Integrated guidance and control for solar sail station-keeping with optical degradation

Current control approaches for solar sail station-keeping on libration point orbits have not considered the degradation of the sail’s optical properties. However, significant optical degradation could lead to poor station-keeping performance or even complete failure. This paper presents an integrated guidance and control strategy to address this problem by updating the reference orbit based on in situ estimation. An exponential optical degradation model is incorporated into the solar radiation acceleration model, and an on-line reference orbit update approach is incorporated into the station-keeping, coupled with an active disturbance rejection controller. The reflection coefficient is estimated on-line and the reference orbit is updated discretely when the optical properties have degraded by a prescribed amount. This strategy provides discrete updates to the reference orbits such that the perturbation due to the optical degradation is maintained within a small range. These smaller perturbations can be dealt with by the controller’s robustness and station-keeping can be sustained for long durations even in the presence of large optical degradation.     

Timing and sex effects on the “Spatial Orientation Test”: A World War II map reading test

The present study aimed to document the psychometric properties of a recently declassified map reading test used in World War II, known as the Spatial Orientation Test (SOT), which measures mostly the ability to match map and aerial images. We also examined the influence of timing conditions and sex of the participants as correlates of performance. A total of 101 participants (41 males, 60 females) completed the SOT, along with other spatial tests and spatial affect scales (tapping spatial anxiety and confidence). Results showed a significant male advantage on this rediscovered map reading test. Additionally, timing affected overall performance but not the magnitude of sex differences. Finally, significant correlations were found between the SOT and other spatial tests and scales. The processes underlying this test and its potential for future use are discussed.     

Global characteristics of ionospheric electric fields and disturbances during the first hours of magnetic storms

The ionospheric plasma density can be significantly disturbed during magnetic storms. In the conventional scenario of ionospheric storms, the negative storm phases with plasma density decreases are caused by neutral composition changes, and the positive storm phases with plasma density increases are often related to atmospheric gravity waves. However, recent studies show that the global redistribution of the ionospheric plasma is dominated primarily by electric fields during the first hours of magnetic storms. In this paper, we present the measurements of ionospheric disturbances by the DMSP satellites and GPS network during the magnetic storm on 6 April 2000. The DMSP measurements include the F region ion velocity and density at the altitude of ∼840 km, and the GPS receiver network provides total electron content (TEC) measurements. The storm-time ionospheric disturbances show the following characteristics. The plasma density is deeply depleted in a latitudinal range of ∼20° over the equatorial region in the evening sector, and the depletions represent plasma bubbles. The ionospheric plasma density at middle latitudes (20°–40° magnetic latitudes) is significantly increased. The dayside TEC is increased simultaneously over a large latitudinal range. An enhanced TEC band forms in the afternoon sector, goes through the cusp region, and enters the polar cap. All the observed ionospheric disturbances occur within 1–5 h from the storm sudden commencement. The observations suggest that penetration electric fields play a major role in the rapid generation of equatorial plasma bubbles and the simultaneous increases of the dayside TEC within the first 2 h during the storm main phase. The ionospheric disturbances at later times may be caused by the combination of penetration electric fields and neutral wind dynamo process.     

某教练机失速特性分析及改进措施研究

分析了某教练机的失速特性及产生根源,提出了改善机翼失速特性的优化翼型和机翼平面形状的改进措施,并进行了CFD仿真验证,计算结果表明,改进后全机的失速特性得到了提高。     

小型化精密电机轴向预紧力调整研究

通过对液浮陀螺电机轴向预紧力调整情况及声音异常现象的分析,归纳和完善了电机轴向预紧力调整过程中的经验调法,并对电机轴向预紧力的量化调整进行了摸索和探讨,提出了较为可行的解决措施,从一定程度上保证了电机装调质量,提高了小型化精密电机装调合格率。     

小型喷气无人机总体设计参数优化与分析

以小型喷气无人机的总体方案研究为背景，建立了一种计算机辅助喷气无人机总体参数优化与分析程序系统。着重对适用于无人机的分析模块，如气动分析模块和重量分析模块的建立进行了较多的探索和尝试。为检验该优化分析系统的正确性，首先以意大利研制成功的喷气无人机（米拉奇－１００）为算例进行了验算和比较，然后对两种喷气无人机方案进行了总体参数优化计算，并对优化参数进行了敏感性分析。结果表明，所建立的喷气无人机总体设计参数优化与分析程序系统是可行的，所得结果合理、可信，对正在进行的喷气无人机总体方案研究有一定参考价值。     

Time-optimal trajectory planning for underactuated spacecraft using a hybrid particle swarm optimization algorithm

A hybrid algorithm combining particle swarm optimization (PSO) algorithm with the Legendre pseudospectral method (LPM) is proposed for solving time-optimal trajectory planning problem of underactuated spacecrafts. At the beginning phase of the searching process, an initialization generator is constructed by the PSO algorithm due to its strong global searching ability and robustness to random initial values, however, PSO algorithm has a disadvantage that its convergence rate around the global optimum is slow. Then, when the change in fitness function is smaller than a predefined value, the searching algorithm is switched to the LPM to accelerate the searching process. Thus, with the obtained solutions by the PSO algorithm as a set of proper initial guesses, the hybrid algorithm can find a global optimum more quickly and accurately. 200 Monte Carlo simulations results demonstrate that the proposed hybrid PSO–LPM algorithm has greater advantages in terms of global searching capability and convergence rate than both single PSO algorithm and LPM algorithm. Moreover, the PSO–LPM algorithm is also robust to random initial values.     

大量程力平衡加速度表的系数标定技术

对比研究了用于加速度表标定的重力场，离心机与电模拟的三种方法，给出了在国内目前没有大ｇ值精密离心机条件下，如何解决大量程加速度表的系数标定问题。     

基于Backstepping方法的非线性控制技术及其应用

基于Backstepping方法的设计思想,讨论了一类级联仿射非线性系统的控制问题,即先通过顺序递推的方式构造出非线性系统的李雅普诺夫函数,然后采用反向回溯求解的方式最终得出相应的非线性控制律,得出了一个一般性的设计结果,并且还进一步分析了李雅普诺夫函数中相关参数的选取方法,把它应用到空空导弹的纵向通道自动驾驶仪的设计中,仿真结果表明,通过选择合适的参数,该控制律能够很好地跟踪阶跃指令。     

Group force mobility model and its obstacle avoidance capability

Many mobility models attempt to provide realistic simulation to many real world scenarios. However, existing mobility models, such as RPGM [X. Hong, M. Gerla, G. Pei, C. Chiang, A group mobility model for ad hoc wireless networks, in: Proceedings of ACM/IEEE MSWiM’99, Seattle, WA, August 1999, pp. 53–60] and others, fail to address many aspects. These limitations range from mobile node (MN) collision avoidance, obstacle avoidance, and the interaction of MNs within a group. Our research, the group force mobility model (GFMM) [S.A. Williams, D. Huang, A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006], proposes a novel idea which introduces the concept of attraction and repulsion forces to address many of these limitations. Williams and Huang [A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006] described some of the limitations and drawbacks that many models neglect. This model effectively simulates the interaction of MNs within a group, the interaction of groups to one another, the coherency of a group, and the avoidance of collision with groups, nodes, and obstacles. This paper provides an overview of GFMM and particularly illustrates the GFMM's ability to avoid collision with obstacles, which is a vital property to posses in order to provide a realistic simulaition. We compare our model with the commonly used RPGM model and provide statistical assessments based on connectivity metrics such as link changed, link duration, and relative speed. All will be detailed and explained in this paper.