US20100201566A1 - System and method for satellite communication - Google Patents

Abstract

A system and method are disclosed which may include providing at least one satellite having a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about an axis of the satellite; causing the at least one satellite to move around the earth along a non-geostationary orbit; establishing a data communication path between a first of the beamformers on the satellite and a communication target, the data communication path having a satellite end at the first beamformer and an target end at the communication target; shifting the satellite end of the data communication path through a succession of the beamformers as the satellite moves along its orbit; and at least substantially reducing an amount of RF wave energy directed to beamformers of the plurality of beamformers not forming part of the data communication path.

Description

• This application is a Continuation of PCT Application Serial No. PCT/US07/81763, entitled “SYSTEM AND METHOD FOR SATELLITE COMMUNICATION”, filed Oct. 18, 2007, [Attorney docket No. 790-2-PCT], and published as Pub. No. WO 2009/051592 A1 on Apr. 23, 2009 which application is hereby incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
• The present invention relates in general to communication systems and in particular to systems and methods for satellite based communication.
• Satellite communication systems provide various benefits to consumers of communication services such as for telephony, internet communications, television communications among others. Various satellite systems are currently available, which are discussed below.
• Satellites employing a geostationary (GSO) orbit provide the convenience of having one or more satellites in such a system remain fixed in relation to points on the surface of the earth that they communicate with. However, at GSO altitude, which is about 36,000 kilometers (km), communication latency is about 600 milliseconds (ms). Such latency leads to very slow communication throughput and is particularly ineffective for Internet communication. For example, the main page at “www.cnn.com”® would take about 24 seconds to load with this latency period in effect.
• For this reason, satellites employing non-geostationary orbits (NGSOs) such as medium earth orbit (MEO) (between 2000 and 36000 km) and low earth orbit (LEO) (below 2000 km) have in certain cases, been used instead. Existing LEO and MEO satellite systems employ inclined orbits to enable such systems to reach high concentrations of customers located in the northern and southern hemispheres. In such orbits, the satellites move continuously with respect to various earth stations with which they communicate. Moreover, successive satellites in such constellations commonly move along different orbits. Thus, many such systems employ omni-directional antennas at earth-based user terminals to enable ongoing communication to take place as the various satellites in a constellation move through their respective orbits. However, such omni-directional antennas have very low gain, thereby limiting the communication throughput (communication bandwidth) achievable using this approach. One way to compensate for the low gain level of the antennas at the user terminal is to significantly increase the power used for satellite antenna transmission. However, such increased satellite transmission power levels may exceed the power available using current satellite power generation technology, and are therefore impractical.
• Moreover, satellites in the LEO and MEO systems may employ mechanical tracking or phased array (electronically steerable) antennas for communication with the earth-based based user terminals to communicate therewith. Such antennas are very expensive, thereby imposing a significant premium on the cost of communication services employing LEO/MEO satellite systems. Accordingly, there is a need in the art for satellite communication systems providing effective communication service at a reduced cost.
SUMMARY OF THE INVENTION
• According to one aspect, the invention is directed to a method that may include providing at least one satellite having a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about an axis of the satellite; causing the at least one satellite to move around the earth along a non-geostationary orbit; establishing a data communication path between a first of the beamformers on the satellite and a communication target, the data communication path having a satellite end at the first beamformer and an target end at the communication target; shifting the satellite end of the data communication path through a succession of the beamformers as the satellite moves along its orbit; and at least substantially reducing an amount of RF wave energy directed to beamformers of the plurality of beamformers not forming part of the data communication path. Preferably, the plurality of respective beams have a plurality of different respective fixed pitch angles about a lateral axis of the satellite. Preferably, the communication target is a first antenna, at an Earth station, configured to communicate with the satellite along a selected segment of the orbit of the satellite, the first antenna being an Earth end of the data communication path.
• Preferably, the communication target is another satellite. Preferably, the at least substantially reducing step comprises: not directing any RF wave energy to beamformers of the plurality of beamformers not forming part of the data communication path. Preferably, the satellite further includes at least one reflector operable to reflect RF wave energy from the plurality of beamformers toward the communication target and to reflect RF wave energy from the communication target toward the plurality of beamformers. Preferably, the orbit is at least substantially equatorial. Preferably, the latitude of the orbit remains between −10 and +10 degrees latitude. Preferably, the latitude of the orbit remains between −5 and +5 degrees latitude. Preferably, the altitude of the satellite orbit is between 600 km and 30,000 km. Preferably, the altitude of the satellite orbit is between 5,000 km and 10,000 km. Preferably, the altitude of the satellite orbit is between 7,000 km and 8,000 km.
• Preferably, the method further includes the first antenna at the earth station tracking the satellite using a steering mechanism to cause the first antenna to substantially continuously point toward the satellite. Preferably, the method further includes the first antenna quasi-tracking the satellite by transferring the earth end of the data communication path through a succession of fixed antenna beams, wherein each antenna beam has a substantially fixed orientation with respect to the surface of the Earth. Preferably, the method further includes directing RF wave energy to the beamformer, of the plurality of beamformers, serving as the satellite end of the data communication path. Preferably, the method further includes maintaining the data communication path between the first antenna and the first beamformer over a range of satellite movement corresponding to a communication alignment range between the beam from the first beamformer and the first antenna. Preferably, the method further includes commencing communication between the first antenna and the first beamformer when the first antenna and the beam generated by the first beamformer reach an initial communication alignment boundary during movement of the satellite along its orbit; and concluding communication between the first antenna and the first beamformer when the first antenna and the beam generated by the first beamformer reach a final communication alignment boundary during movement of the satellite along its orbit.
• Preferably, communication power between the first antenna, at the earth station, and the first beamformer reaches a peak at centroid-to-centroid alignment between the first antenna and the first beamformer. Preferably, the first antenna communicates with the first beamformer while the communication power along the data communication path therebetween is equal to or greater than one half the peak power. Preferably, the shifting step includes transferring the satellite end of the data communication path from the first beamformer to a second beamformer of the plurality of beamformers once a second antenna at the earth station and a beam from the second beamformer enter into communication alignment range. Preferably, the transferring step includes redirecting RF wave energy, originating from an amplifier on the satellite, from the first beamformer to the second beamformer. Preferably, the redirecting step is performed using a waveguide switch. Preferably, the method includes repeating the steps of transferring and redirecting for the plurality of the beamformers on the satellite so as to maintain operation of the data communication path between the satellite and the earth station throughout the movement of the satellite through the selected segment of the orbit of the satellite.
• According to another aspect, the invention is directed to an apparatus that may include a satellite having a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about an axis of the satellite; and a controller operable to direct a data communication path through a first beamformer of the plurality of beamformers, wherein the controller is further operable to shift the data communication path through a succession of the beamformers. Preferably, the plurality of different respective fixed pitch angles are about a lateral axis of the satellite. Preferably, the controller is operable to redirect the data communication path from the first beamformer to a second beamformer of the plurality of beamformers upon detecting a decline in communication power along the data communication path. Preferably, the apparatus further includes an amplifier able to supply RF wave energy to one or more of the plurality of beamformers, wherein the controller is operable to select at least one beamformer, of the plurality of beamformers, to direct the RF wave energy to. Preferably, the plurality of beamformers are disposed in an array on the satellite, having a plurality of rows, wherein each beamformer row includes a sequence of beamformers configured to illuminate footprints on the Earth over a range of longitude but with substantially similar latitude; and wherein the plurality of rows are configured to illuminate respective groups of footprints at a plurality of different respective latitudes.
• According to yet another aspect, the invention is directed to a method that may include providing a first constellation of satellites within a satellite system; providing at least one additional constellation of satellites to provide a plurality of satellite constellations within the satellite system; enabling adjacent ones of the satellites in the satellite system to communicate with a single earth station; and wherein at least one of the satellites in each constellation has a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about a lateral axis of the satellite, and a controller operable to direct a data communication path through a first beamformer of the plurality of beamformers, wherein the controller is further operable to shift the data communication path through a succession of the beamformers. Preferably, the method further includes the adjacent satellites communicating with the earth station employing the same transmission frequency.
• Preferably, the method further includes dedicating at least selected ones of the beamformers in the satellite system substantially completely to one of: transmission; and reception. Preferably, the method further includes supplementing the satellite system in a given state with at least one further constellation to provide a modified satellite system without disrupting an operation of the satellite system in the given state. Preferably, the method further includes dedicating at least selected ones of the satellites in the satellite system substantially completely to one of: transmission; and reception.
• According to yet another aspect, the invention is directed to a method that may include conducting a data communication session between a first computing entity and a second computing entity over a communication network, wherein at least a portion of the data transferred over the communication network during the data communication session is transmitted over a satellite system, and wherein at least one of the satellites in the satellite system has a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about an axis of the satellite; and a controller operable to direct a data communication path through a first beamformer of the plurality of beamformers, and wherein the controller is further operable to shift the data communication path through a succession of the beamformers.
• Other aspects, features, advantages, etc. will become apparent to one skilled in the art when the description of the preferred embodiments of the invention herein is taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• For the purposes of illustrating the various aspects of the invention, there are shown in the drawings forms that are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
• FIG. 1 is a block diagram of acommunication system100 including a satellite system in accordance with one or more embodiments of the present invention;
• FIG. 1A is a block diagram showing communication apparatus betweengateway102 andsubscriber106 in greater detail;
• FIG. 2 is a block diagram of at least a portion the operational components of a satellite in accordance with one or more embodiments of the present invention;
• FIG. 3 is a block diagram of at least a portion the operational components of a satellite in accordance with one or more embodiments of the present invention;
• FIG. 4 is a profile view of a satellite orbiting the earth in a non-geostationary orbit in accordance with one or more embodiments of the present invention;
• FIG. 5A is a plan view of a plurality of satellites orbiting the earth in an equatorial orbit in accordance with one or more embodiments of the present invention;
• FIG. 5B is a schematic view of eight satellites distributed over an equatorial orbit in accordance with one or more embodiments of the present invention;
• FIG. 6 is a partially schematic, partially elevational view of a satellite moving in orbit over an earth station in accordance with one or more embodiments of the present invention;
• FIG. 7 is a partially schematic, partially elevational view of a two satellites moving in orbit over an earth station in accordance with one or more embodiments of the present invention;
• FIG. 8 is a partially schematic, partially elevational view of two satellites moving in orbit over an earth station in accordance with one or more embodiments of the present invention;
• FIG. 9 is a partially schematic and partially elevational view of a satellite beam proceeding along its orbit over an earth station in accordance with one or more embodiments of the present invention;
• FIG. 10 is a partially schematic and partially elevational view of a satellite having a multi-beam antenna in accordance with one or more embodiments of the present invention;
• FIG. 11 is a partially schematic and partially elevational view of a satellite having a plurality of beamformers moving in orbit over an earth station in accordance with one or more embodiments of the present invention;
• FIGS. 12-14 are partially schematic and partially elevational views of the satellite ofFIG. 11 at various stages of advancement along its orbit with respect to the earth station, in accordance with one or more embodiments of the present invention;
• FIG. 15 is a partially schematic and partially elevational view of a satellite proceeding along its orbit over an earth station in accordance with one or more embodiments of the present invention;
• FIG. 16 is a block diagram of a computer system useable in cooperation with one or more embodiments of the present invention;
• FIG. 17 is a schematic plan view of a satellite having an array of beams in accordance with one or more embodiments of the present invention;
• FIG. 18 is a partially schematic and partially elevational view of the satellite ofFIG. 17 showing a front column of beams emerging from the satellite, in accordance with one or more embodiments of the present invention;
• FIG. 19 depicts an array of footprints arising from the beams within the respective beam rows of the satellite ofFIG. 17, in accordance with one or more embodiments of the present invention;
• FIG. 20 is a schematic representation of portions of two constellations of satellites moving in orbit around the earth with respect to an earth station in accordance with one or more embodiments of the present invention; and
• FIG. 21 is a schematic representation of portions of two constellations of satellites moving in orbit around the earth with respect to an earth station in accordance with one or more embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Those skilled in the art will appreciate the fact that antennas, which may include beamformers, are reciprocal transducers which exhibit similar properties in both transmission and reception modes. For example, the antenna patterns for both transmission and reception are generally identical and may exhibit approximately the same gain. For convenience of explanation, descriptions are often made in terms of either transmission or reception of signals, on the understanding that the pertinent description applies to the other of the two possible operations. Thus, it is to be understood that the antennas of the different embodiments described herein may pertain to either a transmission or reception mode of operation. Those of skill in the art will also appreciate the fact that the frequencies received and/or transmitted may be varied up or down in accordance with the intended application of the system. Herein, a beamformer is any device suitable for providing a beam suitable for transmitting and/or receiving radio frequency (RF) communication energy. In one embodiment, the communication enabled by the above-described beamformer may occur between a satellite and an Earth station. In other embodiments, such communication may occur between two satellites, or between any two suitable locations at which a beamformer is located.
• It is noted here that the parts, linear lengths, and angular distances shown in the figures are not drawn to scale. Moreover, for convenience of illustration, some parts may appear larger in relation to others than would be the case in an actual physical implementation of the various physical objects depicted in the figures. Accordingly, while the figures are provided to aid an understanding of the various embodiments disclosed herein, the present invention is not limited to the relative sizes and orientations of the various parts shown in the figures.
• FIG. 1 is a block diagram of acommunication system100 including asatellite system104 in accordance with one or more embodiments of the present invention.Communication system100 may includesubscribers106,satellite system104,communication gateway102, andcommunication network108. The portions ofsystem100 identified above are described further below.
• Communication network108 may include the Internet. However,communication network108 may refer to any communications network or system capable of employing a satellite communications system to enable communication between one ormore subscribers106 with anetwork108 and/or with each other. Such systems may include, either in place of or in addition to the Internet, telephone systems (landline and/or wireless), radio communications (one-way broadcast and/or two-way radio), television broadcasting, international warning system broadcast (such as for weather emergencies or other event), and/or other communication systems.
• Gateway102 may be an interface betweencommunication network108 andsatellite system104.Gateway102 is preferably land-based and preferably provides any needed data communication routing and/or data format conversion needed to enable communication betweencommunication network108 andsatellite system104. For instance,gateway102 may include controllers or other control means for controlling the location of a data communication path, such as by selecting one or more satellites from among a plurality of satellites to conduct data communication and/or selecting one or more beamformers (such as, but not limited to feeds) on one satellite or distributed over a plurality of satellites to conduct data communication.
• Herein, the terms “satellite system104” and “satellites104” are used interchangeably and generally refer to the totality of satellites employed as communication intermediaries in betweengateway102 andsubscribers106.Satellite system104 may include one or more satellite constellations, wherein each constellation may include one or more satellites. Thus,satellite system104 may include any number of satellites from one up to any desired number. Each satellite200 (FIG. 4) ofsatellite system104 may transmit data fromgateway102 to one or more specifiedsubscribers106 and/or to anyother satellite200 withinsatellite system104. Conversely,satellite system104 may transmit data from one ormore subscribers106 togateway102.
• Subscribers106 may include one or more subscriber locations which may be located at fixed locations on the earth. Subscriber locations may also be referred to as user terminals. The nature and communication bandwidth needs ofsubscribers106 may vary widely. For instance,subscriber106 may include one or more telephone companies, one or more Internet service providers, one or more Internet cafés, one or more individual communications customers, and/or other form of communication provider such as a cable television provider, or any combination of the foregoing.
• FIG. 1A shows the communication betweengateway102 and oneexemplary subscriber106 in greater detail. In this embodiment,Gateway router102R is preferably part ofgateway102, andsubscriber router106R preferably forms part ofsubscribers106. In this embodiment, one modem at each of thegateway router102R andsubscriber106R may be dedicated to a respective modem. Thus,gateway router102R may direct data communication throughmodem A222, then throughsatellite A224, then throughmodem A226, and intosubscriber router106R. Likewise,gateway router102R may direct data communication tomodem B232, then tosatellite B234, in turn tomodem B236, and then tosubscriber router106R.
• FIG. 2 is a block diagram of at least a portion of the operational components of asatellite200 in accordance with one or more embodiments of the present invention.Satellite200 may includeprocessor210, dualtracking antenna system202,amplifier204, mux (multiplexer)206, and/or data path control208.Satellite200 may further includebeamformers302,304,306, and308 (collectively “beamformers300”).
• Dualtracking antenna system202 may be a communication interface in between gateway102 (FIG. 1) and the remainder of the communication equipment onsatellite200.Dual tracking system202 may include two or more mechanically or electronically steerable antennas and/or communication data conversion equipment for interfacing betweengateway102 and communication equipment onsatellite200. The structure and operation ofdual tracking system202 is known in the art. Accordingly, a detailed description ofsystem202 is not provided herein.
• Amplifier204 is a conventional radio frequency (RF) amplifier as is known in the art, and commonly could be composed of either a traveling wave tube amplification (twta) or solid state power amplifier (sspa). Accordingly, a detailed description ofamplifier204 is not provided herein. SimilarlyMux206 may be a conventional RF multiplexer as is known in the art and is therefore not described further herein.
• Data path control208 may include computing and/or control equipment for selecting one or more beamformers from amongbeamformers302,304,306, and308 for use in communication with an earth station antenna, or other satellite. Data path control208 may be further operable to provide or deny RF (Radio Frequency) power to one or more ofbeamformers302,304,306, and308. The beamformers shown inFIG. 2 are further described later in this document and are therefore not further described in this section. Thus, data path control208 may also serve as a switch for selecting one ormore beamformers300 to direct RF wave energy to. An alternative embodiment for switching amongbeamformers300 is described in connection withFIG. 3. In other embodiments, the function of controlling the flow of RF wave energy among thebeamformers300 may be provided by other equipment, instead of or in addition to data path control208, which other equipment may be located onsatellite200 and/or elsewhere incommunication system100.
• Processor210 may control the flow of data among thebeamformers302,304,306, and308 (where a single beamformer in general may be referred to simply using the numeral “300”).Routers102R and106R (FIG. 1A) may control the transfer of communication among successive ones of the beamformers. Therouters102R and106R may then recognize the shift in data path among the beamformers and make suitable adjustments to their own data paths.
• FIG. 3 is a block diagram of a particular embodiment ofsatellite200 employing the functions discussed in connection withFIG. 2. The embodiment ofFIG. 3 may includemux206, switches212,214, and216, and/orbeamformers302,304,306, and308.Mux206 andbeamformers302,304,306, and308 are discussed elsewhere herein and are therefore not discussed further in this section.Switches212,214, and216 represent one possible implementation of data path control208.Switches212,214, and216 are preferably one-input-two-output microwave switches having suitable control inputs for selection of one of two possible output ports. Suitable control ofswitches212,214, and216 may enable selection of one or more ofbeamformers302,304,306, and308 for use in conducting data communication betweensatellite200 and a selected earth station, or other satellite. One commercial switch useable forswitches212,214, and/or216 is available from the Bosch® corporation. Suitable control means may be disposed onsatellite200, atgateway200, and/or other location, for controllingswitches212,214, and/or216.
• The following is directed to describing various aspects of the orbit of the satellites, the transfer of communication between successive satellites, the transfer of communication between successive beams on one satellite, and movement of an axis of a communication path within the transmission/reception range of a single satellite beamformer's alignment range. Attention is directed first to the characteristics of a satellite orbit in accordance with one or more embodiments of the present invention.
• It is noted that existing communication enterprises generally do not deploy satellites in non-geostationary equatorial orbit because the cost of enabling earth stations to communicate with the orbiting satellites is generally very high and the customer base is considered insufficiently large and/or insufficiently well funded to justify the expense. Accordingly, to date, the need for high-speed communication having low latency for equatorial regions has gone unmet. The technology disclosed herein enables satisfying this unsatisfied need and doing so cost effectively by deploying the cost-saving measures disclosed herein.
• FIG. 4 is a profile view asatellite200 orbiting theearth250 in anon-geostationary orbit260 in accordance with one or more embodiments of the present invention.Satellite200 preferably orbits the earth in the direction shown at analtitude270 of about 7500 km. At this altitude,satellite200 will complete one full orbit of theearth250 in about 4.5 hours. The direction (from West to East) shown by the arrow onorbit260 shows both the direction of rotation of theearth250 and the direction of the movement ofsatellite200 around theearth250.
• Only asingle satellite200 is shown for the sake of simplicity inFIG. 4. However,satellite200 will typically form part of a constellation of satellites. The angular separation between successive satellites may correspond to 360 degrees (which is by definition, the total angular distance of an entire orbit) divided by the number of satellites in the constellation. At least, this is the case where the satellites are equally spaced over the orbit, which may, but need not, be the case. For example, in a constellation having eight satellites in which thesatellites200 are substantially equally spaced about theorbit260 of theearth250, the angular separation betweensuccessive satellites200 inorbit260 would be about 45 degrees.
• However, in alternative embodiments, unequal angular spacings may be used between successive satellites in an orbit. Moreover, in still other alternative embodiments, more than one constellation may be employed which have the same or different numbers of satellites, and which may include equal or unequal angular spacings among their respective pluralities of satellites.
• Satellite200 may orbit at analtitude270 of 7500 km. However, the present invention is not limited to using this orbit, andsatellite200 may orbit at analtitude270 greater than or less than 7500 km.Satellite200 may orbit at any non-geostationary altitude suitable for a particular embodiment. For instance,orbit altitude270 may be between 600 km and 30,000 km; between 5,000 km and 10,000 km; and/or between 7000 km and 8000 km, and all such variations are intended to be included within the scope of the present invention.
• FIG. 5A is a plan view of a plurality ofsatellites200 orbiting theearth250 in anequatorial orbit260 in accordance with one or more embodiments of the present invention. In an embodiment,satellites200 preferably travel in anorbit260 that is at least substantially equatorial. InFIG. 5A,orbit260 is aligned withequator300. However, in alternative embodiments,orbit260 could be an inclined orbit that includes latitude variation. In some embodiments, this latitude variation could be within 2 degrees of the equator, within 5 degrees of theequator300, within 10 degrees of the equator, or other latitude range. In still other alternative embodiments,orbit260 could reach points more than 10 degrees of latitude away from the equator.
• In the embodiment ofFIG. 5A,satellite system104 includes a single constellation of eightsatellites200 which are preferably equally spaced alongorbit260 about theearth250. Since the horizon-to-horizon view ofFIG. 5A only shows one hemisphere of theearth250, only four of the eightsatellites200 are visible inFIG. 5A. However, it is intended to be understood that fouradditional satellites400 are also in orbit above the hemisphere of theearth250 that is opposite the hemisphere shown inFIG. 3A.
• FIG. 5B shows all eightsatellites200 of the embodiment ofFIG. 5A shown distributed along orbit260 (which is preferably equatorial). The eightsatellites200 are shown substantially equally spaced alongorbit260 between two representations of asingle point310 of fixed longitude alongorbit260. Thiscommon point310 may be any fixed location on theearth250, such as the international date line. Thus, in this embodiment,successive satellites200 are separated by about 45 degrees of longitude along theequator300.
• Thus, in this embodiment, given the substantially equal angular spacing betweensuccessive satellites200, the angular distance between successive satellites is about 45 degrees. However, as previously stated, in other embodiments, unequal angular spacings among thesatellites200 of a constellation may be employed. Moreover, in still other embodiments, additional constellations having the same or different numbers of satellites may be deployed in addition to, or in place of, the 8-satellite constellation shown inFIG. 5.
• Referring toFIG. 5A, while in this embodiment,satellites200 move in anorbit260 at least substantially aligned with theequator300, the antennas onsatellites200 ofsatellite system104 are preferably able to transmit to and receive data from a range of latitude in betweenlimit322 and limit324. In one embodiment,upper limit322 is at about 30 degrees latitude north, and limit324 is at about 30 degrees latitude south. However, in other embodiments, each of the transmission/reception “footprint” limits322,324 ofsatellite system104 may greater than or less than 30 degrees from theequator300.
• The range of latitude over which transmission/reception may be implemented may be enabled by providing one ormore beamformers300 or rows ofbeamformers300 directed to communicating withinlimits322,324 by deployingvarious beamformers300 on satellite200-1 (FIG. 10) at a range of different “roll” angles (the angle about the fore-aft axis730 of satellite200-1 as shown inFIG. 11) in addition to deployingbeamformers300 at a range of different pitch angles.
• In an alternative embodiment, an array ofbeamformers300 could be arranged so as to follow the ground path of the satellite over the customers in a walker pattern (inclined orbit) whereby the earth is rotating underneath the moving satellite. In a version of this embodiment using a highly inclined orbit, such as a polar orbit, the satellites could move within a plane intersecting the North and South poles of the Earth, with the Earth's rotation direction being perpendicular to the direction of travel of the satellite. This creates a swirled ground path for the satellite, starting at one longitude at or near the south pole for instance, and eventually ending at a different longitude at or near the north pole. In this embodiment,beamformers300 may be arranged so as to follow the above-described path and still employ a switching pattern in which a succession of beamformers has RF wave energy directed thereto as the satellite moves along its orbit.
• The following is directed to describing the transfer of communication betweensuccessive satellites200 withinsatellite system104 and between antennas disposed on an earth station at a subscriber site.
• FIG. 6 is a partially schematic, partially elevational view of a satellite200-1 moving in orbit over anearth station400 in accordance with one or more embodiments of the present invention.Earth station400 may haveantennas402 and404 disposed thereon.Earth station400 may be one of thesubscribers106 discussed in connection withFIG. 1. However,earth station400 may include one or more such subscribers. Moreover,earth station400 may form merely one portion of one ofsubscribers106.Earth station400 may include any number of antennas, but is presented in simplified form inFIG. 6 to illustrate a system and method for handing off a data communication path between successive satellites200-1 and200-2.FIGS. 6-8 simplify the geometry of the surface of theearth250 to appear essentially flat. However, theorbit260 ofsatellites200 is preferably unchanged from that discussed in connection withFIGS. 4-5.
• The following description may apply to bothantennas402 and404. However, for the sake of simplicity, the description of theoperation antennas402,404 will described primarily in connection withantenna402.Antenna402 is preferably mounted onearth station400, or suitable portion thereof, and is preferably steerable along angle α410 (shown only forantenna2404 inFIG. 6, for the sake of clarity and convenience) to track the movement of satellite200-1 alongorbit260.
• Antennas402 and404 are preferably steerable along theangle α410 as shown inFIG. 6 forantenna404. While theangle α410 is shown only forantenna404, due to space limitations inFIG. 6, it will be appreciated thatantenna402 may be articulated (that is, rotated) along a similar angular path, though having a different pivot point. Moreover, the following discussion applies toantenna402 as well asantenna404, and to any additional antennas that may be disposed on or in proximity toearth station400. In one embodiment,angle α410 may sweep through a plane of constant latitude of the earth and may rotate about an axis running along a line of constant longitude of the earth. Expressed in terms of linear movement, asantenna404 is rotated clockwise (in the view ofFIG. 6),antenna404 preferably moves from West to East (as shown by the “W” and “E” labels ofFIG. 6) in addition to any vertical motion experienced by theantenna402. By way of further explanation, using the earth as a frame of reference, the axis of theangle α410 for each ofantennas402 and404 may be a substantially horizontal line running substantially due north and substantially due south with respect toearth station400. In the context ofFIG. 6, in this embodiment, the axis of the angle α410 runs into and out of the page. The foregoing description is consistent with the operation ofsteerable antennas402 and404 in conjunction with one or more satellites that follow an equatorial orbit, or an at least substantially equatorial orbit. However, the present invention is not limited to havingsatellites200 move along substantially equatorial orbits.
• Antennas402 and404 are illustrated in schematic form herein for the sake of simplicity.Antenna402 is preferably a dish antenna that includes at least one beamformer (which may be a conventional feed) and at least one reflector dish (not shown), as is known in the art. Directing a communication “beam” generally involves pointing a transmission beam that starts at a beamformer and reflects off a reflector dish toward a destination. Conversely, a received signal generally arrives along the beam direction and reflects off the reflector dish toward the beamformer. However, for the sake of simplicity herein,antennas402 and404 are illustrated as one-piece, Y-shaped antennas that point directly at their respective targets, rather than as beamformer/reflector assemblies. In other embodiments, multi-beam antennas could be used forantennas402 and/or404. In this case, either antenna steering mechanisms, or beam-to-beam shifting could be employed to enableantennas402 and/or404 to track a satellite. Moreover, it will be understood to those of ordinary skill in the art that any suitable type of antenna could be used forantennas402 and404 and that the invention is not limited to the specific embodiments discussed herein.
• In alternative embodiments, theangle α410 ofantennas402 and/or404 could include a component of latitude variation, if the satellites being tracked thereby travel in orbits that include latitude variation, or ifantennas402 and404 are located at higher latitudes. Ifantennas402 and404 are located at such higher latitudes (that is, at latitudes significantly above zero degrees), some latitude variation (elevation change) ofantennas402 and404 may be needed to track satellite orbits due to the curvature of the earth, and typical orbit trajectories, at such non-zero latitudes. The latitude variation of the satellite orbit could be kept within 2 degrees of the equator, and/or within 5 degrees of the equator. In other embodiments, the latitude variation of the satellites could be kept within 10 degrees of the equator. In still other embodiments, the latitude range of the satellites' orbit could be equal to or greater than +/−10 degrees from the equator.
• It is noted that considerable efficiency and cost savings may be achieved by enabling an earth based antenna to track a satellite while articulating only a single axis. Moreover, onceantennas402 and404 are accurately aimed at corresponding beams on satellites200-1 and200-2 respectively (and to additional satellites in the constellation that are not shown inFIGS. 6-8), narrowly focused beams may be employed which enable the resulting communication to experience high gain and high data transmission bandwidth. This presents a favorable contrast to systems of the prior art in which omni-directional antennas were used at earth stations, thereby limiting the gain and effective bandwidth of the resulting data communication.
• Thus, as discussed above, an earth-based, or earth station based antenna such asantenna402 may track a satellite using a steering mechanism to causeantenna402 to adjust its orientation so as to causeantenna402 to continuously point toward satellite200-1. In an alternative embodiment however,antenna402 may omit a steering mechanism and may instead include a plurality of fixed feed horns operable to provide communication beams disposed at a succession of different respective angular positions alongangle α410, and/or along other orientations with respect to the platform, such asearth station400 on which they are located. In this embodiment,antenna402 may “quasi-track” satellite200-1 by transferring its end of a data communication path through a succession of the fixed antenna beams that are disposed a respective succession of orientations, to thereby cause the multi-feed (not shown),multi-beam antenna402 to implement a series of discrete changes in beam orientation and thus maintain data communication contact with satellite200-1. A form of quasi-tracking such as that discussed above is discussed in connection with satellite200-1 in connection withFIGS. 11-15.
• In the discussion that follows, the earlier discussed embodiment ofsatellite system104 is employed for the sake of discussion. Specifically,satellite system104 is considered to include one constellation having eight satellites, with successive satellites separated by an angular distance of 45 degrees alongorbit260. An example of tracking a sequence of satellites by having two steerable antennas take turns tracking successive satellites is presented below.
• In general,satellites200 are tracked by one ofantennas402 and404 upon entering a tracking range of one or more antennas atearth station400.Antennas402 and404 may take turns tracking satellites in the constellation as successive satellites proceed alongorbit260. Thus, in effect, a “relay” system is in effect in which, as one antenna communicates with a satellite, the other of the antennas repositions itself in preparation for tracking the next satellite in the constellation. We now proceed to the discussion of a specific example of the tracking system and method discussed above, as shown inFIGS. 6-8. In the condition shownFIG. 6,antenna1402 (which may be referred to simply as “antenna402”) preferably begins communicating with and tracking satellite200-1 by moving along angle α410 (clockwise in the view ofFIG. 6), as satellite200-1 moves along orbit260 (rightward in the view ofFIG. 6). Turning toFIG. 7, it may be seen that as satellite200-1 nears the end of the segment of itsorbit260 during which it communicates withantenna402,antenna2404 (which may be referred to simply as “antenna404”) is positioned so as to be ready to begin communicating with satellite200-2, once satellite200-2 reaches a suitable location alongorbit260 within the tracking range ofantenna404. It is noted that in this embodiment,antenna402 ofearth station400 preferably tracks satellite200-1 through about 45 degrees of antennarotation angle α410. Correspondingly, in this embodiment, during the tracking of satellite200-1 byantenna402, satellite200-1 preferably travels along about 45 degrees oforbit260.
• Continuing with the example with reference toFIG. 8, satellite200-1 has now moved alongorbit260 beyond the tracking range ofantenna402. And satellite200-2 is now in communication withantenna404, as indicated by the dashed line between satellite200-2 andantenna404. As described previously in connection with satellite200-1 andantenna402, satellite200-2 will preferably be tracked along a 45 degree segment oforbit260 byantenna404. Correspondingly,antenna404 will itself preferably move about 45 degrees along angle α410 (FIG. 6) while tracking satellite200-2. Whileantenna404 tracks satellite200-2,antenna402 preferably repositions itself (by moving counter-clockwise in the view ofFIGS. 4-6) to prepare to communicate with, and track, the next satellite (not shown) in the succession of satellites in the constellation. The data communication path linkingsatellite system104 toearth station400 is preferably transferred from the pairing ofantenna402 and satellite200-1 to the pairing ofantenna404 and satellite200-2 as satellite200-1 moves beyond the tracking range ofantenna402, and as satellite200-2 enters the tracking range ofantenna404.
• Having discussed the transfer of the communication data path for communication system100 (FIG. 1) between successive satellites, the following discussion focuses in greater detail on the intra-satellite transfer of a data communication path betweensuccessive beamformers300 within a single satellite. The numeral “300” is employed to refer asatellite200 beamformer in general or to a plurality of beamformers. However, separate reference numerals are used in connection with specificindividual beamformers300. Likewise, the numeral “700” is employed to refer to a beam, or to beams, in general, while separate reference numerals are employed to refer to specific individual beams.
• FIGS. 11-15 and the discussion directed thereto describe such intra-satellite data path transfer within a satellite200-1 having fourbeamformers300 and four respective resulting beams700. However, the concepts presented herein may be readily scaled down or up to apply to satellites having fewer or more than four beamformers.
• In connection with this discussion,FIG. 9 shows greater detail in connection with the movement of a communication beam center with respect to asingle satellite200beam704 over the course of the movement ofsatellite200 through a portion of its orbit corresponding to a period of communication between asingle beam704 and a single specifiedearth station400antenna402.
• In the following, the structure of satellite200-1 is discussed first, in connection withFIG. 10. After that, an overview is presented of the various pertinent angles and frames of references of theearth station antennas402,404, the satellite200-1, and the moving frame of reference pertinent to the interaction of eachbeam700 with eachantenna402 or404. Thereafter, the detail of the movement ofbeam704 with respect toantenna402 over the alignment range of this single communicator pair (one beam and one earth-based antenna) is discussed. Thereafter, a sequence of intra-satellite data communication path transfers are considered in connection withFIGS. 11-15.
• FIG. 11 is a partially schematic and partially elevational view of asatellite200 having a plurality ofbeams702,704,706, and708, and moving in orbit over anearth station400 in accordance with one or more embodiments of the present invention.FIG. 10 shows one embodiment for implementing the satellite200-1 havingbeams700. Below, the structure ofFIG. 10 is described. Thereafter, the operation of satellite200-1 is described in connection withFIGS. 11-14.
• With reference toFIG. 10, satellite200-1 may includechassis360 andmulti-beam antenna350 which may includereflector340, andbeamformers302,304,306, and308 (collectively beamformers300), which may generatebeams702,704,706, and708, respectively. Elsewhere herein, beams702,704,706, and708 (collectively beams700) are schematically illustrated using a Y-shaped antenna structure for the sake of convenience. Thus, beams700 preferably correspond to data transmission/reception directions. For the sake of convenience, some of the following discussion herein refers to communication occurring “between” abeam700 and an antenna onearth station400. It is to be understood that in this context, beam700 (or a beam having another suitable reference numeral) corresponds to a data communication path, and that thebeam700 is not a structural entity in and of itself.Beamformers300 may be conventional antenna feeds, but are not limited to this implementation.Beamformers300 may have positions and orientations that are fixed with respect toreflector340 andchassis360 of satellite200-1. However, in other embodiments,beamformers300 could be mobile linearly and/or angularly with respect toreflector340 and/orchassis360 of satellite200-1.
• In one embodiment,reflector340 may have a diameter of between 0.3 meters and 1 meter. However, in other embodiments,reflector340 may have a diameter smaller than 0.3 meters, or greater than 1 meter. While in the embodiment ofFIG. 10, onereflector340 is shown, in other embodiments, two ormore reflectors340 may be employed inantenna350. Moreover, any number of (that is, one or more) beamformers300 may used to direct/receive RF wave energy to/from eachsuch reflector340.
• Thebeams700 may be generated by the apparatus shown inFIG. 10. However, the present invention is not limited to employing this apparatus. For instance, fewer or more than fourbeamformers300 may be employed. Moreover, the relative linear positions and orientations ofbeamformers300 may be varied as desired to achieve desired distribution ofbeam700 orientations. Various aspects of the use of themultiple beam antenna350 are discussed below.
• As discussed above in relation toFIG. 10, satellite200-1 may have a plurality ofbeamformers300 disposed thereon, which may be operable to generatebeams700. In the embodiments ofFIGS. 10-15, fourbeams702,704,706,708 are shown, which are also labeled as beams A, B, C, and D, respectively. Thebeamformers300 are preferably disposed in a plurality of different fixed orientations with respect to satellite200-1. This approach is economically effective since the need for highly expensive steerable antennas may be avoided. Moreover, this approach enables communication bandwidth to be concentrated along a relatively narrow and well defined path that is closely aligned with a counterpart antenna (or beamformer) either onearth station400 or on another satellite. This concentration may be accomplished by directing all or substantially all of the RF wave energy used for transmitting data from, and receiving data at, satellite200-1 through just onebeamformer300 to produce just onebeam700 at a time. Thus, in this embodiment,beamformers300 other than the one being used for communication, and therefore forming part of the data communication path, preferably do not have any RF energy directed thereto. However, in alternative embodiments, RF wave energy may be directed through more than one beamformer300 at a time.
• Further, thismultiple beamformer300 approach may enable total power consumption to be reduced to a minimum and may enable the power actually used to be efficiently expended by directing a transmission/reception communication path substantially only to footprints or regions on theearth250 surface where the energy is being received/transmitted. In contrast, certain prior art transmission/reception systems that lack the ability to direct transmission/reception only where needed, transmit to a large reception footprint on the surface of theearth250, where only a small fraction of this reception footprint actually includes data reception equipment capable of receiving the transmitted energy. Such prior art approaches thus waste considerable amounts of transmission energy. Accordingly, considerable improvements in power consumption efficiency may be achieved employing the systems and methods disclosed herein.
• However, in alternative embodiments, satellite200-1 may include one or more steerable antennas (not shown) in place of, or in addition to, one or more fixed-orientation beamformers300. If deployed, a steerable antenna (or plural steerable antennas) on satellite200-1 may be rotated so as to remain in alignment with one or more antennas ofearth station400 while satellite200-1 moves along the segment of its orbit over which communication takes place betweenearth station400 and satellite200-1.
• In one embodiment, eachbeamformer300 may be an individual feed as shown inFIG. 10. However, beamformers300 are not so limited. In other embodiments, eachbeamformer300 may be any device suitable for providing a communication beam.
• With reference toFIG. 11, beams708-702 (D-A) may be oriented at a succession of progressively increasing pitch angles720 (θ) about alateral axis740 ofsatellite200 with respect to a forward end of the satellite200-1.Axis740 runs into and out of the page in the view ofFIG. 11. In general, as stated before, eachbeam700 preferably has a fixed orientation with respect to the structure of satellite200-1. Employing this arrangement, the combination ofbeams700 on satellite200-1 is preferably able to conduct communication withearth station400 over a significant angular range oforbit260, without the need to alter the pitch angle of anyindividual beam700.
• In the above-discussed embodiment, orienting the plurality of beams as described is intended to enable shifting the data communication path from one beam to another to maintain communication withEarth station400 as satellite200-1 proceeds along its orbit. Providingbeams700 having different pitch angles720 aboutlateral axis740 is one way to accomplish this objective, sincelateral axis740 is configured to be at least substantially perpendicular to the direction of travel of satellite200-1. However, the invention is not limited to varying the orientation of thebeams700 about the lateral axis. In other embodiments,beams700 may be provided that have different angular positions about thelateral axis740, about the fore-aft axis730, and/or about the vertical axis (up and down in the views ofFIGS. 11-15.
• For the purpose of the discussion ofFIGS. 11-15, we consider asatellite system104 including a single constellation having eightsatellites200. Thus, in this embodiment,satellites200 are preferably located at 45 degree increments throughoutorbit260. As inFIGS. 6-8, the geometric arrangement of the satellite200-1, itsorbit260, and theearth station400 is simplified so as to portray substantially linear movement of the satellite200-1. However, it will be understood that as shown inFIG. 2,satellite200 moves in an at least substantially circular orbit about theearth250.
• In this embodiment, the range of pitch angle of thebeams700 on satellite200-1, is also preferably 45 degrees. As previously stated herein, the angles shown in the figures are not drawn to scale. Consistent with this, to more clearly illustrate the change in pitch angles among thebeams700 inFIGS. 11-15, the representation of the pitch angle variation amongbeams700 has been exaggerated inFIGS. 11-15. Consequently, the pitch angles ofbeam708 with respect to the forward direction of fore-aft axis730 and ofbeam702 with respect to the rearward direction of fore-aft axis730 are also not drawn to scale inFIGS. 11-15.
• In the below discussion, reference is made to fore-aft axis730 of satellite200-1 which is shown inFIG. 11, with the arrow (at right) showing the forward direction of this axis. In this embodiment,beam708 is preferably oriented at a pitch angle θ of 67.5 degrees with respect to the forward direction of the fore-aft axis730 of satellite200-1, the fore-aft axis730 preferably being substantially aligned with the direction oforbit260. Correspondingly,beam702 may be oriented at a pitch angle of 67.5 degrees with respect to the rearward direction of the fore-aft axis730 of satellite200-1. In this embodiment, the pitch angles preferably increase in consistent increments in progressing from the most forward orientedbeam708 to the most rearward orientedbeam702. In this embodiment, this increment in pitch is preferably 15 degrees. Thus, in this embodiment, the pitch angles θ ofbeams708,706,704, and702, with respect to the forward direction of fore-aft axis730, may be 67.5 degrees, 82.5 degrees, 97.5 degrees, and 112.5 degrees respectively.
• While one embodiment has been described in detail above, it will be appreciated by those of skill in the art that many variations of the above geometric arrangements are available. First, the number of constellations may be increased to any desired number. Moreover, the number of satellites per constellation may be varied to a number above or below eight. Where satellites are equally distributed within a constellation, an increase in the number of satellites per constellation will operate to decrease the angular distance alongorbit260 between neighboring satellites. Moreover, in other embodiments, the angular spacing between neighboring satellites in a constellation need not be constant, but rather may be varied as desired to suit a particular application. In other embodiments, the number of beamformers (whether individual feeds or other implementation) may be less than or greater than four. Further, the angular spacing between successive pitch angles of thebeamformers300, and thebeams700 resulting therefrom, on any given satellite need not be constant as discussed in connection withFIG. 10, above, but rather, may be varied as desired in accordance with the needs of a particular application. More specifically, in alternative embodiments, the pitch angles of any ofbeams700 may have any desired value with respect to the forward direction of fore-aft axis730 of satellite200-1. Furthermore, as discussed earlier, beams700 may be oriented at a range of different “roll” angles (the angle about fore-aft axis730 of satellite200-1) to enable satellite200-1 to communicate with earth stations located at a wide range of latitudes, such as between 30 degrees latitude north and 30 degrees latitude south.Beamformers300 may be suitably deployed and oriented on satellite200-1 so as to provide the above-describedbeams700 oriented at a range of roll angles.
• FIGS. 11-15 show an embodiment in which the linear placement of eachbeam700 along the fore-aft axis730 of satellite200-1 is correlated to the orientation, specifically thepitch angle θ720, thereof. Specifically, in the embodiment ofFIG. 11,beam708 is located closest the front (rightmost end, in the view ofFIG. 10) of satellite200-1 along the linear fore-aft axis730. And,beam708 is also the most forward directed of the four illustrated beams. While this arrangement may offer a certain amount of convenience in the design and operation satellite200-1, the present invention is not limited to this configuration. In other embodiments,beams700 having any of the pertinent pitch angles720 may be located at any linear position along the fore-aft dimension (running left to right inFIG. 10) of satellite200-1. Moreover, beams700 having any of the pertinent pitch angles720 may be located anywhere along thelateral axis740 of satellite200-1. Furthermore, the plurality ofbeams700 need not be arranged along a linear row having a constant position along thelateral axis740. That is, thevarious beams700, with their respective pitch angles, may be located in any position, with respect to thechassis360 of satellite200-1, that enables communication between the satellite200-1 and the earth-station antennas with which satellite200-1 communicates.
• Before discussing the details of the movements of the satellite200-1 and the various communication components (beamformers and antennas), it is believed beneficial at this stage to introduce the various frames of reference and angular ranges pertinent to enabling communication between satellite200-1 (and other satellites) andearth station400.
• We begin with the vantage point ofearth station400 andantenna402 which may be located thereon. The range of rotation over whichantenna402 may be rotated to track a particular satellite200-1 is a “satellite tracking range.” In one or more embodiments, this antenna rotation is intended to track satellite200-1 over a substantially or even completely equatorial orbit. However, the present invention is not so limited and may be practiced using satellites following any type of orbit, including non-equatorial orbits.
• We now turn to the frame of reference of satellite200-1. Various angular ranges are pertinent from the vantage point of satellite200-1 which are discussed in turn below. The portion of theorbit260 of satellite200-1 over which satellite200-1 may be tracked by antenna402 (or other antenna) ofearth station400 may be referred to herein as an earth station communication orbit segment. The described orbit segment may also be the angular range of the orbit of satellite200-1 over which a data communication path is in effect between satellite200-1 and antenna402 (or other antenna) ofearth station400. A subset of the earth station communication orbit segment is the “beam communication orbit segment” which may be the angular range of the satellite200-1 orbit over which a data communication path is in effect betweenearth station400 and aparticular beam700 of satellite200-1. Attention is now directed to the distribution ofbeam700 pitch angles720 on satellite200-1. The angular range along pitch angle720 (FIG. 10) over which thebeam700 pitch angles are distributed may be referred to herein as the “beam orientation range” or, the “beam pitch angle range”.
• The term “data communication path” is employed herein and is further described in this section. A data communication path may exist between any communicating entities, such as between an earth-based antenna and a satellite, or more specifically between the earth-based antenna and a particular beamformer on the satellite. From the vantage point of any given communicating entity, the communicating entity at the other end of a data communication path, or portion of such path, may be referred to as a communication target. The data communication path may have “ends” for each of the communicating entities. Thus, for example, where a data communication path exists between a satellite and a communication target, this data communication path has a “satellite end” and a “target end”. By way of further example, the end of a data communication path located at an Earth-based antenna may be referred to as an “Earth end” or “earth-based antenna end” of the data communication path.
• A further frame of reference bears introduction here. While the following is described in terms ofbeam704 andantenna402, as shown inFIG. 9, for the sake of convenience, it will be appreciated that the frame of reference described in connection therewith is applicable to the geometric interaction between anybeam700 of satellite200-1 and any antenna at any earth station. The pertinent frame of reference may travel with both antenna402 (or other antenna) and beam704 (FIG. 9) asantenna402 rotates along clockwise through a410 (FIG. 6) and asbeam704 travels with satellite200-1 alongorbit260. The term “beam-antenna alignment” may refer to the extent of alignment betweenbeam704 andantenna402. The range of this alignment angle within which communication may successfully occur betweenbeam704 andantenna402 may be referred to herein as the “communication alignment range”.
• Having described the arrangement ofbeams700 on satellite200-1, and the various pertinent frames of reference, it remains to describe interaction ofbeams700 of satellite200-1 withantenna402 as satellite200-1 moves along the segment oforbit260 over which satellite200-1 is tracked byantenna402. However, the sequence of communication activity occurring between asingle beam704 andantenna402 is considered in connection withFIG. 9, since this interaction is pertinent to all of the communicator pairs (pairing of a particular beam and a particular earth station antenna) shown inFIGS. 11-15.
• FIG. 9 is a partially schematic and partially elevational view ofbeam704 proceeding alongorbit260 overearth station400 in accordance with one or more embodiments of the present invention.Beam704 was selected for the sake of convenience. However, it will be appreciated that in this embodiment, the description of the interaction betweenbeam704 andantenna402 is applicable to all ofbeams700 of satellite200-1. For the sake of convenience, most of satellite200-1 is not shown inFIGS. 9A-9C. However, it is to be understood thatbeam704, as shown inFIG. 9, is preferably fixed with respect to satellite200-1, and that satellite200-1 is proceeding alongorbit260 in transitioning through various stages of orbit advancement shown inFIGS. 9A,9B, and9C, respectively. Also, for the sake of convenience,antenna404 is not shown inFIG. 9.
• This section concerns the communication beam power levels, available at various degrees of alignment betweenbeam704 andantenna402. Peak communication power preferably occurs at “centroid-to-centroid” alignment (also referred to as “centroid alignment”) which is illustrated inFIG. 9B. Lower communication power levels prevail at all other degrees of alignment betweenbeam704 andantenna402. Herein, an acceptable range of communication power may prevail within a communication alignment range bounded by an initial communication alignment boundary as shown inFIG. 9A, and a final communication alignment boundary shown inFIG. 9C. In this embodiment, a “boundary communication power level” prevails at the initial and final communication alignment boundaries. In a preferred embodiment, the boundary communication power level prevailing at the communication alignment boundaries (initial and/or final) is equal to about one half the peak communication power that prevails at centroid alignment. However, in alternative embodiments, the ratio of the boundary communication power level to peak communication power level may be less than or greater than one half. The angular range between the satellite200-1 beamformer andantenna402 within which communication takes place is referred to herein as the communication alignment range. The magnitude of the communication alignment range (as measured in degrees, radians, or other unit) may have any value, and depends upon various factors such as, but not limited to, the beam widths enabled by of the use ofbeamformer302 and theantenna402, the altitude oforbit260, and the geometric arrangements of theantenna402 and thebeamformer302.
• In an alternative embodiment, the boundary communication power level may be set to −4 dB (decibels), meaning that the power level of a data communication path or beam is −4 dB (expressed with respect to the peak power level) or higher prior to transmitting or receiving data along the path. The expression −4 dB is further explained here for the sake of clarification. The use of a −4 dB boundary means that the base-10 logarithm of the boundary communication power level divided by the peak power level, all multiplied by 10 should be −4 or higher (meaning more positive). Otherwise stated, in this embodiment, the communication power level of a data path would have to be 39.8% or more of the peak power level for that path, for data communication to be enabled for that path.
• At the stage of advancement shown inFIG. 9A,beam704 has reached a point alongorbit260 at which communication may be initiated betweenantenna402 andbeam704. The arrangement shown inFIG. 9A may correspond to an initial alignment boundary forbeam704 andantenna402. Thus, in this embodiment, the communication power betweenbeam704 andantenna402 as shown inFIG. 9A may be at about one half of the peak power that would preferably prevail in the arrangement shown inFIG. 9B.
• As satellite200-1 proceeds alongorbit260,beam704 andantenna402 eventually reach the degree of alignment shown inFIG. 9B, which is referred to herein as centroid alignment. This degree of alignment generally provides peak communication power between thebeam704 andantenna402, or any other communicator pair. Thus, it is noted that asbeam704 advanced from the stage shown inFIG. 9A to that shown inFIG. 9B, the communication power increased from about one half peak power to peak power.
• Continuing with the example,beam704 then continues to advance alongorbit260 to the position shown inFIG. 9C, which corresponds to the final communication alignment boundary (or “final alignment boundary”). At this point, communication power betweenbeam704 andantenna402 will generally have returned to about one half peak power. It is noted that throughout the communication alignment range portrayed inFIGS. 9A-9C, the communication power betweenbeam704 andantenna402 is preferably sufficient to operate the data communication path between satellite200-1 andearth station400 using beam704 (on satellite200-1) and antenna402 (at earth station400). In this embodiment, the initial communication alignment boundary and the final communication alignment boundary may differ in alignment from the centroid to centroid alignment (ofFIG. 9B) in opposite directions, and by angles of substantially equal magnitude.
• Preferably, at the stage shown inFIG. 9C, a data path transfer would be initiated that may shift the data communication path from a pairing ofbeam704 andantenna402 to a pairing ofbeam702 andantenna402. This transfer may be implemented by data path control208 (FIG. 2) or using other suitable control means.
• The above discussion describes the variation in alignment between communicators in any given communicator pair (that is, one satellite beamformer and one earth station antenna), the variation in communication power, and the continuity of availability of communication bandwidth during movement of abeam700 and anantenna402 along their respective paths throughout a communication alignment range. Accordingly, it remains to describe a series of beam-to-beam transitions, or otherwise stated, beamformer to beamformer transitions, occurring during the travel of a given satellite through a segment of its orbit in which it is tracked by a particular earth station. Accordingly, attention is directed toFIGS. 11-15 for this purpose. It is noted thatFIGS. 11-14, for the sake of brevity and simplicity, show centroid-to-centroid alignment betweenantenna402 andbeams708,706,704, and702, respectively. However, in a preferred embodiment, eachbeam700 of satellite200-1 advances alongorbit260 with respect toearth station400 such that the alignment between eachbeam700 andantenna402 goes through all the alignment stages that are shown inFIG. 9, and that were discussed above in connection therewith.
• FIG. 11 shows a state of advancement of satellite200-1 alongorbit260 in whichbeam708 is in centroid alignment withantenna402 ofearth station400. Preferably, communication betweenbeam708 andantenna402 is available whilebeam708 is within a communication alignment range withantenna402, which alignment range extends by a finite amount oforbit260 in both directions alongorbit260 from the position of satellite200-1 shown inFIG. 10. In this embodiment, eachbeam700 may operate for about eight minutes, during which time the satellite200-1 being tracked may travel over about 200 kilometers (km) of the surface of the Earth.
• As satellite200-1 advances along orbit260 (rightward in the view ofFIG. 10), the communication power betweenbeam708 andantenna402 gradually declines to one half peak power, due to increasing misalignment betweenbeam708 andantenna402, which may occur at a final communication alignment boundary. Once this “half-power” condition is reached, the satellite200-1 end of the data communication path between satellite200-1 andearth station400 is preferably transferred frombeam708 tobeam706. Thus, data communication is preferably established betweenbeam706 andantenna402. Moreover, once communication is established betweenbeam704 andantenna402,beam708 may be discontinued, and communication power from satellite200-1 may be provided exclusively forbeam706. This approach may beneficially operate to conserve energy, by enabling satellite200-1 to provide RF wave energy along only one communication path. However, in other embodiments, RF wave energy may be directed along two ormore beams700 at once, if desired, to suit the needs of a particular application.
• As the transition betweenbeams708 and706 occurs, the alignment betweenbeam706 andantenna402 preferably starts at an initial communication alignment boundary. As satellite200-1 advances further alongorbit260, and asantenna402 continues to advance along angle α410 (toward the right in the view ofFIGS. 10-13),beam706 andantenna402 eventually reach centroid alignment, as shown inFIG. 11, at which point peak communication power may be experienced. As discussed in connection with the communicator pair ofbeam708 andantenna402,beam706 andantenna402 eventually reach a final communication alignment boundary. Once again, communication power declines to about one half peak power at this stage.
• Upon reaching the half-power condition, a transition of the communication data path frombeam706 tobeam704 is preferably conducted. Thus,beam704 is preferably enabled by activating beamformer304 (i.e. providing RF wave energy thereto). Communication is then preferably established between satellite200-1 andantenna402 alongbeam704.
• The sequence of events discussed above in connection withbeam706 may be repeated forbeam704. Accordingly, for the sake of brevity, the entire sequence of events discussed above forbeam706 is not repeated in this section. However, in brief, upon initiating communication therebetween,beam704 andantenna402 may be at an initial communication alignment boundary. Movement ofbeam704 alongorbit260 and ofantenna402 along angle α410 (seeFIG. 6) preferably bring this communicator pair into centroid alignment, as shown inFIG. 13. Further advancement ofbeam704 andantenna402 along their respective paths (orbit260 forbeam704, andangle α410 for antenna402) may bring the alignment betweenbeam704 andantenna402 to a final communication alignment boundary.
• Upon reaching this final communication alignment boundary, a transition of the communication data path and of beamformer power frombeam704 tobeam702 may be conducted. Thus, communication is then preferably established between satellite200-1 andantenna402 alongbeam702.
• The sequence of events discussed above in connection withbeam704 may be repeated forbeam702. Accordingly, for the sake of brevity, the entire sequence of events discussed above forbeam704 is not repeated in this section. As before,beam702 andantenna402 may start off at an initial communication alignment boundary, proceed to centroid alignment, as shown inFIG. 14, and finally, reach a final communication alignment boundary.
• Reference is made toFIGS. 14 and 15 in the following. When the final communication alignment boundary has been reached forbeam702 andantenna402, a transition in the data path and in beamformer power is in order. However, sincebeam702 is the last beam on satellite200-1 with whichantenna402 may communicate as satellite200-1 proceeds alongorbit260, an inter-satellite transfer of the data path is in order, as was discussed in connection withFIGS. 6-8. Thus, the communication data path may transition from the communicator pair ofbeam702 of satellite200-1 andantenna402 to the communicator pair ofbeam708 of satellite200-2 andantenna404 ofearth station400, as shown inFIGS. 14 and 15. As with prior communicator pairs discussed herein, the initial alignment betweenbeam708 of satellite200-2 andantenna404 may be at an initial communication alignment boundary. Once communication is established betweenbeam708 of satellite200-2 andantenna404,beam702 of satellite200-1 may be disabled. Thereafter, control over the power and data communication path for satellite200-2 may be practiced as described above in connection with satellite200-1.
• In an embodiment, the data communication paths may be controlled by each satellite's processor210 (FIG. 2). Arouter102R may control the transition of the data communication path among a succession ofbeamformers300 and theirrespective beams700.Router102R, which may be located at a gateway102 (FIG. 1) may recognize the presence of a first data communication path along a givenbeam700, and operate to shift the data communication path to another beam when the givenbeam700 fails.
• FIG. 16 is a block diagram of acomputing system500 adaptable for use with one or more embodiments of the present invention. For example one or more portions ofcomputing system500 may be useable to perform the functions of data path control208 ofFIG. 2, ofgateway102 ofFIG. 1, ofprocessor210 ofFIG. 2, and/or of one or more processing entities withincommunication network100 ofFIG. 1.
• In one or more embodiments, central processing unit (CPU)502 may be coupled tobus504. In addition,bus504 may be coupled to random access memory (RAM)506, read only memory (ROM)508, input/output (I/O)adapter510,communications adapter522,user interface adapter506, anddisplay adapter518.
• In one or more embodiments,RAM506 and/orROM508 may hold user data, system data, and/or programs. I/O adapter510 may connect storage devices, such ashard drive512, a CD-ROM (not shown), or other mass storage device tocomputing system500.Communications adapter522 may couple computingsystem500 to a local, wide-area, orInternet network524.User interface adapter516 may couple user input devices, such askeyboard526 and/orpointing device514, tocomputing system500. Moreover,display adapter518 may be driven byCPU502 to control the display ondisplay device520.CPU502 may be any general purpose CPU.
• In this description, the term beamformer refers to a “feed”, or otherwise stated “feed horn”, or other passive, open-ended wave guide operable to provide and/or receive an individual satellite communication beam. Also herein, the term “beam” generally corresponds to a beam emanating from, or arriving at, a feed or feed horn.
• FIG. 17 is a schematic plan view of a satellite200-1 having anarray870 of beams800 in accordance with one or more embodiments of the present invention. While the individual beams are individually numbered, an individual beam may, in general, be referred to with the reference numeral800. Likewise the beams may be referred to collectively using the reference numeral800. In this embodiment, satellite200-1 may provide anarray870 of beams800 which may form a grid. Thearray870 preferably includes a plurality of rows and columns of beams over a range of pitch angles720 (seeFIG. 10) aboutlateral axis740 and rollangles750 about fore-aft axis730 of satellite200-1.
• The beams800 referred to in this section may be provided by providing anantenna880 including a reflector dish and suitably locating and orienting a plurality of feeds or feed horns with respect to a reflector dish (not shown). Thus,antenna880 is effectively a modified version ofantenna350 that includes a grid of feeds corresponding to the grid of respective beams800 represented inFIG. 17. In a preferred embodiment, each beam800 is associated with a respective feed “800f”. Thus, for the sake of reference herein,beam812 is provided by812f,beam814 by feed814f, and so forth. For the sake of brevity and convenience in illustrating the inventive concepts disclosed herein, the feeds and reflector suitable for producing beams800 are not illustrated herein.
• Beam array870 may includerows810,820,830, and840 andcolumns802,804,806, and808. Row810 may includebeams812,814,816, and818;row820 may includebeams822,824,826, and828,row830 may includebeams832,834,836, and838, androw840 may includebeams842,844,846, and848.Columns802,804,806, and808 may include respective sets of four beams with reference numerals ending in “2”, “4”, “6”, and “8”, respectively, as shown inFIG. 17. While the embodiment ofFIG. 17 shows anarray870 of beams800 having a 4×4 (rows×columns) arrangement, the present invention may include satellites having any number of rows and/or any number of columns, such numbers being less than or greater than four. In the embodiment ofFIG. 17, the rows and columns of beams800 ofarray870 are shown positioned in substantially straight lines. However, the invention is not so limited. The beams800, and the feeds800f(not shown) providing such beams, may be arranged in any suitable configuration that is operable to provide the distribution of beams over the pertinent angular ranges.
• Beams812,814,816, and818 may be aligned withinrow810 and may be oriented at substantially the same roll angle750 (FIG. 18), that is, the angle about fore-aft axis730 of satellite200-1. However, beams812,814,816, and818 are preferably oriented at a plurality of different pitch angles aboutlateral axis740 of satellite200-1. The provision of beams at a plurality of different pitch angles is shown inFIGS. 11-15 and discussed in connection therewith. In brief, the succession of beam pitch angles withinbeam row810 may enable satellite200-1 to conduct piece-wise tracking, or otherwise stated, quasi-tracking of an earth-based antenna (antenna402 inFIG. 11) while avoiding the expense of deploying a steerable antenna and while providing better gain than an omni-directional antenna. The sequence of beams used for communicating with an earth-based antenna proceed from the front1710 to the rear1720 of satellite200-1, as satellite200-1 proceeds along itsorbit260. However, the present invention is not limited to employing this sequence of beams.
• The embodiment ofFIG. 17 expands on the concepts presented earlier by providing a plurality of rows oriented at different roll angles750 (FIG. 18) to enable communication by satellite200-1 with earth stations at a range of latitudes on the surface of the earth. A latitude range of between +30 degrees latitude and −30 degrees latitude was discussed in connection withFIG. 5A. However, latitude ranges having northern latitude limits more than or less than 30 degrees from the equator may be implemented. Likewise latitude ranges having southern latitude limits more than or less than 30 degrees from the equator may be implemented.
• FIG. 18 is a view of thefront1710 of satellite200-1 which only shows thefront-most column808 of beams800.Beam column808 preferably includesbeams818,828,838, and848, which beams may be distributed over a desired angular range ofroll angle750 of satellite200-1. The roll angle of each beam row ofbeam array870 is preferably fixed and is preferably operable to communicate with an earth station antenna located at a particular earth longitude.
• The embodiment ofFIGS. 17-18 is preferably operable to enable communication between satellite200-1 and earth station antennas located at plurality of different latitudes. Preferably, for communication with antennas at each such latitude, satellite200-1 includes a given row of beams oriented at aroll angle750 suitable for communication therewith. Moreover, the variation of pitch angle720 (FIG. 10) among the beams included in the given row preferably enables practicing the piece-wise steering or quasi-steering discussed in connection withFIGS. 11-15, thereby enabling high-gain and cost effective communication to occur between satellite200-1 and the earth station at that particular latitude.
• While the embodiment ofFIGS. 17-18 is directed to a satellite200-1 in which all the beams800 within a single row have thesame roll angle750 and are therefore configured to point to the same latitude on the surface of the earth, the present invention is not limited to this embodiment. Instead, the beams800 within a given beam row may be oriented at a range of different roll angles750, if desirable for a particular embodiment.
• FIG. 19 shows a plurality offootprints1900 representing communication regions for the respective beams800 on satellite200-1. In the foreground, satellite200-1 is shown, which may includefront end1710 andrear end1720.Footprints1900 correspond to regions on the surface of the earth distributed over a range of latitude. Preferably, each beam row ofbeam array870 is operable to communicate with a respective one of thefootprints1900. It is noted that thefootprints1900 ofFIG. 19 are not drawn to any particular scale, and that the rows of beams800 of satellite200-1 may be configured to communicate with regions on the surface of the earth of any desired size and/or at any desired latitude.
• FIG. 20 is a schematic representation of portions of two constellations C1, C2 of satellites moving in orbit around the earth with respect to anearth station2100 in accordance with one or more embodiments of the present invention. For the sake of convenience, the embodiments discussed earlier in this document were directed tosatellite systems104 including a single constellation including eight satellites. In this section, the effects of supplementingsatellite system104 to include at least one additional constellation are considered.
• In one embodiment,satellite system104 may include two constellations C1, C2 which may each include eight satellites. Thus, constellation C1 may include satellites numbered from C1S1 to C1S8, and constellation C2 may include satellites numbered from C2S1 to C2S8. For the sake of convenience of illustration, only four satellites from each of constellations C1 and C2 are shown inFIGS. 20-21. In the embodiment ofFIG. 20, the satellites of constellations C1 and C2 are preferably equally spaced along theircommon orbit260. Thus, with 16 satellites equally spaced aboutorbit260, adjacent satellites are preferably separated by an angular distance of about 22.5 degrees of the 360 degree angular range oforbit260. However, in alternative embodiments, each constellation may include fewer or more than eight satellites. Moreover, in alternative embodiments, the satellites of the second constellation C2 need not be located so as to provide consistent angular spacings between adjacent satellites throughoutsatellite system104.
• In the embodiments shown inFIGS. 20-21, portions of two constellations C1, C2 are shown. However, it will be appreciated by those of skill in the art that any number of constellations may be added to an initial or original constellation ofsatellite system104. Preferably,satellite system104 may be supplemented by one or more additional constellations without disrupting the operation of any of the satellites already present insatellite system104. The addition of constellations tosatellite system104 is preferably operable to add communication bandwidth and flexibility in allocating such bandwidth, among other benefits. Some of the benefits provided by the addition of constellations are discussed below, followed by a discussion of some specific benefits shown inFIGS. 20-21.
• In one embodiment, the benefits afforded by the provision of additional constellations may include, but are not limited to, the following. A general increase in communication bandwidth may be provided. Improvements in communication redundancy (that is, the ability to continue service in the event of one satellite failing to operate) may be provided. Where desired, the segregation of communication activity into one-directional communication may be provided. More specifically, a first group of satellites may be dedicated only to transmitting information fromsatellite system104 to one or more earth stations. Conversely, another group of satellites may be dedicated only to receiving information atsatellite system104 from one or more earth stations.
• In some embodiments, the total communication bandwidth ofsatellite system104 may be flexibly allocated among the various satellites for greater efficiency. For example, where helpful, a disproportionate share of the bandwidth ofsatellite system104 could be concentrated among satellites present over a region having a large number of customers and/or over customers having high bandwidth requirements. At the same time, the communication bandwidth directed to satellites over customers having low bandwidth requirements may be suitably reduced. Moreover, satellites present over the oceans and/or land having no customers could be shut down partially or completely, thereby conserving power, and freeing up satellite-system104 bandwidth for use by other satellites. Further, in this embodiment, the flexible allocation of bandwidth may be extended still further to include concentrating more bandwidth in selected beams of a particular satellite that are pointed toward high-bandwidth customer areas, than in beams pointing to less demanding customer sites. A selection of the above-described benefits enabled by the provision of additional constellations are illustrated inFIGS. 20-21. However, the present invention is not limited to the specific embodiments shown inFIGS. 20-21.
• FIG. 20 shows an embodiment ofsatellite system104 that includes two constellations C1, C2, each constellation having eight satellites, although only four satellites of each constellation are shown. Thus, among the satellites shown inFIG. 20, constellation C1 includes C1S1, C1S2, C1S3, and C1S4, and constellation C2 includes C2S1, C2S2, C2S3, and C2S4. It is noted that the other four satellites of each constellation are not shown for the sake of convenience of illustration. The structure and function of each of the satellites shown inFIGS. 20-21 may generally correspond to the structure and/or function of satellite200-1 described elsewhere in this document, but are not limited such descriptions.
• In the embodiment ofFIG. 20,earth station2100 may includeantennas2002 and2004. C1S2 preferably communicates withantenna2002, and C2S1 preferably communicates withantenna2004. In this embodiment, communication activity among satellites C1S2 and C2S2 may be segregated according to communication direction. Thus, for example, C1S2 may be dedicated to transmitting data tosatellite2002, and C2S2 may be dedicated to receiving data fromsatellite2004. Such separation of communication activity may be operable to decrease noise arising when conducting bi-directional communication using a single satellite, may increase signal strength, and/or may increase effective data transmission throughput by some finite amount, such as by 10-20%. In other embodiments, satellites C1S2 and C2S2 could communicate with two respectiveearth station antennas2002,2004, but one or both of C1S2 and C2S2 could simultaneously transmit and receive data.
• FIG. 21 shows the multiple constellation embodiment ofFIG. 20 in which adjacent satellites C1S2 and C2S2 both communicate with thesame antenna2002. In this embodiment, the additional bandwidth provided by the use of multiple constellations is preferably operable to provide complete redundancy in the event that one of satellites C1S2 and C2S2 fails. More specifically,communication system100 andsatellite system104 may be configured so as to enable each of satellites C1S2 and C2S2 to fully service the needed communication withantenna2002 ofearth station2100. Thus, if either satellite in communication withantenna2002 were to fail, the other of the two would preferably enable communication withantenna2002 to continue without loss of data or loss of communication bandwidth.FIGS. 20-21 illustrate two respective ways of exploiting the additional communication bandwidth made available by the provision of an additional constellation C2. It is noted that the system and method disclosed herein are not limited to practicing only one of the benefits of additional bandwidth at a time. Otherwise stated, at any given moment,satellite system104 may employ some combination of communication redundancy; dedication of one or more satellites for just one of transmission and reception; and/or other benefit of added bandwidth. Other benefits of such additional benefits were described above.
• The above discussion is directed to embodiments ofsatellite system104 that include two satellite constellations C1 and C2. However, it will appreciated by those of skill in the art that the benefits of supplementingsystem104 with additional constellations may be extended to the addition of any number of constellations, with each such added constellation having any number of satellites.
• It is noted that the methods and apparatus described thus far and/or described later in this document may be achieved utilizing any of the known technologies, such as standard digital circuitry, analog circuitry, any of the known processors that are operable to execute software and/or firmware programs, programmable digital devices or systems, programmable array logic devices, or any combination of the above. One or more embodiments of the invention may also be embodied in a software program for storage in a suitable storage medium and execution by a processing unit.
• Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (34)

1. A method, comprising:

providing at least one satellite having a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about an axis of the satellite;

causing the at least one satellite to move around the earth along a non-geostationary orbit;

establishing a data communication path between a first of the beamformers on the satellite and a communication target, the data communication path having a satellite end at the first beamformer and an target end at the communication target;

shifting the satellite end of the data communication path through a succession of the beamformers as the satellite moves along its orbit; and

at least substantially reducing an amount of RF wave energy directed to beamformers of the plurality of beamformers not forming part of the data communication path.

2. The method ofclaim 1 wherein the plurality of respective beams have a plurality of different respective fixed pitch angles about a lateral axis of the satellite.

3. The method ofclaim 1 wherein the communication target is a first antenna, at an Earth station, configured to communicate with the satellite along a selected segment of the orbit of the satellite, the first antenna being an Earth end of the data communication path.

4. The method ofclaim 1 wherein the communication target is another satellite.

5. The method ofclaim 1 wherein the at least substantially reducing step comprises:

not directing any RF wave energy to beamformers of the plurality of beamformers not forming part of the data communication path.

6. The method ofclaim 1 wherein the satellite further includes at least one reflector operable to reflect RF wave energy from the plurality of beamformers toward the communication target and to reflect RF wave energy from the communication target toward the plurality of beamformers.

7. The method ofclaim 1 wherein the orbit is at least substantially equatorial.

8. The method ofclaim 1 wherein the latitude of the orbit remains between −10 and +10 degrees latitude.

9. The method ofclaim 1 wherein the latitude of the orbit remains between −5 and +5 degrees latitude.

10. The method ofclaim 1 wherein the altitude of the satellite orbit is between 600 km and 30,000 km.

11. The method ofclaim 1 wherein the altitude of the satellite orbit is between 5,000 km and 10,000 km.

12. The method ofclaim 1 wherein the altitude of the satellite orbit is between 7,000 km and 8,000 km.

13. The method ofclaim 3 further comprising:

the first antenna at the earth station tracking the satellite using a steering mechanism to cause the first antenna to substantially continuously point toward the satellite.

14. The method ofclaim 3 further comprising:

the first antenna quasi-tracking the satellite by transferring the earth end of the data communication path through a succession of fixed antenna beams, wherein each said antenna beam has a substantially fixed orientation with respect to the surface of the Earth.

15. The method ofclaim 1 further comprising directing RF wave energy to the beamformer, of the plurality of beamformers, serving as the satellite end of the data communication path.

16. The method ofclaim 3 further comprising:

maintaining the data communication path between the first antenna and the first beamformer over a range of satellite movement corresponding to a communication alignment range between the beam from the first beamformer and the first antenna.

17. The method ofclaim 16 further comprising:

commencing communication between the first antenna and the first beamformer when the first antenna and the beam generated by the first beamformer reach an initial communication alignment boundary during movement of the satellite along its orbit; and

concluding communication between the first antenna and the first beamformer when the first antenna and the beam generated by the first beamformer reach a final communication alignment boundary during movement of the satellite along its orbit.

18. The method ofclaim 17 wherein communication power between the first antenna, at the earth station, and the first beamformer reaches a peak at centroid-to-centroid alignment between the first antenna and the first beamformer.

19. The method ofclaim 18 wherein the first antenna communicates with the first beamformer while the communication power along the data communication path is equal to or greater than one half the peak communication power.

20. The method ofclaim 16 wherein the shifting step comprises:

transferring the satellite end of the data communication path from the first beamformer to a second beamformer of the plurality of beamformers once a second antenna at the earth station and a beam from the second beamformer enter into communication alignment range.

21. The method ofclaim 20 wherein the transferring step comprises:

redirecting RF wave energy, originating from an amplifier on the satellite, from the first beamformer to the second beamformer.

22. The method ofclaim 21 wherein the redirecting step is performed using a waveguide switch.

23. The method ofclaim 21 further comprising repeating the steps of transferring and redirecting for the plurality of the beamformers on the satellite so as to maintain operation of the data communication path between the satellite and the earth station throughout the movement of the satellite through the selected segment of the orbit of the satellite.

24. An apparatus, comprising

a satellite having a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about an axis of the satellite; and

a controller operable to direct a data communication path through a first beamformer of the plurality of beamformers,

wherein the controller is further operable to shift the data communication path through a succession of the beamformers.

25. The apparatus ofclaim 24 wherein the plurality of different respective fixed pitch angles are about a lateral axis of the satellite.

26. The apparatus ofclaim 24 wherein the controller is operable to redirect the data communication path from the first beamformer to a second beamformer of the plurality of beamformers upon detecting a decline in communication power along the data communication path.

27. The apparatus ofclaim 24 further comprising an amplifier able to supply RF wave energy to one or more of the plurality of beamformers, wherein the controller is operable to select at least one beamformer, of the plurality of beamformers, to direct the RF wave energy to.

28. The apparatus ofclaim 24 wherein the plurality of beamformers are disposed in an array on the satellite, having a plurality of rows,

wherein each beamformer row includes a sequence of beamformers configured to illuminate footprints on the Earth over a range of longitude but with substantially similar latitude; and

wherein the plurality of rows are configured to illuminate respective groups of footprints at a plurality of different respective latitudes.

29. A method, comprising:

providing a first constellation of satellites within a satellite system;

providing at least one additional constellation of satellites to provide a plurality of satellite constellations within the satellite system;

enabling adjacent ones of the satellites in the satellite system to communicate with a single earth station; and

wherein at least one of the satellites in each said constellation has a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about a lateral axis of the satellite, and

a controller operable to direct a data communication path through a first beamformer of the plurality of beamformers,

wherein the controller is further operable to shift the data communication path through a succession of the beamformers.

30. The method ofclaim 29 further comprising:

the adjacent satellites communicating with the earth station employing the same transmission frequency.

31. The method ofclaim 29 further comprising:

dedicating at least selected ones of the beamformers in the satellite system substantially completely to one of:

transmission; and

reception.

32. The method ofclaim 30 further comprising:

supplementing the satellite system in a given state with at least one further constellation to provide a modified satellite system without disrupting an operation of the satellite system in the given state.

33. The method ofclaim 31 further comprising:

dedicating at least selected ones of the satellites in the satellite system substantially completely to one of:

transmission; and

reception.

34. A method, comprising:

conducting a data communication session between a first computing entity and a second computing entity over a communication network,

wherein at least a portion of the data transferred over the communication network during the data communication session is transmitted over a satellite system,

and wherein at least one of the satellites in said satellite system has a plurality of beamformers configured to provide a plurality of respective beams having a plurality of different respective fixed pitch angles about an axis of the satellite; and a controller operable to direct a data communication path through a first beamformer of the plurality of beamformers,

and wherein the controller is further operable to shift the data communication path through a succession of the beamformers.

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