地球卫星星光折射导航量测量及其性能对比

星光折射天文导航是一种重要的地球卫星自主导航方式,量测量是影响其导航精度的重要因素。在地球卫星星光折射导航中,折射视高度、星光折射角、折射星像素坐标（折射星矢量）是3种常用的量测量,结合星光折射导航的基本原理重点介绍了这3种量测量的获取方法和量测模型,通过仿真和可观性分析比较了相同条件下3种量测量的导航性能。仿真结果表明,由于折射星像素坐标可以同时反映星光折射的大小和方向可观性高,而星光折射角和折射视高度仅能反映星光折射的大小,无法反映其方向可观性低,因此折射星像素坐标的导航性能优于星光折射角和折射视高度。此外,本文也对星敏感器精度、卫星轨道高度、星敏感器安装夹角3种因素对3种方法导航性能的影响进行了分析。     

基于星光导航分离陀螺仪漂移误差方法研究

星光/惯性组合制导方式集中了两种方式的优点,可在导弹飞出大气层后通过对导航星的观测校正陀螺仪误差系数。在研究了星光导航的特点和陀螺仪误差特性的基础上,提出了通过旋转弹体观测特定位置的导航星,利用星光导航系统分离陀螺仪漂移误差系数的方法。结果表明:利用导航恒星高精度基准可以分离陀螺仪漂移误差系数,准确地确定陀螺仪漂移误差模型,对于提高导弹的精度具有重要意义。     

惯性+星光折射定位组合导航技术研究

由于现有惯性器件精度水平有限,纯惯性导航误差较大,因此需要采用组合导航的方式来提高导航精度。目前,全自主组合导航方式中传统的惯性+星光定姿组合导航方法只能实现定姿,不能实现定位,无法修正加速度表测量误差引起的惯性导航误差,故在精度上可提升空间有限。为此,提出了一种惯性+星光折射定位组合导航方法,重点从星光折射定位原理、大气折射模型、非线性滤波和选星策略几个方面进行论证及分析。通过理论分析与数学仿真相结合的手段,验证了星光折射定位原理的正确性及工程可行性,可将自主导航精度提升至100m,从而为进一步提高自主导航精度提供了一种技术途径。     

考虑星敏感器安装误差的弹道导弹捷联星光/惯性复合制导

弹道导弹捷联星光/惯性制导是在惯性制导基础上辅以星光修正的一种复合制导方法，能够显著提高导弹制导精度。由于星敏感器捷联安装在弹体上，安装误差会影响恒星测量的精度，进而影响复合制导精度，为此提出一种在线辨识并修正星敏感器安装误差的复合制导方法。建立了星敏感器观测量与数学平台失准角、星敏感器安装误差的关系方程，在导弹主动段关机后测量3颗独立的恒星获得6个观测量，利用最小二乘法估计出失准角和星敏感器安装、误差。改进了星光/惯性复合制导的最佳修正系数确定方程，直接修正了星敏感器安装误差的影响。数值仿真结果表明：所提方法可以有效地估计平台失准角和星敏感器安装误差，提高了捷联星光/惯性复合制导的精度。     

高空长航时无人机高精度自主定位方法

针对传统基于轨道动力学模型及非线性滤波进行间接敏感地平天文导航定位方法在实际应用中的局限性,提出了一种适用于高空长航时无人机自主导航定位的快速间接敏感地平天文解析定位新方法。分析了星光折射视高度天文量测的机理,导出天文三维定位的解析表达式,详细阐述了利用最小二乘微分校正法代替非线性滤波的天文定位方法,通过直接求解非线性量测方程组即可得到飞行器的精确位置信息,并对这种定位方法的定位精度进行了理论分析。该天文定位方法利用了星光折射间接敏感地平精度高的特点,又不需要飞行器动力学模型也不需要任何先验知识,算法简单可靠,计算量小,而定位精度与传统方法相当。最后,通过计算机仿真,验证了这种天文定位方法的有效性。     

发展单兵星敏导航装备的必要性及技术特点

星光导航不受电磁干扰、能提供绝对姿态信息，具有重大战略意义。目前的星敏主要是为空天基导航而发展的，将其应用于单兵导航是否必要、需克服哪些技术难点、能达到怎样的效果等，都是值得探索的问题。为此，首先论述了发展单兵星敏导航装备的必要性，包括：不受电磁干扰破坏，是其他单兵导航装备失效时的保底装备；定向精度高，能弥补单兵卫星导航装备无法定向的缺陷；已突破部分气象因素限制，具备了全天时导航条件等。然后探讨了单兵星敏导航与空天基星敏导航、卫星导航、天文大地测量等比较所具有的不同技术特点。提出了发展单兵星敏导航装备需解决的关键技术问题，包括：气象因素影响的消减、时间基准和电源的长期维持、系统探测性能与系统小型化的平衡等。研究结果可为发展单兵星敏导航技术、设计研制单兵星敏导航系统提供参考。     

多源信息融合卫星组合导航系统的可观度分析

针对基于GNSS卫星、地标矢量和星光矢量的多源信息融合的高轨卫星组合导航系统,分别利用系统可观度分析方法和状态可观度分析方法对其进行分析。仿真结果表明:在GNSS导航卫星不可见时,地标矢量和星光矢量可以有效地提供测量信息,并保证滤波器的稳定。可观度分析结果表明:系统可观度主要受GNSS导航星的可见星数目影响较大,地标矢量和星光矢量的引入有助于提高可观度;基于状态的可观度可以大致反映出滤波器每个状态的误差大小。     

飞行器再入时GNC系统一体化仿真研究

首先建立了飞行器再入时制导、导航和姿控ＧＮＣ系统一体的六自由度数学仿真模型。然后对如何消除控制系统和运动方程的交连影响和导航误差给落点精度带来的影响进行了分析和讨论同时还研究了六自由度弹道计算对导引和制导规律的影响，最后对飞行器再入时如针制导，导航和姿控系统组合在一起进行六自由度数学仿真进行了分析和研究，并讨论了一体化仿真可怕一些问题。     

弹道导弹捷联惯导/天文组合导航方案研究

通过分析捷联惯性导航和天文导航的特点,提出利用扩展卡尔曼滤波方法融合捷联惯导和星光测量信息以提高弹道导弹落点精度的可行方案。研究了捷联惯导系统误差模型,建立了滤波误差状态方程和星敏感器原始信息测量方程。星敏感器从发动机关机后开始工作,在滤波过程中对捷联惯导测量误差进行了反馈校正。仿真结果表明,星敏感器开始工作后导弹的位置、速度和姿态误差的方差立即减小,导弹的落点精度也大幅度提高。     

大气折射对电视制导导弹定位精度的影响分析

为了提高电视制导导弹的定位精度,有必要研究大气折射效应的影响。基于大气折射率模型,采用高精度的4阶Runge-Kutta光线追迹方法,以定位误差和俯角误差为大气折射效应的评价标准,建立了电视制导导弹大气折射误差模型,并通过探空仪实测大气参数验证了模型的有效性以及精度测试验证了算法的可靠性。基于该模型,仿真分析了不同发射高度和俯角对定位精度的影响规律。研究结果发现：高海拔时,基于三段模型的大气折射误差要小于其他模型;相同高度下导弹发射的视在俯角扩大10倍,由大气折射造成的定位误差和俯角误差将分别缩小1 000倍和10倍;5 km高度、视在俯角为30°时的定位误差已减小到2 m以内。研究结果表明,该方法可以辅助电视制导导弹的设计,对提高其精确打击能力具有重要意义。     

Orion-2: First scientific results

The ultraviolet spectral images of thousands of faint stars, up to the 13th mag., in the wavelength region of 2000–5000 Å are obtained by means of the space astrophysical observatory Orion-2 aboard the spaceship Soyuz-13. These spectrograms were designed generally for an investigation of the continuous spectra of the stars in ultraviolet. The processing and measurement of part of the material available confirm the expectations for the solution of a large number of problems concerning the physics of stars and stellar atmospheres. Some of the results obtained are included in the present review. Particularly, the observed distribution of continuous energy in the ultraviolet of normal hot stars is in line, according to Orion-2 data, with theoretical prediction; the existence of a new type of high temperature (> 20000K) and low absolute luminosity stars is noticed; the blocking effect of the ultraviolet absorption lines expected for the A-type stars is confirmed; a number of empirical regularities concerning the behaviour of the ultraviolet doublet of ionized magnesium, 2800 Mg ii, in the stellar spectra are derived; the chromosphere in cold stars is detected; the role of a multiplet of ionized titanium, 3080 Ti ii, in stellar spectra is revealed; probably an abnormal silicon-rich stellar envelope around a Be-type star is discovered; a new method for the spectral classification of the stars by their ultraviolet spectral images is developed; a range of interesting facts relating to the structure of the ultraviolet spectra of middle type stars (F-K) come to the fore; an exceptional ultraviolet spectrogram for the planetary nebula II 2149 and its nuclei is obtained; the blocking effect of emission lines in the spectrum of the B-type emission and normal O-type stars has been detected; a remarkably faint (12^itm.6) and high temperature star (No. 1) of strange spectral structure has been discovered.     

An all-sky autonomous star map identification algorithm

The attitude of the spacecraft can be obtained with accuracy by using star sensors. Its key technology is how to identify stellar maps. Triangle algorithm is used most widely in the current star map identification algorithms. In the field of physical geography modelling, Delaunay triangulation cutting algorithm has been widely used because of its important characteristic; the result of this triangulation cutting method is unique from a random set of points. This triangulation algorithm is first applied to identify star map for its particular character. In final, the proposed method is applied to simulation; the results show that compared with the current star map identification algorithms, the algorithm presented in this paper has the advantage of real-time properties and robustness. It needs a smaller database of guidance stars and matches more rapidly.     

Low-Mass Pre–Main-Sequence Stars in the Magellanic Clouds

The stellar Initial Mass Function (IMF) suggests that stars with sub-solar mass form in very large numbers. Most attractive places for catching low-mass star formation in the act are young stellar clusters and associations, still (half-)embedded in star-forming regions. The low-mass stars in such regions are still in their pre–main-sequence (PMS) evolutionary phase, i.e., they have not started their lives on the main-sequence yet. The peculiar nature of these objects and the contamination of their samples by the fore- and background evolved populations of the Galactic disk impose demanding observational techniques, such as X-ray surveying and optical spectroscopy of large samples for the detection of complete numbers of PMS stars in the Milky Way. The Magellanic Clouds, the metal-poor companion galaxies to our own, demonstrate an exceptional star formation activity. The low extinction and stellar field contamination in star-forming regions of these galaxies imply a more efficient detection of low-mass PMS stars than in the Milky Way, but their distance from us make the application of the above techniques unfeasible. Nonetheless, imaging with the Hubble Space Telescope within the last five years yield the discovery of solar and sub-solar PMS stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of such objects are identified as the low-mass stellar content of star-forming regions in these galaxies, changing completely our picture of young stellar systems outside the Milky Way, and extending the extragalactic stellar IMF below the persisting threshold of a few solar masses. This review presents the recent developments in the investigation of the PMS stellar content of the Magellanic Clouds, with special focus on the limitations by single-epoch photometry that can only be circumvented by the detailed study of the observable behavior of these stars in the color-magnitude diagram. The achieved characterization of the low-mass PMS stars in the Magellanic Clouds allowed thus a more comprehensive understanding of the star formation process in our neighboring galaxies.     

Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

Massive stars, at least \(\sim10\) times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy.In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense “clumps”. The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution.Supergiant high mass X-ray binaries (SgXBs) are among the brightest X-ray sources in the sky. A large number of them consist of a neutron star accreting from the wind of a massive companion and producing a powerful X-ray source. The characteristics of the stellar wind together with the complex interactions between the compact object and the donor star determine the observed X-ray output from all these systems. Consequently, the use of SgXBs for studies of massive stars is only possible when the physics of the stellar winds, the compact objects, and accretion mechanisms are combined together and confronted with observations.This detailed review summarises the current knowledge on the theory and observations of winds from massive stars, as well as on observations and accretion processes in wind-fed high mass X-ray binaries. The aim is to combine in the near future all available theoretical diagnostics and observational measurements to achieve a unified picture of massive star winds in isolated objects and in binary systems.     

Star-configuration searching for satellite attitude computation

A star pattern recognition algorithm is described which recovers attitude information by processing data obtained from a modular star sensor (MOSS) mounted on a spacecraft information is obtained by matching the stars detected by the MOSS with those inside a stellar catalogue. The system performance has been evaluated both from the point of view of computation time and error probability. The effect of errors in the MOSS measurements and multiple matches cases are also discussed     

A Celestial Analytic Positioning Method by Stellar Horizon Atmospheric Refraction

This article, in allusion to the limitation of conventional stellar horizon atmospheric refraction based on orbital dynamics model and nonlinear Kalman filter in practical applications, proposes a new celestial analytic positioning method by stellar horizon atmospheric refraction for high-altitude flight vehicles, such as spacecraft, airplanes and ballistic missiles. First, by setting up the geometric connexion among the flight vehicle, the Earth and the altitude of starlight refraction, an expression for the relationship of starlight refraction angle and atmospheric density is deduced. Second, there are produced a novel measurement model of starlight refraction in a continuous range of altitudes (CRA) from 20 km to 50 km on the basis of the standard atmospheric data in stratosphere, and an empirical formula of stellar horizon atmospheric refraction in the same altitudes against the tangent altitude. Third, there is introduced a celestial analytic positioning algorithm, which uses the least square differential correction instead of nonlinear Kalman filter. The information about positions of a flight vehicle can be obtained directly by solving a set of nonlinear measurement equations. The stellar positioning algorithm adopts the characteristics of stellar horizon atmospheric refraction thereby removing needs for orbit dynamics models and priori knowledge of flight vehicles. The simulation results evidence the validity of the proposed stellar positioning algorithm.