JPH0468199B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a method for controlling the attitude of an artificial satellite by releasing the angular momentum accumulated in the satellite. The present invention relates to an attitude control method for an artificial satellite that utilizes the earth's magnetism when releasing the angular momentum stored in the wheels of the satellite.

FIG. 1 is a schematic perspective view showing an embodiment of a three-axis satellite, in which 1 is a momentum wheel as an angular momentum storage device, 2 is a reaction wheel as an angular momentum storage device, and 3 is a magnetic moment generator ( 4 is a roll angle sensor (hereinafter referred to as a magnetic torquer). Further, the coordinate axes X, Y, and Z are a coordinate system fixed to the satellite body, and here, the X axis is called the roll axis, the Y axis is called the pitch axis, and the Z axis is called the yaw axis.

Note that for a three-axis satellite, the X-axis in Figure 1 is the traveling direction, and the Y-axis is the traveling direction.
Control is performed so that the axis is perpendicular to the orbital plane and the Z axis is perpendicular to the XY plane. In a circular orbit, the Z axis coincides with the direction of the Earth's center. Attitude control methods that are controlled in this manner can be roughly divided into bias momentum methods, zero momentum methods, and control bias momentum methods that are located in between and can be combined in various ways.
The configuration shown in the figure belongs to the controlled bias momentum system. The controlled bias momentum method always applies a large angular momentum (bias momentum) in the direction of the pitch axis, and its gyroscopic steel property minimizes changes in attitude due to external torque. Therefore, in an artificial satellite using such a control method, Y
The torque about the axis is absorbed by the change in angular momentum of the momentum wheel 1. On the other hand, the torque around the Z-axis and the torque around the X-axis are the angle of attitude change around the X-axis (roll angle) and the angle of attitude change around the Z-axis (yaw angle), respectively, due to the gyroscopic steel properties due to the bias momentum in the pitch axis direction. It appears as. Torque around the Z-axis can be absorbed by detecting the roll angle by the roll angle sensor 4 and feeding it back to the reaction wheel 2 to change the angular momentum of the reaction wheel. Regarding the yaw angle, it does not have a sensor to detect it (yaw angle sensor) or a device to directly absorb torque around the It can be absorbed indirectly. By utilizing the gyroscopic properties of the steel, the controlled bias momentum system has the feature that it can omit a yaw angle sensor, etc. compared to the zero momentum system. Now, the angular momentum around the X axis is
H _X and the magnitude of the ^resultant angular momentum H _O when the angular momentum around the _Z axis is H _{Z is} H _O = _√ ² and H _Z are exchanged, and H _X and H _Z change periodically in amplitude H _O with the period of the satellite's orbital motion. The yaw angle also changes periodically with an amplitude proportional to H _O.
Therefore, the yaw angle gradually increases due to the absorption of external torque, and over a long period of time may go out of its permissible range. Further, the same can be said about the rotation speeds of the momentum wheel 1 and the reaction wheel 2. In order to avoid such a situation, it is necessary to apply an artificial torque to the satellite in some way and make it absorb it, and as a result, it must be controlled so that it absorbs the external torque and releases the accumulated angular momentum. Bye. Note that the release of H _X and H _Z requires torques around the X and Z axes, respectively. In the configuration shown in FIG. 1, a magnetic torquer 3 is used as a device for artificially applying torque, and this generates a magnetic torque by the interaction between the magnetic moment generated by the magnetic torquer 3 and the earth's magnetic field.

The magnetic moment generated around the Y axis is M _Y ,
The geomagnetism in the X-axis direction is B _X , and the geomagnetism in the Z-axis direction is B _Z
Then, M _Y B _Z around the X axis and Z axis respectively
and −M _Y B _X magnetic torques result. At this time M _Y
It is well known that the angular momentums H _X and H _Z around the X-axis and Z-axis can be effectively released when H is generated as shown in the second equation.

M _Y = -K (B _Z H _X - B _X H _Z ) ... (2) Here, K is selected as an appropriate constant. For B _X and B _Z , values detected by a magnetic sensor (not shown) or values based on an appropriately approximated geomagnetic pattern can be used. Therefore, the above B _X and B _Z are _expressed as B _'
Write it like an expression.

M _Y = _−K ( _{B ′ Z H}
The second term is a term related to the release of H _Z .

As mentioned above, _the angular momentum _H It is difficult. On the other hand, the above-mentioned angular momentum H _Z is expressed as the sum of the accumulated part as a minute roll angle and the accumulated part due to changes in the rotational speed of the reaction wheel 2, but these can be easily detected, and therefore,
Detection of H _Z is easy.

FIG. 2 is a block diagram equivalently showing the operating principle of the conventional example. In the figure, 5 is the equivalent satellite dynamics, 6 is the attitude angle sensor, 7 is the wheel controller, 8 is the reaction wheel, and 9 is the equivalent satellite dynamics. A magnetic moment pattern generator, 10 a magnetic torque controller, 11 an equivalent earth's magnetic field, 12 a magnetic torquer, and 13 an adder circuit. The attitude angle sensor 6 detects, for example, the roll angle of the satellite and outputs a roll angle signal, and corresponds to the roll angle sensor shown in FIG. The wheel controller 7 outputs a control torque signal for controlling the reaction wheel 8 according to the output of the attitude angle sensor 6. The reaction wheel 8 receives a control torque signal from the wheel controller 7 and applies a torque to the satellite dynamics 5, and also supplies a rotational speed signal of the reaction wheel 8 to the magnetic torque controller 10. The magnetic torque pattern generator 9 generates a signal corresponding to _B'X in the third equation. The magnetic torque controller 10 generates an angular momentum signal around the Z axis from the roll angle signal from the attitude angle sensor 6 and the rotation speed signal from the reaction wheel 8, and combines this signal with the signal from the magnetic torque pattern generator 9. is used to generate and output a signal corresponding to the second term on the right side of the third equation, and the magnetic torquer 12 generates and outputs a signal corresponding to the second term on the right side of the third equation.
Generates a magnetic moment around the Y axis that corresponds to the right side of the equation. An artificial torque is generated around the Z-axis by the magnetic moment around the Y-axis generated by the magnetic torquer 12 and the earth's magnetism B _X in the X-axis direction of the earth's magnetic field 11, and angular momentum H _Z around the Z-axis is released.
The magnetic torquer 12 corresponds to the magnetic torquer 3 shown in FIG. The adding circuit 13 equivalently shows that the torque acting on the dynamics 5 of the satellite is the sum of the external force, the torque due to the reaction wheel 8, and the torque due to the magnetic torquer 12.

By the way, in the conventional method shown in Figure 2, there is no yaw angle sensor to detect the yaw angle and _it is difficult to directly detect _H By using the exchange between H _X and H _Z due to the orbital motion of the satellite, as a result, _H
It also emits.

That is, in the conventional method, the release of H _Z is the main one, and the release of H _X is the secondary one. Therefore
The drawback was that _HX was not released effectively, resulting in poor attitude control accuracy.

This invention was made in order to improve the above-mentioned problems, and provides a means for emitting H _X estimated from H _Z by utilizing the dynamics caused by the orbital motion of the satellite.

The features of this invention will be explained below with reference to FIG. In Figure 3, 5 is the equivalent satellite dynamics, 6 is the attitude angle sensor, 7 is the wheel controller, 8 is the reaction wheel,
14 is a rotational speed signal differentiating circuit, 15 is a roll angle signal differentiating circuit, 9 is a magnetic torque pattern generation path, 10
1 is a magnetic torque controller, 11 is an equivalent earth's magnetic field, 12 is a magnetic torquer, and 13 is an adder circuit.

In such a configuration, if the orbital revolution angular velocity of the artificial satellite is ω _O , as shown in Figure 4a,
The X-axis and Z-axis of the artificial satellite rotate around the Y-axis (negative direction) at an angular velocity ω _O . At this time, H→ _O , which represents H _O expressed by the first equation as a vector, rotates at an angular velocity ω _O around the Y axis (positive direction) in the XZ plane, as shown in Figure 4b. It turns out.
At this time, Equation 4a holds true. Here, θ is a constant representing the initial angle.

H _X = H _O cos (θ−ω _O t), H _Z = H _O si
n(θ−ω _O t) (4a) Equation (4b) is obtained by differentiating H _Z in equation (4a) with respect to time. Here, the dot above _H〓Z represents the time differential (the same applies below).

H〓 _Z = H〓 _O sin(θ−ω _O t)−ω _O H
_O cos (θ−ω _O t)……(4b) Mechanics shows that the first term on the right side of equation (4b) represents the torque T applied around the Z axis of the satellite, and also, Applying Equation (4a) to the second term, we obtain Equation 4c.

H〓 _Z = _T −ω _{O H} Since ω _O is a _quantity known _in advance _and H _Z can be easily detected as _H It can be seen that H _X can be estimated from the formula. FIG. 3 shows a general example for releasing H _X based on the relationships shown in equations (4c) and (5) above.

When the angular momentum H _Y (bias momentum) around the Y axis is large and the roll angle is small, equation (6) holds true if the moment of inertia of the reaction wheel 8 is I and the number of rotations (angular velocity) is ω.
Differentiating both sides of equation (6) with respect to time, H _Z = H _Y + Iω ……(6) Note that the product of the time differential H 〓 _Y of H _Y is small compared to other terms. 7) The formula holds true.

H〓 _Z H _Y 〓+Iω〓 ...(7) As is clear from equations (5) and (7), in addition to the conventional example shown in Figure 2, the differential in equation (7) is It can be seen that all that is needed is to add the differentiating circuit necessary to create the signal, and then change the coefficients, etc. necessary to create the signal corresponding to the first term on the right side of equation (3). For this reason, in one embodiment of the present invention shown in FIG. A rotational speed signal differentiating circuit 14 is provided for differentiating the number signal, and the differential signals that are the outputs thereof are inputted to the magnetic torque controller 10 to generate a signal corresponding to H _X estimated from equation (5). In addition, the magnetic torque pattern generator generates a signal corresponding to B′ _Z in equation (3), and using this and the signal corresponding to the estimated _H The magnetic torquer generates a magnetic torque corresponding to the first term on the right side of equation (3). This magnetic torque around the Y-axis and the earth's magnetism _BZ in the Z-axis direction of the earth's magnetic field 11 generate an artificial torque around the X-axis, and release angular momentum around the X-axis.

Even if the method _{of this} invention releases _{only H} can also emit H _Z to control the satellite's attitude. In this case, if the artificial satellite is a so-called polar orbit satellite that passes over the north and south poles of the earth,
The size of B _Z is about 2 compared to B _X above the Earth's equator.
Considering that it is twice as large, it can be used more effectively than conventional methods. Moreover, if the conventional method and the method according to the present invention are used together, the efficiency of releasing H _X and H _Z can be further increased.

The above explained the controlled bias momentum method, but the angular momentum H _Z around the Z axis can be detected, and its differential H _Z
It is clear that the method of the present invention can be applied to a three-axis satellite for which equation (5) holds true.

As described above, according to the present invention, the angular momentum H _Z around the Z axis can be measured without using a yaw angle sensor.
Using the dynamics caused by the orbital motion of the artificial satellite, it is possible to estimate the angular momentum H _X around the X axis and release it.
If used in conjunction with the release of only H _Z , the efficiency can be further increased, and the attitude control of the satellite can be effectively performed, including shortening the time required for control and improving control accuracy.

[Brief explanation of the drawing]

Figure 1 is a schematic perspective view showing an example of a three-axis satellite;
The figure is a block diagram equivalently showing the operating principle of one embodiment of the conventional attitude control method, FIG. 3 is a block diagram equivalently showing the operating principle of one embodiment of the attitude control method according to the present invention, and FIG. Figure 4a is a diagram showing that when the artificial satellite orbits at a revolution angular velocity _ωO , the X-axis and Z-axis rotate around the Y-axis (negative direction) at an angular velocity _ωO , and Figure 4b is shown in Equation 1. FIG. 3 is a diagram showing that H→ _O , which is a vector representation of H _O that is generated, rotates around the Y axis (in the positive direction) in the XZ plane at an angular velocity ω _O. In the figure, 5 is the dynamics of the satellite, 6 is the attitude angle sensor, 7 is the wheel controller, 8 is the reaction wheel, 9 is the magnetic torque pattern generator, 10 is the magnetic torque controller, 11 is the earth's magnetic field, 12 is the magnetic torquer, 14 1 is a rotational speed signal differentiating circuit, and 15 is a roll signal differentiating circuit. Note that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1. An angular momentum storage device for controlling the attitude angle by absorbing external torque that affects the attitude angle of the satellite by changing the angular momentum; It has a magnetic moment generator that generates magnetic torque that affects the angle by interaction with the earth's magnetic field, and by indirectly canceling out the influence of external torque through the action of these components, the attitude of the satellite can be adjusted. In the attitude control method of the artificial satellite to be controlled, among the angular momentum accumulated in the artificial satellite, the angular momentum component about the yaw axis of the artificial satellite and the angular momentum about the roll axis of the artificial satellite when the artificial satellite makes one orbit Using the property that the angular momentum component about the yaw axis and the angular momentum component about the yaw axis are interchanged, the angular momentum component about the roll axis of the satellite is estimated. A method for controlling the attitude of an artificial satellite, characterized in that the attitude of the artificial satellite is controlled by generating torque around the roll axis and releasing an angular momentum component around the roll axis.