Abstract: A terminal 44 44A 44B using standard navigational satellite 142 position determination to find its position on the surface of the earth 14, has its performance enhanced by being linked to a communications satellite system 10 38. In one variant, the communications satellite 10 broadcasts on each of a plurality of spot beams 30, each interactive with a different part of the earth, the broadcast indicating which navigational satellites 142 are accessible for a terminal within that beam 30. The terminal 44 44A 44B receives the broadcast and adjusts the navigational satellite receiver 174 to look for signals only from the nominated navigational satellites 142. In another variant, the communications satellite system 10 38 approximately measures the position of the terminal 44 44B and then informs the terminal 44 44B which navigational satellites are accessible from the terminal 44 44B, the navigational satellite receiver 174 again only looking for signals from the nominated navigational satellites 142.

Abstract: In a communications system, in the embodiment, a satellite communications system, transactional messages 28 36 are exchanged between the user terminal 14 and a base station (earth station) 16 via a communications satellite 10 in order to set up and maintain the progress of a call, encompass occasional user terminal registration and position estimation, allow call termination and attend to a host of other housekeeping processes. The prior art required the sending of acknowledgement messages 32 between transactional messages. The invention replaces the sending and requesting of acknowledgement messages 32 with an each-end recognition of the style of transactional responses as an ipse facto acknowledgement, thereby much speeding up the transactional message and transactional response/message exchange, so releasing time resources to the system.

Abstract: A satellite communications system comprises satellites 9A-C, earth stations 7A-E, user terminals 11 and controlling gateways 3 in the form of mobile satellite switching centers 5A-E. Access to and from a user terminal 11 may be gained from and to a terrestrial telephone system 1 by earth stations 7A-E contacting the satellites 9A-C and by the satellites contacting the user terminals 11. The satellites 9A-C periodically broadcast messages indicative of the earth station 7A-E with which they are instantly in contact. The user terminal 11 listens to these broadcasts, assesses the quality of the received signal, and keeps a league table based on an accumulated score allocated to each earth station 7A-E which can be heard. When calling into the system, the user terminal pages earth stations in descending order of score in the league table. When in contact, the user terminal 11 sends the league table to the system.

Abstract: A communications satellite communications system and method, where a communications satellite 10 can pass messages between a user terminal 44 and an earth station 38, as the communications satellite moves in an orbit 12 12' as indicated by arrow 46, comprises means for estimating 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 communications satellite 10 and the user terminal 44. Where more than one communications satellite 10 is visible to the user terminal 44, combination means are employed using propagation delays to plural communications satellites 10, and/or recordal of the receipt times, by the user terminal 44, of timed broadcasts from one or more communications satellites 10 to determine the propagation delay between the one or more communications satellites 10 and the user terminal 44.

Abstract: A satellite system and method comprises a satellite 10 induced to roll 46 and pitch 52 in its orbit 12 to keep antennae 34 36 pointing ever directly at the nadir 40 as the nadir moves over the surface of the earth 14. The satellite 10 has a yaw rotation 54 designed to keep the solar panels, which rotate only about one axis, ever pointing at ninety degrees to the direction of the sun 42 for maximum solar panel efficiency. The beam pattern of the antennae 34 36 is counter-rotated to oppose the yaw motion 54. Compensation for the season of the year is applied.

Abstract: An antenna assembly comprises a panel (1) with suckers (3) for mounting it to a window or other vertical surface. A foil antenna (2) is formed on the panel (3). The antenna (2) may be coupled to a transceiver (8) by a feeder (6) so that in use it replaces the transceiver's own antenna. In another arrangement, the antenna may simply re-radiate radio signals transmitted by the transceiver using its own antenna.