Satellite Platform Vibration Research Articles

Satellite vibration effects on communication quality of OISN system

Abstract Over space optical communications are considered as the critical technology for high-bandwidth, high-speed, and large-capacity communications. Indeed, the laser wavelength’s narrow beam divergence requires a precise beam pointing at both ends of the optical link. The precise beam pointing makes the laser beam pointing to or from a moving object is one of the most challenging processes for optical space communications. In this work, the effect of the pointing error due to satellite platform vibration over the performance of the laser communication link of the optical inter satellite network (OISN) system in terms of the quality factor is investigated. Indeed, an optical communication system has been built using the OptiSystem program to simulate the link between satellites in space for the OISN system. In addition, the proposed system shows by simulation the optimal parameters’ values required for the design of the optical communication link between satellites of the OISN system. Moreover, the effect of pointing error due to the platform vibration on the performance of the OISN system is investigated for different scenarios of the pointing error (i.e., no pointing error; one side of the link with pointing error, and two sides of the link with pointing error). The simulation shows that, first, the optimal parameters that can be used for the optical communication link between satellites of the OISN system in terms of the laser wavelength; laser power; optical modulation scheme; optical telescope aperture diameter; and telescope optical efficiency. In addition, the simulation shows that existing pointing error due to vibration at one side of the optical link leads to degradation of the performance of the OISN system in terms of the quality factor for different laser beam power; distances between satellites; telescope diameters; and telescope efficiencies. Moreover, existing pointing errors at the two sides of the optical link lead to rapid degradation of the considered OISN system performance even with the increase of the laser power or telescope diameter, which tend to compensate for its effect initially and then quit.

A Combined Stripe Noise Removal and Deblurring Recovering Method for Thermal Infrared Remote Sensing Images

Remote sensing images (RSIs) have been applied to many fields such as environmental monitoring, urban planning, and military defense. All-day thermal infrared imaging observation system can finely portray the trajectory of human activities and provide data support for United Nations sustainable development planning. However, in the process of RSIs, image quality degradation containing image blurring is caused by optical system aberration, satellite platform vibration, imaging system out-of-focus, and atmospheric turbulence. Moreover, stripe noise in the image is produced by the non-uniformity of infrared sensors. Image deblurring and destriping are classical tasks in RSIs, but the above two problems are discussed separately in almost all research. i.e., denoising after adding stripe noise on clear images or deblurring under the assumption that only random noise exists. In this paper, stripe noise and blur are jointly removed from on-orbit RSIs acquired by the thermal infrared spectrometer on the SDGSAT-1 satellite, using a method based on stripe component residuals and gradient property. According to the experimental results, the performance of the proposed method is greatly improved compared with processing these two tasks separately, which can provide a valuable reference for the study of high-resolution thermal infrared RSIs recovery.

Imaging characteristics and image restoration method for large field circular scanning system

Large field circular scanning system obtains remote sensing images by rotating scanning, which is one of the technical ways to effectively expand the field of view of geostationary orbit optical remote sensing imaging system. However, due to its special rotation scanning imaging mechanism, the on-orbit imaging process of this system is affected by the coupling of detector rotation sampling, satellite platform vibration, optical system aberration and other factors, so the image degradation characteristics are very complex. In this paper, the on-orbit imaging characteristics of large field circular scanning system are first analyzed to provide a theoretical basis for the subsequent research of image restoration method. Secondly, aiming at the problems of annular geometric distortion and spatial blur of the system image, the image restoration method is proposed based on ring block and regularization methodology. Experimental results show that under the condition of detector rotation speed ω <0.06 rad/s, the proposed method exhibited a satisfactory processing performance.

Adaptive preload controller design and analysis for electrostatic suspension system

The electrostatic suspension control system (ESCS) is the core component of the inertial sensor in space gravitational wave detection. To adapt to the changes in orbit environment and satellite platform vibration, the test mass stable is kept in the center of the electrode cage, the ESCS requires high-precision parameters calibration and high-stability verification of the control system. This paper studied the ESCS method, an adaptive controller with variable preload was proposed, and the stability conditions of the control system are given to provide a theoretical basis for the design of the controller. The structure and working principle of the system were also introduced. The electrostatic control system model was derived, and the performance of adaptive preload controller was analyzed. Finally, a simulation was conducted under different disturbance conditions. The results show that the control method proposed in this paper can achieve stable control in difference disturbance, and the preload voltage will change with the conditions. Compared with the traditional fixed preload method, we can see that our method has significantly improved the stability margin and the control quality during the process of dynamic response. This paper provides a solid foundation for the future exploration of space gravitational waves in China and clears the optimization direction for the next step.

Satellite platform vibration influence on acquisition system for intersatellite optical communications

Accurate pointing, acquisition and tracking systems are an important part of maintaining stable intersatellite optical communications links. Satellite platform vibration causes system instability and reduces the system precision during the building and maintaining satellite optical communication system. This manuscript studies the satellite platform vibration influence on acquisition system for intersatellite optical communications. Considering the scan parameters and platform vibration, an approximately analytical expression of scan lost possibility (SLP) is derived through newly models for acquisition analysis. Taken scanning restricted condition and SLP into account, vibration influence on the acquisition time of single-scan and multi-scan is also presented. And the theoretical result calculated by the proposed analytical expression is approximately to the result by Monte Carlo simulation.

Denoising and predictive tracking method for the beacon in intersatellite laser communications

In the satellite-to-satellite optical communications, two optical terminals need to keep precise tracking for the beacon each other. However, in the tracking stage, the beacon recognition can be influenced by the star background light, which will result in the decline of tracking precision or the loss of the beacon. To solve these problems, we propose the centroid coordinate sequence fast Fourier transform algorithm, which distinguishes the beacon and the star background light by the frequency feature. Furthermore, for improving the tracking precision, the prediction method for the beacon is also introduced. To study the tracking precision of the algorithm, we simulated the satellite platform vibration. Finally, an experiment was performed to verify the practicability of the algorithm. Compared with the tradition method, the results showed that the prediction accuracy was improved more obviously. When the vibration frequencies are 50 and 80 Hz, the tracking precisions were improved by 58% and 33%, respectively. The new algorithm will be beneficial for improving the tracking precision and maintaining the steady laser link.

Acquisition performance analysis for intersatellite optical communications with vibration influence**Project supported by the Program of Excellent Team in Harbin Institute of Technology, China.

A stable and accurate pointing, acquisition system is an important part of initially building intersatellite optical communication links. Satellite platform vibration can cause the system instability and reduce the system precision in building and maintenance of a satellite optical communication system. In this paper, vibration influence is consciously discussed by acquisition time for intersatellite optical communications. Analytical expression of acquisition possibility is derived, taking the scan parameters and platform vibration into account, and vibration influence on the multi-scan acquisition time is also presented. The theoretical result calculated by the proposed analytical expression is approximate to the result by the Monte Carlo simulation.

The Optimization Design of Sub-Regions Scanning and Vibration Analysis for Beaconless Spatial Acquisition in the Inter-Satellite Laser Communication System

We mainly report an efficient approach to optimize the design of beaconless spatial laser acquisition. In order to analyze the influence of vibration environment on the beaconless spatial acquisition, a demonstration of an efficient method will be presented to simulate the level of satellite platform vibration. An important power spectral density (PSD) model of satellite platform vibration used by the European Space Agency is introduced. Then through LABVIEW, a simulated vibration waveform is generated, and the simulated PSD has a basic consistency with the in-orbit measurement spectral line, referring to the design of the filter, generating the Gaussian white noise sequence, filtering the pseudorandom signal and the whole processing procedure of parameter matching. The variation interval of the vibration amplitude is from −100 to 40 μrad. Then, the model of beaconless acquisition is proposed, which uses the spiral scan pattern, laser with a divergence angle of 80 μrad scan in an uncertainty cone (UC), and also the scan coupled with the simulated vibration is given. Through the beaconless acquisition program, the vibration is suppressed between −10.7 and 5.9 μrad; when the overlap factor is selected as 10%, it does not produce any leakage scanning area. It can be used for a wide variety of platforms. This new method will be good for analysis and test of beaconless spatial acquisition algorithm. Finally, the description of acquisition duration, which mainly includes the fast steering mirror spiral scan and the mechanical rotary table step scan, is introduced. And the corresponding optimal selection method of sub-region is proposed; the design of 1.6-mrad scanning pattern with 7 × 7 sub-regions in the 8-mrad acquisition UC is given. Through the actual measurement, the acquisition time is 18.21 s, the tracking error is better than 0.4 μrad.

Attitude Jitter Detection Based on Remotely Sensed Images and Dense Ground Controls: A Case Study for Chinese ZY-3 Satellite

Satellite platform vibration induced by the onboard dynamic components and exterior perturbation deteriorates platform stability and causes attitude jitter, resulting in image distortion and geometric accuracy degradation. This paper presents an attitude jitter detection method based on images and dense ground controls, which requires neither high-performance attitude measurement devices nor specific sensor configuration like parallax observation. Attitude variations will result in image space discrepancies at control points, from which the attitude jitter can be retrieved. The method was validated by a case study with ZY-3 satellite, which is the first civilian high-resolution stereo mapping satellite in China. The experimental results show that an almost constant jitter frequency of about 0.65 Hz was detected, which was consistent with the direct attitude observations. The photogrammetric method is theoretically capable of detecting attitude jitter up to half of the image line scanning rate according to Shannon's sampling theorem, which is far beyond the detectable range by direct attitude observations at a frequency usually not higher than 4 Hz. Currently, the attitude jitter of the roll angle and the pitch angle can be effectively detected and accurately estimated for the nadir camera. The pitch angle jitter is also well estimable for the forward and the backward cameras. With approximation, the roll angle jitter for the two off-nadir cameras can also be estimated, though with some deviation caused by the influence of the yaw angle jitter.

飞船振动引起的空间相机像移模型分析

In order to analyze space camera image motion change regulation with time caused by the spacecraft vibration, based on the NASA Landsat-4 satellite platform vibration test results on orbit, focal plane disturbance force model which is a linear combination of continuous spectrum and harmonics of nonstrictly integral multiple of fundamental frequency is proposed. The corresponding domain model of focal plane disturbance force is deduced, based on rigid body kinematics, space camera focal plane image motion model of linear combination of continuous spectrum and harmonics of nonstrictly integral multiple of fundamental frequency is established. Experiment proved the correctness of the image motion model caused by spacecraft vibration.

TDI CCD相机的卫星姿态稳定度确定

To solve the image degradation caused by satellite platform vibration and to improve TDI CCD image quality,the range of satellite attitude stabilization and its effect were analyzed. First,the dependence of the satellite platform vibration on the TDI CCD image quality was discussed. Then,equations which gave the relationship between image motion and attitude stabilization were derived. Finally,it was concluded that the satellite attitude stabilization was relevant to orbit altitudes and integral stages. The experiment results indicate that the higher the orbit altitude is and the bigger the integral stages are,the more rigorous the requirement of satellite attitude stabilization is. From obtained data,it is demonstrated that when the orbit altitude changes from200 km to 1 000 km,the requirement of satellite attitude stabilization need to improve from 0. 037 7 to0. 006 35 rad / s. Meanwhile,when the integral stages change from 1 to 100,the requirement of satellite attitude stabilization need to be improved from 0. 014 to 0. 000 14 rad / s. The work in this paper confirms the relationships of satellite attitude stabilization,orbit altitudes and integral stages,which contributes to improve TDI CCD image quality.

Research on Satellite Platform Vibration Compensation Technology for Space Optical Communication

The piezo-electric steering control system is used to compensate the vibration of satellite platform. The mathematical model of piezo-electric steering system is built. The adaptive controller based on improved LMS filter algorithm is designed according to this system characteristic. The adaptive delay filter is designed to solve slow convergence speed problem of traditional algorithm. Meanwhile, the adaptive delay filter can also compensate phase delay of control circuit. The adaptive deviation filter is introduced and it effectively compensates the vibration deviation which is low frequency and high amplitude. The experimental results show that the remained errors are μrad, which meets space optical communication requirement and proves that this control scheme is valid and feasible.

A novel approach for simulating the optical misalignment caused by satellite platform vibration in the ground test of satellite optical communication systems

Satellite platform vibration causes the misalignment between incident direction of the beacon and optical axis of the satellite optical communication system, which also leads to the instability of the laser link and reduces the precision of the system. So how to simulate the satellite platform vibration is a very important work in the ground test of satellite optical communication systems. In general, a vibration device is used for simulating the satellite platform vibration, but the simulation effect is not ideal because of the limited randomness. An approach is reasonable, which uses a natural random process for simulating the satellite platform vibration. In this paper, we discuss feasibility of the concept that the effect of angle of arrival fluctuation is taken as an effective simulation of satellite platform vibration in the ground test of the satellite optical communication system. Spectrum characteristic of satellite platform vibration is introduced, referring to the model used by the European Space Agency (ESA) in the SILEX program and that given by National Aeronautics and Space Development Agency (NASDA) of Japan. Spectrum characteristic of angle of arrival fluctuation is analyzed based on the measured data from an 11.16km bi-directional free space laser transmission experiment. Spectrum characteristic of these two effects is compared. The results show that spectra of these two effects have similar variation trend with the variation of frequency and feasibility of the concept is proved by the comparison results. At last the procedure of this method is proposed, which uses the power spectra of angle of arrival fluctuation to simulate that of the satellite platform vibration. The new approach is good for the ground test of satellite optical communication systems.

Research on Satellite Platform Vibration Compensation Method Based on Liquid Crystal Steering System

This paper presents the disturbance compensation scheme based on liquid crystal steering system according to the problem that satellite platform vibration affects the tracking and pointing accuracy in space optical communication. The mathematical model of liquid crystal steering system is built. For improving convergence speed, the adaptive controller based on posteriori estimation errors RLS lattice filter is designed, which not only achieves fast adaptation, but also reaches optimal steady-state disturbance compensation. Finally, the simulation results show that this control scheme is valid and feasible.

Research on Satellite Platform Vibration Compensation Method Based on Liquid Crystal Steering System

This paper presents the disturbance compensation scheme based on liquid crystal steering system according to the problem that satellite platform vibration affects the tracking and pointing accuracy in space optical communication. The mathematical model of liquid crystal steering system is built. For improving convergence speed, the adaptive controller based on posteriori estimation errors RLS lattice filter is designed, which not only achieves fast adaptation, but also reaches optimal steady-state disturbance compensation. Finally, the simulation results show that this control scheme is valid and feasible.