| Large fully-steerable radio telescope is a kind of high precision electronic instrument widely used in radio astronomy,satellite communication and deep space exploration.With the continuous improvement of the depth and breadth of human space exploration,radio telescopes will also develop towards a larger field of view and higher gain,which also makes large fully-steerable radio telescope forward to have a larger aperture.However,due to the influence of the Earth’s gravity,a larger antenna aperture means a larger gravitational deformation,which will make it harder to ensure the surface accuracy of the antenna structure.Therefore,since the completion of the 100 m Effelsberg antenna in 1972 and the100×110 m Green Bank Telescope in 2000,there is currently no large fully-steerable antenna with an aperture of more than 100 meters in the world,and this technical bottleneck is seriously restricting the development of the next generation large aperture reflector antenna.According to the research status,this paper attempts to carry on the discussion from the angle of system innovation,through the traditional system structure to be replaced by a new system which adopts intelligent structure scheme.In order to break through this bottleneck,key technology for the realization of larger aperture fully-steerable reflector antenna in the future is developed to provide cost-effective technical support.The main contents are as follows:1.A new system structure design scheme for large fully-steerable reflector antenna is proposedFor the existing typical and cost-effective Effelsberg large fully-steerable reflector antenna system structure,the main system structure is a reflector composed of umbrella support structure and a position driving device composed of azimuth-pitch serial mechanism.Our innovative structure scheme mainly includes a uniform grid structure in the form of quasi-geodesic grid and a position driving device based on a parallel mechanism with three telescopic columns.This simple,symmetric,dynamic and static system structure scheme can significantly reduce the self-weight and complexity of the antenna system while satisfying the desired surface accuracy.In view of this new system scheme,this paper analyzed the system structure composition,structure optimization design and environmental load influence,and effectively improved surface accuracy calculation method,and preliminarily demonstrated the outstanding advantages of the new system structure scheme,such as simplicity,lightness and stability.2.Structural design and analysis of 120 m large reflector antennaFully-steerable reflector antenna with an aperture of 120 meters is an urgent application demand at present,and it is also the maximum size design scheme that people expect to realize with the traditional scheme recently.The analysis and design of this aperture reflector antenna can provide strong support for breaking the corresponding technical bottleneck in the near future.In this scheme,the original analysis of the traditional umbrella supported reflector and the innovative three telescopic columns supported reflector was carried out,and the relevant structural parameters of chord and belly rod in the back-up structure were taken as the design variables,and the self-weight and surface accuracy were taken as the objective functions to optimize the design.According to the electrical performance requirements,we proposed that the desired surface accuracy of the reflector under various position conditions should be RMS error of 1 mm,and the basic accuracy to be 3 mm,the field of view to be 120°.When the back-up structure is steel material,the reflector self-weight can be controlled within 800 t;When the back-up structure is made of aluminum alloy or carbon fiber material,the reflector self-weight can be controlled within 400 t.For the position driving device of large antenna,the variation length of each telescopic column and the hinge motion range in the motion space were deduced,and it was proved that the 3-RPS parallel mechanism can meet the tracking requirements of the position driving device.In order to verify whether the system scheme can work normally in the natural environment,this paper analyzed the load bearing under wind load,temperature load and mixed load,it was concluded that the accuracy of the new reflector can still be maintained at about 1.5 mm under the influence of various environmental loads,and the minimum accuracy was better than 3 mm.3.Structural design and analysis of 240 m ultra-large reflector antennaThe ultra-large reflector antenna with an aperture of 240 meters is likely to surpass the existing world’s largest single-aperture fully-steerable reflector antenna by several times in its comprehensive performance.Its application prospect is obvious,but the existing system structure scheme has been difficult to achieve such aperture.In this paper,the innovative system scheme proposed by us was used to discuss the ultra-large aperture antenna and demonstrate its technical feasibility.According to the requirements of the FAST system,the antenna surface accuracy is 5 mm.According to the basic parameters such as aperture and wavelength of the antenna system,the expected accuracy of the reflector is estimated to be within 3 mm,the basic accuracy is required to be 5 mm,the field of view is 90°,and the self-weight of the reflector should meet the requirements of less than 2000 t.According to the above constraints,we took self-weight and surface accuracy as objective functions to perform multi-objective optimization,so as to determine the key structural parameters of the reflector.In order to simulate the real working environment more effectively,this paper analyzed the influence of environmental loads under various wind and warm load conditions,and concluded that our scheme can meet the basic accuracy requirements of 5 mm under the bearing state of the ultra-large reflector antenna.For the position driving device supported by three telescopic columns,the rod length variation and joint angle were also within the working requirements.This scheme provided a useful exploration for the realization of ultra-large aperture reflector antenna in the near future.4.Structural design,analysis and test of the new system structure scheme scaled modelIn view of the above system structure scheme,we carried on the analysis and design experiment with the scale model,in order to preliminarily discuss the technical feasibility indirectly.Based on the principle of equivalence,this paper took the 3 m aperture telescopic reflector antenna scheme as an example to verify the effective formation of the quasi-geodesic grid reflector and the effective large range rotation of the three telescopic columns position driving device under daily environment.Based on a variety of typical working condition,this paper conducted numerical simulation research on tetrahedral and triprism small antennas in the form of belly rod.In the form of typical position condition and environment load condition analysis and comparison,the final results showed that:The new reflector can satisfy the basic accuracy of 0.3 mm,and its reflector weight can be kept within20 kg.Finally,we successively built the prototype of reflector back-up structure,three telescopic rod driving device and subreflector,and verified the feasibility,stability and lightweight effect of the new antenna system through outdoor physical objects.5.System description and structure analysis of lightweight flexible reflectorThe lightweight antenna system structure has a wide range of application value in daily life.As an important part of the solar thermal power system,the portable flexible reflector is mainly used to achieve the convergence effect of solar rays,but also needs to ensure the working requirements of lightweight and convenient.In this paper,the most typical radial rib supported reflector and cable net supported reflector in flexible structures were studied,and were carried on the system structure analysis and optimization:to slightly reduce the reflection area of local cost,through reserving crevices or holes on the surface of the reflection,so as to improve the resistance of the overall system to environmental loads with soft reflective surfaces.Based on the correlation mechanism analysis,convergence analysis and load-bearing performance comparison,it was concluded that the convergence efficiency of radial rib reflector and cable net reflector to be 76.89%and 73.69%,respectively,and the surface density can be controlled within 1.5 kg/m~2.Therefore,compared with traditional solar reflection and convergence structures,the proposed structure scheme is relatively lower in weight,energy consumption and cost,so it can be better adapted to portable applications.Aiming at the main technical bottleneck of large reflector antenna,this paper mainly explored the cost-effective system structure solution from the perspective of system structure innovation,analyzed and demonstrated the antenna system structure performance under typical working conditions.Compared with the existing large antenna system,the proposed system has significant advantages such as lightweight and simple structure,which is expected to provide useful technical reference for the design of large reflector structures.This scheme is not only suitable for large antennas with an aperture of more than 100 meters,but also can replace part of the existing small and medium-sized antenna structure scheme because of its high-cost performance,and then realize the local reform or innovation of reflector antenna structure. |
