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With the development of space technologies, satellite-based data link is becoming more and more popular due to its wide
coverage. However, it needs tens of LEO satellites, short for Low Earth Orbiting satellites, to cover the whole Earth in
real time. Therefore it requires huge investment to fulfill such an engineering. If several TDRS satellites, short for
Tracking and Data Relaying Satellites, are included, the engineering investment might as well be acceptable. Herein,
simulations of coverage and some particular performances are presented in three cases, i.e., a single LEO satellite plus
one TDRS satellite, a single LEO satellite plus two TDRS satellite, a single LEO satellite plus three TDRS satellite.
Simulations have shown that in the case of one LEO satellite and one TDRS satellite, the revisiting period is
5726s,which will shorten the revisiting period by 57%;the encounter frequency between one LEO and one TDRS is 11
times daily; the average duration for every encounter is 2128s. The performances of one LEO satellite and two TDRS
satellites are presented as followings：the revisiting period is 2819s,which will shorten the revisiting period by 79%;the
encounter frequency among one LEO and two TDRS is 23 times daily;the average duration for every encounter is
2049s.The performances of one LEO satellite and two TDRS satellites are presented as followings：the revisiting
period is 1780s,which will shorten the revisiting period by 87%;the encounter frequency among one LEO and two TDRS
is 34 times daily;the average duration for every encounter is 2067s. The above simulations have indicated TDRS
satellites can greatly improve LEO satellite coverage and related performances.
For china customers, the space orbits of TDRS are limited by either geographical positions or by orbital space regulation
in equator. Such limitations make sparsely-distributed LEO satellites global real-time data link difficult, especially above
western hemisphere. LEO satellite data link above some of the western hemisphere has to be retarded. Delayed data link
are hardly acceptable for some emergency rescues. Before the constellation of tens of LEO communication satellites is
deployed in space, it might be a good choice to realize LEO satellite data link via TDRS satellites for China users.
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