The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.765 gigapixels on the primary focal plane for high quality image capture over a 6.5-square-degree field of view. The mosaic CCD camera is the key device for high precision photometric and high frequency observation and the ‘eye’ of the telescope for deep survey with wide field. The focal plane consists of three kinds of CCD including scientific imaging sensors, wavefront sensors and guiding sensors. In the scientific imaging area, there are 9 back-illuminated full frame scientific CCDs –CCD290-99 from E2V company with pixels of 9K by 9K and pixel size of 10um, which is mosaicked by 3 by 3 with flatness of 20μm PV. The R&D of the camera including the high precision large-scale mosaicking of detectors, detectors’ cryocooling and vacuum sealing, readout and driving with low noise and low power, data acquisition, imaging control, data storage and distribution. Furthermore a camera control system (CCS) was developed at same time.
The Earth 2.0 (ET) space mission has entered its phase B study in China. It seeks to understand how frequently habitable Earth-like planets orbit solar-type stars (Earth 2.0s), the formation and evolution of terrestrial-like planets, and the origin of free-floating planets. The final design of ET includes six 28 cm diameter transit telescope systems, each with a field of view of 550 square degrees, and one 35 cm diameter microlensing telescope with a field of view of 4 square degrees. In transit mode, ET will continuously monitor over 2 million FGKM dwarfs in the original Kepler field and its neighboring fields for four years. Simultaneously, in microlensing mode, it will observe over 30 million I < 20.5 stars in the Galactic bulge direction. Simulations indicate that ET mission could identify approximately 40,000 new planets, including about 4,000 terrestrial-like planets across a wide range of orbital periods and in the interstellar space, ~1000 microlensing planets, ~10 Earth 2.0s and around 25 free-floating Earth mass planets. Coordinated observations with ground-based KMTNet telescopes will enable the measurement of masses for ~300 microlensing planets, helping determine the mass distribution functions of free-floating planets and cold planets. ET will operate from the Earth-Sun L2 halo orbit with a designed lifetime exceeding 4 years. The phase B study involves detailed design and engineering development of the transit and microlensing telescopes. Updates on this mission study are reported.
Earth2.0 is a space telescope mission proposed by Chinese scientists to search for exoplanets. It is scheduled for launch in 2027 and will operate in orbit around the Earth-Sun Lagrange point L2 for a minimum of 4 years. The mission includes six 28cm aperture, 550 square degree transit telescopes and one 35cm aperture, 4 square degree microlensing telescope. The microlensing telescope is aimed at the core area of the Milky Way's arm, and is expected to discover approximately 1,000 cold and wandering planets within four years. Currently, the microlensing telescope is considering using Teledyne e2v's CCD290 as the detector, with a focal plane consisting of a 2*2 detector mosaic. To conduct preliminary technical verification, a CCD290 prototype camera was designed and CCD290 performance characterization tests were carried out. Additionally, specific experiments were conducted to study the impact of space radiationontheCCD290 detector's performance through proton displacement damage irradiation. Following cumulative doses of3.072*10 10 p/cm2 and 6.792*10 10 p/cm2 of 60MeV proton irradiation, dark current, dark current non-uniformity, and charge transfer efficiency tests were performed on the CCD290. The test results indicated that after annealing at room temperature for 4 days and at 50°C for 7 days, the CCD performance showed partial restoration, highlighting the necessity of regular annealing in orbit.
The near-infrared spectrum encompasses three primary atmospheric transmission windows corresponding to the wavelengths J, H, and Ks. This paper introduces a practical automated remote-control system based on Web technology, which utilizes NIR sky brightness measurements for calibrating astronomical observational data. The system enables remote control, automated observation and data visualization. EPICS serves as the connection layer between the microcontroller and the server, implementing the underlying event loop. The web server leverages the Tornado framework to efficiently manage automated observational tasks and performs a real-time correction of the Ks device's detector response using a blackbody radiative source. The system provides a client interface constructed with the Vue framework and utilizing the Element UI component library, allowing users to remotely control instruments, monitor and configure observation tasks, as well as visualize data using the Plotly charting tool via a web browser.
KEYWORDS: Charge-coupled devices, Clocks, CCD image sensors, Device simulation, Telescopes, Video, Analog electronics, Field programmable gate arrays, Analog to digital converters, Amplifiers
In this paper, we design a simulation test system to test the readout and drive circuit of the Front-End electronics board (FEB) of the CCD detector system of Wide Field Survey Telescope (WFST). For fast and accurate testing, the CCD simulation test system can c 20-channel clock detection, 16-channel bias, and 16-channel bias noise detection. In addition, the simulation test system can also provide two channels of analog CCD waveform output for testing FEB waveform sampling circuits. The analog CCD waveform output module consists of a digital waveform output module and an analog waveform output module, which can be selected according to specific requirements. The simulation test system has been used to test the FEB performance of the Wide Field Survey Telescope.
The Wide Field Survey Telescope (WFST) is a 2.5m diameter telescope proposed by the University of Science and Technology of China and the Purple Mountain Observatory. The telescope is located at the summit of the Saishiteng Mountain near Lenghu City. The WFST equipped with a mosaic camera on the primary focus plane that includes 9 scientific imaging CCDs, 8 wave-front CCDs, and 4 guiding CCDs. The CCDs are placed in vacuum Dewar, and electronic signals are transmitted through the PCB boards and the vacuum Dewar connectors to the readout electronics outside Dewar. We provided a low-noise readout solution and a high-speed reliable data upload solution for the mosaic CCD camera, and evaluate and tests the performance.
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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