KR20060108370A - Method for attitude control of satellites fluid rings - Google Patents

Abstract

The present invention relates to a three-dimensional flight attitude control system of a satellite. The system according to the invention relies on the application of a fluid ring to provide the necessary torque for satellite flight attitude control. The satellite has a fluid ring attached to the body. A pump is installed above each fluid ring to regulate the flow of fluid. By using the respective pumps in accordance with the law of control to properly regulate the flow of fluid inside each fluid ring, the required torque around the satellite axis is made to achieve the required flight attitude performance. The control law is based on using proportional and derivative terms to mitigate excitation conditions caused by flight attitude disturbances as well as orbital shifts, and the control method is based on information provided by the satellite flight attitude angle and detection device. This is done using analog logic. The present invention generally significantly improves the flight attitude performance of satellites moving in circular orbits as well as elliptical orbits and the system according to the invention only requires a small power pump. Because of this the system according to the invention has great potential for application in future satellite missions.

Flight Stance, Pitch, Roll, Yaw, Environmental Disturbance, Orbital Shift

Description

Satellite attitude control system using fluid rings {Method For Attitude Control of Satellites Fluid Rings}

1 shows a diagram of a satellite that is stable with respect to an axis around the earth.

2 shows a block diagram of a control system for a satellite.

3A illustrates the β _j and η _j angular positions and spans of fluid slugs in the j th fluid ring.

3B illustrates a filled fluid ring with η _j = 2π.

4 shows the system without fluid control torque ( T _j ^c = 0): e = 0, K ₁ = 0.5, K ₂ = 0.3,

D = 0.4, C ₁ = 0.5, C ₂ = 0.1, α ₀ '= Φ ₀ ' = γ ₀ '= 0.1, β ₀ ' = 10 ^-5 is shown.

5 shows the system reacting as fluid controller torque as follows:

T _j ^c : e = 0, K ₁ = 0.5, K ₂ = -0.3, D = 0.2, C ₁ = 0.5, C ₂ = 0.1, α ₀ '= Φ ₀ ' = γ ₀ '= 0.1,

β ₀ '= 10 ^-5 , μ ₁ = 1, μ ₂ = 10, μ ₃ = 2, v ₁ = 10, v ₂ = v ₃ = 5.

6 shows satellite flight attitudes reacting when affected by the following shifts: K ₁ = 0.5, K ₂ = -0.3, D = 0.3, C ₁ = 0.5, C ₂ = 0.1, α ₀ ' = Φ ₀ '= γ ₀ ' = 0.1, β ₀ '= 10 ^-5 , μ ₁ = 1, μ ₂ = 10, μ ₃ = 2, v ₁ = 10, v ₂ = v ₃ = 5.

7A illustrates one embodiment of a fluid ring pyramid shaped arrangement.

FIG. 7B illustrates another embodiment of the fluid ring pyramid shaped arrangement of FIG. 7A.

FIG. 8 illustrates an arrangement of the subsystem of FIG. 7A.

9A illustrates one embodiment of a co-centric fluid ring.

9B illustrates another embodiment of the co-centric fluid ring of FIG. 9A.

10A illustrates one embodiment of a coaxial fluid ring.

FIG. 10B illustrates another embodiment of the coaxial fluid ring of FIG. 10A.

The present invention relates to a system for controlling the three-dimensional flight attitude of a satellite.

Satellite according to the present specification refers to any artificial object of a solar system in orbit around the earth or any other planet or object of the solar system or in solar orbit. The stability of the satellite's flight attitude is an important feature to consider in order to successfully complete the mission of the spacecraft. Disadvantageously, even if the satellite is initially oriented correctly, the proper orientation over time is due to the influence of ambient forces such as gravity gradient, solar radiation pressure, magnetism, aerodynamics, and free molecular reaction forces. To get away from

As a method to solve this problem, a fluid ring / loop for satellite flight attitude control has been proposed.

U.S. Patent No. 3,862,732 proposes a satellite yaw stabilization method and propulsion method using a rotating toroidal tank filled with liquid in the form of liquid and vapor.

U.S. Patent No. 4,662,178 proposes a spacecraft flight attitude control system using a rotator apparatus comprising channels arranged in the form of a fluid loop in a stacked arrangement. The rotor device rotates around the axis to provide the torque required to control the spacecraft's pitch / roll / yaw motion. In the course of flight attitude control, the channels in the rotor device move between the first configuration and the second configuration. In the first configuration, the fluid is accelerated and then maintained at a constant speed to reach the required cosmic velocity. In the next step, the channel is moved to a second configuration and the fluid is decelerated.

U. S. Patent No. 4,776, 541 discloses the neutralization and relaxation of periodic, non-scaled torques, external or internal, acting on a spacecraft using a fluid momentum control device.

US Patent No. 5,026,008 proposes an improved fluid actuation system for the control of satellite flight attitudes. The fluid loop may be located on an inner or outer spacecraft.

According to the present invention, the use of a fluid-loop reaction device for spacecraft flight attitude control is provided. The proposed device controls the flight attitude of the spacecraft by reacting against the fluid contained within the loop. The pump (s) provide momentum to both the spacecraft and the fluid. Hydrodynamic accumulators and valves are added to control the flow.

A method using a fluid loop is also proposed as a method for flight attitude control of a spacecraft rotating around a single axis. The fluid in the fluid loop is driven by a magnetic hydraulic pump.

As such, the fluid loop / ring can be used to stabilize the free dynamics of the satellite with the required level of accuracy. According to the present invention, a satellite three-dimensional flight attitude control system using a fluid ring is provided. The system includes a satellite with a plurality of rings attached to the satellite's body, a pump and sensors for measuring satellite flight attitude and speed. Various alignment methods of fluid rings attached to the satellite are provided. In accordance with a control law implemented through analog logic, the rotation of the fluid inside the fluid rings using a pump generates torque around the satellite axis, thereby making the necessary flight attitude. According to the invention, the problem for the earth-directional asymmetric satellite is analyzed.

It is an object of the present invention to provide a system for controlling the three-dimensional flight attitude of a satellite comprising a fluid ring with a minimum possible additional mass contributing to the sensor and the actuating device.

It is a further object of the present invention to provide a system for the control of satellite flight attitude, which can reduce the power requirement for flight attitude control without having a significant mass or reliability penalty.

It is another object of the present invention to provide a system for controlling the flight attitude of satellites having the greatest advantage.

It is a further object of the present invention to provide a system for controlling the flight posture of a satellite which rotates a fluid at a necessary angle in accordance with certain laws.

For the purposes presented, the present invention proposes a satellite having a fluid ring attached to the body. Pumps with drive motors are made for the execution of a satellite flight posture in which one or all of the fluid rings are rotated at the required angle and thereby torque is required around the satellite according to the law of control. The control law is developed to mitigate flight attitude excitations caused by environmental disturbances or track shifts, or both, and is based on analogue information based on satellite flight attitude angles and corresponding speed information provided by the flight attitude detection device. Is run through

If the satellite is placed in orbit, any kind of fluid ring, including the fluid loop, is installed or superimposed on the outside / inside of the satellite body during firing, or densely stored in any way, and the satellite After entering the orbit such devices are arranged in any alignment method including parallel or pyramid.

An advantage of the present invention lies in the fact that efficient flight attitude control of the satellite is obtained along the pitch, roll or yaw motion.

The objects, features and advantages of the present invention will become apparent from the following detailed description of the invention given by non-limiting examples with reference to the accompanying drawings.

Symbols used in the present specification are used as follows.

^{A = πD 2/4, m} 2 ( cross-sectional area of the fluid ring);

D = m (diameter of the cross-sectional area of the fluid ring);

D1 = D / r (diameterless size of the fluid ring);

e = orbital shift;

f = Darcy-Wiesbach resistance coefficient;

Ik = first moment of inertia of the satellite around the k-axis, k = x, y or z axis and unit is kg-m ² ;

I _kj ^f = moment of inertia of the fluid ring around the k-axis, k = x, y or z axis and unit is kg-m ² ;

K ₁ , K ₂ = (I _x -I _y ) / I _z , (I _x -I _z ) / I _y (satellite mass distribution parameter);

K ₃ , K ₄ = (1-K ₁ ) / (1-K ₁ K ₂ ), (1-K ₂ ) / (1-K ₁ K ₂ );

r = average radius of the fluid ring in m;

R = orbital radius in m;

Tj = fluid friction torque (unit N-m) with respect to jth fluid ring axis symmetry;

T _j ^c = fluid control torque (unit Nm) applied by the pump in the j th fluid ring;

α, Φ, γ = satellite pitch, roll and yaw angle (in degrees) respectively;

α _d , φ _d , γ _d = required or commanded satellite pitch, roll, and yaw angle (unit degree);

α ₀ , φ ₀ , γ ₀ = α, φ, γ (θ = 0, unit degree);

α ₀ ′, Φ ₀ ′, γ ₀ ′ = α ′, φ ′, γ ′ (θ = 0);

β _j , η _j = respective positions and spans of fluid slugs in the j th fluid ring, respectively (FIG. 2, unit views);

β _j '= angular speed associated with fluid ring-j in rad / s;

β ₀ '= β _j ' (when β ₁ '= β ₂ ' = β ₃ 'at θ = 0);

η _t = η _j (η ₁ = η ₂ = η ₃ ; units are degrees);

ρ = fluid density, in kg-m ^-3 ;

τ _j = cleavage stress for fluid ring-j (unit Nm ⁻² );

μ = viscosity of the fluid in kg-m ^-1 s ^-1 ;

θ = actual variation in degrees;

Ω = orbital speed in rad / s;

(.) ₀ , (.) _E = (.) At θ = 0, (.) At equilibrium;

(.) ', (.)''= d (.) / dθ and d ² (.) / dθ ² ;

| (.) | _max = absolute maximum amplitude of (.).

According to a suitable embodiment for achieving the object presented, the control system according to the present invention comprises a satellite body; A plurality of fluid rings, each of which is attached to the main axis of the satellite; A plurality of pumps installed in the respective fluid rings; And a detection device for measuring the flight attitude and flight attitude velocity of the satellite, and the pitch, roll and yoga of the satellite can be controlled by the plurality of fluid rings and the plurality of pumps.

According to another suitable embodiment of the present invention, the satellite is calculated in a plane trajectory and the predetermined axis can be perpendicular to the plane trajectory.

According to another suitable embodiment of the present invention, the fluid inside the fluid ring;

T ₁ ^c = μ ₁ α '+ ν ₁ (α-α _d ); T ₂ ^c = μ ₂ γ '+ ν ₂ (γ-γ _d ); T ₃ ^c = μ _{3 represented by} Φ '+ ν ₃ (φ-φ _d )

According to the control law, the fluid pump can be used to move the required angle.

According to another suitable embodiment of the present invention, the system comprises three fluid rings, each of which fluid rings may be attached to the main shaft of the satellite along three pumps and each detection device.

According to another suitable embodiment of the present invention. Each of the fluid rings may be arranged in a pyramid configuration, and each of the fluid rings may be located at an edge of the pyramid.

According to another suitable embodiment of the present invention, the fluid rings may be fluid rings located at the same center or on the same axis as rings of the same or different sizes arranged in parallel or pyramid configurations.

According to another suitable embodiment of the present invention, if the outer layers of the fluid rings are made of a suitable metal that allows for a particular function, the fluid rings located outside the satellite may serve as antennas or solar plates.

According to another suitable embodiment of the invention, said at least one planar surface may comprise a fluid ring extending in an opposite direction away from said satellite body.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 shows a satellite 1 in earth orbit 2. The satellite 1 has a central body 3 with the center of mass of the system at the S position. Three fluid rings 4, 5, 6 installed with respective fluid pumps 7, 8, 9 are attached to the central body 3 (see FIG. 1). The first fluid ring is attached to the satellite pitch axis, the second fluid ring is attached to the satellite yaw axis, and the third fluid ring is attached to the satellite roll axis. The center of mass S of the system is located at the center of mass of satellite 1. Since the center of the problem solving is to use the effect of fluid motion on the satellite flight attitude, the distance of the fluid ring from the center of mass is assumed to be negligible. The coordinate frame X ₀ Y ₀ Z ₀ through the center of mass S of the system represents an orbital frame of reference. In this coordinate the X ₀ -axis is perpendicular to the orbital plane, the Y ₀ -axis points towards the vertical area and the Z ₀ -axis represents the third axis of the right hand frame. The direction of the satellite is specified by a series of three consecutive rotations, which are α (pitch) about the X ₀ -axis, Φ about the new roll axis (or Z-axis if α = 0), and finally It is represented by γ regarding the yaw axis that results. The corresponding principal body-fixed coordinate axes for the satellite are denoted by S-XYZ. For the fluid ring-j, each β _j is the fluid around the j-axis with respect to the body-fixed Y-axis (j = 1, 2, and 3 represent the X-axis, the Y-axis, and the Z-axis, respectively). The rotation of the slug is shown (FIG. 2). The coordinate frame resulting as a result associated with the vector is represented by S _Lj -X _Lj Y _Lj Z _Lj . The system under discussion has six generalized coordinates, which are three for the rotation of the satellites: pitch (α), roll (Φ) and yaw (γ), three for the fluid ring, β _j , j = 1,2,3. Since the fluid ring is considerably smaller in size compared to satellites, the consequences of the effects of motion of inertia and center of mass are ignored.

The motion of the fluid associated with the annular ring generates energy dissipation through shear stresses acting on the wall of the ring. The cutting stress τ _j for the fluid ring- _j is given by

τ _j = (1/8) fρV ² = (1/8) fρr ² β _j ,... … (One)

For laminar flow [3] in the smooth pipe (Rn <2000) above,

f = 64 / Rn... … (2)

The same applies to the case of small angles (FIGS. 3A and 3B). The empirical formula [3] given by Blasius for the disturbing flow in a smooth pipe 2000 <Rn <10 ⁵ is as follows:

f = (0.316) / (Rn ^1/4 )... … (3).

In the method according to the invention, end effects that do not have a significant effect on the analysis are ignored; It was further assumed that D << r to simplify the coupling of cutting stress across the wetted area of the ring. The fluid torque T _j about the axis of symmetry of the ring is given by

T _j =-sign (β _j ) πτ _j r ² D | β _j | … … (4).

A three-axis flight attitude control system is provided for satellite 1.

In addition, the present invention is compatible with the technical spirit disclosed in the above-described prior art and is incorporated herein by reference, thereby making no minimum or no addition to the satellite.

It will be appreciated that flight attitude control regarding rolls, pitches, and yaw axes is provided entirely by systems utilizing fluid rings relative to the exterior / inside of the satellite.

The present invention proposes a combination of new components per se and has already proved to be in orbit for a long time, such as viscous nutation dampers (all stationary satellites).

In this specification, a method of achieving pitch, roll, and yaw control of satellites is proposed.

By applying the Euler moment equations, the control nonlinear coupled general differential equations of the system are obtained. For the convenience of system representation and reaction simulation, consider system parameters without the following dimensions.

D = D / r; C ₁ = (ρπr ⁵ ) / I _x ; C ₂ = μ / (ρ r D Ω). … (5),

Except for K ₁ and K ₂ , the inertia properties of the satellite mass moments are described. Since these parameters no longer depend on the size, mass and inertia or fluid properties of the particular satellite, such parameters improve the area of application of the results.

Next, the fluid torque T _j ^c applied by the pump is derived. For a suitable variable of T _j ^c , consider a control unit that combines simple proportional and differential control laws as follows.

T ₁ ^c = μ ₁ α '+ ν ₁ (α-α _d ); T ₂ ^c = μ ₂ γ '+ ν ₂ (γ + γ _d ); T _j ^c = μ ₃ Φ '+ ν (Φ-Φ _d ). … (6).

In equation (6), the control gains μ _j and v _j (j = 1, 2,3) are normalized to (I _x Ω ² ). The flight attitude angle and corresponding speed were measured by the flight attitude detector. In the embodiment according to the invention, the desired flight attitude angle is taken to be zero (ie α _d = Φ _d = γ _d = 0).

Balance and stability were analyzed.

result

To study the implementation of the control device proposed in the present invention, a detailed system response was simulated using the following initial conditions:

α ₀ = Φ ₀ = γ ₀ = 5 (unit degree); β _j0 = 0, j = 1,2; η ₁ = η ₂ = η ₃ = η _t = 2π; α _d = Φ _d = γ _d = 0, the program used used the International Mathematical and Statistical Library (IMSL) routine DDASPG based on the Petzoid-Gear BDF Method.

The embodiment according to the invention first considers a system moving in a circular orbit (ie e = 0) and the dynamics of the system with natural damping (ie T _j ^c = 0, j = 1, 2, 3). This was studied. The flight attitude angles of the satellites shown in FIG. 4 were found to decrease with time, and the | α | _max = 0.03 degrees, | Φ | _max = 0.09 degrees and | α | _max = 0.05 was reached. Indeed, a system with natural damping requires a relatively long period of time to reach a steady state and thereby consider applying the fluid control device T _j ^c in accordance with the control law given by equation (6). 5 shows that the satellite responds to the fluid control device. Despite the fluctuations in system parameters D , C ₁ and C ₂ , as well as the presence of high initial flight attitude velocity disturbances and orbital deviations (FIG. 6), the system remained stable as a high flight attitude run.

In order to evaluate the efficiency of the proposed control method, the present invention proposes a stationary flight attitude and water fluid inside the fluid ring (ρ = 998 kg.m ^-3 ; μ = 10 ^-3 kg.m ^-1 s ^-1 , 20 Special case). For this particular case, the present invention may represent system parameters used in the form of dimensions (Table 1).

Table 1: System Parameters Displayed in Dimensional Form

I _x -I _y -I _z (kg.m ² ) r (cm) D (cm) 240-141-198 59 23.6 432-188-488 59 23.6 888-386-1004 68 20.4 2446-1046-2765 83 16.6

The invention can also be applied to any satellite associated with the necessary calculations being made in whole or in part with respect to the ground.

Alignment of the fluid rings as shown in FIG. 1 is referred to as a parallel configuration, in which the system comprises three fluid rings and each of the three fluid rings is connected to the main axis of the satellite along a new pump and each detection device. Attached.

The fluid rings can be arranged in a pyramid configuration (see FIG. 7), wherein the four fluid rings are located at four corners of the pyramid. Each fluid ring is single-gimballed and each fluid ring is rotated by about each υ _j , j = 1, 2, 3, 4 (FIG. 8) using the DC motor 11. Can be. Along the fluid pump 7 the fluid ring 4 is fixed by a motor strut 10.

If large torques are required around any one axis or all axes, one or more fluid rings may be installed on each axis. The fluid rings may be co-centered (FIG. 9) or coaxial (FIG. 10) as parallel or pyramid structures. The cross-sectional areas of the fluid rings can be the same or different. In the case of coaxial alignment (FIG. 10), the rings can be aligned in size from the size of the ring close to the satellite body.

If the outer layers of the fluid rings are made of a suitable material that allows for a certain function, the fluid rings located outside the body of the satellite can serve as antennas or solar panels.

The present invention has the advantage of enabling satellite flight attitude control that can reduce the power requirements for flight attitude control without having a significant mass or reliability penalty. Such control of the flight attitude is effectively made to the satellite along the pitch, roll or yaw motion. The invention also has the advantage that it can be applied to any satellite, in particular low orbit orbit, in connection with the necessary calculations made in whole or in part with respect to the ground.

Claims (12)

A system for controlling the satellite's flight attitude with respect to a predetermined axis, Satellite body; A plurality of fluid rings, each of which is attached to the main axis of the satellite; A plurality of pumps installed in the respective fluid rings; And a detection device for measuring the flight attitude and flight attitude speed of the satellite, wherein the pitch, roll and yoga of the satellite are controlled by the plurality of fluid rings and the plurality of pumps. The control system of claim 1, wherein the satellite is calculated in a plane trajectory and the predetermined axis is perpendicular to the plane trajectory. The method of claim 1, wherein the fluid inside the fluid ring; T ₁ ^c = μ ₁ α '+ ν ₁ (α-α _d ); T ₂ ^c = μ ₂ γ '+ ν ₂ (γ-γ _d ); T ₃ ^c = μ _{3 represented by} Φ '+ ν ₃ (φ-φ _d )  Control system characterized in that the fluid pump is moved by the required angle according to the control law The control system of claim 1, wherein the system comprises three fluid rings, each said fluid ring being attached to the main shaft of the satellite along three pumps and each detection device. The control system of claim 1, wherein the respective fluid rings are arranged in a pyramid configuration, wherein each fluid ring is located at an edge of the pyramid. The control system of claim 1, wherein the fluid rings are fluid rings located at the same center or on the same axis as rings of equal or different size aligned in parallel or pyramid configuration. The control system of claim 1, wherein the outer layers of the fluid rings are made of metal to allow a specific function, and the fluid rings located outside the satellite serve as antennas or solar plates. The control system of claim 2, wherein the at least one planar surface comprises a fluid ring extending in an opposite direction away from the satellite body. A low orbit satellite controlled by the control system of claim 1. A geostationary satellite controlled by the control system of claim 1. A low orbit satellite controlled by the control system of claim 4. A geostationary satellite controlled by the control system of claim 4.

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