Working and walking on small asteroids with circumferential ropes

The low gravity of a small asteroid would present a challenge for an astronaut attempting to work on its surface. Extravehicular activities (EVAs) of the sophistication of the Apollo Moon missions are not likely to be possible if astronauts attempt to walk freely on the asteroid, hover above its surface, or anchor locally into the regolith. Manipulating large rocks, drilling, and excavating at multiple locations is a high priority science objective, but would be difficult without a hold-down mechanism. If the asteroid has even a small rotation rate, maneuvering precisely over its surface could be cumbersome. A plausible means of conducting complex EVAs is to tie ropes entirely around the asteroid, under which the astronaut is pushed downward onto the asteroid surface by the tension in the rope. The downward force provides an artificial gravity that permits the astronaut to drill, excavate, hammer, and carefully document materials on the surface without the worry of being thrown from the asteroid. An astronaut could also use the ropes as handholds or guides to maneuver freely over the surface.     

基于目标分解和SVM的极化SAR图像分类方法

极化SAR图像分类是新体制雷达应用研究中的一类基础前沿问题。文章提出了一种基于目标分解及支持矢量机(Support Vector Machine,SVM)的极化SAR图像分类方法。首先根据Cloude分解和Freeman分解两种方法提取极化SAR图像的多类散射特征,从而构造出图像各像素的特征向量。接着利用样本区域像素的特征向量对SVM进行训练,获得经训练的SVM。最后,以各待分类像素的特征向量为输入,利用经训练的SVM即可完成极化SAR图像的分类。对两幅AIRSAR实测极化SAR图像数据分类的结果表明,文章方法能够有效地利用多类散射特征的互补信息,具有较高的分类精度。     

电子信息系统复杂电磁环境效应研究初探

电子信息系统复杂电磁环境效应是指复杂电磁环境对电子信息系统的影响,是一个涉及社会和国防多个应用领域的重要问题.从电子信息系统复杂电磁环境效应概念出发,首先与电磁环境效应概念进行了比较分析,继而将研究分解为复杂电磁环境特性与模拟、复杂电磁环境综合效应机理和电子信息系统效能评估理论三个方面,最后给出了这三个方面的具体研究思路,并探讨了开展研究的一般性方法.     

A closed-form solution for moving source localization using LBI changing rate of phase difference only

Due to the deficiencies in the conventional multiple-receiver localization systems based on direction of arrival(DOA) such as system complexity of interferometer or array and amplitude/phase unbalance between multiple receiving channels and constraint on antenna configuration,a new radiated source localization method using the changing rate of phase difference(CRPD)measured by a long baseline interferometer(LBI) only is studied. To solve the strictly nonlinear problem, a two-stage closed-form solution is proposed. In the first stage, the DOA and its changing rate are estimated from the CRPD of each observer by the pseudolinear least square(PLS) method,and then in the second stage, the source position and velocity are found by another PLS minimization. The bias of the algorithm caused by the correlation between the measurement matrix and the noise in the second stage is analyzed. To reduce this bias, an instrumental variable(IV) method is derived. A weighted IV estimator is given in order to reduce the estimation variance. The proposed method does not need any initial guess and the computation is small. The Cramer–Rao lower bound(CRLB) and mean square error(MSE) are also analyzed. Simulation results show that the proposed method can be close to the CRLB with moderate Gaussian measurement noise.     

DOA estimation and mutual coupling calibration with the SAGE algorithm

In this paper, a novel algorithm is presented for direction of arrival（DOA） estimation and array self-calibration in the presence of unknown mutual coupling. In order to highlight the relationship between the array output and mutual coupling coefficients, we present a novel model of the array output with the unknown mutual coupling coefficients. Based on this model, we use the space alternating generalized expectation-maximization（SAGE） algorithm to jointly estimate the DOA parameters and the mutual coupling coefficients. Unlike many existing counterparts, our method requires neither calibration sources nor initial calibration information. At the same time,our proposed method inherits the characteristics of good convergence and high estimation precision of the SAGE algorithm. By numerical experiments we demonstrate that our proposed method outperforms the existing method for DOA estimation and mutual coupling calibration.     

Biomedical problems of EVA support during manned space flight to Mars

Current projects of manned missions to Mars are aimed to their realization in the second-third decades of this century. The purpose of this paper is to determine and review the main biomedical problems, that require a first and foremost decision for safety support of extravehicular activity (EVA) carried out by crewmembers of the Mars expedition. To a number of such problems the authors of the paper attribute a creation of adequate EVA equipment intended, first, for assembly of interplanetary spacecraft on the Earth orbit, performance of maintenance operations and scientific researches on the external surface of spacecraft during interplanetary flight and, secondly, for work on the Mars surface. New generation of space suits with low weight, high mobility and acceptable risk of decompression sickness must be as a central component of EVA equipment. The program for preparation to a Mars expedition also has to include special investigations in order to design the means and methods for a reliable protection of crew against space radiation, to elaborate the approach to medical monitoring and primary medical care during autonomous space mission, to maintain good health condition of crewmembers during EVA under the Mars gravity (0.38 g) after super long-term flight in weightlessness.     

一种连续式跨声速风洞总压控制方法设计

总压是连续式跨声速风洞关键流场参数，高总压控制精度能提高试验数据的准确性，加快调节速度对缩短马赫数极曲线时间具有重要意义。针对连续式跨声速风洞试验工况多、调节手段多等特点，对连续式跨声速风洞压力调节系统及多种流场调节手段下的压力耦合特性进行分析研究，建立了连续式跨声速风洞总压控制精度和调节阀特性的对应关系，并以此设计出不同工况的阀门组合控制策略，采用分段变参数加模糊PID控制算法实现总压的闭环控制。风洞试验结果表明:在保证每条马赫数极曲线时间的同时，总压控制精度达到0.1%，控制方法能够有效满足连续式跨声速风洞总压控制要求。     

固有模态函数（IMF）积检测器——以低信噪比情况下超宽带雷达信号检测为例

首次提出了一种固有模态函数积检测器。首先通过经验模式分解（EMD）把带噪信号分解成有限个固有模态函数（IMF）。检测的基本思路是，对各个IMF分量的绝对值作逐点乘积，用于抑制噪声并凸现信号，最后进行滤波和判决。本文以UWB信号为例，数据源于UWB雷达实验系统。在低信噪比（SNR），UWB脉冲与噪声波形相似，且噪声概率密度函数（PDF）未知情况下，进行实验。结果表明，当峰峰信噪比低于5dB时，该检测器性能优于Teager能量算子（TEO）。     

分布式小卫星SAR系统GMTI模式构形优化

对分布式小卫星SAR系统地面动目标检测GMTI模式的研究目前正处于广泛探索阶段。如何评价一个分布式卫星系统的GMTI能力，编队构形对GMTI到底有怎样的影响，怎样设计编队使系统GMTI能力最强等问题是文章讨论的内容。从盲速比例的角度出发，提出对系统的GMTI功能进行衡量的定量指标，分析编队构形方式对该指标的具体影响，寻找GMTI模式下可能的编队优化方法。     

强海杂波背景下目标检测方法综述

高频地波雷达被广泛应用于海面目标的检测,而由于海杂波的分布散射具有很强的动态特性,通常情况下成为了海面目标检测的主要干扰成分.因此,在强海杂波背景下进行目标检测的关键在于如何有效抑制海杂波.从循环对消、子空间分解、模型预测以及分形特征这几方面对海杂波抑制技术进行综述、分析和总结,为后续对海面目标检测提供参考.