KEYWORDS: Antennas, Solar radiation, Signal attenuation, Fiber lasers, Reflectors, Stray light, Solar energy, Light absorption, Transmittance, Radio telescopes
When the large-aperture antenna pose is measured by the laser method, the subreflector has a strong energy due to the convergence of the antenna itself and the instability of the near-ground atmosphere, and then the laser signal is easily drowned out. Atmospheric attenuation and other factors will weaken the laser transmission in different spectral bands, which reduces the recognition accuracy of laser spots. Aiming at the research of measuring the laser spectrum of large-aperture antenna, this paper analyzes the influence of atmospheric attenuation on the signals of different laser spectrum bands under the fixed distance of subreflector measurement, and compares the solar radiation energy of different wavelengths in laser. Finally, the stray light simulation analysis and experiments are carried out on different laser working spectrum bands to verify the accuracy of the spectrum research used in antenna measurement. Experiments show that the 1064nm wavelength spectrum, as the working spectral band of the antenna measurement, the spot information is more obvious, which can effectively realize the extraction and identification of the spot center and provide a strong guarantee for the antenna pose measurement.
With the increasingly widespread and important application of optics in modern human life and production, research on the propagation characteristics and correction methods of light beams in the atmosphere near the ground surface is becoming increasingly important. The complex atmospheric environment near the ground can affect the propagation of light beams, causing effects such as energy attenuation, beam expansion, beam drift, intensity flicker, phase fluctuations, etc., reducing the quality of beam propagation and affecting the performance of optical applications in various fields. A review was conducted on the impact of near-Earth atmosphere on beam propagation and its correction methods, mainly elaborating on the effects of atmospheric absorption, scattering, and turbulence on beam propagation. Correction methods such as adaptive optics, large aperture receiving, spatial diversity, partially coherent light propagation, and image processing are proposed.
Laser measurement technology is widely used in antenna main reflector and subreflector deformation or pose measurement. Based on the laser measurement technology, atmospheric turbulence caused by the atmospheric characteristics or the convergence effect of the antenna itself will affect the refractive index disturbance during laser propagation, which affects the accuracy of the laser measurement of the antenna deformation or pose. In order to solve the problem of laser atmospheric propagation deflection caused by atmospheric turbulence on the near-ground of a large-aperture antenna, firstly, this paper decomposes the laser atmospheric propagation path into multiple isotropic air layers, calculates the atmospheric refractive index of each air layer, obtains the atmospheric refractive index of the whole laser propagation path through curve fitting methods, and then assesses the laser deflection. Secondly, the turbulence intensity under sunny daytime and cloudy nighttime are evaluated, the laser spot position deviation is compared and analyzed, and the matching relationship among turbulence intensity, theoretical deviation of the laser spots, and actual spot deviation is obtained. Finally, the deflection of laser atmospheric propagation is fitted and calculated by measuring environmental data matched to the actual experimental data of the Nanshan 26m radio telescope antenna, which verifies the effectiveness and feasibility of the proposed method.
In terms of optical requirements and launch costs, large-diameter mirror should not only ensure fine surface accuracy, but also pursue high the rate of lightweight. Starting with material selection and shape design, the structure design of the 2 m mirror of a space remote sensor is carried out, and the preliminary mirror body is obtained. Then, combined with a platform of design optimization called Isight that integrated modeling software, finite element analysis software, data processing and analysis software, we optimized the key structural parameters of the mirror in detail, obtained a SiC mirror with the mass of 178 kg, its the rate of lightweight was as high as 90.9% and the RMS of surface shape accuracy under gravity deformation is 2.2 nm. On this basis, we designed and simulated the flexible support and other mirror components. The results indicated that the first-order natural frequency of the mirror components was 113.8 Hz, the RMS of surface shape accuracy was 8.1 nm under gravity deformation when the optical axis is horizontal, and 8.2 nm under the condition of 2°C temperature change, which were better than λ/60, could meet the requirement of the design index completely.
The ultra-efficient standard light baffle plays an important role in the calibration of the stray light test system. In this paper, a three-class baffle is designed. And a design scheme of the baffle with honeycombed wall is proposed, by analyzing the stray light transmission model and suppression mechanism, which can meet the requirements of a baffle with ultra-efficient stray light suppression capability. A simulation model of the baffle was established. The simulation of baffle show that when the stray light suppression angle is greater than 8°, the PST value of the baffle reaches 10-6 magnitude. When the stray light suppression angle is greater than 17°, the PST value of the baffle reaches 10-12 magnitude, which can meet the needs of ultra-efficient calibration of laboratory stray light test systems.
This article aiming at the high performance requirements of the space camera mirror assembly, and in order to ensure that the space camera main mirror has good surface shape accuracy and high first-order natural frequency, the mirror and flexible support structure are studied and designed. First, according to the selection principle of the mirror material, SiC is selected as the mirror blank material of the mirror. According to the empirical formula, the three-point support scheme on the back of the mirror and the structural size parameters of the mirror body are determined. And a flexible support structure with multi-axis flexible hinge and dual-axis flexible hinge in series is designed for the mirror. Finally, the parameter optimization method is used to optimize the position radius of the mirror back support hole and the key dimensions of the flexible structure. The static analysis and modal analysis of the mirror assembly were carried out using the finite element method. The results show that the surface shape accuracy of the mirror is 0.015λ nm, the first-order natural frequency of the mirror is 145.57Hz, the weight is 135.35Kg, and the lightweight rate is 87.57%.
With the development of optoelectronic imaging technology, remote sensing optical system gradually develops towards super large imaging field of view in order to obtain target characteristic information in a wider space. Concentric multiscale system is a new type of large field of view optical system. At present, most of the schemes studied are multiscale system based on concentric spherical lens. Due to the limitation of optical materials, this optical system is generally only used in visible and near infrared optical bands, and is difficult to be applied in long-wave infrared band. Starting from the structure principle of concentric multi-scale system and considering the application of long-wave infrared band, this paper proposes to use spherical reflector instead of concentric spherical lens to construct a retracted multi-scale system based on spherical reflector. The system can achieve all the features of multi-scale system and can be applied in the infrared band. According to the construction principle of the system and the design idea of off-axis deviation field, a multi-scale system based on spherical reflector is designed. The main parameters of the single channel of the system are: the focal length is 72mm, the system F#=2, the working band is 8-12um, and the imaging field of view is 20°×0.1°. The imaging quality of the system is close to the diffraction limit in the full field of view, and the distortion of the full field of view is less than 5%. The circular field of view imaging of 360°×0.1° can be achieved by extending the spherical reflector and multi-channel splicing.
The corner reflector is usually realized by fixing the corner cube prism through a specific structure, which is much easier to install and debugin practical application. As we all know, one of the most important uses of the corner reflector is that it can be used as a passive target marker for satellites and aircrafts. At a certain distance, as the angle of incidence increases, the return light efficiency of the corner reflector gradually decreases, and the return light efficiency directly affects the shape and brightness of the target point. Usually when multiple targets are tracked, the better the target direction consistency, the more uniform the light spot can be obtained. This paper introduces the method of drawing the normal direction of the corner cube prism to the mounting surface. The normal direction of the corner cube prism is tested by the self-collimating theodolite and the direction error is within 1′, and the error of return light efficiency is better than 5%, which provides high-precision pointing for the combination of multiple corner reflectors. On this basis, we expand the pointing design of the sub-corner cube prism for the plane array of the corner reflectors. After testing, the direction error of the sub-corner cube prism is within 5′.
The field of laser remote sensing and laser detection is becoming a research hot spot. Filter wheel is an important part in the process of remote sensing. The purpose of filter wheel is to choose the proper band wavelength of light to realize the specific functions. The paper made a design scheme of a type of filter wheel component and then did structural analysis under different and strict load cases. These various load cases were used to prove that if the component could be safe during the launching time of the rocket. For the initial design scheme, the situation was not good. After that, the paper made an improved design by using special flexible supports, which had flexible links and support glue. At last, structural analysis was made. The result of analysis showed that the improvement was effective and successful.
Nanosatellites usually refer to satellites with mass less than 10 kg and practical functions. With the development of high and new technology and the promotion of demand, nanosatellites play an important role in scientific research, national defense, commercial and other fields with the advantages of small size, low power consumption, short development cycle, formation networking and low cost to complete many complex space tasks. High resolution remote sensing is one of the important applications of microsatellites, because of its small size, it requires more for optical payload. According to the structural form of RC system, this paper presents a compact coaxial four reflection catadioptric system based on the structural form of RC system. The final optical system design results are as follows: the focal length is 192.2mm, the pupil diameter is 136mm (the effective pupil diameter is 105mm), the working band is 500-900nm, the imaging field of view is 4.5°, and the total optical length is 58mm. The analysis shows that the transfer function of the optical system is higher than 0.45 at 100lp / mm, the distortion of the whole market is less than 0.12%, and the relative illuminance of the whole field of view is higher than 96%. It is proved that the optical system has good imaging quality in the full field of view, and the system has good compactness to meet the load requirements of micro nanosatellite.
With the rapid development of modern optical detection technology, higher requirements are put forward for optical detection equipment. Whether it is a ground optical measuring instrument or a space detection camera, it is necessary to reduce or avoid the measurement performance degradation caused by the interference of strong light sources such as the sun.It briefly introduces the current application development of the sunshade deployment mechanism, comparatively analyzes some problems of the current application schemes, and proposes a design scheme of the ropes driven sunshade deployment mechanism. The traction of the constant pressure exhaust valve during the first deployment stage can be achieved by rope traction, which can quickly realize the air pressure balance between the target instrument to be sealed and the external environment, and can avoid the air pressure shock caused by the sealing failure in the initial deployment stage of the sunshade deployment mechanism; Rope traction can effectively control the speed of the unlocking process in the second stage of deployment, reducing the shock of the unlocking moment again; In the third stage of deployment, locking of the deployment joint can be achieved by rope traction, and locking backup can be effectively achieved. This kind of ropes driven sunshade deployment mechanism has the advantages of not only controllable deployment process, small shock, but can be used repeatedly without damaging or destroying the original deployment locking mechanism, and is especially suitable for ground measuring equipment and the ground repeated principle verification of space detection instruments.
In this paper, the photometric characteristics of passively marked corner-cube-reflector-class cooperative targets are studied. The imaging characteristics of corner cube reflector(CCR) are discussed theoretically, and the influencing factors such as surface accuracy, angle error and diffraction effect are analyzed. The reflection uniformity and diffraction characteristics of CCRs with different positions and different precision are simulated and verified. In addition, the influencing factors and control methods of CCR precision are proposed. To the photometric characteristics of cooperative targets, especially the influence of aperture size of cube-corner prism on comprehensive aberration, the transmission surface (bottom surface) on comprehensive aberration was concerned firstly, besides the three reflection surfaces. The conclusion was been drawn that the transmission surface and the three reflection surfaces had most effect on the parallel of emerging beams, and the minimum error was the minimum algebra sum of above four surfaces. It can provide theoretical support for on-orbit services such as companion flight, autonomous rendezvous and docking (RVD).
The sources of stray light were briefly introduced and the necessity of stray light suppression was analyzed. Strong stray light often directly affected the performance of space debris detection camera and even invalidated it. Therefore, the application of stray light suppression in space debris detection camera was particularly important. The design of stray light suppression for space debris detection camera using baffle was proposed. On the basis of re-searching the source of stray light, the influences of the edge width of the baffle rings and the surfaces coating treatment scheme on the stray light suppression ability were finally determined. The stray light suppression ability of the baffle was greatly improved by exploring the limit of the mechanical processing of the baffle ring and optimizing the surface coating treatment method of the inner cavity of the baffle. At the same time, the stray light flow channel inside the optical system was optimized. The critical surfaces inside the optical system were found. After removing the critical surfaces, the stray light suppression design results showed the stray light rejection ratio reached 10-7 finally when off-axis angle was larger than 35°. The flares appearing on the detector disappeared completely in the experiments, and the signal-to-noise ratio was higher. The stray light suppression optimization obtained good results, which could better satisfy the requirements of space debris detection.
In order to meet the requirements of high-precision alignment of primary and secondary mirrors of space camera in
thermal environment, we develop a new supporting structure which can eliminate heat affect between mirrors
automatically. Through the simulation analysis, we have verified this structural design is feasible. According to
requirements of the optical system, an integrated machining scheme with three-bar supporting structure for the secondary
mirror is proposed. The automatic athermalization of the primary and secondary mirrors supporting structure is
confirmed by structural analysis and optimization. The displacement between the primary mirror and secondary mirrors
in the thermal environment range of -20° ~ +60°C is analyzed by using the PATRAN software, and the results show the
position change is within 0.01mm. The structural size of the secondary mirror supporting cylinder is optimized, and the
effect of stray light suppression for the multilayer sleeve visor is analyzed and verified by using the TRACEPRO
software. The results show that the proposed structural design can achieve the high stability of the primary and
secondary mirrors supporting structure and the good effect of stray light suppression.
The retroreflector array consists of multiple cubic corner reflectors, and is used as a cooperative target for space attitude measurement. The position and normal direction of each cubic corner reflector directly affect the measurement accuracy. From the point of view of structural design, a series of practical precision extraction methods are put forward based on machining accuracy in this paper. After the verification of some experiments, the accuracy of the method can be controlled within 5', and the position accuracy is better than 0.05mm.
In order to improve the stability of the secondary mirror mounting structure and reduce the influence of the position change of the secondary mirror on the imaging quality of the camera, the secondary mirror support structure was studied. Aiming at the problems of traditional secondary mirror support, a new type of secondary mirror bracket is proposed in this paper. The finite element analysis results show that under the same obstruction ratio, the torsional stiffness, the stiffness along the optical axis and the thermodynamic properties of the new secondary mirror bracket are similar to the secondary mirror traditional support structure, but the weight of the new s bracket is only 15.2% of the traditional support structure. The new bracket solves the shortcomings of the traditional secondary mirror support structure, such as high cost, long period and heavy weight, and is easy to assemble. It has been successfully applied in the all-day star orientation instrument.
In the final step of approaching and docking proximity of space rendezvous and docking, it is necessary to measure the relative position and posture of two spacecrafts with high precision using by optical imaging sensor. The image quality of the optical system itself of optical image sensor, to a great extent, will influence the accuracy of navigation information of rendezvous and docking, and even determine the success or failure of rendezvous and docking task. The image telecentric optical system, adopted by the multi-components and retrofocus structure and designed by the hyperfocal distance theory, not only can realize clear imaging from 2 meters to infinity, but also can make sure the center position of image that is imaged by the object from 2 meters to infinity basically invariant. It used the method of "S" type correction of distortion and corrected the distortion of edged field of view (FOV) and 0.8FOV synchronously, which realized the relative distortion less than 0.028%(absolute distortion less than 0.78μm)in the range of 30° fields of view, and met the requirements of the high precision of imaging system and illuminancy uniformity of different fields of view.
The optical system of lunar rover navigation camera has a direct influence on imaging quality, and an indirect influence on the programming of march forward of lunar rover. One type of lunar rover navigation camera optical system with the symmetrical structure was introduced. It also set up the suitable position of stop to achieve the relative distortion lower than 0.053 percent under the 60 degrees wide field-of-view. It applied the hyperfocal distance principle to achieve the clear imaging from 0.5 meter to infinity. The modulation transfer function is close to diffraction limit at the Nyquist frequency (at standard object distance). Considering the complicate environment of lunar surface and the demand of exploration, it selected the appropriate work spectral coverage and was cooperated by the irradiation reinforce. As a result, it can bear 1×104 Rad (Si) space irradiation and is capable of keeping working normally in the severe environment with its temperature varying from -60°C to + 90°C.
Space sensors are used in navigation sensor fields. The sun, the earth, the moon and other planets are used as frame of reference to obtain stellar position coordinates, and then to control the attitude of an aircraft. Being the “eyes” of the space sensors, Optical sensor system makes images of the infinite far stars and other celestial bodies. It directly affects measurement accuracy of the space sensor, indirectly affecting the data updating rate. Star sensor technology is the pilot for Space sensors. At present more and more attention is paid on all-day star sensor technology. By day and night measurements of the stars, the aircraft’s attitude in the inertial coordinate system can be provided. Facing the requirements of ultra-high-precision, large field of view, wide spectral range, long life and high reliability, multi-functional optical system, we integration, integration optical sensors will be future space technology trends. In the meantime, optical technologies for space-sensitive research leads to the development of ultra-precision optical processing, optical and precision test machine alignment technology. It also promotes the development of long-life optical materials and applications. We have achieved such absolute distortion better than ±1um, Space life of at least 15years of space-sensitive optical system.
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