To detect exoplanets and study their formation and evolution, several exoplanet space missions, such as Kepler, TESS, GAIA, and CHEOPS, have been successfully developed and fully operated in space. However, China has not yet had its own exoplanet space mission. The Earth 2.0 (ET) space mission is being developed in China aiming at detecting and characterizing exoplanets, especially extra-terrestrial like planets. ET will carry six transit telescopes pointing to the same sky region and a gravitational microlensing telescope, with the goal of finding habitable Earth like planets (Earth 2.0s) around solar type stars and measure its occurrence rate. In order to detect Earth 2.0s, ultrahigh-precision photometry of ∼30 ppm is required, which places tight constrain on camera performance, such as high-speed readout, low readout noise, mosaic detectors, and radiation tolerance. As of now, a prototype camera utilizing a CCD250-82 detector from Teledyne e2v has been developed and its performance has been tested. At a readout rate of 2 M pixels/s, the readout noise of 10.96 e− RMS and the pixel response nonuniformity of 0.66% at 600 nm have been achieved. After receiving radiation doses of 5 krad (Si) and 13.43 krad (Si), the dark current of the CCD increased by 30% and 126%, respectively. The camera’s key performance meets the basic requirements for the ET space mission, except for its high cooling power consumption.
KEYWORDS: Charge-coupled devices, Cameras, Control systems design, Head, Control systems, Resistance, Electronics, CCD cameras, Telescopes, Imaging systems
The Wide Field Survey Telescope (WFST) is a large optical image survey telescope. In order to verify some technologies used in development of camera of WFST, a scientific imaging prototype camera using CCD290-99 is designed. CCD has to work at a low temperature to reduce its dark current. Aiming at the low temperature request of the scientific CCD detector, a high precision temperature control system is designed. The system includes a refrigerator, cooling strips, temperature control electronics and its cooling scheme. Based on the thermal simulation, the temperature control system with high stability is designed and established. The test shows the system can cool the CCD to -100℃ in 3 hours and the temperature stability is less than 0.1℃, which meets requirements of the WFST camera.
Earth 2.0 is a Chinese space satellite mission that uses the transit and microlensing methods to search for exoplanets, especially Earth-sized terrestrial planets, including habitable terrestrial planets around sun-like stars. The satellite will work in the halo orbit of the Sun-Earth L2 point for at least 4 years, and is expected to find about 20 Earth like planets in the 4-year observation period. In this paper a CCD camera prototype based on a 4kx4k CCD250 detector for early technology demonstration and high-accuracy photometric performance verification is introduced. The key performance indicators such as readout noise, gain, and linearity of the camera are tested, and the test results will be described.
The wide field survey telescope (WFST) is a new generation survey telescope that is being built in China. Its optical design is a primary-focus system, and its camera is a mosaic charge-coupled device (CCD) camera composed of nine 9 K × 9 K CCD290-99 chips for scientific imaging. A verification platform to test the CCD290-99 chips is designed. The test platform includes a light source system, CCD controller, vacuum Dewar, and refrigerator for cooling the CCD. The CCD controller is a prototype design of the WFST camera that has a high performance, including low readout noise, flexible readout rate configuration, low power dissipation, etc. The digital double correlated sample method is used for video sampling of the CCD’s 16 channels. The specifications of the CCD detector system using a CCD290, such as gain, noise linearity, and crosstalk, are tested using this platform. The test results show that the CCD test platform meets the requirement of the CCD test and the design of CCD controller meets the scientific imaging requirements for the WFST camera.
KEYWORDS: Black bodies, Calibration, Near infrared, Infrared imaging, Infrared radiation, Temperature sensors, Infrared detectors, Control systems, Coating, Temperature metrology
The Antarctic Plateau is one of the best places for infrared and submillimeter observations in the world, which has the advantages of high altitude, low water vapor and low atmospheric thermal radiation. It is indispensable for the design of instruments to know the environment of the observatory site in advance, especially the infrared sky background brightness. It determines the ultimate magnitude of infrared observation of the equipment, which is an important reference to evaluate whether a candidate site is suitable for constructing corresponding equipment. We have designed a NIR sky brightness monitor (NISBM) based on InGaAs photodiode, which is used to monitor the J, H and Ks bands of sky background brightness at the Dome A. In the Ks band the signal is sensitive to thermal radiation and temperature fluctuations. So, it needs to be calibrated in real time by a surface source blackbody. According to this requirement, we have designed a surface source blackbody that has the property of low temperature resistance, high emissivity, and high temperature uniformity. The device has a compact structure. The control system and the radiation surface are packaged in the same square house, which is suitable for outfield installation and calibration with low ambient temperature.
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