JP2003081196A - Satellite orbit determining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technique for determining a highly precise orbit of a satellite whose orbit is conventionally difficult to determine with high precision. SOLUTION: A reference satellite 20 having selected shape and surface material is used separately from a main satellite 10 so that the orbit of the reference satellite 20, when tracked only by a tracking station on the earth, can be determined with higher precision than that of the main satellite 10. Information for a distance between the reference satellite 20 and the main satellite 10 is acquired as a corrected data via a communication line 31 between the reference satellite 20 and the main satellite 10 and the track of the main satellite 10 which is determined with relatively low precision is improved and highly refined in accordance with the corrected data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining the orbit of an artificial satellite, and more particularly to an improvement for improving the determination accuracy.

[0002]

2. Description of the Related Art Generally, satellite orbit determination is performed through a two-step procedure. That is, first, in order to acquire the tracking data of the target satellite, the tracking station provided on the earth measures the distance, the distance change rate, or the angular direction of the satellite. Then, a procedure for analyzing the tracking data is entered, and a satellite orbit finally considered to be correct is determined based on matching of the collected tracking data with the law of the orbital motion of the satellite.

[0003]

However, there are various kinds of satellites whose orbits should be determined in the first place, depending on the different applications, and the degree of accuracy required for orbit determination differs accordingly. For example, recently, GPS (Global Po
sitioning System (Global Positioning System), in order to let users know their position by supplying signals transmitted by satellites to users on vehicles and aircraft on the ground. Etc. There is a positioning service to be used. The orbit determination of the satellite used for such a purpose is required to be particularly accurate, and the positioning system satellite itself is a special one specialized for that purpose.

On the other hand, there are communication satellites that serve as relay stations for satisfying remote communication on the earth. For this communication satellite, the accuracy in determining the orbit has not been expected so much in the past, but it was a difficult situation even if expected. The reason is explained as follows.

The light of the sun is incident on any satellite in orbit, but part of the light is absorbed by the surface of the satellite and part of it is reflected. Along with this, the light of the sun exerts pressure on the satellite. Such pressure on the satellite has the effect of gradually changing the orbit of the satellite. Therefore, in order to correctly determine the orbit of the satellite, it is necessary to correctly reflect the effect of changing the orbit of the sunlight pressure on the orbital motion law of the satellite used in the last analysis process described above.

However, in recent years, communication satellites have been equipped with a large solar cell panel and a plurality of large antennas.
It has a large and complicated structure. When the sun's light enters such a satellite, part of the incident light is blocked by one antenna and casts shadows on other antennas or the satellite body, or part of the light reflected by the satellite body or antenna. However, it may become incident light on other antennas, solar cell panels, etc., and may generate additional pressure. Moreover, the way in which such shadows and reflections occur varies intricately depending on the attitude of the satellite with respect to the sun. Further, since a large-sized solar cell panel inevitably has a flexible structure, its shape cannot be regarded as constant. Due to these factors, it is extremely difficult to correctly evaluate the magnitude of the total solar pressure generated by all satellites.

Theoretically speaking, the geometrical shape of the satellite and the distribution of the surface material are determined in the design of the satellite. Therefore, it should be possible to evaluate the magnitude of the solar pressure based on this. is there. However, in practice, there are many errors in the theoretical evaluation, and it has been difficult to accurately evaluate the solar pressure before launching the satellite. In other words, the magnitude of the solar pressure generated by the satellite is determined only when the satellite is placed in orbit and started operating, but once the satellite is launched, the solar pressure is measured and evaluated as soon as possible. There is no way to do it. As a result, the only way to evaluate the solar pressure that should be reflected in the orbital motion law of the satellite is to use the theoretical evaluation obtained before launch, and an accurate orbit determination cannot be obtained due to the error included in the evaluation. , There was a problem.

[0008] If this becomes possible, even for a satellite whose orbit determination has been conventionally difficult with a high degree of accuracy, such as the above-mentioned communication satellite, the industrial effect it exerts is immeasurable. For example, in the past, positioning services could not be satisfied without using a specially designed satellite, but if a communication satellite could also serve that function, it would be costly and labor intensive. In addition, extremely favorable results can be obtained in terms of saving physical resources and intellectual resources.

The present invention is aimed at exactly solving this problem, and since the satellite body is inevitably made large and complicated as represented by a communication satellite, conventionally, the orbit with high accuracy is required. Even for satellites that have been difficult to determine,
It is intended to provide a method capable of highly accurate orbit determination.

[0010]

In order to achieve the above-mentioned object, the present invention has a relatively low accuracy in the orbit determination expected when the satellite is tracked only from a tracking station on the earth. A satellite orbit determination method for improving determination accuracy; if the above satellite is used as a main satellite and the satellite is tracked only from a tracking station on the earth separately from this satellite, it is higher than the main satellite. A reference satellite whose shape and surface material are selected so that the orbit can be determined with high accuracy; distance information between the reference satellite and the main satellite is obtained as correction data via a communication line between the reference satellite and the main satellite; Based on this correction data, a satellite orbit determination method is proposed which is characterized by improving the orbit that is determined with relatively low accuracy with respect to the main satellite and increasing the accuracy.

In the above configuration, when the main satellite and the reference satellite are satellites placed in a general geostationary orbit, the orbit determination of the main satellite can be improved based on the inter-satellite distance information, at least as described above. When placed in a non-geostation orbit, the accuracy of determining the main satellite orbit can be improved by using the distance change rate information as correction data instead of or together with the distance information.

The reference satellite preferably has a spherical shape or a polyhedral shape which can be approximated to a spherical shape.
There is no reason to limit it to one. On the contrary, to improve the accuracy of the orbit, which is determined to be relatively inaccurate with respect to the main satellite, based on the correction data obtained from the relationship between each of the reference satellites and the main satellite. Is the preferred means.

Further, for example, if the main satellite is a communication satellite that should also be used for the global positioning system, a satellite dedicated to a special positioning service becomes unnecessary, which is extremely rational.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows an example of the configuration of a reference satellite 20 suitable for use in the present invention. The reference satellite 20 needs to have relatively high orbit determination accuracy expected when being tracked only from a tracking station on the earth, as compared with the main satellite 10 described later in this section, as mentioned in the main configuration of the present application, One of the desirable means to meet this is the reference satellite
The idea is to approximate the shape of 20 to a sphere, ideally a sphere, at least in reality a polyhedron. For the sake of reference, the case shown in the drawing shows a shape close to a regular octahedron, but the shape is not limited to this. In reality, a smaller number of faces may be sufficient, or conversely, a larger number of faces and a more spherical shape may be used. That is, even if it is a polyhedron, it suffices to sufficiently use it, and the requirements for its approximation can be stated as follows.

That is, the satellite 20 stabilizes its attitude by spinning around the spin axis 26, and when the pressure exerted by the sunlight on the satellite is averaged over the time when the spin makes one revolution, The polyhedron shape of satellite 20 approximates a sphere as long as it can be considered that the average sunlight pressure can be regarded as sufficiently constant without depending on the attitude of the satellite with respect to the sun. It can be

Regarding the material forming the surface of the satellite 20,
Ideally, it should be uniform over the entire circumference, but in reality, in addition to attaching the solar cell panel 22 to the surface of the satellite,
It is necessary to attach many communication antennas 23 for tracking. It is desirable that the antenna 23 has a small number of protrusions and has a shape that can be attached in a plane along the surface of the satellite. Further, it is necessary to provide an opening on the surface of the satellite 20 for an earth sensor 24 having a known configuration, a small gas jet 25 for attitude correction, and the like. Regarding the material of the satellite surface as a generic term, it can be considered that the solar pressure averaged over one revolution of the spin does not depend on the attitude of the satellite with respect to the sun and is sufficiently constant. To the extent that is true, it is desirable that the surface material be uniform over the entire circumference of the satellite. It should be noted that the earth sensor 24, the small gas jet 25, and the like are shown schematically in the figure. The arrangement, number, etc. may be in accordance with the places usually adopted in this type of satellite.

Generally speaking, taking a communication satellite as an example, almost all of them are in geostationary orbits.
In such a case, in the orbit determination for those geostationary satellites, the tracking station normally acquires the satellite range data as tracking data normally. The orbit is determined by matching the acquired distance data with the orbital motion law of the satellite, and the process is usually as follows.

A single function is provided during arithmetic processing using a computer, and the function is configured to represent that the distance from the tracking station to the satellite changes with time. Specifically, the function is equipped with the orbital motion law of the satellite inside, and by reflecting the relevant facts such as the rotation of the earth and the position of the tracking station on the earth, when the arbitrary time is given, the time Represents the distance from the tracking station to the satellite as a function of. As is well known, the orbital motion of a satellite is defined by six parameters, called six orbital elements, so the above function contains six parameters. The function provided in this way is called a model function. By comparing the satellite distance represented by the model function with the distance data acquired by the tracking station, it is possible to determine the above six parameters so that they match each other. A means known as the least squares method is usually used to determine the parameters, but in any case, the trajectory determination is nothing but the determination of the six parameters as described above.

As described above, the reference satellite 20 shown in FIG. 2 used in the present invention is constructed so that the generation of the sunlight pressure can be regarded as constant regardless of its attitude. The magnitude of the solar pressure itself must be placed as an unknown number. Even if the material forming the surface is known,
This is because the value that theoretically evaluates the generation of pressure due to the absorption and reflection of light on the surface must have an error. In order to deal with this problem, one more parameter is added to the above model function. The additional parameter represents the magnitude of the sunlight pressure generated on the reference satellite, and the model function is configured so that the effect of changing the orbit due to the sunlight pressure changes depending on the magnitude of the parameter. Accordingly, the model function has a total of 7 parameters.

The satellite range represented by such a model function,
It is possible to compare the distance data acquired by the tracking station and determine the above seven parameters so that they match each other. The least squares method is usually used to determine the parameters. By the above means, the reference satellite 20
An accurate orbit determination regarding is possible.

In other words, although the magnitude of the sunlight pressure generated in the reference satellite 20 is unknown, the reason why accurate orbit determination is possible as described above is that the sunlight pressure is always constant. By configuring the reference satellite 20 so that it can be viewed, the parameter to be added to the model function is 1
This is because it can be done individually.

In contrast, if one were to take steps to add a parameter to the model function in order to address the problem of solar pressure occurring in large and complex communication satellites, Since the way shadows and reflections occur is complicated, it is necessary to add an extremely large number of parameters, and it is difficult to create such a model function correctly. Even if such a model function can be created, it is practically impossible to collectively determine an extremely large number of parameters as unknowns in trajectory determination. This is the reason why it has been difficult to determine an accurate orbit for a communication satellite in the past.

In the present invention, the above-mentioned reference satellite 20 is used as an aid to solve this problem. FIG. 1 shows the concept of the method of the present invention, and shows a situation where the main satellite 10 is tracked by the reference satellite 20 (resulting in mutual tracking situations). Here, with respect to the main satellite 10, the accuracy of the orbit determination expected when tracking the satellite only from the tracking station on the earth is relatively low compared to the reference satellite 20 due to the above reason. However, the request is a satellite, for example, communication satellite 10, which requires more accurate orbit determination or is desired to be more accurate.

In tracking between the satellites 10 and 20, for example, the distance between the satellites 10 and 20 is measured by reciprocating a signal through the inter-satellite communication line 31 by radio waves or light. Therefore, the main satellite 10 is replaced by the reference satellite 20.
Provide a small antenna (not shown) used for communication with.
However, it is desirable to consider the mounting position of such a small antenna so that the large antenna or the solar cell panel originally provided in the main satellite 10 does not interfere with the communication path of the communication line 31 between the satellites 10 and 20.

Since the orbit of the reference satellite 20 used in the present invention can be determined fairly accurately as described above, the position of the reference satellite 20 at an arbitrary time can also be known fairly accurately. Therefore, according to the present invention, more accurate orbit determination with respect to the main satellite 20 is possible due to the background described below.

First, it is assumed that a conventional orbit determination is performed by tracking the main satellite 10 from the earth station. Main satellite 10
Its orbit determination with respect to will be erroneous as a result of inaccuracies in the estimation of solar pressure. In fact
It should be relatively less accurate than that for the reference satellite 20. However, for the time being, the orbit determination is used to predict the distance between the main satellite 10 and the reference satellite 20. The prediction is
There should be a difference compared with the distance actually measured by the inter-satellite tracking, and the difference is caused by the error in the orbit determination of the main satellite 10. Therefore, in order to reduce the difference, the main satellite 10
Improvements are made to the trajectory determined for. When the distance measurement data obtained by the inter-satellite tracking is acquired while being repeated one after another in time, the improvement is sequentially performed according to the acquisition. Specifically, the orbit of the main satellite 10 is represented as a position and a velocity, and the orbit is improved by sequentially correcting them. A technique called real-time filtering is known as a method of performing such correction and improvement, and a Kalman filter is a typical means used for it. As a result of continuously performing such improved correction, the error in orbit determination regarding the main satellite 10 can be reduced as the time for performing inter-satellite tracking elapses.

As described above, in the present invention, the position of the main satellite 10 is determined by determining the position of the reference satellite 20 fairly accurately in advance and determining the position by measuring the distance between the satellites 10 and 20. It can be said that it is reflected in the decision. Furthermore, the reference satellite 20 acts as one of the tracking stations,
Moreover, since this tracking station is much closer to the main satellite 10 compared to the tracking station placed on the earth, it can be said that the effect of contributing to accurate orbit determination is greater.

In the above description, it has been stated that the distance between the satellites is measured based on the round trip of the signal between the main satellite 10 and the reference satellite 20. For example, the signal transmitted from the main satellite 10 is relayed by the reference satellite 20 and sent back to the main satellite 10, and the distance is measured by the main satellite 10, or conversely, the signal is transmitted from the reference satellite 20. It may be returned to the reference satellite 20 by relaying on the main satellite 10 and the distance may be measured by the reference satellite. As a further variation, the signal originates from an earth station (not shown), which is the earth station-main satellite 10-.
It is also possible that the reference satellite 20-main satellite 10-earth station is relayed and transmitted, and the total distance is measured by the earth station. This is because the distance between the earth station and the main satellite 10 is separately measured, and the distance between the satellites can be obtained by subtracting the distance. Similarly, a route of earth station-reference satellite 20-main satellite 10-reference satellite 20-earth station can be used for relaying signals.

FIG. 1 also shows an example of a preferable arrangement relationship between the main satellite 10 and the reference satellite 20. It is desirable that both satellites 10 and 20 are arranged so close to each other that there is no risk of collision. Practically, the maximum latitude range LatMAX = 0.2 that is normally given when the communication satellite is permitted to use the geostationary orbit.
It is appropriate to place both satellites 10 and 20 within the latitude / longitude range of degrees and maximum longitude range LngMAX = 0.2 degrees. In order to keep both the main satellite 10 and the reference satellite 20 so as not to deviate from the permitted longitude range in the geosynchronous orbit, the respective orbit holding control is required, but the holding control follows the already established method. When both satellites 10 and 20 are maintained in orbit separately, the movements of both satellites 10 and 20 in orbit are usually different from each other. At this time, the view direction of the reference satellite 20 observed from the main satellite 10 moves with time. Then, when measuring the inter-satellite distance, the direction of the straight line connecting the satellites changes with time. This increases the effect of orbit improvement based on correcting the position and velocity of the main satellite 10 in the above description. This is because both the position and the velocity are vector quantities having three orthogonal components, but as a result of the change in the direction of the straight line connecting the satellites, any of these three vector components can be corrected. That is, in order to obtain the orbit determination of the main satellite 10 with higher accuracy, it is effective to maintain the orbit of both satellites so that the range in which the direction of the reference satellite 20 changes when observed from the main satellite 10 becomes large. is there.

In the above description, the number of reference satellites 20 is consistently one. However, if the number of reference satellites 20 is plural, the distance between each reference satellite 20 and the main satellite 10 is maintained while keeping the reference satellites 20 in different directions when observed from the main satellite 10. Can be measured. This leads to an increase in the effect of improving the orbit of the main satellite 10, and in particular, requires less elapsed time until the orbit error is reduced. As a special case, the number of reference satellites 20 is 3 and the number of main satellites 20 is 20.
If all the directions of the reference satellites observed from are different, it is possible to determine the exact position of the main satellite 10 almost instantaneously based on the measurement of the inter-satellite distance without waiting any elapsed time. It will be possible.

Up to now, the main satellite 10 and the reference satellite 20
Has been in geostationary orbit. However, the present invention is not limited to this. When the main satellite 10 is placed in a non-geostation orbit, the orbit of the reference satellite 20 is also placed in the vicinity of the main satellite 10, so that it becomes a non-geostation orbit. Regarding geostationary satellites, there was a concept of "latitude / longitude range given when receiving permission to use orbit", but this concept does not apply to non-geostationary satellites. However, even when the satellite is placed in a non-geostation orbit, it is appropriate that the spatial extent in which the main satellite 10 and the reference satellite 20 are arranged conform to the size of the spatial extent shown in FIG. Note that the standard tracking data for geostationary satellites, that is, the correction data for improving the orbit determination of the main satellite 10 was distance data, but the tracking data for non-geostationary satellites includes distance data. In addition, the distance change rate may be used, or the distance and the distance change rate may be used together. In the series of description according to the embodiment of the present invention, the place where the tracking data or the correction data is used as the distance is appropriately replaced with the distance change rate or the combined use of the distance and the distance change rate. The present invention can be similarly applied to the case where the reference satellite 20 is placed in a non-geostation orbit.

[0032]

As described above, according to the method of the present invention, it is possible to target a satellite, for example, a communication satellite, which is difficult to evaluate the sunlight pressure because of its large size and complicated structure. Even if there is, it becomes possible to make a more accurate orbit determination. As a result, it becomes possible to apply such a communication satellite to a positioning service, and it is possible to reduce the labor, labor, cost and resources for launching a dedicated satellite.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a cooperative relationship between a main satellite whose orbit is to be determined and a reference satellite used for determining the orbit in a preferred embodiment of the satellite orbit determination method of the present invention.

FIG. 2 is an explanatory diagram showing an example of a desirable external appearance of a reference satellite used in the present invention.

[Explanation of symbols]

10 Main satellite 20 Reference satellite 22 solar panel 23 antenna 24 Earth sensor 25 gas jet 26 Reference satellite spin axis

Claims (6)

[Claims] 1. A satellite orbit determination method for improving the orbit determination accuracy of a satellite in which the orbit determination accuracy expected when the satellite is tracked only from a tracking station on the earth is relatively low. Shape and surface material so that the satellite can be determined with higher accuracy than the main satellite even if the satellite is the main satellite and the satellite is tracked only from a tracking station on the earth separately from the satellite. The reference satellite selected is used to obtain distance information between the reference satellite and the main satellite as correction data via a communication line between the reference satellite and the main satellite; based on the correction data, the main satellite Regarding the above, the satellite orbit determination method is characterized by improving the orbit determined with relatively low accuracy and increasing the accuracy. 2. A satellite orbit determination method for improving the orbit determination accuracy of a satellite in which the orbit determination accuracy expected when the satellite is tracked only by a tracking station on the earth is relatively low. Shape and surface material so that the satellite can be determined with higher accuracy than the main satellite even if the satellite is the main satellite and the satellite is tracked only from a tracking station on the earth separately from the satellite. Using the reference satellite selected from the above; obtaining the distance change rate information between the reference satellite and the main satellite as correction data through a communication line between the reference satellite and the main satellite; A satellite orbit determination method, characterized in that the orbit determined with respect to the main satellite is determined to have a relatively low accuracy and the accuracy is improved. 3. A satellite orbit determination method for improving the orbit determination accuracy of a satellite in which the orbit determination accuracy expected when the satellite is tracked only from a tracking station on the earth is relatively low. Shape and surface material so that the satellite can be determined with higher accuracy than the main satellite even if the satellite is the main satellite and the satellite is tracked only from a tracking station on the earth separately from the satellite. The reference satellite selected is used; the distance information and the distance change rate information between the reference satellite and the main satellite are obtained as correction data through a communication line between the reference satellite and the main satellite; Based on the main satellite, the orbit determined with relatively low accuracy is improved and the accuracy is improved; 4. The satellite orbit determination method according to claim 1, 2 or 3, wherein the shape of the reference satellite is a sphere or a polyhedron shape that can be approximated to a sphere. . 5. The satellite orbit determination method according to claim 1, 2, or 3, wherein the number of the reference satellites is plural, and a plurality of corrections are obtained by the relationship between each reference satellite and the main satellite. A satellite orbit determination method, characterized by improving the orbit determined with a relatively low accuracy with respect to the main satellite based on the data for use and improving the accuracy. 6. The satellite orbit determining method according to claim 1, 2, or 3, wherein the main satellite is a communication satellite that should be used for a positioning system.