• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.213-218
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• 2010

A cooling system utilizing liquid helium to chill the cryopanel (800 mm $\times$ 700 mm dimensions) down to 4.2 K was designed, implemented, and tested to verify the role of the cryopanel as a heat sink for the payload of a spacecraft inside the large thermal vacuum chamber (effective dimensions : 8 m ($\Phi$) $\times$ 10 m (L)) of KARI (Korea Aerospace Research Institute). Two LHe (Liquid Helium) Dewars, one for the main supply and the other for refilling, were used to supply liquid helium or cold helium gas into this cryopanel, and flow control for the target temperature of the cryopanel within requirements was done through fine adjustment of the pressure inside the LHe Dewars. The return helium gas from the cryopanel was reused as a thermal barrier to minimize the heat influx on the core liquid helium supply pipe. The test verified a cooling time of around three hours from the ambient temperature to 40 K (combined standard uncertainty of 194 mK), the capacity for maintaining the cryopanel at intermediate temperatures, and a 1 K uniformity over the entire cryopanel surface at around 40 K with 20 W cooling power.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.54.3-54.3
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• 2015

To probe the star formation in local and early Universe, the NISS with a capability of imaging spectroscopy in the near-infrared is being developed by KASI. The main scientific targets are nearby galaxies, galaxy clusters, star-forming regions and low background regions. The off-axis optical design of the NISS with 15cm aperture was optimized to obtain a wide field of view (FoV) of $2deg.{\times}2deg.$ as well as a wide spectral coverage from 0.9 to $3.8{\mu}m$. The opto-mechanical structure was designed to be safe enough to endure in both the launching condition and the space environment. The dewar will operate $1k{\times}1k$ infrared sensor at 80K stage. The NISS will be launched in 2017 and explore the large areal near-infrared sky up to $200deg.^2$ in order to get both spatial and spectral information for astronomical objects. As an extension of the NISS, KASI is planning to participate in a new small space mission together with NASA. The promising candidate, SPHEREx (Spectro-Photometer for the History of the Universe Epoch of Reionization, and Ices Explorer) is an all-sky survey satellite designed to reveal the origin of the Universe and water in the planetary systems and to explore the evolution of galaxies. Though the survey concept is similar to that of the NISS, the SPHEREx will perform the first near-infrared all-sky imaging spectroscopic survey with the wider spectral range from 0.7 to $5{\mu}m$ and the wider FoV of $3.5deg.{\times}7deg.$ Here, we report the current status of the NISS and introduce new mission for the near-infrared imaging spectroscopic survey.

• Journal of the Korean Wood Science and Technology
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• v.12 no.3
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• pp.25-34
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• 1984

This experiment was carried out to investigate the effects of monosaccharides extracted by saturated portland cement solution on the cement setting in comparision with the inhibitory index (I) of each lignocellulosic-cement system. The wood species which have been widely reforested in Korea, Populus alba-grandulosa, Larix leptolepis, Abies holophylla, Pinus koraiensis, Pinus rigida, Pinus densiflora and agricultural wastes of rice husk and rice stalk were used at this study. The wood meal, 0.50g on dry weight basis, through 0.83 mm(20 mesh) and retained on 0.35mm (40 mesh) screen was extracted by 25 ml saturated portland cement solution and the pH of saturated portland cement solution Was 12.7. To eliminate cation exsisting in the extracted solution, the cation exchange column was used (Fig. 4). Afterwards the extracted monosaccharides were reduced into alditols with sodium borohydride and analyzed by the gas-liquid chromatography for xylan, mannan, arabinan, galactan, gluean. The heat of cement hydration for lignocellulosic-cement system was measured in Dewar flask (Fig. 2). And then the inhibitory indices were calculated from maximum hydration temperature, time and maximum slops of hydration curve of ligno cellulosic-cement systems. The results obtained were as follows; (1) The inhibitory index of pines-Pinus rigida (I=29.33) and Pinus densiflora (I=35.76), were lower than that of poplar-Populus alba-glandulosa (I=41.48), and the index of Larix ieptoiepis (I=73.00) was the highest among eight lignocellulosic-cement systems, and accordingly both Pinus rigida and Pinus des(flora were seemed to be good wood species for wood-cement composite manufacture. (2) In case of Pinus rigida, the inhibitory index was 29.33 and the ratio of the hexoses to the pemoses was 6.04 and in case of Larix leptolepis, the index and the ratio were 73.00 and 35.19, respectively. Therefore the inhibitory index increased with increasing the ratios of the hexoses to the pentoses. (3) The richer amount of xylose and mannose in species caused decreasing the slops of the hydration curve of the lignocellulosic-cement system, prohahly due to the chemical adsorption of the acetyl groups in the hemicellulose on the surface of cement grains. (4) The amoun of xylose and mannose were significant to the inhibitory index of each lignocellulosic-cement system but any specific relation between the amount of glucose and inhibitory index was not found.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.102-102
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• 2014

The NISS (Near-infrared Imaging Spectrometer for Star formation history) onboard NEXTSat-1 is the near-infrared instrument onboard NEXTSat-1 which is being developed by KASI. The main scientific targets are nearby galaxies, galaxy clusters, star-forming regions and low background regions in order to study the cosmic star formation history in local and distant universe. After the Preliminary Design Review, we have fixed major specifications of the NISS. The off-axis optical design with 15cm apertureis optimized to obtain a wide field of view ($2deg.{\times}2deg.$), while minimizing the sensitivity loss. The opto-mechanical structure of the NISS was designed to be safe enough to endure in the launching condition as well as the space environment. The tolerance analysis was performed to cover the wide wavelength range from 0.95 to $3.8{\mu}m$ and to reduce the degradation of optical performance due to thermal variation at the target temperature, 200K. The $1k{\times}1k$ infrared sensor is operated in the dewar at 80K stage. We confirmed that the NISS can be cooled down to below 200K in the nominal orbit through a radiative cooling. Here, we report the preliminary design of the NISS.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.64.3-65
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• 2016

The NISS (Near-infrared Imaging Spectrometer for Star formation history) is the near-infrared instrument optimized to the Next Generation of small satellite series (NEXTSat). The capability of both imaging and low spectral resolution spectroscopy in the near-infrared range is a unique function of the NISS. The major scientific mission is to study the cosmic star formation history in local and distant universe. For those purposes, the main observational targets are nearby galaxies, galaxy clusters, star-forming regions and low background regions. The off-axis optical design is optimized to have a wide field of view ($2deg.{\times}2deg.$) as well as the wide wavelength range from 0.95 to $3.8{\mu}m$. Two linear variable filters are used to realize the imaging spectroscopy with the spectral resolution of ~20. The mechanical structure is considered to endure the launching condition as well as the space environment. The compact dewar is confirmed to operate the infrared detector as well as filters at 80K stage. The electronics is tested to obtain and process the signal from infrared sensor and to communicate with the satellite. After the test and calibration of the engineering qualification model (EQM), the flight model of the NSS is assembled and integrated into the satellite. To verify operations of the satellite in space, the space environment tests such as the vibration, shock and thermal-vacuum test were performed. Here, we report the test results of the flight model of the NISS.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.49.1-49.1
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• 2014

The NISS (Near-infrared Imaging Spectrometer for Star formation history) onboard NEXTSat-1 is the near-infrared instrument onboard NEXTSat-1 which is being developed by KASI. The imaging low-resolution spectroscopic observation in the near-infrared range for nearby galaxies, low background regions, star-forming regions and so on will be performed on orbit. After the System Requirement Review, the optical design is changed from on-axis to the off-axis telescope which has a wide field of view (2 deg. ${\times}$ 2 deg.) as well as the wide wavelength range from 0.95 to $3.8{\mu}m$. The mechanical structure is considered to endure the launching condition as well as the space environment. The design of relay optics is optimized to maintain the uniform optical performance in the required wavelength range. The stray light analysis is being made to evade a light outside a field of view. The dewar is designed to operate the infrared detector at 80K stage. From the thermal analysis, we confirmed that the telescope can be cooled down to around 200K in order to reduce the large amount of thermal noise. Here, we report the current status of the NISS development.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.90-90
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• 2014

The Immersion Grating Infrared Spectrometer (IGRINS) is the first astronomical spectrograph that uses a silicon immersion grating as its dispersive element. IGRINS fully covers the H and K band atmospheric transmission windows in a single exposure. It is a compact high-resolution cross-dispersion spectrometer whose resolving power R is 40,000. An individual volume phase holographic grating serves as a secondary dispersing element for each of the H and K spectrograph arms. On the 2.7m Harlan J. Smith telescope at the McDonald Observatory, the slit size is $1^{{\prime}{\prime}}{\times}15^{{\prime}{\prime}}$. IGRINS has a plate scale of 0.27" pixel-1 on a $2048{\times}2048$ pixel Teledyne Scientific & Imaging HAWAII-2RG detector with a SIDECAR ASIC cryogenic controller. The instrument includes four subsystems; a calibration unit, an input relay optics module, a slit-viewing camera, and nearly identical H and K spectrograph modules. The use of a silicon immersion grating and a compact white pupil design allows the spectrograph collimated beam size to be 25mm, which permits the entire cryogenic system to be contained in a moderately sized ($0.96m{\times}0.6m{\times}0.38m$) rectangular Dewar. The fabrication and assembly of the optical and mechanical components were completed in 2013. From January to July of this year, we completed the system optical alignment and carried out commissioning observations on three runs to improve the efficiency of the instrument software and hardware. We describe the major design characteristics of the instrument including the system requirements and the technical strategy to meet them. We also present the instrumental performance test results derived from the commissioning runs at the McDonald Observatory.