The classical Laplace plane as a stable disposal orbit for geostationary satellites

The classical Laplace plane is a frozen orbit, or equilibrium solution for the averaged dynamics arising from Earth oblateness and lunisolar gravitational perturbations. The pole of the orbital plane of uncontrolled GEO satellites regress around the pole of the Laplace plane at nearly constant inclination and rate. In accordance with Friesen et al. (1993), we show how this stable plane can be used as a robust long-term disposal orbit. The current graveyard regions for end-of-life retirement of GEO payloads, which is several hundred kilometers above GEO depending on the spacecraft characteristics, cannot contain the newly discovered high area-to-mass ratio debris population. Such objects are highly susceptible to the effects of solar radiation pressure exhibiting dramatic variations in eccentricity and inclination over short periods of time. The Laplace plane graveyard, on the contrary, would trap this debris and would not allow these objects to rain down through GEO. Since placing a satellite in this inclined orbit can be expensive, we discuss some alternative disposal schemes that have acceptable cost-to-benefit ratios.     

Medium Earth Orbit dynamical survey and its use in passive debris removal

The Medium Earth Orbit (MEO) region hosts satellites for navigation, communication, and geodetic/space environmental science, among which are the Global Navigation Satellites Systems (GNSS). Safe and efficient removal of debris from MEO is problematic due to the high cost for maneuvers needed to directly reach the Earth (reentry orbits) and the relatively crowded GNSS neighborhood (graveyard orbits). Recent studies have highlighted the complicated secular dynamics in the MEO region, but also the possibility of exploiting these dynamics, for designing removal strategies. In this paper, we present our numerical exploration of the long-term dynamics in MEO, performed with the purpose of unveiling the set of reentry and graveyard solutions that could be reached with maneuvers of reasonable $\mathrm{\Delta }V$ cost. We simulated the dynamics over 120–200?years for an extended grid of millions of fictitious MEO satellites that covered all inclinations from 0 to 90°, using non-averaged equations of motion and a suitable dynamical model that accounted for the principal geopotential terms, 3rd-body perturbations and solar radiation pressure (SRP). We found a sizeable set of usable solutions with reentry times that exceed $～40$ years, mainly around three specific inclination values: 46°, 56°, and 68°; a result compatible with our understanding of MEO secular dynamics. For $\mathrm{\Delta }V?300$ m/s (i.e., achieved if you start from a typical GNSS orbit and target a disposal orbit with $e<0.3$), reentry times from GNSS altitudes exceed $～70$ years, while low-cost ($\mathrm{\Delta }V?5–35$ m/s) graveyard orbits, stable for at lest 200?years, are found for eccentricities up to $e\approx 0.018$. This investigation was carried out in the framework of the EC-funded “ReDSHIFT” project.     

统计能量分析中几种非共振传输与声场间传输系数研究

简述统计能量分析（SEA）中几种非共振传输（近场、直接场、强迫运动）及共振（混响场）传输特性与处理方法,并用简单方法导出声场间一种强迫运动-非共振传输系数表达式,可以满足工程要求。     

l1-based calibration of POD-Galerkin models of two-dimensional unsteady flows

This paper discusses a physics-informed methodology aimed at reconstructing efficiently the fluid state of a system. Herein, the generation of an accurate reduced order model of two-dimensional unsteady flows from data leverages on sparsity-promoting statistical learning techniques. The cornerstone of the approach is l₁ regularised regression, resulting in sparsely-connected models where only the important quadratic interactions between modes are retained. The original dynamical behaviour is reproduced at low computational costs, as few quadratic interactions need to be evaluated. The approach has two key features. First, interactions are selected systematically as a solution of a convex optimisation problem and no a priori assumptions on the physics of the flow are required. Second, the presence of a regularisation term improves the predictive performance of the original model, generally affected by noise and poor data quality. Test cases are for two-dimensional lid-driven cavity flows, at three values of the Reynolds number for which the motion is chaotic and energy interactions are scattered across the spectrum. It is found that: (A) the sparsification generates models maintaining the original accuracy level but with a lower number of active coefficients; this becomes more pronounced for increasing Reynolds numbers suggesting that extension of these techniques to real-life flow configurations is possible; (B) sparse models maintain a good temporal stability for predictions. The methodology is ready for more complex applications without modifications of the underlying theory, and the integration into a cyber-physical model is feasible.     

Predictive Space Weather: An information theory approach

It is rather well recognized that the global dynamics of the Sun–Earth relationship involves complex nonlinear phenomena. Here we present a preliminary attempt to characterize the influence and the timing of the solar magnetic activity on the near-Earth environment, based on quite novel tools based on concepts from information theory.     

小波变换在动力学系统识别中的应用

试图用小波变换来讨论动力学系统识别中的几个问题，并用以研究在系统分析中利用小波变换这个工具的可能性。只涉及线性时不变结构的动力学系统，它应该适用于非线性或线性时变系统的分析和识别。做为一个具体应用，给出了使用小波变换识别模态阻尼系数的模拟实侧，可用于颤振数据分析。     

某公司供热系统节能减排技改方案浅析

为提高某公司能源利用水平，减少污染物排放，针对该公司现正使用燃煤锅炉蒸汽加热方式所造成的高耗能、高污染、低效益问题，提出应用燃气替代燃煤并辅以部分电加热的技改方案，达到实现节能减排提高效益之目的。     

运载火箭动力系统突发性故障检测与辨识

航天是一个高风险的领域 ,一次不成功的发射试验可能带来的经济损失动辄上亿元 ,甚至会出现灾难性后果。因此 ,故障诊断技术在航天工程领域具有极端的重要性和明显的工程价值。本文以运载火箭动力系统突发性故障为研究对象 ,采用解析冗余方法 ,建立了分别适用于脉冲型故障和阶跃型故障的检测方法 ,并给出了故障幅度的无偏估计算法     

外辐射带动态演化的粒子模拟研究

运用计算机实验方法即三维电磁粒子模拟方法初步研究了暴时扰动情况下外辐射带粒子环境的动态演化特性。模拟计算了暴时辐射带粒子环境的演化情况。模拟计算结果显示，高能质子、电子注入午辐射滞后，两者一方面沿磁力线做弹跳运动，向高纬扩展，部分注入质子和电子沉降于南北两极区域；另一方面，注入质子和电子还经历顺时针和逆时针方向的漂移运动，粒子能量越大，漂移速度越快。暴时多次注入引起整个辐射带粒子能量的大幅增强；粒子注入颗次和强度越大，辐射带粒子通量增幅越大。本项研究为开发研制完整的辐射带动态模式积累了有益的经验。     

电离层峰下结构的数值模拟

在考虑由扩散与中性风引起的动力学输运与有原子离子Ｏ＾＋（＾４Ｓ），Ｏ＾＋（＾２Ｄ）与Ｏ＾＋（＾２Ｐ）以及分子离子Ｏ２＾＋，ＮＯ＾＋，Ｎ２＾＋参加光化学反应的电离层－热层体系中，提出一个一维时变的电离层剖面数值模型，通过数值计算着重讨论了武昌地区Ｆ２层峰以下，尤其是Ｅ／Ｆ与Ｆ１／Ｆ２谷区的电离层形态与有关过程，得到如下结论：（１）对于原子离子，单一成分Ｏ＾＋（＾４Ｓ）的光化学反应与输运，也有助于形成