Patent Publication Number: US-2023133837-A1

Title: Satellite communications system with non-geosynchronous orbits

Description:
BACKGROUND 
     Many satellite communication systems utilize satellites in geosynchronous orbit. Such satellites are often referred to as geosynchronous equatorial orbit (GEO) satellites. GEO satellites appear to Earth-based ground stations to be stationary in the sky relative to a ground station on the Earth because GEO satellites have an orbital period equal to the rotational period of the Earth. The orbital altitude of a GEO satellite is 35,786 km (22,236 miles) above the Earth to achieve geosynchronous orbit. 
     Despite the prevalence of GEO satellites, satellites in geosynchronous orbit may have a number of unfavorable characteristics specific to a satellite communication system. For example, because GEO satellites orbit at a much higher altitude than satellites in low Earth orbit (LEO) or mid-Earth orbit (MEO), the cost to launch and maintain GEO satellites is higher than the cost to launch and maintain satellites at lower orbital altitudes such as LEO and MEO. Furthermore, due to the orbital altitude of GEO satellites being higher than satellites in LEO or MEO, the latency associated with RF communication between a ground station on Earth and a GEO satellites is higher than for satellites in a lower orbit. 
     Further still, all GEO satellites orbit the Earth at a standard altitude to achieve geosynchronous orbit. Many GEO satellites are in an equatorial orbit. In order to provide effective satellite operations, requirements exist that dictate minimum spacing between adjacent satellites at the geosynchronous orbit altitude. In turn, the geosynchronous orbit is divided into “orbital slots” to which a GEO satellite is assigned. The number of orbital slots at the geosynchronous orbit altitude that may be allocated for GEO satellites is limited, such that a limited number of GEO satellites may be in operation at any given time. 
     Accordingly, while GEO satellites remain prevalent in satellite systems, including satellite communication systems, the drawbacks of GEO satellites provide a need to adapt alternative satellite orbits for use in satellite communication systems and the like. 
     SUMMARY 
     In view of the foregoing, the present disclosure presents a satellite communication system that utilizes a non-GEO orbit (e.g., an MEO or LEO) to facilitate satellite communications between at least one ground station an at least one user terminal. Specifically, the satellite communications system facilitated by the present disclosure may address, at least in part, some of the unfavorable characteristics for GEO satellites described above. For example, because a satellite communication system according to the present disclosure utilizes a non-geosynchronous orbit, communication with a satellite in the satellite communication system may exhibit lower latency than those with GEO satellites. In addition, the LEO or MEO options that may be used by the satellite communication system may allow for the use of satellites that may otherwise be precluded from operating at the GEO orbital altitude due to limitations on the number of GEO satellites as described above. Further still, the LEO or MEO orbits described herein may provide continuous communication between ground stations and at least one satellite in at least one repeating sky track. 
     A satellite communication system facilitated by the present disclosure may allow for economic, robust, and relatively simple ground communication systems to be employed in the satellite communication system. For example, GEO satellites are widely used in communication systems because ground communication systems for communication with GEO satellites need not track a GEO satellite because GEO satellites appear stationary relative to the ground station on Earth. In contrast, LEO satellites or MEO satellites move in the sky as viewed from a ground station on the Earth. As such, ground communication systems for communication with LEO satellites and MEO satellites are more complicated than GEO ground communications systems to facilitate two-axis tracking of non-GEO satellites as the non-GEO satellites transit across the sky relative to a ground station. Such tracking of LEO and/or MEO satellites may include mechanical manipulation of an antenna or electrical manipulation of an antenna (e.g., using a phased array antenna or other directionalized antenna technology). Importantly, such ground communication systems include both gateways and user terminals. While relatively few gateways may be provided, a potentially large number of user terminals may be configured for communication with a satellite in a large scale satellite communication system (e.g., one in which Internet access is provided to many subscribers). In turn, user terminal equipment may be costly and/or complicated for use with non-GEO satellites, and the cost of such equipment may be prohibitive in view of a large number of user terminals that are often served by satellite communication systems. 
     The present disclosure features an orbit design that allows for continuous satellite communication between gateways and user terminals using non-GEO satellites in which the cost and/or complexity of such ground communication systems (including both gateways and user terminals) is significantly reduced as compared to other LEO or MEO satellite systems. Specifically, the present disclosure utilizes a satellite constellation in which each satellite in the constellation is at LEO or MEO and configured so that that all satellites follow a common, repeating ground track relative to the Earth. Correspondingly, with respect to a ground station, each satellite follows at least one common, repeating arc or sky track in the sky relative to a ground station. Thus, the tracking mechanism of ground stations of the satellite communication system may be simplified to allow for cost-effective communication equipment at each ground station to preserve continuous satellite communication in the satellite communication system. For instance, the ground stations may have less complex and lower cost antennas (e.g., phased arrays) for tracking satellites in a sky track in a limited extent of the sky relative to the ground station. 
     In this regard, the satellite communications system includes a plurality of satellites each traveling about the Earth in orbit such that each or all of the plurality of satellites of the satellite communication system follows a single repeating ground track relative to the surface of the Earth. Resources for control and station-keeping of the satellites may be reduced in the example in which all satellites in a satellite communication system have an orbit such that all the satellites in the satellite communication system follow a common, repeating ground track. The projected ground path of each satellite is the same and repeats relative to the surface of the Earth. Each respective orbit of the plurality of satellites may share orbital parameters but be offset relative to satellite epoch such that the plurality of satellites are spaced about (e.g., evenly) along the repeating projected ground path. In turn, at least one different respective one of the plurality of satellites may be continuously visible in a repeating sky track relative to a ground station on the Earth. Each satellite may have an orbit that has an orbital period that is an integer factor of a sidereal day. 
     In addition, each of the plurality of satellites is equipped with communication equipment operable to communicate with at least one ground station. The communication equipment of the satellite may also facilitate communication with one or more (and preferably a plurality) of user terminals to facilitate the exchange of data between the at least one ground station and the one or more user terminals. For example, the plurality of satellites may be part of a data communication system to facilitate Internet access to the one or more user terminals provided by one or more gateways that communicate with the user terminals via respective ones of the plurality of satellites. 
     In one example, the orbit may be defined by a critical inclination angle (63.4 degrees relative to the Earth&#39;s equator), an orbital period of 6 sidereal hours, an apogee of 15,000 km above sea level, and a perigee of 6,000 km above sea level. Specifically, the perigee occurring relative to the southern hemisphere of the Earth. The orbit is oriented relative to the Earth to provide continuous satellite visibility between at least one of the plurality of satellites and a ground station in a targeted geographic region of the Earth on at least one repeating sky track relative to the ground station. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     Other implementations are also described and recited herein. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG.  1    depicts an embodiment of a satellite communications system comprising a plurality of satellites in orbit about Earth. 
         FIG.  2    depicts a map of Earth with a ground track of the satellite system depicted relative to ground stations on Earth. 
         FIGS.  3 - 5    depict map views showing three extents of visibility relative to a ground station at three different satellite epochs in which a satellite is in different respective ones of the extents of visibility. 
         FIG.  6    depicts a simplified view from a ground station depicting a repeating sky track defined relative thereto. 
         FIG.  7    depicts a simplified view from a ground station depicting two repeating sky tracks defined relative thereto. 
         FIGS.  8 - 10    depict different path pass characteristics for a plurality of sky tracks visible to a ground station. 
         FIG.  11    depicts a simplified view from a ground station using two distinct sky tracks to communicate with user terminals. 
         FIG.  12    depicts a polar plot showing the sky tracks of each of the first, second, and third extends of visibility of an orbit relative to a ground station. 
         FIG.  13    depicts a schematic view of a computing system that may be used to execute certain features of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    depicts a simplified representation of a satellite communications system  100 . The satellite communications system  100  generally includes a plurality of satellites  130  that move about the Earth  120  in corresponding orbits  110 . The orbits  110  relative to the Earth  120  are represented by ellipses, as shown in  FIG.  1   , although it should be appreciated that  FIG.  1    is not to scale and is for illustrative purposes only. Furthermore, while only two satellites, including a first satellite  130   a  and a second satellite  130   b  are shown in a first orbit  110   a  and a second orbit  110   b  respectively, additional satellites and corresponding orbits may be provided in other examples. In one particular example of the satellite communications system  100  that is described in greater detail below, twelve satellites transit about the Earth  120  in respective orbits. Each of the respective orbits  110  for the plurality of satellites  130  may have shared orbital parameters such that a shape of each orbit  110  relative to the Earth  120  is the same. For example, a satellite communication system  100  may be provided in which all satellites of the satellite communication system have an orbit with the same shape, but with satellites offset in satellite epoch such that each of the satellites is in a different respective portion of the repeating ground track. For instance, each orbit  110  may have a shared or common inclination, apogee, perigee, semimajor axis, orbital period, argument of perigee, and/or longitude of ascending node. 
     Thus, a ground track for each or all of the plurality of satellites may be of the same shape and follow a common ground track relative to the Earth. Each orbit  110  may be offset in relation to satellite epoch. In one example, the orbital period for each orbit  110  may be an integer factor of a sidereal day (e.g., the orbital period may be 12 sidereal hours, 8 sidereal hours, 6 sidereal hours, 4 sidereal hours, 2 sidereal hours, or 1 sidereal hour). A sidereal day is the time it takes for Earth to make one rotation around its axis and is approximately 23 hours, 56 minutes and 4.1 seconds. A sidereal hour is 1/24 of a sidereal day. In any regard, each of the plurality of satellites  130  may follow a common, repeating ground path. By offsetting the plurality of satellites  130  with respect to epoch, each of the plurality of satellites  130  may be spaced along the common, repeating ground path. In one example, each of the plurality of satellites  130  is offset in epoch such that the plurality of satellites  130  are evenly spaced within the common, repeating ground track of the satellite communication system  100   
     The satellite communications system  100  may facilitate communication between ground stations on the Earth. For example, one ground station may be a satellite gateway that acts as a communication gateway to provide Internet access to a plurality of ground stations comprising user terminals on the Earth by way of communication with a satellite of the plurality of satellites. In this regard, each of the plurality of satellites  130  include communication equipment to facilitate communication with one or more ground stations on Earth  120 . For example, the communication equipment may include radiofrequency (RF) transmitters, receivers, and/or transceivers capable of transmitting and/or receiving RF signals. The RF signals may include encoded digital data according to any appropriate encoding scheme for communication. Each satellite may also include a communications module executed by a computing device on the satellite to facilitate communications. In turn, the satellite communication system  100  may provide continuous communication between a gateway and a plurality of user terminals (e.g., which may correspond to subscribers of a communication service facilitated by the plurality of satellites  130 ). 
     In one example, a given sky track in which at least one of the plurality of satellites  130  is continuously visible to a gateway and at least one (and preferably a plurality) of user terminals to provide communication coverage (e.g., internet access) to user terminals in a geographic area of interest, which may correspond to a continent-level, country-level, or region-level service area. In some examples, user terminals in different respective geographic areas may be assigned to different sky tracks of the satellite communications system  100  to facilitate communication with one or more gateways. Moreover, a single gateway may communicate to more than one different satellite in different respective ground tracks at the same time to provide distinct communications channels (e.g., to different ones or subsets of a plurality of user terminals). In this regard, different subsets of subscribers or user terminals may be served by a single gateway using different respective satellites. 
     In an example of the satellite communications system  100 , the plurality of satellites  130  may each be configured as a “bent pipe” satellite, wherein the satellite may frequency convert the received carrier signals before retransmitting these signals to their destination, but otherwise perform little or no other processing on the contents of the signals. There could be a single carrier signal for each service spot beam of a satellite or multiple carriers in different embodiments. Similarly, single or multiple carrier signals could be used for feeder spot beams. A variety of physical layer transmission modulation and coding techniques may be used by the satellite communications system  100  in accordance with certain embodiments, including those defined with the DVB-S2 standard. For other embodiments, a number of configurations are possible. 
     The plurality of satellites  130  may each operate in a multi-beam mode, transmitting a number of spot beams, each directed at a different region of the Earth  120 . Spot beams may be generated in a variety of ways, including single-feed per beam, multiple-feed per beam, onboard beamforming, ground-based beamforming, and the like. Each spot beam may be used to communicate between a satellite and a large group (e.g., thousands) of user terminal systems (e.g., user terminals within user systems of subscribers of the communication service facilitated by the satellite communications system  100 ). The signals transmitted from the satellite may be received by one or more user terminals, via a respective user antenna. In some embodiments, some or all of the user systems include one or more user terminals and one or more customer premise equipment (CPE) devices. User terminals may include modems, satellite modems, routers, or any other useful components for handling the user-side communications. Reference to “users” should be construed generally to include any user (e.g., subscriber, consumer, customer, etc.) of services provided over the satellite communications system  100 . 
     The orbits  110  of the plurality of satellites  130  may be configured relative to the Earth  120  to provide desirable characteristics related to communication, satellite operation, ground station design, or other benefits as will be described in greater detail herein. For example, an orbit  110  may be a critically inclined orbit. A critically inclined orbit is one that is inclined at 63.4 degrees relative to the equatorial plane of the Earth  120 . Satellites traveling in a critically inclined orbit experience zero apogee drift. Accordingly, the duration and/or frequency of station-keeping operations may be minimized for satellites in orbit at a critical inclination. In turn, the critically inclined orbit  110  may reduce fuel consumption of each of the plurality of satellites  130  due to the reduction in station-keeping operations. 
     In addition, the orbit  110  may have an apogee  112  and a perigee  114  that are arranged relative to the Earth  120  to facilitate beneficial characteristics for satellite communication. In some examples, the orbits  110  may be circular orbits. In other examples, the orbits  110  may be elliptical. Specifically, the orbit  110  may have an apogee  112  of 15,000 km and a perigee  114  of 6,000 km. This example includes an eccentricity of 0.26. Regardless of whether circular or elliptical, the semimajor axis of the orbit  110  may be between about 8,000 km and 17,000 km. In examples where the orbits  110  are elliptical, the eccentricity of the orbit may be between 0 and 0.5. In another example, the orbit  110  may include a semimajor axis of 16,727 km, 4 orbits of the Earth per day, a maximum eccentricity of 0.26, and a perigee of 6,000 km. In yet another example, the orbit  110  may include a semimajor axis of 14,412 km, 5 orbits of the Earth per day, a maximum eccentricity of 0.14, and a perigee of 6,000 km. Another example orbit  110  includes a semimajor axis of 12,759 km, 6 orbits of the Earth per day, a maximum eccentricity of 0.03, and a perigee of 6,000 km. In another example, the orbit  110  may include a semimajor axis of 8,013 km, 12 orbits of the Earth per day, a maximum eccentricity of 0.16, and a perigee of 350 km. 
     In examples that include elliptical orbits, the perigee  114  may occur over the Southern hemisphere of the Earth  120 , as shown in  FIG.  1    (i.e., such that a satellite is over the Southern hemisphere when at perigee  114 ). In turn, the apogee  112  occurs over the Northern hemisphere of the Earth  120  (i.e., such that a satellite is over the Northern hemisphere when at apogee  112 ). Such an arrangement maximizes a duration in which the plurality of satellites  130  are each capable of communicating with ground stations in the Northern hemisphere. That is, because a velocity of the satellite  130  is at its slowest near the apogee of the orbit  110  and the apogee is disposed over the Northern hemisphere, each of the plurality of satellites  130  may slow and experience a longer duration in which the satellite  130  is capable of communication with ground stations on the Earth  120  in the northern hemisphere. This is desirable as many desirable targeted satellite geographic regions exist in the Northern hemisphere, including the North American landmass, European landmass, and much of the Asian landmass. 
     As described above, a satellite communication system  100  may provide a ground track that regularly repeats along the same locations relative to the surface of the earth  120 . In this regard, the orbital period for each orbit  110  in the system  100  may be a factor (e.g., an integer factor) of a sidereal day. By integer factor, it is meant that the orbital period divides the 24 sidereal hours in a sidereal day without remainder. For example, the orbital period of each satellite  130  may be 6 sidereal hours. While a 6 sidereal hour orbital period is discussed, other orbital periods that are also evenly divisible factors of a sidereal day such as an orbital period of 12 sidereal hours, 8 sidereal hours, 6 sidereal hours, 4 sidereal hours, 2 sidereal hours, or 1 sidereal hour are also contemplated. In any regard, each of the plurality of satellites  130  may follow a single, repeating ground track relative to the surface of the Earth  120  and may be offset in satellite epoch. Each of the plurality of satellites  130  may include a navigation module operative to maintain the plurality of satellites  130  in orbit  110 . Further still, the epoch of each of the plurality of satellites  130  may be offset to provide a predetermined spacing between the plurality of satellites  130  along the repeating ground track. For example, the spacing between the plurality of satellites  130  in the ground track may be evenly spaced. 
     An orbit  110  having the foregoing orbital parameters may facilitate a number of beneficial characteristics. As briefly stated above, these characteristics may include improved satellite operational characteristics by reducing station-keeping operations and, in turn, reducing fuel consumption of each of the plurality of satellites  130 . In addition, the inclined orbit having the apogee and perigee characteristics described above may allow the plurality of satellites  130  to operate almost entirely in sunlight, which reduces battery capacity requirements because the plurality of satellites  130  may not be required to operate on battery power for significant portions of the orbit  110 . 
     In addition, as described in greater detail below, the orbit  110  may allow for improved communications operations with the satellites. Specifically, the orbit  110  may facilitate continuous communication between a ground station and at least one of the plurality of satellites  130 . Furthermore, it will be understood that because each of the plurality of satellites  130  follows a common ground track, each of the plurality of satellites  130  will correspondingly each follow a common, repeating sky track relative to a ground station on Earth  120 . That is, the locations directly below the orbital path of each satellite is the same for the plurality of satellites. By “directly below,” the locations of the common, repeating ground track may represent the intersection of the Earth&#39;s surface with an imaginary line extending from the center of the Earth to a satellite. The common, repeating ground track represents the locations on the Earth over which each satellite will pass directly overhead at the zenith in the frame of reference of an observer on the surface of the Earth. Each of the plurality of satellites  130  will follow the same path across the sky from the perspective of a ground station on Earth  120 . In turn, ground station antenna requirements may be simplified by permitting less complex tracking when used to communicate with the plurality of satellites  130  in orbit  110 . 
       FIG.  2    depicts a ground path of the orbit  110  on a map of the Earth  120 . The orbit  110  may have a repeating ground track  200  that is constant relative to the surface of the Earth  120 . As the orbital period of the orbit  110  may be an evenly divisible factor of a sidereal day (e.g., 6 sidereal hours) and each satellite may orbit the Earth multiple times in a sidereal day, the ground track  200  of the orbit  110  appears as multiple interleaved ground track projections when projected onto a flat representation of the Earth  120  such that each ground track projection portion represent a portion of the orbit  110  as it repeatedly tracks across the surface of the Earth  120 . Thus, the ground projection may be represented by a first ground track projection  202 , a second ground track projection  204 , and a third ground track projection  206  that collectively define a continuous ground track  200  relative to the surface of the Earth  120 . The appearance of the orbit  110  as a plurality of interleaved ground track projections is a limitation of the projected map view shown in  FIG.  2   , however, each of the first ground track projection  202 , second ground track projection  204 , and the third ground track projection  206  represents a portion of the continuous ground track  200  for the orbit  110  at different satellite epoch of the orbit. Each of the plurality of satellites  130  of the satellite communications system  100  is shown in  FIG.  2   . In this example, the satellite communication system includes 12 satellites such that satellites  130   a - 1301  are shown, but a system need not be limited to that number. and as can be appreciated, each of the plurality of satellites  130  follows the common ground track  200  represented by the interleaved ground track projections. 
     Also shown in  FIG.  2    is a ground station comprising a gateway  250  that is located in central North America.  FIG.  2    also depicts a gateway  252  located in central Europe. The gateway  250  and the gateway  252  may each include communication equipment that may be operable to communicate with the communication equipment of each of the plurality of satellites  130  in orbit  110  when a respective one of the plurality of satellites  130  is in view of the respective gateway along a sky track. Each of the gateway  250  and the gateway  252  may include receivers, transmitters, and/or transceivers capable of communicating with the communication equipment of each of the plurality of satellites  130 . The gateway  250  and/or gateway  252  may include a communication module executed by a computing system at the respective ground station. The gateways  250  and  252  may also facilitate Internet communications by being in operative communication with a wide area network, including the Internet. 
     In the example depicted in  FIG.  2   , the orbit  110  may provide communication coverage to user terminals in at least portions of North America and Europe. Specifically, central North America and Europe may each be referred to as “targeted geographic areas” in which satellite communication is targeted to user terminals in those areas. Thus, satellite communication may be continuously provided between a gateway and user terminals in the targeted geographic areas by at least one of the plurality of satellites  130 . While North America and Europe are shown for purposes of explanation, it may be appreciated that the orbit  110  may be arranged (e.g., the longitude of the ascending node may be controlled) to arrange the orbit  110  in a different relative position to the Earth  120  to target other geographic areas of interest. Also, while ground stations are shown in central North America and Europe in  FIG.  2   , the orbit configuration depicted in  FIG.  2    may also facilitate a repeating sky track relative to a targeted geographic area in other geographic areas (e.g., in Japan, China, Russia, India, other southeast Asian countries, or other regions without limitation) although not expressly shown in  FIG.  2   . 
     The gateway  250  has extents of visibility relative to the plurality of satellites  130  due to, among other factors, the curvature of the Earth, geographic formations, or other obstacles that block or otherwise preclude line-of-sight communication with the plurality of satellites  130 . In this regard, a first extent of visibility  210  of the orbit  110  for the gateway  250  along the first ground track projection  202  is shown as a bolded gray portion of the first ground track projection  202  in  FIG.  2   . A second extent of visibility  212  of the orbit  110  for the gateway  250  is depicted as a bolded gray portion of the second ground track projection  204  in the map view of  FIG.  2   . In addition, a third extent of visibility  214  of the orbit  110  may be defined as a bolded gray portion of the third ground track projection  206 . In this regard, in the time depicted in  FIG.  2   , satellite  1301  is within the first extent of visibility  210  of the gateway  250 , satellite  130   g  is within the second extent of visibility  212  of the gateway  250 , and satellite  130   c  and satellite  130   d  may be within the third extent of visibility  214  of the gateway  250 . In this regard, the gateway  250  may be capable of simultaneous communication with each of the satellites in the different respective sky tracks relative to the gateway  250  defined by the extents of visibility  210 ,  212 , and  214 . 
     The first extent of visibility  210 , the second extent of visibility  212 , and the third extent of visibility  214  for the gateway  250  may facilitate multiple instances in which the orbit  110  passes within view of the gateway  250 . As shown in  FIG.  2   , a different respective one of the plurality of satellites  130  may be in each of the extents of visibility for the gateway  250 . Thus, the gateway  250  may be in simultaneous communication with a respective one or more of the plurality of satellites  130  as the satellite makes a pass relative to the gateway  250  in each of the extents of visibility as the satellite orbits the Earth  120 . 
       FIG.  3    shows a map view including the gateway  250  relative to a first extent of visibility  210 , a second extent of visibility  212 , and a third extent of visibility  214  along the repeating ground track  200  of the orbits  110  of the satellite communications system  100  (portions of the orbit  110  are omitted for clarity). In  FIG.  3   , a satellite  130  may be in the first extent of visibility  210  such that the gateway  250  may establish a communication link with the satellite  130 .  FIG.  3    further depicts a coverage area  218  within which user terminals (not shown) are capable of communicating with the satellite  130 . As such, user terminals within the coverage area  218  may be provided communication services by the gateway  250  via the satellite  130  such that the user terminals in the coverage area  218  may exchange data messages via the satellite  130 . That is, Internet service may be provided to the user terminals in the coverage area  218  by the satellite  130  and the gateway  250 . As can be appreciated, the coverage area  218  may extend to generally all of the contiguous United States, much of Mexico, and much of Canada. Thus, the coverage area  218  provided by the satellite  130  may extend to a large targeted geographic area, including large portions of the North American continent. 
     In  FIG.  4   , the satellite  130  has transited in orbit  110  such that the satellite  130  now is visible to the gateway  250  in the third extent of visibility  214  in a second time shown in  FIG.  4   . In this regard, the coverage area  218  of the satellite  130  also extends to a large portion of the contiguous United States.  FIG.  5    depicts a third time in which the satellite  130  may be in a second extent of visibility  212  relative to the gateway  250  such that the coverage area  218  for the satellite  130  is shown for that time. 
     Specifically, a satellite may transit through an acquisition of signal (AOS) boundary  310 , upon which the satellite becomes visible to the gateway  250  such that communication may be established with the satellite. The satellite may remain visible to the gateway  250  until the satellite transits through a loss of signal (LOS) boundary  312 . Thus, a satellite of the plurality of satellites  130  may provide a pass relative to the ground station  250  as the satellite traverses from the AOS boundary  310  to the LOS boundary  312  for each respective extent of visibility  210 ,  212 , and  214  for the gateway  250 . The period in which the satellite  130  is included in the extent of visibility  212 , the satellite  130  may appear to the gateway  250  in a first sky track relative to the gateway  250 . Because all of the plurality of satellites  130  follow a repeating ground path, each of the plurality of satellites  130  may sequentially traverse the first sky track relative to the gateway  250 . 
     For example, a simplified depiction of a repeating sky track  420  is depicted in  FIG.  6   . In  FIG.  6   , a representation of the local horizon at a gateway  250  is shown, including a horizon  400  that separates the Earth  405  and the sky  410  from the perspective of the gateway  250 . The horizon  400  may be the actual horizon at the gateway  250  or may be an artificial horizon at some elevation angle above or below the actual local horizon of the gateway  250 . In any regard, a repeating sky track  420  is shown that extends between an AOS boundary  310  in which a satellite  130  enters the extent of visibility for the gateway  250  and the LOS boundary  312  in which a satellite  130  exits the first extent of visibility  210  for the gateway  250 . Because each of the plurality of satellites  130  follows an identical ground track  200 , the orbit  110  defines a repeating sky track  420  relative to the gateway  250  in which the plurality of satellites  130  each sequentially traverse from the AOS boundary  310  to the LOS boundary  312  on the repeating sky track  420 . 
     That is, as satellite  130  traverses toward the LOS boundary  312 , at or before the time the satellite  130  exists the first extent of visibility  212  for the gateway  250 , the next satellite along the repeating ground track  200  of the plurality of satellites  130  enters the first extent of visibility  212  by passing through the AOS boundary  310  such that the next satellite may establish communication with the gateway  250 . The AOS for each successive satellite on the repeating sky track  420  may occur at or before LOS for the current satellite in the repeating sky track  420  to provide continuous satellite communication between the gateway  250  and at least one of the plurality of satellites  130  on the repeating sky track  420 . 
     In this regard, the gateway  250  may include communication equipment capable of tracking satellites along the repeating sky track  420  relative to the gateway  250 . For example, the gateway  250  may have at least two antennas, including a first antenna  452  and a second antenna  454 . The first antenna  452  and the second antenna  454  may coordinate to provide constant communication with at least one of the plurality of satellites  130  in the repeating sky track  420 . For example, the first antenna  452  may track a satellite  130  as it transits between the AOS boundary  310  and the LOS boundary  312 . At the time of or before the first antenna  452  tracks satellite  130  as it passes the LOS boundary  312  (i.e., transits out of the visible extent of the gateway  250 ), the second antenna  454  may be tasked with acquiring communication with the next satellite as it enters the visible extent at the AOS boundary  310 . Because an interruption in communication is undesirable, the first antenna  452  and the second antenna  454  may work in tandem to maintain communication using a handoff between a current satellite in the repeating sky track  420  and the next satellite to enter the repeating sky track  420 . Thus, the handoff of communication between the first antenna  452  and the satellite  130   g  as it transits through the LOS boundary  312  may be seamless as the second antenna  454  may provide communication with the next satellite as it travels through the AOS boundary  310 . In turn, the first antenna  452  may cycle back during the transit of the next satellite along the repeating sky track  420  tracked by the second antenna  454  such that the first antenna  452  is ready to acquire communication with a further subsequent satellite as that satellite passes the AOS boundary  310 . The first antenna  452  and the second antenna  454  may alternatively provide communication with each successive satellite in orbit  110  as each successive satellite passes the AOS boundary  310  to provide continuous communication with at least one of the plurality of satellites  130  in orbit  110 . 
     Based on the foregoing discussion regarding the fact that a gateway  250  may have multiple extents of visibility occupied by different respective satellites at the same time, it may be appreciated that multiple repeating sky tracks may be provided relative to a gateway  250 . Thus, with further reference to  FIG.  7   , a gateway  250  may be operative to track two different repeating sky tracks—repeating sky track  420  and repeating sky track  422 —each corresponding with different extents of visibility of the orbit  110  for the gateway  250 . That is, repeating sky track  420  may correspond to a first extent of visibility  210 , as shown in  FIGS.  2 - 5   . The repeating sky track  422  may correspond to a second extent of visibility  212 , as shown in  FIGS.  2 - 5   . For the purpose of discussion of  FIG.  7   , the repeating sky track  422  may be defined between an AOS boundary  314  and a LOS boundary  316 . In the example depicted in  FIG.  7   , satellite  130   g  is in the first repeating sky track  420 . A different one of the plurality of satellites  130  (e.g., satellite  130   c ) than the satellite  130   g  may be simultaneously transiting along repeating sky track  442  while satellite  130   c  transits along repeating sky track  420 . That is, satellite  130   c  may be visible concurrently to satellite  130   g , albeit in different sky tracks. Like the foregoing discussion of the repeating sky track  420 , the repeating sky track  422  may be fixed relative to the gateway  252  and successively occupied by different ones of the plurality of satellites  130 . 
     Accordingly, the ground station may have a third antenna  552  and a fourth antenna  554  to track successive ones of the plurality of satellites  130  along the repeating sky track  422 . Like the first antenna  452  and the second antenna  454  discussed above, the third antenna  552  and the fourth antenna  554  may alternatively track successive ones of the plurality of satellites  130  as they transit through the repeating sky track  442  such that one of the third antenna  552  and the fourth antenna  554  acquires a new satellite passing through the AOS boundary  314  at or before the other antenna of the third antenna  552  and the fourth antenna  554  loses communication with an existing satellite in the repeating sky track  422  passing through the LOS boundary  316 . 
     The number of sky tracks simultaneously visible for a given targeted geographic extent may not be limited to one or two but could include at least three sky tracks in which at least one of the plurality of satellites  130  is visible to a gateway  250 . For instance, as can be appreciated with returned reference to  FIGS.  2 - 5   , the first extent of visibility  210 , the second extent of visibility  212 , and the third extent of visibility  214  may create different respective sky tracks relative to the gateway  250 . Furthermore, the same repeating ground track  200  of the orbit  110  may also provide a plurality of extents of visibility and corresponding repeating sky tracks to a gateway  252  in central Europe as well. While not shown, multiple sky tracks may also be provided to other gateways in other targeted geographic locations (e.g., in Asia) using the orbit  110  that provides the sky tracks relative to the gateway  250  and the gateway  252 . Accordingly, the orbit  110  provides a robust communication system as a plurality of ground stations in different targeted geographic regions may be in communication with a plurality of satellites simultaneously. 
       FIGS.  8 - 10    depict plots representative of three different repeating sky tracks relative to a given ground station. Specifically,  FIG.  8    represents the characteristics of a repeating sky track  600 . The plot in  FIG.  8    has a left vertical axis representing degree values, a right vertical axis representing range values, and the horizontal axis represents time. A pass elevation  602  is represented in a dash-dot line, a pass azimuth  604  is represented as a dashed line, and a pass range  606  is represented as a dotted line. In this regard, pass elevation  602  and pass azimuth  604  are measured relative to the left axis in degrees corresponding to the elevation angle and azimuth angle relative to the ground station. As may also be appreciated in  FIG.  8   , a number of satellite epochs are represented corresponding to passes of each satellite in the plurality of satellites  130  in the sky track  600 . Thus, a first satellite epoch  608  in which a first satellite  130   a  is visible to the ground station is followed successively by a second satellite epoch  610  in which a second satellite  130   b  is visible to the ground station, a third satellite epoch  612  in which a third satellite  130   c  is visible to the ground station, a fourth satellite epoch  614  in which a fourth satellite  130   d  is visible to the ground station, a sixth satellite epoch  618  in which a sixth satellite  130   e  is visible to the ground station, a seventh satellite epoch  620  in which a seventh satellite  130   f  is visible to the ground station, an eighth satellite epoch  622  in which an eighth satellite  130   g  is visible to the ground station, a ninth satellite epoch  624  in which a ninth satellite  130   h  is visible to the ground station, a tenth satellite epoch  626  in which a tenth satellite  130   i  is visible to the ground station, an eleventh satellite epoch  628  in which an eleventh satellite  130   j  is visible to the ground station, and a twelfth satellite epoch  630  in which a twelfth satellite  1301  is visible to the ground station. In turn, a first satellite epoch  608  follows the twelfth satellite epoch  630 , in which the first satellite  130   a  again becomes visible to the ground station, thus representing a complete cycle through each of the plurality of satellites  130  passing along the sky track  600 . As can be appreciated, the pass elevation  602 , pass azimuth  604 , and pass range  606  follow a repetitive cycle for each successive satellite epoch, indicating the repeating sky track  600 , which remains constant. Each satellite epoch may be at least around 2 sidereal hours, such that the twelve satellites defining the twelve satellite epochs span a full day. However, depending on the length of the sky track relative to the ground station, other numbers of satellites and epoch durations may be provided to facilitate continuous communication with at least one of the plurality of satellites  130 . 
       FIG.  9    represents the characteristics of a repeating sky track  700 . The plot in  FIG.  9    has a left vertical axis representing degrees, a right vertical axis representing range values, and the horizontal axis represents time. A pass elevation  702  is represented in a dash-dot line, a pass azimuth  704  is represented as a dashed line, and a pass range  706  is represented as a dotted line. In this regard, pass elevation  702  and pass azimuth  704  are measured relative to the left axis with elevation angle and azimuth angle relative to the ground station. As may also be appreciated in  FIG.  9   , a number of satellite epochs are represented corresponding to passes of each satellite in the plurality of satellites  130  in the sky track  700 . Thus, a first satellite epoch  708  in which a first satellite  130   a  is visible to the ground station is followed successively by a second satellite epoch  710  in which a second satellite  130   b  is visible to the ground station, a third satellite epoch  712  in which a third satellite  130   c  is visible to the ground station, a fourth satellite epoch  714  in which a fourth satellite  130   d  is visible to the ground station, a sixth satellite epoch  718  in which a sixth satellite  130   e  is visible to the ground station, a seventh satellite epoch  720  in which a seventh satellite  130   f  is visible to the ground station, an eighth satellite epoch  722  in which an eighth satellite  130   g  is visible to the ground station, a ninth satellite epoch  724  in which a ninth satellite  130   h  is visible to the ground station, a tenth satellite epoch  727  in which a tenth satellite  130   i  is visible to the ground station, an eleventh satellite epoch  728  in which an eleventh satellite  130   j  is visible to the ground station, and a twelfth satellite epoch  730  in which a twelfth satellite  1301  is visible to the ground station. In turn, a first satellite epoch  708  follows the twelfth satellite epoch  730 , in which the first satellite  130   a  again becomes visible to the ground station, thus representing a complete cycle through each of the plurality of satellites  130  passing along the sky track  700 . As can be appreciated, the pass elevation  702 , pass azimuth  704 , and pass range  706  follow a repetitive cycle for each successive satellite epoch, indicating the repeating sky track  700 , which remains constant. 
       FIG.  10    represents the characteristics of a repeating sky track  800 . The plot in  FIG.  10    has a left vertical axis representing degrees, a right vertical axis representing range values, and the horizontal axis represents time. A pass elevation  802  is represented in a dash-dot line, a pass azimuth  804  is represented as a dashed line, and a pass range  806  is represented as a dotted line. In this regard, pass elevation  802  and pass azimuth  804  are measured relative to the left axis with elevation angle and azimuth angle relative to the ground station. As may also be appreciated in  FIG.  10   , a number of satellite epochs are represented corresponding to passes of each satellite in the plurality of satellites  130  in the sky track  800 . Thus, a first satellite epoch  808  in which a first satellite  130   a  is visible to the ground station is followed successively by a second satellite epoch  810  in which a second satellite  130   b  is visible to the ground station, a third satellite epoch  812  in which a third satellite  130   c  is visible to the ground station, a fourth satellite epoch  814  in which a fourth satellite  130   d  is visible to the ground station, a sixth satellite epoch  818  in which a sixth satellite  130   e  is visible to the ground station, a seventh satellite epoch  820  in which a seventh satellite  130   f  is visible to the ground station, an eighth satellite epoch  822  in which an eighth satellite  130   g  is visible to the ground station, a ninth satellite epoch  824  in which a ninth satellite  130   h  is visible to the ground station, a tenth satellite epoch  826  in which a tenth satellite  130   i  is visible to the ground station, an eleventh satellite epoch  828  in which an eleventh satellite  130   j  is visible to the ground station, and a twelfth satellite epoch  830  in which a twelfth satellite  1301  is visible to the ground station. In turn, a first satellite epoch  808  follows the twelfth satellite epoch  830 , in which the first satellite  130   a  again becomes visible to the ground station, thus representing a complete cycle through each of the plurality of satellites  130  passing along the sky track  800 . As can be appreciated, the pass elevation  802 , pass azimuth  804 , and pass range  806  follow a repetitive cycle for each successive satellite epoch, indicating the repeating sky track  800 , which remains constant. 
     As can be appreciated, each of the repeating sky track  600 , repeating sky track  700 , and repeating sky track  800  have different azimuth angles for each satellite epoch of a respective path. In turn, a ground station may have a corresponding set of antennas dedicated to each unique sky track available to the ground station. Also, the satellite epochs for each respective repeating sky track are offset or out of phase. Thus, different ones of the plurality of satellites  130  are present in each individual sky track in any given epoch of the satellite communications system  100 . 
     With further reference to  FIG.  11   , the utility of multiple sky tracks available to a gateway  950  is demonstrated.  FIG.  11    generally depicts a horizon  900  separating the Earth  905  from the sky  910 , as seen from the gateway  950 . Also in  FIG.  9   , the gateway  950  includes at least a first ground station antenna  902  and a second ground station antenna  904 . As may be appreciated from the foregoing description, the gateway  950  may also include additional antennas (e.g., to provide successive tracking of satellites in a sky track). In any regard, the first ground station antenna  902  may be in operative communication with a satellite  130   c  in a first repeating sky track  920  that may be in further communication with a first user terminal  912 . Also, a second ground station antenna  904  may be in operative communication with a satellite  130   g  in a second repeating sky track  922  that may be in further communication with a second user terminal  914 . 
     In this regard, the first user terminal  912  may be capable of tracking satellites in the first repeating sky track  920  (e.g., with multiple antennae at the first user terminal  912  or a phased array antenna tuned to track the first repeating sky track  920  as described in greater detail below) to exchange a communication  924  with the gateway  950  via satellites in the first repeating sky track  920 . The second user terminal  914  may be capable of tracking satellites in the second repeating sky track  922  to exchange a communication  926  with the gateway  950  via satellites in the second repeating sky track  922 . That is, distinct communication channels may be established by the gateway  950  with different respective sets of user terminals. For example, a first set of user terminals may be tasked with tracking satellites in the first repeating sky track  920 , and a second set of user terminals may be tasked with tracking satellites in the second repeating sky track  922 . This may provide discrete communication modalities to different sets of user terminals and/or may provide additional bandwidth to the satellite communications system  100 . Moreover, while the first user terminal  912  and the second user terminal  914  are shown within the extent of visibility of the single gateway  950  in  FIG.  9   , it may be that the first user terminal  912  and/or second user terminal  914  are beyond the extent of visibility to the single gateway  950  such that communication between the first user terminal  912  and the single gateway  950  and/or the second user terminal  914  and the single gateway  950  requires relay of the communication  924  or communication  926  using a satellite. 
       FIG.  12    illustrates a polar plot  1000  representing the visible sky relative to a ground station. The ground station could be a gateway or a user terminal. In any regard, the polar plot includes an azimuth angle represented in the angular coordinate of the plot  1000  and an elevation angle in the radial coordinate of the plot  1000 . In this regard, a first sky track  1002 , a second sky track  1004 , and a third sky track  1006  may each extend in the sky relative to the ground station. The plot  1000  also includes a first tracking region  1012  for the first sky track  1002 , a second tracking region  1014  for the second sky track  1004 , and a third tracking region  1016  for the third sky track  1006 . Each tracking region may define a range of azimuth and elevation angles that an antenna at the ground station is capable of communicating to achieve communication with satellites in each respective sky track. 
     In the context of the ground station being a gateway, the gateway may be in simultaneous communication with respective satellites in each of the first sky track  1002 , the second sky track  1004 , and the third sky track  1006 . Thus, the gateway may include one or more antennas capable of communication in the first tracking region  1012 , the second tracking region  1014 , and the third tracking region  1016 . The gateway may include one or more antennas for simultaneous communication in each of the tracking regions. Antennas may include mechanical and/or electrical tracking elements to allow for communication with each of the respective tracking regions. 
     In the context of the ground station being a user terminal, it may not be that the user terminal is in communication with a satellite in more than one of the sky tracks. Moreover, as the antenna complexity of a user terminal is advantageously minimized, it may be that the user terminal may be assigned a given sky track to facilitate communication therewith. As can be appreciated, each tracking region for the sky tracks has a different area. The larger the area of the tracking region, the more complex an antenna may be to facilitate communication with the sky track. In this regard, for the example shown in  FIG.  12   , the first tracking region  1012  may have the smallest area of each of the tracking regions for the user terminal. As such, the user terminal may be assigned to track satellites in the first sky track  1002  associated with the first tracking region  1012 . Thus, the antenna design (e.g., including mechanical and/or electrical tracking means such as a phased array antenna) may be simplified. In this regard, the first sky track  1002  may have a more limited extent of azimuth and elevation deviation than the second sky track  1004  and the third sky track  1006 , providing more efficient tracking of satellites in the first sky track  1002 . 
       FIG.  13    illustrates an example schematic of a processing system  1100  suitable for implementing aspects of the disclosed technology, including a communication module  1150  and/or navigation module  1152 , as described above in relation to the satellite communications system  100 . Furthermore, other aspects of the satellite communications system  100  may be controlled by a processing system  1100 . The processing system  1100  may include one or more processor unit(s)  1102 , memory  1104 , a display  1106 , and other interfaces  1108  (e.g., buttons). The memory  1104  generally includes both volatile memory (e.g., RAM) and non-volatile memory (e.g., flash memory). An operating system  1110 , such as the Microsoft Windows® operating system, the Apple macOS operating system, or the Linux operating system, resides in the memory  1104  and is executed by the processor unit(s)  1102 , although it should be understood that other operating systems may be employed. 
     One or more applications  1112  are loaded in the memory  1104  and executed on the operating system  1110  by the processor unit(s)  1102 . Applications  1112  may receive input from various input local devices such as a microphone  1134 , input accessory  1135  (e.g., keypad, mouse, stylus, touchpad, joystick, instrument mounted input, or the like). Additionally, the applications  1112  may receive input from one or more remote devices such as remotely-located smart devices by communicating with such devices over a wired or wireless network using more communication transceivers  1130  and an antenna  1138  to provide network connectivity (e.g., a mobile phone network, Wi-Fi®, Bluetooth®). The processing device  1100  may also include various other components, such as a positioning system (e.g., a global positioning satellite transceiver), one or more accelerometers, one or more cameras, an audio interface (e.g., the microphone  1134 , an audio amplifier and speaker and/or audio jack), and storage devices  1128 . Other configurations may also be employed. 
     The processing system  1100  further includes a power supply  1116 , which is powered by one or more batteries or other power sources and which provides power to other components of the processing system  1100 . The power supply  1116  may also be connected to an external power source (not shown) that overrides or recharges the built-in batteries or other power sources. 
     The processing system  1100  may include a variety of tangible processor-readable storage media and intangible processor-readable communication signals. Tangible processor-readable storage can be embodied by any available media that can be accessed by the processing system  1100  and includes both volatile and nonvolatile storage media, removable and non-removable storage media. Tangible processor-readable storage media excludes intangible communications signals and includes volatile and nonvolatile, removable and non-removable storage media implemented in any method or technology for storage of information such as processor-readable instructions, data structures, program modules or other data. Tangible processor-readable storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CDROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible medium which can be used to store the desired information and which can be accessed by the processing system  1100 . In contrast to tangible processor-readable storage media, intangible processor-readable communication signals may embody processor-readable instructions, data structures, program modules or other data resident in a modulated data signal, such as a carrier wave or other signal transport mechanism. The term “modulated data signal” means an intangible communications signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, intangible communication signals include signals traveling through wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared, and other wireless media. 
     Some implementations may comprise an article of manufacture. An article of manufacture may comprise a tangible storage medium to store logic. Examples of a storage medium may include one or more types of processor-readable storage media capable of storing electronic data, including volatile memory or non-volatile memory, removable or non-removable memory, erasable or non-erasable memory, writeable or re-writeable memory, and so forth. Examples of the logic may include various software elements, such as software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, middleware, firmware, software modules, routines, subroutines, operation segments, methods, procedures, software interfaces, application program interfaces (API), instruction sets, computing code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof. In one implementation, for example, an article of manufacture may store executable computer program instructions that, when executed by a computer, cause the computer to perform methods and/or operations in accordance with the described implementations. The executable computer program instructions may include any suitable type of code, such as source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. The executable computer program instructions may be implemented according to a predefined computer language, manner or syntax, for instructing a computer to perform a certain operation segment. The instructions may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled and/or interpreted programming language. 
     The implementations described herein are implemented as logical steps in one or more computer systems. The logical operations may be implemented (1) as a sequence of processor-implemented steps executing in one or more computer systems and (2) as interconnected machine or circuit modules within one or more computer systems. The implementation is a matter of choice, dependent on the performance requirements of the computer system being utilized. Accordingly, the logical operations making up the implementations described herein are referred to variously as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations may be performed in any order unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language.