In-orbit operation and performance of the CubeSat Soft X-ray polarimeter PolarLight

PolarLight is a compact soft X-ray polarimeter onboard a CubeSat, which was launched into a low-Earth orbit on October 29, 2018. In March 2019, PolarLight started full operation, and since then, regular observations with the Crab nebula, Sco X-1, and background regions have been conducted. Here we report the operation, calibration, and performance of PolarLight in the orbit. Based on these, we discuss how one can run a low-cost, shared CubeSat for space astronomy, and how CubeSats can play a role in modern space astronomy for technical demonstration, science observations, and student training.     

基于电磁波三维结构向量的飞行器姿态估计

以电磁波三维空间结构向量为参照的飞行器姿态/航向测量研究，可弥补空间参照物缺乏，丰富空间飞行器姿态/航向测量工具。本文根据各缺损电磁矢量传感器姿态位置与接收信号之间的变化规律，建立飞行器载电磁矢量传感器阵列导向矢量。根据协同导航的多个信号空间谱和最大化，实现平台姿态/航向测量。飞行器多位置的多个传感器共同测量姿态可避免遮挡，获得更高姿态精度的同时拓展了系统的适用领域。接收电磁信息完备状态下，不需导航信号，测绘平稳的杂波就能作为姿态基准。仿真试验验证了姿态估计的有效性。     

A new inversion algorithm for HF sky-wave backscatter ionograms

HF sky-wave backscatter sounding system is capable of measuring the large-scale, two-dimensional (2-D) distributions of ionospheric electron density. The leading edge (LE) of a backscatter ionogram (BSI) is widely used for ionospheric inversion since it is hardly affected by any factors other than ionospheric electron density. Traditional BSI inversion methods have failed to distinguish LEs associated with different ionospheric layers, and simply utilize the minimum group path of each operating frequency, which generally corresponds to the LE associated with the F₂ layer. Consequently, while the inversion results can provide accurate profiles of the F region below the F₂ peak, the diagnostics may not be so effective for other ionospheric layers. In order to resolve this issue, we present a new BSI inversion method using LEs associated with different layers, which can further improve the accuracy of electron density distribution, especially the profile of the ionospheric layers below the F₂ region. The efficiency of the algorithm is evaluated by computing the mean and the standard deviation of the differences between inverted parameter values and true values obtained from both vertical and oblique incidence sounding. Test results clearly manifest that the method we have developed outputs more accurate electron density profiles due to improvements to acquire the profiles of the layers below the F₂ region. Our study can further improve the current BSI inversion methods on the reconstruction of 2-D electron density distribution in a vertical plane aligned with the direction of sounding.     

基于支持向量回归与多核集成的红外成像导引头抗干扰性能评估方法

面对着日益复杂的对抗环境,红外成像导引头的抗干扰性能需要不断提高。如何全面、客观、准确地对红外成像导引头的抗干扰性能进行评估,是一项急需解决的难题。针对传统基于支持向量机的评估方法中单核学习能力的不足,提出了一种基于支持向量回归与多核集成的评估方法,该方法在抗干扰评估指标体系下得到了综合的抗干扰性能值,为红外成像导引头抗干扰性能评估提供了新的思路。该方法能够训练多个支持向量回归机并融合多个核函数的优势,充分利用了特征的多样性,进一步降低了回归误差。实验结果表明:该算法能够实现高效可靠的红外成像导引头抗干扰性能评估。     

Adaptive maneuvering entry guidance with ground-track control

We demonstrate that a three-dimensional entry guidance with accurate ground-track control can be achieved using a combined strategy of proportional down-range maneuvering and linear quadratic (LQ) technique, thereby precluding the necessity of sophisticated nonlinear programming. It is also shown that heating rate and load-factor constraints can be met by a careful but simple selection of LQ gains. Although the speed, flight path angle, and down-range accuracy are comparable to that of a planar guidance strategy, the present technique also demonstrates an accurate cross-range control, which is not possible with a planar strategy. It is shown that adaptive maneuvering produces a superior performance than that of a nonlinear tracking control derived using feedback linearization. The method can handle much larger deviations in the entry conditions than those published previously, and has the important advantage of a relatively simple implementation in a realistic entry scenario. Furthermore, the LQ technique can take advantage of the good robustness properties of a linear Kalman filter based upon the measurement of longitude, latitude, and speed, wherein little deterioration is observed in the closed-loop performance.     

ISAR干扰及干扰效果评估技术

描述了逆合成孔径雷达（ISAR）干扰技术、干扰评估技术的发展历程与现状,分析了ISAR干扰技术存在的问题,展望了这两种技术的发展趋势。     

Changes of human serum proteome profile during 7-day “dry” immersion

The aim of this study was to characterize changes of serum proteome profile during 7-day “dry” immersion (DI). The experiment with DI consisted of three series: control group without countermeasures (10 men), with using mechanical stimulation (6 men) and low-frequency myostimulation (5 men) as preventive means. Serum samples were fractionated using ClinProt robot (Bruker Daltonics) on magnetic beads (weak cation exchange magnetic beads—MB WCX) prior to mass-spectral profiling. It was obtained 170 peaks after fractionation of serum samples in each group. On 7th immersion day peak areas of fibrinopeptide A (m/z=1206; 1464), angiotensin II (m/z=1051), high molecular mass kininogen fragment (m/z=2133 Da) and C3-fragment of the complement system (m/z=1350 Da) were significantly decreased comparing with pre-experimental values of all experimental series. Peak areas of apolipoprotein C III (m/z=9419) and C4a fragment of the complement system (m/z=3206 Da) were increased. On 7th day of the recovery peak areas of all changed peaks were not close to pre-experimental values. This fact provided evidence of incomplete recovery of an organism after DI. The depth of the alterations had considerable individual variability. Thereby the detected changes of serum proteome profile in the experiment. They indicated a reorganization of the hormonal, immune systems and lipid metabolism. The use of myostimulation and mechanical stimulation as countermeasures partly compensated adverse effects of 7-day dry immersion on the parameters of coagulation system (fibrinopeptide A) and lipid metabolism (apolipoprotein CIII).     

Evaluation of Ir/Al2O3, Ir–Ru/Al2O3 and Ru/Al2O3 catalyst performance in a 5 N satellite thruster

Ir/Al₂O₃, Ir–Ru/Al₂O₃ and Ru/Al₂O₃ catalysts with approximately 33% metallic content in mass were prepared in 20 impregnation steps. For the Ru catalyst, two impregnation methods were employed: incipient wetness (chlorinated precursor) and by excess volume (non-chlorinated precursor). For the remaining catalysts, only incipient wetness impregnation was used with chlorinated precursors. Catalyst textural properties were evaluated before and after catalytic tests: metallic grade, specific area, mesopore volume distribution, metallic dispersion, and metallic particle average diameter. Catalysts were tested for hydrazine (N₂H₄) decomposition reaction in a 5 N satellite thruster and their performances were compared to Shell 405 commercial catalyst. Results showed that catalysts containing Ir were similar in performance to Shell 405 commercial catalyst and that the catalyst containing only Ru should not be used in cold starts.     

基于区间估计与透射率自适应约束的去雾算法

针对去雾算法透射率估计不足与结果偏色等问题,提出了一种基于最小通道区间估计与透射率自适应约束模型的图像去雾算法。首先,采用不同尺寸最大值操作得到有雾图像的亮通道,并结合均值处理和频域滤波得到大气光估计;其次,从大气成像理论出发,以有雾图像最小通道为约束,分别以平面模型和自适应映射模型拟合无雾图像最小通道上下边界,并获得无雾图像最小通道和透射率初始估计;最后,对透射率作滤波平滑与自适应边界约束,得到优化透射率,并根据大气散射模型得到复原结果。实验表明:所提算法复原结果颜色自然、亮度适宜、去雾彻底、细节信息丰富且时间复杂度较低,有效解决了透射率估计不足和偏色等问题。      

GNSS用户端自主完好性监测研究综述

随着全球卫星导航系统的快速发展,对航空安全提出了挑战,完好性监测问题愈发凸显,用户端自主完好性监测(RAIM)是研究的重点之一。针对RAIM问题,首先介绍了所需导航性能的4个重要参数:精度、完好性、可用性和连续性。从单卫星故障下的RAIM、多卫星故障下的RAIM、高斯噪声下的RAIM 3个方面,综述了国内外相关的重要研究,主要涉及了3个层次内容:算法、计算保护限值和可用性,并指出了目前研究存在的不足。其次介绍了近期研究的新趋势与取得的成果。最后,展望了未来的研究方向。