1. Field of the Invention
The present invention relates to a method for acquiring a satellite, in particular to a method for acquiring a satellite, which allows reduction in search time and efficient searches in acquiring orbiting objects such as artificial satellites and space debris.
2. Description of the Related Art
In order to communicate with an artificial satellite, the satellite must first be acquired by an antenna. Generally, the antenna is driven in accordance with predicted values (azimuth or elevation angle) obtained based on orbital calculations for the acquisition.
Also, in acquisition at the launch of an artificial satellite, there are no predicted values based on orbital calculations. Thus, target orbital factors from the launch of the rocket are used instead.
However, the conventional method for acquiring a satellite using such predicted values involves errors in the predicted values. That is, according to the orbital calculation, it is impossible to accurately predict the amount of orbital degradation due to atmospheric resistance, which results in errors in predicted values.
Also, the method causes errors due to launch precision in addition to atmospheric resistance when lofting the artificial satellite into orbit.
Accordingly, in the method for acquiring a satellite by using such predicted values, the antenna needs to be basically directed in a direction based on predicted values, but also to be adjusted by performing some further search or operations.
Conventionally, accurate and fast satellite search, in consideration of such errors, can be achieved by virtually increasing the beam width of the antenna.
One of these methods is to provide a search mode as a drive mode for the antenna. This is a method for searching a region of expected maximum displacements with respect to rapidly changing predicted values by moving the antenna in a circle, a rectangle, or a zigzag.
Another method is accomplished by additionally building a small acquisition antenna having a beam in parallel with a main antenna beam. When an antenna with higher gain and thinner beam requires too much time for searches in the search mode, possible acquisition failures may result. Thus, this is a method for acquisition using an acquisition antenna with wider beams.
With the increase in antenna aperture or operational frequency in accordance with the increase in communication data rate, the antenna beams have become progressively narrow. On the other hand, since the deviation of orbits occurs without any relationship to frequencies and/or antenna beam width, the search range over which the antenna must scan relatively increased.
The acquisition antenna obtains lower gains and cannot have a larger effective aperture (wider beams) at a radio strength in accordance with a main antenna. Increases in effective aperture increase costs.
The present invention was made in order to overcome the above problem. Accordingly, it is an object of the present invention to provide a method for acquiring a satellite, which allows reduction in search time without increasing the effective aperture of the antenna by analyzing a satellite orbit from an acquisition viewpoint and narrowing the search range. Furthermore, it is an object of the present invention to provide a method for acquiring a satellite including precise measurements of the amounts of orbital errors at a level without any operational problems for easier satellite tracking thereafter.
A method for acquiring a satellite by using predicted values for a satellite according to an aspect of the present invention includes the steps of analyzing a behavior unique to a satellite orbit, calculating a search range based on the analysis, and searching the search range in accordance with the forecast value.
The satellite may be an artificial satellite, and the step for analyzing a behavior may include the step of analyzing a behavior unique to an orbit of the artificial satellite.
The xe2x80x9csatellitexe2x80x9d may be space debris, and the step for analyzing a behavior may include the step of analyzing the behavior of an orbit of space debris.
Furthermore, the forecast value may be corrected in consideration of the movement of an earth station due to the earth""s rotation.
In this case, a search range and a search speed may be determined arbitrary by using a corrected time amount used for correction calculation of the predicted value as a parameter for the search.
Furthermore, the search preferably includes horizontal and orbital plane searches within the search range.
Also, the method for acquiring a satellite may further include the steps of using a corrected time amount as a parameter for a correction calculation, detecting an optimum value of the parameter and fixing the parameter to the optimum value after a determination signal reaches a predetermined value.
Preferably, the method for acquiring a satellite further includes the steps of using an antenna angle error signal as the determination signal, and fixing the parameter to the optimum value after the antenna angle error signal is at a minimum.
Furthermore, the method for acquiring a satellite may further include the steps of using a receiving level of a receiver as the determination signal, and fixing the parameter to the optimum value after the antenna angle error signal is at a maximum.
In addition, the method for acquiring a satellite may further include the steps of calculating orbital factors to calculate predicted values and using an Epoch time of the orbital factors as a parameter for correction calculation.
Preferably, the method for acquiring a satellite further includes the steps of sending the calculated parameter for correction calculation to another earth station, which in turn corrects the predicted values by using the received parameter so as to search for the artificial satellite.
In accordance with the present invention, the search range is narrowed so that the search time can be reduced. A small antenna for acquisition does not need to be installed, which can reduce maintenance costs. Since the acquisition is not performed with a small antenna, it can be used for satellite acquisition using micro-power. Furthermore, the analysis of the behavior unique to the artificial satellite orbit provides an accurate search range with respect to the artificial satellite orbit, which can further reduce the search time. Also, the analysis of the behavior unique to the space debris orbit provides an accurate search range with respect to the artificial satellite orbit, which can further reduce the search time. In accordance with the present invention, correct predicted values can be obtained so that a satellite can be reliably acquired. Also, accurate satellite searches can be performed. After the parameter is fixed to an optimum value, the satellite search at steady state can be performed accurately. In this case, the parameter can be fixed to the optimum value by using a simple method. In addition, a parameter calculated based on an observation at one station can be used at the other earth station, which in turn can acquire a satellite in accordance with a corrected predicted value without any search.