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.
KEYWORDS: Control systems, Design, Data modeling, Instrument modeling, Data storage, Computer simulations, Logic, Control systems design, Process control, Telescopes
Modern astronomical telescopes often rely on control systems for observations. Many factors may affect the development of control systems, such as the differences in the development phases of devices, the robustness of devices. A simulation framework which mocks the component of each device is needed to speed up the development of control system, facilitating behavior-level simulation to support the upper layer development. Presently, many industry-standard simulation systems are predominantly based on actual hardware systems, which necessitate the development of independent hardware logic, such as the simulator of LSST. We have designed the Rsimu framework. This framework is built upon the RACS2 and is highly proficient in behavior simulation of devices. Rsimu's behavior is entirely configurable, and the properties of different components can be dynamically defined by pluggable configuration files. A shared data-plane is provided for components to synchronize their status, therefore helps developers to separate the behavior model of components apart. A series of designs, including pull-update, state-machine etc. are provided to help users to establish the simulation system.
The Camera Control System (CCS) of the Wide Field Survey Telescope (WFST) serves as the core imaging module and is a complex distributed system composed of multiple devices. Building upon the Remote Autonomous Control System 2nd (RACS2), in this paper the RACS2-CCS framework was proposed and characterized mainly by its event-driven nature. The design incorporates basic control functions, a component manager mechanism, a file management mechanism, and a site interface component mechanism. The RACS2-CCS system can efficiently organize complex control processes, monitor system status, manage data files, and facilitate interactions between systems (such as the Observatory Control System (OCS) and the Telescope Control System (TCS)). This system is practically applied within WFST CCS.
Chinese scientists plan to build an 80 centimeter caliber near-infrared astronomical telescope in Antarctica, consisting of one telescope and two terminal devices. The K-band astronomical imaging system is one of the main terminals. We designed and characterized a 1x3 K-band near-infrared mosaic camera and the MCT detectors form Shanghai Institute of Technical Physics. The single pixel array of this camera is 640x512, with a single pixel size of 15 μm. Three detectors arranged in a mosaic configuration generated a focal plane pixel array of 1920x512. To ensure the optimal performance of the K-band astronomical imaging system, we used Dewar sealing, vacuum maintenance, and thermoacoustic refrigerator to cool the detector to 80K and the optical lens and components to 150K. In addition, a low-noise power supply design and electronic devices with low readout noise are adopted to ensure the minimum dark current and low readout noise of the mosaic infrared camera. The flatness of the mosaic detector is less than 20 μm . Complies with the design specifications for K-band astronomical imaging system.
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: 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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