FEC design for remote control and data transmission of aeronautic and astronautic vehicles

This paper focuses on the advanced Forward Error Correction(FEC) based on LowDensity Parity-Check(LDPC) codes for remote control and data transmission of Aeronautic and Astronautic Vehicles(AAV). It shows that the nontransparent LDPC codes with odd row weights are able to resist phase inversion with a small computational overhead. To the best of our knowledge, it is the first time to use FEC to resist phase inversion. Then, a high hardware-efficient FEC design for AAV, which is capable of correcting random errors as well as phase inversion, is proposed based on circulant decomposition with circulant size of 2s. Such a(4096, 2048) LDPC code has been adopted in a data transmission system due to its excellent error performance and hardware efficiency.     

Fostering research aptitude among high school students through space weather competition

Cultivating research culture at an early stage is important for capacity building in a community. The high school level is the appropriate stage for research to be introduced because of students’ competitive nature. Participation in the space weather competition is one of the ways in which research aptitude can be fostered in high school students in Malaysia. Accordingly, this paper presents how research elements were introduced to the students at the high school level through their participation in the space weather competition. The competition required the students to build a system to detect the presence of solar flares by utilizing VLF signals reflected from the ionosphere. The space weather competition started off with proposal writing for the space weather related project where the students were required to execute extensive literature review on the given topic. Additionally, the students were also required to conduct the experiments and analyse the data. Results obtained from data analysis were then validated by the students through various other observations that they had to carry out. At the end of the competition, students were expected to write a comprehensive technical report. Through this competition, the students learnt how to conduct research in accordance to the guidelines provided through the step by step approach exposed to them. Ultimately, this project revealed that the students were able to conduct research on their own with minimal guidance and that participation in the competition not only generated enjoyment in learning but also their interest in science and research.     

高温对单搭接接头强度的影响

对不同温度下单搭接接头进行拉伸试验,对比不同温度对接头强度的影响。结果表明,温度越

高,接头强度越低,同时,随着温度的升高,胶层的破坏模式也发生变化。通过有限元数值仿真,模拟不同温度

下胶层表面上等效应力的分布情况,得出温度越高,胶层热应力越大,接头强度越低等结论。

     

基于随机模糊参数的结构模糊可靠性分析模型

结构模糊可靠性理论研究主要是建立仅考虑失效准则模糊性的结构模糊可靠性分析模型.在现有结构模糊可靠性分析理论研究的基础上,同时考虑工程中结构参数的随机性和区间模糊性,提出了模糊概率密度函数的概念,并推导相应的模糊概率密度函数公式,给出了反映随机参数区间模糊性的隶属函数的类型和选取方法.建立了同时考虑随机参数区间模糊性和失效准则模糊性的结构模糊可靠性分析模型.讨论了模糊可靠性分析模型与常规的随机可靠性分析模型的相容性.并给出算例进行验证,研究结果表明,采用该结构模糊可靠性分析方法更能全面地利用结构参数信息.     

The quiet nighttime low-latitude ionosphere as observed by TIMED/GUVI

In this paper, we examine the nighttime ionosphere climatology structure in the low latitude region and discrepancies between Global Ultraviolet Imager (GUVI) observations and the IRI model predictions using (1) the magnetic zonal mean of electron number density as a function of altitude and magnetic latitude, (2) vertical electron density profiles at various levels of F10.7 index, (3) nighttime descent and magnitude decrease of the ionosphere, (4) point-to-point comparisons of F-peak height (hmF2) and density (NmF2), and (5) the magnetic longitudinal variations of hmF2 and NmF2. The data collected from the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission since its launch in December 2001 have provided great opportunities for many scientific investigations of the ionosphere. In this analysis, we investigate the climatology of the nighttime low-latitude ionosphere under low geomagnetic activity (kp ? 4) using the electron density profiles inferred from the airglow measurements obtained by the GUVI aboard the TIMED spacecraft and compared with the results obtained from IRI (International Reference Ionosphere) model-2001. The observed climatology is an essential tool for further understanding the electrodynamics in the low-latitude region and improving the model’s prediction capability. The time range of the GUVI data used in this study is from 2002 (day 053) to 2006 (day 304), and the IRI model predictions were produced at every GUVI location. The ionosphere observed is generally of greater density than what IRI predicts throughout the night for all four seasons for low and moderate solar activity while the model over-predicts the electron density near the F-region peak at high solar activity before midnight. Observations show that the height of the F-region peak has a steep descent from dusk to midnight and near midnight the height of layer is insensitive to solar conditions, significantly different than what is predicted by IRI. Longitudinal features shown in GUVI data are present in the low-latitude ionosphere after sunset and continue through to midnight after which the low-latitude ionosphere is largely zonally symmetric.     

微纳卫星混合推进技术研究综述

首先介绍了微纳卫星混合推进系统的特点与优势,总结了星载混合推进技术的发展现状,并结合微纳卫星动力系统要求,指出了星载混合推进技术的发展趋势及存在的问题.然后在此基础上,从卫星工程应用的角度,重点综述了星载混合推进系统需攻克的主要关键技术,包括先进一体化制造、可靠低功耗多次点火启动、比冲提升、高效燃烧等,并分析了相应关键...     

(70~100)MeV准单能中子参考辐射场设计

国内基于串列加速器建立了144keV~15MeV的单能中子参考辐射场，解决了20MeV以下能区中子探测器注量、剂量等参数的量值溯源，但尚未建立20MeV以上能区准单能中子参考辐射场。随着航天空间中子探测任务的需要以及地面高能质子加速器的发展，20MeV以上能区准单能中子参考辐射场需求越来越突出。发展20MeV以上能区高能中子参考辐射场对于满足国防需求、推动中子计量学科发展具有重要意义。     

Improvements in bottomside electron density definition in the Autoscala program

Some improvements introduced in the Autoscala program are presented. They include improvements in E valley modeling of the electron density profile N_e(h), and in the link between the E valley and bottom-side F regions. An abrupt variation in N_e(h) generated by the previous version of Autoscala under night conditions has been eliminated.A series of ionograms recorded by the Millstone Hill digisonde (42.6°, 288.5°) were automatically interpreted by the previous version of Autoscala and by the new one. Data from Incoherent Scatter Radar (ISR) were used to comparatively assess the performance of the two versions. For this purpose, the root mean square errors (RMSEs) of the N_e(h) provided by Autoscala were calculated relative to the corresponding values provided by ISR.A more accurate overall modeling of N_e(h) was achieved by the new Autoscala version (RMSE = 0.51 MHz for the new version against RMSE = 0.67 MHz for the previous one).     

Symplectic integration of space debris motion considering several Earth’s shadowing models

In this work, we present a symplectic integration scheme to numerically compute space debris motion. Such an integrator is particularly suitable to obtain reliable trajectories of objects lying on high orbits, especially geostationary ones. Indeed, it has already been demonstrated that such objects could stay there for hundreds of years. Our model takes into account the Earth’s gravitational potential, luni-solar and planetary gravitational perturbations and direct solar radiation pressure. Based on the analysis of the energy conservation and on a comparison with a high order non-symplectic integrator, we show that our algorithm allows us to use large time steps and keep accurate results. We also propose an innovative method to model Earth’s shadow crossings by means of a smooth shadow function. In the particular framework of symplectic integration, such a function needs to be included analytically in the equations of motion in order to prevent numerical drifts of the energy. For the sake of completeness, both cylindrical shadows and penumbra transitions models are considered. We show that both models are not equivalent and that big discrepancies actually appear between associated orbits, especially for high area-to-mass ratios.