Toshio Matsumoto

Flight performance of the Near-Infrared Spectrometer

The near-infrared spectrometer (NIRS) is one of the focal plane instruments of the infrared telescope in space (IRTS). The NIRS is a simple grating spectrometer with two element InSb linear arrays, and was designed to measure the absolute sky brightness at the wavelengths from 1.4 to 4.0 micrometer with a spectral resolution of 0.13 micrometer and a beam size of 8 feet by 8 feet. The IRTS was launched on 1995 March 18. The NIRS worked well throughout the observation period from March 29 to April 25, and scanned about 7% of the entire sky. Multiple passage of bright stars through the NIRS field of view enabled us to reconstruct the beam pattern and to calibrate the sensitivity. Those flight data confirmed good performance of the NIRS on the orbit as was expected from the preflight measurements.

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.

REQUIREMENTS AND FEASIBILITY STUDY OF FPC-G FINE GUIDING IN SPACE INFRARED TELESCOPE, SPICA

The SPICA (SPace Infrared Telescope for Cosmology & Astrophysics) project is a next-generation infrared space telescope optimized for midand far-infrared observation with a cryogenically cooled 3m-class telescope. It will achieve the high resolution as well as the unprecedented sensitivity from mid to far-infrared range. The FPC (Focal Plane Camera) proposed by KASI as an international collaboration is a near-infrared instrument. The FPC-S and FPC-G are responsible for the scientific observation in the near-infrared and the fine guiding, respectively. The FPC-G will significantly reduce pointing error down to below 0.075 arcsec through the observation of guiding stars in the focal plane. We analyzed the pointing requirement from the focal plane instruments as well as the error factors affecting the pointing stability. We also obtained the expected performance in operation modes. We concluded that the FPC-G can achieve the pointing stability below 0.075 arcsec which is the requirement from the focal plane instruments.

Integration and instrument characterization of the cosmic infrared background experiment 2 (CIBER-2)

The extragalactic background light (EBL) is the integrated emission from all objects outside of the Milky Way galaxy. Imprinted by the history of stellar emission, the EBL in the near infrared traces light back to the birth of the first stars in the Universe and can allow tight constraints on structure formation models. Recent studies using data from the Spitzer Space Telescope and the first Cosmic Infrared Background ExpeRiment (CIBER-1) find that there are excess fluctuations in the EBL on large scales which have been attributed to either high redshift galaxies and quasars, or to stars that were stripped from their host galaxies during merging events. To help disentangle these two models, multi-wavelength data can be used to trace their distinctive spectral features. Following the success of CIBER-1, CIBER-2 is designed to identify the sources of the EBL excess fluctuations using data in six wavebands covering the optical and near infrared. The experiment consists of a cryogenic payload and is scheduled to launch four times on a recoverable sounding rocket. CIBER-2 has a 28.5 cm telescope coupled with an optics system to obtain wide-field images in six broad spectral bands between 0.5 and 2.5 μm simultaneously. The experiment uses 2048 × 2048 HAWAII-2RG detector arrays and a cryogenic star tracker. A prototype of the cryogenic star tracker is under construction for a separate launch to verify its performance and star tracking algorithm. The mechanical, optical, and electrical components of the CIBER-2 experiment will have been integrated into the payload by mid-2018. Here we present the final design of CIBER-2 and our team’s instrument characterization efforts. The design and analysis of the optical focus tests will be discussed. We also report on the performance of CIBER-2 support systems, including the cooling mechanisms and deployable components. Finally, we outline the remaining tasks required to prepare the payload for launch.

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.

Development of data storage system and GSE for cosmic infrared background experiment 2 (CIBER-2)

Cosmic Infrared Background ExpeRiment-2 (CIBER-2) is an international project to make a rocket-borne measurement of the Cosmic Infrared Background (CIB) using three HAWAII-2RG image sensors. Since the rocket telemetry is unable to downlink all the image data in real time, we adopt an onboard data storage board for each sensor electronics. In this presentation, the development of the data storage board and the Ground Station Electronics (GSE) system for CIBER2 are described. We have fabricated, integrated, and tested all systems and confirmed that all work as expected, and are ready for flight.