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Issue 3 ， 2021
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Analysis of sun pointing error of spaceborne solar spectroradiometer based on Monte Carlo method
Abstract：To guarantee the efficient operation， that is， capture of solar spectral data， of a solar spectroradiometer， the two-dimensional pointing turntable that carries the spectrometer should precisely track the sun over long periods. Highly precise sun pointing ensures that the sun stays in the effective field of vision of the guide telescope. Specifically， according to the solar vector and positioning data received from the satellite， the assembly error is corrected and the reference data for pointing are calculated after correction， ensuring that the pointing error is less than 1°. To accomplish this， coordinate systems were built into all the hexahedral reference prisms on the turntable. and the mathematical model of sun pointing was implemented using the transformation matrices of the coordinate systems. Further， the relationship between the turntable's angle of adjustment and the solar vector on the orbit coordinate system was derived using inverse kinematics. then the main source of error during operation of the spectrometer was analyzed along with its mode of operation in orbit； from these analyses， the pointing error model was built based on the Monte Carlo method on MATLAB. The model was employed to perform a simulation and analysis of sun pointing. The simulation results demonstrate that the pointing error is less than 0.35°. Finally， the simulationwas performed to obtain the result that the pointing error under the vernal equinox orbit is less than 0.16°， meeting the requirement for the field of view of the guide telescope. The correctness and effectiveness of the mathematical model presented in this paper are validated based on the test results， which simultaneously offer a design reference for the spectrometer.Keywords：spaceborne spectrometer;transformation of coordinate system;inverse kinematics;Monte Carlo;pointing error- 396
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Published：2021-04-09 -
External calibration methods for geosynchronous ultraviolet-visible hyperspectral instrument
Abstract：A geosynchronous ultraviolet-visible hyper-spectral instrument （GUVI） is deployed into a geosynchronous Earth orbit （GEO）. The GUVI has high temporal and spectral resolution as well as a long lifespan. Accordingly， the research into in-orbit calibration methods is crucial to eliminating the influence of attenuation on the precision of the internal calibration device. Consequently， highly precise calibration of orbiting sensors was achieved； this ensured that GUVI remained reliable in orbit. Solar， lunar， and stellar calibration along with a GEO were proposed based on the simulation. Then an absolute in orbit radiometric calibration comprising solar and stellar calibration was proposed； the diffuser monitor was based on lunar calibration. Thus， an external calibration program was determined. Further， the corresponding equations were formulated considering the signal-to-noise ratio of stellar calibration. Finally， the uncertainties of solar， lunar， and stellar calibrations were computed as 3.6%， 3.87%， and 3.55%， respectively， thus meeting the requirements of on-orbit calibration.Keywords：atmospheric optics;onboard calibration;geosynchronous Earth orbit;hyper-spectral- 360
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Published：2021-04-09 -
Stereo measurement of position and attitude of non-cooperative spacecraft
Abstract：For in-orbit servicing， a binocular stereo vision measurement method was proposed to precisely determine the relative position and attitude of non-cooperative spacecraft. First， two wide-field visible light cameras were used to capture high-resolution images； the images were then preprocessed via bilateral filtering. Next， the docking ring from the target surface was extracted using arc line segments. The rectangular border features of the target were extracted by Hough transform. Polar line constraints， the size constraint of the docking ring， and the optical flow method were introduced to improve the extraction accuracy and efficiency of the algorithm. The docking ring plane and the corner of the frame of the non-cooperative target were determined using stereo vision. Further， the target's coordinate system was established and its relative position was calculated using the world coordinate system. Accordingly， a binocular-camera system approximation （12.0-2.0 m） experiment performed in a dark room reveals that the accuracy of relative position exceeds 1.0 cm， whereas that of relative attitude exceeds 0.41°； the relative position accuracy exceeds 1.3 cm， whereas relative attitude accuracy exceeds 0.88° in the target attitude rotation experiment， which can provide continuous position and attitude navigation information for tracking spacecraft.Keywords：binocular stereo vision;non-cooperative target;bilateral filter;attitude measurement;on-orbit servicing- 251
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Published：2021-04-09 -
Starlight-inertial integrated navigation based on single star vector
Abstract：A small-field optical system is typically used in an all-day star sensor to reduce the stray light effect. Generally， only one star can be observed at a particular time by an all-day star sensor， and attitude information cannot be output. Therefore， a method of starlight-inertial integrated navigation based on a single star vector was developed in this study. First， the turntable and the mirror were controlled using the position and attitude information provided by the inertial navigation system to track the star. Next， the state equation was derived using the inertial navigation error model， and the measurement equation was established based on the direction vector of a single star， which was measured using the star sensor. The position and the attitude information were corrected through Kalman filtering. Because the installation attitude error was pulled in the state quantity， the installation attitude error and the navigation information were estimated simultaneously. It was unnecessary to calibrate the installation attitude between the star sensor and inertial navigation in the laboratory. Therefore， this method was proven to show stronger project practicability. The effects of the star sensor and inertial navigation error and the calibration error of the installation attitude were analyzed through simulation， which showed that the position and attitude errors after 1 h were less than 90 m and 8″， respectively. Compared to the navigation method， which is typically used for installation attitude calibration in the laboratory， this integrated navigation algorithm showed better accuracy. Finally， the validity of the integrated navigation algorithm was verified through static navigation tests. The navigation position error was 102.90 m， which was lower than that obtained based on the calibrated installation attitude by 45.39%.Keywords：starlight-inertial integrated navigation;installation attitude error;error analysis;kalman filtering- 215
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Published：2021-04-09 -
Design and manufacture of micro-nano satellite optical payload for aerospace rapid launch
Abstract：This study focuses on the design and fabrication of a catadioptric optical camera used in rapid-launch aerospace systems. We first introduce the optical design principles followed by the structural design， mechanical analysis， processing， and inspection process of the optical components. Finally， an optical payload with a resolution of 3.1 m to 500 km is obtained. The results show that the follow-up development process can be greatly simplified through reasonable optical principles and opto-mechanical structural design. Optical components that meet the accuracy requirements can be quickly processed using single-point diamond turning （SPDT）， magneto-rheological finishing （MRF）， and computer-controlled optical surfacing （CCOS）. The above methods can fulfil the technical requirements of rapid-launch aerospace technology for optical satellite payloads； the methods are quick， highly efficient， lightweight， and economical. This article provides a reference for the development of the same type of camera and the improvement of rapid-launch aerospace technology.Keywords：aerospace rapid launch;optical payload;design and manufacturing;opto-mechanical integrated design- 243
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Published：2021-04-09 -
Application of metal rubber vibration absorber in coaxial dual-reflection space camera
Abstract：This paper presents a damped metal-rubber vibration absorber modeled on the response of a coaxial dual-reflection space camera to random vibration. First， we analyze the metal-rubber structure and develop a corresponding metal-rubber damper. We then use finite element analysis （FEA） to develop a model of the space camera and perform a modal analysis and random vibration response analysis of the model. Finally， we verify the accuracy of the FEA via a sinusoidal-sweep vibration test and a random-vibration test. The test results demonstrate that， in the X， Y， and Z directions， the first-order natural frequency of a coaxial dual-reflection space camera equipped with the metal-rubber damper exceeds 100 Hz； this frequency is beyond the natural frequency of the satellite. Hence， the camera will resonate with neither the satellite nor the ground sinusoidal sweep vibration. The response of the coaxial dual reflection space camera to excitation in the X， Y， and Z directions is 4.98grms in the random vibration test； the vibration responses of a secondary mirror in the X， Y and Z directions are 3.381grms， 2.884grms， and 1.969grms， respectively. After the vibration test， no evident aberration can be observed in the system. The damped metal-rubber vibration absorber has a significant damping effect on the space camera and has a patent.Keywords：space camera;metal rubber;vibration isolation;finite element analysis;random vibration- 186
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Published：2021-04-09 -
Design of imaging model for cone-pendulum scanning integrated space camera
Abstract：Achieving super-wide coverage for high-resolution cameras is difficult. To address this difficulty， this study designs a cone-pendulum scanning integrated imaging mode. First， by analyzing the principle of cone-pendulum scanning integrated imaging， a cone-pendulum scanning integrated imaging model was established. Then， the optimal ground trajectory model was designed， and the relationship between the orbital velocity， angular velocity of the platform rotation， and angular velocity of the pendulum scanning rotation was analyzed. Simultaneously， based on the ground trajectory， a calculation scheme of exposure time and frame frequency was provided. Finally， MATLAB was used to perform simulations， and the ground coverage width and ground pixel resolution were analyzed. The results show that when the orbital altitude is 500 km， pixel size is 2.5 μm， focal length is 360 mm， and pixel number is 5 120×5 120， then the camera installation angle is 30°， number of frames of pendulum scanning imaging is 10， ground coverage width is 1 105.7 km， which is 31.1 times that of the image sub-satellite point push scanning imaging， and ground sample distance （GSD） is less than 6.4 m. The cone-pendulum integrated imaging mode can completely cover the ground target and considerably increase the width for specific resolutions.Keywords：space camera;imaging model;wide field imaging;geometric parameters;ground track- 214
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Published：2021-04-09 -
Structural optimization of 2-D tracking turntable with carbon fiber framework for spatial target detection
Abstract：To optimize solar spectroradiometers on satellites， a spatial turntable is designed according to performance indexes； finite element analysis is conducted and the properties of the prototype are tested. First， various articles were consulted to determine the fundamental structure of the turntable， and the azimuthal structure was selected. By researching the properties of different materials， M55J carbon fiber—which uses TC4 inserts for connection—was chosen as the main material for the turntable. The three main parts of the turntable are designed based on topological results and engineering experience； thus， a turntable frame with a size of 966 mm× 400 mm× 730 mm and mass of 27.3 kg is designed. Next， simulation analysis is carried out， from which the natural frequency of the entire turntable is established as 58 Hz. This implies that the strength and stiffness of the turntable fulfill the optimization criteria. Finally， resistance and thermal vacuum tests are conducted on the prototype. Test results showed that the natural frequency of the turntable was 53 Hz and the variation of the turntable’s natural frequency was within 2% （sinusoidal vibration） and 4% （random vibration）. Furthermore， we observed that the turntable functioned normally in a vacuum. Accordingly， the proposed design is tenable.Keywords：spatial target detection;2-D turntable;carbon fiber structure;topology optimization;finite element analysis- 213
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Published：2021-04-09 -
Design of primary mirror assembly with compound support for
Φ 816 mm near space telescopeAbstract：To meet the requirements of the near-surface telescope's high surface accuracy and 0°-65° observation angle， a Φ816-mm SiC aperture primary mirror assembly was designed. The design of the primary mirror was completed according to the empirical formula and topology optimization method. Based on the principle of compound support of large-aperture mirrors and the methods of function allocation and index allocation， a primary mirror support assembly was designed， and decoupling standards were formulated. According to the supporting structure and assembly tolerance design requirements for the primary mirror component assembly tooling and assembly process. Finite-element software was used to verify the statics and dynamics of the primary mirror assembly， and the primary mirror assembly was verified by performing experiments such as vibration， surface shape detection， and inclination. The test results show that the primary mirror assembly is at the optical axis level， RMS value of the profiling accuracy under the action of 1 g gravity is 0.019λ （λ=632.8 nm）， and RMS of the surface shape after the mirror is turned by 180° is 0.02λ. The total mass is 102.7 kg， fundamental frequency is 171 Hz， and RMS values before and after vibration are unchanged， which is consistent with the analysis results. The results proved that the design and installation process of the composite support are reasonable， and that they meet the design requirements of near-space telescopes.Keywords：near space;compound support;simulation analysis;surface shape error test;mechanical test- 182
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Published：2021-04-09 -
Design of lightweight split support structure for large space off-axis three mirror camera
Abstract：According to the design requirements of lightweight and high-stiffness large-scale space camera frame support structures with a 1-m resolution and 200-km width， a lightweight split support structure is designed. In this study， a high-volume SiCp/Al composite material with good performance is selected based on the development requirements of a large space off-axis three-mirror camera， including the specific stiffness， thermal stability， and processing technology. Then， with the structure mass fraction as the constraint condition， a topology optimization mathematical model is established with the fundamental frequency as the objective function， and the optimal force transfer path of each split structure with clear topological results is obtained. The size of each part of the main support structure is optimized， and the optimal configuration and design size of each split structure are obtained. After the design， the total weight of the split support structure was 227.8 kg， and the lightweight rate reached 93.9%， which meets the requirements of high lightweight and stiffness. The results of finite-element analysis and mechanical prototype test show that the split support structure meets the stiffness requirements of the whole remote sensing camera with the fundamental frequency greater than 50 Hz， and the deformation of the mirror is within the tolerance range under the working condition of 5 °C， which fully satisfies the requirements of the satellite platform for optical loads. The mechanical prototype mirror assembly offset angle is less than 22° before and after the vibration test， showing its good stability， which proves the rationality and feasibility of the topology optimization and size optimization methods. The design of the proposed split support structure has a high engineering practice value for the support design of large space off-axis cameras.Keywords：large size space camera;topology optimization;split support;lightweight;size optimization- 197
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Published：2021-04-09 -
Identification method of micro-vibration parameters of satellite reaction wheelsunder continuous rotating speed
Abstract：Owing to manufacturing and assembling errors， the harmonic interference generated by a reaction wheel assembly （RWA） is the primary factor leading to the micro-vibration of optical remote sensing satellites， which seriously hinders the development of high-resolution optical remote sensing satellites. To achieve more effective micro-vibration suppression in the design of optical remote sensing satellites， it is necessary to accurately grasp the relevant parameters of RWA micro-vibrations. This paper proposes a parametric identification method for RWA at continuous rotating speeds. The micro-vibration characteristics of the RWA are obtained in the time-frequency domain. First， a time-frequency analysis is used to obtain a time-frequency distribution of non-stationary disturbing force/moment signals. Then， a linear least squares （LLS） estimator with a sector window is established to identify the harmonic characteristics. Subsequently， a speed-dependent parameterized model is built to describe the RWA model； further， using a weighted nonlinear least-square （WNLS） estimator， the parameters of the parameterized model are estimated and transformed into modal parameters. By combining modal parameters and harmonic characteristics， the speed-frequency peaks of the disturbing forces/moments can be estimated. Experiments are performed to verify the proposed method. The results demonstrate that the proposed method presents practical trends of disturbing forces/moments. Compared with the results obtained under traditional fixed-speed states， the errors are less than 1%， confirming the accuracy of the proposed method.Keywords：reaction wheel assembly;parameter identification;micro-vibration;time-frequency analysis- 177
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Published：2021-04-09 -
Anti-disturbance and fault-tolerant control of dual-satellite formation configuration maintenance
Abstract：To solve the problem of low precision and poor stability of dual-satellite formation orbit control caused by system modeling errors， external disturbances， and actuator faults， this paper proposes an anti-disturbance and fault-tolerant linear quadratic regulator （LQR） control strategy based on an observer. First， according to a relative motion dynamic model of two satellites， an augmenting observer is designed based on the double proportional integral adaptive law， which not only can estimate intermittent faults and fast time-varying faults， but can also simultaneously estimate the system state and disturbance quickly and accurately. Regarding unmodeled disturbances， the optimization technology is used to suppress their influence on the control system. Second， the existence condition and design method of the observer are given using the linear matrix inequality （LMI） technique. The asymptotic stability of the dynamic error system is guaranteed using Lyapunov stability theory. Then， a closed-loop feedback fault-tolerant and anti-interference LQR control law is designed by adding feedforward compensation to the controller using unknown dynamic estimation information. Finally， the experimental results show that the proposed method can accurately and quickly track external interferences， actuator faults， and system states. Compared with the control methods reported in the literature， the proposed method significantly enhances the accuracy of fault estimation and improves by 49.93% the relative position control accuracy of formation satellites. This verifies the superiority of the anti-interference fault-tolerant LQR control law， which can provide an accurate configuration maintenance control strategy for dual-satellite formation configuration maintenance.Keywords：dual-satellite formation;disturbance observer;fault estimation;fault-tolerant control- 147
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Published：2021-04-09 -
Automatic registration of optical and SAR remote sensing image based on phase feature
Abstract：Optical SAR image registration is highly difficult because of the geometric and nonlinear radiation differences between optical and SAR remote sensing images， as well as the speckle noise of SAR. Thus， this paper proposes an automatic algorithm， based on phase congruency， to register optical and SAR images. First， the maximum and minimum moments of phase consistency are calculated， and the results are superimposed. The feature points are extracted from the superimposed image by the Harris operator， and then， the stable corner points and edge points are obtained as the feature points to be matched. Subsequently， the phase-consistent orientation and the maximum amplitude index map， based on multi-scale fusion， are constructed with the help of the HOG template. The maximum amplitude index map based on multi-scale fusion is voted using the phase consistency orientation， and a novel local feature descriptor is established. Finally， Euclidean distance is used as the measure of the feature vector， the nearest neighbor ratio is calculated to realize feature matching， and the fast sampling consistency algorithm is used to eliminate mismatched points. Experimental results on three sets of image data show that the proposed algorithm has more correct matching points and a higher matching accuracy than the gradient-based OS-SIFT algorithm. The number of correct matching points is increased by 11， 8， 15 and 11 pairs， and the root mean square error is increased by 57.5%， 57.9%， 23.5% and 58%， respectively.Keywords：optical and SAR images;radiation difference;image registration;phase congruency- 188
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Published：2021-04-09 -
Optimize satellite imaging parameters using meteorological forecast data
Abstract：Satellite sensor imaging parameters include gain， integration level， integration time， etc.， which need to be input by command through a ground station before imaging. Reasonable imaging parameter settings are important prerequisites for obtaining high-quality remote sensing image data. In this paper， a satellite sensor imaging parameter optimization method that employs meteorological prediction data is proposed. First， according to an imaging link model combined with surface albedo data， which can better reflect surface state changes in meteorological prediction data， the radiance at the top of the atmosphere of a target during the imaging time is determined. Then， the corresponding grayscale image under different imaging parameters is obtained using the absolute radiation calibration coefficient of the sensor. Finally， reasonable imaging parameters are selected based on the appropriate strategy of obtaining grayscale images. The algorithm proposed in this paper is verified using the line-push broom imaging mode of the Jilin SP04 satellite. The image comentropy is improved by 4.37%-23.71% for panchromatic and multispectral bands. The results show that the imaging parameter optimization strategy proposed in this paper can improve the effective dynamic range of images and meet the demand for high-quality remote sensing image data acquisition.Keywords：satellite imaging parameters;meteorological forecast data;image-link model;surface albedo data;absolute radiation calibration- 197
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Published：2021-04-09 -
Attitude determination for satellite using adaptive unscented Kalman filter
Abstract：Poor stability and low tracking accuracy are significant issues in existing algorithms for satellite attitude determination. An adaptive unscented Kalman filter （AUKF） algorithm was proposed to overcome these issues and estimate the three-axis attitude of satellite by modeling error and external disturbance. First， the working principle of attitude determination based on gyro sensor was analyzed， following which the satellite attitude kinematics equation， with error quaternion as state variable， was derived. An adaptive matrix was introduced to adjust the measurement noise covariance matrix. Based on the filtering divergence criterion， the system noise covariance matrix was adaptively modified to suppress potential divergence in the filtering process， and a good adaptive performance was obtained. Finally， it is demonstrated through experimental verification that， compared with robust AUKF algorithm， the accuracy of three-axis estimation （RMSE） of AUKF improves by 30.0%， 34.1%， and 22.4%， respectively， when the parameter estimation is not accurate. Thus， the algorithm meets the requirements of high precision and strong robustness for satellite attitude determination.Keywords：satellite attitude determination;adaptive filtering;error quaternion;robustness- 224
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Published：2021-04-09
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