8PSK TCM调制在TDRSS信道中的性能

随着NASA局走向21世纪,新的航天计划,例如国际空间站、载人火星飞行计划和新的陆地星计划逐步展开,对TDRSS的数传要求很可能超出现有带宽。按NASA资助合同NAG5—1491,新墨西哥州大学(NMSU)空间遥测和通信系统的小Manual Lujan中心正在研究提高TDRSS数传容量的技术。这些技术包括利用高带宽效率调制格式来提高TDRSS转发器的数传     

利用TDRSS星上导航系统为地球观测卫星精密导航

地球观测系统卫星EOS—AM1的基本导航系统是TDRSS星上导航系统(TONS),为成象仪器标校和例行操作提供精密位置和速度信息。本文给出实时导航性能评价结果,看一下基于TONS的轨道和频率测定精度能否满足这一要求。给出了利用陆地—4卫星实际数据对EOS—AM1导航精度进行协方差分析和仿真研究的结果。研究了利用单向前向链路业务的局部(半圈)和全球(多圈)跟踪情况。还研究了利用比GEM—T3更精确重力模型提高导航精度的问题。本项研究的主要目的是评价额定性能、潜在敏感性并设法改进算法,例如TDRS星历加偏,电离层模型和重力过程噪声模型,这些都是已经准备采取的措施。结果表明TONS可以做得满足已明确的仪器导航精度要求—20m(3σ)。     

Tírez lake as a terrestrial analog of Europa

Tírez Lake (La Mancha, central Spain) is proposed as a terrestrial analogue of Europa's ocean. The proposal is based on the comparison of the hydrogeochemistry of Tírez Lake with the geochemical features of the alteration mineralogy of meteoritic precursors and with Galileo's Near Infrared Mapping Spectrometer data on Europa's surface. To validate the astrobiological potential of Tírez Lake as an analog of Europa, different hydrogeochemical, mineral, and microbial analyses were performed. Experimental and theoretical modeling helped to understand the crystallization pathways that may occur in Europa's crust. Calculations about the oxidation state of the hypothetical Europan ocean were estimated to support the sulfate-rich neutral liquid model as the origin of Europa's observed hydrated minerals and to facilitate their comparison with Tírez's hydrogeochemistry. Hydrogeochemical and mineralogical analyses showed that Tírez waters corresponded to Mg-Na-SO(4)-Cl brines with epsomite, hexahydrite, and halite as end members. A preliminary microbial ecology characterization identified two different microbial domains: a photosynthetically sustained community represented by planktonic/benthonic forms and microbial mat communities, and a subsurficial anaerobic realm in which chemolithotrophy predominates. Fluorescence in situ hybridization has been used to characterize the prokaryotic diversity of the system. The subsurficial community seemed to be dominated by sulfate-reducing bacteria and methanogens. Frozen Tírez brines were analyzed by Fourier-transform infrared techniques providing spectra similar to those reported previously using pure components and to the Galileo spectral data. Calorimetric measurements of Tírez brines showed pathways and phase metastability for magnesium sulfate and sodium chloride crystallization that may aid in understanding the processes involved in the formation of Europa's icy crust. The use of fluorescence hybridization techniques for microbial detection and characterization in hypersaline environments makes this methodology strongly advisable for future Europa astrobiological missions.     

多目标地面炸点测量定位的盲区问题

利用CCD测角相机系统对地面同时爆炸目标点进行测量定位,是一个颇为复杂的问题。本文讨论了测角误差引起的辨识真、假目标炸点及个数的“盲区”问题。为了减小和减少这些盲区,笔者提出了若干实际对策。     

香港新机场刚性道面的设计和施工

阐述了香港赤腊角机场刚性道面设计、材料选择和施工方法等问题。道面结构的设计、优质材料的选择、合理的混合料设计、混合料施工机械选用,以及有效的养护措施和施工质量保证体系等,对于道面的长期性能来说都是特别重要的。     

俄罗斯研制新的深空跟踪设备

现有的俄罗斯深空网是以70年代中期研制的“Kvant-D”为基础建立的。1980至1986年期间,“Kvant-D”在埃弗帕托里亚(乌克兰)、乌苏里斯克(远东)与熊湖(莫斯科附近)跟踪站投入运行。以该设备为基础形成的跟踪网能够控制在太阳系范围内活动的星际探测器,以及高远地点地球卫星(高达6×10~6km)。 经过几个阶段的现代化改造,“Kvant-D”虽可以满足目前的需要,但该设备已经过时,使用寿命已满。而且,俄罗斯未来的深空任务将使用X频段,“Kvant-D”的工作频段也不能满足需要。     

利用基于模型的推理进行卫星异常诊断

目前大多数卫星的监视和控制需要使用复杂的地面站,并驻有技术高超的操作手。卫星操作手必须能快速识别和诊断异常情况。许多情况下,不能完成此任务就会丢失重要信息,不能完成任务,极端情况是卫星损坏。许多负责操作卫星的政府和商业机构都面临削减预算,故要寻求用更少、技术水平较低的人员来操作卫星。这些机构寻找各种人工智能（ＡＩ）技术作为减少卫星地面控制设施人力以及技术水平的措施。至今将指出这种技术的不足,介绍利