JPH0316612B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to attitude control of an artificial satellite. In particular, the present invention relates to a device that uses a two-dimensional solid-state imaging device (hereinafter referred to as "CCD") as a detector to correct dark current and variations thereof in acquired data during tracking with a star tracker equipped with a light shielding mechanism.

[Prior art] When a conventional star tracker corrects dark current, it treats the output of the optical black part where part of the CCD is shielded by a mask as dark current, and corrects it using its average value. If there are variations in the dark current of each light-receiving element (hereinafter referred to as "pixel") of the CCD, it is not possible to correct the variations. Therefore, when there is a large variation in the dark current of the pixels, the variation is output as an error signal, resulting in the drawback that the position of the star cannot be determined with high precision.

There is also a method in which the image position of the star on the CCD light-receiving surface is random, and information on the dark current of all pixels is obtained. However, in the case of a 384 x 490 pixel CCD,
To store dark current information for all pixels, a memory is required to store data for 188 or 160 pixels.
At this time, even if one pixel was quantized by several bits, the memory capacity would be enormous, making it impractical for use on a satellite.

Furthermore, the method of transmitting the dark current data of each pixel to the ground in real time has the drawback that the visible time is limited in the case of an orbiting satellite, and dark current data cannot be acquired.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks and to provide a device that can obtain star brightness and position data with high accuracy using a low-capacity memory.

[Means for solving problems]

The present invention is characterized by a configuration in which the dark current value of only the pixel corresponding to the light-condensing portion on the light-receiving surface of the CCD can be measured.

That is, the present invention comprises an optical system that focuses starlight, a shutter mechanism that blocks light incident on this optical system, a CCD that detects the focused star image and converts it into an electrical signal, and a CCD that detects the focused star image and converts it into an electrical signal. A drive circuit that generates a drive signal for sequential scanning, means for converting the CCD scanning output from analog to digital, an address generation circuit that generates an image signal address based on the output of the drive circuit, and identifying the presence or absence of a star image. It includes a reference voltage generation circuit that generates a reference voltage corresponding to the threshold level, a comparison circuit that uses the output of this reference voltage generation circuit as one input, and the other input that uses the scanning output of the CCD, and further includes an image signal In a star tracker device that receives the output of an address generation circuit and the analog-to-digital converted output of a CCD, and is equipped with a control device that includes a data processing circuit that processes star brightness data and position data, and a memory circuit that stores this data. , the control device operates in a first mode in which the shutter mechanism is in an open state and collects CCD output data, a second mode in which the shutter mechanism is in a closed state and dark current data is collected from the CCD output data; means for setting the mechanism in an open state and a third mode in which output data of the CCD is collected and corrected with dark current data; The present invention is characterized in that it is configured to collect dark current data for positions of the CCD where the temperature is above the Tsushold level.

[Effect]

The present invention has the effect of being able to correct dark current and its dispersion with a low capacity memory by acquiring dark current data of a small number of pixels for the part where a star is imaged by the CCD light receiving section.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The principle of the star sensor is that star light is focused by an optical system 11, imaged onto the light receiving element surface of the CCD 12, and photoelectrically converted.

In FIG. 1, the shutter drive control circuit 14
The output of is connected to the shutter drive circuit 15, CCD drive circuit 16 and dark current correction circuit 17,
The output of the CCD drive circuit 16 is connected to the CCD 12, a dark current correction control circuit 18, and an image signal address generation circuit 19. The output of the CCD 12 is connected to a CCD image signal amplification circuit 20, and the output thereof is further connected to one input of an analog/digital conversion circuit 21 and a comparison circuit 22. The output of the dark current correction control circuit 18 is connected to the dark current correction circuit 17, and the output thereof is further connected to the image signal address generation circuit 19 and the analog/digital conversion circuit 21. The other input of the comparison circuit 22 is connected to a reference voltage generation circuit 23, and its output is connected to an image signal address generation circuit 19 and an analog-to-digital conversion circuit 21. The outputs of the image signal address generation circuit 19 and the analog/digital conversion circuit 21 are connected to a multiplexing circuit 24, and the multiplexed output is connected to a data processing circuit 25 for processing. The dark current value memory circuit 26 is connected to the dark current correction circuit 17, the dark current correction control circuit 18, and the data processing circuit 25. The output of the control device 27 that controls the operation mode, which is composed of the data processing circuit 25 and the dark current value memory circuit 26, is as follows.
It is connected to the shutter drive control circuit 14.
Further, the output of the data processing circuit 25 is connected to an attitude control signal output terminal 28, and the signal from this output terminal 28 is used by an attitude control device (not shown). On the other hand, a shutter 13 is attached to the shutter drive circuit 15, and operates to allow or block starlight captured by the optical system 11 by opening or closing. As described above, the star tracker dark current correction device is configured.

Here, the feature of the present invention is the dark current correction portion surrounded by a dashed line. In other words, since the imaging range of a star is usually about 3 x 3 pixels,
By measuring the dark current value of only the pixel corresponding to the light-condensing portion on the light-receiving surface of the CCD 12, the dark current and its variations can be corrected using a low-capacity memory.

The operation of the dark current correction device for a star tracker having such a configuration will be explained.

This star tracker has three operating modes: The first operating mode is the shutter 13
opens to capture starlight, and images the star onto CCD 12 to collect data. In the second operation mode, the shutter 13 is closed and dark current data of the pixels imaged in the first operation mode is collected. In the third operation mode, the shutter 13 is opened again, and based on the dark current data obtained in the second operation mode, the CCD
The luminance data at the output of No. 12 is corrected.

In the first operation mode, the output control signal of the shutter drive control circuit 14 controls the shutter drive circuit 15 according to the control output signal of the operation mode control device 27, the shutter 13 is in an open state, and the starlight is emitted. The light is focused by the optical system 11 and the CCD 1
The image is formed on the light receiving surface of 2. On the other hand, the CCD drive circuit 16 is controlled by the output control signal of the shutter drive control circuit 14;
Image signal address generation circuit 19
In addition to generating position information, the CCD 12 performs an imaging operation, and the photoelectrically converted data is
Output to the CCD image signal amplification circuit 20 and amplified,
The signals are output to the inputs of the analog-to-digital conversion circuit 21 and the comparison circuit 22, respectively. Comparison circuit 2
2, when a signal higher than the threshold level of the output voltage of the reference voltage generation circuit 23 is input from the CCD image signal amplification circuit 20, the image signal address generation circuit 19 and the analog-to-digital conversion circuit 21 operate. output to each circuit. Address output signal of image signal address generation circuit 19 and analog/digital conversion circuit 2
The output signals subjected to analog-to-digital conversion in 1 are multiplexed in a multiplexing circuit 24 in a 1:1 correspondence.
The data is sent to the data processing circuit 25 and processed.

FIG. 2 shows the image formation state on the CCD 12.

In the first mode of operation, the star tracker is tracking one star. Then, the coordinate points of the H-V coordinates and the analog-to-digital converted digital voltage signal are stored in the dark current value memory circuit 26 of FIG.

Next, in the second operation mode, the output control signal of the shutter drive control circuit 14 controls the shutter drive circuit 15 in response to the control output signal of the operation mode control device 27, and the shutter 13 is closed. At this time, no light enters CCD12 at all, and the CCD
Each of the 12 pixels outputs a voltage corresponding to the dark current. This output is similarly amplified by the CCD image signal amplification circuit 20 and output to the analog-to-digital conversion circuit 21. At this time, the dark current correction control circuit 18 is controlled by the output signal of the shutter drive control circuit 14, and the address (position) of the pixel that was illuminated in the first operation mode is stored in the dark current value memory circuit 26. The current correction control circuit 18 reads out the signal, counts the timing waveform with the CCD drive circuit 16, and outputs a trigger to the dark current correction circuit 17 at the matched pixel address. The dark current correction circuit 17 outputs a control signal corresponding to this trigger signal to the image signal address generation circuit 19 and the analog/digital conversion circuit 21, where the dark current level of only the corresponding pixel is converted from analog to digital. Further, the output is multiplexed with the address output signal of the image signal address generation circuit 19 in the multiplexing circuit 24, sent to the data processing circuit 25, and processed, and the address and dark current data are stored together in the dark current value memory circuit 26 again. be done.

From the above, as shown in Figure 3, regarding the part of the CCD light-receiving surface where the starlight was focused,
The output in the absence of light, that is, the dark current value of only the pixel corresponding to the light condensing portion can be measured and stored.

Next, in the third operation mode, the shutter drive control circuit 14 again controls the shutter drive circuit 15 in response to the control output signal of the operation mode control device 27, and the shutter 13 is opened. The starlight is again focused on the CCD 12, and as described above, data corresponding to the imaging position of the starlight is acquired and processed by the data processing circuit 25. At this time, the dark current correction circuit 17 outputs a dark current value for each corresponding pixel based on the dark current data stored in the dark current value memory circuit 26, and the differential Dark current and its dispersion can be corrected by performing analog-to-digital conversion processing on the result subtracted by the amplifier.

The configuration and operation of the above CCD will be explained with reference to FIG. The CCD includes a photoelectric conversion unit 31 that converts input light into charges according to the amount of light and accumulates them, a transfer electrode 33 that transfers the accumulated signal charges to a vertical transfer register 32 using a transfer signal clock _φTG , The vertical transfer register 32 transfers the charge to the horizontal transfer register 34 using the transfer signal clocks φ _V1 and φ _V2 , and the signal is sequentially sent to the output gate 35 from the horizontal transfer register 34 using the transfer signal clocks φ _H1 and φ _H2 . It is composed of a detection section 36 that converts electric charge into a voltage signal and outputs it from the CCD.

When using this CCD as a star tracker detector, the optical system
A star image is formed on the light-receiving surface of the CCD, and the imaging operation described above is performed to obtain star brightness data and position data.

〔Effect of the invention〕

As described above, the present invention makes it possible to correct dark current and its dispersion with a simple configuration and a small amount of memory, and can significantly improve the accuracy of the star tracker.

Furthermore, by increasing the memory a little, it is possible to acquire dark current data over a wide range, which has the advantage of being able to deal with slight changes in the satellite's attitude without having to close the shutter and correct dark current each time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a star tracker dark current correction device according to an embodiment of the present invention. Figure 2 is a CCD
The figure which shows the image formation state on the upper part. Figure 3 is a configuration diagram of the CCD. 11...Optical system, 12...CCD, 13...Shutter, 14...Shutter drive control circuit, 1
5... Shutter drive circuit, 16... CCD drive circuit, 17... Dark current correction circuit, 18... Dark current correction control circuit, 19... Image signal address generation circuit, 20... CCD image signal amplification circuit, 21 ……
Analog-digital conversion circuit, 22... Comparison circuit, 23... Reference voltage generation circuit, 24... Multiplex circuit, 25... Data processing circuit, 26... Dark current value memory circuit, 27... Operation mode control device, 2
8...Attitude control signal output terminal, 31...Photoelectric conversion unit, 32...Vertical transfer register, 33...Transfer electrode, 34...Horizontal transfer register, 35...
...output gate, 36...detection section.

Claims (1)

[Scope of Claims] 1. An optical system that focuses star light, a shutter mechanism that blocks light incident on this optical system, and a two-dimensional system that converts the star image focused on the optical system into an electrical signal. a solid-state image sensor; a drive circuit that generates a drive signal to sequentially scan the two-dimensional solid-state image sensor; means for converting the scanning output of the two-dimensional solid-state image sensor from analog to digital; An address generation circuit that generates an image signal address, a reference voltage generation circuit that generates a reference voltage corresponding to a threshold level for identifying the presence or absence of a star image, and the output of this reference voltage generation circuit as one input, and the above A comparison circuit whose other input is the scanning output of the two-dimensional solid-state image sensor, and the output of the image signal address generation circuit and the analog-digital converted output of the two-dimensional solid-state image sensor are input, and the brightness data of the star is and a control device including a data processing circuit that processes position data and a memory circuit that stores this data, wherein the control device opens the shutter mechanism and outputs the output of the two-dimensional solid-state image sensor. a first mode for collecting data; a second mode for collecting dark current data from the output data of the two-dimensional solid-state image sensor with the shutter mechanism in the closed state; and a second mode in which the shutter mechanism is in the open state and dark current data is collected from the output data of the two-dimensional solid-state image sensor; and a third mode in which output data of the two-dimensional solid-state image sensor is collected and corrected using the dark current data. A dark current correction device for a star tracker, comprising means for collecting dark current data at a position of the two-dimensional solid-state image sensor where the luminance data is equal to or higher than the threshold level in the first mode. .