Leighton Chajnantor Telescope (LCT) will be moved from the summit of Mauna Kea, Hawaii to Chajnantor Plateau, Chile. At the new site, strong wind load will cause structural deformation of LCT’s reflector antenna and hence influence its electromagnetic (EM) performance significantly. Radiation pattern is an important indicator of the EM for a reflector antenna and will also be greatly affected by structural deformation. For accurately and rapidly compensating for the affected EM of LCT’s reflector antenna, it is essential to develop a quick calculation method for radiation pattern analysis under varying wind loads based on our previous work on the effect of gravitational load on radiation pattern. In this paper, we propose an approximate calculation method for the optical path difference (OPD) due to the deformation of LCT’s reflector antenna under wind load. Then a mathematical formulation based on modified Zernike polynomials is presented to fit the calculated OPD. Finally, the radiation pattern will be obtained by the aperture field integration method. Numerical experiments demonstrate the effectiveness of the proposed quick calculation method for analyzing the radiation pattern of LCT’s reflector antenna at its highest working frequency. In comparison with the numerical simulation by physical optics (PO) and physical theory of diffraction (PTD), the proposed quick calculation method exhibits high accuracy for the performance criteria of the radiation pattern and reduces the time consumption for radiation pattern analysis significantly.
Leighton Chajnantor Telescope (LCT) will be moved to the new site at Chajnantor Plateau, Chile in 2024. The new site has high wind speed and large temperature difference, which leads to strong wind disturbance and beam offset for LCT due to the deformation of the primary reflector. To achieve a high pointing control accuracy, we propose a composite feedforward/feedback control policy (CFFCP), which integrates disturbance observer-based feedforward control policy (DOB-FFCP) and the robust feedback control policy (RFBCP) to compensate the wind disturbance and the beam offset compensation strategy (BOCS) to reduce the negative effect caused by the beam offset respectively. The results of simulation on the synthesized model of LCT’s pointing control system reveal that the proposed CFFCP can signific antly reduce the pointing error during the observations.
KEYWORDS: Computing systems, Telescopes, Control software, Control systems, Telecommunications, Equipment, Databases, Data storage, Data communications, Operating systems
The Caltech Submillimeter Observatory (CSO) telescope in Mauna Kea, Hawaii, USA, has been disassembled and will be transported to Chajnantor Plateau, Chile by the end of 2024 and renamed as Leighton Chajnantor Telescope (LCT). LCT’s scientific objectives include multiwavelength imaging and spectroscopic survey of the galactic plane, magnetic fields in star formation via dust polarimetry, etc. To achieve these objectives, the instrumentation and control systems of LCT need to be upgraded such that its technological criteria can be improved significantly (e.g., 12 μm surface accuracy, 1 arcsec pointing accuracy, 10×17 W/Hz1/2 detecting sensitivity). This necessitates a comprehensive reconstruction of the computer, software, and data systems of LCT. In this work, we propose a four-phase reconstruction scheme. The first phase is dedicated to the design of the observation data management system, software system, and the computer and network system. The second phase focuses on infrastructure reconstruction which involves evaluating the computer environment, unifying the operating system across all the computers, and updating and developing the user interface program. The third phase focuses on application systems reconstruction to achieve higher accuracy, faster rotating speed and better capability of disturbance rejection. The final phase includes experiment and implementation of the developed systems on LCT to discover and correct the deficiencies. This work will provide a fundamental framework for upgrading LCT’s control systems, thereby enhancing its scientific capabilities.
The Caltech Submillimeter Observatory telescope (CSO) will be moved from Mauna Kea, Hawaii to Chajnantor Plateau, Chile in 2022, and renamed as Leighton Chajnantor Telescope (LCT). The altitude of the new site of LCT is 5050 m, and the average wind speed is about 10 m/s. However, the pointing accuracy of LCT will be improved to 1 arc-second (rms), and the rotating speed of LCT’s antenna will be improved to 2 degrees/sec, in order to achieve its new scientific aim of large survey in the sub-millimeter waveband. More precise pointing accuracy and faster rotating speed under higher wind speed makes the servo control of LCT very challenging, because both the steady-state and the transient performances of the servo control system are required to get improved under larger disturbance, while the mechanical structure of LCT is less rigid due to the adoption of lean and optimized design. To solve this problem, in this work, a state-space model of the LCT servo control system is constructed, and the Davenport wind disturbance model for LCT is also constructed for simulating wind disturbance. To improve the stability and controllability, a robust controller of the servo system is designed based on H∞ control theory with considering the disturbance of high wind speed. Simulation analysis verifies the capability of the designed controller for improving LCT’s pointing accuracy and its antenna’s rotating speed. This research is of good significance for the refurbishment of LCT and the achievement of its new scientific aim.
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