The off-axis three-mirror optical system is a typical class of off-axis systems. In order to ensure excellent imaging quality in the full field of view, the alignment process involves multiple components with multiple degrees of freedom which is difficult and challenging. This article focuses on the research of automatic adjustment technology for the off-axis three-mirror optical system. By quantitatively studying the relationship between component misalignment and aberrations, we aim to explore alignment method for this type of system, providing effective and reliable methods for active adjustment. The method studied in this paper has been verified on an off-axis three-mirror optical system, achieving a full-field RMS better than 0.05@632.8nm, reaching the diffraction limit.
Compared to traditional spherical and aspherical surfaces, freeform surfaces offer extensive design freedom, which can be fully utilized to correct and balance asymmetric aberrations, achieving system parameters, structures, and functions that are difficult to realize with conventional optical systems. This has made freeform surfaces a research hotspot in the fields of optical detection and imaging. Currently, freeform surface off-axis reflective systems are widely used in space detection and extreme ultraviolet lithography objective lenses due to their advantages of no obstruction, no ghost images, and a large field of view. This paper focuses on a four-mirror off-axis optical system, studying the alignment methods for such systems. By deeply investigating the relationship between aberration characteristics and misalignment, the aim is to address issues of blind alignment and long assembly cycles associated with traditional methods, thereby providing more precise technical support for optical system assembly.
The America and Russia set their new space surveillance and detection equipment s to the near GEO orbit , and frequently conducted rendezvous and proximity operations(RPO) tests, which may pose great threats to our effect in protecting the precious GEO satellite assets. But the satellites‟ operator schema, the satellites‟ on-orbit status modes were kept secret by the owners, it was difficult for others to acquire detailed information. Firstly both the America and Russia space surveillance system capacities were investigated and summarized. Secondly, taking the distribution characteristics of GEO debris in mind, simulations were conducted based on the near GEO orbit dynamics and few satellite orbit data, to deduce the satellites trace during the valid TLE intervals. The accuracy verification was checked by the “classified” information disclosed mutually by the America and Russia. Finally, the similarities and differences between the American and Russian near GEO satellites were summarized, and suggestions were towed out when using the near-GEO orbit. According to the suggestion, for a near GEO surveillance equipment, it was proper to take enough flue to pushing themselves for more than 2000km, and was better to satay in every near-GEO orbit for more than 20 days when performing the RPO tests.
Spaceborne two-dimensional turntable is the main carrier of the space camera and other optoelectronic equipment, and the stability of the thin-walled angular contact ball bearings used in its shaft system will affect the control accuracy and service life of the satellite. Research on slip rate, the deviation ratio of centroid whirl velocity and vibration of bearing with different pocket clearances, outer clearances and velocity and axial loads. For 71928AC type angular contact ball bearing, when pocket clearance is between 0.30-0.40mm, outer clearance is 1.60mm, the cage of bearing has better stability. According to the experimental results, after the parameter optimization, the bearing stability is enhanced. The research results provide a theoretical basis for the optimal design of angular contact ball bearing cages.
The laser coherent field imaging system emits multiple beams of laser from earth to space, and the laser scans remote space target by passing through turbulent atmosphere. Turbulent atmosphere is a key factor affecting imaging quality of the coherent field imaging system. Aiming at quantitative simulating of degradation imaging effect caused by atmospheric scintillation, the quantificational simulating experiment platform of atmosphere scintillation is established. Based on the simulating platform, the effect of different intensity turbulence on imaging quality is quantificationally researched. The research draws the conclusion that the greater fluctuation of atmosphere turbulence is, the more serious the degradation of imaging quality is. Thus, in order to improve the imaging quality, the turbulent atmosphere scintillation need to be restrained by signal processing method in the following research. The study provides a achievable quantitative simulating method of turbulent air scintillation for analyzing degradation imaging quality caused by the turbulent atmosphere scintillation.
When the infrared imaging system measuring the radiation characteristics of the target, the internal stray radiation is an important factor affecting the measurement results, and the environmental temperature will directly lead to the change of the internal stray radiation. This paper analyzes the phenomenon of the gray drift of the system output caused by the environmental temperature change, and derives the functional relationship between the drift amount and the ambient temperature. A simulation analysis model of internal stray radiation was established to verify the theoretical analysis.
The single-mode fiber coupling efficiency with graded-index rod lenses can achieve higher coupling efficiency, compared with the direct alignment coupling of the single-mode fiber. The assembly error of direct alignment has a far greater impact on the coupling efficiency of the fiber than the GRIN lenses coupling to fiber. The analysis of the influence of the coupling error on the optical fiber coupling efficiency provides important theoretical support and guidance for processing and assembly. Axial error, radial error and angular tilt will all have different effects on fiber coupling efficiency. However, the fiber coupling system is not only limited to the coupling of the fiber and GRIN lenses, but also can be coupled with one or more lenses to analyze the advantages and disadvantages of multiple coupling methods.
Solar Array Drive Assembly(SADA) is a core component of high-power and long-life satellites, and the shafting is an important part of SADA. Its vibration characteristics analysis is very important in structural design and dynamic analysis. The paper theoretically derived and calculated the natural frequency of the shaft system under the action of bearing preload and span, and established a corresponding finite element simulation model in ANSYS. It is concluded that the natural frequency of the shafting increases with the increase of the bearing preload and the span, and the influence of the bearing span is more significant.
The spacecraft micro-vibration restricts the smoothness of satellite-born pointing assembles, especially for space-based laser communication, it may cause more capacity loss. A precision shafting is often the key component, connecting the satellite and the optical antenna, and transferring micro-vibration from the satellite bus to the above payload. The oscillation characteristics of the Reaction Wheel(RW) subjected to mechanical tests was implemented via pairs of liner accelerometers and acquisition system, then the micro-vibration transfer property through shafting were studied. The results showed that the RW vibration standard deviation (STD) magnified about 5 times to 30mg~50mg in time domain after the mechanical test, the FFT analysis in frequency domain showed the vibration response frequency was spurious, but the main frequency of about 430Hz and 860Hz which matched the frequency multiplication of the frequency the RW bearing balls passing the point defects in the bearing inner part. The liner acceleration and angular velocity was almost direct ratio to the RW speed, and the RW tangential vibration seemed to be more sensitive to the speed. The space used precision shafting showed perfect attenuation for a high frequency angular vibration transferring, the attenuation ratio was about 70%.
The angular micro-vibration of a high resolution camera mounting on an agile satellite was achieved based on pairs of liner accelerometers alignment and numerical integration method. Three pairs of sensors were mounted at different portion of the satellite for studying the structure transfer character, including the Reaction Wheel (RW)interface, the camera interface and the camera tail. The results showed that the RW original micro-vibration standard deviation (STD) output acquired at the RW interference was 1.63μrad at RW 400rpm and increased to 2.43μrad when the RW speed up to 800rpm. When transferring from RW to the camera interface, the angular vibration response STD was attenuated to 0.31μrad@400rpm and 0.27μrad@800rpm, and finally to the camera tail the angular vibration response STD became 0.31μrad@400rpm and 0.30μrad@800rpm. We can see that the satellite-camera structure has a good attenuation effect on the micro-vibration, the output angular micro-vibration STD is about 0.31μrad with an input of 1.63μrad~2.43μrad. the stiffness of the camera is pretty good, ensuring that the micro-vibration STD difference between the camera flange and the camera tail is smaller 0.03μrad. In addition, we found that the FOGs useful bandwidth wasn’t insufficient when acquiring about 340Hz main frequency vibration signal in our case, even though a higher stiffness flange was recommended which connecting the FOG and camera.
Aiming at the shortage of the incremental encoder with simple process to change along the count "in the presence of repeatability and anti disturbance ability, combined with its application in a large project in the country, designed an electromechanical switch for generating zero, zero crossing signal. A mechanical zero electric and zero coordinate transformation model is given to meet the path optimality, single, fast and accurate requirements of adaptive fast change algorithm, the proposed algorithm can effectively solve the contradiction between the accuracy and the change of the time change. A test platform is built to verify the effectiveness and robustness of the proposed algorithm. The experimental data show that the effect of the algorithm accuracy is not influenced by the change of the speed of change, change the error of only 0.0013. Meet too fast, the change of system accuracy, and repeated experiments show that this algorithm has high robustness.
In order to avoid the resonance between the two dimensional turntable and the satellite, the modal simulation of the two dimensional turntable is carried out in this paper. And the simulation results are compared with the experimental results, combined with modal experiment, the simulation results before and after optimization are further verified. Firstly, two dimensional turntable as the research object in this paper, and it is modeled with the finite element method, then we use Patran/Nastran to conduct the modal simulation. In the modal simulation process, the bearing can be equivalent to the spring element, and the MPC element is used to instead of the spring element. And we introduce the modeling method of the MPC unit, the fundamental frequency of two dimensional turntable is obtained through modal simulation. At last, the model experiment is verified by hammering method, the frequency response functions in each direction of x, y and z are measured. Simulations and experimental results show: after optimization, the fundamental frequency of the two dimensional turntable is 42 Hz, which is higher than that of the base frequency 25 Hz, illustrating that the optimized structural design of the two dimensional turntable meets the requirements; The natural frequency and the experimental errors of three - dimensional turntable in x, y, z are 5%, which shows that MPC can simulate the bearing accurately, and is suitable for the simulation of two dimensional turntable.
Collimation frame is the key supporting component of Space two-dimensional turntable. Its stiffness characteristics are vital for the performance of turntable. In order to reduce weight and improve rigidity, a lightweight collimation frame is designed. Compared with some commonly used aerospace materials, titanium alloy is chosen as the material of collimation frame for its excellent advantages. Modal analysis of the collimation frame is realized by using finite element analysis software MSC. Patran /Nastran to verify whether the stiffness of frame meet the design requirements. The results of analysis show that the first natural frequency of collimation frame is 169.5Hz, which satisfies the design requirement of stiffness. Then, modal experiment is conducted to verify the correctness of the results obtained from finite element modal analysis. The results of experiment show that simulation and experiment results agree well, which further confirm the correctness of the finite element modal analysis. Therefore, it proves that the selection of material and the design of structure are feasible.
The multi-axes synchronous system about the spatial two-axis turntable is the key equipment for semi-physical simulation and test in aerospace. In this paper, the whole structure design of the turntable is created by using Solidworks, then putting the three-dimensional solid model into ANSYS to build the finite element model. The software ANSYS is used to do the simulation about the static and dynamic analysis of two-axis turntable. Based on the modal analysis, we can forecast the inherent frequencies and the mode of vibration during the launch conditions which is very important to the design and safety of the structure.
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