.533 times per orbit for a week. Furthermore, on average, the Iridium satellite communication is linked for 70.597 min daily. Moreover, 4.625 min is the average duration of an individual orbit.

Characteristics of Horizontal Winds in the Mesosphere and Lower Thermosphere Region over Korean Peninsula Observed from the Korea Astronomy and Space Science Institute Meteor Radar

We present for the first time the characteristics of upper atmospheric horizontal winds over the Korean Peninsula. Winds and their variability are derived using four-year measurements by the Korea Astronomy and Space Science Institute (KASI) meteor radar. A general characteristic of zonal and meridional winds is that they exhibit distinct diurnal and seasonal variations. Their changes indicate sometimes similar or sometimes different periodicities. Both winds are characterized by either semi-diurnal tides (12 hour period) and/or diurnal tides (24 hour period) from 80–100 km. In terms of annual change, the annual variation is the strongest component in both winds, but semi-annual and ter-annual variations are only detected in zonal winds.

한국형 우주망원경 개발을 위한 공동기획 Working Group 제안

In order to satisfy the intellectual curiosity of mankind to explore the unknown, National Aeronautics and Space Administration (NASA) in the United States and European Space Agency (ESA) in Europe are embarking on various R&D under the motto of the grand dream of pioneering space into a safe and sustainable environment. In the 2020s and 30s, it is expected that advanced giant observation equipment will be in operation, such as the development of a 10-meter-class telescope in space. In Korea, following the development of the 0.15 m Near-Infrared Imaging Spectrometer (NISS), Korea Astronomy and Space Science Institute (KASI) is also participating a 0.2 m Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) as an international cooperation partner in small exploration telescope. However, domestic experience in the development and operation of the space telescopes is still insufficient, and there is no plan with long-term prospects for constructing telescopes. In order to answer questions about the unknown world that mankind has not experienced using our own equipment, planning and preparation for the construction of a space telescope through close cooperation among industry-university-institute-government is urgently needed. In this paper, the necessity, background, development goals, and expected effects of the development of the Korean Space Telescope are summarized conceptually, and a working group (WG) is also proposed. In the WG activities, Korea shall take the lead in establishing the Korean-style space telescope development plan, and will start a valuable step to establish the national direction in the field of space astronomy and related technologies. We hope that the WG will be another milestone in Korea

Scientific Goals of Rendezvous Mission to Apophis

The asteroid Apophis is one of the most potentially hazardous objects to Earth in human history, and many countries are paying attention to its 2029 approach to Earth. The asteroid’s 2029 encounter will not only greatly help promote understanding of the asteroid itself, but will also be a great opportunity to acquire knowledge of this Earth-threatening asteroid. The KASI (Korea Astronomy and Space Science Institute) is now conducting a pre-phase A study for the rendezvous mission to Apophis. In this article, I would like to explain the importance of research on the asteroid Apophis and address the scientific goals of this exploration mission.

Development of a Diagnostic Coronagraph for Use on the International Space Station

The Korea Astronomy and Space Science Institute (KASI), in collaboration with the NASA Goddard Space Flight Center (GSFC), has been developing a diagnostic coronagraph to be deployed in 2023 on the International Space Station (ISS). The mission is known as “Coronal Diagnostic Experiment (CODEX)”, which is designed to obtain simultaneous measurements of the electron density, temperature, and velocity in the 2.5- to 10-Rs range by using multiple filters. The coronagraph will be installed and operated on the ISS to understand the physical conditions in the solar wind acceleration region and to enable and validate the next generation space weather models.

Photometric observations of the potentially hazardous asteroid (99942) Apophis from Kawabe Cosmic Park

Abstract Asteroid (99942) Apophis is a potentially hazardous asteroid. The Korea Astronomy and Space Science Institute (KASI) recently proposed a rendezvous mission with Apophis, with a planned asteroid observation campaign to help determine the mission strategy in advance. In this study, we performed multicolor photometric observations of Apophis using the 1.0 m telescope at Kawabe Cosmic Park on 2021 March 10. The visible colors (g′, r′, and i′) of Apophis were obtained. The average colors of Apophis during our observations were as follows: g′ − r′ = 0.618 ± 0.021 and r′ − i′ = 0.180 ± 0.021. No significant color variation was observed in r′ − i′, but a slight variation may have occurred in g′ − r′ during the observation period of 4.63 hr. The obtained colors appeared to match those of an Sq-class asteroid, which is the asteroid type previously determined for Apophis by Binzel et al. (2009, Icarus, 200, 480) using the visible to near-infrared (0.55–2.45 μm) reflectance spectrum.

The Balloon-Borne Investigation of Temperature and Speed of Electrons in the Corona (BITSE): Mission Description and Preliminary Results

We report on the Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE) mission launched recently to observe the solar corona from approx 3 Rs to 15 Rs at four wavelengths (393.5, 405.0, 398.7, and 423.4 nm). The BITSE instrument is an externally occulted single stage coronagraph developed at NASA’s Goddard Space Flight Center in collaboration with the Korea Astronomy and Space Science Institute (KASI). BITSE used a polarization camera that provided polarization and total brightness images of size 1024 times 1024 pixels. The Wallops Arc Second Pointer (WASP) system developed at NASA’s Wallops Flight Facility (WFF) was used for Sun pointing. The coronagraph and WASP were mounted on a gondola provided by WFF and launched from the Fort Sumner, New Mexico station of Columbia Scientific Balloon Facility (CSBF) on September 18, 2019. BITSE obtained 17,060 coronal images at a float altitude of approx mbox{128,000} feet (approx 39 km) over a period of approx 4 hrs. BITSE flight software was based on NASA’s core Flight System, which was designed to help develop flight quality software. We used EVTM (Ethernet Via Telemetry) to download science data during operations; all images were stored on board using flash storage. At the end of the mission, all data were recovered and analyzed. Preliminary analysis shows that BITSE imaged the solar minimum corona with the equatorial streamers on the east and west limbs. The narrow streamers observed by BITSE are in good agreement with the geometric properties obtained by the Solar and Heliospheric Observatory (SOHO) coronagraphs in the overlapping physical domain. In spite of the small signal-to-noise ratio (approx 14) we were able to obtain the temperature and flow speed of the western steamer. In the heliocentric distance range 4 – 7 Rs on the western streamer, we obtained a temperature of approx 1.0pm 0.3 MK and a flow speed of approx 260 km s−1 with a large uncertainty interval.

Operational Dst index prediction model based on combination of artificial neural network and empirical model

In this paper, an operational Dst index prediction model is developed by combining empirical and Artificial Neural Network (ANN) models. ANN algorithms are widely used to predict space weather conditions. While they require a large amount of data for machine learning, large-scale geomagnetic storms have not occurred sufficiently for the last 20 years, Advanced Composition Explorer (ACE) and Deep Space Climate Observatory (DSCOVR) mission operation period. Conversely, the empirical models are based on numerical equations derived from human intuition and are therefore applicable to extrapolate for large storms. In this study, we distinguish between Coronal Mass Ejection (CME) driven and Corotating Interaction Region (CIR) driven storms, estimate the minimum Dst values, and derive an equation for describing the recovery phase. The combined Korea Astronomy and Space Science Institute (KASI) Dst Prediction (KDP) model achieved better performance contrasted to ANN model only. This model could be used practically for space weather operation by extending prediction time to 24 h and updating the model output every hour.

고층건물 건설에 따른 주변지역 일조환경 영향평가

In this study, the effect of construction of high-rise buildings on sunshine environment in N-newtown was predicted and analyzed by using a sunshine duration model. Three-dimensional topography and buildings in the target area were numerically constructed, based on the geographic information system(GIS) data. The azimuth and altitude angles of the sun for the target area on spring equinox, summer solstice, autumn equinox and winter solstice in 2019 were calculated as the root mean square errors(RMSE) below 0.4°, compared with the data provided by Korea astronomy and space science institute(KASI). The shadow length formed by the construction of new buildings was predicted as 205 m ~ 270 m(about three times of the building height) for the lower altitude angles of the sun. The gross shadow area for the target area on winter solstice was estimated as the increase rate of 17.5 % by the construction of new buildings. For the apartment complex located adjacent to the north-northwest side of the construction site of new buildings, the gross shadow area on winter solstice was estimated as the increase rate of 87.6 %(intensive damage) by the construction of new buildings. The results indicated that the assessment of sunshine environment should be necessary for new construction of high-rise buildings.

건물벽면 연직그림자 형성에 의한 일조장애 평가

In this study, the blocking effect of building shadows on sunshine environments was assessed for the new construction of high-rise buildings, using a numerical model of sunshine duration. Three-dimensional surface boundary of buildings in the target area was numerically constructed, based on the geographic information system (GIS) data. The solar positions and the shadow areas were calculated for the target area on spring equinox, summer solstice, autumn equinox and winter solstice in 2019. The azimuth and altitude angles of the sun calculated in this study were compared with the data provided by Korea astronomy and space science institute (KASI), and evaluated as the root mean square errors (RMSE) below 0.3° and the correlation 0.999. The gross shadow area in the target area was estimated as the increase rate of 48.6% ~ 87.6% by the construction of new buildings. The blocking effect of vertical building shadows on sunshine duration was assessed for the apartment complex located adjacent to the construction site of new buildings, by considering the legal limit of sunshine duration. The layers less than the eighth floor were not satiated with 4-hours of the total sunshine duration during the time from 08 to 16 on winter solstice. The layers less than the sixth floor were not satiated with 2-hours of the continuous sunshine duration during the time from 09 to 15 on winter solstice.

Characterization of a new tissue equivalent proportional counter for dosimetry of neutron and photon fields: comparison of measurements and Monte Carlo simulations

The tissue equivalent proportional counter (TEPC) is widely recognized as an important dosimetric technique particularly for complex radiation fields. The Korea Astronomy and Space Science Institute (KASI) has recently developed a new spherical TEPC to monitor the space radiation environment in the low earth orbit. The purpose of this study is to examine the performance of the TEPC against standard photon (137Cs) and neutron (252Cf) sources through ground-based measurements and Monte Carlo simulations prior to its actual implementation. Lineal energy distributions, microdosimetric spectra and dosimetric quantities for a 2 µm simulated site in pure propane gas were determined for both sources. Both the measured and calculated 137Cs spectra were shown to occur below 11 keV µm−1 that is the typical range covered by photon sources. Complete coincidence of their electron edge regions was also observed. Meanwhile, the proton edge from the measured 252Cf spectra was found to be in good agreement with those from the simulated ones and the literature. The gamma, recoil proton and heavy ions peaks expected for neutron sources were well defined, albeit deviations in the gamma region. The absorbed dose and dose equivalent for both irradiation conditions were also successfully obtained. The dose equivalent for 252Cf was found to be ten times the absorbed dose whereas it remained the same for 137Cs. The discrepancies observed in the low lineal energy region for both irradiation conditions were caused by intrinsic limitations on the experimental set-up and simulation configurations. This mainly contributed to a difference in the measured and calculated dose mean lineal energies of about 4.1% and 8.7% for the photon and neutron cases, respectively. Nevertheless, fair consistency with published data suggested that our TEPC could adequately reproduce the expected microdosimetric distributions for complex radiation fields.

Satellite Laser Ranging System at Geochang Station

Korea Astronomy and Space Science Institute (KASI) has been developing the space optical and laser tracking (SOLT) system for space geodesy, space situational awareness, and Korean space missions. The SOLT system comprises satellite laser ranging (SLR), adaptive optics (AO), and debris laser tracking (DLT) systems, which share numerous subsystems, such as an optical telescope and tracking mount. It is designed to be capable of laser ranging up to geosynchronous Earth orbit satellites with a laser retro-reflector array, space objects imaging brighter than magnitude 10, and laser tracking low Earth orbit space debris of uncooperative targets. For the realization of multiple functions in a novel configuration, the SOLT system employs a switching mirror that is installed inside the telescope pedestal and feeds the beam path to each system. The SLR and AO systems have already been established at the Geochang station, whereas the DLT system is currently under development and the AO system is being prepared for testing. In this study, the design and development of the SOLT system are addressed and the SLR data quality is evaluated compared to the International Laser Ranging Service (ILRS) tracking stations in terms of single-shot ranging precision. The analysis results indicate that the SLR system has a good ranging performance, to a few millimeters precision. Therefore, it is expected that the SLR system will not only play an important role as a member of the ILRS tracking network, but also contribute to future Korean space missions.

Evaluation of the KASI Detector Performance Test System Using an Andor iKon M CCD Camera

The characterization of detectors installed in space- and ground-based instruments is important to evaluate the system performance. We report the development of a detector performance test system for astronomical applications using the Andor iKon M CCD camera. The performance test system consists of a light source, monochromator, integrating sphere, and power meters. We adopted the Czerny–Tuner monochromator with three ruled gratings and one mirror, which covers a spectral range of 200–9,000 nm with a spectral resolution of ~1 nm in the visible region. Various detector characteristics, such as the quantum efficiency, sensitivity, and noise, can be measured in wide wavelength ranges from the visible to mid-infrared regions. We evaluated the Korea Astronomy and Space Science Institute (KASI) detector performance test system by using the performance verification of the Andor iKon-M CCD camera. The test procedure includes measurements of the conversion gain (2.86 e−/ADU), full well capacity (130 K e−), nonlinearity, and pixel defects. We also estimated the read noise, dark current, and quantum efficiency as a function of the temperature. The lowest measured read noise is 12 e−. The dark current at 223 K was determined to be 7 e−/s/pix and its doubling temperature is 5.3°C ± 0.2°C at an activation energy of 0.6 eV. The maximum quantum efficiency at 223 K was estimated to be 93 % ± 2 %. We proved that the quantum efficiency is sensitive to the operating temperature. It varies up to 5 % in the visible region, while the variation increases to 30 % in the near-infrared region. Based on the comparison of our results with the test report by the vendor, we conclude that our performance test results are consistent with those from the vendor considering the test environment. We also confirmed that the KASI detector performance test system is reliable and our measurement method and analysis are accurate.

Space Weather Operation at KASI With Van Allen Probes Beacon Signals

AbstractThe Van Allen Probes (VAPs) are the only modern National Aeronautics and Space Administration (NASA) spacecraft broadcasting real‐time data on the Earth's radiation belts for space weather operations. Since 2012, the Korea Astronomy and Space Science Institute (KASI) has contributed to the receipt of these data via a 7 m satellite‐tracking antenna and used these beacon data for space weather operations. An approximately 15 min period is required from measurement to acquisition of Level‐1 data. In this paper, we demonstrate the use of VAP data for monitoring space weather conditions at geostationary orbit (GEO) by highlighting the Saint Patrick's Day storm of 2015. During that storm, Probe‐A observed a significant increase in the relativistic electron flux at 3 RE. Those electrons diffused outward resulting in a large increase of the electron flux >2 MeV at GEO, which potentially threatened satellite operations. Based on this study, we conclude that the combination of VAP data and National Oceanic and Atmospheric Administration‐Geostationary Operational Environmental Satellite (NOAA‐GOES) data can provide improved space environment information to geostationary satellite operators. In addition, the findings obtained indicate that more data‐receiving sites would be necessary and data connections improved if this or a similar system were to be used as an operational data service.

Tomography Reconstruction of Ionospheric Electron Density with Empirical Orthonormal Functions Using Korea GNSS Network

In South Korea, there are about 80 Global Positioning System (GPS) monitoring stations providing total electron content (TEC) every 10 min, which can be accessed through Korea Astronomy and Space Science Institute (KASI) for scientific use. We applied the computerized ionospheric tomography (CIT) algorithm to the TEC dataset from this GPS network for monitoring the regional ionosphere over South Korea. The algorithm utilizes multiplicative algebraic reconstruction technique (MART) with an initial condition of the latest International Reference Ionosphere-2016 model (IRI-2016). In order to reduce the number of unknown variables, the vertical profiles of electron density are expressed with a linear combination of empirical orthonormal functions (EOFs) that were derived from the IRI empirical profiles. Although the number of receiver sites is much smaller than that of Japan, the CIT algorithm yielded reasonable structure of the ionosphere over South Korea. We verified the CIT results with NmF2 from ionosondes in Icheon and Jeju and also with GPS TEC at the center of South Korea. In addition, the total time required for CIT calculation was only about 5 min, enabling the exploration of the vertical ionospheric structure in near real time.

고반복율 인공위성 레이저추적을 위한 운영 소프트웨어 개발

한국천문연구원은 인공위성 정밀궤도 결정, 우주측지 및 인공위성 자세역학 연구를 위해서 2kHz 반복율을 가지는 SLR 시스템을 운영하고 있다. 그러나 측지위성의 회전속도를 보다 정밀히 결정하고 거리 측정 정밀도 향상을 위해서 고반복율의 SLR 관측 데이터가 요구된다. 따라서 고반복율 시스템 구현을 위해 운영 소프트웨어 및 레인지 게이트 생성기를 개발하여 최대 10kHz 반복율로 레이저추적이 가능한 HSLR-10(High repetition-rate Satellite Laser Ranging-10kHz) 시스템으로 개선하였다. 본 연구에서는 10kHz 반복율을 가지는 HSLR-10 시스템의 운영 소프트웨어 개발 방법, 구성 및 검증 결과를 제시한다. Korea Astronomy and Space Science Institute (KASI) has been operating SLR (Satellite Laser Ranging) system with 2kHz repetition rate for satellite precise orbit and spin determination as well as space geodesy. But the SLR system was improved to be capable of laser ranging with high repetition rate, up to 10kHz by developing new operation software and novel range gate generator, called HSLR-10. The HSLR-10 will contribute to the accurate spin rate determination of geodetic satellites and geodetic research due to its largest repetition rate in the world. In this study, the development methodology and configuration of operation software are addressed, and its validation results are also presented.

1m급 인공위성 레이저추적 시스템용 고속·고정밀 추적마운트 개발 및 예비 성능분석

본 연구에서는 국내 최초 개발 예정인 1m급 인공위성 레이저추적 시스템(Satellite Laser Ranging, SLR)의 추적마운트 (Tracking Mount) 모듈 개발을 위한 예비설계 및 성능분석 결과를 제시한다. 인공위성 레이저추적 시스템은 위성까지의 거리를 정밀하게 측정하는 시스템으로 지상의 관측소에서 반사경을 탑재하고 있는 인공위성까지 레이저를 발사하여 되돌아오는 레이저 사이의 시간간격을 측정하는 시스템으로서, 현존하는 인공위성까지의 거리측정 시스템 중 가장 정밀한 측정 시스템이다. 본 논문에서 제안하는 인공위성 레이저 추적 시스템용 고속 고정밀 추적마운트의 추적범위는 고도 300 km에서 정지궤도(고도 36,000 km)까지 가능하며, 레이저 반사경을 탑재한 인공위성에 대해 주 야간 레이저추적이 가능해야 한다. 이러한 요구사항을 만족하기 위해, 본 연구에서는 고속 고정밀 추적마운트 기구부 설계 및 구조해석을 수행하였고, 추적마운트의 원활한 제어를 위한 모션 제어 시스템을 설계하여 예비 성능 분석을 실시한 결과를 소개하였다. This paper presents preliminary design and performance analysis of a fast and high precision Tracking Mount for 1m Satellite Laser Ranging(SLR) which is development by Korea Astronomy and Space science Institute(KASI). SLR is considered to be the most accurate technique currently available for the precise orbit determination of Earth satellites. The SLR technique measures the time of flight between pulses emitted from laser transmitter and pulses returned from satellites with laser retro-reflector array. It provides millimeter level precision of range measurements between SLR stations and satellites. A fast and high precision Tracking Mount for SLR which is proposed in this research should be capable of day and nighttime laser tracking about the satellites with laser reflectors from 200 km to 36,000 km altitude(geosynchronous orbit). In order to meet this requirement, we performed mechanical design and structural analysis for Tracking Mount. Also we designed the motion control system and conducted pre-performance analysis to obtain good performance results for a fast and high precision Tracking Mount.

KMTNET: A NETWORK OF 1.6 M WIDE-FIELD OPTICAL TELESCOPES INSTALLED AT THREE SOUTHERN OBSERVATORIES

The Korea Microlensing Telescope Network (KMTNet) is a wide-field photometric system installed by the Korea Astronomy and Space Science Institute (KASI). Here, we present the overall technical specifications of the KMTNet observation system, test observation results, data transfer and image processing procedure, and finally, the KMTNet science programs. The system consists of three 1.6 m wide-field optical telescopes equipped with mosaic CCD cameras of 18k by 18k pixels. Each telescope provides a 2.0 by 2.0 square degree field of view. We have finished installing all three telescopes and cameras sequentially at the Cerro-Tololo Inter-American Observatory (CTIO) in Chile, the South African Astronomical Observatory (SAAO) in South Africa, and the Siding Spring Observatory (SSO) in Australia. This network of telescopes, which is spread over three different continents at a similar latitude of about -30 degrees, enables 24-hour continuous monitoring of targets observable in the Southern Hemisphere. The test observations showed good image quality that meets the seeing requirement of less than 1.0 arcsec in I-band. All of the observation data are transferred to the KMTNet data center at KASI via the international network communication and are processed with the KMTNet data pipeline. The primary scientific goal of the KMTNet is to discover numerous extrasolar planets toward the Galactic bulge by using the gravitational microlensing technique, especially earth-mass planets in the habitable zone. During the non-bulge season, the system is used for wide-field photometric survey science on supernovae, asteroids, and external galaxies.