JPH02187623A - Star sensor - Google Patents

Abstract

PURPOSE:To detect attitude information of high precision of a base body by comparing stored star information and information from an actual star image signal with each other to lead out attitude information of the base body and correcting the error of a detecting means and stored information. CONSTITUTION:When this star sensor is used to detect attitude information of an artificial satellite, an image pickup means 10 is fixed to a satellite base body, and a signal processing means 12 is provided with a central processing unit to lead out first star information of the magnitude, the elongation, the position, etc., of a star from the star image signal from the means 10. Second star information preliminarily generated on the ground is stored in a storage device 14 consisting of a RAM. The means 12 compares first and second star information with each other; and when they coincide with each other, the means 12 leads out first attitude information of the star based on first star information and corrects the detection error of second attitude information outputted from a detecting means 16 and holds it at each time to keep the precision. When first and second star information do not coincide with each other, information in the means 14 is corrected to that of the means 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a star sensor used, for example, in a navigation system for a space body such as an artificial satellite.

(Prior Technology) In general, a star sensor is a navigation device that performs highly accurate attitude control of a cosmic body using the position of a star on the celestial sphere. Used to obtain posture information.

Figure 8 shows the conventional star sensor in this way.
Parallel rays from star 2 are focused by lens unit 1 to create star image 2
a is imaged on the star image capturing device 3. The star image 2a formed by the star image capturing device 3 is guided to the star image processing device 5 via the interface 4, and is used for detecting attitude information of the spacecraft.

Image processing by the star image processing device 5 is performed in accordance with the procedure shown in FIG. That is, in step S1, star image information is input to the central processing unit (CPU) 5a, and in step S2
In step S3, the elongation of star 2 on the star image is determined, and in step S3, it is matched with star information indicating the position of star 2 on the celestial sphere, which has been stored in advance in the image information storage device 5b. Then, in step S4, if the matching is successful, in step S5, a combination of stars 2 that matches the elongation of three or more stars 2 on the star image is found, and the above image information indicates which position on the celestial sphere. It is detected whether the image has been taken and fixed, and in step S6, the attitude information of the spacecraft in inertial space is output.

If the matching fails in step S4, it becomes impossible to fix the star image 2a, and the process returns to the initial step S1, where the input star image 2a is processed again.

However, in the above configuration, since the star information of the celestial sphere set in the star image information storage device 5b of the star image processing device 5 is the star information measured using an astronomical telescope on the ground, it is difficult to detect faint stars or The problem was that atmospheric fluctuations caused errors in the position information of Star 2, or so-called information omissions. According to this, it becomes difficult to fix the star image 2a on the orbit, or it becomes difficult to obtain highly accurate attitude information.

(Problems to be Solved by the Invention) As mentioned above, conventional star sensors have had problems in that it is difficult to fix star images and it is difficult to obtain highly accurate attitude information. .

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a star sensor that can accurately fix star images and detect attitude information with high accuracy.

[Structure of the Invention] (Means for Solving the Problems) A star sensor according to the present invention combines first star information stored in advance in a storage means and second star information obtained from an output star image signal of an imaging means. It is configured to derive first attitude information of the base body when they match, and to correct an error of the second attitude information detection means using this first attitude information. Furthermore, if the first star information and the second star information do not match, the first star information stored in advance in the storage means is configured to be corrected to the second star information obtained from the star image signal. .

(Function) According to the star sensor according to the present invention, when the first star information stored in advance and the second star information obtained from the star image signal match, the star sensor outputs the first star information of the base body. Using the first attitude information, the error of the detection means that outputs the second attitude information is corrected. This improves the detection accuracy of the detection means to the same degree as the accuracy of the star sensor. Therefore, the first. If the second star information does not match, the second
The orientation of the star sensor can be accurately detected based on the attitude information, and the first star information corresponding to this can be accurately selected. Furthermore, by correcting this selected first star information to second star information, from now on,
Highly accurate posture information of the base body can be detected.

(Example) Hereinafter, an example of a star processor according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of an embodiment of a star sensor according to the present invention. A star sensor is typically mounted on, for example, an artificial satellite and used as a sensor for detecting attitude information of the artificial satellite. Here, an example will be explained in which a star sensor is used to detect attitude information of this artificial satellite. The imaging means (10) is fixed to an artificial satellite as a base, and images the outer space and outputs a star image signal. This imaging means (10) is, for example, a CCD (Charge Co.
(upledDevice) camera, etc. The signal processing means (12) is composed of, for example, a central processing unit (CPU), and introduces star image signals from the imaging means (10) to derive star information. The star information derived here includes the magnitude of each layer, the elongation between the legs, and the position information of each layer.

The storage means (14) is, for example, a rasodum access memory (R
AM), which stores the grade of each layer, the elongation angle between feet, and the location information of specialty products created in advance on the ground.

The signal processing means (12) compares the first star information stored in the storage means (14) with the second star information obtained from the output star image signal of the imaging means (10), and determines that the two coincide. In this case, the first attitude information of the satellite is derived based on the star position information included in the first star information. The detection means (16) is fixed to the satellite and outputs second attitude information of the satellite, and is constituted by, for example, an inertial navigation system (INs), a sun sensor, an earth sensor, or the like. This detection means (16)
The second attitude information output from the signal processing means (12)
The accuracy is lower than the first attitude information derived in , and has a larger error than the star sensor output. Correction means (18)
is processed by the signal processing means (12). The detection means (16) uses the first attitude information of the satellite derived by the signal processing means (12) when the second star information is matched.
to correct the detection error. This correction means (18) corrects the detection error of the detection means (16) (by doing so,
The accuracy of the attitude information output from the detection means (16) is maintained at the same level as the accuracy of the attitude information output from the signal processing means (12).

In the signal processing means (12), the first. If the second star information is not matched, the orientation of the imaging means (10) is detected from the satellite attitude information output from the detection means (16), and the star information stored in the storage means (14) is detected. Of these, star information corresponding to the orientation of the imaging means (10) is
10) is corrected to the star information derived from the output star image signal.

FIG. 2 is a diagram illustrating a star image obtained by the imaging means (10). In the optical system (20) of the imaging means (10), the range in which images can be captured, that is, the angles of view θa and θb, are, for example, 8 inches each in the horizontal and vertical directions (±4 inches each with respect to the central axis of the optical system (20)). ), and the image detection element (22
), each layer ( 24, 26, 28) and their positions on the image detection element (22) are detected. Imaging means (
1"0) converts the output analog signal of the image detection element (22) into a digital signal and outputs it.

FIG. 3 is a diagram illustrating the operation of the apparatus shown in FIG. 1. The signal processing means (12) processes the image signal through steps 81 to S8. That is, in step S1, a digital signal from the imaging means (10) is introduced, and in step S2, the elongation (L1 to L3) of the star on the image detection element (22) is calculated. This star's elongation (Ll ~
L3) corresponds to the distance between each foot on the image. Next, in step S3, the elongation calculated in step S2 is matched with the elongation of the star stored in advance in the storage means (14). Here, in the storage means (14), as shown in FIGS. 4 and 5, information on the 9th magnitude of the star's position and information on the elongation of the star are stored in advance. This information is measured as star information in the sky using an astronomical telescope on the ground, and due to atmospheric fluctuations, it does not necessarily match the information measured in space. The location of the river shown in Figure 4.

Among the magnitude information, star numbers are numbers sequentially assigned to stars in the sky, for example, about 5,000 stars.

Right ascension 9 Declination is the position information of the star, and the equatorial plane of the earth at midnight of the position of the vernal equinox in 1950 is plotted on the X-Y plane 2.
The longitude of the star on the celestial sphere with the axis perpendicular to this as the Z axis 2. Represents latitude. The magnitude corresponds to the brightness of the star, and for example, information on magnitudes 1 to 6 is stored.

As shown in Figure 5, the elongation information of the star is, for example, 0.
．． A combination of stars having an elongation within that range is stored for every 01". In step S3,
After extracting information on multiple combinations of stars in the range of elongation that includes the elongation derived in , the accurate elongation for each combination is determined from the right ascension and declination information for each layer.

In step S4, this accurate elongation information and step S2
Comparison is made with the elongation angle obtained in . Here, if the elongation angles match, the combination of stars that have the elongation angles can be specified, so in step s5 the star image can be fixed, that is, the star information imaged by the imaging means (10) can be specified. can. In step S6, attitude information of the satellite is derived from the right ascension and declination of the identified star. The star elongation specified in step S5 has an accuracy of 0.001°, and the satellite attitude information derived based on this can be used for extremely highly accurate satellite attitude control.

If the elongation angles cannot match in step S4, the process proceeds to step S7. In this case, the star information stored in the storage means (14) is corrected in the steps starting from step S7. For this correction, it is necessary to specify the orientation of the imaging means (10) and correct the star information corresponding to this orientation. The detection means (16) is used to detect the direction of the imaging means (10). However, this detection means (
16) is an inertial navigation system (INS), for example, and its detection accuracy is one order of magnitude inferior to the output of a star sensor. A sun sensor or an earth sensor can also be used as the detection means (]6), and their detection accuracy is comparable to that of the INS. Therefore, if the output of the detection means (16) is simply used to correct the star information, the detection accuracy as a starsessor will be impaired. Therefore, in the star sensor according to the present invention, if the elongation angles match in step S4, that is, steps S1 to S6 are executed, and this attitude information is used while the star sensor is outputting attitude information satisfactorily. It operates to correct the detection error of the detection means (16).

That is, assuming that the detection means (16) is constituted by an INS, the detection means (16) detects the attitude of the satellite from the detection output of the gyro (1, 61) and the gyro (161) that detects changes in the attitude angle of the satellite. A computing unit that computes information (162
) is included. The Shinyairo (161) is a mechanical type with three rotating wheels arranged on three axes, or a previous model without a mechanical drive, or one that changes the rotation angle around each of the three mutually perpendicular axes. To detect. Arithmetic unit (162
) calculates the attitude angle of the satellite by introducing the output signal of the gyro (161) and integrating the change in rotation angle around each axis over time. The correction means (18) includes an error model memory (in which the error model of the detection means (16) is stored).
181) and an error source estimation filter (, 182) for estimating the error source of the detection means (16). The error model stored in advance in the error model memory (1, 81) is usually the bias error (crbx, cyby
, crbz) and the detection means (16) outputs 3
The dynamics of errors (σex, σey, σez) in shaft attitude information is expressed by a differential equation, and is expressed by the following formula.

The error source estimation filter (182) is called a Kalman filter, and uses the dynamic model stored in the error model memory (181) to detect the detection means (16) at time t.
), and is designed to optimally estimate the error source of the detection means (16) from the difference in the attitude information of the star sensor and the detection means (16) supplied from the subtractor (183). ing. The error source estimation filter (182) supplies a correction signal for correcting the output error of the gyro (161) corresponding to the estimation result to the subtracter (163), and also supplies a correction signal for correcting the output attitude error of the arithmetic unit (162). is supplied to the arithmetic unit (16, 2). With this configuration, the error source is estimated and corrected to such an accuracy that the output of the detection means (16) matches the output of the star sensor on average, and the detection means (16) is at the same level as the star sensor. High-precision posture information will be output.

While the operations from step S1 to step S6 are performed and the star sensor is outputting satellite attitude information satisfactorily, the detection means (16) is constantly correcting the output error by the correction means (18) as described above. Its accuracy is maintained at the same level as the star sensor.

Therefore, if the elongation angles cannot be matched in step S4 and the star sensor cannot obtain satellite attitude information, the satellite attitude with the same high accuracy as the star sensor output from the detection means (16) Using the information, the star information in the storage means (14) to be corrected can be optimally determined from step S7 onwards. That is, if the elongation cannot be matched in the chip S4, in step S7, the output attitude information of the detection means (16) is used to obtain the star image of the imaging means (10) when matching cannot be achieved. Calculate the position of the star above by 1. Figure 6 shows step S
7 is a diagram showing a more detailed flow of step 7. FIG. Step S72
Now, the satellite attitude information outputted from the detection means (16) is converted to be represented by a direction cosine matrix C5. The direction cosine matrix represents the amount of inclination of each of the three axes of the satellite as a component on the three reference axes, and is a matrix of 3×3 rows. Next, in step S74, the direction cosine matrix C1 representing the attitude information of this satellite is multiplied by the matrix C5 representing the direction in which the star sensor is attached to the satellite to obtain the direction matrix of the star sensor in inertial space + ib C Calculate (-C, XC5).

In the next step S76, the direction matrix Ci is multiplied by the star direction vector Ss on the star image to calculate the star direction vector S+ in the inertial space.

Note that the star direction vector Ss is a direction vector in the sensor space based on the optical axis of the optical system (Fig. 2) of the imaging means (10), and is calculated separately in the signal processing means (12). The calculation result is used in step S76. In step 878, the position of the star in inertial space, that is, the right ascension and declination, is calculated from the star direction vector St in inertial space. In step S76.378, calculations are made for each of the six stars imaged by the imaging means (10). In step 8, it is determined whether to correct the star information stored in advance in the storage means (10) based on the star information Sl calculated in step S7. FIG. 7 is a diagram showing a specific flow of step S8. That is, after the start in step s8, it is first determined in step S82 whether the accuracy of the satellite attitude information output from the detection means (16) is at the same level as the accuracy of the star sensor. ) is not corrected (step 584) and the flow ends. On the other hand, if they are at the same level, star information SN (right ascension, declination) in the direction the star sensor is facing.

grade) from the storage means (14) (step 88
6). That is, the read star information SM originally has a one-to-one correspondence with the star information obtained by the imaging means (10). Next, the star information SM read out from the storage means (14) is compared with the star information St (calculated in step S7) corresponding to the output of the imaging means (10). (Step 588). In this comparison, first of all, the right ascension of both.

Declination matches, only magnitude information does not match (Step 3)
881), the corresponding star magnitude information stored in the storage means (14) is corrected to the magnitude information obtained from the output of the imaging means (10) (step 5882). If the magnitude information does not match and there is no star information having the same position information in the stored information (step 8883), star information is added to the storage means (14) (step 5884). In addition, storage means (1
If the star information stored in step 4) is not on the imaging screen, the stored information is identified as star information that does not originally exist and is identified as a candidate for information to be deleted (steps 3885 and 38).
86). Whether or not to actually delete it is determined, for example, on the ground, and if it is to be deleted, it is executed by a command from the ground.

If the elongation cannot be matched in step S4, the star information stored in the storage means (14) in this way is
Since the correction is based on the star information actually obtained in space, from now on, when the star sensor points in the same direction, the elongation angle will be matched in step s4, and the satellite's By outputting highly accurate attitude information, highly accurate attitude control of the satellite becomes possible.

Note that the storage means (14) is a read-only memory (ROM).
) and random access memory (RAM), R
The star information measured on the ground may be stored in the OM, and only the corrected star information may be written in the RAM. In this case, priority is given to reading the star information from the RAM, and if there is no star information in the RAM, the star information is read from the ROM.

[Effects of the Invention] As explained above, according to the star sensor according to the present invention, a star image can be accurately fixed, and highly accurate attitude information of the base can be detected.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of a star sensor according to the present invention, FIG. 2 is a diagram illustrating a star image obtained by the imaging means shown in FIG. 1, and FIG. FIG. 4 and FIG. 5 are diagrams explaining the star information stored in the storage means shown in FIG. 1, and FIG. 6 is a more detailed flowchart of step S7 shown in FIG. 3. FIG. 7 is a diagram explaining a more detailed flow of step S8 shown in FIG. 3, and FIGS. 8 and 9 are diagrams explaining a conventional star sensor. 10... Imaging means, 12... Signal processing means. 14...Storage means 2]6...Detection means. 18...Correction means. Agent: Patent attorney Nori Kon'ken, Yudo Yamashita, Indication of the case, Patent Application No. 1, No. 5947, 2, Name of the invention, Suyusensen 3, Person making the amendment, Relationship to the case

Claims (1)

[Claims] an imaging means attached to a base whose direction changes and images a plurality of stars and outputs a star image signal; a storage means for storing first star information including magnitude and position information of the plurality of stars in advance; connected to a storage means and the imaging means,
Second star information including star magnitude and position information is derived from the star image signal, and this second star information and the first star information are derived.
a signal processing means for deriving first attitude information of the base body based on the first star information when the two star information match, and a signal processing means for deriving first attitude information of the base body based on the first star information; detecting means for outputting first attitude information having a larger error than attitude information; and detecting means for outputting first attitude information having a larger error than attitude information; a correction means for correcting an error in the second attitude information using attitude information; and a correction means provided in the signal processing means to obtain information from the second attitude information when the first and second star information do not match. the first direction corresponding to the orientation of the imaging means
and correction means for correcting the star information of the second star to the second star information.