JP2014058176A - Earth sensor and earth edge detection method using earth sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized and low cost earth sensor and an earth edge detection method using the earth sensor, suitable for mounting a small artificial satellite, in the present invention.SOLUTION: The earth sensor includes at least three earth edge detectors having a detection part including a plurality of thermopile elements arranged in a line shape or arranged in a skew in the vertical direction to the earth edge and a signal processing part for digitally converting and outputting a signal detected by the detection part, and can detect the earth edge 708 in arrangement of the thermopile elements, by determining arrangement De, Dn, Dw and Ds of the thermopile elements of becoming 1 in a digital value as an earth area 700 and arrangement of the thermopile elements of becoming 0 in the digital value as space, by being converted into the digital value with every thermopile element, by binarizing to a value of 0 or 1 with every thermopile element, by comparing an infrared radiation amount outputted with every thermopile element with a predetermined threshold value by the signal processing part.

Description

  The present invention relates to attitude control of an artificial satellite, and more particularly to an earth sensor mounted on an artificial satellite for detecting the position of the earth and an earth edge detection method using the earth sensor.

  Earth sensors mounted on artificial satellites are widely used for attitude control of artificial satellites. An artificial earth sensor in outer space detects the outline of the earth (ie, the “earth edge”) in order to know the position of the earth. From the detected earth edge, the attitude angle of the artificial satellite with respect to the center of the earth can be obtained, and the attitude of the artificial satellite such as a low orbiting satellite or geostationary satellite can be controlled.

Conventional earth sensors employ various earth edge detection methods. The earth edge detection methods can be roughly classified into three types: a horizon scanner method, a horizon tracker method, and a static thermal balance method. Both methods use infrared detectors to detect infrared radiation from the earth (hereinafter simply referred to as “earth infrared radiation”), but most devices have a relatively stable radiation intensity regardless of day or night. The infrared rays in the 14-16 μm band (black body radiation from the CO ₂ layer at an altitude of about 40 km) are detected (see FIG. 8).

  FIG. 1 is a diagram for explaining the operating principle of a conventional horizon scanner type earth sensor. The scanning unit 100 of the horizon scanner-type earth sensor includes a lens 102 that captures an image of the earth 110 by adjusting the focal point and the viewing angle of an infrared detector (S infrared detector 106, N infrared detector 108), and S And a scan mirror 104 that controls a scan direction 112 by the infrared detector 106 and a scan direction 114 by the N infrared detector 108.

  The scan mirror 104 can scan the earth 110 from left to right (or from left to right) by rotating about the vertical axis. When scanning from left to right (or right to left) scan directions 112 and 114 using the S infrared detector 106 and the N infrared detector 108, the earth edge 116 can be detected. In general, an infrared detector hardly detects infrared radiation in outer space, and the output of the infrared detector is almost zero, but it detects earth infrared radiation for the earth. Output higher than that of outer space.

  In the conventional example shown in FIG. 1, the S infrared detector 106 performs scanning in the scanning direction 112 from the left to the right, and the output state is shown in the S infrared detector output waveform 126. When the S infrared detector 106 captures the earth 110 from outer space by scanning, the S infrared detector output waveform 126 changes from the previous low value to the high value. In addition, while the scan progresses and the S infrared detector 106 is capturing the earth 110 (ie, in the earth region 124), the S infrared detector output waveform 126 remains high and deviates from the earth 110 into space. The S infrared detector output waveform 126 changes from a high value to a low value. Thus, two places where the S infrared detector output waveform 126 changes can be detected as the earth edge 116. Similarly, with respect to the N infrared detector, two places where the N infrared detector output waveform 128 changes can be detected as the earth edge 116.

  Using the earth edge information detected at the four locations as described above, the space space and the earth region 124 are grasped by the artificial satellite, and the satellite coordinate center 122 coincides with the earth center 120 without departing from the earth region 124. Thus, the attitude of the artificial satellite is controlled.

  FIG. 2 is a diagram for explaining the operation principle of the earth sensor of the horizon tracker system. The earth sensor of the horizon tracker type can detect the earth edge 116 by causing the viewing angle 202 of the infrared detector to vibrate slightly (scan tracking 200) in a direction perpendicular to the horizon (earth edge) of the earth 110. Specifically, a location where the infrared detector output waveform (infrared sensor output) greatly changes can be detected as the earth edge in the output waveform. The artificial satellite can control the attitude so as to capture the earth edge 116 within the viewing angle 202 of the infrared detector using the earth edge in the infrared detector output waveform (output of the infrared sensor).

  FIG. 3 is a diagram for explaining the operating principle of a static thermal equilibrium earth sensor. The static thermal balance type earth sensor detects the satellite coordinate center 302 of the artificial satellite and the earth from the ratio of the amount of earth infrared radiation (An and As of the infrared detector output 300, Aw and Ae) detected by the opposite infrared detector. Deviations (roll angle, pitch angle, etc.) of the center 120 can be detected. The artificial satellite can perform attitude control using information on deviations such as the detected roll angle and pitch angle.

JERG-2-510-HB002 Attitude Control System Component Technology Handbook, Japan Aerospace Exploration Agency (JAXA)

  However, the conventional earth sensor shown in FIGS. 1 to 3 has several points to be improved. In the horizon scanner system shown in FIG. 1, the scan mirror 104 and the drive unit are required, so that the apparatus is large and complicated. In addition, wear of the mechanical drive unit may increase. The horizon tracker method shown in FIG. 2 also requires a drive unit as in the case of the horizon scanner method, and since it has a drive system, the equipment becomes large and complicated, and there is a risk of wear failure in the drive unit.

  In the static thermal equilibrium system shown in FIG. 3, the amount of earth infrared radiation detected by the infrared detector varies depending on the latitude and season of the earth. The fluctuation of the earth's longitude and season greatly affects the output result of the infrared detector, and the attitude of the satellite may not be controlled well. Therefore, it is necessary to know the characteristics by conducting an accurate thermal test of the sensitivity characteristics of devices such as infrared detectors when manufacturing a static thermal equilibrium earth sensor.

  As described above, since the conventional earth sensor (conventional example shown in FIGS. 1 to 3) has been developed on the premise that it is mounted on a large artificial satellite, it is possible to detect the earth edge with high accuracy. However, since a mirror, a drive unit, and the like are provided, the size becomes large, and further, a device for preventing wear of the drive unit has to be taken, which generally increases the cost for manufacturing the device. In addition, a large earth sensor cannot be mounted on a small satellite. Therefore, there is a need for a small and lightweight earth sensor suitable for mounting on a small satellite.

  In order to solve such a problem, the present invention provides a small and low-cost earth sensor suitable for mounting on a small artificial satellite, and an earth edge detection method using the earth sensor.

In order to solve the above problems, the present invention proposes a new earth sensor and an earth edge detection method (method) (hereinafter referred to as “horizon digital detection method”) adopted for the earth sensor.

In one embodiment of the earth sensor according to the present invention, the earth sensor includes a detection unit including a plurality of thermopile elements arranged in a line or obliquely in a direction perpendicular to the earth edge, and the detection unit includes: A housing cover that stores at least three earth edge detectors including a signal processing unit that digitally converts and outputs detected signals;
A housing base including a connection connector for outputting an output value from the signal processing unit to the outside,
The detection unit includes a cylindrical lens unit having a lens and an element unit in which the plurality of thermopile elements are arranged,
The casing cover is provided with holes for exposing the lens part of the earth edge detector to the outside at equal angular intervals with the center of the earth sensor as a base point,
The earth edge detectors are stored in the housing cover at the equal angular intervals;
Infrared detection is performed by a plurality of thermopile elements included in the detection unit of each of the earth edge detectors, and an infrared radiation amount is output to the signal processing unit for each thermopile element,
The infrared radiation amount output for each thermopile element by the signal processing unit is compared with a predetermined threshold value, and binarized to a value of 0 or 1 for each thermopile element, and digital for each thermopile element Converted to a value,
The digital value for each thermopile element corresponds to the arrangement of the thermopile elements, and the arrangement of the thermopile elements with a digital value of 1 is determined as the earth region, and the arrangement of the thermopile elements with a digital value of 0 is determined as outer space. The earth edge is detected in the arrangement of the thermopile elements.

In a preferred embodiment of the earth sensor according to the present invention, the earth sensor stores at least three sensor blocks in which the enclosure cover is mounted with the earth edge detector,
The sensor block has a block opening for exposing the lens portion of the earth edge detector to the outside, and a mounting surface having an inclination corresponding to an angle for detecting the earth edge,
The earth edge detector has the detection unit and the signal processing unit on a rectangular substrate, the rectangular substrate is aligned with the mounting surface, and the lens unit is disposed in the block opening. Is attached to the sensor block,
In the case cover, the case openings are provided at equal angular intervals with the center of the earth sensor as a base point to expose the lens portion exposed from the block opening to the outside.
The sensor block on which the earth edge detector is mounted is stored in the center housing at the same angular interval with the center of the earth sensor as a base point, with the long axis of the sensor block being vertical.

In a further preferred embodiment of the earth sensor according to the present invention, the earth sensor has first to fourth sensor blocks mounted with first to fourth earth edge detectors, respectively.
Each of the first to fourth sensor blocks has a front surface on the block opening side, a back surface on the mounting surface side, a right side surface, and a left side surface,
The first to fourth sensor blocks are symmetric with respect to the center of the earth sensor,
The rear surface of the first sensor block is opposed to the right side surface or the left side surface of the second sensor block,
The rear surface of the second sensor block is opposed to the right side surface or the left side surface of the third sensor block,
The rear surface of the third sensor block is opposed to the right side surface or the left side surface of the fourth sensor block,
The back surface of the fourth sensor block is opposed to the right side surface or the left side surface of the first sensor block so as to be combined in a bowl shape and stored in the housing cover.

  In still another embodiment of the earth sensor according to the present invention, the earth sensor includes first to fourth earth edge detectors. Further, the pitch angle and roll angle of the artificial satellite are calculated based on the digital value for each thermopile element obtained from each of the earth edge detectors and the viewing angle for each thermopile element. .

In an embodiment of the earth sensor having first to fourth earth edge detectors, the earth sensor has a viewing angle θ ₀ per thermopile element;
The number of thermopile elements Dn determined as the earth region by the first earth edge detector,
The number Ds of thermopile elements determined as the earth region by the second earth edge detector,
The number of thermopile elements Dw determined as the earth region by the third earth edge detector,
Formula using the number of thermopile elements De determined as the earth region by the fourth earth edge detector:
Pitch angle = θ ₀ × (Ds−Dn) / 2
Roll angle = θ ₀ × (Dw−De) / 2
Thus, the pitch angle and roll angle of the artificial satellite are calculated.

  As another embodiment of the earth sensor according to the present invention, at least one of the earth edge detectors is an infrared detector using another kind of infrared detecting element instead of the thermopile element. .

In one embodiment of the earth edge detection method according to the present invention, a detection unit including a plurality of thermopile elements arranged in a line or obliquely in a direction perpendicular to the earth edge, and detected by the detection unit. An earth edge detection method for an earth sensor including at least three earth edge detectors including a signal processing unit that digitally converts the output signal and outputs the signal.
Performing infrared detection by a plurality of thermopile elements included in the detection unit of each of the earth edge detectors, and outputting an infrared radiation amount to the signal processing unit for each thermopile element;
The infrared radiation amount output for each thermopile element by the signal processing unit is compared with a predetermined threshold value, and binarized to a value of 0 or 1 for each thermopile element, and digital for each thermopile element Converting to a value;
Calculating the pitch angle and roll angle of the satellite based on the digital value for each thermopile element obtained from each of the earth edge detectors and the viewing angle per thermopile element,
The digital value for each thermopile element corresponds to the arrangement of the thermopile elements, and the arrangement of the thermopile elements with a digital value of 1 is determined as the earth region, and the arrangement of the thermopile elements with a digital value of 0 is determined as outer space. , Detecting an earth edge in the array of thermopile elements.

  By adopting a multi-element line array thermopile array having a constant viewing angle in the detection part of the earth edge detector, the mechanical drive system required in the conventional earth edge detector can be omitted. As a result, the mechanism of the earth sensor can be greatly simplified, and the earth sensor can be reduced in size, weight, and cost. Moreover, it is not necessary to take measures against wear and failure of the drive unit.

  A multi-element line array thermopile array, which has been calibrated in advance, can detect earth and space areas, that is, detect the earth edge in units of thermopile elements. The earth edge can be detected more easily than the earth edge detector. As a result, the algorithm for calculating the attitude angle (pitch angle / roll angle) of the artificial satellite can be simplified. If the number of earth edge detectors is at least three or more, the attitude angle (pitch angle / roll angle) of the artificial satellite can be calculated, but the earth sensor is configured using four earth edge detectors. Then, the pitch angle and roll angle can be calculated more easily.

  Furthermore, in determining the earth edge, by appropriately setting the threshold value of the earth edge, it is possible to eliminate the difference in the amount of earth infrared radiation between the equatorial region and the polar region and the influence of the fluctuation amount. Further, by using a thermopile array composed of more thermopile elements as the earth edge detector, the viewing angle per element can be reduced, and the resolution can be further improved.

FIG. 1 is a diagram for explaining the operation principle of the earth sensor of the horizon scanner type. FIG. 2 is a diagram for explaining the operation principle of the earth sensor of the horizon tracker system. FIG. 3 is a diagram for explaining the operating principle of a static thermal equilibrium earth sensor. FIG. 4 is a diagram showing a thermopile array used as an earth edge detector. FIG. 5 is a diagram showing one embodiment of the arrangement of the thermopile elements in the element portion of the thermopile array. FIG. 6 is a diagram showing an XY axis and a viewing angle in the thermopile array. FIG. 7 is a graph showing an infrared detection wavelength region in a thermopile array. FIG. 8 is a graph showing the relationship between the amount of terrestrial infrared radiation and the wavelength in the low latitude region, middle latitude region, and polar region of the earth. FIG. 9 is a diagram illustrating one embodiment of an earth sensor using four thermopile arrays as earth edge detectors. FIG. 10 is a diagram showing the relationship between the orbit altitude of the artificial satellite and the viewing angle of the earth edge detector mounted on the artificial satellite. FIG. 11 is a diagram for explaining a method of detecting an earth edge in an earth edge detector using a thermopile array. FIG. 12 is a diagram illustrating a relationship between a signal output from each thermopile element in the thermopile array and a threshold value. FIG. 13 is a diagram for explaining a method for calculating the attitude angle of the artificial satellite. FIG. 14 is a diagram illustrating a relationship between an output signal of each thermopile element and a threshold value when the earth edge detection method according to another embodiment is used. FIG. 15 is a diagram showing a sensor block for mounting the earth edge detector. FIG. 16 is a diagram showing a housing cover for storing the sensor block equipped with the earth edge detector in a bowl shape. FIG. 17 is a top view, a side view, and a cross-sectional view of an earth sensor in which four sensor blocks are housed and fixed in a bowl shape in a housing cover. FIG. 18 is a diagram showing an embodiment of the earth sensor that is miniaturized by mounting four sensor blocks in a bowl shape. FIG. 19 is a diagram illustrating the offset angle of the downsized earth sensor. FIG. 20 is a diagram illustrating an example in which a downsized earth sensor is fixed to a structure panel of an artificial satellite.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  FIG. 4 shows a thermopile array used as an earth edge detector in an earth sensor as one embodiment of the present invention. The thermopile array 400 includes a detection unit 402 and a signal processing unit 404 on a substrate 405. As shown in FIG. 5, the detection unit 402 has a plurality of thermopile elements in which element numbers 1 to 16 are alternated, such that number 2 is behind the first and second is the second, and the third is behind the second. It consists of element parts 410 arranged in two rows and a cylindrical lens part 408 having a lens 406. As shown in FIG. 5, an alternate two-row array is called a “diagonal array”. The plurality of thermopile elements can also be arranged in a straight line (line shape). The element portion 410 is on the substrate surface inside the lens portion 408 (see FIG. 5). In addition, the substrate 405 is provided with a connection terminal 414 for outputting the electrical signal processed in the signal processing unit 404 to a device outside the thermopile array 400. The shape of the substrate 405 is a rectangle, but other than the rectangle, an optimum shape can be adopted for storage in the case of the earth sensor.

  The thermopile array 400 detects infrared radiation from the object by the detection unit 402 and outputs an electrical signal corresponding to the amount of infrared radiation by the signal processing unit 404. Specifically, the infrared rays incident through the lens unit 408 having the lens 406 are detected by a plurality of thermopile elements of the element unit 410, and the infrared rays are detected according to the infrared radiation amount detected by the signal processing unit 404. It is converted into a signal and output to the outside from the connection terminal 414.

  In another embodiment of the present invention, instead of the plurality of thermopile elements of the thermopile array 400, an infrared detector in which other infrared detection elements are arranged in a line or in an oblique arrangement may be used as the earth edge detector. it can.

  FIG. 5 shows one embodiment of the arrangement of the thermopile elements 412 in the element part 410 of the thermopile array 400 shown in FIG. The 16 thermopile elements 412 are alternately arranged in two rows on the substrate inside the lens unit 408 (that is, an oblique arrangement). In FIG. 5, element numbers 1 to 16 are assigned in order from the left thermopile element. The thermopile element 412 is an individual element that detects infrared rays emitted from an object, and can output a voltage proportional to the temperature of the object. The thermopile array 400 used in one embodiment of the present invention is a type in which 2 × 8 thermopile elements 412 are diagonally arranged, but the object is sufficiently distant from the satellite to the earth. In this case, it can be regarded as a 1 × 16 line element array. In another embodiment, a plurality of thermopile elements can be arranged in a line. Further, the number of the thermopile elements 412 is not limited to 16, and can be increased or decreased in response to demands for improving the detection accuracy of the earth edge, reducing costs, and reducing the size. Generally, by increasing the number of thermopile elements, the viewing angle per element can be reduced, the resolution of the earth edge detector can be improved, and the earth edge detection system can be improved.

  FOV (X) and FOV (Y) in FIG. 5 indicate the field angle of view (FOV) of the thermopile array 400 and the field angle of the Y axis direction, respectively. When the thermopile array 400 is used as the earth edge detector, the X axis is an axis perpendicular to the earth edge, and the Y axis is an axis parallel to the earth edge. By arranging the plurality of thermopile elements 412 in the direction perpendicular to the earth edge (X-axis direction), the earth edge can be captured with a wide viewing angle FOV (X).

  FIG. 6 shows an XY axis direction and a viewing angle in a thermopile array 400 used as an earth edge detector. FIG. 6A is a plan view of the thermopile array 400 showing the axial direction. The major axis direction of the rectangular thermopile array 400 is the X axis, and the minor axis direction is the Y axis. As described above, when the thermopile array 400 is mounted on an earth sensor as an earth edge detector, the X axis is perpendicular to the earth edge of the earth, and the Y axis is parallel.

  FIG. 6B shows an example of the viewing angle FOV (X) in the X-axis direction. Although the viewing angle is determined by the focal length of the lens, as one embodiment of the present invention, an earth edge detector using the thermopile array 400 has a focal length of 10.6 mm and a viewing angle FOV (X) in the X direction. Is 17 °, and the viewing angle FOV (Y) in the Y direction is 2.5 °. Since 16 elements are arranged in the X direction, the viewing angle per element, that is, the edge detection accuracy is about 1 °.

  FIG. 7 is a graph showing an infrared detection wavelength region in a thermopile array. The vertical axis of the graph is the infrared transmittance, and the horizontal axis is the wavelength. An uncoated silicon lens (G12) can be used as one embodiment of the lens 406 used in the earth edge detector of the present invention (thermopile array 400 in the example of FIG. 4). The STANDARD line in the graph of FIG. 7 represents the infrared detection wavelength range of a conventional lens, and the G12 line represents the infrared detection wavelength range when an uncoated silicon lens (G12) is used. It can be seen that the non-coated silicon lens (G12) indicated by the G12 line has a characteristic of a constant transmittance in a wide wavelength range, compared to the conventional lens indicated by the STANDARD line.

FIG. 8 is a graph showing the relationship between the amount of terrestrial infrared radiation and the wavelength in the low latitude region, middle latitude region, and polar region of the earth. The vertical axis of the graph is the amount of infrared radiation (radiance), and the horizontal axis is the wavelength. Many conventional earth sensor, the absorption band of CO ₂ as a detection wavelength range of infrared 14～16Myuemu (CO ₂ bands) is adopted (in FIG. 8 (1) Detection wavelength range of conventional earth sensor ). The reason is that the CO ₂ profile is formed in the upper layer of the atmosphere, so that the influence of weather fluctuations in the troposphere is small and the infrared radiation amount is stable. From the graphs of (a) low longitude region, (b) medium longitude region, and (c) polar region shown in FIG. 8, almost constant values in the wavelength region of 14 to 16 μm (CO ₂ band) (around 50) It can be understood that it is stable. These conventional earth sensors usually have CO ₂ profile (infrared radiation amount) data inside and detect a position where the relative intensity with respect to the peak level is ½ as an “earth edge”. .

However, although the CO ₂ profile is stable, there are various fluctuation factors depending on the latitude, longitude, season, time zone, etc., and the high-accuracy earth sensor also corrects for these fluctuation factors. Computation becomes quite complicated.

  On the other hand, the earth edge detector used in the present invention employs an uncoated silicon lens (G12), so that the detection wavelength region is flat in the far infrared region as shown in FIG. Most of the wavelength range of the earth infrared radiation shown in FIG. 8 ((2) the wavelength range of the earth edge detector according to the present invention in FIG. 8) is detected.

This is because each detection element is digitally used only for distinguishing between the earth region (with earth infrared radiation) and the space region (without earth infrared radiation), and highly accurate detection using the CO ₂ band. This is because there is no need to perform. As a result, costs associated with lens coating processing and complicated parameter calculation processing are reduced.

  FIG. 9 illustrates one embodiment of an earth sensor using four thermopile arrays 400 as earth edge detectors. In order to control the attitude of the artificial satellite, if there are at least three earth edge detectors, it is possible to detect the earth edge and grasp the position of the earth. That is, it is possible to configure an earth sensor using at least three earth edge detectors.

  An earth sensor 500 according to an embodiment of the present invention includes a housing cover 502 that houses four earth edge detectors and a housing base 504. In addition, a connection connector 506 is installed on the housing base 504. As the four earth edge detectors in the earth sensor 500, the four 16-element thermopile arrays 400 shown in FIGS. 4 and 5 can be used. A control information generation unit (not shown) that processes electric signals output from the connection terminals 414 of each thermopile array 400 to generate control information (such as a posture control angle such as a pitch angle and a roll angle) serves as an earth sensor 500. Can also be included. The output (control information) from the control information generation unit is transmitted to the artificial satellite body connected to the earth sensor 500 via the connection connector 506.

  In another embodiment, an infrared detector composed of another infrared detecting element can be used as the four earth edge detectors, and can be used in combination with the thermopile array 400.

  The four earth edge detectors are stored in the housing cover 502 at 90 ° intervals with the center of the earth sensor 500 as a base point, and are arranged so that the lens 406 and the lens portion 408 of the thermopile array 400 face outward. It is fixed inside the housing cover 502. In other words, four earth edge detectors (referred to as first to fourth earth edge detectors for convenience) inside the housing cover 502 are symmetrical with respect to the center of the earth sensor 500. One earth edge detector and a second earth edge detector are arranged, and a third earth edge detector and a fourth earth edge detector are arranged symmetrically with respect to the center of the earth sensor. At this time, a straight line connecting the first earth edge detector and the second earth edge detector intersects with a straight line connecting the third earth edge detector and the fourth earth edge detector at a right angle.

  In the earth sensor 500 that is one embodiment of the present invention, the lens portion 408 of the thermopile array 400 is exposed from the opening of the housing cover 502. In another embodiment, only the lens 406 may be exposed from the opening of the housing cover 502 and the lens unit 408 may not be exposed.

The earth edge detectors located on opposite sides should be arranged such that the center axis of the viewing angle of one earth edge detector and the center axis of the viewing angle of the other earth edge detector form an offset angle θ _offset. Can do. The offset angle θ _offset is determined according to the orbital altitude of the artificial satellite.
In FIG. 9, as an example, the offset angle θ _offset of one set of earth edge detectors located on the opposite sides is shown, but the other set of earth edge detectors are also arranged to form the same offset angle. The

FIG. 10 shows the relationship between the orbital altitude of the artificial satellite and the viewing angle of the earth edge detector mounted on the artificial satellite. When an artificial satellite equipped with the earth sensor 500 is flying in the outer space 602 with an orbital altitude of 900 km (H = 900 km), the offset angle θ _offset between the earth edge detectors located on the opposite sides is set to 123 °. If the attitude angle is 0 ° in both the pitch / roll angles, that is, when the artificial satellite is facing the center of the earth 600, the arrangement of the infrared detection elements (ie, thermopile elements) of each earth edge detector. The edge of the earth can be captured by the central element. In the example of FIG. 5, among the 16 thermopile elements of the thermopile array 400, the earth edge can be captured between the element number 8 or 9 or the element numbers 8 and 9. By adjusting the offset angle θ _offset , it is possible to mount the satellites on various orbital altitudes.

  Here, with reference to FIGS. 11A to 11C, a method for detecting the earth edge in the earth edge detector using the thermopile array 400 will be described. The four earth edge detectors of the earth sensor mounted on the artificial satellite are arranged so that the earth edge 708 comes to the center of the visual field 706 when the attitude angle is 0 ° in both the pitch angle and the roll angle as described above. At this time, the satellite coordinate center 704 of the artificial satellite overlaps the earth center 702 in the earth infrared region 700. One square of the visual field 706 corresponds to one thermopile element 412 arranged in the element unit 410 of the thermopile array 400.

  In FIG. 5, 16 thermopile elements 412 are arranged. However, in FIG. 11, the number of squares in the visual field 706 is displayed by a number smaller than 16 for simplification.

  When the attitude angle of the artificial satellite changes as shown in FIG. 11A, the position of the earth edge 708 detected in the field of view 706 (An, As, Aw, Ae) of each earth edge detector is shifted from the center. Become.

  FIG. 11B is a schematic diagram when the attitude of the artificial satellite changes to the right, that is, when the earth edge shifts to the left in the field of view 706 (Ae) of the detector. In this example, among the thermopile elements corresponding to 8 squares in the field of view 706, the thermopile elements corresponding to the 1st to 4th squares from the left capture the earth infrared radiation, and the 4th and 5th squares from the left The earth edge 708 can be detected from the detection result of the corresponding thermopile element. A specific detection method will be described with reference to FIG.

  FIG.11 (c) shows the signal output (voltage output) of the thermopile element corresponding to each square of the visual field 706 (Ae) in the example of FIG.11 (b). That is, the thermopile element that captures the earth infrared region 700 and the thermopile element that captures the space region 701 can obtain voltage outputs corresponding to the infrared radiation intensity, respectively, but the temperature of the space region 701 is Since the temperature is extremely low (absolute temperature 3 k), the output is a constant value almost close to zero. Therefore, the boundary point can be detected as the earth edge by setting a threshold value for determining the earth / space region.

  FIG. 12 shows the relationship between the signal output from each thermopile element in the thermopile array and the threshold value. In the atmosphere layer outside the ground surface, the infrared radiation intensity has a profile that attenuates according to the altitude from the ground surface, and in the space region, the output reaches a constant value close to zero. As in one embodiment of the present invention shown in FIG. 10, in the case of a 16-element earth edge detector with an orbital altitude of 900 km and a viewing angle of 17 °, the viewing area at the earth edge is approximately 1065 km. The visual field area is about 67 km. If the thickness of the atmospheric layer is about 100 km (although there are slight variations depending on the season and time zone), an intermediate value due to the influence of the atmospheric layer is output over a maximum of three elements.

Since the infrared wavelength range of the earth edge detector according to the present invention covers a wide range (for example, the range (2) in FIG. 8), it varies depending on the latitude and time zone, and depends on O ₃ and H ₂ 0 in the atmosphere. There are various fluctuation factors such as absorption, and it is expected that the infrared radiation intensity of the atmosphere layer and the surrounding earth region is also unstable. Among them, the most unstable and the cause of misrecognition in the conventional earth sensor is the difference in the amount of infrared radiation and the amount of fluctuation in the low latitude (equator) and polar regions shown in FIG. It is difficult to predict.

  Since the earth edge detector using the thermopile array 400 which is one embodiment of the present invention is sensitive to infrared radiation in a wider wavelength band, the earth infrared radiation in FIG. 8 is integrated over almost the entire wavelength band. Output the amount. That is, as shown in FIGS. 12 (a) to 12 (c), within the earth infrared region, the output is in accordance with the infrared radiation integration amount in each region (low latitude region, middle latitude region, polar region). The output is attenuated toward a constant value in the space region.

  Therefore, in the present invention, the threshold value is set to a low value within a possible range (a height slightly higher than the amount of radiation in the cosmic region and the altitude at which the influence of infrared radiation in the earth's atmosphere has begun to be detected). The influence of the difference in the amount of external radiation and the fluctuation amount can be eliminated as much as possible.

  The columns 1 and 0 in the graphs of FIGS. 12A to 12C indicate that the electrical signal corresponding to the amount of infrared radiation detected by the detection unit 402 of the thermopile array 400 is greater than the threshold set in advance as described above. Is larger (or greater than or equal to the threshold value), the digital value output from the signal processing unit 404 is set to 1, and when it is less than or equal to the threshold value (or smaller than the threshold value), the digital value is set to 0. ing. In other words, by determining the array of thermopile elements with a digital value of 1 as the earth infrared region (earth region) and the array of thermopile elements with a digital value of 0 as space (space region), The earth edge can be detected.

FIG. 13 is a diagram for explaining a method of calculating the attitude angle (pitch angle / roll angle) of the artificial satellite with respect to the earth center. As shown in FIG. 12, the number of elements determined that the signal output of the elements in each earth edge detector is larger than the threshold (earth area) (that is, 1) is obtained. In the case of an earth sensor using four earth edge detectors, as shown in FIG. 13, the number of elements determined as the earth region is Dn, Ds, Dw, and De, respectively, and the viewing angle of one element is θ _0. Then, the attitude angle (pitch angle / roll angle) of the artificial satellite with respect to the earth center is
Pitch angle = θ ₀ × (Ds−Dn) / 2
Roll angle = θ ₀ × (Dw−De) / 2
It can be calculated by the following formula.

  For example, in the earth sensor 500 that is one embodiment of the present invention shown in FIG. 9, the digital value (1 or 0) output from the signal processing unit 404 of each of the four thermopile arrays 400 via the connection terminal 414. Can be added to obtain the values of Dn, Ds, Dw, and De, respectively. Then, control information including a pitch angle and a roll angle calculated using the above equations can be generated by a control information generation unit (not shown in FIG. 9) in the earth sensor.

Although the earth edge detection method and the satellite attitude angle (pitch angle / roll angle) calculation method as shown in FIGS. 11 to 13 are extremely simple, the signal output of the earth edge detector is digitally set to 0 and 1. Therefore, the calculation accuracy of the pitch angle and the roll angle depends on the viewing angle θ ₀ of one element.

  Therefore, as a method for further improving the attitude angle accuracy while eliminating the influence of the difference in the amount of earth infrared radiation depending on the region (low latitude region / mid latitude region / polar region) where the earth edge is detected, The earth edge detection method and the attitude angle calculation method can be used. In other embodiments, unlike the previous embodiment, the signal output of the earth edge detector is not digitized but is used as an analog voltage value.

  FIG. 14 is a diagram for explaining the earth edge detection method and the attitude angle calculation method according to another embodiment, and the relationship between the output signal of each thermopile element and the threshold value when the earth edge detection method is used. Indicates. As shown in FIG. 14, it is understood that the signal output voltage in the earth infrared region detected by the earth edge detector has a characteristic that it varies depending on the temperature of each region such as low latitude region / mid latitude region / polar region. .

  A method for calculating the attitude angle of an artificial satellite using this feature is as follows. First, for each earth edge detector, a signal output from an element whose field of view is completely directed to the earth region is used. The amount of radiation (VR_low, VR_middle, VR_high) is determined. Next, for each earth edge detector, the signal output from the element including the earth edge in the field of view is set as the earth edge radiation amount (VE_low, VE_middle, VE_high). Further, the amount of cosmic infrared radiation (VR_space) is determined by using a signal output from an element whose field of view is completely directed to the space region.

For each earth edge detector, the difference between the earth infrared radiation amount and the cosmic infrared radiation amount (VR_low-VR_space, VR_middle-VR_space, VR_high-VR_space) is obtained, and the respective earth edge radiation amounts (VE_low, VE_middle, VE_high) ) Is weighted and distributed within the viewing angle θ ₀ of one element, a posture angle with higher accuracy than the viewing angle θ ₀ can be calculated.

As described above, the earth edge detection method and the attitude angle calculation method based on the other embodiments are more accurate even when the viewing angle θ ₀ of one element of the earth edge detector to be used is as wide as several degrees or more. A posture angle within θ ₀ can be determined.

  As another embodiment of the present invention, one more miniaturized earth sensor embodiment is shown in FIGS.

  FIG. 15 shows a sensor block for mounting the earth edge detector. As shown in FIGS. 15A and 15B, the sensor block 800 has a fixing surface 804 between the block opening 802 and the housing cover on the front surface, and a mounting surface 808 on the back surface. The fixed surface 804 and the fixed surface 812 are surfaces for fixing to the housing cover 900 (FIG. 16). The center block has a left side 806 and a right side 810 on the left and right sides. FIGS. 15C and 15D show a sensor block 801 with a detector in which an earth edge detector (for example, a thermopile array 400) is mounted on a sensor block 800 made of aluminum.

  FIG. 16 shows a housing cover for storing the sensor block equipped with the earth edge detector in a bowl shape. In one embodiment of a downsized earth sensor, a housing cover 900 and a housing base 906 (see FIGS. 17 and 18) for storing four sensor blocks with detectors 801 each equipped with an earth edge detector. Consists of. Referring to FIG. 16A, the housing cover 900 includes a housing opening 902 for exposing the lens of the earth edge detector, and a fixing flange for fixing the housing of the earth sensor to the main body of the artificial satellite. 904.

  As shown in FIG. 16 (b), the sensor block with detector 801 fitted with the earth edge detector is inserted into the housing cover 900, and the sensor block with detector and the hole on the outside of the housing cover 900 are provided. The sensor block with detector 801 is fixed to the inside of the housing cover 900 through a fixing member such as a screw in the holes in the fixing surface 804 and the fixing surface 812 of 801.

  By integrating the earth edge detector and the sensor block in this way, the work of inserting the earth edge detector into the housing cover is simpler, more reliable and more accurate than the work of fixing only the earth edge detector inside the housing. Can be fixed.

  When the thermopile array 400 shown in FIG. 4 is used as the earth edge detector, the lens unit 408 and the substrate 405 are fixed to the housing cover 900 after being fixed to the sensor block 800. Increases vibration resistance. Furthermore, the aluminum thickness of the sensor block 800 can be secured in addition to the aluminum thickness of the housing cover 900, and the effect of shielding cosmic radiation from the outside of the housing (space) against the earth edge detector can be enhanced.

  When attaching the earth edge detector to the sensor block, the connection terminal is removed and the wiring cable is directly attached to the control circuit board. For example, when the thermopile array 400 is used as the earth edge detector, the connection terminal 414 on the board 405 of the thermopile array 400 is removed, and the wiring cable is directly attached to the control circuit board. Thereby, the height of the housing cover 900 for housing the sensor block with detector 801 equipped with the earth edge detector can be kept low, and the earth sensor can be miniaturized.

  Also, by setting the inclination of the mounting surface 808 on which the earth edge detector of the sensor block 800 is mounted, it is possible to easily cope with the offset angle of the satellite orbit altitude.

  FIG. 17 shows a top view, a side view, and a cross-sectional view of a downsized earth sensor by storing and fixing four sensor blocks in a bowl shape in a housing cover. When storing four sensor blocks with detectors 801 (for convenience, the first sensor block, the second sensor block, the third sensor block, and the fourth sensor block) in the housing cover 900, The first to fourth sensor blocks are point-symmetric with respect to the center of the earth sensor so that the back surface (mounting surface 808) of the first sensor block is the right side surface 810 (or left side surface) of the second sensor block. 806), the rear surface (mounting surface 808) of the second sensor block is opposed to the right side surface 810 or the left side surface 806 of the third sensor block, and the rear surface (mounting surface 808) of the third sensor block is The right side 810 (or left side 806) of the fourth sensor block is opposed to the back side (mounting surface 808) of the fourth sensor block, and the right side 810 (or left side) of the first sensor block. By made to face the surface 806) are alternately combined. As shown in FIG. 17, combining in a staggered manner is referred to herein as “combining in a bowl shape”. In the embodiment shown in FIG. 17, the back surface of one sensor block is opposed to the right side surface of the other sensor block, but may be opposed to the left side surface.

  FIG. 17A shows a side view of the downsized earth sensor. The case of the earth sensor includes a case cover 900 and a case base 906. FIG. 17B is a cross-sectional view taken along the line bb shown in FIG. It can be confirmed that the sensor blocks 801 with a detector of the four cases are combined in a bowl shape.

  FIG. 17C shows the upper surface of the downsized earth sensor. It can be confirmed that the lenses of the four earth edge detectors combined in a saddle shape are oriented in four directions. FIG. 17D is a sectional view taken along the line dd shown in FIG. It can be confirmed that the back surface (mounting surface side) of one detector-equipped sensor block 801 faces the right side surface of the other detector-equipped sensor block 801 in the housing cover 900. The four earth edge detectors are mounted on the sensor block 800, are closely fixed in a bowl shape in the casing cover 900, and are closed by a casing base 906 in which a control circuit board is housed.

  FIG. 18 is a perspective view of a downsized earth sensor. FIG. 18A shows a view of the earth sensor including the housing cover 900 and the housing base 906 as seen from the housing base 906 side. The housing base 906 includes a connector bracket 908 that includes a connection connector 910. Through the connection connector 910, an output signal detected by the earth edge detector of the earth sensor or attitude control information such as a pitch angle / roll angle can be transmitted to the main body of the artificial satellite. For example, when the thermopile array 400 is used as the earth edge detector, the lens 406 is exposed from the housing opening 902 of the housing cover 900 as shown in FIG.

FIG. 19 shows the offset angle of a miniaturized earth sensor. Similarly to the earth sensor shown in FIG. 9, the earth edge detectors located on opposite sides of each other have a central axis of the viewing angle of one earth edge detector and a central axis of the viewing angle of the other earth edge detector. It can arrange _| position so that the offset angle (theta) _offset may be made.

  FIG. 20 shows an example in which a downsized earth sensor is fixed to a structure panel of an artificial satellite. At the time of mounting, a hole corresponding to the case of the earth sensor is made in the satellite structure panel and inserted from the outside, and the connection connector 910 is connected to the connection connector inside the artificial satellite. And it fixes to a satellite structure panel with the fixing flange 904 in the side surface of the housing | casing cover 900. FIG. As a result, protrusions exposed to outer space outside the satellite structure can be limited to the minimum range of the lens field of view, reducing the severe thermal and radiation environment from space for the detector and control circuit board. Can do.

  The earth edge detection method according to the present invention can be used as an earth edge detection method of an earth sensor mounted on a small satellite in the space field. In addition, since the earth sensor according to the present invention can be mounted on a small satellite, it can be widely used for various artificial satellites.

DESCRIPTION OF SYMBOLS 100 Scan part 102 Lens 104 Scan mirror 106 S infrared detector 108 N infrared detector 110 Earth 112,114 Scan direction 116 Earth edge 120 Earth center 122 Satellite coordinate center 124 Earth region 126 Output waveform of S infrared detector 128 N Infrared detection Output waveform 200 scan tracking 202 infrared detector viewing angle 300 infrared detector output 302 satellite coordinate center 400 thermopile array 402 detection unit 404 signal processing unit 405 substrate 406 lens 408 lens unit 410 element unit 412 thermopile element 414 connection terminal 500 Earth sensor 502 Case cover 504 Case base 506 Connector 600 Earth 602 Space 700 Earth infrared region 701 Space region 702 Earth center 704 Satellite coordinate center 706 Field of view 70 8 Earth Edge 800 sensor block,
801 Sensor block with detector 802 Block opening 804, 812 Fixed surface 806 Left side 808 Mounting surface 810 Right side 900 Case cover 902 Case opening 904 Fixing flange 906 Case base 908 Connector bracket 910 Connector

Claims (10)

A detection unit including a plurality of thermopile elements arranged in a line or obliquely in a direction perpendicular to the earth edge, and a signal processing unit that digitally converts and outputs a signal detected by the detection unit. A housing cover for storing at least three earth edge detectors;
A housing base including a connection connector for outputting an output value from the signal processing unit to the outside,
The detection unit includes a cylindrical lens unit having a lens and an element unit in which the plurality of thermopile elements are arranged,
The casing cover is provided with holes for exposing the lens part of the earth edge detector to the outside at equal angular intervals with the center of the earth sensor as a base point,
The earth edge detector is an earth sensor stored in the housing cover at the equal angular interval,
Infrared detection is performed by a plurality of thermopile elements included in the detection unit of each of the earth edge detectors, and an infrared radiation amount is output to the signal processing unit for each thermopile element,
The infrared radiation amount output for each thermopile element by the signal processing unit is compared with a predetermined threshold value, and binarized to a value of 0 or 1 for each thermopile element, and digital for each thermopile element Converted to a value,
The digital value for each thermopile element corresponds to the arrangement of the thermopile elements, and the arrangement of the thermopile elements with a digital value of 1 is determined as the earth region, and the arrangement of the thermopile elements with a digital value of 0 is determined as outer space. An earth sensor for detecting an earth edge in the array of thermopile elements. The enclosure cover stores at least three sensor blocks equipped with the earth edge detector,
The sensor block has a block opening for exposing the lens portion of the earth edge detector to the outside, and a mounting surface having an inclination corresponding to an angle for detecting the earth edge,
The earth edge detector has the detection unit and the signal processing unit on a rectangular substrate, the rectangular substrate is aligned with the mounting surface, and the lens unit is disposed in the block opening. Is attached to the sensor block,
In the case cover, the case openings are provided at equal angular intervals with the center of the earth sensor as a base point to expose the lens portion exposed from the block opening to the outside.
The sensor block equipped with the earth edge detector is stored in the center housing at the same angular interval with the long axis of the sensor block as a vertical axis from the center of the earth sensor as a base point. Item 10. The earth sensor according to item 1. The earth sensor has first to fourth sensor blocks mounted with first to fourth earth edge detectors, respectively.
Each of the first to fourth sensor blocks has a front surface on the block opening side, a back surface on the mounting surface side, a right side surface, and a left side surface,
The first to fourth sensor blocks are symmetric with respect to the center of the earth sensor,
The rear surface of the first sensor block is opposed to the right side surface or the left side surface of the second sensor block,
The rear surface of the second sensor block is opposed to the right side surface or the left side surface of the third sensor block,
The rear surface of the third sensor block is opposed to the right side surface or the left side surface of the fourth sensor block,
The back of the fourth sensor block is opposed to the right side or left side of the first sensor block so as to be combined in a bowl shape and stored in the housing cover. The earth sensor described.   The earth sensor according to claim 1, wherein the earth sensor includes first to fourth earth edge detectors.   The pitch angle and roll angle of an artificial satellite are calculated based on a digital value for each thermopile element obtained from each of the earth edge detectors and a viewing angle for each thermopile element. The earth sensor as described in any one of 1-4. Viewing angle θ ₀ per one thermopile element,
The number of thermopile elements Dn determined as the earth region by the first earth edge detector,
The number Ds of thermopile elements determined as the earth region by the second earth edge detector,
The number of thermopile elements Dw determined as the earth region by the third earth edge detector,
Formula using the number of thermopile elements De determined as the earth region by the fourth earth edge detector:
Pitch angle = θ ₀ × (Ds−Dn) / 2
Roll angle = θ ₀ × (Dw−De) / 2
The earth sensor according to claim 3 or 4, wherein the pitch angle and the roll angle of the artificial satellite are calculated by the above.   The at least one of the earth edge detectors is an infrared detector using another type of infrared detection element instead of a thermopile element. Earth sensor. A detection unit including a plurality of thermopile elements arranged in a line or obliquely in a direction perpendicular to the earth edge, and a signal processing unit that digitally converts and outputs a signal detected by the detection unit. In an earth edge detection method of an earth sensor including at least three earth edge detectors,
Performing infrared detection by a plurality of thermopile elements included in the detection unit of each of the earth edge detectors, and outputting an infrared radiation amount to the signal processing unit for each thermopile element;
The infrared radiation amount output for each thermopile element by the signal processing unit is compared with a predetermined threshold value, and binarized to a value of 0 or 1 for each thermopile element, and digital for each thermopile element Converting to a value;
Calculating the pitch angle and roll angle of the satellite based on the digital value for each thermopile element obtained from each of the earth edge detectors and the viewing angle per thermopile element,
The digital value for each thermopile element corresponds to the arrangement of the thermopile elements, and the arrangement of the thermopile elements with a digital value of 1 is determined as the earth region, and the arrangement of the thermopile elements with a digital value of 0 is determined as outer space. An earth edge detection method comprising detecting an earth edge in the array of thermopile elements. The earth sensor includes first to fourth earth edge detectors;
A first earth edge detector and a second earth edge detector are installed symmetrically with respect to the center of the earth sensor,
A third earth edge detector and a fourth earth edge detector are installed symmetrically with respect to the center of the earth sensor,
A straight line connecting the first earth edge detector and the second earth edge detector intersects with a straight line connecting the third earth edge detector and the fourth earth edge detector,
Calculating the pitch angle and roll angle of the satellite;
Viewing angle θ ₀ per one thermopile element,
The number of thermopile elements Dn determined as the earth region by the first earth edge detector,
The number Ds of thermopile elements determined as the earth region by the second earth edge detector,
The number of thermopile elements Dw determined as the earth region by the third earth edge detector,
Formula using the number of thermopile elements De determined as the earth region by the fourth earth edge detector:
Pitch angle = θ ₀ × (Ds−Dn) / 2
Roll angle = θ ₀ × (Dw−De) / 2
The earth edge detection method according to claim 8, wherein the pitch angle and the roll angle are calculated by:   The earth edge detection method according to claim 8 or 9, wherein at least one of the earth edge detectors is an infrared detector using another type of infrared detecting element instead of a thermopile element.

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