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.
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.
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.
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.
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.
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 space mission called “Earth 2.0 (ET)” is being developed in China to address a few of fundamental questions in the exoplanet field: How frequently habitable Earth-like planets orbit solar type stars (Earth 2.0s)? How do terrestrial planets form and evolve? Where did floating planets come from? ET consists of six 30 cm diameter transit telescope systems with each field of view of 500 square degrees and one 35 cm diameter microlensing telescope with a field of view of 4 square degrees. The ET transit mode will monitor ~1.2M FGKM dwarfs in the original Kepler field and its neighboring fields continuously for four years while the microlensing mode monitors over 30M I< 20.6 stars in the Galactic bulge direction. ET will merge its photometry data with that from Kepler to increase the time baseline to 8 years. This enhances the transit signal-to-noise ratio, reduce false positives, and greatly increases the chance to discover Earth 2.0s. Simulations show that ET transit telescopes will be able to identify ~17 Earth 2.0s, about 4,900 Earth-sized terrestrial planets and about 29,000 new planets. In addition, ET will detect about 2,000 transit-timingvariation (TTV) planets and 700 of them will have mass and eccentricity measurements. The ET microlensing telescope will be able to identify over 1,000 microlensing planets. With simultaneous observations with the ground-based KMTNet telescopes, ET will be able to measure masses of over 300 microlensing planets and determine the mass distribution functions of free-floating planets and cold planets. ET will be operated at the Earth-Sun L2 orbit with a designed lifetime longer than 4 years.
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.
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: Databases, Optical instrument design, Astronomical telescopes, Telescopes, Local area networks, Process control, Visualization, Observatories, Control systems, Automatic control
RACS2 (Remote Autonomous Control System V2) is a special distributed control system for telescope control. In order to complete the heavy and complex observation task in astronomical observation, RACS2 fully considered the modular design and extensible design at the beginning of design, which has the characteristics of decentralization and automatic component discovery. The bottom layer of RACS2 is written in modern C + + language, which provides rich scalability. In addition, RACS2 also provides full-featured Python interface binding, which is convenient for modular management of device components. Aiming at the actual process of telescope automatic observation, RACS2 has designed three modules: task management module, task execution module and log management module. These three modules correspond to the three components of RACS2, including Scheduler, Executor and Logger, which covering the creation, management, execution and recording of observation tasks, so that RACS2 can meet the complex astronomical observation requirements.
The infrared astronomy is a very important branch of astronomy. Imaging observation is the basic approach to conduct infrared astronomy observation. Therefore, infrared Focus Plane Array (FPA) detector is needed for an infrared telescope. Detection toward celestial body need the detector to have high performance like extremely low dark current and low readout noise. Therefore, we designed a test equipment based on a 640 × 512 InGaAs array detector with a cryocooler which can cool the detector down to 77K. The detector is InGaAs of SITP-Hu-I type which is sensitive to 0.9us ~ 1.7um band. The test equipment is composed of a vacuum cryocooling system, a mechanical system and an electronical system. The vacuum cryocooling system can provide a low-temperature vacuum environment for the detector, and the mechanical system provides firm supporting. The electronic system provides the driver and readout of the detector.
With the increase of human activities in space, a large number of space artifacts have been generated around the Earth which called Near Earth Objects (NEO), most of which are space debris. CMOS image sensor can achieve very high frame rate by electronical shutter and suitable for NEO observation with its fast moving. For space objects observation, key technologies of a large-format and high-rate scientific CMOS camera were studied, including low-noise readout and low-interference refrigeration technology, real-time processing algorithm, high-speed data transmission technology, system integration technology and high precision timing technology , etc. A 4K*4K pixel scientific CMOS camera is introduced in this paper with 24fps rate in full frame mode and high timing accuracy of exposure synchronization with 10ns, which has great advantages for the initial orbit positioning of the space objects. The overall size of the camera is 143mm * 160mm * 168mm. The readout noise of the camera is about 4.4e-. At present, the camera has been installed and running at Xinglong Observatory.
In the field of radio astronomy, the 21cm absorption line of HI is an important way to explore the large-scale structure and evolution history of the universe. The working frequency of FAST's 19 beam receiver is 1.05GHz to 1.45GHz, and the main observation object is to conduct an accurate and rapid intensity mapping survey of extragalactic HI’s signal. Aiming at the 21cm spectral line of the object, we designed a parallel data processing platform to mitigate the influence of foreground, instrument, radio frequency, standing wave and other noises on the spectral data, then generate the image data of the whole sky region. At present, we divide the process into flux calibration, bandpass and baseline correction, radio frequency interference marking and data gridding work, etc. The whole project was programmed in Python, and Cython was used for some projects to speed things up.
KEYWORDS: Charge-coupled devices, Imaging systems, CCD cameras, Data acquisition, Telescopes, Image quality, Control systems design, Clocks, Field programmable gate arrays, Power supplies
The Wide Field Survey Telescope (WFST) is a proposed 2.5m-aperture wide field survey telescope intended for dedicated wide field sciences in China. The focal-plane instrument is a mosaic CCD camera comprising 9 pieces of 9K×9K pixels CCD chips. In order to verify the WFST mosaic solution, we designed a 2×2 mosaic camera test system using CCD303- 88. The mechanical design of vacuum chamber, cryogenic refrigeration of CCD, mosaic CCD technique and multi CCD control electronic have been implemented on this system. We design a CCD controller capable of controlling two pieces of CCDs and a power supply module for the controller. The cryogenic refrigeration control is implemented with a refrigerator and temperature control electronics.
Effective and continuous monitoring of space debris in satellite orbit is an important issue in resolving potential threats to aerospace equipment. The SDM (Space Debris Monitoring)-16803 is a front-illuminated high-readout-speed, low-noise scientific CCD camera designed for the needs of space debris monitoring telescopes. The camera is designed with drift scanning function in which mode the moving target will be presented as a static image, so that a fixed telescope can track the moving space target. The electronics of the camera provides driving signals for the CCD, samples the video signals of the CCD, and also communicates with the host computer. The maximum readout speed of the CCD is 10Mpixels. The mechanics structure of the camera is designed with a sealed chamber in which a TEC (Thermo Electric Cooler) is used for cooling the sensor and provide a stable temperature.
Scientific Complementary Metal-Oxide Semiconductor (sCMOS) image sensor has higher readout speed, higher resolution, lower readout noise than traditional Charged Coupled Device (CCDs). Since the orbital debris observation has the demand for high speed imaging system, we designed and built a sCMOS camera, and developed the corresponding operational software system. The operational software contains three lays: a software development kit (SDK), Common Language Runtime(CLR) library and an operational software with a Graphic User Interface (GUI) named PXViewer. Each of them were tested and benchmarked. Several data acquisition modes including photo, timer, continuously capture and video are implemented for different observation scenarios. Users can get fully control and operation of the sCMOS camera through the software system, including cooling, data acquisition and configuration. During the benchmark, the sCMOS camera is able to capture image of 4128*4096 pixels at 7.8 frame per second (fps), and 2064*2048 pixels at 30 fps.
EPICS (experimental physics and industrial control system) is an open source, cross platform, distributed real-time control framework, which is widely used to control devices such as particle accelerators, large-scale experiments, large telescopes and other large-scale experiments. In the telescope control system, it is necessary to meet the real-time and distributed control requirements. For the distributed telescope observation and control system RACS2 (Remote Autonomous Control System), it can be divided into three layers: user interface layer, observation control layer and equipment control layer. This paper mainly discusses the content related to the device control layer, which is mainly used to control the equipment of a telescope. We use EPICS framework to realize the unified control of telescope, camera, dome, weather station and other equipment. The device control layer of RACS2 realizes the conversion from EPICS protocol to RACS2 protocol through EPICSBridge module, so users can control the devices through RACS2.
Many specs of scientific CMOS cameras characterize the performance of camera, which can help developers analyze the quality of cameras. In order to test the performance of sCMOS cameras, we designed and built a test platform for performance test of sCMOS cameras which has been developed. The test platform includes a group of test devices and a automatic test software system. The software system is designed based on remote controllable WEB technology and EPICS-based real-time control framework, making the test platform flexible and convenient. According to the features of sCMOS camera, in the test platform four test procedures are designed to test various specs of sCMOS camera, including FPN test, dark current test, gain, noise, linear error, full well capacity test and dead pixel test. Users can perform automatic tests on camera through web UI, including the control of test platform device, data acquisition and data processing. At the same time, the test platform also provides users with various functions such as test data query and test report generation.
The Antarctica Plateau with high altitude, low water vapor and low thermal emission from the atmosphere is known as one of the best sites on the earth for conducting astronomical observations from the near infrared to the sub-millimeter. Many optical astronomical telescopes are proposed by Chinese astronomical society at present, such as Kunlun Dark Universe Survey Telescope (KDUST), 6.5-meter optical telescopes and 12-meter optical and infrared telescopes. Accurate estimation of the sky background brightness of proposed sites provides the scientific basis for instruments design and observatory site selection. Based on this requirement, a near-infrared sky brightness monitor (NISBM) based on InGaAs photoelectric diode is designed by using the method of chopper modulation and digital lock-in amplifier in the near infrared band of J, H, Ks. The adaptability of the monitor under extremely low temperature conditions in Antarctica is promoted by taking advantage of PID heating and fault detection system. Considering the weak signal of Ks band in Antarctica, a surface blackbody is equipped for real-time calibration. For the adverse circumstances to human, an EPICS and Web based Remote Control Software is implemented for unattended operation. The NISBM has been successfully installed in Dome A, Antarctica on January 2019.
CSTAR2 is a new telescope array which consists of two telescopes with 145mm-aperture and an equatorial mount, which was planned to update the CSTAR (Chinese Small Telescope Array) installed at Dome A, Antarctica in 2008. Since the previous camera was out of product, a brand new CCD camera with 1K*1K pixels was developed for CSTAR2, which was tested function well at -80℃ to prove the ability to work at Antarctica in a long period. The camera has a well performance and the readout noise is as low as 3.99e-rms. An equatorial mount made by NIAOT (Nanjing Institute of Astronomical Optics & Technology) can rotate the telescope to point almost entire sky area. In order to control CSTAR2 in an efficient way, a multi-level software control system was developed which contains three main layers: device control layer, coordinating operation layer, user interface layer. The whole system was planned to achieve automatic observation and remote operation under the conditions of poor satellite-link network.
KEYWORDS: Sensors, Observatories, Calibration, Black bodies, Near infrared, Indium gallium arsenide, Temperature metrology, Signal to noise ratio, Infrared radiation, Electronics
The Ngari (Ali) observatory is located in Ngari, Tibet, a region known as “the roof of the roof of the world.” The observatory benefits from abundant photometric nights, low perceptible water vapor, high transmittance, and good seeing. Due to these advantages, it promises to be one of the best locations in the world at which to make infrared and submillimeter observations. However, no data on the sky background radiation at this location are available, impacting the planning of future facilities at the observatory. To remedy this deficiency, a near-infrared sky brightness monitor (NISBM) has been designed to obtain data in the J, H, and Ks bands. This monitor is based on an InGaAs photoelectric diode and uses chopper modulation and digital lock-in amplifier processing, which considerably enhance its signal-to-noise ratio, detectivity, and data acquisition speed. An independent device has been designed for each band (J, H, and Ks) and calibrated in the laboratory. The NISBM was installed at the Ngari observatory in July 2017 and has obtained the first NIR sky brightness data for that location.
Infrared sky background level is an important parameter of grounded infrared astronomy observations, which should be firstly measured in a good infrared observatory site, and only the site with low background level is suitable for infrared observations. Infrared sky background level can provide background data for the design of related infrared instruments. However, there is no such data available for major sites in China. Based on the requirement, In order to supplement the current site survey data and guide the design of future infrared instruments, a multiband near-infrared sky brightness monitor (MNISBM) based on an InSb sensor is designed in this paper. The MNISBM consists of optical system, mechanical structure and control system, detector and cooler, high gain readout electronic system, operational software. It is completed and carried out an experimental measurement in the laboratory. The result shows that the sensitivity of the MNISBM meets the requirements of the measurement of near-infrared sky background level.
Tibet is known as the third pole of the earth. The Ngari (Ali) observatory in Tibet is a good site, and promising to be one of the best place for infrared and submillimeter observations in the world. However, there is no data available for sky background brightness in such place. In the near infrared band of J, H, Ks, a NIR sky brightness monitor (NISBM) is designed based on InGaAs photoelectric diode. By using the method of chopper modulation and digital lock-in amplifier processing, the SNR (Signal Noise Ratio), detectivity and the data acquisition speed of the device is greatly improved. The NISBM has been installed in Ngari observatory in July of 2017 and obtained the first data of NIR sky brightness at Ngari observatory.
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