深空探测器自主天文导航技术综述

在深空探测中,单独使用无线电测控存在精度、实时性、覆盖性等方面的限制。作为无线电测控的有效补充,自主天文导航是保证深空探测任务成功的关键技术之一。面向深空探测对自主天文导航的迫切需求,概述了深空探测器自主天文导航的基本原理,简要介绍了深空探测器自主天文导航的研究进展,并重点分析探讨了深空探测器自主天文导航的关键技术和发展趋势。分析结果可为我国未来深空探测器天文导航系统研制提供参考,并为深空探测任务的总体设计提供帮助。     

Mapping lunar surface chemistry: New prospects with the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS)

Surface chemistry of airless bodies in the solar system can be derived from remote X-ray spectral measurements from an orbiting spacecraft. X-rays from planetary surfaces are excited primarily by solar X-rays. Several experiments in the past have used this technique of X-ray fluorescence for deriving abundances of the major rock forming elements. The Chandrayaan-2 orbiter carries an X-ray fluorescence experiment named CLASS that is designed based on results from its predecessor C1XS flown on Chandrayaan-1. We discuss the new aspects of lunar science that can be potentially achieved with CLASS.     

低能自由空气电离室优化设计

借助于空气比释动能的基本定义和概念以及空气比释动能绝对测量的理论方法,分析了自由空气电离室可以作为空气比释动能绝对测量方法的原理和条件。通过平板型与圆柱型自由空气电离室的优劣比较,选择平板型作为研究对象,详细介绍了经典的平板型自由空气电离室,并通过理论分析计算以及模拟计算的方法,优化设计包括：光阑半径、空气衰减长度、极间距等低能自由空气电离室的关键几何尺寸,以最小化空气比释动能测量时产生的总不确定度。     

X射线衍射技术对InSb材料的无损检测

采用2θ-ω对称扫描,对(111)、(333)、(044)不同衍射面进行了ω扫描,得到了InSb不同衍射面之间强度和半峰宽度的规律;对晶片上不同位置进行了同一衍射面的ω扫描,得到半峰宽度的mapping,此外,还对材料进行了倒易空间(RSM)扫描。测试结果表明InSb材料结晶质量完好,均匀性好,符合制造良好光电器件的标准。     

He-like Ar xvii triplet observed by RESIK

We present the observations of He-like Ar triplet lines obtained by RESIK spectrometer aboard CORONAS-F. Interpretation of intensity ratios between triplet lines of lower Z elements is known to provide useful diagnostics of plasma conditions within the emitting source. Here, we investigate whether triplet line ratios are useful for interpretation of higher Z element spectra. A high sensitivity, low background and precise absolute calibration of RESIK allow to consider in addition also the continuum contribution. This provides a way to determine the Ar absolute abundance from the observed triplet component ratios. The method is presented and the results are shown for two selected flares. Derived values of Ar absolute abundance for these flares are found to be similar: 2.6 × 10⁻⁶ and 2.9 × 10⁻⁶. They fall in the range between presently accepted Ar photospheric and coronal abundances.     

Early effects of low dose C ion or X-ray irradiation on human peripheral blood lymphocytes

The aim of this study was to estimate the acute effects of low dose ¹²C⁶⁺ ions or X-ray radiation on human immune function. The human peripheral blood lymphocytes (HPBL) of seven healthy donors were exposed to 0.05 Gy ¹²C⁶⁺ ions or X-ray radiation and cell responses were measured at 24 h after exposure. The cytotoxic activities of HPBL were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT); the percentages of T and NK cells subsets were detected by flow cytometry; mRNA expression of interleukin (IL)-2, tumor necrosis factor (TNF)-α and interferon (IFN)-γ were examined by real time quantitative RT-PCR (qRT-PCR); and these cytokines protein levels in supernatant of cultured cells were assayed by enzyme-linked immunosorbent assays (ELISA). The results showed that the cytotoxic activity of HPBL, mRNA expression of IL-2, IFN-γ and TNF-α in HPBL and their protein levels in supernatant were significantly increased at 24 h after exposure to 0.05 Gy ¹²C⁶⁺ ions radiation and the effects were stronger than observed for X-ray exposure. However, there was no significant change in the percentage of T and NK cells subsets of HPBL. These results suggested that 0.05 Gy high linear energy transfer (LET) ¹²C⁶⁺ radiation was a more effective approach to host immune enhancement than that of low LET X-ray. We conclude that cytokines production might be used as sensitive indicators of acute response to LDI.     

UKF方法在脉冲星自主导航中的应用

针对X射线脉冲星自主导航中的非线性系统滤波问题,将无迹卡尔曼滤波方法应用于自主导航计算过程中。首先,在简述脉冲星导航可行性的基础上,研究了脉冲星自主导航系统的基本原理和实施方案。然后,根据牛顿二体引力模型构建了航天器运动状态方程,根据脉冲到达时间模型建立了系统观测方程,并对二者进行了误差分析和建模。最后,将UKF算法应用于航天器自主导航过程中,仿真结果表明该方法能够实现航天器自主导航信息的解算。     

利用增量相位和星光仰角增强XNAV

针对X射线脉冲星导航系统(XNAV)中过程噪声统计特性难以准确获取,对其不当假设导致滤波器估计性能不佳的问题,提出基于自适应差分卡尔曼滤波器(ADDF)的多信息融合算法。为了降低导航误差,在传统脉冲星计时观测的基础上,增加恒星星光仰角及两个时刻间的相位增量观测量,共同增强XNAV。首先,分别建立计时观测模型、相位增量模型及星光仰角模型;然后将多信息测量模型集成到卫星轨道动力学方程中,以建立ADDF滤波模型;最后对所提方法进行仿真验证。实验结果表明,在相同的初始状态和初始噪声误差条件下,与传统X射线脉冲星导航算法相比,多信息融合算法能将导航位置估计精度提高70%以上,位置估计误差降低到 200 m 左右,速度估计精度提高40%以上,且ADDF性能优于无迹卡尔曼滤波器。     

The gas pixel detector as a solar X-ray polarimeter and imager

The Sun is the nearest astrophysical source with a very intense emission in the X-ray band. The study of energetic events, such as solar flares, can help us to understand the behaviour of the magnetic field of our star. There are in the literature numerous studies published about polarization predictions, for a wide range of solar flares models involving the emission from thermal and/or non-thermal processes, but observations in the X-ray band have never been exhaustive.The gas pixel detector (GPD) was designed to achieve X-ray polarimetric measurements as well as X-ray images for far astrophysical sources. Here we present the possibility to employ this instrument for the observation of our Sun in the X-ray band.     

XMM-Newton study of soft excess X-ray emission in clusters of galaxies

We discuss the detection of soft excess X-ray emission in a sample of 19 clusters of galaxies observed by XMM-Newton. In 6/19 clusters evidence for a soft X-ray excess is found. Four of these clusters show soft X-ray and O VII line emission from gas with a temperature of 0.2 keV. The centroid of this oxygen line is consistent with the redshift of the cluster. The intensity and spatial extend of the soft excess agrees with previous PSPC measurements. These observations are interpreted as emission from warm-hot intergalactic medium filaments, with density enhancements near the cluster centers, consistent with theoretical predictions. In the other two soft excess clusters a non-thermal origin is consistent with the data.