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Xu M.,Beihang University | Tan T.,DFH Satellite Co. | Xu S.,Beihang University
Science China: Physics, Mechanics and Astronomy | Year: 2012

This paper discusses the evolutions of invariant manifolds of Halo orbits by low-thrust and lunar gravity. The possibility of applying all these manifolds in designing low-thrust transfer, and the presence of single-impulse trajectories under lunar gravity are also explained. The relationship between invariant manifolds and the altitude of the perigee is investigated using a Poincaré map. Six types of single-impulse transfer trajectories are then attained from the geometry of the invariant manifolds. The evolutions of controlled manifolds are surveyed by the gradient law of Jacobi energy, and the following conclusions are drawn. First, the low thrust (acceleration or deceleration) near the libration point is very inefficient that the spacecraft free-flies along the invariant manifolds. The purpose is to increase its velocity and avoid stagnation near the libration point. Second, all controlled manifolds are captured because they lie inside the boundary of Earth's gravity trap in the configuration space. The evolutions of invariant manifolds under lunar gravity are indicated from the relationship between the lunar phasic angle and the altitude of the perigee. Third and last, most of the manifolds have preserved their topologies in the circular restricted three-body problem. However, the altitudes of the perigee of few manifolds are quite non-continuous, which can be used to generate single- impulse flyby trajectories. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.

Xu M.,Beihang University | Zhu J.,Beihang University | Tan T.,DFH Satellite Co. | Xu S.,Beihang University
Celestial Mechanics and Dynamical Astronomy | Year: 2012

The bounded quasi-periodic relative trajectories are investigated in this paper for on-orbit surveillance, inspection or repair, which requires rapid changes in formation configuration for full three-dimensional imaging and unpredictable evolutions of relative trajectories for non-allied spacecraft. A linearized differential equation for modeling J 2 perturbed relative dynamics is derived without any simplified treatment of full short-period effects. The equation serves as a nominal reference model for stationkeeping controller to generate the quasi-periodic trajectories near the equilibrium, i. e., the location of the chief. The developed model exhibits good numerical accuracy and is applicable to an elliptic orbit with small eccentricity inheriting from the osculating conversion of orbital elements. A Hamiltonian structure-preserving controller is derived for the three-dimensional time-periodic system that models the J 2-perturbed relative dynamics on a mean circular orbit. The equilibrium of the system has time-varying topological types and no fixed-dimensional unstable/stable/center manifolds, which are quite different from the two-dimensional time-independent system with a permanent pair of hyperbolic eigenvalues and fixed-dimensions of unstable/stable/ center manifolds. The unstable and stable manifolds are employed to change the hyperbolic equilibrium to elliptic one with the poles assigned on the imaginary axis. The detailed investigations are conducted on the critical controller gain for Floquet stability and the optimal gain for the fuel cost, respectively. Any initial relative position and velocity leads to a bounded trajectory around the controlled elliptic equilibrium. The numerical simulation indicates that the controller effectively stabilizes motions relative to the perturbed elliptic orbit with small eccentricity and unperturbed elliptic orbit with arbitrary eccentricity. The developed controller stabilizes the quasi-periodic relative trajectories involved in six foundational motions with different frequencies generated by the eigenvectors of the Floquet multipliers, rather than to track a reference relative configuration. Only the relative positions are employed for the feedback without the information from the direct measurement or the filter estimation of relative velocity. So the current controller has potential applications in formation flying for its less computation overload for on-board computer, less constraint on the measurements, and easily-achievable quasi-periodic relative trajectories. © 2012 Springer Science+Business Media B.V.

Feng X.,DFH Satellite Co. | Yang R.,Central University of Finance and Economics
Chinese Control Conference, CCC | Year: 2016

Industry-University-Research (IUR) cooperative innovation has been regarded as the frontier innovation mode to promote the major innovations of knowledge and technology. It has been the general consensus of small satellite enterprises, universities and scientific research institutes that the superiority of IUR cooperative innovation should be further developed and the level of technical service of small satellites should be further enhanced to promote the innovation and development of the small satellite industry. In this paper, based on the study of the IUR cooperative innovation system, we analyze the concept and connotation of IUR cooperative innovation, present the deficiencies in the current research, put forward the management and control method, design the path of cooperative innovation, and provide the strategy and suggestion. © 2016 TCCT.

Wang S.,DFH Satellite Co. | Zheng C.,CAS Institute of Software
IEEE Transactions on Aerospace and Electronic Systems | Year: 2012

A hierarchical evolutionary trajectory planner (HETP) for spacecraft formation reconfiguration is presented. Two levels are included in HETP. The high-level planner performs global planning which includes configuration optimization and collision avoidance between spacecraft. The low-level planners design multiple optimal or near optimal trajectories which are separated one from another for each spacecraft by parameterizing the controls in terms of Chebyshev polynomials. Based on the attributes of the system dynamics, a flexible scheme is used to select final trajectories and to avoid collisions. Our approach scales well with the number of spacecraft by planning trajectories for each spacecraft in parallel. The high level and the low level can coevolve, and multiple trajectories can be generated simultaneously as alternatives. The control precision constraints which could reduce control errors are also taken into account. The experiments described here demonstrate the efficiency of the proposed algorithm. © 2006 IEEE.

Hou B.,Xidian University | Yang W.,Xidian University | Wang S.,Xidian University | Hou X.,DFH Satellite Co.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2013

This paper proposes a novel Synthetic Aperture Radar (SAR) image ship detection method based on human visual attention mechanism. Firstly, we obtain water segmentation image by combining the bottom-up and the top-down visual attention mechanisms. Secondly, we detect ship targets based on bottom-up the visual attention mechanism. The interested regions are extracted by measuring the visual conspicuity of each water regions. Then, the ships targets are detected in the interested regions by the k-means clustering algorithm. Finally, real SAR image is used to test our algorithm. Besides, we analysis the ship detection results using different band. The experiment results indicate that our algorithm can effectively detect ship targets from SAR images and C-band is superior to L-band in SAR image ship detection. © 2013 IEEE.

Fan D.,DFH Satellite Co.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

The B3M-FTS instrument, inherited from ACE-FTS and PARIS, is built by Canadian ABB and Beijing Vision Sky Aerospace Co., Ltd. The B3M is a complete stand-alone spectrometer designed to operate from the ground in moderate environment. It can acquire atmospheric spectra with the Sun as back illumination. This instrument is an adapted version of the classical Michelson interferometer using an optimized optical layout, and it is a high-resolution infrared Fourier transform spectrometer operating in the 750 to 4100cm -1 spectral range. In this paper, the instrument concept of a compact, portable, high-resolution Fourier transform spectrometer is introduced. Some test results of the instrument such as ILS and SNR are presented, and the spectral resolution of 0.028cm-1 @ 750cm-1 and SNR over 100:1 are achieved. Sample atmospheric absorption spectra and corresponding retrieval results measured by the FTS are given. The B3M-FTS, with its high performance, provides the capability to monitor the atmospheric composition changes by measuring the atmospheric absorption spectra of solar radiance. Lots of measurements have been acquired at the Olympics atmospheric observation super-station. Up to now, the VMRs of near 10 trace gases have been retrieved. The success of atmospheric composition profile retrieval using the FTS measurements makes the further application of FTS type payload possible in China.

Han X.,DFH Satellite Co.
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2014

Agile satellite can point to any interested place very deftly and fast, improving observe range and time efficiency of mission greatly. Most agile satellite take pictures either along satellite track or parallel with satellite track. Imaging parameter and imaging quality of change time delay and integration charge coupled devices (TDICCD) during dynamic imaging process are analysed, error effects on image quality are given, and simulation result of main parameters change is acquired, in the end satellite control method is proposed.

Wang X.,DFH Satellite Co.
19th International Congress on Sound and Vibration 2012, ICSV 2012 | Year: 2012

A new approach for updating the finite element model of a satellite structure using frequency response obtained in the vibration test is presented in this paper. The algorithm uses a mathematical optimization strategy to minimize deviations between measured and analytical frequency response. The destination of optimization is the frequency and amplitude of the peaks on the spectrum in three vibrating direction. The variables are Young's Modulus of composite plate and viscous damping of all model frequency in analysis frequency rang. The strategy was successfully implemented using LMS Virtual lab software. The results demonstrate the precision of the updating model is enough for satellite dynamic simulation.

Huang Q.-D.,DFH Satellite Co. | Yang F.,DFH Satellite Co. | Zhao J.,DFH Satellite Co.
Guangxue Jingmi Gongcheng/Optics and Precision Engineering | Year: 2012

According to the principle of push-broom imaging of a linear array Time Delay Integration(TDI) CCD, the image motion in dynamic imaging of a agile satellite is analyzed in three-axis attitude maneuvering. As the changed continuously attitude points to the earth can change the spatial orientation and result in a changed image motion velocity, the image quality and image resolution will be deteriorated. To decrease the influence of attitude change on image quality, this article uses the coordinate transformation to acquire the mathematical expression of the image motion velocity in dynamic imaging, and obtains the variety of the image motion velocity in simulation analysis to quantify the magnitude of the integration time. Numerical simulation shows that the current level of space camera can achieve the max angular velocity limit dynamic push-broom imaging of 0.5(°)/s on an orbit height of 700 km. When the attitude maneuvering angular velocity is greater than 0.5(°)/s , it needs to design a high level camera because the exposure time is shorter and shorter. Based on the above conclusion, it suggests that the magnitude of integration time for TDI CCD TDI) should be quantified for dynamic imaging at different angle speeds, and only in this way can the push-broom dynamic imaging be implemented in three-axis attitude maneuvering.

Xu M.,DFH Satellite Co.
Lixue Xuebao/Chinese Journal of Theoretical and Applied Mechanics | Year: 2010

The paper deals with the occurrence conditions and trajectory constructions for low-energy transfers in the cislunar space, from the views of libration point theories and nonlinear dynamical techniques. The classical concept of "libration" is unavailable for spatial bicircular model (SBCM) because of the time-dependent perturbations. So the equivalent equilibrium is defined according to the geometry of instantaneous Hill's boundary, i.e., LL1 or LL2 The altitudes of periapsis and eccentricities of all the lunar capture trajectories are presented via the Poincare map, and the minimum energy to capture on the lunar surface is deduced which is quite different from ones obtained in circular restricted three-body problem (CR3BP) and Hill Models. The asymptotical behaviors of invariant manifolds flown from libration point or Halo orbit are destroyed by SBCM: the durations flown in and out of the libration point or Halo orbit have shifted from infinite to finite, and the directions have changed from reversible to nonreversing. The minimum energy cislunar transfer is acquired by the trajectory transiting LL1 point, and the (M,N)- loopy transiting trajectories are attained by transiting LL1-Halo orbits. Similarly, the minimum energy of weak stability boundary (WSB) transfer is induced by the trajectory transiting LL2 point, and the earth's escape and lunar capture windows for WSB transfers are yielded by transiting LL2-Halo orbits. All three transfer manners, as low-thrust, impulse and WSB, are applied to the transfer from Earth to Moon and the insertion of the distant retrograde orbit (DRO).

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