Study of high-precision earth sensor with triple-FOV

Earth sensors are widely used in spacecraft for attitude determination. They need to have a very large field of view(FOV)( > 120°) and relatively low accuracy while being used in the aircrafts around orbit. A triple-FOV infrared earth sensor is proposed in this paper. It uses three pieces of standard infrared detectors with a wavelength range of 14;16μm,to sense the horizontal circle by detecting the infrared light emitted from the earth. From which,the geocentric vector can be obtained. A mathematic model is established and a validation model is set up to provide input parameters for the mathematic model. The simulation results of the two models show that the output of the mathematic model coincides with the known parameters. Based on the above analysis,a prototype has been built and tested. The test results show that the angle measurement error is about 0. 002° and hence such a triple-FOV earth sensor is capable to provide high-precision position information for autonomous navigation.

Infrared Earth sensor with a large field of view for low-Earth-orbiting micro-satellites

Infrared Earth sensors are widely used in attitude-determination and control systems of satellites.The main deficiency of static infrared Earth sensors is the requirement of a small field of view(FOV).A typical FOV for a static infrared Earth sensor is about 20°to 30°,which may not be sufficient for low-Earth-orbiting microsatellites.A novel compact infrared Earth sensor with an FOV of nearly 180°is developed here.The Earth sensor comprises a panoramic annular lens(PAL)and an off-the-shelf camera with an uncooled complementary-metaloxide-semiconductor(CMOS)infrared sensor.PAL is used to augment FOV so as to obtain a complete infrared image of the Earth from low-Earth-orbit.An algorithm is developed to compensate for the distortion caused by PAL and to calculate the vector of the Earth.The new infrared Earth sensor is compact with low power consumption and high precision.Simulated images and on-orbit infrared images obtained via the micro-satellite ZDPS-2 are used to assess the performance of the new infrared Earth sensor.Experiments show that the accuracy of the Earth sensor is about 0.032°.

Component Content Soft-sensor Based on Neural Networks in Rare-earth Countercurrent Extraction Process

Throught fusion of the mechanism modeling and the neural networks modeling,a compo- nent content soft-sensor,which is composed of the equilibrium calculation model for multi-component rare earth extraction and the error compensation model of fuzzy system,is proposed to solve the prob- lem that the component content in countercurrent rare-earth extraction process is hardly measured on-line.An industry experiment in the extraction Y process by HAB using this hybrid soft-sensor proves its effectiveness.

Information gain based sensor search scheduling for low-earth orbit constellation estimation

This paper addresses the problem of sensor search scheduling in the complicated space environment faced by the low-earth orbit constellation.Several search scheduling methods based on the commonly used information gain are compared via simulations first.Then a novel search scheduling method in the scenarios of uncertainty observation is proposed based on the global Shannon information gain and beta density based uncertainty model.Simulation results indicate that the beta density model serves a good option for solving the problem of target acquisition in the complicated space environments.

Detection of Methanol by a Sensor Based on Rare-earth Doped TiO_2 Nanoparticles

The rare earth doped TiO（2） was prepared and characterized with Nd,Ho and Y as the doping agents,which have obvious absorption in visible light area.The particle size of the glomeration was about 200-400 nm.TiO2 sensor performed a significant change in resistance when exposed to methanol vapor.By comparison,the Nd,Ho and Yb doped TiO2 sensors exhibited a response of 2.22,4.05 and 3.78,and lowered response and recovery times of 91,56 and 67 s,respectively.The Ho doped TiO2 showed the best methanolsensing properties,which exhibited high selectivity and response to methanol compared with the other tested vapors.In concentration of 0-10 ppm,the sensor exhibited excellent stability for detecting methanol at various concentrations.

Neural Networks Based Component Content Soft-Sensor in Countercurrent Rare-Earth Extraction

The equilibrium model for multicomponent rare earth extraction is developed using neural networks, which combined with the material balance model could give online prediction of component content in countercurrent rare earth (extraction) production. Simulation experiments with industrial operation data prove the effectiveness of the hybrid soft-(sensor).

Gasoline Sensor Based on Rare Earth-Doped Indium Oxide with Low Power Consumption

Nanocrystalline indium oxide powders were prepared by microemulsion and then Y2O3 and Nd2O3 doped In2O3 were synthesized separately by impregnation and chemical co-deposition. The structure and morphology were characterized by XRD and TEM, respectively. Gas sensing properties were tested at static state. The results show that homogeneous indium oxide nanopowder with main grain size of 20 nm can be obtained from microemulsion after sintered at 600 ℃ for 1 h. Pure indium oxide gas sensor has higher sensitivity to gasoline than that to ethanol, HCHO, C6H6, NH3, C4H10, but the selectivity is not as well as sensitivity.

Optical Fiber Torsion Sensor with Mechanically Induced Long Period Fiber Gratings in Rare-Earth Doped Fibers

In this work wavelength sensitivity in mechanically induced long period fiber gratings (MLPFG) is analyzed. This analysis is first carried out both in standard single-mode fiber SMF-28 and in Er-doped fibers. The mechanical analysis for both types of fibers under different torsion conditions is presented. In order to apply the torsion one of the fiber ends is fixed while torsion is applied on the other end. A MLPFG whose period is 503 μm is used to press the fiber after torsion is applied. This allows for micro curvatures to be formed on the fiber, which in turn generates a periodical index perturbation on it. Here, it was noted that the sensitive wavelength shift of the rejection bands is bigger for Er-doped fibers. For a torsion of 6 turns applied to 10 cm of doped fiber the wavelength peaks can be moved up to 25 nm, which is longer to what was detected on standard fibers. Therefore, by using Er-doped fibers to monitor torsion on structures will give more sensitive and accurate results than using standard fibers. These results can be employed for sensing applications, especially for small to medium size structures, which can be mechanical, civil or aeronautics.

Research on star-tracking correction technology for near-earth flight vehicles

By analyzing the traditional star-tracking correction technology,this paper studies the star-tracking direct correction method which is based on star sensor dynamic separation initial displacement angles and main errors of inertial measure unit（IMU） in order to carry out automatic navigation and improve the hitting accuracy and quick reaction capability of near-earth flight vehicles.Through comprehensive application and improvement of the best correction factor method,this paper proposes the startracking comprehensive correction method which combines the two methods above-mentioned and the accelerometer dynamic error separation technology.The simulation results show that obvious effects can be achieved by using the star-tracking integrated correction method.

Situation and Developing Trend of Rare-Earth Countercurrent Extraction Processes Control

On the basis of the description of the rare-earth countercurrent extraction process, the on-line detecting method and equipments of rare-earth elements and the application in the process of the rare-earth countercurrent extraction are summarized. The procedure simulation of the computer, the automation control method and its current application are also mentioned in the process of rare-earth countercurrent extraction. The method of soft sensor is proposed. Optimal control method based on object-oriented rare-earth countercurrent extraction process and integrated automation system composed of process management system and process control system are presented, which are the developing direction of the automation of rare-earth countercurrent extraction process.

Synthesis and Characterization of Y-Doped SnO_2 as Sensor Materials

Yttrium-doped SnO2 powders were successfully synthesized by solution co-precipitation method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The sensitivity of sensors based on Y-doped SnO2 and SnO2 nanocrystals were investigated comparatively. The results indicated that Y-doped SnO2 was with the result of enhancement of sensitivity and selectivity to ethanol and reduction of sensitivity to other gas components. The enhancements of selectivity and sensitivity could be contributed to for two reasons. The first is that rare metal yttrium has a high alkalescence and good catalysis, and the second is that the nanosized crystallite and large specific surface area of Y-doped SnO2 is advantageous for gas-diffusion control as well as an increase in active sites for gas detection.

OBE理念和前沿科研成果融入无机化学实验教学——稀土配合物的制备及其抗生素传感研究

针对本校无机化学实验教学中存在的问题,设计了一个基于蒽基羧酸配体的发光稀土配合物并将其用于抗生素传感的研究。首先,利用溶剂热合成方法制备发光稀土配合物。其次,利用单晶X射线衍射仪,红外光谱仪,X-射线粉末衍射等技术表征配合物的结构。此外,借助荧光光谱仪记录发光稀土配合物对抗生素的荧光传感。本实验将OBE理念和科技前沿引入无机化学实验有助于激发学生的科研兴趣、提升科研素养,为进一步优化实验课程教育模式、提高学生的实践和创新能力奠定基础。

基于精化预积分的GNSS/IMU/视觉多源融合定位方法

针对传统预积分算法固定地球重力值和忽略地球自转的问题,提出一种考虑地球自转和重力变化的惯性测量单元(inertial measurement unit, IMU)预积分算法。参照高精度捷联惯性导航解算的动力学模型,在IMU预积分动力学模型的姿态更新中引入地球自转角速率,速度和位置更新中引入由地球自转引起的科里奥利加速度,同时将由载体位置引起的地球重力变化及时反馈至预积分算法中,详细推导了引入地球自转和重力变化后预积分算法的具体过程,实现对传统预积分模型的精化。并将精化的预积分算法应用于基于紧耦合全球导航卫星系统(global navigation satellite system, GNSS)/IMU/视觉多源融合系统中,实测实验结果表明:利用精化的预积分模型可使系统预积分的模型误差有效减小,显著提升多源融合系统整体的定位定姿精度,其中系统定位精度提升32.41%,航向角精度提升4.23%。

稀土掺杂热障涂层体系及其荧光效应研究现状与发展趋势

稀土掺杂热障涂层是指将稀土元素掺杂到热障涂层(ThermalBarrierCoatings,TBCs)陶瓷面层中,不仅可以在一定程度上改善热障涂层的隔热性能和力学性能,还可以赋予其荧光特性,利用其荧光特性可以实现温度测量、热历史追踪、无损检测等方面的应用,从而达到寿命预测的目的。重点围绕国内外稀土荧光效应在热障涂层中的研究和发展趋势进行了系统阐述,分别介绍了稀土掺杂热障涂层的结构以及荧光效应在时间效应和强度效应上的检测原理,分析了热障涂层稀土掺杂原理及其制备工艺,讨论了稀土元素的掺杂对热障涂层热力学性能以及抗CMAS(CaO、MgO、Al_(2)O_(3)、SiO_(2))腐蚀性的影响,阐述并分析了基于稀土荧光效应的热障涂层在荧光测温、热历史传感器和无损检测等方面的研究和应用,为后续基于稀土荧光效应的热障涂层研究和应用奠定了理论基础,最后对基于稀土荧光效应的热障涂层今后需要解决的问题和发展方向进行了展望。

一种基于Madgwick-EKF融合算法的卫星姿态测量方法

针对低地球轨道卫星姿态测量时,传感器易受噪声干扰、陀螺仪漂移等问题,提出一种基于Madgwick扩展卡尔曼滤波合算法(EKF)的卫星姿态测量方法。该方法采用陀螺仪、加速度计、磁强计等多传感器数据进行融合,并结合Madgwick算法和EKF算法的优点,实现姿态测量。首先,通过Madgwick算法,利用多个传感器测量数据计算初始姿态。然后,基于初始姿态和实际测量数据,应用EKF算法进行数据融合和噪声滤除,以获得最终准确的姿态估计。实验结果表明:相较Madgwick算法,本算法在测量精度上提升了65.8%,且具有较高的鲁棒性,为低地球轨道卫星姿态测量提供了一种有效的方案。

小型准直式红外地球模拟器研究

地球模拟器是卫星姿态测量控制关键部件—摆动扫描式红外地球敏感器的一种重要地面模拟试验与精度标定仪器。本文针对卫星同步轨道高度(35786km),采用准直式方案,研制了一种口径为Φ150mm的准直式红外地球模拟器,它能提供17.46°的地球张角,实现了地面上模拟卫星在太空中所看到的地球。文中详细介绍了准直式红外地球模拟器的组成和总体结构,采用红外光学技术,设计了锗准直透镜,通过理论分析得出地球光阑、热地球位置和大小与地球张角、锗准直透镜光学参数之间的关系,为地球模拟器的研制提供了设计依据。地球张角是衡量地球模拟器精度的指标,通过实验对地球张角进行了测试,结果表明地球张角误差小于±0.05°。

长波红外广角地平仪镜头的光学设计

介绍适用于非致冷凝视式焦平面阵列的长波红外 (LWIR)广角地平仪镜头的光学设计。其工作波长范围 1 0～ 1 6 μm ,全视场角为 1 35°。采用“负 -正 -正”型式的反远距像方远心光路镜头结构 ,仅有三块非球面锗透镜构成。能够很好地解决广角镜头轴外像差校正和像面照度均匀性问题。此镜头结构简单、体积很小、后工作距离大 ,成像质量接近于衍射极限 ,在 2 0lp/mm空间频率处的调制传递函数值超过 0 .6 ,像高与视场角关系偏离线性的相对误差不超过 1 5 %。

圆锥扫描式红外地球模拟器研究

针对适用于低轨道卫星的圆锥扫描式红外地球敏感器地面模拟试验、标定和可靠性测试等问题,采用开有120°V型槽的扇形冷板模拟地球弦宽、金属热板模拟地球热源的方案,研制了圆锥扫描式红外地球模拟器和零姿态模拟器,其能模拟卫星在低轨道上看到的地球,提供120°地球弦宽。

广角f-θ静态红外地平仪镜头的光学设计

为了满足航天器对轻小、价廉,性能可靠的自主导航系统的要求,设计了广角静态红外地平仪系统。该系统选择辐射稳定的14～16.25μm作为工作波段,并设定全视场角为136°,F数为0.61;采用反远距结构,使系统后工作距达到15mm;利用f-θ镜头设计原理,并合理地选用非球面对广角系统进行优化设计,使系统的线性特性的相对误差<0.5%;在空间频率为15lp/mm处,系统的调制传递函数>0.6,接近衍射极限;在半径为20μm的圆内,系统径向能量>85%。另外,采用了像方远心光路,提高了像面的照度均匀性,实现了整个像面照度均匀性>99%。设计结果表明,该镜头结构简单、体积小、后工作距大,很好地解决了广角镜头轴外像差平衡问题,实现了地平仪系统的高精度设计。

基于地球敏感器和加速度计的月球车自主定向算法研究

月球车定向是月球车导航的一个重要组成部分,它是月球车定位的基础和前提。针对这一问题,提出了一种适用于月球车长时间、长距离导航的绝对定向算法。该算法利用非线性最小二乘平差原理对CCD地球敏感器成像进行处理,实现了在月球表面CCD地球敏感器的矢量观测功能。结合加速度计的测角原理,实现了航向角确定。以理论分析和实际推算描述了该定向方法的具体实现过程,最后以仿真结果验证了该方案的可行性,为未来我国月球探测中月球车的实际应用提供了技术参考。