Vision-aided inertial navigation for pinpoint planetary landing

Autonomous and safe landing spacecraft on moon and planetary bodies is a rather difficult and risky task. Accurate relative navigation between the spacecraft and the planetary surface is essential, together with the autonomous hazard detection and avoidance. This paper describes the vision-aided inertial navigation (VAIN) scheme to meet the pinpoint landing requirement of the next generation planetary lander. Images of distinctive surface feature called feature points/landmarks are detected and tracked autonomously to improve the performance of inertial navigation. Landmark image information derived from optical navigation camera and the spacecraft state information sensed by IMU (Inertial Measurement Unit) are integrated in extended Kalman filter algorithm. The validity of the proposed navigation scheme is confirmed by computer simulation.     

Model-based spacecraft pose estimation and motion prediction using a photonic mixer device camera

Determination of relative distances and orientations, as well as motion identification is essential in rendezvous and docking and formation flying tasks. A 3D-image generated by a PMD (photonic mixer device) camera, which employs a phase shift measurement of emitted modulated light to derive distance and color information on each pixel, provides in this contribution the basis for near range motion detection and prediction. A novel algorithm based on rotation- and scale-invariant features commonly used for scan matching in high-resolution images is presented. The performance of the PMD camera and of the proposed data processing is characterized in scenarios, considering factors like relative velocities, rotation dynamics, illumination and optical properties of target surface materials, which are major effects for disturbances in this context.     

Damage tolerance of composite structures for large transport aircraft

Damage of composite materials is studied at a coupon level from both a fracture mechanics and a damage mechanics point of view. Methods developed are applied to sub-elements and sub-structures with the objective of decreasing the amount of testing needed in the certification procedures of composite structures.     

Ni基合金与γ-TiAl基合金的固态连接规律研究

通过对Ni基合金进行激光熔覆γ-TiAl基合金涂层处理,对γ-TiAl基合金进行激光表面熔凝处理,提出了一种采用激光表面改性技术和超塑扩散连接相结合的Ni基合金/γ-TiAl基合金连接新技术。研究了合金激光改性层的显微组织特征,探讨了Ni基合金/γ-TiAl基合金固态扩散连接的规律。结果表明:激光表面改性技术提高了Ni基合金/γ-TiAl基合金的连接质量,合金通过激光表面改性处理后,采用连接温度850℃、连接压力60MPa、连接时间1h的连接条件及900℃保温0.5h连接后续热处理,实现了Ni基合金/γ-TiAl基合金的连接。     

Nonlinear relative position control of precise formation flying using polynomial eigenstructure assignment

A nonlinear relative position control algorithm is designed for spacecraft precise formation flying. Taking into account the effect of J₂ gravitational perturbations and atmospheric drag, the relative motion dynamic equation of the formation flying is developed in a quasi-linear parameter-varying (QLPV) form without approximation. Base on this QLPV model, polynomial eigenstructure assignment (PEA) is applied to design the controller. The resulting PEA controller is a function of system state and parameters, and produces a closed-loop system with invariant performance over a wide range of conditions. Numerical simulation results show that the performance can fulfill precise formation flying requirements.     

水平非均匀大气条件下的抛物方程模型研究

在分析传统分步傅立叶(SSFT)和中心差分离散混合傅立叶变换(DMFT)算法的基础上,针对算法复杂度及数值稳定性问题,提出了前向-后向混合差分DMFT算法及其具体实现步骤,提高计算效率的同时解决了传统算法在复杂条件下的盲点问题.给出了算法中水平非均匀大气折射剖面及复杂条件下最大传播仰角θmax等关键参数的计算方法,并与传统模型及经典文献实验数据进行了仿真比较,验证了该算法及模型在复杂大气条件下的正确性和有效性.     

基于多层感知器神经元的空间柔性机器人位置跟踪控制

针对基体位置及姿态均不受控的自由漂浮柔性空间机器人轨迹跟踪问题,提出了一种前馈多层感知器(MLP)神经网络控制策略.建立了末端柔性的自由漂浮基机器人的耦合动力学模型,再利用MLP神经网络良好的逼近能力来自适应补偿非线性柔性臂的逆动力学模型,其误差代价函数由PID控制器提供,权重及阀值的调整采用改进的BP反传算法.最后通过仿真比较详细分析了所提方案的工作机理及对非线性强耦合系统控制的有效性.     

P70霍尔推力器新型缓冲腔磁路对预电离及放电的影响

为有效利用从P70霍尔推力器放电通道进入缓冲腔的快电子能量,考虑两个磁场特征以提高缓冲腔预电离率。一是提高磁感应强度,二是缓冲腔内从气体分配器到放电通道方向的负梯度。采用FEMM有限元磁场计算软件,在不改变推力器电离和加速通道内优化磁场特征的前提下,设计的新型缓冲腔磁路满足上述磁场特征。放电实验结果表明,在新型缓冲腔磁路下放电电流低频振荡幅值更小。新型磁路有助于延长推力器寿命,有助于电离和加速通道内电离与加速区的分离。     

舰船燃一蒸联合循环的稳态与动态特性分析

燃气-蒸汽联合循环（COGAS）是提高燃气轮机经济性有效途径之一。对舰船燃-蒸联合循环系统建立了数学与仿真模型,对其性能进行分析。由分析结果可知,在高或低工况下,燃气轮机采用燃-蒸联合循环后,其效率都显著提高。     

A self-deploying and self-stabilizing helical antenna for small satellites

Space antennas with a helical geometry are an advantageous choice for many applications, for instance if the transmission of electromagnetic waves with a circular polarization is intended, or if signals from terrestrial objects shall be received with a high angular resolution. In all these cases the desired electromagnetic properties of a helical geometry can be combined with the mechanical advantage that the antenna acts as a compression spring, provided that its core structure has the necessary high spring stiffness but can nevertheless easily be compressed. Such an antenna has been developed by DLR Institutes in Bremen and Braunschweig together with some industrial partners for a small satellite named AISat, which shall be able to pursue the position of individual ships in critical sea areas in order to improve the security of seafare trade. The development was very challenging since the antenna must expand from a stowed stack length of only 10 cm to a total length of 4 m. Only a special carbonfiber core under the conductive coating and a system of stabilizing cords led to a satisfying solution. Both the self-deployment and the self-stabilization function of this innovative antenna concept have been successfully tested and verified under zero-g-conditions in the course of a parabolic flight campaign. It could be convincingly demonstrated that the helical antenna can really achieve its desired contour in weightlessness within some seconds and maintain the required stability. Beyond the current application for the AISat satellite it is therefore quite a promising concept for future satellites.