Improving regional ionospheric TEC mapping based on RBF interpolation

Radial basis function (RBF) interpolation with multi-quadric is developed to perform ionospheric total electron content (TEC) mapping for the Chinese region between 15°N ~ 40°N and 100°E ~ 125°E. TEC measurements from the Centre for Orbit Determination in Europe (CODE) covering the solar maximum year 2011 are used to investigate the performance of the proposed RBF interpolation method. The differences between the RBF interpolated TEC and the CODE TEC are within 0.5 TECU and the root mean square error (RMSE) is very small when 49 data points are used. The maximum difference is ~5 TECU and the error is less than 1 TECU with 25 samples. Our study suggests that a random distribution of measurement points gives smaller RMSEs than a homogenous distribution when the number of sample points is low. The study indicates that RBF interpolation offers a powerful and reliable tool for ionospheric TEC mapping.     

In-orbit operation and performance of the CubeSat Soft X-ray polarimeter PolarLight

PolarLight is a compact soft X-ray polarimeter onboard a CubeSat, which was launched into a low-Earth orbit on October 29, 2018. In March 2019, PolarLight started full operation, and since then, regular observations with the Crab nebula, Sco X-1, and background regions have been conducted. Here we report the operation, calibration, and performance of PolarLight in the orbit. Based on these, we discuss how one can run a low-cost, shared CubeSat for space astronomy, and how CubeSats can play a role in modern space astronomy for technical demonstration, science observations, and student training.     

Analysis of the solar sail deformation based on the point cloud method

The deformation of the solar-sail membrane is an important factor for causing inaccuracies in the solar-sail missions. This paper describes the solar sail under deformation by using a new modelling technique based on point cloud and triangular mesh generation. Two types of deformation, stemming from wrinkling and billowing, are modelled. The changes in the solar radiation pressure force and the moment caused by deformation are calculated and compared to the ideal non-deformed case. The heliocentric spiral trajectory and the orbital angular momentum reversal trajectory are taken as examples to quantify the influence of the deformation from an orbit point of view. Additionally, point cloud simplification, based on the normal vector and bounding box, is utilized to simplify the original deformed-sail model. It involves a reasonable reduction and renewal of the points in the model considering the variation of surface curvature. The simplification and its modelling accuracy are numerically investigated as well as computational efficiency.     

Robust Design of Supercritical Wing Aerodynamic Optimization Considering Fuselage Interfering

Robust optimization approach for aerodynamic design has been developed and applied to supercritical wing aerodynamic design. The aerodynamic robust optimization design system consists of genetic optimization algorithm, improved back propagation (BP) neural network and deformation grid technology. In this article, the BP neural network has been improved in two major aspects to enhance the training speed and precision. Uniformity sampling is adopted to generate samples which will be used to establish surrogate model. The testing results show that the prediction precision of the improved BP neural network is reliable. On the assumption that the law of Mach number obeys normal distribution, supercritical wing configuration considering fuselage interfering of a certain aerobus has been taken as a typical example, and five design sections and twist angles have been optimized. The results show that the optimized wing, which considers robust design, has better aerodynamic characteristics. What's more, the intensity of shock wave has been reduced.     

Trajectory Planning Algorithm Based on Quaternion for 6-DOF Aircraft Wing Automatic Position and Pose Adjustment Method

 A 6-degree of freedom (6-DOF) aircraft wing position and pose automatic adjustment method is presented to improve ARJ21 wing-fuselage connection precision and efficiency. Wing position and pose are adjusted by three pillars which are driven by six high-precision servo motors. During the adjustment process, wing is tracked and positioned by laser tracker. Wing initial posi-tion and pose are calibrated by using the measurement coordinates of assembly reference points. Wing target position and pose are calculated according to wing initial, fuselage position and pose, and relative position and pose requirements between wing and fuselage for the connection. Combining Newton-Euler method with quaternion position and pose analyzing method, the inverse kinematics of servo motors, together with the adjustment system dynamics is obtained. Wing quintic polynomial trajec-tory planning algorithm based on quaternion is proposed; the initial, target position and pose need to be solved and the inter-mediate moving path is uncertain. Simulation results show that the adjustment method has good dynamic characteristics and satisfies engineering requirements. Preliminary engineering application indicates that ARJ21 wing adjustment efficiency and precision are improved by using the proposed method.     

Nonlinear dynamics and station-keeping control of a rotating tethered satellite system in halo orbits

The dynamics of a rotating tethered satellite system （TSS） in the vicinity of libration points are highly nonlinear and inherently unstable. In order to fulfill the station-keep control of the rotating TSS along halo orbits, a nonlinear output tracking control scheme based on the θ- D technique is proposed. Compared with the popular time-variant linear quadratic regulator （LQR） controller, this approach overcomes some limitations such as on-line computations of the algebraic Riccati equation. Besides, the obtained nonlinear suboptimal controller is in a closed form and easy to implement. Numerical simulations show that the TTS trajectories track the periodic reference orbit with low energy consumption in the presence of both tether and initial injection errors. The axis of rotation can keep pointing to an inertial specific object to fulfill an observation mission. In addition, the thrusts required by the controller are in an acceptable range and can be implemented through some low-thrust propulsion devices.     

某型机进气道利用真空夹具加工的方法

真空夹具是飞机制造工艺中的一项特殊的工艺装备。它是利用真空吸附力来夹紧工件,特点是吸力均匀,单位面积上的压力不超过一个大气压。十分适用于加工大而薄、刚性差的飞机部分零件,如进气道、机翼壁板、中翼大梁、蜂窝块等。     

发动机喘振裕度自适应控制

本文研究飞行 /推进系统一体化控制中的发动机喘振裕度自适应控制。通过一定的控制作用 ,使发动机在所有飞行条件和工况下都保持一定的喘振裕度 ,从而充分发挥发动机的潜力。将发动机大偏差模型、进气道及飞机模型综合在一起 ,构成飞机 /推进系统一体化数学模型 ,以进行发动机自适应控制的仿真。计算机仿真表明 ,发动机自适应控制具有很好的性能效益 ,例如在飞行高度 H=10公里 ,飞机由 Ma=0 .65加速到 Ma=0 .90 ,在采用自适应喘振裕度控制后 ,双发动机推力提高 16 ,飞机加速时间缩短 2 3 ,大大提高了飞机性能。     

Seasonal variability of GPS-VTEC and model during low solar activity period (2006–2007) near the equatorial ionization anomaly crest location in Chinese zone

Variability of vertical TEC recorded at Fuzhou (26.1°N, 119.3°E, geomagnetic latitude 14.4°N), Xiamen (24.5°N, 118.1°E, geomagnetic latitude 13.2°N), Nanning (22.8°N, 108.3°E, geomagnetic latitude 11.4°N), China, during the low solar activity in 2006–2007 have been analyzed and discussed. Remarkable seasonal anomaly was found over three stations with the highest value during spring and the lowest value during summer. The relative standard deviation of VTEC is over 20% all the time, with steady and smooth variation during daytime while it has a large fluctuation during nighttime. The biggest correlation coefficient was found in the VTEC-sunspot pair with a value of over 0.5. It seems that solar activity has a better correlation ship than geomagnetic activity with the variation of VTEC and better correlations are found with more long-term data when comparing our previous study. The results of comparing observation with model prediction in three sites reveal again that the SPIM model overestimates the measured VTEC in the low latitude area.