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Yao N.,Qian Xuesen Laboratory of Space Technology | Qi W.,CAS Institute of Mechanics | Shi Y.,Qian Xuesen Laboratory of Space Technology
Proceedings of the International Astronautical Congress, IAC | Year: 2016

For some special tasks of remote sensing satellites, such as natural disaster or emergency observation, the in-orbit cameras are required to image quickly during satellite rapid maneuver (or immediately after maneuver completion) to obtain ground images accurately and promptly. In order to guarantee TDICCD camera imaging quality and efficiency during satellite attitude maneuver, this paper first studied the TDICCD push-broom imaging mechanism during arbitrary flight path imaging. The TDICCD adaptation during flight path imaging, the requirement for camera integrating time, and the requirement for satellite attitude stability have been analyzed respectively. The traditional in-orbit push-broom imaging mechanism has secondly been analyzed and compared with side-sway imaging during satellite attitude maneuver. Then, the area array CCD imaging mechanism has been investigated for image motion detection and compensation. Based on the above investigation, the paper finally proposed a space camera system optimization design method based on image quality. With this method, small relative aperture, ground image restoration processing, and full-chain optimization design methods have been adopted for TDICCD camera multimode imaging in order to obtain the required image information quickly and effectively. Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved.

Li H.,Qian Xuesen Laboratory of Space Technology | Man Y.,Qian Xuesen Laboratory of Space Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The image phase coherences (PCs) remain invariant when brightness and contrast changes. A new method of remote sensing image registration is proposed. PCs are firstly extracted from the reference image and the input image. In order to improve the registration efficiency, in the first step the PCs are firstly down-sampled using Gaussian pyramid method, and the coarse translation parameters are calculated using phase correlation. In the second step, Harris corners are detected from the two images, and normalized cross-correlation (NCC) function based on PCs is used to find the corresponding matching corners of the two images, and then obtain parameters of an alignment transform model. Experiments have demonstrated that the coarse-to-fine method can be successfully applied to multi-source images registration. © 2015 SPIE.

Fan C.,China Academy of Space Technology | Fan D.,Qian Xuesen Laboratory of Space Technology
Chinese Control Conference, CCC | Year: 2016

In recent years, high performance smallsats have experienced a rapid advancement, micro/nanosatellites based space system turned more powerful platforms and are to be aggregated as building blocks to construct large spacecraft with enhanced payload capabilities. The mission and technique development requires more compact while better precision and agility attitude control system. Magnetically levitated spherical momentum actuator, namely the reaction sphere or 3 Dimensional Reaction Wheel, is a promising novel kind of control devices to meet the above requirements. We proposed a system level attitude dynamics model of a microsatellite equipped with single and multiple reaction sphere actuators. With analytical comparisons to their flywheel-based counterpart and numerical simulations, we have revealed two unique advantages of the reaction sphere based system as low-level coupling of actuator gyroscopic momentum and a simple additive control torque synthesis among multiple actuators. A rotor inertial momentum direction preservation control method is proposed for diminished cross coupling. © 2016 TCCT.

Zhang X.,Qian Xuesen Laboratory of Space Technology | Zhang X.,University of Electronic Science and Technology of China | Liu B.,Qian Xuesen Laboratory of Space Technology
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2016

Suffering from ambiguous estimation or heavy computation complexity load, the radial velocity estimation of moving targets becomes the bottleneck of the synthetic aperture radar-ground moving target indication system. In order to improve the radial velocity estimation efficiency, we have proposed an efficient Radon transform (RT) estimation (ERTE) method by using the never exploited geometry information, which performs well in high SNR scenarios but bad for low SNR. Focusing on these, we propose the least square RT estimation (LSRTE) method to improve the estimation accuracy by utilizing the geometry information of multiple RT results. Given the geometry information determining measurement error, we modified the LSRTE into a weighted LSRTE (WLSRTE) method to improve the estimation robustness and accuracy. Experiments results validate the effectiveness of the proposed methods, and the proposed methods perform much more accurate and efficient than the conventional method. © 2016 IEEE.

Bo L.,Qian Xuesen Laboratory of Space Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Spaceborne Synthetic Aperture Radar (SAR), with "all weather", day or night imaging capabilities, has been playing an important role in the domination of Earth observation. Spaceborne high-resolution wide-swath SAR (HRWS-SAR) can quickly obtain wide range of the earth's surface information, which is of great significance to Earth mapping, geological exploration, vegetation and biomass estimates, marine monitoring, target search, disaster relief, etc. As a result, spaceborne HRWS-SAR has been gaining more and more attention. However, considering the restrictions on pulse repetition frequency (PRF) and power-aperture product, space-based SAR imaging cannot achieve high resolution and wide swath at the same time. Currently existing solutions mainly focus on the antenna system hardware devices, such as MIMO, DBF; other signal-processing-bias solutions, such as Mosaic imaging technology, have higher requirements of the antenna pointing or beam control. These methods adopt more antenna elements or complex beam control method, which greatly increased the demand for hardware performance, and the signal processing method become more complicated as well. In order to relieve the pressure on the system hardware devices, this paper presents a new orthogonal coded waveform method based on the theory of communication. By using this method, the LFM signal is coded by the orthogonal codes to make the neighboring pulses irrelevant, which ensures the azimuth sampling rate as well as a wide swath. Theoretically, this method can alleviate the contradiction between PRF and high resolution wide swath imaging. © 2014 SPIE.

Yiyun M.,Qian Xuesen Laboratory of Space Technology | Haichao L.,Qian Xuesen Laboratory of Space Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

In this paper an accurate measurement method for optics system based on the lunar imaging is presented, and this method has the following steps. Firstly, the optical imaging system observes the lunar and acquires the image on the ground or in orbit, and records the position and the time simultaneously, with which the distance to the lunar can be computed. Secondly, the initial region of the lunar in the acquired image is decided by the gray value threshold, and the Canny edge detection method with parabola fitting is used to acquire the sub-pixel image edge points. Thirdly, the extracted edge points are used to preliminary fit the lunar disc, and the lunar ring is formed based on the fitted lunar disc expanded two pixels, then the initial coarse fitting disc is acquired according to the maximum number of edge points located in the lunar ring. Fourthly, the sub-pixel lunar disk can be obtained via the least squares fitting on the base of the initial coarse fitting disc. At last, the focal length of the optical imaging system can be computed with the position relationship between the optical imaging system and the lunar. Experiments show that this method has the ability to focal length measurement with high accuracy and frequency. By the means of imaging to the lunar, taking advantage of the long distance, sub-pixel edge detection and fitting for the lunar disc diameter, etc, whether in the full lunar and the waning lunar, the focal length could be measured accurately. It has a wide application prospects both in the developing and in orbit operating stage for optical imaging system. © 2014 SPIE.

Wang X.,Beihang University | Yang C.,QIAN Xuesen Laboratory of Space Technology | Wang L.,Beihang University | Qiu Z.,Beihang University
Acta Mechanica Solida Sinica | Year: 2014

The probabilistic damage identification problem with uncertainty in the FE model parameters, external-excitations and measured acceleration responses is studied. The uncertainty in the system is concerned with normally distributed random variables with zero mean value and given covariance. Based on the theoretical model and the measured acceleration responses, the probabilistic structural models in undamaged and damaged states are obtained by two-stage model updating, and then the Probabilities of Damage Existence (PDE) of each element are calculated as the damage criterion. The influences of the location of sensors on the damage identification results are also discussed, where one of the optimal sensor placement techniques, the effective independence method, is used to choose the nodes for measurement. The damage identification results by different numbers of measured nodes and different damage criterions are compared in the numerical example. © 2014 The Chinese Society of Theoretical and Applied Mechanics.

Du Y.,Qian Xuesen Laboratory of Space Technology
Lecture Notes in Electrical Engineering | Year: 2015

Six X-ray pulsars (PSR J0218+4232, PSR J0437-4715, PSR B0531-21, PSR J1939+2134, PSR J1024-0719 and PSR J0751+1807) are selected for the mission of deep-space autonomous navigation, and the relevant parameters (including position, proper motion, period and period derivative, etc.) are also listed. Based on the XMM-Newton X-ray timing data and the radio ephemeris for the young pulsar PSR B1509-58, we adopted both absolute timing and relative timing methods to fold its pulse profile in the 0.2–12 keV band. In addition, for the sake of both pulsar-based deep-space autonomous navigation and scientific research, we take the Crab pulsar as an example to fit its X-ray (0.2–30 keV band) spectrum, and obtain its power-law fitted spectrum. Then we estimate the navigation accuracy of the detectors with different effective areas. Finally, we discuss a preliminary probe design principle of X-ray detectors for the pulsar navigation, and give the rough estimations on the effective area and sensitivity. © Springer-Verlag Berlin Heidelberg 2015.

Wang J.,Beihang University | Wu Y.,Beihang University | Dong X.,Qian Xuesen Laboratory of Space Technology
Nonlinear Dynamics | Year: 2015

A recursive terminal sliding mode controller (RTSMC) based on sliding mode disturbance observer (SMDOB) is proposed for the longitudinal dynamics of a generic hypersonic flight vehicles (HFVs) in the presence of parametric uncertainties, measurement noises and external disturbances. First, a sliding mode tracking controller is presented by introducing recursive terminal sliding mode manifolds, in which each manifold will reach zero subsequently in finite time as well as the usual singularity problem will not occur. The RTSMC embraces advantages of both nonsingular terminal sliding mode control and high-order sliding mode control. Next, for the sake of enhancing the robustness of controller for uncertainties, a SMDOB is proposed to estimate and compensate the disturbances. Then, a composite controller that is composed of RTSMC and SMDOB is designed, and its stability is analyzed utilizing Lyapunov function method. Finally, numerical simulation is conducted for cruise flight condition of HFV. Simulation results show the expected control performance. © 2015, Springer Science+Business Media Dordrecht.

Liu Y.,Qian Xuesen Laboratory of Space Technology | Yang C.,Qian Xuesen Laboratory of Space Technology
Chinese Control Conference, CCC | Year: 2014

This paper investigates the solar radiation pressure force model and its estimation approach for solar sail spacecraft. Estimation of solar sail force model in space is the key factor for successful solar sail navigation, solar sail orbit determination and orbit propagation. The solar sail force model accounts for the sail film optical properties, sail shape and changing sail temperature. In this paper, a square solar sail model is introduced. Three solar sail force models exerted on the square solar sail considering the deformation of the sail are presented. Firstly, the force model exerted on an ideal, perfectly reflecting solar sail is calculated. The second force model exerted on a non-perfectly solar sail is obtained by considering reflection, absorption and re-radiation. The last force model is a simplification force model which accounts for the billow of the sail under load. © 2014 TCCT, CAA.

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