Goo-Hwan Shin

High Voltage DC-DC Converter of Pulsed Plasma Thruster for Science and Technology Satellite-2 (STSAT-2)

Normally, +28V is used to provide the power with a micro satellite, which is generated the solar panel as well as a power regulation unit. However, the pulsed plasma thruster (PPT) requires a high power around +1500V to work for satellite attitude control. Therefore, this paper describes the power processing unit (PPU) for the pulsed plasma thruster by using a flyback switching circuitry as well as a protective circuitry with a feedback control to avoid an over charging.

Scientific Missions and Technologies of the ISSS on board the NEXTSat-1

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Development of optical system for the NISS onboard NEXTSat-1

Korea Astronomy and Space Science Institute (KASI) successfully developed the Near-infrared Imaging Spectrometer for Star formation history (NISS), which is a scientific payload for the next-generation small satellite-1 (NEXTSat-1) in Korea and is expected to be launched in 2018. The major science cases of NISS are to probe the star formation in local and early Universe through the imaging spectroscopic observations in the near-infrared. The off-axis catadioptric optics with 150mm aperture diameter is designed to cover the FoV of 2x2 deg with the passband of 0.95-2.5μm. The linear variable filter (LVF) is adopted as a disperse element with spectral resolution of R~20. Given the error budgets from the optical tolerance analysis, all spherical and non-spherical surfaces were conventionally polished and finished in the ultraprecision method, respectively. Primary and secondary mirrors were aligned by using interferometer, resulting in residual wave-front errors of P-V 2.7μm and RMS 0.61μm, respectively. To avoid and minimize any misalignment, lenses assembled were confirmed with de-centering measurement tool from Tri-Optics. As one of the key optical design concepts, afocal beam from primary and secondary mirrors combined made much less sensitive the alignment process between mirrors and relay lenses. As the optical performance test, the FWHM of PSF was measured about 16μm at the room temperature, and the IR sensor was successfully aligned in the optimized position at the cryogenic temperature. Finally, wavelength calibration was executed by using monochromatic IR sources. To support the complication of optical configuration, the opto-mechanical structure was optimized to endure the launching condition and the space environment. We confirmed that the optical performance can be maintained after the space environmental test. In this paper, we present the development of optical system of NISS from optical design to performance test and calibration.

Development of High Energy Particle Detector for the Study of Space Radiation Storm

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Conceptual opto-mechanical design of a NIR imaging spectrometer for the Korean NEXTSat-1 mission

Since the end of 2012, Korea Astronomy and Space Science Institute (KASI) has been developed the Near-infrared Imaging Spectrometer for Star formation history (NISS), which is a payload of the Korean next small satellite 1 (NEXTSat-1) and will be launched in 2017. NISS has a cryogenic system, which will be cooled down to around 200K by a radiation cooling in space. NISS is an off-axis catadioptric telescope with 150mm aperture diameter and F-number 3.5, which covers the observation wavelengths from 0.95-3.8μm by using the linear variable filter (LVF) for the near infrared spectroscopy. The entire field of view is 2deg x 2deg with 7arcsec pixel scale. Optics consists of two parabolic primary and secondary mirrors and re-imaging lenses having 8 elements. The main requirement for the optical performance is that the RMS spot diameters for whole fields are smaller than the detector pixel, 18μm. Two LVFs will be used for 0.9- 1.9μm and 1.9-3.8μm, whose FWHM is more than 2%. We will use the gold-coated aluminum mirrors and employ the HgCdTe 1024x1024 detector made by Teledyne. This paper presents the conceptual opto-mechanical design of NISS.

Development of near-infrared imaging spectrometer (NISS) onboard NEXTSat-1

The NISS (Near-infrared Imaging Spectrometer for Star formation history) have been developed by KASI as one of the scientific payloads onboard the first small satellite of NEXTSat program (NEXTSat-1) in Korea. The both imaging and low spectral resolution spectroscopy in the wide near-infrared range from 0.95 to 2.5µm and wide field of view of 2° x 2° is a unique capability of the NISS for studying the star formation in local and distant Universe. In the design of the NISS, special care was taken by implementing the off-axis system to increase the total throughput with limited resources from the small satellite. We confirmed that the mechanical structure of the NISS could be maintained in space through passive cooling of the telescope. To operate the infrared detector and spectral filters at 80K stage, the compact dewar module was assembled after the relay-lens module. The integrations of relay-lens part, primary-secondary mirror assembly and dewar module were independently performed, which alleviated the complex alignment process. The telescope and infrared sensor were validated for the operation at cryogenic temperatures of around 200K and 80K, respectively. The system performance of the NISS, such as focus, cooling efficiency, wavelength calibration and system noise, was evaluated by utilizing our constructed test facility. After the integration into the NEXTSat-1, the flight model of the NISS was tested under the space environments. The NISS is scheduled to be launched in late 2018 and it will demonstrate core technologies related to the future infrared space telescope in Korea.

Development of optomechanical structure for the NISS onboard NEXTSat-1

The Korea Astronomy and Space Science Institute has developed NISS (Near-infrared Imaging Spectrometer for Star formation history) as a scientific payload for the first next generation of small satellite, NEXTSat-1 in Korea. NISS is a NIR imaging spectrometer exploiting a Linear Variable Filter (LVF) in the spectral passband from 0.95 um to 2.5 um and with low spectral resolution of 20. Optical system consists of 150mm aperture off-axis mirror system and 8-element relay-lenses providing a field of view of 4 square degrees. Primary and secondary aluminum mirrors made of RSA6061 are precisely fabricated and all of the lenses are polished with infrared optics materials. In principle, the optomechanical design has to withstand the vibration conditions of the launcher and maintain optical performance in the space environment. The main structure and optical system of the NISS are cooled down to about 200K by passive cooling for our astronomical mission. We also cool the detector and the LVF down to about 90K by using a small stirling cooler at 200K stage. The cooling test for whole assembled body has shown that the NISS can be cooled down to 200K by passive cooling during about 80 hours. We confirmed that the optomechanical structure is safe and rigid enough to maintain the system performance during the cooling, vibration and thermal vacuum test. After the integration of the NISS into the NEXTSat-1, space environmental tests for the satellite were passed. In this paper, we report the design, fabrication, assembly and test of the optomechanical structure for the NISS flight model.

Near-Infrared Imaging Spectrometer onboard NEXTSat-1

The NISS (Near-infrared Imaging Spectrometer for Star formation history) is the near-infrared instrument optimized to the first next generation of small satellite (NEXTSat-1) in Korea. The spectro-photometric capability 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 NISS will perform the large areal imaging spectroscopic survey for astronomical objects and low background regions. We have paid careful attention to reduce the volume and to increase the total throughput. The newly implemented off-axis optics has a wide field of view (2° x 2°) and a wide wavelength range from 0.9 to 3.8μm. The mechanical structure is designed to consider launching conditions and passive cooling of the telescope. The compact dewar after relay-lens module is to operate the infrared detector and spectral filters at 80K stage. The independent integration of relay-lens part and primary-secondary mirror assembly alleviates the complex alignment process. We confirmed that the telescope and the infrared sensor can be cooled down to around 200K and 80K, respectively. The engineering qualification model of the NISS was tested in the space environment including the launch-induced vibration and shock. The NISS will be expected to demonstrate core technologies related to the development of the future infrared space telescope in Korea.

Communications Link Design and Analysis of the NEXTSat-1 for SoH File and Mission Data Using CAN Bus, UART and SerDesLVDS

The communications link in a space program is a crucial point for upgrading its performance by handling data between spacecraft bus and payloads, because spacecraft`s missions are related to the data handling mechanism using communications ports such as a controlled area network bus (CAN Bus) and a universal asynchronous receiver and transmitter (UART). The NEXTSat-1 has a lot of communications ports for performing science and technology missions. However, the top level system requirements for the NEXTSat-1 are mass and volume limitations. Normally, the communications for units shall be conducted by using point to point link which require more mass and volume to interconnect. Thus, our approach for the novel communications link in the NEXTSat-1 program is to use CAN and serializer and deserializer low voltage differential signal (SerDesLVDS) to meet the system requirements of mass and volume. The CAN Bus and SerDesLVDS were confirmed by using already defined communications link for our missions in the NEXTSat-1 program and the analysis results were reported in this study in view of data flow and size analysis.

Operational Concept of the NEXTSat-1 for Science Mission and Space Core Technology Verification

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