Yarkovsky-Schach effect on space debris motion

The Yarkovsky-Schach effect is a small perturbation affecting Earth satellites and space debris illuminated by the Sun. It was first applied to the orbit of LAGEOS satellites as an explanation of the residuals in orbital elements. In this work, we carry out several numerical integration tests taking into consideration various orbit and rotation parameters, in order to analyse this effect in a broader context. The semi-major axis variations remain small and depend on the spin axis attitude with respect to the Sun. We show that the force amplitude is maximised for orbits inclined with $i\approx$?20–30°. We also observe the influence on other orbital elements, notably on the orbit inclination. However, these effects are clearly observed only on long timescales; in our simulations, we propagated the orbits for 200?y. The Yarkovsky-Schach effect is thus confirmed to have a minuscule magnitude. It should be taken into account in studies requiring high-precision orbit determination, or on expanded timescales.     

Quantum dosimetry and online visualization of X-ray and charged particle radiation in commercial aircraft at operational flight altitudes with the pixel detector Timepix

We investigate the application of the hybrid semiconductor pixel detector Timepix for precise characterization, quantum sensitivity dosimetry and visualization of the charged particle radiation and X-ray field inside commercial aircraft at operational flight altitudes. The quantum counting capability and granularity of Timepix provides the composition and spectral-characteristics of the X-ray and charged-particle field with high sensitivity, wide dynamic range, high spatial resolution and particle type resolving power. For energetic charged particles the direction of trajectory and linear energy transfer can be measured. The detector is operated by the integrated readout interface FITPix for power, control and data acquisition together with the software package Pixelman for online visualization and real-time data processing. The compact and portable radiation camera can be deployed remotely being controlled simply by a laptop computer. The device performs continuous monitoring and accurate time-dependent measurements in wide dynamic range of particle fluxes, deposited energy, absorbed dose and equivalent dose rates. Results are presented for in-flight measurements at altitudes up to 12 km in various flights selected in the period 2006–2013.     

A simulation study on the mode conversion process from slow Z-mode to LO mode by the tunneling effect and variations of beaming angle

For a particular angle of incidence wave, it is possible for a slow Z-mode wave incident on an inhomogeneous plasma slab to be converted into an LO mode wave. But for another wave normal angle of the incident wave, it has been considered impossible, since an evanescence region exists between two mode branches. In this case we expect that the mode conversion takes place through the tunneling effect. We investigate the effect of the spatial scale of the density gradient on the mode conversion efficiency in an inhomogeneous plasma where the mode conversion can occur only by the tunneling effect. We use the computer simulation solving Maxwell’s equations and the motion of a cold electron fluid. By considering the steepness of the density gradient, the simulation results show the efficient mode conversion could be expected even in the case that the mismatch of the refractive indexes prevents the close coupling of plasma waves. Also, we show for these cases the beaming angle does not correspond to Jones’ formula. This effect leads to the angles larger and smaller than the angle estimated by the formula. This type of mode conversion process becomes important in a case where the different plasmas form a discontinuity at their contact boundary.     

离子推力器羽流热效应仿真分析

离子推力器工作时向外喷出的羽流与航天器表面碰撞,会引起敏感材料热变形等热效应,严重时会导致航天任务失败。针对兰州空间技术物理研究所研制的LIPS-200型离子推力器羽流热效应进行了仿真分析。仿真中,使用粒子网格（PIC）方法处理等离子体运动,使用直接模拟蒙特卡罗（DSMC）方法处理粒子间碰撞,使用Maxwell模型处理粒子与壁面的能量交换,对电推进羽流热效应测量中的部分测点进行了数值模拟。结果表明,仿真结果与实验数据符合较好,离子推力器出口轴线上滞止热流仿真值与实验测量值误差小于17.0%。此外,热流计对流场的影响主要集中在热流计附近0.1 m范围内,对整体流场影响较小。      

星载辐射计扫描镜太阳辐射热-结构建模与仿真

三轴稳定卫星平台搭载的光学有效载荷都存在午夜太阳辐射干扰问题,由此产生的热变形效应对光学系统的成像品质影响显著。采用复杂外热流近似建模技术,以及多软件耦合有限元仿真方法,以FY-4卫星的扫描辐射计为应用背景,研究了昼夜太阳辐射对星载辐射计扫描镜产生的热效应,并对不同热设计条件下的工况进行了对比分析。分析结果显示：扫描镜侧面及背面的热控涂层选取对其热变形有重要影响,但是仅仅通过热设计解决温度波动和热变形的矛盾是不够的,需要通过改进扫描镜的材料和优化光机结构加以改善。     

翼型波浪水面巡航地面效应数值模拟

数值求解非定常不可压缩流动的雷诺平均N-S(Navier-Stokes)方程和标准k-ε湍流模型,用VOR(Volume Of Fluid)方法模拟波浪水面,模拟了NACA2410翼型在波浪水面上方飞行的流场.研究了余弦波浪水面的生成方法,选取合适的计算网格和时间步长,避免了在生成规则余弦波浪水面时由于数值耗散使波面形状衰减.比较了固壁波浪与水面波浪计算结果的差异,发现固壁波浪的结果更接近余弦曲线分布.研究了波浪等级对翼型气动性能的影响,分析计算结果发现:在规则的余弦水面波浪上方飞行,翼型气动力呈现周期性,给出了一个周期内气动力的变化过程,以及波长和波幅对气动力平均值和波动幅度的影响规律.      

微小空间碎片与原子氧协同效应研究

利用等离子体驱动微小碎片加速器和潘宁源的原子氧模拟装置在中国首次开展了微小碎片撞击与原子氧协同作用对Kapton膜和镀铝Kapton膜的侵蚀效应研究. 实验结果表明, 碎片撞击能明显加剧原子氧对Kapton和镀铝Kapton膜的侵蚀效应, 对航天器的寿命及可靠性构成威胁, 制约中国长寿命高可靠性航天器的发展.     

基于多米诺效应的锂离子电池热释放速率分析方法

常用实验手段测得单节锂离子电池热释放速率无法真实反映航空运输包装件内大量锂离子电池因发生多米诺效应导致热量散失及传递过程间歇性变化。本文提出一种基于多米诺效应的锂离子电池热释放速率等效分析方法,即通过自主设计的实验平台对3×3排布的典型18650型锂离子电池热失控后发生的多米诺效应及各节电池表面温度进行分析。利用FLUENT使用标准18650型锂离子电池热释放速率曲线用于同等实验条件下的锂离子电池热失控传播仿真模拟,采用二分法逐次修正标准热释放速率、使仿真和实验的锂离子电池表面温度相符。将获得等效的锂离子电池热释放速率曲线再次应用于仿真,得到各电池的最高温度及达到最高温度的时间和实验数据相吻合,验证了修正后的等效热释放速率模型可靠性。该方法可适用于各型号及不同数量包装件内锂离子电池热释放速率获取,指导航空运输锂离子电池火灾防控工程实际。     

Testing the blast wave model with Swift GRBs

The complex structure of the light curves of Swift GRBs (e.g. superimposed flares and shallow decay) has made their interpretation and that of the blast wave caused by the burst, more difficult than in the pre-Swift era. We aim to constrain the blast wave parameters: electron energy distribution, p, density profile of the circumburst medium, k, and the continued energy injection index, q. We do so by comparing the observed multi-wavelength light curves and X-ray spectra of a Swift sample to the predictions of the blast wave model.