Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2001-11-21
2003-11-25
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S374000, C455S429000
Reexamination Certificate
active
06653975
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a method of configuring satellite constellation designs using multiple discrete switchable beams. Further, the present invention relates to a method of configuring antenna feeds in a feed array of an antenna in a satellite and the positioning of the satellite in orbit to maximize coverage for profitability, flexibility, changing demand, and redundancy for a satellite network.
2. Discussion of the Related Art
Today the skies above us have become crowded with communication satellites whose sole function is to relay information received from ground stations to other ground stations. The types of satellites utilized for communication generally fall into two categories based on the satellites' position above the planet. The first type is low Earth orbiting satellites, while the second are in a geo-synchronous Earth orbit. In the case of geo-synchronous Earth orbiting satellites, the satellite remains in the same relative position above the earth, and a parabolic satellite dish is typically used to send and receive signals to and from the satellite. In the early days of satellite communication, these geo-synchronous orbiting satellites were confined to telephone communications. However, today all forms of information are being relayed by these geo-synchronous satellites including, but not limited to, voice, computer data, video, television, radio and satellite telephones.
Therefore, today several major industries are heavily dependent upon reliable communications service via satellites being continuously available. Unfortunately, satellites fail, just as all electronic equipment made by man eventually must be repaired or replaced. However, it is at present impossible to send a repairman immediately to repair a satellite in geo-synchronous orbit. In the early days when satellites were used exclusively for telephone communications, landlines and undersea cables still could be used to provide access for customers if a satellite failed. However, this is no longer the case for other applications for which communications satellites in geo-synchronous orbit are used for.
FIG. 1
is an illustration of a satellite communication network configuration in which total redundancy is provided by two satellites. Satellites
20
and
40
are used to communicate to ground stations
30
located within a region of the planet Earth
10
using a uniform distribution methodology. This uniform distribution methodology would allow for communications to an entire region of Earth
10
, such as, but not limited to, North America. Should either satellite
20
or satellite
40
fail, the other satellite may completely take over its communications function. However, this complete redundancy solution is expensive to implement since two satellites must be used just in case one fails. Further, should demand increase in one location it may not be possible to reconfigure the satellites in orbit to handle the additional load from the increased traffic seen in one area. In addition, building in excess capacity in a satellite may not be possible at the time the satellite is being designed, since that may be more than a year in advance of it being launched.
FIG. 2
is an example illustration of the coverage that may be seen from three satellites using the uniform distribution methodology. Coverage areas
200
and
210
may be generated by satellites
20
and
40
in which, rather than complete overlap and redundancy, only partial overlap in a geographical area is accomplished. Via this mechanism satellite
20
would provide coverage area
200
and satellite
40
would provide coverage area
210
. Overlap would occur in such areas as the East Coast of United States, Central America, and portions of South America. Therefore, should satellite
20
fail, the East Coast of United States could still be covered through satellite
40
. However, this still leaves the West Coast of United States without service, and should traffic increase in demand in the Midwest, such as Chicago, even with both satellites
20
and
40
in full operation, inadequate service could potentially be seen via communications through satellite
20
.
One mechanism utilized to overcome the foregoing problems of redundancy and capacity has been to utilize multiple feeds to form multiple spot beams to target specific locations on the planet Earth
10
. However, the performance degradations of spot beams over a wide geographic region have previously limited the spot beam applications to a relatively small number of feeds within a single antenna. However, as illustrated in U.S. Pat. No. 6,211,835 to Pebbles et al., U.S. Pat. No. 6,236,375 to Chandler et al., and U.S. Pat. No. 6,215,452 to Chandler et al., herein incorporated by reference in their entireties, it is now possible to have a large number of spot beams in which each spot beam individually targets specific locations on the planet Earth
10
using what is hereinafter referred to as a hemispherical earth coverage antenna.
FIG. 3
is an illustration of spot beams positioned over predefined Earth locations utilizing the previously mentioned hemispherical earth coverage antenna. Three different satellites
300
,
310
,
320
are shown respectively located at 101 degrees west longitude, 47 degrees west longitude, and 122.5 degrees east longitude. The satellite
300
has most of its spot beams
330
directed towards the North American continent. Satellite
310
positions its spot beams
340
to cover South America and the East Coast of The United States. Satellite
320
in turn has its spot beams
350
distributed to cover portions of Asia and Australia. It should be noted that more than one spot beam may be directed at any given location within the range of the satellite. Further, the positioning of the spot beams is dependent upon the physical alignment of the feeds in the antenna of the satellite and the longitude at which the satellite is positioned in geo-synchronous orbit, as detailed in U.S. Pat. Nos. 6,211,835, 6,236,375, and 6,215,452, incorporated herein by reference in their entireties. Once the feeds are set within a satellite, they may not be changed individually to target another geographical location. However, unlike a uniform distribution method, using this non-uniform methodology the spot beams may be directed towards those areas where demand is highest and profitability maximized. Therefore, the positioning of feeds to generate spot beams is critical in determining the profitability and redundancy of a satellite communications network.
However, a tool such as a hemispherical earth coverage antenna, without a comprehensive method of configuring the feeds and positioning the satellites, is like having all the materials to build a house without the blueprints. Even an experienced contractor might discover needlessly duplicated work or work items completely left off the structure. In the case of a global satellite communications system in geo-synchronous Earth orbit, several factors must be taken into consideration in the configuring of feeds on individual antennas and the positioning of satellites in geo-synchronous orbits to maximize profitability, coverage and redundancy in case of failure of a satellite. These factors include present demand for satellite communications, population shifts which may impact future demand, areas which may be prone to sudden shifts in demand, areas where constant uninterrupted service is absolutely necessary. Predicting such factors in order to properly configure a satellite and place it in the proper orbit is difficult, to say the least. Further, unforeseen circumstances may require thereplacement, substitution or reconfiguration of a satellite, which may be extremely difficult to do while the satellite is being built.
Therefore, what is needed is a system, method and computer program that will enable spot beam coverage of identified high traffic/profit geographical locations such as cities. Further, this system, method and computer program should allow for the switc
Branscombe Steven L.
Courtney William F.
Mezger Fritz B.
Munoz Michael S.
Nuber Ray M.
Antonelli Terry Stout & Kraus LLP
Blum Theodore M.
Northrop Grumman Corporation
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