Evaluation of craters formation in hypervelocity impact of debris particles on solid structures

The aim of this work is to develop simplified model of space debris particle collision on solid structures, which would provide closed form solution formulas for determining crater depth, radius and ejected mass being functions of impactor mass, speed and material of both impactor and target. The model will be verified with results of experiments.     

航天飞机最优交会轨道及其控制

本文在文[2]、[4]的基础上,研究了最优交会轨道,导出了在推力作用下最优交会轨道的解析表达式;并对最优交会轨道和最优控制规律作了数值计算,求得了最优解。结果表明,对于目标航天器绕圆形轨道运行的情况,要求最优空间交会轨道和最省燃料的控制规律,此法有较好的实用价值。     

Low-altitude,near-polar and near-circular orbits around Europa

The dynamics of orbits around planetary satellites, taking into account the gravitational attraction of a third-body and the non-uniform distribution of mass of the planetary satellite, is studied. The Hamiltonian considered is explicitly time-dependent. Conditions for frozen orbits are presented. Low-altitude, near-polar orbits, very desirable for scientific missions to study planetary satellites such as the Jupiter’s moon Europa, are analyzed. Lifetimes for these orbits are computed through the single and double averaged method. Comparison between the results obtained by the single and double averaged method is presented. The single-averaged model is more realistic, since it does not eliminate the term due to the equatorial ellipticity of the planetary satellite as done by the double-averaged problem. Considering the single-averaged method, we found unstable frozen orbits where the satellite does not impact with the surface of Europa for at least 200 days. We present an approach using the unaveraged disturbing potential to analyze the effects of these terms in the amplitude of the eccentricity.     

Resonance transitions associated to weak capture in the restricted three-body problem

An interesting dynamics is studied in the restricted three-body problem where a particle abruptly transitions between resonance states, called a resonance hop. It occurs in a region about the secondary mass point which supports weak capture. This region, called a weak stability boundary, was recently proven to give rise to chaotic dynamics. Although it was numerically known that the resonance hop was associated with this boundary, this process was not well understood. In addition, the dynamical structure of the weak stability boundary has not been well understood. In this paper, we give a way to reveal the global structure of the weak stability boundary associated to resonance motions. This structure is shown to be surprisingly rich in resonant periodic motions interconnected by invariant manifolds. In this case, nearly all the motions are approximately resonant in nature where resonance hops can occur. The correlation dimension of orbits undergoing resonant motions, associated to the weak stability boundary, is also examined. The dynamics analyzed in the present paper is related to that studied by J. Marsden et al. under the perspective of Lyapunov orbits and the associated invariant manifolds. Applications are discussed.     

精密进近阶段的多系统GNSS组合RAIM可用性算法及分析

给出了多系统全球卫星导航系统（GNSS）组合接收机自主完好性监测（ReceiverAutonomousIntegrityMonitoring,RAIM）可用性计算方法,在此基础上利用GPS、GLONASS实测数据与BDS、Galileo全星座仿真数据,分析了BDS、GPS、GLONASS和Galileo不同组合在精密进近阶段的RAIM可用性。通过试验分析发现,BDS的5颗地球同步轨道卫星和3颗倾斜地球同步轨道卫星对亚洲、非洲和欧洲大部分地区的RAIM可用性有很大的贡献。这些地区站星间几何观测结构得到改善,使得RAIM可用性相对于其他地区有很大幅度的提升。在亚太地区APV-I阶段单系统导航情况下,北斗导航系统RAIM可用性达到99.5%,高于其他三个导航系统。在精密进近阶段（APV-I、APV-II和CAT-I）,BDS与其他导航系统（GPS、GLONASS和Galileo）的组合导航可以满足全球大部分区域的RAIM可用性需求,大多可达到100%。     

Numerical orbit integration based on Lie series with use of parallel computing techniques

This article outlines necessary steps to perform numerical orbit integrations based on a Lie series approach. Its implementation requires an efficient evaluation of resulting series coefficients. As an example we treat the classical main problem in satellite orbit calculation (_J2$J_2$ only) and the case of a 4×4$4\times 4$-gravity field. All calculations were performed in very high precision with up to 100 significant digits. In comparison to independent third party computations this approach led to superior results referring to the verifiable constancy of various integrals of motion. To achieve a performance similar to classical numerical integrations in terms of acceptable computing time, at least for non-Keplerian motion problems, we exploited parallel computing capabilities. For our examples, run times were improved by several orders of magnitude, depending on the actual chosen precision level (up to a factor of 50,000 in case of double precision). Here we present the mathematical framework of the proposed orbital integration scheme as well as the work flow for its application in a multi-core, parallel computing environment.     

On the effects of each term of the geopotential perturbation along the time I: Quasi-circular orbits

This paper provides a useful new method to determine minimum and maximum range of values for the degree and order of the geopotential coefficients required for simulations of orbits of satellites around the Earth. The method consists in a time integration of the perturbing acceleration coming from each harmonic of the geopotential during a time interval T. More precisely, this integral represents the total velocity contribution of a specific harmonic during the period T  . Therefore, for a pre-fixed minimum contribution, for instance 1×10^-8$1\times {10}^{-8}$ m/s during the period of time T, any harmonic whose contribution is below this value can, safely, be neglected. This fact includes some constraints in the degree and order of the terms which are present in the geopotential formula, saving computational efforts compared to the integration of the full model. The advantage of this method is the consideration of other perturbations in the dynamics (we consider the perturbations of the Sun, the Moon, and the direct solar radiation pressure with eclipses), since these forces affect the value of the perturbation of the geopotential, because these perturbations depend on the trajectory of the spacecraft, that is dependent on the dynamical model used. In this paper, we work with quasi-circular orbits and we present several simulations showing the bounds for the maximum degree and order (M) that should be used in the geopotential for different situations, e. g., for a satellite near 500 km of altitude (like the GRACE satellites at the beginning of their mission) we found 35?M?198$35?M?198$ for T=1$T=1$ day. We analyzed the individual contribution of the second order harmonic (_J2$J_2$) and we use its behavior as a parameter to determine the lower limit of the number of terms of the geopotential model. In order to test the accuracy of our truncated model, we calculate the mean squared error between this truncated model and the “full” model, using the CBERS (China-Brazil Earth Resources Satellite) satellite in this test.     

箔片摩擦效应对转子-箔片轴承系统动力学特性影响试验

为了研究波纹箔片和轴承壳之间的摩擦特性对转子-箔片轴承系统动力学特性的影响,设计了波箔型径向气体箔片轴承-转子试验台,通过在该试验台上对以两组不同轴承壳圆柱孔内表面粗糙度的箔片轴承支承的质量为0.458kg的转子进行转速为0~8000r/min的运行试验,对比分析了波纹箔片与轴承壳内壁之间的摩擦效应对系统转子动力学特性的影响.结果表明:直径为19.98mm的波箔型径向气体箔片轴承能够实现转子高速运行,在转子起飞后具有良好的运行稳定性,其轴承支承处的振动幅值一直维持在20μm附近,并且降低轴承壳内表面粗糙度(摩擦因数)能够让波纹箔片相对容易地在平箔片和轴承壳之间周向滑移,使其吸收并消除转子高频振动,提高转子系统运行稳定性.      

高精度重力场下回归轨道半解析优化设计

为解决太阳同步回归轨道的标称设计问题,提出一种基于高精度重力场的半解析优化方法。建立地球非球形引力摄动阶数为J15 的高精度重力场解析模型,并分离出引力摄动的长期项和长周期项。构建回归轨道从半长轴到平交点周期的对应关系,平交点周期变化随引力摄动阶数的提高而逐渐收敛。通过微分修正迭代算法所确定的半长轴相对于传统J2摄动模型的半长轴确定值具有更高的精度和更好的稳定性。考察摄动短周期项影响下的密切交点周期,结果表明其受初始位置(平近点角)影响较大,变化范围为0.015s,并由此给出精确回归轨道优化设计的基准：不同的初始位置上满足星下点轨迹严格回归的半长轴期望值。