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.
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.
The performance of the camera is a decisive factor in astronomical observations. The scientific CCD fits this need. In order to realize remote control of CCD camera and obtain its performance parameters, a test platform of a scientific CCD camera is built. The test parameters include gain, noise, linearity, full well capacity test, crosstalk test, dark current test. At present, our test platform has carried out multi-group tests of gain, noise, full well and linearity by connecting with a CCD scientific camera. In this paper, a remote control system of the test platform is designed using WEB technology and EPICS, which is convenient for test operators.
With the development of astronomy, more requirements of low noise and high frame rate are put forward for observation instruments. With the advancement of CMOS technology, scientific CMOS camera can provide excellent quantum efficiency, noise performance, and higher frame rate compared to CCD camera. Based on this, we have designed a scientific CMOS camera with 2K*2K pixels and 11um pixel size. The frame rate of the camera could reach 48fps, with very low readout noise. The structural design, electronic design, cooling method and data processing of the camera will be introduced in this paper.
KEYWORDS: Cameras, Control systems, Imaging systems, Control systems design, Databases, Web services, Local area networks, Data storage, CCD image sensors
In order to meet the requirement of scientific camera system with remote control, a set of distributed remote control system is built based on EPICS framework and Web service for a camera system. EPICS provides an implementation framework of distributed soft real-time control system based on Channel Access protocol. A single device control program is named IOC. It's convenient to monitor and maintain the status of devices by operating the interfaces of IOC program, namely Process Variable (PV). This paper mainly discusses the IOC implementation of CCD controller, ion pump controller, vacuum pressure sensor and temperature controller, as well as the construction of Web monitoring platform based on Quasar and Flask framework. At present, the remote control system has been put into CCD290-99 camera named PXE290.
A telescope has been an important way to observe the stars since it was invented. With the development of the times, people have higher and higher requirements for telescopes. In order to further improve the imaging quality and observation accuracy, the aperture of the telescope is becoming larger and larger, the associated devices are becoming more and more complex, and the working environment is becoming more and more diverse. A good telescope control system can effectively reduce labor costs and improve the utilization efficiency of observation time, so people put forward higher requirements for telescope control system. The emergence of computers has promoted the rapid development of a control system for a telescope system. Faced with the development trend of large-scale, networked and diversified observation requirements of telescopes, the control system realizes robustness and scalability on the basis of automatic observation. In this paper a control system for a telescope system based on RACS2 framework is introduced. This control system includes front-end services, back-end services, observation control components and device components. The device components are designed, which is responsible for interacting with the devices such as a telescope mount, a camera and a weather station. The remote control is realized based on Web service. The observational operation of the telescope system is tested with good results.
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