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This work is concerned with the minimum-fuel power descent to a prescribed landing site on a irregular-shaped asteroid. With the small and complicated gravitational field taken into account, we present the equations of spacecraft motion in the asteroid-fixed Cartesian coordinate frame. To solve the minimum-fuel problem, we construct a performance index which links the minimum-fuel problem with the minimum-energy problem by a homotopy parameter. Based on the Pontryagin's maximum principle and the numerical continuation method, we transform the optimal control problem into a series of two-point boundary-value problems. we solve the optimal problems by starting from a solution of the energy-optimal problem, which is obtained by the using of the pseudo-spectral method. We reduce the homotopy parameter by following a certain series and take the solution obtained in the current iteration as an initial guess for that in the next one. Finally, we obtain a minimum-fuel power descent trajectory for soft landing on a irregular-shaped asteroid with easy convergence and high precision.

Normal methods of spatial filtering methods may change the coherent characteristic of the target, which reduces the effect of accumulation in coherent systems despite the improvement of signal-to-interference and noise ratio (SINR). To avoid the amplitude and phase distortion introduced by the filters, null phase-shift spatial filter (NPSF) is proposed in this paper. NPSF can suppress the interference while keeping the original information of the target signal. However, the performance of NPSF will be influenced by the estimation error of the target's spatial parameter. To solve this problem, an improved NPSF, narrow-band null phase-shift spatial filter (NNPSF), is proposed. The method to construct the weight vector of NNPSF is introduced. Theoretical analysis and simulation results demonstrate that the NNPSF is a valid spatial filtering technology. With reducing the accuracy of estimation, NNPSF is more suitable and robust in practical systems.

Radio frequency interference (RFI) cancellation is a main problem to be solved in High Frequency Surface Wave Radar (HFSWR) system. To minimize the impact of RFI, a number of signal processing techniques, such as adaptive beamforming and polarization filtering, have been developed. However, the performance of these conventional methods degrades a lot when the target and interferences have similar parameters within the corresponding processing domains. According to the fact that target usually differs with RFI in more than one domain, it will be beneficial to suppress interferences by constructing a joint filter that includes multiple domains like frequency, space and polarization, etc. In this paper, a multi-domain collaborative filer (MDCF) based on oblique projection is proposed. The construction of oblique projection spatial-frequency-polarization filter (OPSFPF), oblique projection spatial-polarization filter (OPSPF) and oblique projection spatial filter (OPSF) is introduced. Theoretical analysis and simulation results demonstrate that the multi-domain collaborative filter is feasible and performs better when more processing domains are included. Such filter could take full advantage of the differences between the target and interference and, consequently improves the effect of RFI suppression in HFSWR.

Interference suppression is a main problem to be solved in both radar and wireless communication systems. To minimize the impact of interference, a number of signal processing techniques, such as adaptive beamforming and frequency filtering, have been developed. However, the performance of these conventional methods degrades a lot when the target and interferences have similar parameters. In this paper, a collaborative spatial-frequency filer (CSFF) is proposed. Such CSFF is constructed with oblique projection operators to suppress the interferences and extract the target signals while keeping its amplitude and phase unchanged. Theoretical analysis and simulation results demonstrate that the CSFF performs better than spatial filtering. Moreover, there is no requirement to increase the number of antenna elements, which increases the application scope of CSFF.

Multi-domain signal filtering is a perspective technology in both radar and wireless communication systems. To obtain extra benefits compared with conventional methods, a novel joint space-frequency-polarization filter (SFPF) based on vector sensitive array (VSA) is presented in this paper. An orthogonal dual-polarization sensitive array (DPSA) and time delay units are applied to offer frequency, polarization and spatial information. Then the SFPF is constructed with oblique projection operators to suppress the interferences and extract the target signals without introducing any phase amplitude distortion. Performance analysis and simulation are undertaken. It can be concluded that the signal can be recovered more effectively compared with a space-polarization filter (SPF), since more information in multiple domains are utilized in the proposed SFPF.

Two aquatic plants, Zizania latifolia and Sagittaria sagittifolia, were used to study the variation of physiological responses and the water qualities under mild, moderate and weighty eutrophic water in plastic pot scale experiments. The physiological characteristics of both plants were investigated, which included contents of leaf malondialdehyde (MDA) and proline, membrane permeability (MP), and activities of catalase (CAT) and peroxides (POD). The water qualities were analyzed correspondingly. The results showed remarkable effects of different degree of eutrophic water on physiological characteristics of the plants. Compared with mild eutrophic water, increasing degree of eutrophication significantly increased the contents of MDA and MP, decreased POD activity, especially in Zizania latifolia. The proline content increased more evidently in Sagittaria sagittifolia than that in Zizania latifolia, and the CAT activity showed no significant change in both plants. Removals of TN, NH4+-N and TP increased with increasing degree of eutrophication, reaching the highest value 96.5%, 97.2% and 92.7%, respectively, in Sagittaria sagittifolia under weighty eutrophic water. However, Zizania latifolia achieved its highest remove efficiency of TN and NH4+-N under moderate eutrophic water and that of TP under weighty eutrophic water. Besides, TN, NH4+-N and TP removals were higher in Zizania latifolia than those in Sagittaria sagittifolia under mild eutrophic water. These results suggested that Zizania latifolia and Sagittaria sagittifolia were the recommended aquatic plants in phytoremediation of mild and weighty eutrophicated water, respectively.

The Mode of Grid Urban Management is proposed as a modern management mode based on the rapid construction and development of digital city. It brings forth the new challenges and opportunities to urban management. Through investigation on the application of the model in practice, it indicated that there are problems existing in popularization application, technology, management processes and other aspects. To solve these problems, a new mode is proposed. The innovation of technology method and management system is described.

According to the similarity of the equations of motion between around the asteroid and in the circular restricted three-body problem (CRTBP), equilibrium theory in CRTBP are introduced to the asteroid's satellite orbital dynamics in this paper. Using this theory, we calculate the position of equilibrium point in body fixed frame and analyze the stability of these points. By choosing a suitable initial state, we eliminate the unbounded modal effects on the orbits, which have been the Halo-orbit and Lassjous-orbit around the asteroid's equilibrium point. A small force controller based on linear feedback control law is also designed to keep the spacecraft's orbit round the norm orbit.

Autonomous hazard avoidance is a key technology for planetary pinpoint landing. In this paper, passive image based hazard detection and landing point selecting methods are presented. Craters on planetary surface are detected by edge detection, edge matching and geometry fitting. Rocks are another familiar terrain feature on planetary surface and it are detected by variance map segmentation. For landing point selecting, fuzzy rules are researched to reasoning the hazard detection result and any other landing constraints, the output of fuzzy reasoning engine is fed into a landing point searching algorithm to return the best landing point. Simulation results will be given to show that the proposed hazard detection and landing point selecting methods are simple and effective.

An autonomous large angular slew of deep spacecraft is studied, which is a key factor in the development of future spacecraft autonomous platform. The objective is to minimize some performance index and rotate the spacecraft to a desired attitude while subject to dynamic and geometric constraints. The investigated literature did not handle this problem very well either in performance or constraints consideration. In this paper, we propose a new approach based on pseudospectral method for autonomous attitude control, not only satisfies the nonconvex constraints but also optimizes performance. We approach this by two stages: (1) get the feasible path using RRT in Rodrigues space and (2) transform the optimal control problem to a nonlinear planning problem (NLP) utilizing Pseudospectral method. Finally, attitude path is obtained by solving the NLP with an initial value from (1). Simulation example is presented and discussed.

For understanding the regional response to climate change, we explain the characteristics and change of landscape patterns at Huihe National Nature Reserve, Hulun Buir, Inner Mongolia, China. By the visual interpretation method and three-period TM images, we generated landscape classification information with the support of the Arcmap software platform and in combination with ground investigation. The results are as follows: (1) There are four types of landscape in the nature reserve: steppe, wetland, sand and man-made landscapes. (2) The area of the steppe landscape has expanded, and the wetland landscape is gradually diminishing. The area of the sand landscape has remained stable. (3) According to landscape level analysis, there was obvious degradation of landscape in the nature reserve from 1995 to 2006. The change of landscape pattern is influenced mainly by climate change, and human disturbance plays a very important role. Environmental protection could slow the rate of degradation of the ecosystem.

The problem of autonomous robust attitude control for flexible spacecraft is considered. A novel autonomous design approach is introduced based on the normal matrix design theory of the multivariable control system, and the parameters of controller are optimized by genetic algorithm (GA). The robustness of proposed approach is independent of the parameters of the spacecraft attitude dynamics, including the inertia tensor of the spacecraft and the vibration of the flexible appendages. Under a class of feedback perturbation, named inverse additive perturbation, the robust stabilization criterion in normal matrix description is obtained based on the structure and numerical properties of spacecraft attitude dynamics, and this criterion converts the robustness requirement into a constrain to the control designing parameters. Applying this criterion into GA, the chromosome is shortened, and therefore the running of GA is effectively promoted. A design example shows the efficiency of the algorithm.

Buckwheat (Fagopyrum esculentum Moench) cultivars differred in aluminum (Al) resistance were selected to investigate the possible role of cell wall pectin content and its binding capacity to Al in Al resistance. Al contents in root apices of Al-resistant cultivars were lower than those in Al-sensitive cultivars, suggesting the Al exclusion mechanism was acting in Al-resistant buckwheat cultivars. We observed that pectin contents in Al-resistant cv. Jiangxi were significantly lower than those in other three cultivars, irrespective of with or without Al treatment. Further investigation was conducted with the most Al resistant cv. Jiangxi and Al sensitive cv. Yq3h. Pectin and Al contents were higher in Yq3h than those in Jiangxi from 0-5 and 5-10 mm root sections. After 6-h exposure to 50 muM Al, 48% and 60% of the Al were retained in the cell wall for Jiangxi and Yq3h, respectively. Consequently, more Al was removed by 30-min citrate desorption in Yq3h. The kinetics study with cell wall extracted from 0-5 mm root section showed that the total amount of Al adsorbed was higher and the desorption rate was lower in Yq3h than those in Jiangxi, suggesting that cell walls in Yq3h could bind more Al and the bound Al was retained more tightly compared with Jiangxi. From all these results, we concluded that the differences in cell wall pectin content and its binding capacity to Al contribute to the genotypic differences in Al resistance in buckwheat.

In researching the problems of stochastic system, we usually use the linearization method, the approximate decoupling method, and the truncated method etc. to simplify the system model. The traditional criterion is the ratio of the simplification part and the initial model. If the ratio is small enough or the model errors can be regarded as noise, we think the simplification method is reasonable. The shortage of the criterion is that it hasn't a very definite value or bound, and it can't combine the performance of the whole system. Therefore we propose a new criterion which calculates the errors and error covariance matrix of the state between the initial system and the simplified system based on Kalman filter. The new criterion judges the trace of the matrix and its convergence property. Because it uses the state equation and the measurement equation of the stochastic system, it is more suitable for the whole system performance.

In lunar exploration mission, it is very critical to determine the attitude and position of the lunar rover with a high degree of accuracy both for exploration achievement of scientific goals and for safe navigation. In this paper we address the problem of determining the attitude and position on the moon surface and provide a celestial navigation algorithm for lunar rover autonomous navigation. A CCD sun sensor is used to provide lunar rovers a vector observation by sun imaging and sun vector is computed in the lunar navigation frame using ephemeris data. A CCD earth sensor is designed to provide another vector observation, the image processing and earth centroid computation based on nonlinear least square is described. Finally, the attitude estimate using q-method and the position propagation is presented, simulation experiments are conducted, that corroborate the presented algorithm.

In order to explore the moon more efficiently, it is very important to endow lunar rovers with increased autonomy both for exploration achievement of scientific goals and for safe navigation. In this paper, autonomous navigation techniques for lunar rovers are discussed, and an autonomous navigation scheme is presented. First, algorithm and technique of initial position determination of lunar rovers are introduced. Then, matched-features set is build by multi steps of image processing such as feature detection, feature tracking and feature matching. Based on the analysis of the image processing error, a two-stage estimation algorithm is used to estimate the motion, robust linear motion estimation is executed to estimate the motion initially and to reject the outliers, and Levenberg-Marquardt nonlinear estimation is used to estimate the motion precisely. The sun sensor is used to update the rover's heading periodically for long range navigation. Next, a weighted ZSSD algorithm is presented to estimate the image disparities by analyzing the traditional ZSSD. Finally, a virtual simulation system is constructed using the development tool of Open Inventor, this simulation system can provide stereo images for simulations of stereo vision and motion estimation techniques, simulation results are provided and future research work is addressed in the end.