JPH0436920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to three-axis attitude control of an artificial satellite flying in a geostationary orbit.

[Prior art] Three mutually orthogonal axes fixed to an artificial satellite, that is, a roll axis, a pitch axis, and a yaw axis, are arranged so that they point in order to the direction of travel of the satellite, the direction perpendicular to the orbital plane, and the direction toward the center of the earth. The controlled satellite is called a three-axis attitude control satellite. The attitude error is defined as a rotation error from a reference direction around the roll axis, pitch axis, and yaw axis, and is called a roll angle, a pitch angle, a yaw angle, or a roll error, a pitch error, and a yaw error, respectively. An example of a three-axis attitude control type artificial satellite is one having the configuration shown in FIG. In the figure, 1 is an earth sensor that detects the roll angle and pitch angle of the satellite, 2 is the satellite body, 3 is the roll axis, 4 is the pitch axis, 5 is the yaw axis, and 6 is the rotation axis parallel to the pitch axis 4. Momentum wheel attached to the satellite so that 7
8 is a reaction wheel mounted on the satellite so that its axis of rotation is parallel to an axis lying in the plane formed by the roll axis 3 and the yaw axis 5; 8 is a control electronic circuit;

Attitude control of a satellite configured in this example is as follows:
This is called a controlled bias momentum method, and the rotation speed of the reaction wheel 7 is determined based on the roll angle signal detected by the earth sensor 1, and the rotation speed of the momentum wheel 6 is determined based on the pitch angle signal. This is achieved by accelerating and decelerating. Here, the yaw angle is based on the principle that it is passively maintained within a certain accuracy by the gyro rigidity of the momentum wheel 6, even without active control using a sensor. This method is unique to the controlled bias momentum method and the bias momentum method that does not use a reaction wheel, and is widely put into practical use because it eliminates the need to detect the yaw angle, which is relatively difficult to detect. Furthermore, in addition to controlling the roll angle, the roll angle control described above can also attenuate the nutrition motion, which is a coupled motion of the roll angle and yaw angle, so it is sometimes called roll/yaw control. Since there are many types, we will refer to it as roll/yaw control hereafter. Further, the pitch control can be easily realized by accelerating or decelerating the speed of the momentum wheel 6 based on the pitch angle signal from the earth sensor 1 as described above, so it will not be described here. Roll/yaw control is designed based on the transfer function equation (1) that includes the dynamics of the satellite's roll angle and pitch angle and the transfer characteristics of the earth sensor.

G _P1 (S)=cosα/I _X S+hB/I _Z tanα/S ² +ω _N ²・G
_S1 (S)...(1) Here, S is the Laplace operator, G _P1 (S) is the angular momentum of the reaction wheel 7, and
The transfer function whose output is the roll angle signal of the earth sensor 1, I _X and I _Z are the moments of inertia of the entire satellite around the roll and yaw axes, and hs is the magnitude of the angular momentum of the momentum wheel 6 (-pitch axis (assuming the direction is positive), ω _N is the nutrition angular velocity defined by equation (2), and α is the offset angle of the reaction wheel, defined as shown in FIG.

In the figure, 9 is an offset angle. In addition, the
Equation (1) is derived from Equation (2-a) and Equation (2-b) below. Equation (2-a) is the roll angle φ
_{and yaw angle ψ I _} It is a linearized version of the governing equation of motion. Here, φ・, ψ・ are φ, ψ, respectively.
where H is the angular momentum of the reaction wheel. Equation (2-b) is an equation that relates the roll angle and the roll angle output φ _S of the earth sensor. G _S1(S) is usually modeled as a first-order or second-order delay element. Section (2-a)
Laplace transform the equation and equation (2-b) to obtain φ _S /H
The result obtained is the transfer function of equation (1).

For this controlled object, the reaction wheel 7 is appropriately adjusted based on the roll angle signal of the earth sensor 1.
It is well known that the roll angle and yaw angle can be stably controlled by increasing or decreasing the rotational speed of. Also, as can be seen from equation (1), the offset angle α9
The magnitude (including the sign) of is a typical parameter representing the characteristics of the controlled object, and an appropriate control system is configured for this value.

[Problem that the invention seeks to solve]

However, in communication satellites and the like, it is required to improve the pointing accuracy of the antenna with respect to the earth station. To meet these requirements, the above-mentioned attitude control uses an earth sensor as a reference for its attitude, and is capable of directing the yaw axis of the satellite toward the center of the earth and aligning the roll axis with the direction of travel of the satellite. Even if the attitude errors of roll, pitch, and yaw are completely controlled to zero, they will still be affected by orbit errors, and the earth sensor will be affected by the carbon dioxide gas distributed around the earth. Since the method detects layers, there was a problem in that the accuracy could not be improved to a certain level due to fluctuations in the distribution of the carbon dioxide layer.

The present invention was made to solve these problems, and an object of the present invention is to obtain a three-axis attitude control device that improves the pointing accuracy of an antenna with respect to an earth station.

[Means for solving problems]

The three-axis attitude control device according to the present invention uses elevation angle signals from an RF sensor attached to the satellite body, instead of roll angle signals and pitch angle signals from an earth sensor used in the conventional controlled bias momentum system. , which uses an azimuth angle signal.

[Effect]

In this invention, the attitude angle is not detected by the roll angle or pitch angle relative to the center of the earth, but the elevation angle and azimuth angle relative to the earth station are directly detected by the RF sensor and used for control, so the influence of orbit errors is eliminated. I don't accept it. Furthermore, since an earth sensor with limited detection accuracy is not used, highly accurate attitude control is possible.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention, and numerals 2 to 8 are completely the same as the conventional device. 10 is an RF sensor that detects the relative azimuth angle and elevation angle with respect to the satellite in the direction of the earth station. Roll/yaw control of the bias momentum satellite configured in this example is performed using the elevation angle signal of the RF sensor 10, and pitch control is performed using the azimuth angle signal, but these signals are subject to orbit errors and alignment errors. When there is no relationship between the roll angle and yaw angle of the satellite, there is a relationship approximately expressed by equation (3).

El=φ−β ₁ ψ Az=θ+β ₂ ψ …(3) Here, φ, θ, and ψ are the roll angle, pitch angle, and yaw angle of the satellite in order, and El and Az are the elevation angle signals of the RF sensor in order. , azimuth angle signals, β ₁ and β ₂ are constants determined by the geostationary longitude of the artificial satellite and the latitude and longitude of the earth station, and are defined in FIG. In the figure, 11 is the direction of the earth's north pole axis,
12 is the equatorial plane of the earth, 13 is β ₁ , and 14 is β ₂ .

Here, when performing roll/yaw control using the above elevation signal, the transfer function G _P2 (S) when the input is the angular momentum of the reaction wheel and the output is the elevation signal of the RF sensor is It becomes as shown in equation (4).

G _P2 (S)=cos(α−β ₁ /IS+hB/Itan(α−β
₁ )/S ² +ω _N ² G _S2 (S)...(4) Here, G _S2 (S) is the transfer function of the RF sensor. Further, this equation (4) is an approximate equation when α and β ₁ are smaller than 1 radian. Furthermore, to simplify the explanation, it is assumed that I _X and I _Z are also equal, and are represented by I.

Equation (4) is equivalent to Equation (1) in which the offset angle α of the reaction wheel is replaced by α−β ₁ . That is, if the value obtained by subtracting _β1 from the offset angle of the reaction wheel is considered as the equivalent offset angle, this system has exactly the same structure as the conventional system. α−β ₁ has a certain desired range from the viewpoint of system stability, control accuracy, etc. Since β ₁ is a positive amount when the satellite is stationary to the west of the earth station and negative when it is stationary to the east, the offset angle α of the reaction wheel is determined according to the size of β ₁ . By increasing or decreasing the amount by the amount and attaching it to the satellite, it can be controlled under exactly the same conditions as the conventional system. On the other hand, regarding the pitch system, since the dynamics of the controlled object are completely separated from the roll/yaw system, the azimuth signal of the RF sensor mixed with the influence of the yaw angle can be used instead of the pure pitch angle signal. Since it does not affect the stability of the product at all, it can be used without any problem.

〔Effect of the invention〕

As explained above, this invention improves control accuracy by using the elevation angle signal and azimuth angle signal of the RF sensor instead of the roll angle signal and pitch angle signal of the conventional earth sensor. The rotational axis direction of the reaction wheel is determined by taking into account the angle determined by the satellite's geostationary longitude and the earth station's longitude, and the rotational axis direction of the reaction wheel is determined by attaching it to the satellite and accelerating or decelerating the rotation speed of the reaction wheel. This has the effect of allowing control.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 is a diagram defining the direction of the earth station as seen from the artificial satellite, and Fig. 3 is a configuration diagram of a conventional three-axis attitude control type artificial satellite. FIG. 4 is a diagram defining the offset angle of the reaction wheel. In the figure, 1 is an earth sensor that detects the roll angle and pitch angle of the satellite, 2 is the satellite itself, and 3
is the roll axis, 4 is the pitch axis, 5 is the yaw axis, 6 is the momentum wheel, 7 is the reaction wheel, 8 is the control electronic circuit, 9 is the offset angle, 10
is the RF sensor, 11 is the direction of the earth's north pole axis,
12 is the equatorial plane of the earth, 13 is β ₁ , and 14 is β ₂ . It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1. A momentum wheel for imparting gyroscopic rigidity to an artificial satellite by maintaining angular momentum in the vicinity of the pitch axis, and controlling the attitude angle of the artificial satellite around the pitch axis by changing its rotational speed; The satellite has a rotation axis in the vicinity of the plane formed by the roll axis and the yaw axis, and controls the attitude angle of the satellite about the roll axis and damps the nutrition motion by changing the rotation speed of the rotation axis. reaction wheel and
By being fixedly attached to the above artificial satellite and receiving beacon waves emitted from the earth station,
A three-axis attitude control device for an artificial satellite comprising an RF sensor that detects an azimuth angle and an elevation angle relative to the satellite in the direction of an earth station, wherein the reaction is adjusted based on the elevation angle of the RF sensor. A three-axis attitude control device for an artificial satellite, characterized in that the rotational speed of a wheel is accelerated or decelerated, and the rotational speed of the momentum wheel is accelerated or decelerated based on the azimuth angle of the RF sensor.