JPS61129400A - Triaxial star sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a three-axis star sensor used for attitude control of a space vehicle such as a rocket or an artificial satellite.

C Technical Background and Problems of the Invention] Spacecraft systems, such as artificial satellites, control the power supply system that controls the power necessary to maintain the functions of the satellite, and the temperature inside the satellite structure! A thermal control system that controls the satellite, an attitude control system that directs the satellite's roll, pitch, and core axes and antennas in predetermined directions, and a telemetry command that receives command signals from the ground station and transmits data to the ground station. It consists of mission systems such as systems, communication equipment, and observation equipment.

Attitude control of space vehicles (hereinafter referred to as satellites) such as artificial satellites and rockets configured in this way involves directing the antennas and imaging devices of the onboard mission equipment toward the Earth, and maintaining the stability of their pointing. Its control methods include spin control and three-axis control.

By the way, in the space environment, there are disturbance torques that disturb the satellite's attitude, such as aerodynamic force, gravity gradient, geomagnetism, and solar radiation pressure. Stability may be disrupted. For this reason, earth sensors.

Attitude control is performed by detecting pointing direction and pointing stability using attitude +l and I+ sensors such as sun sensors and star sensors, and correcting errors.

Among the attitude control sensors, star sensors use stars as attitude standards and are indispensable for ultra-precise control, and can be roughly divided into star scanners and stellar drafkas.

Star Scanner, also called Star Matupa, has a stable spin of 111M. It is used for slow spin satellites, etc.
The attitude of the satellite is detected by scanning the celestial sphere using the spin or orbital angular velocity of the satellite itself, and detecting the direction of the star based on the timing of star detection by a light receiving section with a V-shaped slit or the like.

When the satellite's attitude moves only very slowly relative to the celestial sphere, the star tracker can
- They are used in the above-mentioned earth-oriented three-axis stable satellites, astronomical observation satellites, deep space exploration satellites, etc., and are roughly divided into two types based on their operating modes, such as single-star sensors and fixed-head stellar Drafkas.

A single-star sensor detects changes in the satellite's attitude with high precision and controls the control system by constantly tracking a specific star, such as a relatively bright and independent star such as Volaris or Cappus. be. On the other hand, a fixed-head star tracker identifies the stars and performs pattern recognition from the detection signals of multiple stars within a fixed field of view, and detects the satellite attitude with high precision.

In any case, these star trackers only have two-dimensional position information, so they are only capable of detecting the attitude of two wheels. Moreover, they require large-scale software using star catalogs, and they also require the ability to detect the satellite's three axes. In order to control the attitude of the star, another system of star sensors (usually installed in the orthogonal direction) must be provided.

[Purpose of the invention]

The present invention was made in order to solve the above-mentioned problems of conventional star sensors such as stellar Dravka. The purpose of this invention is to provide a three-axis star sensor that has a simple configuration and has a long life.

[Summary of the invention]

The present invention uses two-dimensional CC to obtain star images of two or more stars in different directions.
D includes a twin-lens optical system for forming an image on the image sensor, and a drive system for rotating the optical system about its optical axis,
This makes it possible to easily detect the three-axis attitude of the satellite based on the position information of the star image on the two-dimensional CCD image sensor and the rotation angle information of the drive system, thereby extending the life of the sensor and simplifying its configuration. be.

[Principle and Examples of the Invention]

Prior to detailed description of the present invention, the principle of the present invention will be explained first.

FIG. 1 is an explanatory diagram for explaining the principle of the three-axis star sensor according to the present invention, where l is a binocular optical system, one star X,
For example, a lens barrel 2 for introducing the light beam from Volaris,
A lens 4 is provided to form a two-dimensional CCD image of the incident light beam introduced into the lens barrel 2 onto the lens 3, and a lens 4 is provided at a predetermined position with respect to the lens barrel 2 to introduce the light beam from the target star Y. It is composed of a branching lens barrel 5 arranged at an angle of inclination, and a semi-reflection mirror 6 or a total reflection mirror 6' for imaging the incident light beam from the lens 4 onto the CCD image sensor 3. ing.

In the case of an earth-oriented, three-axis stable satellite, it rotates once every 24 hours as the earth rotates, and the star is fixed in inertial space, so there is always a specific point within the field of view of the twin-lens optical system. In order to accommodate the two stars, a rotational drive system is used to rotate them in the opposite direction to the satellite around the optical axis. This rotation control is performed by giving a command to a stepping motor or the like that rotates by a fixed angle per pulse when the positional deviation of the star image on the CCD image sensor exceeds a certain level. And in this way, the twin-lens optical system 1
While rotating the two-dimensional CCD image element 3, a star image of the stars X and Y is formed on the two-dimensional CCD image element 3, and based on the position information on the CCD image element 3 of the star image and the rotation angle information of the drive system. It performs three-axis attitude detection.

The binocular optical system consists of two constants IX and Y, as shown in Figure 2.
Two branching lens barrels 7.8 and two reflecting mirrors 9.10 may be arranged so that the incident direction of the light beam from the optical system is tilted with respect to the optical axis of the optical system. , can perform exactly the same operation. Incidentally, the inclination angles α and β of the branched lens barrels 7 and 8 are set corresponding to the target stars X and Y.

Next, a specific configuration example of the present invention shown in FIG. 3 will be explained. In FIG. 3, reference numeral 11 denotes a twin-lens optical system having the same configuration as that shown in the principle explanatory diagram of FIG. It is composed of a semi-reflecting mirror 15 for making the light beam from lY enter the lens 12 via the branching lens barrel 14. Note that 16 and 17 are hoods attached to the tips of the lens barrel 13 and the branch lens barrel 14. The lens barrel 13 is integrally fixed to the inside of a cylindrical rotating shaft 18, and the rotating shaft 18 is fixed to the inside of a cylindrical shaft support portion 21 integrally formed on the main body 20 via a bearing 19. It is rotatably supported. Reference numeral 22 denotes a drive motor (azimuth drive unit) for rotating the binocular optical system 11, which is engaged with the lower end of the lens barrel 13 via gears or the like. 23 is a null detector (azimuth detection section) that detects the rotation angle of the binocular optical system 11.

At the focal plane of the 21IN optical system 11, there are two stars X and Y.
A two-dimensional CCD image sensor 24 is disposed to form a star image. 25 is an electronic circuit that drives and controls the CCD image sensor and performs A/D conversion of the constant detection signal, etc.; 26 is a cooler that cools the CCD image sensor 24 and reduces its dark current; It is. 27 is a shafter mechanism, which operates the shafter 2 based on the detection signal of the luminous object sensor 28.
9 to protect the CCD image sensor 24. 30 is a signal processing unit which receives stellar position data from the electronic circuit 25 and a null signal from the null detector 23, outputs an attitude angle or a coordinate transformation matrix (direction cosine matrix), and receives a capture command. It outputs a rotation command to the drive motor 22.

Next, the operation of the three-axis star sensor configured as described above will be explained with reference to the signal system diagram shown in FIG.

The configuration example shown in Figure 3 shows a three-axis Volaris sensor for Earth-oriented three-axis stability display, but as mentioned earlier, such a satellite rotates with the rotation of the Earth. Therefore, in order to always keep the two specific stars in the field of view of the star sensor used for it, it is necessary to rotate the optical system in the opposite direction to satellite I. In this configuration example, the signal processing unit 30
A rotation command (azimuth drive command) is output from , and the drive motor 22 is rotated in order to capture the star Y. Then, the rotation angle is detected by the null detector 23, and a null signal serving as rotation angle information is sent to the signal processing unit 30.
is input.

On the other hand, the star images of stars X and Y are formed on the CCO image sensor 24, and by photoelectric conversion, a star detection signal (image data) giving the brightness and two-dimensional coordinates is sent to the signal processing unit via the electronic circuit 25. It is man-powered to 30.

Using the star detection signal obtained in this way, the star is identified by identifying whether or not it is a preset target star. Next, the rotation angle information (null signal) from the null detector 23 and the two-dimensional Based on the image information from the CCD image sensor 24, the signal processing unit 30 calculates an attitude angle or a coordinate transformation matrix (direction cosine matrix) using an algorithm described later, and performs three-axis attitude detection.

Next, an algorithm for calculating the coordinate transformation matrix Cma for posture detection will be explained with reference to the flowchart shown in FIG.

(1) First, manually input the directional vectors St and Sx of the star to be measured, which are shown by the following equations, and perform initial settings. However, i and j are orthogonal unit vectors with the celestial body as the reference. .

S + -3111+ S + z J +S + s
kSt -3i+i +S*xj +5iikS ■Electric ""S+t""513t=1 Si+""51m"+Szs" = 1 (2)
From the inclination angle α of the semi-reflective mirror 15 with respect to the rotating optical axis, a matrix C,i, which is one element of the transformation matrix bow that relates the mirror to the aircraft (satellite carrying a three-axis star sensor), is determined.

(3) Read the rotation angle (azimuth angle) β of the optical axis, and calculate the transformation matrix bow that relates the aircraft and the mirror according to the following equation.

+41 Read the positions of the two star images projected onto the CCD illll elementary image plane and calculate the direction vector b+
.

Normalize to b2. However, 1. m and n are orthogonal unit vectors with the measurement axis of the CCD image sensor as a reference.

bl=b1J+b+11n+b+3nbz-b,
+j +bt, m+bt! ab 11” + b, -
+ b +s"-1bH" + b2t" + bg
3" = 1 (5) From the direction vector b2 of the star Y refracted by the mirror, the actual direction vectors b,' of the star IY with respect to β, m, n [target are calculated by the following formula.

Direction vector Sl of the fixed star with respect to the coordinates b□'-Lbo+61i,j,
,S! and,! , m, and n coordinates, a coordinate transformation matrix C〒 for obtaining measurement coordinates from inertial coordinates is determined according to the following equation.

cti gc: C3 c3 − [b+ jb□'xb, i b, x (
bx□xb, )) (7) By repeating the processes from (3) to (6) above, the coordinate transformation matrix C〒 is updated.

(8) Euler angles (roll angle, pitch angle, I-angle) are analytically determined from the elements of this coordinate transformation matrix 6.

That is, the coordinate transformation matrix C? The Euler angle of the measurement coordinates with respect to the inertial coordinates is determined by the following equation when the rotation angle is small.

Pitch angle θ=sin-' (-Cz+) ” -C31
0-le angle φ-5in-' (C)z/cosθ)”
Cxt yaw horn=sin-'(C!I/CO3θ)'
:t(:,.

As described above, the present invention does not require large-scale software using a star catalog by rotating the binocular optical system around the optical axis and simultaneously tracking the movements of two stars in different directions. It is possible to determine the three-axis attitude using one star sensor with only a slight increase in hardware.

Although the present invention has a drive unit as described above, it rotates once per day for geostationary satellites and 20 times per 10 times for orbiting satellites, so it has little impact on longevity and deterioration. It's not a problem.

In addition, since a CCD image sensor is used as a detection element, there is no need for a high pressure source like a desector tube, and when a CCD image sensor with 400 x 500 pixels is used, the viewing angle is ±10''. , 0.02'' accuracy (
(all three axes) can be achieved, and a resolution of 0.5 x lo"deg can be obtained by CCDtIlCCD imager toroid processing.

Furthermore, as a sensor for geostationary satellites, it is possible to continuously measure the three-axis attitude.

〔Effect of the invention〕

As described above based on the embodiments, the present invention provides a twin-lens optical system for forming star images of two stars in different directions on a two-dimensional CCD image sensor, and The system is equipped with a drive system that rotates around the axis, and detects the three-axis attitude based on the position information of the star image on the CCD image sensor and the rotation angle information of the drive system, so large-scale software is not required. With only a slight increase in hardware,
Three-axis attitude determination can be performed with one star sensor. Furthermore, since a cco fil image element is used as a detection element, a star sensor with high resolution, low power consumption, and long life can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the principle of the present invention, FIG. 2 is an explanatory diagram showing a modification thereof, FIG. 3 is a schematic configuration diagram of an embodiment of the present invention, and FIG. FIG. 5, which is a signal system diagram of the signal processing system of the embodiment shown in the figure, is a flowchart showing an algorithm for obtaining a coordinate transformation matrix. In the figure, 11 is a binocular optical system, 12 is a lens, 13 is a lens barrel, 14 is a branch lens barrel, 15 is a semi-reflective mirror, 16°1
7 is a hood, 22 is a drive motor, 23 is a null detector, 24 is a two-dimensional CCDCD image element 5 is an electronic circuit, 26
27 is a cooler, 27 is a shutter mechanism, 28 is a luminous object sensor, 29 is a shutter, and 30 is a signal processing section. Patent Applicant Space Development Business Letter 1
Diagram ↓ East 3 Dia.

Claims (1)

[Claims] In a three-axis star sensor mounted on a space vehicle such as an artificial satellite and used as a sensor for attitude control of the vehicle, star images of two or more stars in different directions are formed on a two-dimensional CCD image sensor. and a drive system that rotates the optical system about its optical axis to maintain the star image on the two-dimensional CCD image sensor, A three-axis star sensor characterized in that it is configured to perform three-axis attitude detection based on image position information and drive system rotation angle information.