Abstract:
A method and computer program to configure feeds on a satellite ( 300, 310, 320 ) to provide for redundant coverage when a satellite ( 300, 310, 320 ) fails. Further, this method and computer program can enable the switching of feeds from commands from a ground station ( 30 ) to activate certain feeds and deactivate other feeds when demand for service changes. In addition, this method and computer program allow for repositioning of satellites so that when one satellite fails another satellite may take over its area of coverage by switching active feeds without the need for placing another satellite in orbit.

Description:
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&#39; 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 switching of spot beams to concentrate capacity on a particular geographic area when unexpected high demand is seen in that area. Further, this system, method and computer program should further build in redundancy in the positioning of spot beams and satellites so that when a failure occurs in a satellite, other antennas on that satellite or other satellites in orbit may immediately be reconfigured from a controlling ground station to cover the lost area. Further, in the case where an entire satellite is lost due to a malfunction, the configuration of spot beams should be such that another satellite in orbit may be moved to a different longitude and have certain of its feeds set up to take over for the satellite that has malfunctioned. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, a method and a computer program are disclosed in which a constellation of satellites is configured. This method and computer program determine a first set of population centers to be covered by a first satellite. The method and computer program then determine a second set of population centers to be covered by a second satellite. Thereafter, the method and computer program determine a third set of population centers which are all common population centers between the first set of population centers and the second set of population centers. Thereafter, mapping of a first union of the first set of population centers and the second set of population centers onto a feed antenna array for the first satellite is done. Finally, the method effects a mapping of a second union of the second set of population centers and the third set of population centers onto a feed antenna array for the second satellite. 
     Further, in accordance with the present invention. there are provided a method and a computer program for configuring feeds on an antenna of a satellite. This method and computer program determine a first set of primary population centers to be covered by the satellite. The method and computer program then determine a second set of secondary population centers to be covered by the satellite. Thereafter, a mapping occurs of the first set and the second set into the feeds of the antenna of the satellite. Finally, the connectivity is determined between the first set and the second set to maximize at least one optimization criterion. 
     Further in accordance with the present invention, a method and computer program for configuring several feeds on several satellites are disclosed to supply backup redundancy for a failed satellite. This method and computer program determine a first set of population centers to be covered by a first satellite. The method and computer program then determine a second set of population centers to be covered by a second satellite. Mapping is then done on the first set of population centers onto the feed array of the first satellite. Then, mapping of a second set of population centers onto the feed array of the second satellite is done. Finally, the union between the mapped first set of population centers and the mapped second set of population centers is determined. 
     Additional objects, features and advantages of the present invention will become apparent from the following description and the appended claims when taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustration of a satellite communication network configuration in which total redundancy is provided by two satellites; 
     FIG. 2 is an example illustration of the coverage that may be seen from three satellites using the uniform distribution methodology; 
     FIG. 3 is an example illustration of spot beams positioned over predefined Earth locations utilizing a hemispherical earth coverage antenna. 
     FIG. 4 is a diagram illustrating the coverage areas of a failed satellite being taken over by two other satellites in an example embodiment of the present invention, as further detailed in FIGS. 7 through 9; 
     FIG. 5 is a diagram illustrating the switching of spot beams in a single satellite in order to concentrate on a single geographical area where demand has unexpectedly increased in an example embodiment of the present invention; 
     FIG. 6 is a diagram illustrating the movement of a satellite to another longitudinal location in order to take over the coverage of a failed satellite or to provide additional capacity when needed to meet demand in an example embodiment of the present invention, as further detailed in FIGS. 7 through 9; 
     FIG. 7 is a flowchart illustrating the configuring of two satellites to provide dual coverage in an example embodiment of the present invention; 
     FIG. 8 is a flowchart illustrating configuring a satellite to provide maximum flexibility and coverage in an example embodiment of the present invention; and 
     FIG. 9 is a flowchart illustrating configuring a satellite in a particular longitudinal slot to act as backup for another satellite in another longitudinal slot in an example embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following discussion of the example embodiments directed to a process for configuring a satellite constellation is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. 
     FIG. 4 is a diagram illustrating the coverage areas of a failed satellite being taken over by two other satellites in an example embodiment of the present invention, as further detailed in FIGS. 7 through 9. As illustrated in FIG. 4, satellites  300  and  320  are operational, while satellite  310  has experienced a failure. Satellite  310  would normally generate spot beams  420  and  430 . However, with the failure of satellite  310  the geographical areas corresponding to spot beams  420  and  430  are no longer covered. However, as detailed in FIG. 7 it is possible to configure satellites to provide dual coverage for any given geographical area. Therefore, satellite  300  may also cover the areas for spot beams  420 , as well as spot beams  400 , while satellite  320  would generate spot beams  430 , as well as spot beam  410 . This may be done as discussed in further detail in reference to FIG. 7 relating to the method for configuring satellites for dual coverage. In addition, it may be possible to utilize the operations illustrated in FIG. 8 to configure satellites for flexible coverage. 
     FIG. 5 is a diagram illustrating the switching of spot beams in a single satellite in order to concentrate on a single geographical area where demand has unexpectedly increased in an example embodiment of the present invention. In this example embodiment, a single satellite  300  is depicted in which spot beams  500 ,  510 ,  520  and  530  are typically covered by the feeds located within the antenna of satellite  300 . The hemispherical earth coverage satellite makes it possible to build coverage flexibility into each antenna through the placement of additional feeds that could be activated upon the issuance of a ground station  30  command. As indicated in FIG. 5, tour feeds could be directed to the same geographical area as spot beams  540 . Therefore, when unanticipated demand arises within a particular area, it is possible to have additional feeds, which would not normally be active, oriented to service a particular geographical area. Altering which group of feeds are active at any given moment in time could be done, utilizing either hardware or software or any combination or by any well-known mechanism. 
     FIG. 6 is a diagram illustrating the movement of a satellite to another longitudinal location in order to take over the coverage of a failed satellite or to provide additional capacity when needed to meet demand in an example embodiment of the present invention, as detailed further in FIG.  9 . As exemplified in FIG. 6, coverage areas  200 ,  210  and  220  would be covered by separate satellites. However, in the case of the failure of the satellite covering area  210 , it is possible to move the satellite handling coverage area  220  to a longitudinal position so that it now has a coverage area  230 . However, since the satellite was originally designed to handle locations in coverage area  220  it is unlikely that any of the feeds would generate spot beams that would be associated with major population centers in the new longitudinal location. However, again utilizing the hemispherical earth coverage satellite populated with excess feed horns and excess feed capacity, it is possible to configure the feed horns prior to launch in groups so that one group of feeds would handle coverage area  220 , but also a second set of feeds could be designed to handle coverage area  230 . It should be noted that these two sets of feeds may overlap, with several feeds utilized in both sets. The process utilized to enable this movement of a satellite to cover a new longitudinal area is discussed in further detail in reference to FIG.  9 . 
     FIGS. 7 through 9 are flowcharts of the processes used in the embodiments of the present invention. These processes may be implemented manually, in software, firmware, or hardware, or any combination of the foregoing methods. The elements illustrated in FIGS. 7-9 represent operations, modules, code, code segments, commands, firmware, hardware, instructions and data that may be executable by a processor-based system(s) and may be written in a programming language, such as, but not limited to, C++. 
     FIG. 7 is a flowchart illustrating the configuring of two satellites to provide dual coverage in an example embodiment of the present invention. Processing begins in operation  700  and immediately proceeds to operation  710 . In operation  710 , a determination is made of cities or population centers that will be covered by a particular satellite A, such as satellite  300  previously discussed. This set of population centers is given the arbitrary designation of set number one. In operation  720  another set of cities or population centers are identified to be covered by spot beams emanating from a second satellite B, such as satellite  310  previously discussed. This second set of population centers is arbitrary designated as set number two. The criteria utilized in the selection of population centers may include, but are not be limited to, overall population size, projected population growth, demographics, demand for service, projected demand for service, economic growth and stability, etc. As would be appreciated by one of ordinary skill in the art, a database containing the foregoing criteria associated with each population center may be generated, as well as a priority schema for ranking the population centers for sorting and selection by computer program. 
     Still referring to FIG. 7, processing then proceeds to operation  730 . In operation  730 , it is determined which population centers are covered by both satellite A and satellite B. This may also be accomplished by software that determines the intersection between population centers in set number one and population centers in set number two. This intersection of population centers between sets number one and number two would be designated as set number three. In operation  740 , the union of sets number one and three, representing population center locations, would then be mapped into the antenna feed array for satellite A, such that at least one feed would be associated and properly positioned for a given population center. The determination of which feeds to select for each population center and the alignment of each feed would be a mathematical process of mapping, readily accomplished utilizing a computer program knowing the longitudinal position for the designated satellite. In operation  750 , the union of sets number two and three of population center locations would then be mapped into the antenna feed array for satellite B, such that at least one feed would be associated and property positioned for a given population center. Again, the determination of which feeds to select for each population center and the alignment of each feed would be a mathematical process readily accomplished utilizing a computer program knowing the longitudinal position for the designated satellite. Processing then proceeds to operation  760 . 
     Still referring to FIG. 7, in operation  760  a determination is made of the connectivity between set number one and set number three on satellite A to maximize revenue. For example, satellite A may provide double coverage of some high revenue producing population centers that are also covered by satellite B. It should be noted that satellite A is primarily used to service the population centers in set number one. However, after launch it may be determined that some population centers in set number two may produce significantly more revenue than those in set number one. By being able to switch feeds and spot beams from less profitable population centers in set number one to more profitable population centers in set number two, potential revenue may be maximized. This would of course entail the double coverage of the highly profitable population centers by both satellite A and satellite B. Thereafter, in operation  770 , the connectivity between sets two and three on satellite B is determined for maximum revenue in a similar fashion as that previously discussed for satellite A in operation  760 . Thereafter, processing proceeds to operation  780  where processing terminates. 
     FIG. 8 is a flowchart illustrating configuring a satellite to provide the maximum flexibility and coverage in an example embodiment of the present invention. Processing begins in operation  800  and immediately proceeds to operation  810 . In operation  810 , a determination is made for selection of primary cities or population centers to be covered by spot beams generated by satellite A. As previously discussed, the criteria utilized in the selection of population centers may include, but is not be limited to, overall population size, projected population growth, demographics, demand for service, projected demand for service, economic growth and stability, etc. As would be appreciated by one of ordinary skill in the art, a database containing the foregoing criteria associated with each population center may be generated, as well as a priority schema for ranking the population centers for sorting and selection by computer program. In operation  820 , a second set of population centers to be covered by satellite A is determined based upon the same selection criteria previously discussed or a different set of selection criteria. Thereafter, in operation  830  the first set of population centers generated in operation  810  and the second set of population. centers generated in operation  820  are mapped to the antenna feed array of satellite A. Where the first set of population centers overlaps with the second set of population centers, a determination may be made of whether to apply a single feed for a given population center or two feeds. Processing then proceeds to operation  840  where the connectivity or switching between the first set of population centers and second set of population centers is determined to meet one or more optimization criteria. For example, this criterion may be the selection of population centers that will produce revenue that exceeds a certain minimum required. Thereafter, processing proceeds to operation  850  where processing terminates. 
     FIG. 9 is a flowchart illustrating configuring a satellite in a particular longitudinal slot to act as backup for another satellite in another longitudinal slot in an example embodiment of the present invention. Processing begins in operation  900  and immediately proceeds to operation  910 . In operation  910 , a set of population centers to be covered by satellite A is determined and arbitrarily referred to as set number one. In operation  920 , a set of cities is determined to be covered by satellite B. and is referred to arbitrarily as set number two. As previously discussed, the criteria utilized in the selection of population centers may include, but is not limited to, overall population size, projected population growth, demographics, demand for service, projected demand for service, economic growth and stability, etc. As would be appreciated by one of ordinary skill in the art, a database containing the foregoing criteria associated with each population center may be generated, as well as a priority schema for ranking the population centers for sorting and selection by a computer program. Processing then proceeds to operation  930  where the population centers designated set number one are mapped to the antenna feed array for satellite A and labeled as map number one. In operation  940  the population centers designated set number two are mapped to the antenna feed array for satellite B and labeled as map number two. Thereafter, processing proceeds to operation  950  where the union between map one and map two is determined, and feeds in the antenna on satellite A are determined for the union of population centers in both map one and map two. In operation  960  a feed is selected in the feed array of the antenna of satellite B using the population centers designated in map two. Thereafter in operation  970 , due to the coverage created in operation  950  and  960 , satellite A may now be utilized to cover the population centers covered by satellite B, since satellite A now has feeds oriented towards spot beams for the population centers designated for service by satellite B. This would entail physically moving satellite A to a different longitudinal position in geo-synchronous orbit and turning on the feeds that would be normally handled for that location in orbit by satellite B. Of course the prior feeds utilized by satellite A would be turned off once repositioning is accomplished. Processing then proceeds to operation  980  where processing terminates. 
     While we have shown and described only a few examples herein, it is understood that numerous changes and modifications, as known to those skilled in the art, could be made to the present invention. For example, any type of computer architecture may be utilized for the embodiments of present invention. Further, the present invention may be implemented in any general-purpose computer language, or the method steps of the invention could even be performed manually. Therefore, we do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.