| 摘要 |
A satellite communications system and method, where a satellite 10 can pass messages between a user terminal 44 and an earth station 38, as the satellite moves in an orbit 12 12' as indicated by arrow 46, comprises means for measuring the position of the user terminal 44, on the surface of the earth 14, relative to the nadir 50, by means of doppler shift measurements and propagation delay measurements between the satellite 10 and the user terminal 44. Where more than one satellite 10 is visible to the user terminal 44, combination means are employed using propagation delays to plural satellites 10, and/or recordal of the receipt times, by the user terminal 44, of timed broadcasts from one or more satellites 10 to determine the propagation delay between the one or more satellites 10 and the user terminal 44.
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