GNSS弱信号两级快速傅里叶变换捕获方法

高动态弱信号条件下,为了提高捕获过程实现的灵活性,提出了两级快速傅里叶变换(FFT)多普勒频率捕获方法,第一级FFT使用较短的相干积分时间将多普勒频率搜索范围划分为多个粗分格,第二级FFT在每一个分格内对多普勒频率进行更精细的搜索.采用文章提出的捕获方法,可以降低FFT点数,简化实现复杂度;另一方面,计算第一级FFT时可通过流水线操作提高资源利用率.为了验证所提方法的正确性,仿真实现了两级FFT捕获方法.结果表明,两级FFT方法能在高动态弱信号条件下正确捕获多普勒频率.     

一种地标点修正的高精度双目视觉导航方法

自主导航技术是无人机、智能机器人以及智能车辆等技术领域中的一项关键技术。为了克服传统视觉导航方法存在的不足,以摄像机自运动估计为理论基础,提出了一种使用地标点修正的高精度双目视觉导航方法。该方法从连续图像序列的帧间变化中提取摄像机自运动信息,再通过速度、角速度积分求得载体的位置姿态等参数。同时,通过引入地标点提供的绝对定位信息,进一步提高了长时间导航的精度。将地标点绝对定位与双目视觉相对定位相结合,并对双目视觉量测噪声建模和解相关,抑制了单纯使用双目视觉长时间导航时误差的积累发散。仿真结果表明此方法具有精度高、自主性强、导航信息完备等优点。     

分时段实时观测脉冲星的单探测器导航方法

传统的X射线脉冲星导航系统需要同时观测3~4颗脉冲星,有效载荷的质量和功耗极大。针对航天器环地飞行中受地球遮挡、探测器可探测范围等因素影响,导致脉冲星并非所有时刻均可见的现象,提出了单探测器分时段实时观测脉冲星的导航方法。根据航天器的实际飞行情况,系统分析探测器在不同探测范围下对脉冲星实时的可见性状况,从每时段的可见星中选取单星进行导航。仿真表明,该方法可大大提高单探测器的导航性能,导航位置误差达到337m,同时有效地减小了导航系统的重量,为X射线脉冲星导航的工程实现提供了参考依据。     

四种卡尔曼滤波器在仅视线测量相对导航中的性能比较

针对航天器交会时在仅有视线测量条件下的相对导航问题,比较了扩展卡尔曼滤波（extended Kalman filter,EKF）、无迹卡尔曼滤波（unscented Kalman filter,UKF）及平方根形式的卡尔曼滤波（square-root extended Kalman filter,SREKF以及square-root unscented Kalman filter,SRUKF）在这一导航问题中的性能.介绍了仅有视线测量条件下相对导航的特点以及上述4种卡尔曼滤波算法;建立了追踪航天器和目标航天器间相对动力学方程以及基于仅视线测量相对导航时的量测方程;结合3种典型的相对运动形式进行了数值仿真.仿真结果表明：在仅视线测量相对导航中,4种算法的精度处于同一量级;UKF估计相对距离的精度稍优于EKF;SREKF和SRUKF估计相对距离的精度稍优于EKF和UKF.     

An innovative high accuracy autonomous navigation method for the Mars rovers

Autonomous navigation is an important function for a Mars rover to fulfill missions successfully. It is a critical technique to overcome the limitations of ground tracking and control traditionally used. This paper proposes an innovative method based on SINS (Strapdown Inertial Navigation System) with the aid of star sensors to accurately determine the rover?s position and attitude. This method consists of two parts: the initial alignment and navigation. The alignment consists of a coarse position and attitude initial alignment approach and fine initial alignment approach. The coarse one is used to determine approximate position and attitude for the rover. This is followed by fine alignment to tune the approximate solution to accurate one. Upon the completion of initial alignment, the system can be used to provide real-time navigation solutions for the rover. An autonomous navigation algorithm is proposed to estimate and compensate the accumulated errors of SINS in real time. High accuracy attitude information from star sensor is used to correct errors in SINS. Simulation results demonstrate that the proposed methods can achieve a high precision autonomous navigation for Mars rovers.     

Earth observation with MEO transmitters and UAS receivers: A potential utilization of Galileo constellation

Remote sensing application of Galileo upcoming constellation in the field of civil security is preliminarily analyzed, defining low resolution (25 m) and high resolution (7.5 m) working modes for a bistatic Synthetic Aperture Radar system utilizing Galileo satellites as transmitters and Unmanned Aerial Systems as receivers. Simulations offshore Somali coast and in a South Mediterranean Sea region showed that both low and high resolution acquisitions are feasible. For the low resolution mode a probability of successful image formation no matter the azimuth position of the receiving UAS has been estimated at nearly 100%. Whereas, for the high resolution mode it decreases to about 90%, which, if deemed unsatisfactory for the application, leads to the need for UAS to adapt its route to the actual Galileo satellite coverage.     

A six-degree-of-freedom hardware-in-the-loop simulator for small spacecraft

This paper presents a novel six degree of freedom, ground-based experimental testbed, designed for testing new guidance, navigation, and control algorithms for the relative motion of nano-satellites. The development of innovative guidance, navigation and control methodologies is a necessary step in the advance of autonomous spacecraft. The testbed allows for testing these algorithms in a one-g laboratory environment. The system stands out among the existing experimental platforms because all degrees of freedom of motion are controlled via real thrusters, as it would occur on orbit, with no use of simulated dynamics and servo actuators. The hardware and software components of the testbed are detailed in the paper, as is the motion tracking system used to perform its navigation. A Lyapunov-based strategy for closed loop control is used in hardware-in-the loop experiments to successfully demonstrate the full six-degree-of-freedom system׳s capabilities. In particular, the test case shows a two-phase regulation experiment, commanding both position and attitude to reach specified final state vectors.     

采用连续旋转检偏器的天空偏振光探测装置设计与实现

为了实现对运动目标与天空散射光的偏振分布模式进行快速、有效的探测,根据连续旋转检偏器光强度透射的数学模型,利用光电传感器的积分特性,设计并构建了采用连续旋转检偏器的偏振成像探测装置。测试结果表明,该装置对偏振光的角度的测量精度优于0.069°（3σ）,偏振度的测量精度优于0.12%（3σ）。一幅偏振图像的探测时间达到0.7s。在偏振度低于4%的情况下,仍可以探测到有规律的偏振分布模式,其抵抗恶劣天气的性能优于现有的偏振导航探测装置。     

导航星座星间链路信号捕获搜索策略研究

针对导航星座星间链路信号动态范围大、捕获性能要求高之间的矛盾,利用星历信息辅助信号捕获。在此基础上,分析了信号捕获串行搜索、码并行搜索和频率并行搜索的计算代价,给出了不同信号体制和星历误差下各搜索策略对应的运算量表达式,并结合典型的应用场景进行了算例分析。分析结果表明星间信号捕获在星历误差较小时采用串行搜索策略具有最少的计算量,在星历误差较大时采用码并行搜索策略计算量最少。     

国外自主交会测量敏感器技术发展趋势

基于空间任务的高可靠性要求,在传统传感器通过技术改进等方式提升性能的同时,新型探测传感器逐渐进入人们的视野。结合国外自主交会任务,通过介绍自主交会敏感器的发展历程,分析了未来交会对接敏感器的发展方向。