Antenna for communicating with low earth orbit satellite

The object of the present invention is to provide an antenna for communicating with a low earth orbit (LEO) satellite which is small-sized and light and can track a LEO satellite at high speed at a small-sized earth station using a LEO satellite. The antenna according to the present invention uses two offset parabolic antenna-type reflectors and each primary feed is installed in the focal position of a paraboloid forming the reflector. The quantity of an offset of the offset parabolic antenna is selected so that antenna gain is maximum at the minimum operational elevation angle. Each primary feed is mechanically independent of the mobile reflector, is attached and fixed to a feed line. In the meantime, each reflector is turned based upon an azimuth axis and an elevation axis according to Az-EL mounting.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an antenna for communicating with a low
 earth orbit satellite, particularly relates to an antenna for
 communicating with a low earth orbit satellite used for an earth station
 in a satellite communication system in which plural low earth orbit (LEO)
 satellites revolve around the earth for automatically tracking each
 satellite.
 2. Description of the Related Art
 Recently, a scheme that high-speed data at approximately a few Mbps to a
 few tens Mbps is provided to users all over the world using a
 high-frequency signal in Ka band (20 to 30 GHz) via multiple LEO
 satellites is formed.
 In such a satellite communication system using multiple LEO satellites, as
 each satellite goes off a visual field in relatively short time when
 viewed from a small-sized earth station, it is required to be tracked in a
 large range.
 Heretofore, for an antenna for tracking a satellite, plural techniques are
 widely known as the antenna of an earth station for a geostationary
 satellite and a mobile satellite.
 For example, for a method of tracking, a monopulse tracking method of
 continuously detecting whether an antenna tracks a satellite in the center
 of a beam or not and controlling so that an antenna bearing is always
 equal to the bearing of a satellite, a step tracking method of shifting an
 antenna at a fixed interval of time by degrees and adjusting it in a
 bearing in which a receiving level is maximum and a program tracking
 method of changing the bearing of an antenna based upon the estimated
 information of a satellite orbit are known.
 For a method of supporting a mobile antenna, Az-EL mounting in which the
 azimuth angle and the elevation angle of the mobile antenna are shifted
 and XY mounting which the mobile antenna is shifted in a direction
 perpendicular to a satellite orbital direction are widely known. The Az-EL
 mounting is currently the most adopted method, one axis (the azimuth axis)
 is arranged perpendicularly to the ground and the other axis (the
 elevation axis) is arranged horizontally. In the XY mounting, the x-axis
 horizontal with the ground is perpendicular to the y-axis and the y-axis
 is turned together with the x-axis. The XY mounting is suitable for
 tracking a LEO satellite which moves near the zenith at high speed,
 however, as both axes are located in high positions from the ground, the
 XY mounting has a mechanical defect.
 Next, referring to the drawings, the satellite tracking technique of an
 antenna of a conventional type concrete earth station will be described.
 FIG. 13 shows the constitution of a conventional type antenna of an earth
 station for tracking a satellite. FIG. 13 shows an example of a
 large-sized antenna of an earth station for tracking a satellite and the
 main reflector is Cassegrainian antenna 13 m in diameter. The antenna
 tracks a satellite using a driving mechanism according to Az-EL mounting,
 and both the azimuth axis and the elevation axis are driven by a jackscrew
 driving mechanism. To simplify structure, the driving mechanism is allowed
 to continuously drive only within a range of .+-.10.degree. in the
 direction of an azimuth and a limited driving method that when an antenna
 is required to be directed at a larger angle in another direction, a set
 screw is loosened and the antenna is turned slowly is adopted. For the
 elevation axis, continuous driving between 0.degree. and 90.degree. is
 enabled. A primary feed is attached to the main reflector and is
 integrally driven with the main reflector.
 FIG. 14 shows another conventional type antenna of an earth station for
 tracking a satellite and a small-sized antenna of an earth station for
 tacking a satellite in which miniaturization and lightening are realized
 though an aperture antenna is used as the above large-sized antenna is
 known.
 FIG. 14 shows a parabolic antenna used for a ship earth station according
 to International Maritime Satellite Organization (INMARSAT) standard A,
 and a cross dipole and a reflector are located in the focus of a reflector
 with a paraboloid as a primary feed. In the antenna, the reflector and the
 feed are also integrated. To track a satellite, the above parabolic
 antenna is driven using four-axes mounting obtained by combining the above
 Az-EL mounting and XY mounting.
 The above technique is described in "Guide to maritime satellite
 communication" written by Mr. Toshio Sato and published on Jul. 25, 1986
 by Institute of Electronics and Communication Engineers of Japan.
 As described above, technique for tracking a satellite used for the
 conventional type antenna for satellite communication can be effectively
 applied to a case in which a tracking range is relatively small as a
 geostationary satellite, however, the above conventional type antenna is
 not suitable for the above antenna for tracking and communicating with a
 LEO satellite for the following reasons:
 That is, in the conventional type antenna for satellite communication, as
 the primary feed and the reflector are integrated and turn an antenna in
 tracking a satellite, the antenna to be turned is heavy, a driving system
 is also large-sized, high-speed tracking is difficult and the area of a
 radome for housing the antenna is also increased. In a satellite
 communication system using LEO satellites, considering that multiple
 small-sized earth stations are installed in each home and others, the size
 of the whole antenna is required to be as small-sized as possible and as
 light as possible, and miniaturization and lightening are a large problem.
 Further, as the primary feed and the reflector are integrated and turn an
 antenna, a feeding system is required to be provided so that a radio
 frequency (RF) sending/receiving part such as a low noise amplifier and a
 high-frequency power amplifier is also mounted near the primary feed so as
 to stably feed to the primary feed also during turning, however, in this
 case, the weight of the antenna is also increased by the weight of the RF
 sending/receiving part.
 In this case, it is also conceivable that the RF sending/receiving part is
 separated from the reflector and fixed, however, to maintain stable
 connection independent of the displacement by turning of the feeding part,
 an electric supply line is required to be flexible, a rotary joint and
 others are required to be used and there is a problem that an antenna for
 satellite communication is complicated and high-priced.
 When a satellite being tracked in a certain orbit disappears from the north
 to the south because LEO satellites revolve in plural orbits, another
 satellite revolving in the same orbit is required to be tracked next. In
 this case, information communicated using the former satellite is required
 to be communicated using the latter satellite and hand over for
 instantaneously switching to the latter satellite is required.
 However, the above conventional type technique has a problem that it is
 difficult to provide hand over for switching to another satellite in the
 same orbit.
 SUMMARY OF THE INVENTION
 As described above, the object of the present invention is to provide an
 antenna for communicating with a low earth orbit satellite used for a
 small-sized earth station for communicating with multiple LEO satellites,
 which is small-sized and light, tracks a LEO satellite at high speed and
 further, is provided with hand over.
 To achieve the above object, an antenna for communicating with a low earth
 orbit satellite according to the present invention is based upon an
 antenna for communicating with a low earth orbit satellite used on the
 side of the ground in a satellite communication system using low earth
 orbit satellites and is characterized in that the above antenna
 mechanically tracks the above low earth orbit satellite using two offset
 aperture antennas (offset antennas) separated by predetermined distance.
 The above antenna according to the present invention is characterized in
 that it mechanically tracks a low earth orbit satellite by fixing the
 respective primary feeds of the above two aperture antennas and turning
 only the respective reflectors of the two aperture antennas based upon an
 azimuth axis and an elevation axis in a direction of a low earth orbit
 satellite. The above antenna according to the present invention is
 characterized in that an antenna feed line for respectively feeding the
 above two aperture antennas and an RF sending/receiving part connected to
 the above antenna feeding part for sending or receiving a high-frequency
 signal by switching the above antenna feed lines are further provided. The
 above antenna feeding part and the RF sending/receiving part are
 characterized in that they are both mounted between the above two aperture
 antennas.
 Further, concretely, the antenna for communicating with a low earth orbit
 satellite according to the present invention is based upon an antenna for
 communicating with a low earth orbit satellite used on the side of the
 ground in a satellite communication system using low earth orbit
 satellites and is characterized in that two reflectors the respective
 centers of which are separated by predetermined distance and which
 respectively have a predetermined offset paraboloid, two Az-EL mounts
 respectively connected to the above reflectors for turning the respective
 reflectors based upon an azimuth axis and an elevation axis and tracking a
 low earth orbit satellite, two primary feeds for radiating predetermined
 beams to the respective reflectors, two feed lines for respectively
 feeding to the above primary feeds and respectively supporting the primary
 feeds so that each primary feed can be fixed independently of the
 reflectors and an RF sending/receiving part connected to the above feed
 lines for sending or receiving a high-frequency signal by selecting either
 are provided.
 The above antenna according to the present invention is characterized in
 that the value of the above offset is set so that antenna gain is maximum
 at a predetermined minimum operational elevation angle.
 The above antenna according to the present invention is also characterized
 in that the above predetermined minimum operational elevation angle is the
 limit of tracking in the direction of the elevation angle of the above low
 earth orbit satellite and is determined based upon the altitude of the
 above low earth orbit satellite and the number of satellites arranged in
 the same orbit.
 Any of an offset parabolic antenna, an offset Cassegrainian antenna and an
 offset Gregorian antenna is used for the above antenna.
 The above azimuth axis is an axis turned around a straight line connecting
 the center of the above reflector and the center of the above primary feed
 and the above elevation axis is an axis which is in contact with a line
 perpendicular to a radial straight line passing the paraboloid of an
 offset reflector from an intersection point (the center) of the axis of
 the paraboloid and the paraboloid on the paraboloid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Next, referring to the drawings, a first embodiment of the present
 invention will be described in detail. FIG. 1 shows the constitution of an
 antenna for communicating with a low earth orbit satellite according to
 the present invention.
 As shown in FIG. 1, an antenna for communicating with a low earth orbit
 satellite 100 according to the present invention is provided with two
 aperture antennas respectively mainly composed of a fixed primary feed and
 a mobile offset reflector. The reason why the two aperture antennas are
 used is that two satellites in the same orbit are required to be tracked
 and handed over in a system using low earth orbit satellites though the
 details are described later.
 A first aperture antenna is composed of a primary feed (horn) 1 for sending
 or receiving a signal mainly in Ka band, an offset reflector 3 provided
 with a predetermined paraboloid, an Az-EL mount 5 connected to the
 reflector 3 for turning an azimuth axis and an elevation axis and tracking
 a satellite and a feed line 7 for feeding to the primary feed 1. A second
 aperture antenna is composed of a primary feed (horn) 2 for sending or
 receiving a signal mainly in Ka band, an offset reflector 4 provided with
 a predetermined paraboloid, an Az-EL mount 6 connected to the reflector 4
 for turning an azimuth axis and an elevation axis and tracking a satellite
 and a feed line 8 for feeding the primary feed 2.
 The primary feeds 1 and 2 are respectively fixed using the feed lines 7 and
 8 and distance between the centers of both feeds is a fixed value D.
 Further, the feed lines 7 and 8 are connected to an RF sending/receiving
 part 9 composed of a low noise amplifier and a high-frequency power
 amplifier, either of both feed lines is selected and a high-frequency
 signal is sent or received.
 It is desirable that these feed lines 7 and 8 and the RF sending/receiving
 part 9 are mounted in a position between two aperture antennas to
 miniaturize the whole antenna and reduce loss in feeding.
 The whole antenna is fixed on a supporting part 10.
 Next, the constitution shown in FIG. 1 will be described.
 The primary feed 1 is installed in the focal position of a paraboloid
 forming the reflector 3. The offset quantity of the offset parabolic
 antenna is selected so that antenna gain is maximum at the minimum
 operational elevation angle described later. The primary feed 1 has
 constitution mechanically independent of the reflector 3 with mobile
 structure, is attached to the feed line 7 and fixed.
 Similarly, the primary feed 2 is installed in the focal position of a
 paraboloid forming the reflector 4 in a position separated by distance S
 from the center of the primary feed 1. The offset quantity of the offset
 parabolic antenna is selected so that antenna gain is maximum at the
 minimum operational elevation angle described later. The primary feed 2
 has constitution mechanically independent of the reflector 4 with mobile
 structure, is attached to the feed line 8 and fixed.
 As described above, the feed lines 7 and 8 are also provided with a
 function for respectively supporting the primary feeds 1 and 2 in addition
 to a feeding function. It is because the feed lines 7 and 8 can be fixed
 relatively easily without using a special supporting mechanism for
 respectively fixing the primary feeds 1 and 2 because the feed lines are
 respectively constituted by a waveguide.
 Although the primary feeds 1 and 2 are fixed, the reflectors 3 and 4 are
 respectively provided with structure turned based upon the azimuth axis
 and the elevation axis by the Az-EL mounts 5 and 6.
 The primary feeds 1 and 2 are connected to the RF sending/receiving part 9
 respectively via the feed lines 7 and 8 connected to the primary feeds. It
 is desirable to reduce loss in feeding that the RF sending/receiving part
 9 is installed near the primary feeds 1 and 2.
 FIG. 2 shows the configuration of the RF sending/receiving part 9. As shown
 in FIG. 2, the feed lines 7 and 8 are connected to the RF
 sending/receiving part 9 and either is selected by an RF switch 91
 according to an antenna switching control signal. A diplexer 92 is
 connected to the output of the RF switch 91 to separate a sent signal and
 a received signal. That is, for a sent signal, a sent signal input via the
 RF switch is amplified by a power amplifier 96 after the sent signal is
 converted to a required high frequency in Ka band by a sending local
 section 90 and a sending mixer 98 and is input to the diplexer 92 via a
 lowpass filter 94. In the meantime, output from the diplexer 92 is input
 to the low noise amplifier 95 via the lowpass filter 93, is converted to a
 high frequency by a receiving mixer 97 and a receiving local section 99
 and high-frequency output can be obtained.
 FIGS. 3A and 3B explain the tracking mechanism of this antenna and
 particularly shows the reflector 3 and the primary feed 1 respectively
 related to tracking. Offset antennas with parabolic reflectors are both
 used for the first and second aperture antennas of this antenna. As each
 of the offset antennas with parabolic reflectors has common structure, it
 is described only using the primary feed 1 and the reflector 3, however,
 the combination of the primary feed 2 and the reflector 4 is constituted
 similarly.
 FIG. 3A shows the reflector 3 and the primary feed 1 viewed from a front, a
 full line shows the position of the reflector 3 at the minimum operational
 elevation angle .theta. MIN and a dotted line shows the position of the
 reflector 3 in case an elevation angle is approximately 90.degree.. FIG.
 3B shows the reflector 3 and the primary feed 1 respectively viewed from
 the side. As also clear from these drawings, an azimuth axis 11 is turned
 around a straight line connecting the center of the reflector 3 and the
 center of the primary feed 1 and the reflector 3 is turned 360.degree.
 with the azimuth axis 11 in the center. A reference number 13 denotes the
 axis of a paraboloid.
 In the meantime, FIG. 4 explain an elevation axis 12 and the elevation axis
 12 in these drawings means an axis which is in contact with a line
 perpendicular on a paraboloid to a radial straight line passing the
 paraboloid of the offset reflector 3 from an intersection point (the
 center) of the axis 13 of the paraboloid and a paraboloid 14. An angle
 varies between the minimum operational elevation angle and 90.degree. with
 the elevation axis in the center.
 The Az-EL mount 5 drives the reflector 3 so that the reflector 3 is turned
 around the azimuth axis 11 and the elevation axis 12 to track a satellite.
 Therefore, the primary feed 1 is always fixed in the focal position of the
 paraboloid even if the reflector 3 is turned because the primary feed is
 fixed by the supporting part 10.
 As described above, the antenna for communicating with a low earth orbit
 satellite according to the present invention turns the reflectors 3 and 4
 around the azimuth axis and can track a satellite in the omnibearing. The
 elevation angle showing directivity can be varied by turning the
 reflectors 3 and 4 around the elevation axis and directivity in the
 direction of the zenith at which the elevation angle is 90.degree. can be
 obtained.
 Next, a required range of tracking angles of the above antenna for
 communicating with a low earth orbit satellite will be described.
 FIG. 5 is an imaginative drawing showing that multiple LEO satellites are
 arranged on plural orbital planes over the earth to cover the whole world.
 As shown in FIG. 5, a satellite communication system for covering the
 whole world is provided by arranging multiple LEO satellites over the
 earth so that any satellite can be seen in any place on the earth.
 A LEO satellite means a satellite on an elliptical orbit including a
 circular orbit at the altitude of approximately 1500 km over the ground or
 less and assuming that the orbital period of each satellite is 1000 km at
 altitude, each satellite revolves over the earth in approximately one hour
 and forty-five minutes.
 Assuming that the altitude of a satellite is 765 km and the minimum
 operational elevation angle is 30.degree., the number of satellites to be
 arranged on the same orbital plane is 20 and ten orbital planes are
 required to cover the whole world. That is, the total number of required
 satellites is 200. The number of the required satellites is determined
 based upon the altitude and the minimum operational elevation angle of
 satellites and even if satellites are at the same altitude, the number of
 required satellites is 98 if the operational elevation angle is 20.degree.
 and the number of required satellites is 45 if the operational elevation
 angle is 10.degree..
 FIG. 6 is a conceptual drawing showing a wide-band satellite communication
 system provided using LEO satellites. As shown in FIG. 6, in this system,
 a low-speed channel of approximately 64 kbps using multi-beams in L band
 (1.5 to 1.6 GHz) is provided to a small-sized user such as a portable
 terminal and high speed data is provided to a large-sized user such as a
 ship, an airplane and a small-scale office using multiple spot beams in Ka
 band (generally called a quasi-millimeter wave band and 20 to 30 GHz) at a
 small-sized earth station.
 The present invention relates to the antenna for communicating with a low
 earth orbit satellite used at a small-sized earth station mainly for the
 latter user of high-speed data.
 FIG. 7 shows a satellite tracking range in case a LEO satellite provided
 with an orbital plane 16 (FIG. 7 shows only three LEO satellites 1, 2 and
 3 to simplify) is viewed from a small-sized earth station 15 on the ground
 mounting the antenna for communicating with a low earth orbit satellite
 according to the present invention. As shown in FIG. 7, the minimum
 operational elevation angle .theta. MIN is determined based upon
 relationship between the number of LEO satellites and altitude as
 described above and the satellite tracking range 12 is equivalent to an
 area shown by an oblique line, that is, the whole area in the omnibearing
 from the minimum operational elevation angle .theta. MIN to the zenith.
 Also, as shown in FIG. 7, for the state of the satellites 1, 2 and 3 in
 the satellite tracking range 17, the satellite 1 moves from inside the
 tracking range to outside the tracking range, the satellite 2 exists in
 the zenith and the satellite 3 moves from outside the tracking range to
 inside the tracking range. For example for the two aperture antennas of
 this antenna, the first aperture antenna tracks the satellite 1 and the
 second aperture antenna tracks the satellite 2. The RF switch 91 selects
 the side of the satellite 1. Afterward, simultaneously when the satellite
 1 moves outside the tracking range, the RF switch 91 selects the side of
 the satellite 2 and the first aperture antenna tracks the satellite 3 in
 place of the satellite 1.
 As described above, hand over is realized by tracking a revolving
 satellite, alternately selecting the two aperture antennas.
 Next, FIG. 8 shows relationship between propagation loss (A) composed of
 free-space loss based upon an elevation angle and loss due to attenuation
 by rainfall and the gain of the offset parabolic antenna (B). FIG. 8 also
 shows the sum of propagation loss (A) and the gain of the antenna (B),
 that is, the total propagation loss (C=A+B) including antenna gain. In
 FIG. 8, the minimum operational elevation angle .theta. MIN is set to
 40.degree.. The quantity of an offset is adjusted so that antenna gain is
 maximum at the elevation angle and propagation loss is calculated using a
 sending frequency 30 GHz in Ka band.
 FIG. 8 shows that as a result, the total propagation loss is the largest at
 the minimum operational elevation angle 40.degree. and as an elevation
 angle approaches the zenith, the total propagation loss decreases.
 The reason is that directional gain in the direction of the zenith is low
 because it is off from the ideal condition of an offset parabolic
 reflector, however, in satellite communication in a microwave band, a
 millimeter wave band and others, antenna gain is required because a
 satellite is the farthest, free-space loss is increased, distance passing
 a rain-fall area is the longest and the quantity of attenuation by
 rainfall is the most when an elevation angle is small, while in the
 direction of the zenith, the above attenuation is the least.
 Therefore, problems can be really decreased by setting a suitable value as
 the minimum operational elevation angle even if an elevation angle is set
 to a direction of the zenith.
 Next, referring to FIG. 9, large distance S between the two aperture
 antennas which has an effect upon the size of the antenna according to the
 present invention will be described. FIG. 9 shows a case that the two
 aperture antennas according to the present invention are arranged in
 parallel. "D" denotes a diameter of the offset reflector and to simplify,
 each diameter of the two aperture antennas is set to the same value. An
 angle .phi. denotes an angle between the reflector and a horizontal plane.
 In a case shown in (1), the minimum value of distance S between the centers
 of the two reflectors as shown in FIG. 9 under a condition on which
 blocking is not caused is as shown in (2).
 .phi.=(90.degree.-.theta.MIN)/2 (1)
EQU S=D (cos .theta.+sin .theta./tan .theta.MIN) (2)
 The first embodiment of the present invention using the offset parabolic
 antenna is described above, however, the present invention is not limited
 to such an antenna provided with a single reflector.
 That is, for a second embodiment of the present invention, an offset
 Cassegrainian antenna provided with plural reflectors shown in FIG. 10 may
 be also used.
 As shown in FIG. 10, reference numbers 21 and 22 respectively denote a main
 reflector having a paraboloid and as described above, a predetermined
 offset is applied to the main reflector so that the maximum antenna gain
 is obtained at the minimum operational elevation angle. Reference numbers
 23 and 24 respectively denote a deputy reflector formed by a hyperboloid
 of revolution sharing the focus of a paraboloid as one focus. As another
 focus of the hyperboloid of revolution is located in each area of the main
 reflectors 21 and 22, circular holes 25 and 26 for radiating beams from
 primary feeds 1 and 2 are respectively provided to the main reflectors 21
 and 22. As the other reference numbers are similar to those shown in FIG.
 1, the description is omitted.
 In this embodiment, as an antenna provided with plural reflectors is
 adopted as each offset antenna, the structure of the antenna is
 complicated, however, effect that loss in feeding is reduced, connection
 to a sending/receiving part is facilitated and blocking in a tracking
 range is prevented is produced because the primary feeds 1 and 2
 respectively feed from the rear surface of the main reflectors 21 and 22.
 Further, for a third embodiment of the present invention, anther type
 offset Cassegrainian antenna provided with plural reflectors shown in FIG.
 11 may be also used. In this embodiment, the offset Cassegrainian antenna
 provided with plural reflectors shown in FIG. 10 is also used, however,
 this embodiment is different from the second embodiment in that each
 position of primary feeds 1 and 2 is outside each area of main reflectors
 21 and 22.
 Further, for a fourth embodiment of the present invention, an offset
 Gregorian antenna provided with plural reflectors shown in FIG. 12 may be
 also used. In this embodiment, a predetermined offset is applied to main
 reflectors 25 and 26 having a paraboloid so that the maximum antenna gain
 is obtained at the minimum operational elevation angle. Deputy reflectors
 27 and 28 respectively have an ellipsoid of revolution sharing the focus
 of the paraboloid. The center of each phase of primary feeds 1 and 2 is
 located in another focus of the ellipsoid of revolution.
 According to the constitution described in the above second to fourth
 embodiments using the antenna provided with plural reflectors, loss in
 feeding is further reduced, the primary feed is fixed and the height of
 the whole antenna is further reduced, compared with the antenna in the
 first embodiment.
 As described above, the antenna for communicating with a low earth orbit
 satellite according to the present invention produces the following
 effect:
 First, the best characteristics can be obtained at the minimum elevation
 angle at which propagation loss and attenuation by rainfall are the
 largest in a channel to a satellite by optimizing the side lobe
 characteristic of the antenna and the cross-polarized electromagnetic
 radiation isolation because the two offset parabolic antennas in which the
 maximum gain is obtained at the minimum operational elevation angle are
 used. Particularly, the above effect is remarkable because a LEO satellite
 uses a microwave band and a millimeter wave band and attenuation by
 rainfall is large.
 Second, as the primary feed is fixed, a flexible part is not required for a
 feeder and a waveguide, the structure is simplified and the reliability
 can be enhanced.
 Third, as a part driven for tracking a satellite is only the reflector,
 driven weight is small, tracking at high speed is enabled and the driving
 mechanism can be miniaturized and lightened.
 Fourth, as the mobile two aperture antennas are used based upon an azimuth
 axis and an elevation axis, plural LEO satellites on the same orbital
 plane are sequentially tracked and hand over among the satellites is
 enabled.