Universal replacement communications satellite

A practicable universal replacement C band/Ku band communications satellite designed for orbiting the Earth in a storage orbit and a method for its use as a replacement for a failed satellite are disclosed. The universal replacement satellite can be controlled by an external control system (e.g., a ground station) and is reconfigurable by remote command (e.g., from a ground station). The satellite is designed to make several fast moves during its design life from its storage slot to the geostationary slot to which it needs to move when it is to act as a replacement for a failed satellite. The ability to make fast moves helps minimize down time. After its then-current mission of sparing a particular failed satellite has been completed, the communications payload can be turned off and the satellite can be moved back to its storage slot to await its next replacement mission. Various design features allow it to be able to satisfactorily mimic (that is, emulate) the communications capabilities of a very high percentage of the existing geostationary C band and Ku band satellites while still being economically and otherwise practicable. The satellite can also contain means for handling BSS signals so that the satellite can act as a replacement for both FSS and BSS failed satellites.

BACKGROUND OF THE INVENTION
 1. Technical Field
 This invention concerns the field of communication satellites and, more
 specifically, the problem of providing a practicable satellite that is
 capable of acting as a satisfactory replacement satellite for the majority
 of Fixed Satellite Service ("FSS") communications satellites that are in
 orbit and desirably also for the majority of such satellites that are to
 be placed in orbit.
 2. Background
 Communications (or telecommunications) satellites have been used for many
 years. Uplink signals are sent by one or more Earth stations, received by
 one or more uplink antennas on the satellite, processed by circuitry in
 the satellite (e.g., frequency-shifted and amplified), sent back
 (retransmitted) to Earth by one or more downlink antennas on the
 satellite, and received by one or more Earth stations. The satellites may
 be placed in various orbits around the Earth. One particularly desirable
 orbit for certain communications satellites is an equatorial orbit (that
 is, substantially in the plane of Earth's equator) at an altitude of
 approximately 22,300 miles. In that orbit at that altitude, the period of
 revolution of the satellite around the Earth is equal to the period of
 rotation of the earth. Accordingly, transmitting (uplink) and receiving
 (downlink) stations on Earth "see" the satellite remaining at a fixed
 point in the sky and, thus, the satellite may be considered to be in a
 geosynchronous equatorial orbit or to be geostationary. As a result, a
 geostationary satellite's position can be defined by its equatorial
 longitude. For example, satellites useful for broadcast to the continental
 United States and its territories may be located from about 69 degrees
 west longitude to about 139 degrees west longitude.
 One advantage of using a geostationary satellite is that the transmitting
 and receiving stations on Earth do not need to track a satellite in a
 preselected orbital slot across the sky to maintain the desired uplink and
 downlink communications characteristics (strength of the signals received
 by the satellite, footprint of the downlink signals on Earth, etc.). In
 other words, the antennas on a geostationary satellite can be fixed (or
 stationary) and the footprints of the downlink antennas can also be fixed.
 In addition to typically having fixed antennas, geostationary satellites
 also typically are designed to receive certain signals on preselected
 frequency bands (the uplink bands) from one or more preselected geographic
 areas on Earth according to the uplink frequency plan, to amplify the
 signals to the desired power level, and to retransmit them down to Earth
 on other preselected frequency bands (the downlink bands) to one or more
 preselected geographic areas on Earth according to the downlink frequency
 plan.
 Unfortunately, as is well-known, there is a significant probability of a
 malfunction or complete failure during the launch sequence, and even after
 a successful launch, there may be a problem while trying to deploy the
 satellite in the desired orbital position (slot). Failures may also occur
 after the satellite has been successfully positioned in its slot and
 operated for a period of time. Failures include sudden or gradual, partial
 or complete loss of telecommunications capability.
 In view of the serious economic loss that can result from not having a
 fully and properly functioning telecommunications satellite operating in
 its slot throughout the entire expected time period, it is desirable to
 provide a replacement satellite (i.e., a spare or back-up satellite) that
 can assume the telecommunications functions of a failed satellite.
 Replacement satellites may be stored in orbit or on the ground, and each
 mode of storage has advantages and disadvantages. Regardless of which
 storage mode is used, because of cost, weight, and other considerations,
 the replacement satellite will typically be designed for the same uplink
 and downlink frequency plans, power levels, footprints, telemetry and
 command subsystem frequencies, etc. as of the satellite for which it is
 designed to be the spare.
 The substantial cost of spare satellites represents a significant expense
 for providers of satellite communications channels (e.g., organizations
 owning satellites and leasing their channels for retransmission). That is
 particularly true because the spare may not ever be needed. Therefore, it
 would be highly advantageous if such providers could avoid or at least
 substantially reduce that expense.
 Various methods of providing spares have been proposed. See, e.g., U. S.
 Pat. Nos. 3,995,801, 5,120,007, and 5,813,634. Other documents concerning
 or mentioning spare satellites, back-up coverage, and/or replacing a
 failing or failed satellite include U.S. Pat. Nos. 4,502,051, 5,289,193,
 5,410,731, and PCT WO 98/04017. Other documents concerning communication
 satellites, communication systems comprising constellations of satellites,
 communication satellite subsystems and components thereof, and methods of
 operating communication satellites and systems include U.S. Pat. Nos.
 4,688,259; 4,858,225; 4,965,587; 5,020,746; 5,175,556; 5,297,134;
 5,323,322; 5,355,138; 5,523,997; 5,563,880; 5,860,056; and 5,890,679; EPO
 Published Application EP 0 915 529 A1; F. Rispoli, "Reconfigurable
 Satellite Antennas: A Review," Electronic Engineering, volume 61, number
 748, pages S22-S27 (April 1989); and Electronics Engineers' Handbook,
 Section 22-63, "Satellite Communications Systems," pages 22-61 to 22-62
 (1975). (All of the foregoing documents and any other documents discussed
 or otherwise referenced herein are incorporated herein in their entireties
 for all purposes.)
 Some of those documents concern movable antennas. See, e.g., EP 0 915 529
 A1.
 Some of those documents concern reconfigurable satellites. See, e.g., U.S.
 Pat. Nos. 4,688,259; 4,858,225; 4,965,587; 5,175,556; 5,289,193;
 5,355,138; PCT WO 98/04017; EP 0 915 529 A1; and F. Rispoli:
 "Reconfigurable Satellite Antennas: A Review," Electronic Engineering,
 volume 61, number 748, pages S22-S27 (April 1989). Some of those documents
 concern moving satellites, e.g., from one slot to another or for
 station-keeping. See, e.g., U.S. Pat. Nos. 5,020,746; 5,813,634; and PCT
 WO 98/04017.
 Replacement satellites that are essentially perfect spares (or clones) for
 essentially all FSS (C band/Ku band) communications satellites may have
 been considered by others, but, as far as is known, were never built,
 probably because they were impractical and/or were prohibitively
 expensive. The problem of providing such a satellite is made all the more
 complicated by the fact that the conventional C band/Ku band
 communications satellites have widely differing characteristics
 concerning, for example, the uplink and downlink communications
 frequencies used, power levels, and coverage patterns. Furthermore,
 conventional satellites well before being launched and put in orbit have
 been designed for particular orbital slots having neighboring satellites
 with known telemetry and command frequencies and other characteristics.
 Accordingly, there has been a long-standing need for practicable but
 satisfactory replacement satellites for C band/Ku band communications
 satellites (FSS satellites). In other words, there has been a
 long-standing need for practicable C band/Ku band replacement satellites
 that can emulate the performance of a substantial percentage (and
 preferably a very high percentage) of orbiting C band/Ku band
 communications satellites while still being technologically, economically,
 and otherwise practicable.
 SUMMARY OF THE INVENTION
 Such satellites having those features and advantages, as well as other
 features and advantages that will be apparent to those skilled in the art,
 have now been developed. Broadly, in one aspect this invention concerns a
 universal replacement communications satellite designed for orbiting the
 Earth in a geostationary orbit, which can be controlled by an external
 control system, which is reconfigurable, and which can emulate the
 communications performance of a substantial percentage of existing
 geostationary C band and Ku band communications satellites and therefore
 for which it can be a replacement, the universal replacement satellite
 being designed to receive uplink C band and Ku band signals and to output
 C band and Ku band downlink signals, the universal replacement
 communications satellite comprising:
 (a) Ku band processing means for (i) receiving Ku band uplink signals in
 the channels of three 250 MHz uplink bands of 13.75-14.00 GHz, 14.00-14.25
 GHz, and 14.25-14.50 GHz, each uplink band having a plurality of uplink Ku
 band channels, (ii) amplifying the signals, (iii) down converting their
 frequencies, and (iv) outputting any of those amplified, reduced-frequency
 Ku band signals as Ku band downlink signals in the channels of any of six
 250 MHz bands within the 10.95-11.20 GHz, 11.45-11.70 GHz, 11.70-12.20
 GHz, and 12.25-12.75 GHz downlink Ku bands, each downlink Ku band having a
 plurality of downlink Ku band channels;
 (b) two or more Ku band downlink antennas, each antenna capable of
 outputting a downlink beam comprising Ku band downlink signals, each
 downlink beam being separately directable to different locations on Earth;
 (c) means for directing the Ku band downlink signals to any one of the two
 or more Ku band downlink antennas;
 (d) C band processing means for (i) receiving C band uplink signals in the
 channels of two uplink bands of about 5.925 to 6.425 GHz and 6.425 to
 6.725 GHz, each uplink band having a plurality of uplink C band channels,
 (ii) amplifying the signals, (iii) down converting their frequencies, and
 (iv) outputting those amplified, reduced-frequency C band signals as C
 band downlink signals in the channels of the 3.70-4.20 GHz and 3.40-3.70
 GHz downlink C bands, each downlink C band having a plurality of downlink
 C band channels;
 (e) two or more C band downlink antennas, each antenna capable of
 outputting a downlink beam comprising downlink C band signals, each
 downlink beam being separately directable to different locations on Earth;
 (f) means for directing the C band downlink signals to any one of the two
 or more C band downlink antennas;
 (g) a propulsion subsystem designed to allow the satellite to make at least
 three fast moves, each of at least three degrees per day, during the
 design life of the satellite;
 (h) a power subsystem to provide electrical power for satellite operation;
 (i) a telemetry and command subsystem to allow the satellite to monitor
 itself and for communicating with the external control system, the
 subsystem comprising a telemetry sub-subsystem that can transmit on at
 least two different frequencies and a command sub-subsystem that can
 receive on at least two different frequencies;
 (j) an attitude and orbit control subsystem for helping to properly orient
 the satellite with respect to Earth;
 (k) a thermal control subsystem for helping to maintain the satellite
 within the proper temperature range for operation; and
 (l) means to reconfigure the satellite, said means comprising (i) means to
 remotely adjust the Ku band processing means to direct a bundle of at
 least two but of fewer than all of the signals in each of the uplink Ku
 bands to any one of the downlink Ku bands, (ii) means to remotely adjust
 the downlink beam from at least one of the Ku band downlink antennas to
 direct the beam to different locations on Earth, (iii) means to remotely
 adjust the downlink beam from at least one of the C band downlink antennas
 to direct the beam to different locations on Earth, (iv) means to remotely
 change the footprint of the downlink beam from at least one of the
 downlink antennas, and (v) means to remotely change the polarity of at
 least one of the downlink antennas.
 In another aspect this invention concerns a universal replacement
 communications satellite designed for orbiting the Earth in a
 geostationary orbit, which can be controlled by an external control
 system, which is reconfigurable, and which can emulate the communications
 performance of a substantial percentage of existing geostationary C band
 and Ku band communications satellites and therefore for which it can be a
 replacement, the universal replacement satellite being designed to receive
 uplink C band and Ku band signals and to output C band and Ku band
 downlink signals, the universal replacement communications satellite
 comprising:
 (a) Ku band processing means for (i) receiving Ku band uplink signals in
 the channels of three 250 MHz uplink bands of 13.75-14.00 GHz, 14.00-14.25
 GHz, and 14.25-14.50 GHz, each uplink band having a plurality of uplink Ku
 band channels, (ii) amplifying the signals, (iii) down converting their
 frequencies, and (iv) outputting any of those amplified, reduced-frequency
 Ku band signals as Ku band downlink signals in the channels of any of six
 250 MHz bands within the 10.95-11.20 GHz, 11.45-11.70 GHz, 11.70-12.20
 GHz, and 12.25-12.75 GHz downlink Ku bands, each downlink Ku band having a
 plurality of downlink Ku band channels;
 (b) two or more Ku band downlink antennas, each antenna capable of
 outputting a downlink beam comprising Ku band downlink signals, each
 downlink beam being separately directable to different locations on Earth;
 (c) means for directing the Ku band downlink signals to any one of the two
 or more Ku band downlink antennas;
 (d) C band processing means for (i) receiving C band uplink signals in the
 channels of two uplink bands of about 5.925 to 6.425 GHz and 6.425 to
 6.725 GHz, each uplink band having a plurality of uplink C band channels,
 (ii) amplifying the signals, (iii) down converting their frequencies, and
 (iv) outputting those amplified, reduced-frequency C band signals as C
 band downlink signals in the channels of the 3.70-4.20 GHz and 3.40-3.70
 GHz downlink C bands, each downlink C band having a plurality of downlink
 C band channels;
 (e) two or more C band downlink antennas, each antenna capable of
 outputting a downlink beam comprising downlink C band signals, each
 downlink beam being separately directable to different locations on Earth;
 (f) means for directing the C band downlink signals to any one of the two
 or more C band downlink antennas;
 (g) a propulsion subsystem designed to allow the satellite to make at least
 three fast moves during the design life of the satellite;
 (h) a power subsystem to provide electrical power for satellite operation;
 (i) a telemetry and command subsystem to allow the satellite to monitor
 itself and for communicating with the external control system;
 (j) an attitude and orbit control subsystem for helping to properly orient
 the satellite with respect to Earth;
 (k) a thermal control subsystem for helping to maintain the satellite
 within the proper temperature range for operation; and
 (l) means to reconfigure the satellite.
 In another aspect this invention concerns a universal replacement
 communications satellite designed for orbiting the Earth in a
 geostationary orbit, which can be controlled by an external control
 system, which is reconfigurable, and which can emulate the communications
 performance of a substantial percentage of existing geostationary C band
 and Ku band communications satellites and therefore for which it can be a
 replacement, the universal replacement satellite being designed to receive
 uplink C band and Ku band signals and to output C band and Ku band
 downlink signals, the universal replacement communications satellite
 comprising:
 (a) Ku band processing means for (i) receiving Ku band uplink signals in
 the channels of three uplink bands, each uplink band having a plurality of
 uplink Ku band channels, (ii) amplifying the signals, (iii) down
 converting their frequencies, and (iv) outputting any of those amplified,
 reduced-frequency Ku band signals as Ku band downlink signals in the
 channels of any of at least four downlink Ku bands, each downlink Ku band
 having a plurality of downlink Ku band channels;
 (b) two or more Ku band downlink antennas, each antenna capable of
 outputting a downlink beam comprising Ku band downlink signals, each
 downlink beam being separately directable to different locations on Earth;
 (c) means for directing the Ku band downlink signals to any one of the two
 or more Ku band downlink antennas;
 (d) C band processing means for (i) receiving C band uplink signals in the
 channels of at least one uplink band, each uplink band having a plurality
 of uplink C band channels, (ii) amplifying the signals, (iii) down
 converting their frequencies, and (iv) outputting those amplified,
 reduced-frequency C band signals as C band downlink signals in the
 channels of at least one downlink C band, each downlink C band having a
 plurality of downlink C band channels;
 (e) one or more C band downlink antennas, each antenna capable of
 outputting a downlink beam comprising downlink C band signals, each
 downlink beam being separately directable to different locations on Earth;
 (f) means for directing the C band downlink signals to any one of the one
 or more C band downlink antennas;
 (g) a propulsion subsystem designed to allow the satellite to make at least
 two fast moves during the design life of the satellite;
 (h) a power subsystem to provide electrical power for satellite operation;
 (i) a telemetry and command subsystem to allow the satellite to monitor
 itself and for communicating with the external control system, the
 subsystem comprising a telemetry sub-subsystem that can transmit on at
 least two different frequencies and a command sub-subsystem that can
 receive on at least two different frequencies;
 (j) an attitude and orbit control subsystem for helping to properly orient
 the satellite with respect to Earth;
 (k) a thermal control subsystem for helping to maintain the satellite
 within the proper temperature range for operation; and
 (l) means to reconfigure the satellite, said means comprising (i) means to
 remotely adjust the Ku band processing means to direct a bundle of at
 least two but of fewer than all of the signals in each of the uplink Ku
 bands to any one of the downlink Ku bands, (ii) means to remotely adjust
 the downlink beam from at least one of the Ku band downlink antennas to
 direct the beam to different locations on Earth, (iii) means to remotely
 adjust the downlink beam from at least one of the one or more C band
 downlink antennas to direct the beam to different locations on Earth, (iv)
 means to remotely change the footprint of the downlink beam from at least
 one of the downlink antennas, and (v) means to remotely change the
 polarity of at least one of the downlink antennas.
 In some of the preferred embodiments, the C band processing means can
 output the amplified, reduced-frequency C band signals as C band downlink
 signals in the channels of either of the 3.70-4.20 GHz and 3.40-3.70 GHz
 downlink C bands; the Ku band processing means can direct some but not all
 of the signals in one of the Ku uplink bands to any one of the six 250 MHz
 downlink Ku bands and can direct other signals in that one of the Ku
 uplink bands to the same or a different one of the six downlink Ku bands;
 the means to remotely adjust the Ku band processing means to direct the
 signals comprises means to remotely adjust the Ku band processing means to
 change the frequencies to which the signals are down converted; the means
 for down converting the signals comprises, for example, a frequency
 synthesizer or fixed oscillators; the satellite has at least two uplink C
 band antennas and at least two uplink Ku band antennas and all of the
 uplink antennas are independently steerable to different locations on
 Earth; the uplink antennas also function as the downlink antennas; the
 satellite is designed so that at the start of its design life, the signals
 of at least thirty-two uplink Ku band channels can be processed by the Ku
 band processing means and the signals of at least thirty-two uplink C band
 channels can be processed by the C band processing means; the satellite is
 designed so that at the end of its design life, the signals of at least
 twenty-four uplink Ku band channels can be processed by the Ku band
 processing means and the signals of at least twenty-four uplink C band
 channels can be processed by the C band processing means; the satellite
 has means to remotely change the polarity of at least one of the downlink
 antennas and those means comprise means to remotely change the polarity
 from linear to circular or vice versa, and/or from vertical to horizontal
 or vice versa, and/or from clockwise to counterclockwise or vice versa;
 the means to reconfigure the satellite includes means to remotely adjust
 the Ku band processing means to direct a bundle of fewer than all of the
 signals in each of the uplink Ku bands to any one of the downlink Ku
 bands, for example, two, three, six, or a different number of signals; the
 satellite has means to remotely change the footprint of the downlink beam
 from at least one of the Ku band downlink antennas and from at least one
 of the C band downlink antennas; the downlink beam from at least one of
 the downlink antennas is independently directable to different locations
 on Earth; the satellite is designed so that it can make a minimum of three
 fast moves, each of at least five degrees per day, during the design life
 of the satellite; the telemetry and command subsystem comprises a
 telemetry sub-subsystem that can transmit on at least two (preferably
 four) different frequencies and a command sub-subsystem that can receive
 on at least two (preferably four) different frequencies; some (or more
 preferably all) of the Ku band channels are of a standard bandwidth and
 the standard bandwidth is nominally 36 MHz (which includes some of the
 channels being 35 MHz wide); and the replacement satellite further
 comprises BSS band processing means comprising means for (i) receiving BSS
 uplink signals at frequencies ranging from 17.3 GHz to 18.1 GHz, (ii)
 amplifying the BSS signals, (iii) down converting their frequencies, and
 (iv) outputting those amplified, reduced-frequency BSS band signals as BSS
 downlink signals in the channels of the bands provided for downlink Ku
 band signals.
 In another aspect, the invention concerns a method for replacing a
 geostationary communications satellite handling C band and Ku band
 signals, the method comprising providing the universal replacement
 communications satellite of this invention, placing the replacement
 satellite in a suitable geostationary slot, and reconfiguring the
 satellite to emulate the communications performance of the satellite being
 replaced. The method preferably further includes placing the replacement
 satellite in a storage orbit whose plane typically will be inclined with
 respect to the orbital plane of the geostationary slot and moving the
 replacement satellite from its storage orbit to the suitable geostationary
 slot by means of a combined drift and inclination maneuver.
 Other features and advantages of the invention will be apparent to those
 skilled in the art from this disclosure.

DETAILED DESCRIPTION OF THE INVENTION
 The replacement satellite of this invention is a practicable
 (technologically, economically, and otherwise) satellite that can emulate
 the communications performance of the vast majority of existing and future
 geostationary communications satellites operating in the Fixed Satellite
 Service (FSS) bands (that is, C band/Ku band communications satellites),
 as defined by the International Telecommunications Union ("ITU"). The
 design of the satellite of this invention is generally not critical and
 any design that has the required features of this invention and allows the
 benefits of this invention to be achieved may be used.
 The design life of the satellite of this invention should be at least 9
 years, desirably at least 10 years, more desirably at least 11 years, most
 desirably at least 12 years, preferably at least 13 years, more preferably
 at least 14 years, and most preferably at least 15 years. As discussed
 below, desirably 14 years will be used as the target design life for
 designing a satellite of this invention that is capable of making 4 "fast
 moves" of at least 5 degrees (longitudinal Earth equatorial degrees) per
 day.
 Important aspects of the satellite of this invention include its
 reconfigurability (e.g., it has a reconfigurable communications payload,
 flexible transponder design, and flexible telemetry and command design),
 the ability to pick up signals from a variety of locations on Earth and to
 amplify and retransmit them to a variety of different locations on Earth
 while tailoring the one or more downlink footprints, and the ability to
 quickly move from a storage slot to a slot where it is needed (i.e., a
 slot that allows it to assume the telecommunications functions of the
 failed or failing satellite).
 Broadly, a communications satellite may be thought of as having seven
 subsystems: structures, power, thermal control, attitude and orbit
 control, propulsion, telemetry and command, and communications.
 The structures subsystem comprises the framework of the satellite on which
 and in which are mounted the rest of the components of the satellite. The
 design of the structures subsystem of the satellite of this invention is
 not critical and is well within the skill of the art once the features of
 this invention disclosed herein are understood. Broadly speaking, the
 structures subsystem of the satellite of this invention will be
 substantially the same as that of a conventional C band/Ku band
 communications satellite. Large buses are preferred. Thus, for example,
 buses such as the Lockheed Martin A2100, Loral FS1300, or the Hughes
 HS601HP or HS702 may be used. The Loral FS1300 may be preferred for
 certain embodiments.
 The power subsystem comprises the solar panels, which generate electricity
 and are located on the outside of the satellite, batteries for storing
 electricity (e.g., electricity generated by the solar panels that is not
 used at the time of generation), and the distribution network for
 delivering electricity to the various components of the satellite
 requiring electrical power. When the solar panels can not provide all of
 the electricity required, electricity is withdrawn from the batteries. The
 design of the power subsystem of the satellite of this invention is not
 critical and is well within the skill of the art once the features of this
 invention disclosed herein are understood.
 Broadly speaking, the power subsystem of the satellite of this invention
 will be rated at least 8 kilowatts and desirably at least 10 kilowatts.
 The power subsystem should be capable of providing sufficient power at the
 end of the design life of the satellite to operate at least 24 channels
 (transponders) on C band and at least 24 channels (transponders) on Ku
 band. Preferably, the power subsystem will provide sufficient power to
 operate at least 30 (desirably at least 32 and preferably at least 36) C
 band channels and at least 30 (desirably at least 32 and preferably at
 least 36) Ku band channels at the beginning of the life of the satellite.
 In the satellite of this invention, the C band channels desirably have a
 downlink power of about 35-40 watts per channel and the Ku band channels
 desirably have a downlink power of about 100-150 watts per channel.
 The thermal control subsystem helps maintain the operating parts of the
 satellite within the desired temperature operating range so that the
 satellite can function properly. Accordingly, some of the heat generated
 as a byproduct of satellite operations (e.g., by the communications
 subsystem) will be directed out of the satellite. The design of the
 thermal control subsystem is not critical and is well within the skill of
 the art once the features of this invention disclosed herein are
 understood. The satellite of this invention may use a circulating heat
 transfer medium (roughly akin to heat pump) to move heat from areas of
 higher temperature to areas of lower temperature. The satellite may also
 use heat-radiating surfaces. Broadly speaking, the thermal control
 subsystem of the satellite of this invention will be similar to the
 thermal control subsystem of a conventional satellite, the main difference
 being as follows.
 In a conventional C band/Ku band communications satellite, the
 communications subsystem operates throughout essentially the entire life
 of the satellite, thereby constantly producing a significant amount of
 byproduct heat, and the thermal control system is designed accordingly;
 however, in the satellite of this invention, the communications subsystem
 typically will operate (and thereby produce byproduct heat) only when the
 satellite is being used to spare or back-up a failed or failing satellite.
 Thus, heaters are provided in the satellite of this invention and operated
 when the communications subsystem is not being used so as to produce
 approximately the same amount of heat that the communications subsystem
 produces when it is operational. That results in keeping the thermal load
 on the thermal control subsystem approximately constant, thereby
 simplifying its design.
 The attitude and orbit control subsystem helps point the satellite towards
 the Earth so that the satellite is oriented properly with respect to the
 Earth. The design of the attitude and orbit control system is not critical
 and is well within the skill of the art once the features of this
 invention disclosed herein are understood. Broadly speaking, the attitude
 and orbit control subsystem of the satellite of this invention will be
 essentially the same as the attitude and orbit control subsystem of any
 conventional FSS satellite that has the same size, weight, weight
 distribution, etc.
 The propulsion subsystem of the satellite includes thrusters and a fuel
 supply. Generally speaking, various forces (for example, from the
 gravitational effects of the sun and moon, atmospheric drag, the
 elliptical shape of the earth, and solar radiation) cause a satellite to
 move from its desired location. Therefore, the satellite's thrusters
 (engines or motors) are fired (typically at regular intervals) for
 station-keeping to return the satellite to the desired location, in other
 words, to control the inclination, eccentricity, and drift of the
 satellite. By "inclination" is meant the inclination of the plane of the
 satellite's actual orbit (in degrees of latitude) relative to the plane of
 the Earth's equator (i.e., the north/south position). "Eccentricity" is
 the measure of the non-circularity of the satellite orbit, in other words,
 an indication of the variation in distance between the satellite and the
 Earth as they move. By "drift" is meant the position of the satellite in
 an east/west direction, for example, relative to a location on the Earth.
 The design of the propulsion subsystem of the satellite of this invention
 is not critical and is well within the skill of the art once the features
 of this invention disclosed herein are understood. The geostationary
 satellites for which the satellite of the present invention can be a
 replacement are typically three-axis stabilized satellites. Such
 satellites usually use liquid chemical propulsion systems for
 station-keeping, for example, with one set of thrusters being used to
 control inclination and a second set being used to control drift and
 eccentricity.
 Broadly speaking, a conventional satellite does not need to make any "fast
 moves" because sufficient time usually can be allowed for the satellite to
 move in an east/west direction or for north/south station-keeping (for
 example, usually anywhere from 30 to 60 days can be allowed for east/west
 moves). However, a major difference between the satellite of this
 invention and a conventional satellite is that the satellite of this
 invention must be capable of making fast moves. Because the satellite of
 this invention must be moved (usually from its storage orbital location)
 to the equatorial slot required for it to spare or replace a failed or
 failing satellite, it must be moved to that slot as quickly as possible to
 minimize down time (i.e., the time when the desired communications
 capability is not being provided).
 The satellite of this invention will typically be allowed to move north and
 south of the equatorial plane while it is in storage (i.e., is in its
 storage orbit around the Earth). As is known to those skilled in the art,
 if a satellite is placed in a geostationary equatorial orbit and there is
 no station-keeping, the satellite will slowly move either north or south
 of the equatorial plane, reach a maximum of roughly 8 degrees inclination
 either above or below the equatorial plane, and then move in the opposite
 direction until it again reaches a maximum inclination of roughly 8
 degrees in the other direction. In other words, if left in storage for a
 long time without any station-keeping, the satellite of this invention
 will oscillate slowly over a period of years between an inclination of
 roughly +8 degrees and -8 degrees.
 Under applicable regulations, e.g., Federal Communications Commission
 ("FCC") regulations, C band/Ku band geostationary satellites must be about
 2 longitudinal (east/west) degrees apart. The circumference of the
 equatorial planar ring around the Earth in which those geostationary
 satellites are located (at an altitude of about 22,300 miles) is roughly
 160,000 miles. Therefore, the two longitudinal degrees of separation is
 equivalent to roughly 800 miles. Because it will not be cost effective to
 provide a replacement satellite of this invention near each orbiting C
 band/Ku band communications satellite that it can spare, it will often be
 necessary to move the replacement satellite of this invention many
 thousands of miles to reach the appropriate slot to spare the failed or
 failing satellite. Hence, the need for the satellite of this invention to
 be able to make fast moves.
 By a "fast move" is meant a move of at least about 2.5 degrees
 (longitudinal Earth equatorial degrees) per day, desirably at least 3,
 more desirably at least 4, most desirably at least 5, preferably at least
 6, more preferably at least 7, most preferably at least 8 degrees per day,
 and sometimes even at least 10 degrees a day.
 The satellite of this invention will generally be designed so that during
 its design life it is capable of making at least 2 fast moves, desirably
 of at least 3 degrees (longitudinal Earth equatorial degrees) per day,
 usually at least 3 fast moves of at least 3 degrees per day, desirably at
 least 3 fast moves of at least 4 degrees per day, more desirably at least
 3 fast moves of at least 5 degrees per day, most desirably at least 3 fast
 moves of at least 6 degrees per day, preferably at least 3 fast moves of
 at least 7 degrees per day, more preferably at least 3 fast moves of at
 least 8 degrees per day, sometimes at least 3 fast moves of at least 10
 degrees per day, and most preferably at least 4 fast moves of at least 5
 degrees per day. Thus, the replacement satellite of this invention will
 carry substantially more fuel than the typical conventional communications
 satellite for which it is a spare because it will need to be able to move
 substantially more quickly than a conventional satellite.
 As noted above, desirably 14 years will be used as the target design life
 for designing a satellite of this invention that is capable of making 4
 fast moves of at least 5 degrees (longitudinal Earth equatorial degrees)
 per day. If the moves (or relocations) made by a satellite of this
 invention during its lifetime are equivalent to less than that (in other
 words, less than the equivalent of 4 fast moves of at least 5 degrees per
 day), the satellite life will be greater than the 14-year design life
 (assuming no other factor becomes limiting). Because the amount of fuel
 carried by a satellite of this invention may become the factor that limits
 the life of the satellite, various techniques for reducing fuel
 consumption will be used when appropriate, for example, using a "combined
 drift and inclination maneuver" (described below) to go from the storage
 (or parking) slot to the slot suitable for replacing (or sparing) the
 failed or failing satellite and using a slow drift for returning the
 satellite from the replacement (or sparing) slot to the storage (or
 parking) location (slot).
 Any propulsion subsystem capable of making the required number of fast
 moves can be used, for example, fluid (e.g., liquid) or solid or plasma
 systems, e.g., an oxidizer-based system (e.g., one using a hydrazine such
 as monomethyl hydrazine). Propulsion means that are not powerful enough or
 otherwise suitable for making the required number of fast moves, e.g.,
 Xenon ion propulsion systems ("XIPS"), may still be used for north/south
 station-keeping.
 Desirably the replacement satellite of this invention can make a combined
 drift and inclination maneuver while it is moved from its storage location
 to the slot suitable for backing-up or sparing the failing or failed
 satellite (the "suitable slot"), thereby reducing the amount of fuel
 required that would otherwise be required for the move. By "combined drift
 and inclination maneuver" is meant a maneuver in which the satellite is
 oriented and its thrusters are fired so that east/west (drift) and
 north/south (inclination) movement occur simultaneously at some point
 during the movement from the storage location to the suitable slot. (If
 the satellite is being used in a first suitable slot to spare a first
 failed or failing satellite and then is moved to a second suitable slot to
 spare a second failed or failing satellite, the first suitable slot would
 be considered to be the storage location from which the replacement
 satellite was being moved to the second suitable slot.)
 The telemetry and command subsystem comprises two sub-subsystems, the
 telemetry sub-subsystem and the command sub-subsystem. The telemetry
 sub-subsystem monitors the health of the satellite and transmits the
 information externally (for example, to a ground control station), and the
 command sub-subsystem receives commands from outside the satellite (for
 example, from a ground control station). The design of the telemetry and
 command subsystem of the satellite of this invention is not critical and
 is well within the skill of the art once the features of this invention
 disclosed herein are understood. Broadly speaking, that subsystem of the
 satellite of this invention will be substantially the same as that of a
 conventional C band/Ku band communications satellite, with the following
 exception.
 The typical conventional C band/Ku band communications satellite being
 spared or replaced by the satellite of this invention is designed to use
 only one or two frequencies for transmission by the telemetry
 sub-subsystem and only one or two frequencies for reception by the command
 sub-subsystem. It is a feature of this invention that the satellite of
 this invention is designed so that at least two different frequencies
 (desirably at least three, preferably at least four, and most preferably
 at least five different frequencies) are available for use and can be used
 by the telemetry sub-subsystem for transmission and that at least two
 different frequencies (desirably at least three, preferably at least four,
 and most preferably at least five different frequencies) are available for
 use and can be used by the command sub-subsystem for reception. In the
 satellite of this invention, generally four different frequencies will be
 available for use by the telemetry sub-subsystem and four different
 frequencies will be available for use by the command sub-subsystem. Any
 means known to those skilled in the art can be used to change the
 frequency in each sub-subsystem, for example, frequency synthesizers or
 fixed oscillators.
 Having so many different frequencies available for each sub-subsystem is
 important because it allows the frequencies used in a given replacement
 slot in any ITU region to be selected from the ones that are available in
 the satellite of this invention so as to avoid interference with, for
 example, functioning satellites that are near the replacement slot.
 Desirably the polarization of one or more the telemetry and command
 antennas can also be switched (e.g., from linear to circular or circular
 to linear, and/or from vertical to horizontal or from horizontal to
 vertical, and/or from clockwise to counterclockwise or from
 counterclockwise to clockwise). That further enhances the ability of the
 satellite of this invention to avoid interference with, for example,
 neighboring satellites. Also desirably, one or more of the telemetry and
 command antennas can be adjusted to improve the quality of the
 transmission and/or reception. Thus, for example, the beam of the
 telemetry antenna may be positioned so that the beam reaches different
 locations on Earth, e.g., by moving the antenna itself and/or by adjusting
 its transmission beam using means such as a phased array. Similarly, the
 receiving antenna of the command sub-subsystem may be positioned to point
 it as different locations on Earth.
 Preferably omni (omnidirectional) antennas are the primary antennas used
 for the telemetry and command subsystem, for the following reason.
 Typically a conventional C band/Ku band communications satellite will,
 once it is in orbit and operational, receive and transmit the telemetry
 and command signals within the C band or Ku band themselves, and those
 bands typically use high gain antennas; however, because the satellite of
 this invention can back-up so many satellites of different designs and
 those satellites may be at so many different locations throughout the
 geostationary equatorial plane, the high gain antennas used in the
 replacement satellite of this invention may be out of view of the ground
 telemetry and command station(s) customarily used for the replacement
 satellite. Hence, on the replacement satellite of this invention, omni
 antennas and not the high gain antennas are preferred for the telemetry
 and command subsystem.
 The communications subsystem receives signals from Earth according to the
 uplink frequency plan, amplifies them, and retransmits them according to
 the downlink frequency plan. Design of the communications subsystem of the
 satellite of this invention is not critical and is well within the skill
 of the art once the features of this invention disclosed herein are
 understood.
 The communications subsystem of the satellite of this invention is designed
 to handle C band and Ku band signals. The C band has uplink frequencies in
 the 6 GHz range and downlink frequencies in the 4 GHz range. The Ku band
 has uplink frequencies in the 14 GHz frequency range and downlink
 frequencies in the 12 GHz range.
 Broadly speaking, the communications subsystem includes (a) uplink
 antennas, which receive the uplink communications signals over one or more
 preselected bands, each band having more than one channel, (b) one or more
 filters that allow the signals in the preselected bands to pass while
 blocking any noise or signals at frequencies outside the preselected
 bands, (c) one or more amplifiers to increase the strength of the desired
 signals (e.g., to increase the strength of the signals after they leave
 the one or more filters), (d) a down converter for reducing the uplink
 frequencies to the downlink frequencies, (e) means for directing the
 uplink signals (which are received by one or more C band antennas and one
 or more Ku band antennas) to the appropriate one or more downlink C band
 antennas and one or more Ku band antennas, and (f) one or more C band
 antennas and one or more Ku band antennas. The means for directing the
 signals to the appropriate antennas can include the down converter (which
 itself may include switches, fixed oscillators, frequency synthesizers,
 etc., so that the various signals can be down converted to the desired
 frequencies and those frequencies can be changed), switches, input
 multiplexers (IMUXs), output multiplexers (output MUXs), etc.
 The original C band uplink range allocated by the ITU was 5.925 GHz to
 6.425 GHz (a bandwidth of 500 MHz) and the corresponding downlink range
 was 3.7 GHz to 4.2 GHz (also a bandwidth of 500 MHz). The ITU later made a
 second band available, namely, 6.425 to 6.725 GHz for the uplink (a
 bandwidth of 300 MHz) and 3.4 to 3.7 GHz for the corresponding downlink
 (also a bandwidth of 300 MHz). More recently a third band for C band
 uplink signals has been made available, namely, 5.85 GHz to 5.925 GHz (a
 bandwidth of 75 MHz) but there was no additional band allocated for the
 downlink. To date, there has been little or no use of this third 75 MHz
 uplink C band. Thus, C band uplink signals may be in any of the three
 allocated uplink bands, which happen to be contiguous and occupy 5.85 GHz
 through 6.725 GHz (a total bandwidth of 875 MHz), and C band downlink
 signals may be in either of the two allocated downlink bands, which happen
 to be contiguous and occupy 3.4 GHz through 4.2 GHz (a total bandwidth of
 800 MHz).
 Principally because of ITU regulations governing which frequencies can be
 used by C band/Ku band communications satellites in each of the three
 different ITU regions of the Earth, a satellite handling C band
 communications will typically operate in only 500 MHz (of the 875 MHz) on
 the uplink and in only 500 MHz (of the 800 MHz) on the downlink. Thus, a
 universal replacement satellite must be able to handle at least the 800
 MHz of the two earliest uplink C bands from 5.925 GHz through 6.725 GHz
 (and desirably the entire uplink range of 875 MHz, with the addition of
 the 75 MHz between 5.85 and 5.925 GHz) and must also be able to handle the
 entire 800 MHz of the two downlink C bands.
 Broadly speaking, within a 500 MHz C band, there will be 24 channels, 12
 with one polarization (either vertical or horizontal if linear
 polarization is used, or either clockwise or counterclockwise if circular
 polarization is used). Assuming for example that linear polarization is
 used, each of the 12 vertically polarized channels will be nominally 36
 MHz wide, with guard bands between the channels and a guard or buffer band
 at the top of the 500 MHz range and a guard or buffer band at the bottom
 of the 500 MHz range. That accounts for the difference between the
 approximately 41.7 MHz total per channel one calculates by dividing 500
 MHz by 12 and the nominal 36 MHz per channel that is usable. The same is
 true for the 12 horizontally polarized channels. As will be understood by
 one skilled in the art, the two sets of 12 channels, each channel being
 nominally 36 MHz wide, can co-exist in the same 500 MHz because the two
 sets have different polarizations. The same analysis applies for the 24
 channels in a band of 500 MHz if circular polarization is used.
 For a conventional satellite, the 24 uplink channels may all be transmitted
 by one or more antennas at substantially the same location on Earth or the
 channels may be fed by one or more antennas at each of several different
 locations. Therefore, a conventional satellite designed for a
 predetermined slot will be designed to capture the 24 channels from all of
 the transmitting antennas that will be feeding it, and that may require 2
 or more uplink antennas. Because the conventional satellite will be in a
 predetermined slot, the geometry is known prior to design (i.e., the
 spatial relationship between the one or more transmitting antennas on
 Earth and the one or more receiving antennas on the satellite is known)
 and, accordingly, the position and orientation of each satellite uplink
 antenna on and to the body of the satellite can be predetermined and
 fixed.
 On the other hand, to allow the replacement satellite of this invention to
 emulate a substantial percentage of the FSS satellites, some (and
 desirably all) of its uplink antennas must be independently steerable so
 that they can adequately capture all of the signals being sent by the
 transmitting antennas on Earth that were feeding the failed or failing
 satellite being replaced by the satellite of this invention. The
 replacement satellite will use at least two uplink C band antennas,
 possibly at least three, and sometimes at least four. The polarity of at
 least one (and desirably all) of the C band uplink antennas can be changed
 to accommodate the pre-established uplink frequency plan of the failed or
 failing satellite being replaced.
 Similar considerations apply to the downlink C bands and the downlink
 antennas. Thus, in a conventional FSS satellite the C band downlink will
 be 500 MHz wide, with 24 channels (each nominally 36 MHz wide) polarized
 either in two groups of vertical and horizontal signals or in two groups
 of clockwise and counterclockwise signals, and the downlink signals will
 be aimed at one or more receiving antennas in one or more locations on
 Earth. Again, because the geometry is known prior to designing a
 conventional FSS satellite (i.e., that distance and direction between each
 downlink antenna on the satellite and the desired receiving area or
 antennas on Earth), the downlink antennas will be fixed in location and
 orientation on that satellite.
 The replacement satellite of this invention will use at least two downlink
 C band antennas, desirably at least three, preferably at least four, and
 in some cases at least five. The polarity of at least one (and desirably
 two, three, four, or more) of the C band downlink antennas can be changed
 to accommodate the pre-established downlink frequency plan of the failed
 or failing satellite being replaced. At least some and desirably most of
 the antennas have sufficient gain with broad coverage. The minimum EIRP
 (effective isotropic radiated power) for the C band downlink antennas is
 desirably 36 dbw (decibels with a reference point of a watt).
 At least one (and desirably two, three, four, or more) of the C band
 downlink antennas must have beams that are independently directable so
 that they can send strong enough signals to all of the antennas on Earth
 that were receiving signals from the failed or failing satellite being
 replaced by the satellite of this invention. Directing the beam emanating
 from an antenna may be accomplished in any appropriate manner, e.g., by
 steering the antenna itself, by using a multiple beam antenna, by using a
 phased array antenna, or by using any other type of reconfigurable antenna
 (see, e.g., U.S. Pat. No. 4,965,587).
 In contrast to the C band uplink signal, which may come from only a few
 antennas (and perhaps as few as just one transmitting antenna on Earth),
 one or more of the downlink signals may have to be sent to many antennas
 over a wide area, for example, to the receiving antennas of all of the
 television cable companies throughout the entire continental United States
 that carry a particular signal for redistribution to their own customers
 (e.g., the signal from a nationally distributed movie or sports content
 provider, which signal is uplinked to a satellite and downlinked from the
 satellite to cable companies throughout the United States for
 redistribution by each cable company to its own customers). Alternatively,
 a particular downlink beam may have to be sent to a rather circumscribed
 geographic region. Thus, it is desirable that the footprint of at least
 one (and desirably of two, three, four, or more) of the C band downlink
 antennas be able to be changed. The footprint of an antenna's downlink
 beam may be changed using any appropriate means, for example, by steering
 (moving or redirecting) the antenna and/or by changing the shape of the
 antenna's beam (e.g., by using a phased array antenna, a reconfigurable
 antenna, or by any other suitable method).
 The entire uplink Ku band occupies 13.75 GHz through 14.5 GHz and may be
 thought of as having 3 uplink bands, which is each 250 MHz wide and which
 are contiguous, in other words, one band from 13.75 GHz to 14.00 GHz, a
 second band from 14.00 GHz to 14.25 GHz, and a third band from 14.25 GHz
 to 14.50 GHz. In contrast, there are several downlink Ku bands, but only
 some are contiguous. The first nominal downlink band is at 10.95 GHz to
 11.20 GHz (250 MHz bandwidth), the second nominal band runs from 11.45 GHz
 to 11.70 GHz (250 MHz bandwidth), the third nominal band runs from 11.70
 GHz to 12.20 GHz (500 MHz bandwidth), and the fourth nominal band runs
 from 12.20 GHz to 12.75 GHz (550 MHz bandwidth). The fourth nominal band
 may itself be considered to comprise two nominal bands, one running from
 12.2 to 12.5 GHz, which is a 300 MHz band, and the other running from 12.5
 to 12.75 GHz, a 250 MHz band, for a total of 5 bands.
 As noted above, the satellite of this invention is practicable,
 technologically, economically, and otherwise. Practicability has been
 achieved by carefully determining the features necessary for
 practicability as opposed to including by rote all features needed for
 perfect emulation of all existing and future FSS satellites. Thus,
 although the 50 MHz of bandwidth from 12.20 to 12.25 GHz is part of the
 spectrum allocated by the ITU for downlink Ku band signals, in some
 preferred embodiments of the present invention, that 50 MHz will not be
 used. Thus, in those embodiments, the fourth band will run from 12.25 GHz
 to 12.75 GHz (a 500 MHz band). Not using the 50 MHz of bandwidth between
 12.20 and 12.25 GHz in some preferred embodiments simplifies the design of
 the satellite of this invention because in those embodiments, all of the
 uplink and downlink Ku band spectrum used can be conveniently divided into
 blocks of 250 MHz (3 uplink 250 MHz bands and 6 downlink 250 bands). That
 is not the case in those embodiments also utilizing the 50 MHz from 12.20
 to 12.25 GHz (because the fourth band used, from 12.20 to 12.75 GHz, would
 be 550 MHz wide).
 Accordingly, viewed one way, in those preferred embodiments not using the
 50 MHz from 12.20 to 12.25 GHz, nominally there are 4 downlink Ku bands,
 two having bandwidths each of 250 MHz and two having bandwidths each of
 500 MHz (i.e., 10.95-11.20, 11.45-11.70, 11.7-12.2, and 12.25-12.75 GHz).
 Viewed another way, in those preferred embodiments, there are 6 downlink
 Ku bands, each having a bandwidth of 250 MHz. Regardless of how many Ku
 bands one considers there to be, there is a total of 1550 MHz (1.55 GHz)
 of non-contiguous bandwidth allocated by the ITU for Ku band downlink
 signals within the range of 10.95 GHz to 12.75 GHz; however, in some of
 the preferred embodiments of the present invention, only 1500 MHz (1.5
 GHz) will be used.
 It will be understood that in the claims, a band from 12.25 to 12.75 GHz,
 which may be thought of as comprising 2 bands each of 250 MHz, is within a
 band of 12.20 to 12.75 GHz. Thus, in the claims, "outputting any of those
 amplified, reduced-frequency Ku band signals as Ku band downlink signals
 in the channels of any of six 250 MHz bands within the 10.95-11.20 GHz,
 11.45-11.70 GHz, 11.70-12.20 GHz, and 12.25-12.75 GHz downlink Ku bands,
 each downlink Ku band having a plurality of downlink Ku band channels" is
 not avoided merely by using in addition the 50 MHz between 12.20 and 12.25
 GHz.
 Principally because of ITU regulations governing which frequencies can be
 used by C band/Ku band communications satellites in each of the three
 different ITU regions of the Earth, a satellite handling Ku band
 communications will typically operate in only 500 MHz (of the 750 MHz
 allocated) on the uplink and in only 500 MHz (of the 1550 MHz allocated)
 on the downlink. Thus, a universal replacement satellite must be able to
 handle all 750 MHz of the uplink Ku bands (which the present invention
 does) and must also be able to handle most, if not all of the 1550 MHz of
 allocated downlink Ku band (as noted, in some preferred embodiments of the
 present invention, only 1500 MHz of the 1550 MHz available will be used).
 Broadly speaking, in a satellite of this invention, there will typically be
 a total for both polarities (i.e., vertical and horizontal, or clockwise
 and counterclockwise) of 72 Ku band downlink channels available, each
 nominally 36 MHz wide (1500 MHz divided by 36 for each polarity is
 approximately 41.7 MHz, and the difference between 41.7 and 36 arises from
 the presence of guard bands, etc.). Broadly speaking, not more than 750
 MHz of downlink Ku bandwidth is used in any one conventional FSS
 satellite. Accordingly, the satellite of this invention will preferably be
 designed to power up only 36 channels (total for both polarities) at start
 of life (the design point for end of life is 24 channels), although at
 which frequencies those 36 are powered up will depend upon which
 conventional FSS satellite is being replaced by the satellite of this
 invention.
 One important feature of the satellite of this invention is that it can
 receive and direct signals in any one of the three uplink Ku bands to any
 one of the four nominal downlink Ku bands (or to any one of the five
 downlink Ku bands if there are considered to be five such bands).
 Preferably the satellite of this invention can receive and direct signals
 in any one of the three uplink Ku bands to any one of the six 250 MHz-wide
 downlink Ku bands. This helps the satellite of this invention emulate the
 communications performance of the failed or failing C band/Ku band
 communications satellite that it is replacing.
 As with C band, the Ku band channels of a satellite of this invention are
 each nominally 36 MHz wide, and polarization (linear or circular)
 desirably is used. Thus, the 500 MHz uplink bandwidth has a total of 24
 channels, 12 channels polarized vertically and 12 channels polarized
 horizontally (or 12 channels polarized clockwise and 12 channels polarized
 counterclockwise). Considering the 12 vertically polarized channels first,
 the presence of guard bands between the channels, a guard or buffer band
 at the top of the 500 MHz range, and a guard or buffer band at the bottom
 of the 500 MHz range accounts for the difference between the approximately
 41.7 MHz total per channel one calculates by dividing 500 MHz by 12 and
 the nominal 36 MHz per channel that desirably is used in the satellite of
 this invention. The same is true for the 12 horizontally polarized
 channels. As will be understood by one skilled in the art, the two sets of
 12 channels, each channel being nominally 36 MHz wide, can co-exist in the
 same 500 MHz because the two sets have different polarizations. The same
 analysis applies for the 24 channels in a band of 500 MHz if circular
 polarization is used.
 There is no one standard channel bandwidth for the Ku band, and bandwidths
 of 27, 36, 43, 54, 72, and 108 MHz have been or are being used. Thus,
 another preferred feature of this invention is that a standard bandwidth
 is used for the majority of Ku bands (and most preferably for all Ku
 bands), and most preferably that bandwidth is nominally 36 MHz. For the
 two non-contiguous downlink Ku bands (i.e., from 10.95 to 11.2 GHz and
 from 11.45 to 11.70 GHz), the channels preferably are 35 MHz wide, but
 that width is considered to be within the terms "nominally 36 MHz wide"
 and "a nominal bandwidth of 36 MHz." Use of a standard bandwidth for all
 uplink and downlink Ku bands (whether nominally 36 MHz or some other
 value) allows, for example, filters and multiplexers necessary for
 handling the other bandwidths to be omitted, thereby simplifying the
 design and helping to make the satellite of this invention practicable.
 As with C band, for a conventional satellite, the 24 uplink channels may
 all be transmitted by one or more antennas at substantially the same
 location on Earth or the channels may be fed by one or more antennas at
 each of several different locations. Therefore, a conventional satellite
 designed for a predetermined slot will be designed to capture the 24 Ku
 band channels from all of the transmitting antennas that will be feeding
 it (assuming that the preferred nominal bandwidth of 36 MHz is used), and
 that may require 2 or more uplink antennas. Because the conventional
 satellite will be in a predetermined slot, the geometry is known prior to
 design (i.e., the spatial relationship between the one or more
 transmitting antennas on Earth and the one or more receiving Ku band
 antennas on the satellite is known) and, accordingly, the position and
 orientation of each satellite uplink antenna on and to the body of the
 satellite can be predetermined and fixed.
 On the other hand, to allow the replacement satellite of this invention to
 emulate a substantial percentage of the FSS satellites, some (and
 desirably all) of its Ku band uplink antennas must be independently
 steerable so that they can adequately capture all of the signals being
 sent by the transmitting antennas on Earth that were feeding the failed or
 failing satellite being replaced by the replacement satellite of this
 invention. The replacement satellite will use at least two uplink Ku band
 antennas, possibly at least three, and sometimes at least four. The
 polarity of at least one (and desirably all) of the Ku band uplink
 antennas can be changed to accommodate the pre-established uplink
 frequency plan of the failed or failing satellite being replaced.
 In a conventional FSS satellite, the Ku band downlink will be 250, 300, or
 500 MHz wide, with channels (each desirably nominally 36 MHz wide)
 polarized either in two groups of vertical and horizontal signals or in
 two groups of clockwise and counterclockwise signals, and the downlink
 signals will be aimed at one or more receiving antennas in one or more
 locations on Earth. Again, because the geometry is known prior to
 designing a conventional FSS satellite (i.e., that distance and direction
 between each downlink Ku band antenna on the satellite and the desired
 receiving area or antennas on Earth), the downlink antennas will be fixed
 in location and orientation on that satellite.
 The replacement satellite of this invention will use at least two downlink
 Ku band antennas, desirably at least three, preferably at least four, and
 in some cases at least five. The polarity of at least one (and desirably
 two, three, four, or more) of the Ku band downlink antennas can be changed
 to accommodate the pre-established downlink frequency plan of the failed
 or failing satellite being replaced. At least some and desirably most of
 the antennas have sufficient gain with broad coverage. The minimum EIRP
 (effective isotropic radiated power) for the Ku band downlink antennas is
 desirably 48 dbw to 50 dbw (spot) at the edge of coverage. The Ku band
 downlink antennas should have a variety of beam shapes and gain levels,
 and their design is well within the skill of the art.
 At least one (and desirably two, three, four, or more) of the Ku band
 downlink antennas must have beams that are independently directable so
 that they can send strong enough signals to all of the antennas on Earth
 that were receiving signals from the failed or failing satellite being
 replaced by the satellite of this invention. As for the C band downlink
 antennas, directing the beam emanating from a Ku band antenna may be
 accomplished in any appropriate manner, e.g., by steering the antenna
 itself, by using a multiple beam antenna, by using a phased array antenna,
 or by using any other type of reconfigurable antenna (see, e.g., U.S. Pat.
 No. 4,965,587).
 In contrast to the uplink Ku band signals, which may come from only a few
 antennas (and perhaps as few as just one transmitting antenna on Earth),
 one or more of the downlink signals may have to be sent to many antennas
 over a wide area, for example, to the receiving antennas of all of the
 television cable companies throughout the entire continental United States
 who carry a particular signal for redistribution to their own customers.
 Alternatively, a particular downlink beam may have to be sent to a rather
 circumscribed geographic region. Thus, it is desirable that the footprint
 of at least one (and desirably of two, three, four, or more) of the Ku
 band downlink antennas be able to be changed. The footprint of an
 antenna's downlink beam may be changed using any appropriate means, for
 example, by steering (moving or redirecting) the antenna and/or by
 changing the shape of the antenna's beam (e.g., by using a phased array
 antenna, a reconfigurable antenna, or by any other suitable method).
 For example, for one possible embodiment of the satellite of this
 invention, for the Ku band, one antenna with broad coverage would be used
 to provide coverage of at least 48 dbw for the continental United States,
 a section of lower Canada, and the upper portion of Mexico and a spot
 antenna would be used to provide coverage of at least 42 dbw for Hawaii.
 With respect to another use of that embodiment of this invention, the
 satellite being replaced has five Ku band coverage areas, one centered on
 India at 42 dbw, one centered on China at 42 dbw, one centered on South
 Africa at 50 dbw, one centered on the Middle East at 42 dbw, and one
 covering Turkey, northern Africa, and southern Europe at 42 dbw, but the
 replacement satellite uses four coverage areas, one covering South Africa
 and countries north of it at 50 dbw, one covering most of India and China
 at 48 dbw, one covering northern Australia and the area between it and
 China at 48 dbw, and one covering the Middle East, Turkey, northern
 Africa, and southern Europe at 48 dbw . The coverage patterns and power
 levels of the replacement satellite of this invention are not identical to
 those of the satellite it would replace but are close enough to be
 considered to satisfactorily mimic or emulate the communications
 capabilities of that satellite.
 With respect to both C band and Ku band, another desirable feature of this
 invention is that some and preferably all of the uplink and downlink
 antennas on the replacement satellite are steerable (or movable), both
 north/south and east/west, by at least 2 degrees from the normal,
 desirably at least 3 degrees, more desirably at least 4 degrees, most
 desirably at least 5 degrees, preferably at least 6 degrees, more
 preferably at least 7 degrees, and in some cases at least 8 degrees from
 the normal. In a conventional FSS satellite, the antennas are seldom
 movable by more than 1 degree north/south or east/west from the normal.
 The steerability of the antennas of the satellite of this invention helps
 make that satellite practicable while still allowing it to maintain
 sufficient flexibility to meet the frequency plans of just about any FSS
 satellite. The steerability of the downlink antennas may be in addition to
 means that may be used to direct the beams emanating from the downlink
 antennas (e.g., phased array or beam forming technology).
 As is known, with a conventional FSS satellite, a given signal received by
 the satellite in a particular C band or Ku band channel may have to be
 retransmitted along with another uplinked C band or Ku band signal to a
 particular geographic area. Thus, for example, a first Ku band uplink
 signal may have to be directed to a Ku band downlink antenna on the
 satellite serving that geographic area and a second Ku band uplink signal
 may have to be directed to that same downlink antenna. It may also be the
 case that the two uplink Ku band signals are on channels having uplink
 frequencies such that they will require different "amounts" of down
 conversion to be on the same antenna. It may also be the case that various
 uplinked signals in a band, perhaps even signals transmitted by the same
 ground antenna, must be directed to two or more different downlink
 antennas. Thus, the conventional FSS satellite will be designed with
 knowledge of the uplink frequency plan (e.g., the location on Earth of
 each antenna sending the uplink signals, what frequency each signal has)
 and the downlink frequency plan (e.g., what frequency each signal should
 have and the location to which the signals have to be sent). That makes it
 relatively easy to design the down converter, input multiplexers, output
 multiplexers, etc.
 As will be appreciated by one skilled in the art, the numerous existing and
 planned FSS satellites have many different uplink and downlink frequency
 plans and many different plans for redirecting the various uplinked
 signals to the appropriate downlink antennas. It is an important feature
 of this invention that the replacement satellite can accommodate the wide
 variety of uplink and downlink frequency plans found in the majority (and
 preferably the vast majority) of existing and planned FSS satellites.
 A perfect clone replacement satellite would contain all the switches, down
 conversion means, input multiplexers, output multiplexers, etc. needed to
 allow perfect emulation of all of the uplink and downlink frequency plans
 in all FSS satellites. For perfect emulation, each uplink signal in the
 clone would have to be able to be sent to any of the downlink channels
 without in any way affecting to where any of the other uplink signals was
 being sent; however, that would make the design impractical (e.g., overly
 complex) and costly.
 In contrast, the satellite of this invention is practicable,
 technologically, economically, and otherwise. As previously noted,
 practicability has been achieved by carefully determining the features
 necessary for practicability as opposed to including by rote all features
 needed for perfect emulation. Thus, for example, instead of being able to
 individually and independently switch each uplink signal to any downlink
 channel in any band, all least some, desirably most, and preferably all of
 the uplinked signals are switched in bundles. Those bundles contain at
 least 2 signals each, desirably at least 3, more desirably at least 4,
 most desirably at least 6, preferably at least 7, more preferably at least
 8, and most preferably at least 9. In some preferred embodiments, a bundle
 will contain 12 signals. Obviously the more signals per bundle, the less
 the flexibility the processing means (and therefore the satellite) has for
 emulating FSS satellites. Therefore, in some preferred embodiments, 3 or 6
 signals will be bundled. Although not all of the signals in a band need be
 bundled or need to be in the same size bundles, it is preferred that all
 signals in a band be bundled and that the bundles have the same size.
 Thus, for example, for Ku band, for which 36 channels may be used at start
 of life and for which at least 24 channels may be used at end of life,
 desirably all signals are bundled and each bundle may contain 3 or 6
 signals. As will be understood by one skilled in the art, the fewer the
 number of signals per bundle, the lesser is the granularity of the
 processing means.
 The down conversion (downward frequency shift) of the frequencies of the
 uplink signals to the appropriate frequencies for the downlink channels to
 be used may be made using any means that performs that function and allows
 the benefits of this invention to be achieved. The design is not critical
 and is well within the skill of the art once the features of this
 invention disclosed herein are understood. Thus, means that allow
 flexibility in down converting the signals are needed. Such means include
 frequency synthesizers and oscillators (e.g., fixed oscillators) plus
 switching. Further switching directs the reduced-frequency signals to
 various input multiplexers where two or more (e.g., preferably 3 or 6) are
 selected (e.g., by filters) and sent on to amplifiers for boosting their
 power. The output of the amplifiers is then sent to the output
 multiplexers where the individual signals are combined for sending to the
 antennas. As will be understood by one skilled in the art, the particular
 pathways and equipment and means used for these various tasks is not
 critical, and any means can be used that performs the necessary functions
 and allows the benefits of this invention to be achieved. The design of
 those means is not critical and is well within the skill of the art once
 the features of this invention disclosed herein are understood.
 As will be understood by one skilled in the art, directing a particular
 uplink signal to a particular downlink antenna will generally involve
 determining what the downlink frequency to be for that signal and then
 converting it to that frequency using the down conversion means provided
 in the replacement satellite, which means may be, e.g., a frequency
 synthesizer or fixed oscillators plus switches. The change in frequency
 for that first signal (uplink frequency minus downlink frequency) will be
 of a certain number of Hz. Directing another uplink signal to the same
 downlink antenna may involve making a change in frequency of a
 substantially different number of Hz. With the switching and the input and
 output multiplexers in the replacement satellite, the two uplink signals
 can be processed so that they are sent to the same downlink antenna. In
 other words, as a result of this, those signals will be bundled together.
 Another important feature of this invention is that it can be remotely
 reconfigured, that is, signals can be sent from a ground command station
 to the satellite not only to have the satellite move from its then-current
 location (which may be in a storage slot) but also to reconfigure it to
 remotely adjust the Ku band processing means to direct a bundle of at
 least two but of fewer than all of the signals in each of the uplink Ku
 bands to any one of the downlink Ku bands, and/or to remotely adjust the
 downlink beam from at least one of the Ku band downlink antennas to direct
 the beam to different locations on Earth, and/or to remotely adjust the
 downlink beam from at least one of the C band downlink antennas to direct
 the beam to different locations on Earth, and/or to remotely change the
 footprint of the downlink beam from at least one of the downlink antennas,
 and/or to remotely change the polarity of at least one of the downlink
 antennas. The means to cause such reconfiguration, as well as additional
 changes that are desired (e.g., moving one or more of the uplink antennas)
 can be any means that performs that function and allows the benefits of
 this invention to be achieved. The design is not critical and is well
 within the skill of the art once the features of this invention disclosed
 herein are understood.
 The satellite of this invention may be launched and positioned in a storage
 orbit using means and techniques known to those skilled in the art. Thus,
 for example, launch vehicles such as Sea Launch, Ariane, and Proton may be
 used. The satellite of this invention when first placed in orbit will
 typically weigh between 4,000 and 5,000 kilograms and more likely between
 4,300 and 4,900 kilograms.
 The initial storage orbit is typically in a plane inclined to the
 equatorial plane. As discussed above, the storage plane of the satellite
 of this invention will slowly oscillate between inclinations of roughly +8
 and roughly -8 degrees to the equator unless the satellite is purposely
 moved. Thus, even though the replacement satellite may initially be placed
 in a plane inclined to the equator for storage, by the time the
 replacement satellite is to be moved from its storage orbit to an
 operational slot, that storage orbit may be in a plane different from the
 one in which it was initially placed.
 Desirably a constellation of at least two (and preferably at least five)
 universal replacement satellites of this invention will be used. They
 generally will be stored in different locations in an east/west direction,
 although they may not be evenly spaced in an east/west direction. Storing
 a replacement satellite closer to the conventional satellites for which it
 is designated to be the replacement usually reduces the amount of
 communications downtime arising from a failure of the conventional
 satellite (because the replacement satellite has less distance to travel
 from the storage slot to the operational slot of the satellite it is
 replacing).
 The satellite of this invention may be launched and placed into an orbital
 (storage) slot that does not require a separate ITU license. The orbit of
 the satellite may be allowed to move up and down with respect to the
 equatorial plane (i.e., become inclined). After a conventional satellite
 for which the present satellite can act as a back-up fails to an
 unacceptable degree (which may be anywhere from a partial failure to a
 complete failure), the appropriate command is sent from outside the
 replacement satellite (for example, from a ground control station) to the
 replacement satellite's command sub-subsystem. That results in the
 satellite moving from its storage slot to the slot in which it will
 operate to replace the failing or failed satellite. At the appropriate
 time, one or more external command signal cause reconfiguration of the
 satellite to the extent necessary, for example, to match the uplink and
 downlink frequency plans of the satellite being emulated, to correctly
 position all of the uplink and downlink antennas, to change the downlink
 footprints, and to change the telemetry and command frequencies (if
 necessary) so that the replacement satellite will not interfere with the
 functioning of adjacent operating satellites.
 The reconfiguration of the replacement satellite can include adjusting the
 Ku band processing means so that it can direct a bundle of at least two
 but of fewer than all of the signals in each of the uplink Ku bands to any
 one of the downlink Ku bands, adjusting the downlink beam from at least
 one of the Ku band downlink antennas to direct the beam to the appropriate
 location on Earth, adjusting the downlink beam from at least one of the C
 band downlink antennas to direct the beam to different locations on Earth,
 changing the footprint of the downlink beam from at least one of the
 downlink antennas, and changing the polarity of at least one of the
 downlink antennas. The other changes described herein may also be made so
 that the satellite can emulate insofar as is possible the communications
 capabilities of the satellite being replaced.
 The replacement satellite of this invention will stay in the operational
 slot to which it has been moved until, for example, the failed satellite
 is replaced. The replacement satellite of this invention will then be
 moved back to a storage slot or possibly moved to a new operational slot
 and reconfigured to spare another failed or failing satellite.
 Preferably within C band and within Ku band all of the transponders (each
 of which for an uplink channel may be thought of as comprising the
 amplifier after the initial filter and the down converter) can be switched
 to any of the downlink antennas within that band and the polarizations of
 the downlink antennas can be varied. Both of those allow the replacement
 satellite to transmit downlink signals in accordance with the previously
 established downlink frequency plan for the failed or failing satellite
 being replaced. The fact that preferably all the signals are bundled (in
 bundles of at least 2 signals) helps make the satellite of this invention
 practicable while still maintaining sufficient flexibility to meet the
 frequency plans of just about any FSS satellite. The use of amplifiers of
 sufficient power and the use of reconfigurable downlink antennas further
 makes the replacement satellite practicable. As explained above, in some
 preferred embodiments, the 50 MHz between 12.20 and 12.25 GHz in the Ku
 band is not used. That simplifies the design of the satellite because both
 the uplink and the downlink Ku bands can be dealt with in standard size
 bands of 250 MHz, there further making the satellite of this invention
 practicable. The use of a standardized bandwidth for the Ku band
 simplifies the design and also helps make the satellite of this invention
 practicable.
 In some preferred embodiments, the replacement satellite has a telemetry
 sub-subsystem that can transmit on four different frequencies and a
 command sub-subsystem that can receive on four different frequencies, each
 with variable frequencies and switchable polarizations. That allows the
 replacement satellite to be stored and to be used in a wide variety of
 slots without frequency interference in any of the three ITU regions,
 further making the satellite of this invention practicable.
 As will be appreciated by those skilled in the art, the satellite of this
 invention is technologically, economically, and otherwise practicable
 while still providing effective back-up coverage (that is, acting as a
 virtually transparent replacement) for the majority (generally at least
 75%, desirably at least 85%, preferably at least 90%, and most preferably
 at least 95%) of existing and planned FSS satellites. As used in the
 claims, "emulate the communications performance of a substantial
 percentage of existing geostationary C band and Ku band communications
 satellites" refers to this capability. As will be appreciated by one
 skilled in the art, emulating the communications performance does not mean
 that the replacement satellite of this invention can always be
 reconfigured to perfectly mimic the communications performance of a failed
 or failing satellite. Thus, as discussed above, there may be a difference
 in coverage patterns and some reassignment of signals to different
 channels may be necessary.
 As will also be appreciated by those skilled in the art, that the satellite
 of this invention is technologically, economically, and otherwise
 practicable while still providing effective back-up coverage for the
 majority of existing and planned FSS satellites is made possible by the
 unique design of the satellite, which features a combination of frequency
 agility, the preferred use of a standard bandwidth for the Ku band,
 independently steerable uplink antennas, independently directable downlink
 beams, independently variable downlink beams whose footprints can be
 tailored, amplifiers of sufficient power, flexible telemetry and command
 design, and the ability to make a sufficient number of fast moves over the
 satellite's design life.
 Variations and modifications of what has been explicitly disclosed herein
 will be apparent to those skilled in the art and the following claims are
 intended to cover all variations and modifications falling within the true
 spirit and scope of the invention. For example, the universal replacement
 satellite of this invention may also contain means for handling BSS
 (broadcast satellite services) communications.
 For all three ITU regions, the BSS uplink frequency band is 17.3 GHz to
 18.1 GHz. For ITU Region I, the downlink BSS band is 11.7 to 12.5 GHz, for
 Region II the downlink BSS band is 12.2 to 12.7 GHz, and for Region III
 the downlink BSS band is 11.7 to 12.2 GHz. Thus, the downlink BSS bands
 for Earth are within the range of 11.7 GHz to 12.7 GHz. The ranges for the
 downlink Ku bands (if considered to be four downlink bands) preferably
 used herein are 10.95-11.20 GHz, 11.45-11.70 GHz, 11.7-12.2 GHz, and
 12.25-12.75 GHz. (As explained above, the 50 MHz between 12.2 and 12.25
 MHz is allocated by the ITU for use for Ku band downlink signals but
 preferably is not used herein.) Thus, the downlink BSS bands are within
 the scope of the downlink Ku bands (except for the preferred omission of
 the 50 MHz between 12.2 and 12.25 GHz). Therefore, with not too much
 additional equipment, the satellite of this invention may also contain
 means for receiving BSS signals, down converting their signals to the same
 Ku bands already present for handling Ku band downlink signals,
 amplifying, and transmitting the down converted, amplified BSS signals
 back to Earth. Thus, in one embodiment, the universal replacement
 satellite of this invention will be able to act as a spare to handle BSS
 signals and FSS signals although at any one time it may be used to act as
 a replacement for only an FSS or a BSS satellite. The design of the
 additional means needed to handle BSS signals is well within the skill of
 the art.
 Still other variations and modifications will be apparent to those skilled
 in the art, and the claims are intended to cover those variations and
 modifications as well.