Ho Jin

Loss of geosynchronous relativistic electrons by EMIC wave scattering under quiet geomagnetic conditions

We have examined relativistic electron flux losses at geosynchronous orbit under quiet geomagnetic conditions. One 3 day period, from 11 to 13 October 2007, was chosen for analysis because geomagnetic conditions were very quiet (3 day average of Kp 2 MeV electron flux at geosynchronous orbit shows typical diurnal variations with a maximum near noon and a minimum near midnight for each day. The flux level of the daily variation significantly decreased from first day to third day for the 3 day period by a factor of >10. The total magnetic field strength (BT) of the daily variation on the third day, however, is comparable to that on the first day. Unlike electron flux decreases, the flux of protons with energies between 0.8 and 4 MeV adiabatically responses to the daily variation of BT. That is, there is no significant decrease of the proton flux when the electron flux decreases. During the interval of quiet geomagnetic conditions, well-defined electromagnetic ion cyclotron (EMIC) waves were detected at geosynchronous spacecraft. Low-altitude polar-orbiting spacecraft observed the precipitation of energetic protons and relativistic electrons in the interval of EMIC waves enhancement. From these observations, we suggest that the EMIC waves at geosynchronous orbit cause pitch angle scattering and relativistic electron losses to the atmosphere under quiet geomagnetic conditions.

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.

Spectral characteristics of steady quiet-time EMIC waves observed at geosynchronous orbit

We have studied the spectral properties of quiet-time electromagnetic ion cyclotron (EMIC) waves following a steady quiet condition, which is defined with Kp values 1 during 12h, using GOES 10, 11, and 12 magnetometer data for solar minimum years 2007-2008. We identified 6584 steady quiet-time EMIC wave samples using a semiautomated procedure. Approximately 82% of the samples were observed in the morning-to-early afternoon sector (0700-1500 magnetic local time) with a maximum occurrence near noon, and their peak frequencies were mostly in the He band. We found that the occurrence rate of steady quiet-time EMIC waves is higher than that of EMIC waves for all or quiet geomagnetic conditions (Dst > 0nT or AE < 100nT) reported in previous studies by a factor of 2 or more. The frequency ratio f(peak) (samples peak frequency)/ fH+ (the local proton gyrofrequency) of the He-band waves (approximate to 0.11-0.16) under steady quiet conditions is lower than that (approximate to 0.14-0.24) in previous studies. These results may be due to the fact that the plasmasphere expanded more frequently to the geosynchronous region under extremely quiet geomagnetic conditions in 2007-2008 than the periods selected in previous studies. The amplitude and frequency of He-band EMIC waves for nonlinear wave growth are examined as changing cold plasma density at geosynchronous orbit. We confirm that the spectral properties of observed EMIC waves are in good agreement with the nonlinear theory.

Wide-field telescope design for the KMTNet project

The Korea Astronomy and Space Science Institute (KASI) are under development three 1.6m optical telescopes for the Korea Micro-lensing Telescope Network (KMTNet) project. These will be installed at three southern observatories in Chile, South Africa, and Australia by middle 2014 to monitor dense star fields like the Galactic bulge and Large Magellanic Cloud. The primary scientific goal of the project is to discover numerous extra-solar planets using the gravitational micro-lensing technique. We have completed the final design of the telescope. The most critical design issue was wide-field optics. The project science requires the Delivered Image Quality (DIQ) of less than 1.0 arcsec FWHM within 1.2 degree radius FOV, under atmospheric seeing of 0.75 arcsec. We chose the prime-focus configuration and realized the DIQ requirement by using a purely parabolic primary mirror and four corrector lenses with all spherical surfaces. We present design results of the wide-field optics, the primary mirror coating and support, and the focus system with three linear actuators on the head ring.

Statistical analysis of geosynchronous magnetic field perturbations near midnight during sudden commencements

When an interplanetary (IP) shock passes over the Earths magnetosphere, the geosynchronous magnetic field strength near noon is always enhanced except for the magnetopause crossing events. Near midnight, however, it increases or decreases. This indicates that the nightside magnetosphere is not always compressed by a sudden increase in the solar wind dynamic pressure. To understand midnight geosynchronous magnetic field responses to IP shocks, we statistically examined geosynchronous magnetic field perturbations, corresponding to 120 sudden commencements (SCs), observed when geosynchronous spacecraft were near midnight between 2200 and 0200 magnetic local times. Out of the 120 SCs, 107 SCs were identified by one geosynchronous spacecraft, and 13 SCs were identified by two geosynchronous spacecraft. Thus, 133 events were used in our statistical study. We observed 23 events in spring, 40 events in summer, 32 events in fall, and 38 events in winter, respectively. A statistical study of the midnight geosynchronous SC perturbations reveals the following characteristics. (1) In summer, all events show a positive enhancement (+ΔBT) in the magnetic field strength. (2) In winter, however, ΔBT exhibits a positive (+ΔBT) or negative (–ΔBT) enhancement. (3) In summer, the midnight geosynchronous SC perturbations in the BH component (positive northward) in VDH coordinates are mostly (∼88%, 35 out of 40 events) positive (+ΔBH), while the occurrence rate of the positive perturbation (∼43%) in the Bz component (positive northward) in GSM coordinates is lower than that of the negative perturbation (∼57%). (4) In winter, the negative perturbations in ΔBH (∼61%) and ΔBz (∼74%) are dominant. (5) Both the north-south components (BH and Bz) in spring and fall are scattered around zero. To explain the observations, we suggest that SC-associated cross-tail current (JSC) has a peak intensity around geosynchronous orbit and thus is a main controlling factor of midnight geosynchronous magnetic field perturbations during SCs. Specifically, we suggest that the seasonal variation of the sign of ΔBH, ΔBz, and ΔBT is due to the seasonal variation of the spacecraft position relative to JSC.

Calibration of TEPC for CubeSat Experiment to Measure Space Radiation

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MULTI-BAND POLARIMETRY OF THE LUNAR SURFACE. I. GLOBAL PROPERTIES

We have conducted multi-band (U, B, V, R, and I) polarimetric observations of the whole near-side of the Moon for phase angles between 22° and 121° with a spatial resolution of 1.1 km. A median grain size () map of the near-side regolith of the Moon has been constructed using our polarimetry. We find that is a monotonically increasing function of selenographic latitude β; at is estimated to be up to 40% larger than that at the equator. At the same latitude, is larger in the maria than in the highlands, confirming the initial findings of Shkuratov et al. The former is thought to be a result of reduced space weathering effects at high latitudes, where the flux of weathering agents such as micrometeoroids and solar wind particles is smaller. The latter probably indicates that the regolith material in the maria is more resistant to comminution by space weathering than is the material in the highlands. We also find that three photometric or polarimetric maturity indices—optical maturity, and the color ratio of parallel-component polarization ()—have different sensitivities on young small craters and rays of large craters. We present possible causes of these different sensitivities.

Optical Design of a Reflecting Telescope for CubeSat

Space telescope optics is one of the major parts of any space mission used to observe astronomical targets or the Earth. This kind of space mission typically involves bulky and complex opto-mechanics with a long optical tube, but attempts have been made to observe a target with a small satellite. In this paper, we describe the optical design of a reflecting telescope for use in a CubeSat mission. For this design we adopt the off-axis segmented method for astronomical observation techniques based on a Ritchey-Chr

The Photometric Brightness Variation of Geostationary Orbit Satellite

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DESIGN OF THE OPTICAL SYSTEM FOR A PROTOMODEL OF SPACE INFRARED CRYOGENIC SYSTEM

tien type telescope. The primary mirror shape is a rectangle with dimensions of