DUAL LEO SATELLITE SYSTEM AND METHOD FOR GLOBAL COVERAGE
The present invention relates to satellite systems and more particularly, to the provision of a satellite system and method for communications applications, with global coverage. An optimal method of providing global broadband connectivity has been discovered which uses two different LEO constellations with inter-satellite links among the satellites in each constellation, and inter-satellite links between the constellations. The first constellation is deployed in a polar LEO orbit with a preferred inclination of 99.5 degrees and a preferred altitude of 1000 km. The second constellation is deployed in an inclined LEO orbit with a preferred inclination of 37.4 degrees and a preferred altitude of 1250 km.
1 . A satellite system for global communications comprising:
a first set of satellites in a polar LEO (low Earth orbit) constellation;
a second set of satellites in an inclined LEO constellation;
a first user terminal for transmitting to, and receiving signals from, said first and second set of satellites; and
a Gateway, a base station or a second user terminal for transmitting to, and receiving signals from, said first and second set of satellites;
each of said first and second set of satellites having an ISL (inter-satellite link) functionality with respect to satellites in the polar LEO constellation and with satellites in the inclined LEO constellation.
2 . The satellite system of claim 1 , wherein said polar LEO constellation comprises six planes, equally spaced.
3 . The satellite system of claim 2 , wherein said planes of said polar LEO constellation are inclined between 80 degrees and 100 degrees.
4 . The satellite system of claim 3 , wherein said planes of said polar LEO constellation are inclined about 99.5 degrees.
5 . The satellite system of claim 1 , wherein said inclined LEO constellation comprises five planes, equally spaced.
6 . The satellite system of claim 5 , wherein said planes of said inclined LEO constellation are inclined between 5 degrees and 75 degrees.
7 . The satellite system of claim 6 , wherein said planes of said inclined LEO constellation are inclined about 37.4 degrees.
8 . The satellite system of claim 1 , wherein said polar LEO constellation comprises about 72 satellites and said inclined LEO constellation comprises about 45 satellites, the system thereby providing global coverage with a minimum elevation angle of about 20 degrees.
9 . The satellite system of claim 1 , wherein said satellites of said polar LEO constellation orbit at an altitude of between 800 km and 1400 km.
10 . The satellite system of claim 9 , wherein said satellites of said polar LEO constellation orbit at an altitude of about 1000 km.
11 . The satellite system of claim 1 , wherein said satellites of said inclined LEO constellation orbit at an altitude of between 800 km and 1400 km.
12 . The satellite system of claim 11 , wherein said satellites of said inclined LEO constellation orbit at an altitude of about 1250 km.
13 . The satellite system of claim 1 , wherein the Gateway, the base station, or the second user terminal are operable to avoid interference with a GEO satellite user terminal by switching the Gateway, the base station or the second user terminal to an alternate LEO satellite that has an angular separation with a GEO satellite greater than a calculated discrimination angle, as measured at the GEO user terminal.
14 . The satellite system of claim 1 , wherein excess capacity in the polar LEO constellation in the higher latitudes is used to transfer data traffic, via the ISL, from both LEO constellations to a Gateway located in the North for a connection to a terrestrial network.
15 . The satellite system of claim 1 , each of said first and second set of satellites having an IP router functionality.
16 . The satellite system of claim 15 , each of said first and second set of satellites having an IP router load management functionality.
17 . The satellite system of claim 1 , wherein said communications comprises broadband communications.
18 . The satellite system of claim 1 , wherein said first user terminal includes an electronically scanned array antenna for communicating with said first and second set of satellites.