Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
1999-12-23
2004-02-24
Eldred, J. Woodrow (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C455S427000, C455S429000, C455S430000
Reexamination Certificate
active
06695259
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a communication system, and a communication sending and receiving device and a communication terminal in the system, and particularly to a communication system suitable for a satellite, a satellite orbit and a satellite orbit configuration algorithm usable in the field of communication and broadcast such as satellite communication, satellite broadcast, satellite mobile communication and in the field of observation with regard to a celestial body of the satellite traveling around, and suitable for a communication and broadcast system to which the satellite is applied, and a satellite communication sending and receiving device and a communication terminal in the system.
(a) The Prior Art with Regard to Setting of an Orbital Element (Argument of Perigee) of an Artificial Satellite
In a case where an artificial satellite is traveling around the earth as the center, the orbit of the artificial satellite always fluctuates under the influence of the nonuniformity of the earth's gravitational field, the attractive forces of the moon and the sun, the atmospheric drag and the sun's light pressure. From this viewpoint, the orbit of the artificial satellite traveling around the earth as the center can not be a circular orbit but is an elliptical orbit in a broad sense having a little eccentricity.
Accordingly, the “elliptical orbit” in the present specification is defined as an “orbit having an eccentricity larger than zero and smaller than 1, and the eccentricity is not intended to become zero in a process of setting an orbital element of the orbit onto which the artificial satellite is injected in order to attain the purpose”.
As an example of practically used artificial satellites having an elliptical orbit, there is the Molniya satellite (about a 12-hour orbital period) which has been used by Russia since the era of the former USSR. As artificial satellites having an elliptical orbit, a communication satellite called as Archimedes (about an 8-hour orbital period) is proposed in Europe. Further, a tundra orbit of about a 24-hour orbital period is proposed though it is not practically used yet. A common point in these satellites is that all the satellites has an orbital inclination angle of approximately 63.4 degrees.
In general, the perigee of an orbit on which an artificial satellite is traveling will rotate on the orbital plane under the influence of the nonuniformity of the earth's gravitational field (oblateness of the earth's shape). However, by setting an orbital inclination angle to 63.4 degrees in a mathematical model for calculating a time-varying rate of the argument of perigee, a multiplicative term becomes zero to make the time-varying rate zero. Therefore, it is considered that the rotation is stopped.
(b) The Prior Art with Regard to Orbit Configuration Methods for a Plurality of Artificial Satellites
Communication systems using a plurality of artificial satellites traveling on elliptical orbits have been in practical use and studied. Although arranging of a plurality of artificial satellites in the above-mentioned Molniya satellite and Archimedes is described, no detailed method of arranging the orbits is described.
Although in resent years a communication system using a plurality of artificial satellites is proposed, no detailed technique with regard to orbit configuration method is disclosed. Therefore, a detailed orbit configuration technique is required.
On the other hand, “an artificial satellite on an orbit having a long stretch of time staying in the zenith direction, a method of controlling the orbit and a communication system using the artificial satellite and the method” is proposed in Japanese Patent Application Laid-Open No.11-34996.
(c) The Prior Art with Regard to Mobile Communication and Broadcast to a Mobile Object
In the past, when a television broadcast was tried to receive in a mobile object such as a vehicle, there were problems in that the picture came out badly in an area far from a broadcasting facility of a television station, that screen flicker occurred even at a place near the broadcasting facility of the television station, and that receivable channel varied by moving. When a television broadcast from a communication and broadcast satellite on a stationary orbit was received on the mobile object, it was difficult to comfortably enjoy watching television on the mobile object because the electromagnetic wave was frequently shielded by artificial structures such as buildings, trees and natural geographical features.
Transmission of a large volume of data such as images from a mobile object such as an ambulance can not be performed by an existing ground communication infrastructure and an existing communication satellite.
In order to solve the above-mentioned problems, a method of setting orbital elements of an artificial satellite for transmitting a large volume of data to a mobile object such as a vehicle is proposed and in addition an orbital element of the artificial satellite is also proposed in Japanese Patent Application Laid-Open No.11-34996.
The problems in the prior art will be described below, corresponding to each of the above items (a), (b) and (c) based on examples known in the art.
(a) Problems with Regard to Setting of an Orbital Element (Argument of Perigee) of an Artificial Satellite, and an Object of the Present Invention
In the above mentioned Molniya satellite, Archimedes and Tundra orbit, all the orbital inclination angles of them are fixed to approximately 63.4. It seems that the main object is to suppress the rotation of the perigee on the orbit plane. On the other hand, there is an advantage in using an orbital inclination angle as large as approximately 63.4 degrees because the area using the above-mentioned artificial satellites is a higher latitude area such as Europe and Russia.
As for the location of Japan, the territory spreads from a middle latitude to a low latitude as Etorofu island in the northernmost end is situated in latitude approximately 45 degrees north and Okino-torishima in the southernmost end is situated in latitude approximately 20 degrees north. Therefor, when the orbital inclination angle of 63.4 degrees is employed as described above, the artificial satellite system becomes difficult to be used from the territory of Japan unless an altitude of the orbit is sufficiently high. Accordingly, when an orbit of an artificial satellite matching the location of the territory of Japan is taken into consideration, the orbital inclination angle can not help employing a value other than approximately 63.4 degrees, and consequently the perigee of orbit rotates.
In order to control the rotation of the perigee, propellent for controlling the rotation needs to be mount on the artificial satellite. An analytical simulation was performed on a case where the orbital inclination angle is 40 degrees and the eccentricity is 0.24 among the orbital elements proposed in, for example, Japanese Patent Application Laid-Open No.11-34996. As a result, it was found that an amount of the propellent for controlling the argument of perigee becomes dominant to the total amount of poropellent depending on a condition of setting the orbital elements because there occurs a case where the orbit control propellent of approximately 75% must be used at maximum for controlling the argument of perigee to nearly 270 degrees. Thereby, devices mountable on the artificial satellite may be reduced, or on-orbit lifetime of the artificial satellite may be shortened.
SUMMARY OF THE INVENTION
An object of the present invention is to set an argument of perigee of one of the six-orbital elements at a setting stage of the orbital elements of an orbit on which the artificial satellite travels in order to solve the above-mentioned problem.
(b) Problems with Regard to Orbit Configuration Methods for a Plurality of Artificial Satellites, and an Object of the Present Invention
Many communication systems which use an elliptical orbit of about a 270-degree argument of perigee and a
Hamano Nobuo
Ikeda Masahiko
Ito Masahiro
Maeda Toshihide
Nakamura Shigeki
Antonelli Terry Stout & Kraus LLP
Eldred J. Woodrow
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