面向分布式GIS空间数据的Key-value缓存

Orbit Determination and Analysis for Chang’ E-2 Extended Mission

  • 摘要: 设计了一种基于Key-value结构的缓存KV-cache,旨在简化数据结构,高效管理缓存数据。KV-cache由Mem-cache和F-cache构成。其中,Mem-cache为第一级缓存,并采用缓存回写机制以异步方式将数据写入F-cache进行持久化存储。F-cache使用大文件存储数据,并构建了基于B树的缓存索引以加快检索速度。数据写入F-cache的位置由基于B树的空闲空间管理器进行分配。在100Mbps局域网内测试KV-cache读写性能。实验表明,KV-cache读写性能优于传统文件目录方式的缓存,能够安全、高效地管理所缓存的各种空间数据。

     

    Abstract: The Chang’E-2 spacecraft was sent to the Lissajous orbit around the L2 of the Sun-Earth for an extended mission in June,2011.During that mission,the maximum distance between the satellite and the Earth was about 1 700 000 km.With an increase in the Earth-Satellite distance,the noise level in three-way ranging increases significantly on the one hand,and the constraint of flight dynamic decreases rapidly on the other hand.Moreover,the geometry for POD deteriorates,therefore the calculation for orbit determination also gets correspondingly more difficult during the process.These factors present challenges to the tracking system.In this paper,the POD for the Chang’E-2 extended mission is described in detail,and the accuracy is assessed using several methods.The results show that the degree of accuracy is better than 1km in the escape phase,and as the distance increases,the required arc-length for POD increases correspondingly.In the late phase of a transfer orbit,orbit determination calculation executed with 20 consecutive days’ data and and orbital comparison using overlaps and prediction analysis,show that the orbital error as a root mean square is at the level of 2 km.

     

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