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1.
北斗卫星导航系统(BDS)地面跟踪站都配置有高精度的氢原子钟,并基于精密定轨数据处理与主站的时间基准进行同步.在卫星轨道机动以及机动恢复期间,通常采用几何法定轨以及单星定轨确定卫星的轨道.而在这两种定轨模式中,需要提供精确的测站钟差作为输入.为提高定轨的实时性,需要对测站钟差进行预报处理.分析了2次多项式模型、附加周期项模型、灰色模型3种模型对北斗地面跟踪站钟差短期拟合和预报的性能,并将钟差预报结果应用于单星定轨,同时还分析了不同预报钟差用于定轨的精度.试验发现,以上3种模型对6个测站钟差的平均拟合精度分别为0.14 ns、0.05 ns、0.27 ns,预报1 h的平均精度分别为1.17 ns、0.88 ns、1.28 ns,预报2 h的平均精度分别为2.72 ns、2.09 ns、2.53 ns.采用3种模型对测站钟差进行预报并用于单星定轨,采用附加周期项的钟差预报模型轨道3维误差最小,不同模型轨道径向精度差异在3 cm以内.以上结果表明,附加周期项的站钟拟合及预报模型在北斗系统机动期间的轨道恢复数据处理具有最好的效果. 相似文献
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根据我国广域差分GPS系统对GPS卫星定轨的要求,通过对国内GPS跟踪网实测数据的处理,分析和讨论了区域网定轨的数据处理方法和可能达到的定轨精度。为了提高所定轨道的稳定性和先进实时预报的精度,通过对所定轨道的误差分析提出在轨道沿迹方向引入经验加速度计算方案。计算结果表明,采用此方法后GPS卫星的定轨精度有了显提高。既论证了利用我国区域GPS网和广播星历进行独立定轨的可行性,也阐述了提高轨道预报精度的方法。 相似文献
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连线干涉测量(Connected Element Interferometry, CEI)是一种全天时全天候的被动测角技术, 已用于空间目标的跟踪监视. 地球静止轨道(Geostationary Earth Orbit, GEO)卫星需要频繁机动以保持轨位或完成其他任务, 其机动后的快速轨道恢复能力对于监视预警极为重要. 针对基于CEI的GEO短弧定轨和预报, 分析了定轨算法的形亏和数亏, 在附加先验轨道约束的短弧定轨基础上, 提出了轨道半长轴初值的自适应优化方法. 利用亚太七号卫星的CEI仿真和实测数据进行了短弧定轨和预报, 实验结果表明, 采用优化后的半长轴初值, 30min短弧定轨和10min预报的卫星位置分量精度均优于4km, 能够满足非合作GEO目标机动后快速轨道恢复的需求. 相似文献
6.
利用VLBI数据确定"探测一号"卫星的轨道 总被引：5，自引：0，他引：5
双星计划的“探测一号”是中国首颗真正严格意义上的科学实验卫星,其运行轨道为中国迄今所发射的卫星中距地球最远,远地点地心距达7．8万公里．采用射电天文的VLBI技术可以对“探测一号”以及更远的深空目标,如探月飞行器实现跟踪．为了验证VLBI技术在我国探月计划中的作用,上海天文台组织了国内目前仅有的上海、乌鲁木齐和昆明3个台站对“探测一号”进行试跟踪,利用对“探测一号”约两天的VLBI观测数据,确定“探测一号”卫星的轨道,对VLBI的定轨能力做初步的探讨．按照测控部门提供的初轨 (其精度仅保证跟踪)推算的轨道与VLBI时延的拟合误差平均约2 km,时延率的拟合误差平均约15 cm／s．而利用VLBI数据定轨后的拟合程度相对于初轨有了很大的改善,结果表明,单独利用VLBI时延定轨,时延的拟合精度约5．5 m,作为外部检核的VLBI时延率的拟合精度在2 cm／s左右．单独利用VLBI时延率定轨,时延率的拟合精度约为1．3 cm／s,作为外部检核的VLBI时延的拟合精度约为29 m．而若将时延和时延率数据联合定轨,采用其内符精度加权,VLBI时延和时延率的残差分别为5．5 m和 2 cm／s．为了合理地评估VLBI定轨的真实精度,利用模拟数据进行误差协方差分析,结果表明VLBI定轨精度受动力学模型误差的影响较大,由于"探测一号”卫星的动力学模型难以精确确定,所以利用两天弧段的VLBI数据确定“探测一号”卫星轨道的位置误差为km量级,而速度误差可达cm／s量级．模拟计算还表明, VLBI和USB数据联合定轨可以大大提高定轨精度． 相似文献
7.
《天文学报》2015,(5)
地球引力场模型是人造卫星轨道计算中最重要的动力学模型之一.近年来国际上空间重力卫星计划取得了极大成功,相继推出了一系列新的引力场模型.从近地卫星轨道计算的角度检验了2种传统引力场模型(JGM3,EGM96)和4种新引力场模型(EIGENCHAMP05S,GGM03S,GOCE02S,EGM2008)的精度,利用4颗近地卫星的激光测距资料进行精密定轨预报,统计比较了不同模型的定轨残差和预报误差.结果表明:(1)4种新引力场模型精度基本在同一水平,对于近地卫星定轨精度普遍优于9 cm,最高达到5cm,相对于JGM3和EGM96模型有明显改善;(2)以JGM3模型为基准,EGM96模型的精度有所提高,2000年以后的4种新模型的精度则普遍提高了12%～47%(定轨)和63%(预报).70阶之前定轨精度随着模型阶次增大而提高,70阶以后定轨精度基本保持稳定,这表明对于近地卫星轨道计算而言,70阶的引力场已经能够满足厘米级的精度需求. 相似文献
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地球定向参数(Earth orientation parameters, EOP)是地球参考系到地心天球参考系之间转换的桥梁,是卫星精密定轨过程中不可缺少的重要参数。以国际地球自转服务(International Earth Rotation Service, IERS)和中国科学院上海天文台(Shanghai Astronomical Observatory,SHAO)提供的EOP参数为例,分析了北斗三号仅区域网观测模式和星地星间联合观测模式下的定轨精度与EOP预报误差间的关系。研究表明,对于IERS提供的产品,其预报误差对仅区域站定轨模式的定轨精度影响较小,但是其10 d内的预报误差对星地星间联合定轨模式定轨精度的影响可达到分米级。对于SHAO提供的产品,两种定轨模式的定轨精度均随着EOP预报天数的增大而逐渐衰减。除此之外,不同产品的星地星间联合定轨模式下定轨精度均小于仅区域网监测下的定轨模式下的定轨精度,表明星间链路的加入可以降低卫星定轨对EOP预报误差的依赖。该研究对区域观测条件下的卫星精密定轨工程实现具有重要意义。 相似文献
9.
SGP4/SDP4模型精度分析 总被引：2，自引：0，他引：2
本文基于最新发布的SGP4/SDP4(Simplified General Perturbation Version 4/Simplified Deep-space Perturbation Version 4)模型设计了一套定轨方案,从空间目标库中挑选出不同类型和轨道参数的1120个目标进行计算,定量给出了SGP4/SDP4模型处理不同类型空间目标的定轨预报精度.结果表明:近地目标定轨精度为百米量级;半同步和同步轨道定轨精度平均为0.7和1.9km.椭圆轨道目标的定轨精度与偏心率有关,除少数e>0.8的椭圆轨道目标,绝大多数椭圆轨道目标定轨误差均小于10km.用SGP4/SDP4模型对近地目标预报3天,半同步轨道预报30天,同步轨道预报15天,椭圆轨道预报1天,预报误差一般不超过40km. 相似文献
10.
《天文学报》2016,(4)
低轨卫星轨道预报精度受到大气模型和大气阻力系数精度的制约,给一些高精度的空间和航天任务带来不利影响.提出了一种基于沿迹方向误差发散规律的大气阻力系数计算新方法.首先通过理论推导给出低轨卫星轨道预报中沿迹误差发散的分析表达式,定量描述初值误差和模型误差对沿迹误差的综合影响;提出利用定轨段的基本信息,优选预报段所采用的阻力系数,抑制沿迹误差的发散速率,从而降低沿迹方向预报误差的最大值,提高短期预报精度.以400 km附近的GRACE-A卫星的全弧段星载GPS高精度资料为基础,检验了方法的精度和成功率.结果表明:相对于传统的定轨预报方法,新方法能提高24 h短期预报精度约45%,成功率约71%,总体有效率约86%;方法对低、中、高等3种太阳辐射水平均有效,对于中低等级的地磁扰动也有效,具备较好的应用价值. 相似文献
11.
C. M. Andreazza E. P. Marinho P. D. Singh † 《Monthly notices of the Royal Astronomical Society》2006,372(4):1653-1656
The rate coefficients for the formation of carbon monophosphide (CP) and silicon monophosphide (SiP) by radiative association are estimated for temperatures ranging from 300 to 14 100 K. In this temperature range, the radiative association rate coefficients are found to vary from 1.14 × 10−18 to 1.62 × 10−18 cm3 s−1 and from 3.73 × 10−20 to 7.03 × 10−20 cm3 s−1 for CP and SiP, respectively. In both cases, rate coefficients increase slowly with the increase in temperature. 相似文献
12.
R. Rummel 《Earth, Moon, and Planets》2004,94(1-2):103-111
Planetology serves the understanding on the one hand of the solar system and on the other hand, for investigating similarities
and differences, of our own planet. While observational evidence about the outer planets is very limited, substantial datasets
exist for the terrestrial planets. Radar and optical images and detailed models of gravity and topography give an impressive
insight into the history, composition and dynamics of moon and planets. However, there exists still significant lack of data.
It is therefore recommended to equip all future satellite missions to the moon and to planets with full tensor gravity gradiometers
and radar altimeters. 相似文献
13.
Both Uranus and Neptune are thought to have strong zonal winds with velocities of several 100 m s−1. These wind velocities, however, assume solid-body rotation periods based on Voyager 2 measurements of periodic variations in the planets’ radio signals and of fits to the planets’ magnetic fields; 17.24 h and 16.11 h for Uranus and Neptune, respectively. The realization that the radio period of Saturn does not represent the planet’s deep interior rotation and the complexity of the magnetic fields of Uranus and Neptune raise the possibility that the Voyager 2 radio and magnetic periods might not represent the deep interior rotation periods of the ice giants. Moreover, if there is deep differential rotation within Uranus and Neptune no single solid-body rotation period could characterize the bulk rotation of the planets. We use wind and shape data to investigate the rotation of Uranus and Neptune. The shapes (flattening) of the ice giants are not measured, but only inferred from atmospheric wind speeds and radio occultation measurements at a single latitude. The inferred oblateness values of Uranus and Neptune do not correspond to bodies rotating with the Voyager rotation periods. Minimization of wind velocities or dynamic heights of the 1 bar isosurfaces, constrained by the single occultation radii and gravitational coefficients of the planets, leads to solid-body rotation periods of ∼16.58 h for Uranus and ∼17.46 h for Neptune. Uranus might be rotating faster and Neptune slower than Voyager rotation speeds. We derive shapes for the planets based on these rotation rates. Wind velocities with respect to these rotation periods are essentially identical on Uranus and Neptune and wind speeds are slower than previously thought. Alternatively, if we interpret wind measurements in terms of differential rotation on cylinders there are essentially no residual atmospheric winds. 相似文献
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Daniel Pfenniger 《Celestial Mechanics and Dynamical Astronomy》1998,72(1-2):37-67
An elementary review about stellar and galactic dynamics is presented. Despite involving extremely classical Newtonian physics,
stellar dynamics presents some fundamental difficulties rarely discussed in the literature, such as why the phase space distribution
is assumed to be a smooth function of coordinates. Many systems are found to be unstable over intermediate time-scales, as
more instabilities have been discovered over the years, so the old aim of describing equilibrium stable systems shifts presently
toward understanding evolutive systems. From the linearized variational Boltzmann equation a distinction can be made between
instabilities triggered by the chaotic part of phase space, and instabilities caused by steep gradients in the velocity part
of the distribution function. The new challenges to include evolutive systems can presently only be studied efficiently with
computer techniques. Future studies are likely to involve orders of magnitude more advanced computers in which parallelism
will play a major role.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
V. A. Shefer 《Celestial Mechanics and Dynamical Astronomy》2002,82(1):19-59
A method of construction of intermediate orbits for approximating the real motion of celestial bodies in the initial part of trajectory is proposed. The method is based on introducing a fictitious attracting centre with a time-variable gravitational parameter. The variation of thisparameter is assumed to obey the Eddington–Jeans mass-variationlaw. New classes of orbits having first-, second-, and third-order tangency to the perturbed trajectory at the initial instant of time are constructed. For planar motion, the tangency increases by one or two orders. The constructed intermediate orbits approximate the perturbed motion better than the osculating Keplerian orbit and analogous orbits of otherauthors. The applications of the orbits constructed in Encke's methodfor special perturbations and in the procedure for predicting themotion in which the perturbed trajectory is represented by a sequenceof short arcs of the intermediate orbits are suggested.The use of the constructed orbits is especially advantageous in the investigation of motion under the action of large perturbations. 相似文献
16.
We study the temporal variation of subsurface flows of 788 active regions and 978 quiet regions. The vertical-velocity component
used in this study is derived from the divergence of the measured horizontal flows using mass conservation. The horizontal
flows cover a range of depths from the surface to about 16 Mm and are determined by analyzing about five years of GONG high-resolution
Doppler data with ring-diagram analysis. We determine the change in unsigned magnetic flux during the disk passage of each
active region using MDI magnetograms binned to the ring-diagram grid. We then sort the data by their flux change from decaying
to emerging flux and divide the data into five subsets of equal size. The average vertical flows of the emerging-flux subset
are systematically shifted toward upflows compared to the grand average values of the complete data set, whereas the average
flows of the decaying-flux subset show comparably more pronounced downflows especially near 8 Mm. For flux emergence, upflows
become stronger with time with increasing flux at depths greater than about 10 Mm. At layers shallower than about 4 Mm, the
flows might start to change from downflows to upflows, when flux emerges, and then back to downflows after the active regions
are established. The flows in the layers between these two depth ranges show no response to the emerging flux. In the case
of decaying flux, the flows change from strong upflows to downflows at depths greater than about 10 Mm, whereas the flows
do not change systematically at other depths. A cross-correlation analysis shows that the flows in the near-surface and the
deeper layers might change about one day before flux emerges. The flows associated with the quiet regions fluctuate with time
but do not show any systematic variation. 相似文献
17.
18.
Edward R.D. Scott 《Icarus》2006,185(1):72-82
Thermal models and radiometric ages for meteorites show that the peak temperatures inside their parent bodies were closely linked to their accretion times. Most iron meteorites come from bodies that accreted <0.5 Myr after CAIs formed and were melted by 26Al and 60Fe, probably inside 2 AU. Rare carbon-rich differentiated meteorites like ureilites probably also come from bodies that formed <1 Myr after CAIs, but in the outer part of the asteroid belt. Chondrite groups accreted intermittently from diverse batches of chondrules and other materials over a 4 Myr period starting 1 Myr after CAI formation when planetary embryos may already have formed at ∼1 AU. Meteorite evidence precludes accretion of late-forming chondrites on the surface of early-formed bodies; instead chondritic and non-chondritic meteorites probably formed in separate planetesimals. Maximum metamorphic temperatures in chondrite groups are correlated with mean chondrule age, as expected if 26Al and 60Fe were the predominant heat sources. Because late-forming bodies could not accrete close to large, early-formed bodies, planetesimal formation may have spread across the nebula from regions where the differentiated bodies formed. Dynamical models suggest that the asteroids could not have accreted in the main belt if Jupiter formed before the asteroids. Therefore Jupiter probably reached its current mass >3-5 Myr after CAIs formed. This precludes formation of Jupiter via a gravitational instability <1 Myr after the solar nebula formed, and strongly favors core accretion. Jupiter probably formed too late to make chondrules by generating shocks directly, or indirectly by scattering Ceres-sized bodies across the belt. Nevertheless, shocks formed by gravitational instabilities or Ceres-sized bodies scattered by planetary embryos may have produced some chondrules. The minimum lifetime for the solar nebula of 3-5 Myr inferred from the total spread of CAI and chondrule ages may exceed the median lifetime of 3 Myr for protoplanetary disks, but is well within the 1-10 Myr observed range. Shorter formation times for extrasolar planets may help to explain their unusual orbits compared to those of solar giant planets. 相似文献
19.
Solar filaments exhibit a range of eruptive-like dynamic activity from the full, or partial, eruption of the filament mass
and surrounding magnetic structure, as a CME, to a fully confined dynamic evolution or “failed” eruption, sometimes producing
a flare but no CME. Additionally, observations of erupting filaments often show a clear helical structure, indicating the
presence of a magnetic flux rope. Dynamic helical structures, in addition to being twisted, frequently show evidence of being
kinked, with the axis of the flux rope exhibiting a large-scale writhe. Motivated by the fact that kinking motions are also
detected in filaments that fail to erupt, we investigate the possible relationship between the kinking of a filament and its
success or failure to erupt. We present an analysis of kinking in filaments and its implications for other filament phenomena
such as the nature of the eruption, eruptive acceleration, and post-eruptive re-formation. We elucidate the relationship between
kinking and the various filament phenomena via a simple physical picture of the forces involved in kinking together with specific
definitions of the types of filament eruption. The present study offers results directly applicable to observations, allowing
a thorough exploration of the implications of the observational relationship between kinking and filament phenomena and provides
new insight for modelers of CME initiation. 相似文献
20.
Irina N Belskaya Vasilij G Shevchenko Yurij N Krugly Yurij S Efimov Alberto Cellino 《Icarus》2003,166(2):276-284
The first results of the observational program devoted to simultaneous investigation of asteroid polarimetric and photometric opposition phenomena are presented. UBVRI polarimetric and V-band photometric observations of the S-type Asteroid 20 Massalia and the E-type Asteroids 214 Aschera and 620 Drakonia were carried out in 1996-1999 down to phase angles of 0.08°, 0.7°, and 1.2°, correspondingly. The S-type Asteroid 20 Massalia is characterized by the pronounced brightness opposition surge with an amplitude larger than that observed for the E-type asteroids. A sharp peak of negative polarization at small phase angles was not observed for this asteroid. The value of polarization degree at phase angle α<1° is less than 0.5% for both S and E types. The negative polarization branches of S and especially E-asteroids have an asymmetrical shape. The phase angle at which the polarization minimum occurs is close to the angle at which non-linear increase begins in the asteroid magnitude phase curves. A relation of the observed effects to the mechanism of coherent backscattering is discussed. 相似文献