JP3366095B2 - Disturbance torque estimation device for satellites - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial satellite disturbance torque estimating apparatus for estimating a disturbance torque applied to an artificial satellite orbiting the earth. 2. Description of the Related Art Artificial satellites orbiting the earth always receive disturbance torques such as solar radiation pressure torque, aerodynamic torque, geomagnetic torque, gravity gradient torque and the like. The influence of the disturbance torque increases due to an increase in the size of the satellite, an imbalance in mass characteristics, and the like, and deteriorates the accuracy of the satellite attitude control. [0003] Normally, disturbance torque which deteriorates the control accuracy is dealt with by forming a closed loop including an attitude control system as shown in FIG. That is, when the disturbance torque Td is applied to the satellite dynamics 11, the attitude angle of the satellite becomes θ. The attitude control system 12 feeds back the attitude angle θ, calculates a control torque Tc of the control system so that the attitude angle becomes zero, and sends it to the actuator 13. The actuator 13 outputs an actuator control torque (Tc) from the input control torque Tc, and controls the attitude of the satellite so that the attitude angle becomes zero. By repeating the above operation, it is possible to suppress the posture variation due to the disturbance torque Td. However, in the above-described method of passively dealing with disturbance torque, there is a limit to the control accuracy that can be achieved. As the disturbance torque increases, the control accuracy exceeds the allowable range, or conversely. Attempting to achieve the desired accuracy places excessive demands on the attitude control system. [0005] As described above, in the conventional attitude control of the artificial satellite, since the disturbance torque is passively dealt with, the control accuracy deteriorates as the disturbance torque increases. In addition, it imposed excessive demands on the attitude control system. For this reason, conventionally, it has been demanded that disturbance torque be estimated to achieve a desired control accuracy so that it can be actively dealt with. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is possible to estimate a disturbance torque given to a satellite with respect to an artificial satellite orbiting the earth, and to actively use the estimated disturbance torque. An object of the present invention is to provide a disturbance torque estimating device for an artificial satellite that enables attitude control. In order to achieve the above object, a disturbance torque estimating apparatus for an artificial satellite according to the present invention provides a disturbance torque applied to an artificial satellite orbiting the earth to the nth order (n is a natural number). Profile registration means for approximating the Fourier series with the Fourier series and registering the approximated Fourier series as a profile, and measuring the wheel speed at which the speed changes according to the attitude change of the satellite at 2n + 1 points on the orbit of the satellite. Wheel speed measuring means, parameter calculating means for obtaining the parameters of the Fourier series from the measured values of 2n + 1 wheel speeds obtained by the means, and disturbance obtained by substituting the parameters obtained by the means for the Fourier series. create a torque estimation equation, Ri <br/> by the and substituting child an arbitrary position on the track in the disturbance torque estimating equations Constituted by and a disturbance torque estimating means for estimating a disturbance torque at that location. The disturbance torque estimating apparatus for an artificial satellite having the above configuration focuses on the periodicity of the disturbance torque received by an artificial satellite orbiting the earth in a circular orbit, and sets the profile of the disturbance torque to n.
Approximate by the next Fourier series, which is registered in advance. The parameter of the approximated Fourier series is obtained from the wheel speed of the 2n + 1 points on the orbit, and this is substituted into an approximate expression to create a disturbance torque estimation equation. By substituting a position on a desired orbit into this equation, a disturbance torque at that position can be estimated. An embodiment of the present invention will be described below with reference to FIGS. First, referring to FIG. 2, the position of the artificial satellite in orbit is defined. In the figure, M is the earth A
Is an artificial satellite that orbits in a circular orbit. The position of the artificial satellite M is represented by an angle β from a point a (Midnight) farthest from the sun S. The angle β is represented by β = ω ₀ · t (1), where trajectory rate is ω ₀ . Here, the main environmental disturbances acting on the satellite are:
It changes greatly depending on the positional relationship between the artificial satellite M and the earth A, the sun S, and the like. Further, in the artificial satellite orbiting the earth A in a circular orbit, since the positional relationship changes periodically, the disturbance received by the satellite M also changes periodically. Therefore, the disturbance torque Td received by the artificial satellite M in orbit is substantially as shown in FIG. The locus of the disturbance torque Td can be approximated by a _first -order Fourier series Td = a ₀ + a ₁ sin (ω ₀ t + α ₁ ) (2). In the equation (2), a ₀ is the bias of the disturbance torque, a ₁ is the amplitude of the disturbance torque, α ₁
Is the phase of the disturbance torque. Here, the parameters a ₀ , a ₁ , α ₁ are:
For example, any three points t ₁ and t on the orbit about the roll axis
_The wheel speeds Hw (t ₁ ), Hw (t ₂ ), Hw (t ₃ ) and the wheel speed measured at the measurement time ΔT at ₂ and t ₃ .
Speed change ΔHw (t ₁ ), ΔHw (t ₂ ), ΔHw
From (t ₃ ), ΔHw (t ₁ ) / ΔT + ω ₀ Hw (t ₁ ) = a ₀ + a ₁ sin (ω ₀ t ₁ α ₁ ) ΔHw (t ₂ ) / ΔT + ω ₀ Hw (t ₂ ) = a ₀ + a ₁ sin (ω ₀ t ₂ + α ₁ ) ΔHw (t ₃ ) / ΔT + ω ₀ Hw (t ₃ ) = a ₀ + a ₁ sin (ω ₀ t ₃ + α ₁ ) It is obtained by solving a simultaneous equation of (3). . The measurement position is selected so as to exclude a position where a large disturbance such as unloading / trajectory control / antenna through drive temporarily occurs. Parameter a obtained by equation (3)
By substituting ₀ , a ₁ and α ₁ into equation (2), a disturbance torque estimation equation for obtaining an estimated disturbance torque [Td] at an arbitrary position on the trajectory is obtained. That is, a desired position is obtained from the equation (1), and the obtained position is substituted into the disturbance torque estimation equation, whereby the disturbance torque can be obtained by calculation. The same can be calculated for other pitch / yaw axes. FIG. 1 shows a configuration of a disturbance torque estimating device for estimating the disturbance torque Td on the basis of the above conditions. Reference numeral 14 denotes a parameter calculation unit, and 15 denotes a disturbance torque estimation unit. The parameter calculation unit 14 includes the simultaneous equations of the equation (3), and measures the measurement time ΔT, the wheel speeds Hw (t ₁ ), Hw (t) at any three points t ₁ , t ₂ , and t ₃ on the orbit. ₂ ), Hw
(T ₃ ), wheel speed change ΔHw (t ₁ ), ΔHw
Information of (t ₂ ) and ΔHw (t ₃ ) is input and substituted into the simultaneous equations of the equation (3), and the substituted simultaneous equations are solved to obtain parameters a ₀ , a ₁ and α _1. . The disturbance torque estimating unit 15 has a Fourier series of the formula (2) as a profile, and substitutes a ₀ , a ₁ , and α ₁ obtained by the parameter calculation unit 14 into the Fourier series to estimate the disturbance torque. An estimated disturbance torque [Td] at that position is calculated by creating an equation and substituting the designated position β into this equation. In the above, the case where the periodic fluctuation of the disturbance torque is approximated by a first-order Fourier series has been described. it can. Therefore, the trajectory of the disturbance torque in one round of the trajectory is represented by the n-th order Fourier series: Approximation. In this case, the parameters a ₀ , a _i , and α _i can be obtained from the disturbance torque values at 2n + 1 points on the trajectory. Incidentally, the disturbance torque value at the point 2n + 1 on the orbit is obtained as follows. That is, when the disturbance torque Td is given, the system momentum H becomes (H) ′ = Td−ω · H (5) Assuming that the satellite orbiting the earth is well controlled by the wheel, Therefore, equation (5) is given by the following equation. Therefore, (Hw _x ) ′ = Td _x −ω ₀ Hw _z (Hw _y ) ′ = Td _y (Hw _z ) ′ = Td _z + ω ₀ Hw _x (7) Accordingly, the disturbance torque Td _{is, Td x = (Hw x)} '+ ω 0 Hw z Td y = (Hw y)' Td z = (Hw z) '- can be obtained by _{ω 0 Hw x ... (8)} . Therefore, according to the above-described disturbance torque estimation, the wheel speed at an arbitrary 2n + 1 point on the trajectory is measured, and the trajectory of the disturbance torque with respect to one round of the trajectory is represented by the nth order trajectory.
Approximate by Rie series, and parameters when this series is expanded
Since an equation for estimating the disturbance torque at an arbitrary orbital position is established by using the parameters, the disturbance torque can be estimated only by designating a desired position. In this case, the higher the order n, the higher the estimation accuracy. In selecting a measurement position, a position where a large disturbance such as unloading / trajectory control / antenna through drive is temporarily generated is selected.
By estimating the disturbance torque, it is possible to actively cope with the disturbance torque in the attitude control of the artificial satellite, and it is possible to reduce a demand for the attitude control system due to the disturbance torque. As described above, according to the present invention, it is possible to estimate a disturbance torque applied to a satellite orbiting the earth, and an active attitude using the estimated disturbance torque. It is possible to provide a disturbance torque estimating device for an artificial satellite that enables control.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a disturbance torque estimation device for an artificial satellite according to the present invention. FIG. 2 is a schematic diagram for explaining the definition of the orbital position of the artificial satellite orbiting in a circular orbit of the embodiment. FIG. 3 is a characteristic diagram showing a trajectory of a typical disturbance torque received by the artificial satellite of FIG. 2, and FIG. 4 is a block diagram for explaining a disturbance torque compensation method by a feedback attitude control system in a conventional artificial satellite. It is. [Description of Signs] Td: disturbance torque, θ: attitude angle, Tc: control system control torque, (Tc): actuator control torque, 11: satellite dynamics, 12: attitude control system, 13: actuator, M
... artificial satellite, A ... Earth, S ... _{sun, a 0, a 1, α} 1 ...
Parameter, ΔT: Measurement time, Hw (t ₁ ), Hw (t
₂ ), Hw (t ₃ ): Wheel speed, ΔHw (t ₁ ),
ΔHw (t ₂ ), ΔHw (t ₃ ): change in wheel speed, β: estimated position, [Td]: estimated disturbance torque, 14: parameter calculation unit, 15: disturbance torque estimation unit.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Soga 1 Kosuka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Komukai Plant (56) References JP-A-63-125498 (JP, A) Kaisho 60-4497 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B64G 1/00-1/36 G05D 1/08

Claims (1)

(57) [Claim 1] A profile in which a disturbance torque given to an artificial satellite orbiting the earth is approximated by an nth-order (n is a natural number) Fourier series, and the approximated Fourier series is registered as a profile. Registration means; wheel speed measuring means for measuring the speed of a wheel whose speed changes in accordance with the attitude change of the satellite at 2n + 1 points on the orbit of the satellite; 2n + 1 wheel speeds obtained by this means Parameter calculating means for obtaining the parameters of the Fourier series from the measured values of the above, and a parameter obtained by this means is substituted for the Fourier series to create a disturbance torque estimation equation. Substituting the position of
Yo is, the disturbance torque estimating device of artificial satellites and a disturbance torque estimating means for estimating a disturbance torque at that location.