共查询到20条相似文献,搜索用时 46 毫秒
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Lunar Orbital Station (LOS) is proposed as support of manned lunar exploration missions. A fast-converging iteration method for determining the initial conditions of two-impulse transfer trajectories between the Earth and the LOS is proposed based on the patched conic approach. In the Earth phase, near Earth state is connected with the state at the lunar sphere of influence (LSOI) based on the relationship between the initial and terminal orbital state. Then, an analytical algorithm is proposed to find the state vector at LSOI, such to satisfy the LOS orbital constraint. An iterative process is finally adopted to generate favorable initial solutions that satisfy the constraint near the Earth and at the perilune. The algorithm convergence is investigated, and two types of transfer trajectories are found for both Earth-LOS and LOS-Earth transfer. Based on the algorithm, orbital transfer windows, velocity impulse and time of flight are analyzed in the typical years 2025 and 2034. At last, the initial solution is corrected with a high fidelity model based on the active-set method, which shows the precision of this algorithm. The novel procedure for the transfer trajectories design and the analytic result can be used as a basis for rapid mission evaluation and design for future manned lunar missions based on the LOS. 相似文献
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We employ Friden's algorithm based on the maximum likelihood principle to restore one-dimensional star image data in the presence of noise. The algorithm is made iterative and its performance discussed. 相似文献
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幸运成像技术是一种从大量短曝光图像中选取少量幸运好图进行配准、叠加的高分辨率图像恢复技术,能够有效减小大气湍流对图像质量的影响,但传统的基于中央处理器(Central Processing Unit,CPU)的幸运成像算法难以实现实时化.利用现场可编程门阵列(Field Programmable Gate Array,... 相似文献
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《天文和天体物理学研究(英文版)》2017,(3)
The increasing number of space debris has created an orbital debris environment that poses increasing impact risks to existing space systems and human space flights. For the safety of in-orbit spacecrafts, we should optimally schedule surveillance tasks for the existing facilities to allocate resources in a manner that most significantly improves the ability to predict and detect events involving affected spacecrafts. This paper analyzes two criteria that mainly affect the performance of a scheduling scheme and introduces an artificial intelligence algorithm into the scheduling of tasks of the space debris surveillance network. A new scheduling algorithm based on the particle swarm optimization algorithm is proposed, which can be implemented in two different ways: individual optimization and joint optimization. Numerical experiments with multiple facilities and objects are conducted based on the proposed algorithm, and simulation results have demonstrated the effectiveness of the proposed algorithm. 相似文献
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Dae-Won Kim Pavlos Protopapas Charles Alcock Yong-Ik Byun Federica B. Bianco 《Monthly notices of the Royal Astronomical Society》2009,397(1):558-568
We present a detrending algorithm for the removal of trends in time series. Trends in time series could be caused by various systematic and random noise sources such as cloud passages, changes of airmass, telescope vibration, CCD noise or defects of photometry. Those trends undermine the intrinsic signals of stars and should be removed. We determine the trends from subsets of stars that are highly correlated among themselves. These subsets are selected based on a hierarchical tree clustering algorithm. A bottom-up merging algorithm based on the departure from normal distribution in the correlation is developed to identify subsets, which we call clusters. After identification of clusters, we determine a trend per cluster by weighted sum of normalized light curves. We then use quadratic programming to detrend all individual light curves based on these determined trends. Experimental results with synthetic light curves containing artificial trends and events are presented. Results from other detrending methods are also compared. The developed algorithm can be applied to time series for trend removal in both narrow and wide field astronomy. 相似文献
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L. Shamir 《Astronomische Nachrichten》2005,326(6):428-431
An algorithm for cosmic‐ray rejection from single images is presented. The algorithm is based on modeling human perception using fuzzy logic. The proposed algorithm is specifically designed to reject multiple‐pixel cosmic ray hits that are larger than some of the point spread functions of the true astronomical sources. Experiments show that the algorithm can accurately reject ∼97.5% of the cosmic rays hits, while mistakenly rejecting 0.02% of the true astronomical sources. The major advantage of the presented algorithm is its computational efficiency. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The forecasting technique of the target tracking based on the short arcs at single station is an important way to guarantee that high-precision photoelectric theodolites can normally track and capture the targets in unconventional environments. We construct the tracking prediction algorithm based on nonlinear filter, which can provide the guiding data for the closed loop tracking under normal circumstances. At the same time we also construct the target prediction algorithm based on the nonlinear transformation, without valid observational data, which can provide a track guidance for the theodolite and ensure that the targets will not be lost. It is demonstrated that the nonlinear filtering is more effective than the EKF (extended Kalman filter) in the tracking prediction algorithm of the short arcs at single station. The results indicate that the nonlinear filter designed in this paper can be used as the guiding algorithm for the optical tracking equipments. And its guiding accuracy is in the same order of magnitude of the theodolite's random measurement accuracy. When the systematic error of the equipments reaches 50″, the accuracy can achieve 20″ for predictions in 60 s. This still satisfies the requirement of the field of view of the tracking equipments. 相似文献
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基于离散小波变换(DWT)方法,提出了一种可用于计算三维数值模拟样本面密度的平滑算法.为检验方法的有效性,利用该算法研究了两组不同质量解析度的引力透镜数值模拟样本,样本采用了暗物质晕的等温椭球模型,使用蒙特卡罗方法生成.计算结果表明此算法能够在很高的精度上构建引力透镜模拟样本的面密度分布轮廓,由面密度计算出来的透镜的临界曲线和焦散曲线也能较好地和理论曲线吻合,结果是令人满意的.同时比较了三组不同的小波基的计算结果,包括Daub4,Daub6和B-spline 3th,给出了最优的选择.在不损失平滑效果的同时,此算法具有非常高的速度,非常适合于处理以后更高精度的N体数值模拟. 相似文献
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Bing Dong De-Qing Ren Xi Zhang Physics & Astronomy Department California State University Northridge CA - USA National Astronomical Observatories/Nanjing Institute of Astronomical Optics & Technology Chinese Academy of Sciences Nanjing China 《中国天文和天体物理学报》2011,(8)
An adaptive optics(AO) system based on a stochastic parallel gradient descent(SPGD) algorithm is proposed to reduce the speckle noises in the optical system of a stellar coronagraph in order to further improve the contrast. The principle of the SPGD algorithm is described briey and a metric suitable for point source imaging optimization is given. The feasibility and good performance of the SPGD algorithm is demonstrated by an experimental system featured with a 140-actuator deformable mirror and a Hartmann-... 相似文献
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《Chinese Astronomy and Astrophysics》2020,44(4):413-427
The new generation of large sky area spectroscopic survey project has produced nearly 10 million low-resolution stellar spectra. Based on these spectroscopic data, this paper introduces a machine learning algorithm named The Cannon. This algorithm is completely based on the known spectroscopic data of stellar atmospheric parameters (effective temperature, surface gravity, and metal abundance, etc.), this algorithm builds the characteristic vector by means of data driving, and establishes the functional relation between spectral flux characteristics and stellar parameters. Then it is applied to the observed spectral data to calculate the atmospheric parameters. The main advantage of The Cannon is that it is not directly based on any stellar physical models, it has an even higher applicability. Moreover, because of the use of full-spectrum information, even for the spectra with a low signal-to-noise ratio (SNR), it still can obtain the parameter solutions of high reliability. This algorithm has significant advantages in the data processing and parameter determination of large-scale stellar spectra. In addition, this paper presents two examples of using The Cannon to obtain the stellar parameters of K and M giants from the LAMOST spectral data. 相似文献
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Glenn Sugar Althea Moorhead Peter Brown William Cooke 《Meteoritics & planetary science》2017,52(6):1048-1059
We present a new method to detect meteor showers using the density‐based spatial clustering of applications with noise algorithm (DBSCAN; Ester et al. 1996 ). The DBSCAN algorithm is a modern cluster detection algorithm that is well suited to the problem of extracting meteor showers from all‐sky camera data because of its ability to efficiently extract clusters of different shapes and sizes from large data sets. We apply this shower detection algorithm on a data set that contains 25,885 meteor trajectories and orbits obtained from the NASA All‐Sky Fireball Network and the Southern Ontario Meteor Network (SOMN). Using a distance metric based on solar longitude, geocentric velocity, and Sun‐centered ecliptic radiant, we find 25 strong cluster detections and six weak detections in the data, all of which are good matches to known showers. We include measurement errors in our analysis to quantify the reliability of cluster occurrence and the probability that each meteor belongs to a given cluster. We validate our method through false‐positive/negative analysis and with a comparison to an established shower detection algorithm. 相似文献
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Martin Bange Stefan Jordan Michael Biermann Thomas Kämpke Ralf-Dieter Scholz 《Experimental Astronomy》2002,13(2):101-117
We propose an object detection algorithm which is efficient and fast enough to be used in (almost) real time with the limited
computer capacities onboard satellites. For stars below the saturation limit of the CCD detectors it is based on a four neighbourhood
local maximum criterion in order to find the centre of a stellar image. For saturated stars it is based on the assumption
that the image is increasing monotonically towards the centre in the unsaturated part of the image. The algorithm also calculates
approximate stellar magnitudes and efficiently rejects most of the cosmics which would otherwise lead to a large number of
false detections. The quality of the algorithm was evaluated with the help of a large set of simulated data for the DIVA satellite
mission; different assumptions were made for the noise level, and the presence of cosmics or for a variable sky background.We
could show that our algorithm fulfills the requirements for DIVA; only in the case of simulated images which included the
bright galaxy M31 some fainter stars could not be detected in the galaxy's vicinity. Since stellar images contain large areas
without any stars, we propose an additional block-skipping algorithm which can be coded on special-purpose hardware.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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A principle of restoration methods based on multichannel blind deconvolution (MBD) is introduced. The methods assume that
for every un-degraded unobservable image several degraded observed images are available. It is better conditioned than classical
single channel approach. The first algorithm represents a generalization of iterative deconvolution scheme introduced for
single images. The second MBD algorithm is based on so-called subspace technique. The subspace method is not iterative and
this possibly implies an implementation that can be computationally more efficient. Both methods are presented in applications
to artificial image data (computer-generated multichannel degraded data) with known ideal image to get a comparison with restored
one. Performance in a real situation on solar photosphere images is shown. 相似文献
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新一代大规模光谱巡天项目产生了近千万条低分辨率恒星光谱,基于这些光谱数据,介绍一种名为The Cannon的机器学习方法。该方法完全基于已知恒星大气参数(有效温度、表面重力加速度和金属丰度等)的光谱数据,通过数据驱动来构建特征向量,建立光谱流量特征和恒星参数的函数对应关系,进而应用到观测光谱数据中,实现对恒星光谱的大气参数求解。The Cannon的主要优势为不直接基于任何恒星物理模型,适用性更广;由于使用了全谱信息,即便对于低信噪比光谱也能得到较高可信度的参数结果,该算法在大规模恒星光谱的数据处理和参数求解方面具有明显的优势。此外,还利用The Cannon得到LAMOST光谱数据中K巨星和M巨星的恒星参数。 相似文献