JP4583820B2 - Stellar sensor - Google Patents

Description

  The present invention relates to a star sensor, and more particularly to a star sensor that is mounted on a flying object such as an aircraft, an artificial satellite, or a space transporter and detects the position of a star using a two-dimensional solid-state imaging device.

  For aircraft, artificial satellites, and space transport aircraft flying in the atmosphere, it is the position of the star that is the base for maintaining the normal operation posture, and it is extremely important to detect the position of the star correctly. In order to detect the position of a star, a two-dimensional solid-state image sensor is generally used.

  Conventionally, this type of star sensor monitors the imaging state of a star image on a two-dimensional solid-state image sensor from a pixel level signal representing the output of the two-dimensional solid-state image sensor, and based on the monitor information, the two-dimensional solid-state image sensor By controlling the exposure time or the threshold level, the image formation state of the star image is kept in an optimum state, and an error caused by the geometric shape of the detector is corrected (for example, see Patent Document 1). ).

  The other star sensor detects a pixel level signal representing the output of the two-dimensional solid-state imaging device, and amplifies the imaging time of the two-dimensional solid-state imaging device or the output signal of the two-dimensional solid-state imaging device based on the detection result. The gain of the signal amplifier is automatically controlled (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 3-51713 (page 3, FIG. 1) JP-A-1-321311 (2nd page, FIG. 1)

  However, in the above-described prior art, the amplifier gain or the exposure time is adjusted based on the imaging state in the imaging field and the pixel level signal. However, normally, a plurality of stars (hereinafter simply referred to as “stars”) are included in the imaging field. Therefore, the amplifier gain or exposure time is not necessarily controlled by the information specific to the star to be tracked (tracking), and proper information cannot be supplied to the flight attitude control system. There is a point.

  For example, in the conventional method of detecting the saturation state of the image signal level and adjusting the amplifier gain or exposure time, the gain or exposure time is determined by the bright star, so an error occurs in the calculation of the position of the dark star, It becomes difficult to identify dark stars.

  That is, until the first tracking star is detected / determined, the magnitude information (image signal level) of the star in the field of view is required, so control is performed so that the image signal level of the star in the field of view is not saturated. However, when adjusting the image signal level, if the saturation level is detected and the amplifier gain or exposure time is adjusted, the image signal level is adjusted so that the bright star image data level is not saturated in the field of view. When there is a dark star in the field of view, the image data level of the dark star becomes small, and the quantization error at the time of quantization cannot be ignored. Therefore, in an environment where it is necessary to track a dark star, an error occurs in position calculation, and it is difficult to identify the star. As a result, star identification is lost during tracking, and position information cannot be output.

  An object of the present invention is to provide a stellar sensor that can obtain high calculation accuracy of a star position regardless of the star grade (brightness).

  The invention described in claim 1 is a stellar sensor mounted on a flying object such as an artificial satellite for detecting the position of a stellar, which captures a star and converts its optical signal into an electrical signal (1 in FIG. 1). And a gain controller (4 in FIG. 1) for amplifying according to the star grade information so that the level of the image signal extracted from the electrical signal is constant for any star, and the position of the star based on the image signal A star position calculation circuit (8 in FIG. 1) for determining the star to be used for tracking and controlling the attitude of the flying object based on the star position calculated by the star position calculation circuit. The star detection / determination circuit (9 in FIG. 1) which detects the magnitude of the star from the catalog data of the star and outputs the grade information to the gain controller, and the position information of the star determined by the star detection / determination circuit is the attitude of the flying object Output to decision system That is a star sensor, characterized in that a star identification circuit (10 in FIG. 1).

  According to the second aspect of the present invention, the gain controller according to the first aspect of the invention includes a decoder (21 in FIG. 2) for decoding the grade information into a grade, and an analog switch (FIG. 2) that is turned ON / OFF by the decoded grade signal. 2 and SW1 to SW8), a resistor group (23 in FIG. 2) composed of analog switches and one-to-one correspondence resistors, and an operational amplifier whose output is fed back to the input by the resistors corresponding to the analog switches that are turned on. A star sensor comprising a gain amplifier (24 in FIG. 2).

  According to a third aspect of the present invention, there is provided a star sensor for detecting the position of a star mounted on a flying object such as an artificial satellite, and the like (1 in FIG. 5) for photographing a star and converting its optical signal into an electric signal. An exposure time timing generation circuit (11 in FIG. 5) that changes the exposure time of the CCD in accordance with the star grade information so that the level of the electrical signal is constant for any star, and an image extracted from the electrical signal A star position calculation circuit (8 in FIG. 5) that obtains the star position based on the signal, and detects a star to be used for tracking control of the flying object based on the star position calculated by the star position calculation circuit. The star detection / determination circuit (9 in FIG. 5) and the star detection / determination circuit determine the determined star grade from the star catalog data and output the grade information to the exposure time timing generation circuit. Star position A star sensor, characterized in that a star identification circuit for outputting the broadcast to the attitude determination system of projectile (10 in FIG. 5).

  According to a fourth aspect of the present invention, in the first, second or third aspect of the invention, a preamplifier (2 in FIGS. 1 and 5) for amplifying an electrical signal from the CCD and an electrical output from the preamplifier. A CDS (Correlated Double Sampling) circuit (3 in FIGS. 1 and 5) that extracts only the star image signal from the signal and the image signal output from the gain controller are converted into image data. An image having a predetermined threshold value or more among image data based on the A / D converter (5 in FIGS. 1 and 5) and threshold information or star address information supplied from the star detection / determination circuit based on a command from the ground. A star data extraction gate (6 in FIGS. 1 and 5) that extracts data or image data in a specified window, and which star constitutes a star for each pixel of the extracted image data. Grouping circuit (Figure 1, 7 of FIG. 5) to output and isolate whether the pixel in a star position calculation circuit for a star sensor, characterized in that a.

  According to the present invention, since the image signal level is made constant by controlling the gain value of the star image signal level according to the detected star grade (star brightness), the image of the star is wide and wide. Since the signal level is constant and the star position can be detected with the same accuracy, the star position can be detected with high accuracy even in a dark star, and the effect of facilitating star identification can be obtained.

  Gain value control is made autonomous so that it can be automatically performed according to grade information, so there is no need to send commands etc. from the ground, star position calculation is possible by conventional autonomous operation, artificial satellite etc. Does not affect the operation method.

  The star sensor of the present invention is a star sensor that is mounted on a flying object such as an artificial satellite and detects the position of the star. The star sensor captures a star and converts its optical signal into an electrical signal, and is extracted from the electrical signal. A gain controller that amplifies according to the star grade information so that the level of the image signal is constant for any star, a star position calculation circuit that obtains a star position based on the image signal, and a star position calculation circuit Tracks based on the calculated star position and detects and determines the star to be used to control the attitude of the flying object, and detects the star grade from the star catalog data and outputs the grade information to the gain controller And a star identification circuit that outputs the position information of the star determined by the star detection / determination circuit to the attitude determination system of the flying object.

  FIG. 1 is a block diagram of the star sensor of the present invention. The star sensor is mounted on a flying object such as an aircraft, an artificial satellite, or a space transporter, and includes a CCD 1, a preamplifier 2, a CDS circuit (hereinafter referred to as “CSD”) 3, a gain controller 4, and an A / D converter. 5, a star data extraction gate 6, a star data grouping circuit 7, a star position calculation circuit 8, a star detection / determination circuit 9, and a star identification circuit 10.

  The CCD 1 performs tracking imaging of a star and converts the optical signal into an electric signal. The preamplifier 2 amplifies a minute electric signal from the CCD 1. The CDS 3 extracts only the star image signal from the amplified electrical signal.

  The gain controller 4 amplifies the star image signal from the CDS 3 in accordance with the grade information output from the star detection / determination circuit 9. For stars with a lower grade (bright stars), the amplification factor is lowered, and for stars with a higher grade (dark stars), the amplification factor is increased. Thereby, the level of the star image signal can be kept constant.

  The A / D converter 5 digitally converts the star image signal output from the gain controller 4 into image data. The star data extraction gate 6 extracts the image data from the A / D converter 5 that is equal to or greater than a predetermined threshold value or the image data in the designated window. The threshold information or star address information is supplied from the star detection / determination circuit 9 based on a command from the ground. The significance of extracting image data above the threshold is to remove noise, and the significance of extracting image data in the window is to identify the star to be tracked in the field of view of the CCD 1.

  The grouping circuit 7 performs a segmentation (grouping process) on the star image data extracted by the star data extraction gate 6 as to which pixel constitutes a star or which star constitutes a pixel. The star position calculation circuit 8 obtains the star's center of gravity (star position) by performing centroid processing on the grouped image data.

  The star detection / determination circuit 9 detects and determines a star to be tracked and used for attitude control of a flying object such as an artificial satellite in accordance with a command from the ground based on the star position calculated by the star position calculation circuit 8. Further, the star catalog data stored in the RAM included in the star identification circuit 10 is detected and the grade information is output to the gain controller 4. Further, threshold information or star address information based on a command from the ground is supplied to the star data extraction gate 6.

  The star identification circuit 10 outputs the star determined by the star detection / determination circuit 9 and its position information to the attitude determination system of the flying object.

  FIG. 2 shows details of the gain controller 4, which is composed of a 3-bit decoder 21, a switch group 22, a resistance group 23, and a gain amplifier 24. The 3-bit decoder 21 can be realized by a general-purpose CMOS with low power consumption. By using FET switches (ON resistance: 100Ω or less) having a small ON resistance for the analog switches SW1 to SW8 constituting the switch group 22, the gain fluctuation range can be suppressed and the gain accuracy can be improved. The resistor group 23 is composed of temperature compensation resistors.

  The gain amplifier 24 constitutes an operational amplifier whose output is fed back to the input by one of the resistors in the resistor group 23. Upon receiving the grade information (3 bits) from the star detection / determination circuit 9, the 3-bit decoder 21 decodes the grade information into a grade. In the switch group 22, the analog switch SW corresponding to the class is turned ON / OFF by the decoded class signal.

  One end of the analog switch SW is led to the input end of the amplifier 25 of the gain amplifier 24, the other end of the analog switch SW is led to one end of the resistors constituting the resistor group 23, and the other ends of all the resistors are connected to the output of the gain amplifier 24. Has been. As a result, the feedback amount to the input of the output of the gain amplifier 24 is determined depending on which analog switch SW is turned ON / OFF, and the gain value of the gain amplifier 24 is changed. That is, each resistance of the resistance group 23 determines a gain value corresponding to each grade, and the gain amplifier 24 amplifies the star image signal with the gain value corresponding to each grade. The amplifier 25 can improve the gain accuracy by using an amplifier having a small offset variation.

  FIG. 3 shows an analog switch SW that is turned on for 3-bit grade information B0 to B2, and a grade for each grade information B0 to B2. For example, if the grade information B0 to B2 is “000”, the analog switch SW1 is turned on, which indicates that the grade is 1, and if the grade information B0 to B2 is “100”, the analog switch SW5 is turned on and it is the grade 5. It shows that.

  Initially, the gain controller 4 is set in advance to a gain of grade 1 (the brightest star), that is, the minimum gain. This is a measure for allowing the gain controller 4 to amplify the image signal without saturating the star image signal of any grade. This image signal is amplified by the gain controller 4 and reaches the star detection / determination circuit 9 via the A / D converter 5, the star data extraction gate 6, the star data grouping circuit 7 and the star position calculation circuit 8, where The star to track with is determined.

  The star detection / determination circuit 9 outputs the determined star grade information B0 to B2 to the gain controller 4. Then, the gain controller 4 amplifies the star image information with a gain value corresponding to the grade information B0 to B2. That is, if the determined star grade is small, it is amplified with a small gain value, and if the determined star grade is large, it is amplified with a large gain value.

  FIG. 4 shows the level of the image signal output from the gain controller 4 for each of classes 1 to 8. Conventionally, the gain value is not controlled in accordance with the grade, and the gain value remains small. As shown in FIG. 4A, the image signal level decreases as the grade increases. However, in the present invention, since the gain value is controlled in accordance with the grade as described above, the image signal level is maintained constant regardless of the grade as shown in FIG. 4B.

  As a result, the quantization error when calculating the star position in the star position calculation circuit 8 is reduced. Therefore, the star identification circuit 10 can easily identify the star. Since the gain controller 4 is controlled in conjunction with software, it can be operated by a conventional method and there is no need to change the operation method.

  In the first embodiment, the gain value of the gain amplifier 4 is changed according to the grade information. Instead, as shown in FIG. 5, an exposure time timing generation circuit 11 is provided, and the grade information from the star detection / determination circuit 9 is used. The exposure time of the CCD may be changed by changing the timing of the exposure time (shutter speed) in the exposure time timing generation circuit 11.

  By controlling the exposure time to be shorter for stars with a lower grade and to increase the exposure time for stars with a higher grade, the image signal level is made constant as shown in FIG. The same effect as in can be obtained.

1 is a block diagram showing a first embodiment of a star sensor of the present invention. Detailed view of the gain controller in FIG. The figure which displays switch SW and grade for each grade information for grade information The figure which shows the image signal level in each grade about a prior art and this invention FIG. 3 is a block diagram showing a second embodiment of the star sensor of the present invention.

Explanation of symbols

1 CCD
2 Preamplifier 3 CDS
4 gain controller 5 A / D converter 6 star data extraction gate 7 star data grouping circuit 8 star position calculation circuit 9 star detection / determination circuit 10 star identification circuit 11 exposure time timing generation circuit 21 3-bit decoder 22 switch group 23 resistance group 24 gain amplifier 25 amplifier SW analog switch

Claims (4)

In a star sensor that is mounted on a flying object such as an artificial satellite and detects the position of the star,
A CCD that shoots stars and converts the light signals into electrical signals;
A gain controller that amplifies according to star grade information so that the level of the image signal extracted from the electrical signal is constant for any star;
A star position calculation circuit for obtaining a star position based on the image signal;
The star position is calculated based on the star position calculated by the star position calculation circuit, and the star used to control the attitude of the projectile is detected and determined, and the grade of the determined star is detected from the star catalog data. A star detection / determination circuit that outputs to the gain controller;
A star sensor comprising: a star identification circuit that outputs star position information determined by a star detection / determination circuit to an attitude determination system of a flying object. The gain controller is
A decoder for decoding the grade information into grades;
An analog switch that is turned ON / OFF by a signal of a decoded grade;
Analog switch and one-to-one resistance,
2. The star sensor according to claim 1, comprising a gain amplifier constituting an operational amplifier in which an output is fed back to an input by a resistor corresponding to an analog switch that is turned on. In a star sensor that is mounted on a flying object such as an artificial satellite and detects the position of the star,
A CCD that shoots stars and converts the light signals into electrical signals;
An exposure time timing generation circuit that changes the exposure time of the CCD according to the star grade information so that the level of the electrical signal is constant for any star;
A star position calculation circuit for determining a star position based on an image signal extracted from the electrical signal;
The star position is calculated based on the star position calculated by the star position calculation circuit, and the star used to control the attitude of the projectile is detected and determined, and the grade of the determined star is detected from the star catalog data. A star detection / determination circuit that outputs to the exposure time timing generation circuit;
A star sensor comprising: a star identification circuit that outputs star position information determined by a star detection / determination circuit to an attitude determination system of a flying object. A preamplifier for amplifying an electrical signal from the CCD;
A correlated double sampling circuit that extracts only the star image signal from the electrical signal output by the preamplifier;
An A / D converter that digitally converts an image signal output from the gain controller into image data;
A star for extracting image data of a predetermined threshold value or more, or image data in a specified window, from the image data based on threshold information or star address information supplied from the star detection / determination circuit based on a command from the ground A data extraction gate;
A grouping circuit that performs a segmentation of the extracted image data to determine whether each pixel is a pixel that constitutes a star or which star constitutes a pixel and outputs it to the star position calculation circuit. The star sensor according to claim 1, claim 2, or claim 3.

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