U.S. patent application number 09/885021 was filed with the patent office on 2001-11-15 for overhead system of inclined eccentric geosynchronous orbiting satellites.
This patent application is currently assigned to Hughes Electronics Corporation. Invention is credited to Cellier, Alfred.
Application Number | 20010041950 09/885021 |
Document ID | / |
Family ID | 22884148 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041950 |
Kind Code |
A1 |
Cellier, Alfred |
November 15, 2001 |
Overhead system of inclined eccentric geosynchronous orbiting
satellites
Abstract
A system of inclined geosynchronous satellite orbits has a
service area defined on a surface of the earth. The service area
has elevation angles greater than a predetermined minimum elevation
angle from the horizon. A satellite has an orbit with respect to
the earth having a sky track when viewed from within said service
area. An operating arc is defined by a subset of points on the sky
track within the service area. The satellites operate consecutively
on the operating arc.
Inventors: |
Cellier, Alfred; (Rancho
Palos Verdes, CA) |
Correspondence
Address: |
HUGHES ELECTRONICS CORPORATION
PATENT DOCKET ADMINISTRATION
BLDG 001 M/S A109
P O BOX 956
EL SEGUNDO
CA
902450956
|
Assignee: |
Hughes Electronics
Corporation
|
Family ID: |
22884148 |
Appl. No.: |
09/885021 |
Filed: |
June 20, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09885021 |
Jun 20, 2001 |
|
|
|
09235112 |
Jan 21, 1999 |
|
|
|
Current U.S.
Class: |
701/13 ;
244/158.4 |
Current CPC
Class: |
H04B 7/195 20130101 |
Class at
Publication: |
701/13 ;
244/158.00R |
International
Class: |
B64G 001/00 |
Claims
What is claimed is:
1. A system of inclined geosynchronous satellite orbits above a
landmass comprising: a service area on a surface of the earth
having a predetermined minimum elevation angle from the horizon; a
satellite having an orbit with respect to the earth having sky
track when viewed from within said service area; and an operating
arc defined by a subset of points on said sky track over said
service area, said satellite operating on said operating arc.
2. A system as recited in claim 1 wherein said orbit has a
predetermined inclination with respect to an equatorial plane of
the earth.
3. A system as recited in claim 1 wherein said orbit has a
predetermined eccentricity.
4. A system as recited in claim 3 wherein said orbit has an
eccentricity factor between about 0.1 and 0.5.
5. A system as recited in claim 1 wherein said minimum elevation
angle is greater than thirty degrees.
6. A system as recited in claim 1 wherein said minimum elevation
angle is greater than sixty degrees.
7. A system as recited in claim 1 wherein in said orbital track
having an apogee and a perigee, said apogee is over said service
area.
Description
[0001] This application is a continuation of application Ser. No.
09/235,112, filed Jan. 21, 1999 (CPA pending).
TECHNICAL FIELD
[0002] The present invention relates generally to an overhead
system of inclined eccentric geosynchronous orbit satellite orbits
and, more particularly, to a satellite system whose operation is
concentrated overhead as viewed from within a service area.
BACKGROUND OF THE INVENTION
[0003] Satellites in geostationary orbits (GSOs) have been widely
preferred for several decades because of the economic advantages
afforded by such orbits. In a geostationary orbit, a satellite
traveling above the Earth's equator, in the same direction as that
in which the Earth is rotating, and at the same angular velocity,
appears stationary relative to a point on the Earth. These
satellites are always "in view" at all locations within their
service areas, so their utilization efficiency is effectively 100
percent. Antennas at Earth ground stations need be aimed at a GSO
satellite only once; no tracking system is required.
[0004] Coordination between GSO's and with terrestrial services is
facilitated by governmental allocation of designated "slots"
angularly spaced according to service type. Given the desirability
of geostationary satellite orbits and the fact that there are only
a finite number of available "slots" in the geostationary "belt,"
the latter capacity has been essentially saturated with satellites
operating in desirable frequency bands up through the Ku-band (up
to 18 GHz). As a result, the government has been auctioning the
increasingly scarce remaining slots.
[0005] This has encouraged the development of complex and expensive
new systems including those using low Earth orbits (LEO's), medium
Earth orbits (MEO's), and/or higher frequencies, for example, the
Ka band (up to approximately 40 GHz). Growth to higher frequencies
is limited by problems of technology and propagation, and expansion
in satellite applications requires exploitation of the spatial
dimension (i.e., above and below the GSO belt). A host of proposed
LEO and MEO systems exemplify this direction. A drawback of LEO and
MEO systems for users is the relative uncertainty of satellite
position, and rapid motion, leading typically to the use of
omnidirectional antennas having low gain, which limits data
rate.
[0006] Highly elliptical orbits (HEO) such as the 12-hour "Molniya"
long used by Russia, and the European Space Agency's 8-hour
"Archimedes" have been used. HEO's disadvantages include a shorter
fraction of service to a given area (fractionally geosynchronous
period causes multiple nodes over the earth) and require specific
63.degree. inclination (to minimize fuel requirements due to low
perigee). LEO, MEO, and HEO systems require more satellites for
coverage at a specified elevation angle to a single service area
than does the present invention.
[0007] Another apparent drawback to the use of all inclined orbits
is that of relative movement with respect to the ground. For wide
bandwidths, two-dimensional tracking ground station antennas would
be required. Tracking antennas are relatively expensive and thus
are not considered for consumer applications.
[0008] There has been no known prior effort to exploit overhead
systems of inclined eccentric geosynchronous orbits (IEGOs) in a
systematic manner, even though the unused domain of inclined
eccentric geosynchronous orbits offers great potential for the
coordinatable growth of satellite service.
[0009] While the various prior systems function relatively
satisfactorily and efficiently, none discloses the advantages of
the overhead system of inclined, eccentric geosynchronous satellite
orbits in accordance with the present invention as is hereinafter
more fully described.
DISCLOSURE OF THE INVENTION
[0010] The present invention provides a satellite system that takes
advantage of inclined eccentric geosynchronous orbits to provide
relatively low cost satellite service particularly suitable for
consumer markets.
[0011] The present invention also provides a satellite system with
continuous coverage of the service area using a synchronized set of
two or more satellites.
[0012] In one aspect of the invention, a synchronized system of
inclined eccentric geosynchronous satellite orbits (IEGO) has a
service area defined on a surface of the earth. The service area is
defined with elevation angles greater than a predetermined minimum
from the horizon, from anywhere within the service area to the
satellite system. An IEGO satellite has an orbit with respect to
the earth having an orbital sky track fixed in the sky when viewed
from within said service area. Of course, the sky track has a
ground track which corresponds thereto. An operating arc is defined
by a subset of the orbital sky track over the service area. The
satellites of the set operate successively on the operating arc
portion of the sky track.
[0013] An advantage is that the overhead system can provide
continuous high elevation coverage, with handover to another
satellite phased in the same track. Another advantage of the
present invention is that it allows the use of conical-pattern
upward-looking user antenna rather than a tracking antenna.
[0014] The objects, advantages and features of the present
invention are readily apparent from the following detailed
description of the best mode for carrying out the invention when
taken in connection with the accompanying drawings and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A more complete appreciation of the invention and many of
the attendant advantages and features thereof may be readily
obtained by reference to the following detailed description when
considered with the accompanying drawings in which like reference
characters indicate corresponding parts in all the views,
wherein:
[0016] FIG. 1 is a perspective view of an inclined elliptic
geosynchronous orbit, an inclined geosynchronous orbit, and a
geostationary (IEGO) orbit with respect to the earth. The latter
two orbits are for reference only.
[0017] FIG. 2 is a perspective view similar to that of FIG. 1 five
hours later in time.
[0018] FIG. 3 is a perspective view of an alternative embodiment
according to the present invention in which two IEGO orbit planes
are established so that a phased pair of satellites will follow
each other in a common ground or sky track.
[0019] FIG. 4 is an equirectangular projection map showing a
typical ground track associated with the present invention.
[0020] FIG. 5 is a upward looking view of an operating arc of the
IEGO system of FIG. 4.
[0021] FIG. 6 is a perspective view of a upward receiving cone with
respect to an antenna in one application of the invention.
[0022] FIG. 7 is a skyward plot of a two IEGO system having an
eccentricity of 0.463 from five locations in the continental
U.S.
[0023] FIG. 8 is a variation of FIG. 7 having an eccentricity of
0.31.
[0024] FIG. 9 is a skyward plot of a three IEGO system having an
eccentricity of 0.505.
[0025] FIG. 10 is a skyward plot of a three IEGO system having an
eccentricity of 0.203.
[0026] FIG. 11 is a skyward plot of a two IEGO system having an
eccentricity of 0.24.
[0027] FIG. 12 is a plot of elevatnion angle in degrees versus
eccentricity comparing an IEGO system and a Molniya system.
[0028] FIG. 13 is a directivity versus eccentricity plot comparing
an IEGO system and a Molniya system.
[0029] FIG. 14 is a plot of elevation angle in degrees versus
eccentricity comparing an IEGO system and a Molniya system.
[0030] FIG. 15 is a directivity versus eccentricity plot comparing
an IEGO system and a Molniya system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS(S)
[0031] The present invention is illustrated herein in terms of a
satellite orbit system using various inclination angles,
eccentricity values and other values. It should be understood that
specific numerical values are introduced as examples and not as
final design values.
[0032] The essence of the invention is the establishment of
inclined, preferably geosynchronous, satellite orbits with
repeating ground tracks on the earth are whose sky tracks include
operating arcs which are confined to a fixed one over the service
area.
[0033] In the present invention, (24 hour), inclined elliptic
geosynchronous orbits (IEGO) satellites enable operation to provide
high elevation angle service for a predetermined service region on
a landmass with possible spectrum re-use for small service
areas.
[0034] Referring now to FIG. 1, Earth 10 is shown with an inclined
eccentric geosynchronous orbit (IEGO) 12 that has an IEGO satellite
14. IEGO orbit 12 is shown in contrast to an inclined
geosynchronous orbit (IGO) 16. IGO orbit 16 is an inclined circular
orbit centered about the Earth 10. IGO orbit 16 has an IGO
satellite 18 in a first position, which is used for reference. A
geostationary (GSO) orbit 20 is also shown for contrast and has a
GSO satellite 22. Each of the satellites 14, 18 and 22 follow their
respective orbits 12, 16, 20 as they travel around Earth 10.
[0035] FIGS. 1 and 2 illustrate some general differences between a
GSO, an IGO and an IEGO orbit. In this example, GSO orbit 20 has a
radius R. GSO orbit 20 is defined on the equatorial plane of Earth
10. As Earth 10 rotates daily, GSO satellite 22 maintains a
substantially constant position over the Earth. As seen from a
point on the Earth, the elevation angle of the satellite is
constant.
[0036] IGO orbit 16 also has a radius R that is the same as that of
GSO orbit 20. IGO orbit 16 is disposed on a plane that has an
inclination angle 24 with respect to the equatorial plane having
GSO orbit 20. The plane defined by IGO orbit 16 and GSO orbit 20
intersect at a line of nodes 26 that extends through the center of
Earth 10. IGO satellite 18 and GSO satellite 22 take one sidereal
day (23 hours, 56 minutes) to complete an orbit. The elevation
angle of an IGO orbit with respect to a point on the Earth depends
on the position of IGO satellite 18 in its IGO orbit 16.
[0037] IEGO orbit 12 has an apogee 28 being set at the northernmost
point of the orbit when viewed with respect to the Earth and an
perigee 30 being the southernmost point of the orbit when viewed
with respect to the Earth. IEGO in elliptical orbit 12 has a focus
that is shifted from that of IGO orbit 16 so that apogee 28 is
shifted in the direction of the northern hemisphere. Consequently,
perigee 30 is shifted toward the southern hemisphere. Thus, the
altitude of apogee 28 above the surface of the Earth is increased
while the elevation of the perigee 30 is decreased. The major
diameter of IEGO orbit 12 is 2R as in the case of an IGO orbit 16.
IEGO orbit 12 is, however, shifted with respect to the center of
IGO orbit 16 by an eccentricity factor e. Thus, the distance of the
apogee 28 from line of nodes 26 is given by the formula (1+e)R. The
distance of perigee 30 from the line of nodes 26 is given by the
formula (1-e)R.
[0038] A ground track 32 on the surface of Earth 10 may be
developed from IEGO satellite 14. Ground tracks are imaginary lines
representing the loci of subsatellite points that are repeatedly
traced on the surface of the Earth by lines extending from the
center of the Earth to orbiting satellites. IEGO ground tracks are
located at specified longitudes and retrace repeatedly each
sidereal day (23 hr. 56 min.).
[0039] The position of satellites 14, 18, 22 are shown about five
hours later in FIG. 2 from that shown in FIG. 1. The Earth has thus
rotated with respect to the orbits. Correspondingly, the elevation
angle with respect to IGO satellite 18 and IEGO satellite 14 also
changes.
[0040] Referring now to FIG. 3, a second IEGO orbit 12' is shown
having an IEGO satellite 14'. IEGO orbit 12' also has an
inclination angle 24'. The inclination angle 24' and phasing are
chosen so that the satellite placed in IEGO orbit 12' substantially
traces the same ground track 32 as the satellite in IEGO orbit 12.
The IEGO satellites 14, 14' are positioned so that as one satellite
is leaving a service area, the other satellite is entering the
service area. In this manner, continuous coverage may be provided
to a particular service area.
[0041] Although not illustrated, the above example may be extended
to three or more planes of IEGO orbits all synchronized so that
continuous coverage may be provided to a service area within
corresponding similar cones. More satellites may be required if a
larger service area or a higher elevation angle within the service
area is desired. By providing service at high elevation angles,
applications in fixed satellite service, broadcast satellite
service, or mobile satellite service may be more efficiently
realized. Thus, a synchronized overhead IEGO system is generally
indicated by reference numeral 34.
[0042] Referring now to FIG. 4, an equirectangular-projection map
36 shows North America and a substantial portion of South America.
An example ground track 32 is shown that is projected from an IEGO
orbit. The inclination of the ground track is 63.45.degree. and has
an eccentricity value e equal to 0.240 and is centered
symmetrically on 96.degree. west longitude (ascending at
69.0.degree. west) and has an argument of perigee of 270.degree..
Two similar satellites, A & B, are shown sharing ground track
32 and are separated by a half a period. Active satellite A is
about to start operation as it rises through a eastern handover
point 38 (latitude, longitude=24.0N, 83.0W). Satellite B is
concurrently setting through an western handover point 40
(latitude, longitude=24.0N, 109.0W). At the time when satellite A
will set in the west, Earth stations 42 will again communicate with
satellite B rising in the east. The distance between eastern
handover point 38 and western handover point 40 is defined as the
operating arc 44. The operating arc 44 is the portion of the ground
track or a portion of the sky track (which remains in a cone
overhead), when viewed from a point on the ground, over which the
satellites operate.
[0043] Referring now to FIG. 5, a skyward looking plot of the
orbital path as seen from the center of the service area as shown
in FIG. 4 is illustrated. On this plot, 0.degree. represents the
horizon while 90.degree. represents the zenith over a particular
point on the landmass. Handover points 38, 40 and operating arc 44
are also shown in skyward plot 46. A plot of the geostationary belt
48 is illustrated to contrast the inclined eccentric geosynchronous
orbit.
[0044] Referring now to FIG. 6, a ground based user unit such as a
mobile satellite receiving antenna 50 is positioned on an
automobile 52. Thus, one advantage of the present invention is
illustrated. That is, the present invention is suitable for mobile
applications such as an automobile because a generally planar
antenna 50 may be provided to receive signals from IEGO satellite
14 overhead. Cone 54 is directed in an upward direction toward the
zenith. Because the elevation angle may be controlled, a relatively
narrow cone 54 having a cone angle 55 may be generated by antenna
50 in an upward direction. This configuration provides higher gain
than an omnidirectional antenna. The high elevation angles 51 from
the horizon 53 of the system are more amenable to urban operation
and being less affected by multi-path effects and atmospheric
losses. No steering is required if an antenna providing an upward
cone is provided that receives satellite signals throughout the
service area.
[0045] Referring now to FIG. 7, a skyward plot 58 is shown having
an operating arc at about 45.degree. or more in elevation angle
above the horizon at (0.degree. elevation angle) from each of five
cities within the continental United States service area. The
cities were chosen to provide a representative view from
essentially four corners of the continental United States and the
center of the United States. Also plotted is the geostationary belt
as seen from Miami and Seattle. Orbital parameters have been chosen
to extend to maximize the minimum elevation angle for plots 62a for
all the cities within the service area. Plots 62a of FIG. 7 use two
IEGO satellites with orbital eccentricity of 0.43 and an
inclination angle of 63.45.degree. resulting in a minimum elevation
angle of 46.9. These plots are subsets of points on the operating
arc portion 62 of the orbital track within the service area. Plots
62a are shown in contrast to GSO belts 63 as viewed from Miami and
Seattle.
[0046] Referring now to FIG. 8, plots 62b similar to that of FIG. 7
are shown having an eccentricity of 0.31, an inclination angle of
50.degree. for a two-IEGO satellite system resulting in a minimum
elevation angle of 39.1.degree..
[0047] Referring now to FIG. 9, plots 62c having eccentricity of
0.505 and an inclination angle of 63.45.degree. are illustrated for
a three-IEGO satellite system resulting in a minimum elevation
angle of 46.9.degree..
[0048] Referring now to FIG. 10, plots 62d having an eccentricity
of 0.203 and an inclination angle of 50.degree. are illustrated for
a three-IEGO satellite system resulting in a minimum elevation
angle of 59.2.degree..
[0049] Referring now to FIG. 11, plots 62e having an inclination
angle of 63.45.degree. and an eccentricity of 0.24 are illustrated
for a two-IEGO system resulting in a minimum elevation angle of
45.1.degree..
[0050] Thus, it can be observed that by changing the eccentricity
values and the angle of inclination values, the shapes of the
operating arc may be substantially changed to center the operating
arc and maximize the minimum elevation angle within the service
area.
[0051] Smaller eccentricity is preferred for the advantages of the
more circular orbit, with small impact on the minimum elevation
angle. In the case of the smaller service area such as a single
state or city, the optimum eccentricity may differ from that of the
larger service area. Thus, an optimum eccentricity may be between
0.1 and 0.5.
[0052] Referring now to FIG. 12, a plot of minimum elevation angle
in degrees versus eccentricity for an inclination of 63.45.degree.
is shown resulting in a minimum elevation angle of 63.45.degree..
Thus, the maximum of the minimum elevation angles occur as the
eccentricity is about 0.3 to 0.5 for IEGOs at this inclination.
[0053] Referring now to FIG. 13, the associated plot of geometric
directivity of the receiving antenna versus eccentricity is plotted
for a three IEGO system and a two IEGO system. As is shown, the
directivity is maximized for eccentricity of about 0.3 to 0.5.
[0054] Referring now to FIG. 14, the minimum elevation angle versus
eccentricity plot is shown for an inclination of 50.degree.. In
this case, near-maximum of the minimum elevation angle occurs for
eccentricity of about 0.2.
[0055] Referring now to FIG. 15, a plot corresponding to that of
FIG. 14 is shown for directivity in decibels versus eccentricity.
The directivity is maximized for eccentricity of about 0.2 to 0.3
for two IEGO and three IEGO systems.
[0056] In FIGS. 12 through 15, the curve of minimum elevation angle
for IEGO orbits is broad with maxima at low eccentricity. In
contrast, such curves for HEOs including Molniyas rise with
eccentricity, and peak at high eccentricity above 0.6.
Consequently, the combination of elevation angles and number of
satellites is more favorable for the more circular IEGO orbit of
this invention than for HEO systems previously employed.
[0057] In operation, for a particular landmass, a service area must
be defined on the surface of the Earth. A service area is defined
as a region (such as the continental U.S. or smaller such as a
city) which the satellite beams toward, with a predetermined
minimum elevation angle above the horizon of any point in the
service area. A satellite pair or a plurality of satellites sharing
the same ground track are launched above the surface of the earth
in an inclined eccentric geosynchronous orbit. The region of
operation of each of the satellites within the orbit is the
operating arc which is overhead of that service area on the Earth.
Thus, as the satellites traverse their orbits, a loci of points is
defined on the orbital track which define the service area and the
operating arc above the service area. It is preferred that as one
satellite is leaving the service area, a second satellite is
entering the service area. Handover points are defined as the
points where operation is changed from one satellite to another
satellite. Thus, by defining the service area as a region having a
relatively high elevation angle, better service coverage may be
provided by a less expensive antenna not requiring adjustments by
the user.
[0058] Orbital parameters are chosen to realize certain ground
track shapes. Consideration is given to specified constraints on
the service region, service area coverage, and coverage time.
[0059] While the invention has been described in detail, those
familiar with the art to which this invention relates will
recognize various alternative designs and embodiments for
practicing the invention as defined by the following claims.
* * * * *