跟踪与数据中继卫星(TDRS)跟踪用户星的条件分析

中继卫星是航天测控网发展的必然趋势．一颗中继卫星对不同轨道的用户星测控支持能力是不同的，受多种因素的影响．从理论上详尽地分析了地球同步轨道中继卫星（TDRS）对近地航天器的跟踪条件，计算了中继卫星对各种轨道高度近地航天器的测控覆盖率，给出了中继星到用户星可视算法、地球遮挡和受太阳直射的计算公式，通过专业STK软件仿真验证了所得结论的正确性，它们可以作为确定天基网的中继星数量和对在轨中继卫星进行资源分配的理论依据．

Term Analysis of a TDRS Tracking a User Satellite

The space-based TT&C network is a trend to be developed. The coverage of a TDRS tracking a user satellite is the first consideration for designers and depends on different elements. From the view point of engineering application, the terms of a TDRS tracking a user satellite are analyzed here in detail. Based on their orbital characteristics, the algorithm of a TDRS tracking user satellites without the earth blocking, which will diminish the coverage, is presented. Then the terms to decide whether the earth blocking happens are divided into three cases to be discussed in detail. The ways to accurately predicate the occurrence of earth block and sun interference are given here too. Despite of the two satellites being in line of sight, the position of the antenna fixed onboard a user satellite will cause exclusion sometimes. But, with the appropriate mast's length, it is sure for a TDRS to track the use satellite without any block when they are in line of sight. Therefore, the presented formulas and conclusions, which are verified by simulation means, are suitable for all cases. They can be used as means to determinate the number of TDRS to construct a space TT&C network and strategies to allocate the resource of an on-orbit TDRS to user satellites. It can improve the TT&C coverage for a TDRS tracking user satellites.