首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The alidade's non-uniform temperature field of a large radio telescope is very obvious under solar radiation. Estimating a radio telescope's pointing errors, caused by the alidade deformation under solar radiation, is significant to improve the telescope's pointing accuracy. To study the effect of the alidade thermal behavior on the pointing accuracy of a large radio telescope, a temperature experiment is first carried out in a 70-m radio telescope on a sunny day. According to the measured results, the temperature distribution rule of the alidade is summarized initially. In addition, the alidade's temperature field is calculated by finite element thermal analysis. The simulated results are proved to be in good agreement with the experimental results. Finally, the alidade deformation under solar radiation is computed by finite element thermalstructure coupling analysis. The telescope's pointing errors caused by alidade deformation are estimated via the alidade's node displacements. The final results show that the effect of alidade thermal behavior on the telescope's elevation pointing errors ?ε_2 + ?ε_r is much more than the effect on the telescope's crosselevation pointing errors ?ε_1. The maximum of ?ε_2 + ?ε_r is more than 45, while the maximum of ?ε_1 is less than 6. This study can provide valuable references for improving the pointing accuracy of large radio telescopes.  相似文献   

2.
The pointing accuracy of a telescope is influenced by its encoder system, by the alignments of the mounting relative to the earth's axis of rotation, by the alignment of the optics, by mechanical effects like the flexture of the tube and by systemtic errors of the drive system. As to the 2.16m telescope, it is necessary to establish a pointing model to make normal obsercation easier. In this paper, an empirical approach to set up the pointing model for the 2.16m telescope was reported together with a physical interpretation of most of the individual parameters of this model.  相似文献   

3.
An effort towards understanding the problems associated with stray light related to the Xinglong2.16-m telescope is presented to estimate the stray light performance of the telescope itself and provide a method for improving stray light suppression. Stray light analysis for the 2.16-m telescope model, which consists of an onion shaped dome, telescope structure, equatorial mount and telescope optics, has been developed in two cases(1) pointing to 60?and(2) pointing to zenith, in both azimuth and elevation directions.The Point Source Normalized Irradiance Transmittance(PSNIT), which is generally used for assessing stray light and is uncorrelated to entrance aperture, is calculated with a series of off-axis angles. It shows that the PSNIT values are less than 10~(-7) when off-axis angles are larger than ±20?. The dominant contributors to stray light(primary and secondary mirror, telescope structure and dome) are identified to guide performance improvement. The analyses indicate that significant benefit can be realized by adding only five vanes inside the bottom portion of the secondary baffle. In the case of pointing to zenith, the PSNIT values will decrease about 40% on average.  相似文献   

4.
A large reflector antenna has been widely used in satellite communications, gravitational wave detection, galaxy origin observation and other fields due to its narrow beam and high gain. With the increase of the antenna aperture and the improvement of the working frequency, the requirements for the pointing accuracy of an antenna are also rising. However, the effect of environmental load on the deformation of the antenna structure, which in turn affects its beam pointing, has become a key problem to be solved urgently in the antenna engineering applications. The key issue to solving this problem involves accurately estimating the pointing error caused by the structural deformation and designing an effective controller that is based on the structural deformation. In this paper, we first establish a dynamic model for antenna structure based on the modal superposition method. The model is then modified by using modal characteristics and the dynamic displacement information of the sampling points to achieve the purpose of accurately estimating the structural deformation. Secondly, by considering the influence of the deformation of the rotating shaft and the reflector surface on the pointing accuracy, a control-oriented pointing error analysis model is established for estimating the pointing error caused by the environmental load in real time. Thirdly, based on considering the influence of the shaft deformation on the error compensation, the feedback error amount is decoupled and corrected to improve the accuracy of the compensation error. Finally, this paper analyzes and verifies the 65 m S/X-band dual reflector antenna with a numerical example. We consider a fluctuating wind with an average wind speed of 10 m s~(-1) as an example, which results in a maximum pointing error of 55.82′′as calculated by the antenna theoretical model, whereas the maximum pointing error as predicted by our model is 68.27′′. The pointing error after compensating for the cause of the environmental load with the modified controller is reduced to 10.57′′, which effectively improves the antenna pointing performance.  相似文献   

5.
Precise fiber positioning is crucial to a wide field,multi-fiber spectroscopic survey such as the Guoshoujing Telescope(the Large Sky Area Multi-Object Fiber Spectroscopic Telescope,LAMOST).Nowadays,most position error measurements are based on CCD photographic and image processing techniques.These methods only work for measuring errors orthogonal to the telescope optical axis,but there are also errors that lie parallel to the optical axis of the telescope,such as defocusing,and errors caused by the existing deviation angle between the optical axes of a fiber and the telescope.Directly measuring the two latter types of position errors is difficult for an individual fiber,especially during observations.Possible sources of fiber position errors are discussed in brief for LAMOST.By constructing a model of magnitude loss due to the fiber position error for a point source,we propose an indirect method to calculate both the total and systematic position errors for each individual fiber from spectral data.Restrictions and applications of this method are also discussed.  相似文献   

6.
Friction torque severely weakens the tracking accuracy and low-speed stability of an m-level TCS(telescope control system).To solve this problem,a friction compensation method is proposed,based on high-precision LuGre friction model parameters identification.Together with dynamometer calibration,we first design a DOB(disturbance observer)to acquire high-accuracy TCS friction value in real time.Then,the PSO-GA(a hybrid algorithm combined particle swarm optimization algorithm and genetic algorithm)optimization algorithm proposed effectively and efficiently realizes the LuGre model parameters identification.In addition,we design a TCS controller including DOB and LuGre model parameters identification based on double-loop PID controller for practical application.Engineering verification tests indicate that the accuracy of DOB calibrated can reach 96.94%of the real measured friction.When azimuth axis operates in the speed cross-zero work mode,the average positive peak to tracking error reduces from 0.8926"to 0.2252"and the absolute average negative peak to tracking error reduces from 0.8881"to 0.3984".Moreover,the azimuth axis tracking MSE reduces from 0.1155"to 0.0737",which decreases by 36.2%.Experimental results validate the high precision,facile portability and high real-time ability of our approach.  相似文献   

7.
This paper presents a method for simulating Wolter type Ⅰ grazing incidence telescope imaging of an X-ray region. The imaging quality of a soft X-ray telescope is mainly affected by geometric aberrations,surface scatter and alignment errors. Using a Legendre-Fourier polynomial to fit the figure errors in the cylindrical coordinate system, the geometry of the mirror barrel with the figure errors can be modeled by the User Defined Object in ZEMAX. Based on the Harvey-Shack surface scatter theory, surface scatter is achieved by the Bidirectional Scatter Distribution Function(BSDF) scattering model. The alignment errors are calculated by a combination of experiment and simulation according to the shape of the spot resulting from the finite distance imaging experiment. By combining these factors that affect image quality,the telescope imaging of an infinity point is simulated by ZEMAX. According to the simulation results, the angular resolution of the telescope is calculated to be less than or equal to 1.86′ at a wavelength of 1.33 nm.The simulation method improves the ability of ZEMAX to simulate grazing incidence telescope imaging.This is of great significance for the research and manufacture of X-ray grazing incidence telescopes.  相似文献   

8.
Discovery of pulsars is one of the main goals for large radio telescopes.The Five-hundred-meter Aperture Spherical radio Telescope (FAST),that incorporates an L-band 19-beam receiver with a system temperature of about 20 K,is the most sensitive radio telescope utilized for discovering pulsars.We designed the snapshot observation mode for a FAST key science project,the Galactic Plane Pulsar Snapshot (GPPS) survey,in which every four nearby pointings can observe a cover of a sky patch of 0.1575square degrees through beam-switching of the L-band 19-beam receiver.The integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 minutes.The goal of the GPPS survey is to discover pulsars within the Galactic latitude of ±10° from the Galactic plane,and the highest priority is given to the inner Galaxy within ±5°.Up to now,the GPPS survey has discovered 201 pulsars,including currently the faintest pulsars which cannot be detected by other telescopes,pulsars with extremely high dispersion measures (DMs) which challenge the currently widely used models for the Galactic electron density distribution,pulsars coincident with supernova remnants,40 millisecond pulsars,16 binary pulsars,some nulling and mode-changing pulsars and rotating radio transients (RRATs).The follow-up observations for confirmation of new pulsars have polarization-signals recorded for polarization profiles of the pulsars.Re-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 pulsars.The GPPS survey discoveries are published and will be updated at http://zmtt.bao.ac.cn/GPPS/.  相似文献   

9.
Polarimetry plays an important role in the measurement of solar magnetic fields. We developed a high-sensitivity and high-accuracy polarimeter(HHP) based on nematic liquid crystal variable retarders(LCVRs), which has a compact setup and no mechanical moving parts. The system design and calibration methods are discussed in detail. The azimuth error of the transmission axis of the polarizer as well as the fast axes of the two LCVRs and the quarter-wave plate were determined using dedicated procedures. Linearly and circularly polarized light were employed to evaluate the performance of the HHP. The experimental results indicate that a polarimetric sensitivity of better than 5.7 × 10~(-3)can be achieved by using a single short-exposure image, while an accuracy on the order of 10~(-5)can be reached by using a large number of short-exposure images. This makes the HHP a high-performance system that can be used with a ground-based solar telescope for high-precision solar magnetic field investigations.  相似文献   

10.
The radio jet axis of NGC 1068 is characterised by energetic activity from x-ray to radio wavelengths. Detailed kinematic and polarization studies have shown that this activity is confined to bipolar cones centered on the AGN which intersect the plane of the disk. Thus, molecular clouds at 1 kpc distance along this axis are an important probe of the nuclear ionizing luminosity and spectrum. Extended 10.8μm emission coincident with the clouds is reasonably understood by dust heated to high temperatures by the nuclear radiation field. This model predicts that the nuclear spectrum is quasar-like (power law + blue excess) with a luminosity 2-5 times higher than inferred by Pier et al. (1994). Consequently, there is little or no polyaromatic hydrocarbon (PAH) emission associated with the radio-axis molecular clouds. We review this model in the light of new observations. A multi-waveband collage is included to illustrate the possible orientations of the double cones to our line of sight and the galaxian plane. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
To pursue a higher imaging resolution for exploring more details in the information conveyed by the Universe, the next generation of optical telescopes based on a direct drive widely employ the extremely large aperture structure, which also introduces more disturbances and uncertain factors to the control system. Facing this new challenge, the PID control method in main-axis control systems of traditional astronomical telescopes cannot suffice for the requirement of the tracking precision and disturbance sensitivity in angular velocity. To overcome this shortcoming, we establish a dynamic model and propose an H∞ controller for a 4-meter azimuth direct drive control system that consists of a revolving platform(azimuth axis), a three-phase torque motor, a motor drive, an encoder, a data acquisition card and a small computers. Simulations are carried out to analyze the model and guide the real experiments.Experimental results show that the proposed H∞ controller reduces the tracking error by a maximum of 80.69%(average 57.8%) and the disturbance sensitivity by a maximum of 82.3%(average 50.96%) compared with the traditional tuned PI controller;furthermore, the order of the model describing the proposed controller can be reduced to three, thus its feasibility in real systems is guaranteed.  相似文献   

12.
Adaptive optics （AO）, which provides diffraction limited imaging over a field-of-view （FOV）, is a powerful technique for solar observation. In the tomographic approach, each wavefront sensor （WFS） is looking at a single reference that acts as a guide star. This allows a 3D reconstruction of the distorted wavefront to be made. The correction is applied by one or more deformable mirrors （DMs）. This technique benefits from information about atmospheric turbulence at different layers, which can be used to reconstruct the wavefront extremely well. With the assistance of the MAOS software package, we consider the tomography errors and WFS aliasing errors, and focus on how the performance of a solar telescope （pointing toward zenith） is related to atmospheric anisoplanatism. We theoretically quantify the performance of the to- mographic solar AO system. The results indicate that the tomographic AO system can improve the average Strehl ratio of a solar telescope in a 10＂ - 80＂ diameter FOV by only employing one DM conjugated to the telescope pupil. Furthermore, we discuss the effects of DM conjugate altitude on the correction achievable by the AO system by selecting two atmospheric models that differ mainly in terms of atmospheric prop- erties at ground level, and present the optimum DM conjugate altitudes for different observation sites.  相似文献   

13.
This paper presents a new method to determine precisely the barycentric positions of the outer planets(Saturn - Neptune)by optical observations. It requires the CCD observations from a long focal distance telescope which is used to observe a planet and its satellites and ones from a meridian circle when it works in a CCD drift scanning manner. The key part of the method is tested by the observations with 1 meter telescope of Yunnan Observatory. The result shows that the new method is feasible to carry out.  相似文献   

14.
This work analyzes the annual fluctuation of the observation data of the Mingantu Solar radio Telescope(MST) in S, C and X bands. It is found that the data vary with local air temperature as the logarithmic attenuation of equipment increases with temperature and frequency. A simplified and effective calibration method is proposed, which is used to calibrate the MST data in 2018–2020, while the correction coefficients are calculated from data in 2018–2019. For S, C and X bands, the root mean square errors of one polarization are 2.7, 5.7 and 20 sfu, and the relative errors are 4%, 6% and 8% respectively. The calibration of MUSER and SBRS spectra is also performed. The relative errors of MUSER at 1700 MHz,SBRS at 2800 MHz, 3050 MHz and 3350 MHz are 8%, 8%, 11% and 10% respectively. We found that several factors may affect the calibration accuracy, especially at X-band. The method is expected to work for other radio telescopes with similar design.  相似文献   

15.
Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the world’s largest single dish radio telescope,which is located in Guizhou Province,in southwest China.The FAST feed cabin is supported and positioned by six steel cables.The deviation of the feed position and orientation would lead to loss in the telescope efficiency.In this paper,a series of electromagnetic(EM)simulations of the FAST facility with varying feed positions and orientation offsets was performed.The maximum gain of FAST is about 82.3 dBi and the sibelobe is–32 dB with respect to the main beam at 3 GHz.The simulation results have demonstrated that the telescope efficiency loss is more sensitive to the lateral feed deviation compared with the axial deviation.The telescope efficiency would decrease by 8.2%due to the FAST feed position deviation of 10 mm rms when the observing frequency is 3 GHz.The FAST feed deviation basically has no effect on the sidelobes and cross polarization characteristic according to the simulations.  相似文献   

16.
The first mapping observations of the bipolar HII region S106 in HCN J = 3 - 2 line were made by KOSMA submillimeter telescope in April, 2004. The results show that there is a bipolar outflow centered on the high-mass star S106 IRS4 and that the flat structure of molecular cloud core is perpendicular to the axis of the outflow. This image roughly corresponds to the optical image where a dark lane bisects the bipolar HII region. Together with the optical, infrared and radio data, we conclude that the central UC HII region and molecular outflow formed before the  相似文献   

17.
Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is one of the major national projects under construction in China. Active optics is one of the most important technologies for new large telescopes. It is used for correcting telescope errors generated by gravitational and thermal changes. Here, however, we use this technology to realize the configuration of LAMOST, -a task that cannot be done in the traditional way. A comprehensive and intensive research on the active optics used in LAMOST is also reported, including an open-loop control method and an auxiliary closed-loop control method. Another important development is in our pre-calibration method of open-loop control, which is with some new features: simultaneous calculation of the forces and displacements of force actuators and displacement actuators; the profile of mirror can be arbitrary; the mirror surface shape is not expressed by a fitting polynomial, but is derived from the mirror surface shape formula which is highly accurat  相似文献   

18.
A tracking control algorithm based on active disturbance rejection controller(ADRC) is proposed to overcome the telescope's mount fluctuation. The fluctuations are caused by internal and external disturbance when the large aperture telescope runs at ultra-low speed with direct drive. According to the high-precision and high-stability requirements of a large aperture telescope, the ADRC position controller is designed based on segmented arc Permanent Magnet Synchronous Motors(arc PMSMs). The tracking differentiator of ADRC is designed to undergo a transition process to avoid overshoot in the position loop.The speed of target tracking process is observed by the extended state observer and the position information in the system is estimated in real time. The current control variable of the segmented arc PMSM is generated by implementing a non-linear state error feedback control law. The simulation results demonstrate that the proposed control strategy can not only accurately estimate the position and speed of the tracking target, but also estimate the disturbance to compensate the control variables. Experiments showed that the speed error is less than 0.05′′s~(-1) when using the ADRC, and it can realize high tracking performance when compared with PID controller, which improves the robustness of a large aperture telescope control system.  相似文献   

19.
It is widely accepted that mirror seeing is caused by turbulent fluctuations in the index of air refraction in the vicinity of a telescope mirror. Computational Fluid Dynamics(CFD) is a useful tool to evaluate the effects of mirror seeing. In this paper, we present a numerical method to estimate the mirror seeing for a large optical telescope(～ 4 m) in cases of natural convection with the ANSYS ICEPAK software. We get the FWHM of the image for different inclination angles(i) of the mirror and different temperature differences(?T) between the mirror and ambient air. Our results show that the mirror seeing depends very weakly on i, which agrees with observational data from the Canada-FranceHawaii Telescope. The numerical model can be used to estimate mirror seeing in the case of natural convection although with some limitations. We can determine ?T for thermal control of the primary mirror according to the simulation, empirical data and site seeing.  相似文献   

20.
We report about observations of solar U+Ⅲ bursts on 2020 June 5 by means of a new active antenna designed to receive radiation in 4–70 MHz. This instrument can serve as a prototype of the ultralong-wavelength radio telescope for observations on the farside of the Moon. Our analysis of experimental data is based on simultaneous records obtained with the antenna arrays GURT and NDA in high frequency and time resolution, e-Callisto network as well as by using the space-based observatories STEREO and WIND. The results from this observational study confirm the model of Reid and Kontar.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号