Hong-Kyu Moon

Development of a Data Reduction algorithm for Optical Wide Field Patrol

The detector subsystem of the Optical Wide-field Patrol (OWL) network efficiently acquires the position and time information of moving objects such as artificial satellites through its chopper system, which consists of 4 blades in front of the CCD camera. Using this system, it is possible to get more position data with the same exposure time by changing the streaks of the moving objects into many pieces with the fast rotating blades during sidereal tracking. At the same time, the time data from the rotating chopper can be acquired by the time tagger connected to the photo diode. To analyze the orbits of the targets detected in the image data of such a system, a sequential procedure of determining the positions of separated streak lines was developed that involved calculating the World Coordinate System (WCS) solution to transform the positions into equatorial coordinate systems, and finally combining the time log records from the time tagger with the transformed position data. We introduce this procedure and the preliminary results of the application of this procedure to the test observation images.

ORBIT DETERMINATION OF GPS AND KOREASAT 2 SATELLITE USING ANGLE-ONLY DATA AND REQUIREMENTS FOR OPTICAL TRACKING SYSTEM

Gauss method for the initial orbit determination was tested using angle-only data obtained by orbit propagation using TLB and SGP4/SDP4 orbit propagation model.. As the analysis of this simulation, a feasible time span between observation time of satellite resulting the minimum error to the true orbit was found. Initial orbit determination is performed using observational data of GPS 26 and Koreasat 2 from 0.6m telescope of KAO(Korea Astronomy Observatory) and precise orbit determination is also performed using simulated data. The result of precise orbit determination shows that the accuracy of resulting orbit is related to the accuracy of the observations and the number of data.

A Study on the Strategies of the Positioning of a Satellite on Observed Images by the Astronomical Telescope and the Observation and Initial Orbit Determination of Unidentified Space Objects

An optical tracking system has advantages for observing geostationary earth orbit (GEO) satellites relatively over other types of observation system. Regular surveying for unidentified space objects with the optical tracking system can be an early warning tool for the safety of five Korean active GEO satellites. Two strategies of positioning on the observed image of Communication, Ocean and Meteorological Satellite 1 are tested and compared. Photometric method has a half root mean square error against streak method. Also null eccentricity method for initial orbit determination (IOD) is tested with simulation data and real observation data. Under 10 minutes observation time interval, null eccentricity method shows relatively better IOD results than the other time interval. For follow-up observation of unidentified space objects, at least two consecutive observations are needed in 5 minutes to determine orbit for geosynchronous orbit space objects.

Korea Microlensing Telescope Network: science cases

We present the science cases with the Korea Microlensing Telescope Network (KMTNet) which consists of three widefield 1.6 m telescopes distributed in Chile, South Africa, and Australia, respectively, providing unique continuous sky coverage with the three telescopes. The primary scientific goal of the KMTNet project is to explore the structure and diversity of planetary systems and variable objects. Since the system is mainly optimized to conduct gravitational microlensing surveys, it will enable detections of very low-mass exoplanets, potentially down to the mass of Mars that are inaccessible by other ground-based techniques. In addition to the primary science, it is possible to conduct a variety of other observational programs with the KMTNet system, including photometric studies of nearby galaxies and galaxy clusters, discovery of supernovae and their follow-up observations, and observations of near-Earth objects. We expect synergies between the KMTNet project with other similar or complementary projects in the southern sky, such as SkyMapper.

Visibility Analysis of Domestic Satellites on Proposed Ground Sites for Optical Surveillance

The objectives of this study are to analyze the satellite visibility at the randomly established ground sites, to determine the five optimal ground sites to perform the optical surveillance and tracking of domestic satellites, and to verify the acquisition of the optical observation time sufficient to maintain the precise ephemeris at optimal ground sites that have been already determined. In order to accomplish these objectives, we analyzed the visibility for sun-synchronous orbit satellites, low earth orbit satellites, middle earth orbit satellites and domestic satellites as well as the continuous visibility along with the fictitious satellite ground track, and calculate the effective visibility. For the analysis, we carried out a series of repetitive process using the satellite tool kit simulation software developed by Analytical Graphics Incorporated. The lighting states of the penumbra and direct sun were set as the key constraints of the optical observation. The minimum of the observation satellite elevation angle was set to be 20 degree, whereas the maximum of the sun elevation angle was set to be -10 degree which is within the range of the nautical twilight. To select the candidates for the optimal optical observation, the entire globe was divided into 84 sectors in a constant interval, the visibility characteristics of the individual sectors were analyzed, and 17 ground sites were arbitrarily selected and analyzed further. Finally, five optimal ground sites (Khurel Togoot Observatory, Assy-Turgen Observatory, Tubitak National Observatory, Bisdee Tier Optical Astronomy Observatory, and South Africa Astronomical Observatory) were determined. The total observation period was decided as one year. To examine the seasonal variation, the simulation was performed for the period of three days or less with respect to spring, summer, fall and winter. In conclusion, we decided the optimal ground sites to perform the optical surveillance and tracking of domestic satellites and verified that optical observation time sufficient to maintain the precise ephemeris could be acquired at the determined observatories.

Minimum Number of Observation Points for LEO Satellite Orbit Estimation by OWL Network

By using the Optical Wide-field Patrol (OWL) network developed by the Korea Astronomy and Space Science Institute (KASI) we generated the right ascension and declination angle data from optical observation of Low Earth Orbit (LEO) satellites. We performed an analysis to verify the optimum number of observations needed per arc for successful estimation of orbit. The currently functioning OWL observatories are located in Daejeon (South Korea), Songino (Mongolia), and Oukaimeden (Morocco). The Daejeon Observatory is functioning as a test bed. In this study, the observed targets were Gravity Probe B, COSMOS 1455, COSMOS 1726, COSMOS 2428, SEASAT 1, ATV-5, and CryoSat-2 (all in LEO). These satellites were observed from the test bed and the Songino Observatory of the OWL network during 21 nights in 2014 and 2015. After we estimated the orbit from systematically selected sets of observation points (20, 50, 100, and 150) for each pass, we compared the difference between the orbit estimates for each case, and the Two Line Element set (TLE) from the Joint Space Operation Center (JSpOC). Then, we determined the average of the difference and selected the optimal observation points by comparing the average values.

2MASS NEAR-IR COLOR-MAGNITUDE DIAGRAM OF THE OLD OPEN CLUSTER KING 11

We study near-infrared properties of the old open cluster King 11, based on the 2MASS photometric data. We determine the location of the red giant clump(RGC) in the (K;J i K) color-magnitude diagram and derive the distance modulus of King 11 to be (m i M)0 = 12.50§0.10 using the mean K magnitude of RGC. From the red giant branch slope i [Fe/H] relation we obtain the metallicity of this cluster, [Fe/H]=i0.17§0.07. The age and interstellar reddening of this cluster are estimated to be log t = 9.48§0.05, E(B i V )=0.90§0.03, by applying Padova isochrone flts to the data.

Determining the Rotation Periods of an Inactive LEO Satellite and the First Korean Space Debris on GEO, KOREASAT 1

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Development of a Reduction Algorithm of GEO Satellite Optical Observation Data for Optical Wide Field Patrol (OWL)

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Near-Earth Object Survey Simulations with a Revised Population Model

We carried out a set of simulations to reproduce the performance of wide-field NEO surveys based on the revised population model of Near Earth Objects (NEOs) constructed by Morbidelli (2006). This is the first time where the new model is carefully compared with discovery statistics, and with the exception of population model, the simulation is identical to the procedure described in Moon et al. (2008). Our simulations show rather large discrepancy between the number of NEO discoveries made by the actual and the simulated surveys. First of all, unlike Bottke et al. (2002)s, Morbidelli (2006)s population model overestimates the number of NEOs. However, the latter reproduces orbit distributions of the actual population better. Our analysis suggests that both models significantly underestimate Amors, while overestimating the number of Apollos. Our simulation result implies that substantial modifications of both models are needed for more accurate reproduction of survey observations. We also identify Hungaria region (HU) to be one of the most convincing candidates that supply a large fraction of asteroids to the inner Solar System.