CN113772127B - Space debris racemization control method - Google Patents

Abstract

The invention discloses a space debris racemization control method, which is based on a rope system for capturing space debris, wherein the rope system is a combination body composed of a parent star, the space debris and a tether connected between the parent star and the space debris, in the racemization process of a target, namely the space debris, the speed of the target and the parent star is monitored, when the speed of the target is greater than the speed of the parent star, the position of the parent star is adjusted through a propeller, and the collision of the target and the parent star is prevented. Compared with the traditional method for detecting the state of the tether, the method for adjusting the position of the parent star by opening the propeller once the tether is not straightened, avoids the waste of fuel for adjusting the position of the parent star when the distance between the target and the parent star is shortened but the speed is the same and the position of the parent star cannot collide, saves the consumption of fuel of the parent star, does not need to open all the propellers each time, further saves the fuel of the parent star, is more beneficial to maintaining the stability of the system, and ensures the safe off-orbit of the target and the parent star.

Description

A method for controlling space debris racemization

Technical field

The invention relates to the field of aerospace technology, and in particular to a method for controlling space debris racemation.

Background technique

According to records from the U.S. satellite monitoring network, the number of space debris larger than 10 centimeters in the Earth's orbit currently exceeds 20,000, which undoubtedly poses a huge threat to spacecraft in orbit. The flexible connection capture method is one of the most effective methods for active space debris removal. This method means that after capturing the target, the main star and the target are connected through a flexible medium, usually a tether. The flexible connection capture method has the characteristics of light weight, low launch cost and long range. Commonly used flexible connection capture methods include flying net capture method, flying claw capture method, harpoon method, etc. Due to the existence of residual angular momentum of space debris, it often spins in space. After successfully capturing such a target using the flexible connection capture method, the target needs to be deracinated through the tether, otherwise it will easily cause the target to wrap around the tether and collide with the main star.

In the existing tether race control system, the control algorithm is often relatively complex and the traditional method requires continuous detection of the tether status. Once the tether is not straightened, the thruster is turned on to adjust the position of the parent star to keep the tether in a straightened state. The propeller needs to be constantly moved, but the tether is not straightened. This only means that the distance between the main star and the target is closer than when the tether is straightened. If the speed is still synchronized, there will be no collision. Therefore, it depends on whether the tether is straightened. Adjustments were made, resulting in a huge waste of fuel for the main star.

Contents of the invention

In view of this, the present invention provides a space debris despin control method, which can perform a limited number of actions with a limited number of thrusters to reduce the angular velocity of the target to near zero in a short time range, greatly saving valuable space on the main star. fuel, and prevent the target from colliding too close to the main star, ensuring the safe deorbiting of the system composed of the main star and the target.

The specific technical solutions of the present invention are as follows:

A method for controlling space debris decycling, which is used for capturing space debris in a tether system. The tether system is a combination composed of a parent star, space debris, and a tether connected between the parent star and the space debris; During the process of decycling the target, that is, space debris, the speed of the target and the parent star is monitored. When the speed of the target is greater than the speed of the parent star, the position of the parent star is adjusted through the thruster to prevent the target from colliding with the parent star; when the speed of the target is greater than the speed of the parent star, When the speed is less than or equal to the speed of the parent star, the target and the parent star will not collide, and there is no need to adjust the position of the parent star;

The speed of the target and the speed of the parent star both include velocity components in the three directions of x, y, and z. When the component speed of the target in only one direction is greater than the component speed of the parent star in the corresponding direction, only the propulsion in the direction of the corresponding speed component is turned on. device to adjust the position of the parent star.

Further, by monitoring the speed of the target and the parent star, the position of the parent star is adjusted, including the following steps:

Step 1: Establish a dynamic model of the assembly, including a tether dynamic model, a parent star dynamic model and a target dynamic model;

Step 2: According to the parent star's dynamic model, use the PD control algorithm to solve the parent star's momentum wheel output control torque to control the parent star's attitude;

Step 3: Control the position of the mother star through the thruster according to the monitored speed. The thrust F _thru of the thruster is determined based on the speed difference ΔV between the target and the mother star and the time Δt expected to adjust the speed difference. .

Further, the tether dynamic model is expressed as:

Among them, m is the concentrated mass of the tether, r is the position vector of the tether, is the second derivative of the tether position vector r with respect to time; n is the number of nodes connected to point P; T _j is the pulling force of the corresponding tether on point P, G is the spatial microgravity vector of point P, F _k are other external forces on point P, p is the number of external forces on point P, and point P is the connection point between the main rope and the sub-rope in the tether;

The parent star dynamic model is expressed as:

m _S a _S ＝F _S +F _thru ,

Among them, m _S is the mass of the main star, a _S is the acceleration of the main star, F _S is the tether tension experienced by the main star, F _thru is the thrust of the propeller, J _S is the inertia matrix of the main star, ω _S is the rotation angular velocity of the main star, τ _S is the torque produced by the tether tension and torsion on the main star, τ _c is the control torque produced by the momentum wheel of the main star, is the first derivative of the main star’s rotation angular velocity ω _S with respect to time;

The target dynamics model is expressed as:

m _T a _T = F _T ,

Among them, m _T is the mass of the target, a _T is the acceleration of the target, F _T is the tether tension exerted by the target, J _T is the inertia matrix of the target in its body coordinate system, ω _T is the target rotation angular velocity, and τ _T is The moment caused by the pulling force of the sub-rope on the target, is the first derivative of the target rotation angular velocity ω _T with respect to time.

Further, the attitude of the parent star is described by the Euler angle Φ _S = [α, β, γ] ^T , where the Euler angles corresponding to the zxz rotation are α, β, and γ respectively;

The momentum wheel output control torque is expressed as:

Among them, α _Sd , β _Sd , γ _Sd represent the expected Euler angle of the parent star, Represents the first derivative of the Euler angle of the parent star with respect to time,/> Represents the first derivative of the Euler angle of the expected parent star with respect to time,/> Represents the second derivative of the expected parent star Euler angle with respect to time, the parameter k _p > 0 represents the proportional control gain, k _d > 0 represents the differential control gain, τ _cx , τ _cy , τ _cz represents the momentum wheel control torque in x, y , the components in the three directions of z, J _Sx , J _Sy , J _Sz represent the components of the main star inertia matrix in the three directions of x, y, and z, τ _Sx , τ _Sy , τ _Sz are the torque generated by the tether on the main star in x , components in the three directions of y and z.

Further, the size of the thrust F _thru of the thruster is determined based on the speed difference ΔV between the target and the parent star and the time Δt expected to adjust the speed difference, specifically as follows:

The speed difference between the target and the parent star is expressed as: ΔV=[v _Tx -v _Sx , v _Ty - v _Sy , v _Tz - v _Sz ], where v _Tx , v _Ty and v _Tz respectively represent the target speed at x, The velocity components in the three directions of y and z, v _Sx , v _Sy , and v _Sz respectively represent the velocity components of the parent star’s velocity in the three directions of x, y, and z;

The thrust of the propeller:

Among them, m _S is the mass of the parent star.

Furthermore, when only considering the velocity component of the target and the parent star along the tether direction, that is, the x-axis direction, ΔV = [v _Tx - v _Sx ,0,0], at this time, it is only necessary to turn on the position corresponding to the x-axis direction. Just propeller.

Further, the tether system also includes a tether ejection device and a spring damping unit; the tether ejection device is installed on the main satellite; the tether and the spring damping unit are stored inside the tether ejection device. , when it is necessary to capture the space debris, the tether ejection device is triggered, and the tether and the spring damping unit are ejected together;

The tether includes a main rope and a sub-tether; the main rope is connected to the main star, and the sub-tether is connected to the space debris;

The spring damping unit is provided on the main rope and the sub-rope.

Further, the number of the sub-ropes is n, and the n sub-ropes and the main rope are connected at the same point P; where n is a positive integer greater than or equal to 2;

A plurality of spring damping units are provided on the main rope, and one spring damping unit is provided on each of the sub-ropes.

Beneficial effects:

(1) The present invention monitors the speed of the target and the parent star. When the speed of the target is greater than the speed of the parent star, the position of the parent star is adjusted through the thruster, and the tether status is detected using the traditional method. Once the tether is not straightened, it is opened. Compared with the method of using the thruster to adjust the position of the main star to straighten it, it avoids the waste of fuel in adjusting the position of the main star when the distance between the target and the main star is close but the speed is the same and they will not collide, thus saving the fuel consumption of the main star; at the same time, when the speed is x , the velocity components in the three directions of y and z are monitored and can be adjusted according to the velocity changes of the individual direction components. There is no need to turn on all the thrusters every time, which further saves the main star fuel and is more conducive to maintaining the stability of the system. safety to ensure the target is safely de-orbited from the parent star.

(2) Fully consider the flexibility of the tether and establish a dynamic model for the tether, which will help to understand the status of the system body more clearly. While monitoring the speed, the distance factor should still be considered to avoid that the speed is always the same but the distance is getting closer and closer. A direct collision.

(3) Use the PD control algorithm to calculate the momentum wheel output control torque of the parent star. During the process of derotating and adjusting the position of the parent star, the attitude of the parent star is controlled to further ensure the stability of the system and further reduce the distance between the target and the parent star. The possibility of a star collision.

Description of the drawings

Figure 1 is a schematic diagram of the assembly model of the present invention.

Figure 2 is a schematic diagram of the target swing during the racemization process.

Figure 3 is a simulation change diagram of the target angular velocity.

Detailed ways

A space debris race control method that captures space debris based on a tether system. The tether system is a combination of a parent star, space debris, and a tether connected between the parent star and the space debris. When targeting the target, that is, space During the process of debris descycling, the speed of the target and the parent star is monitored. When the speed of the target is greater than the speed of the parent star, the position of the parent star is adjusted through the thruster to prevent the target from colliding with the parent star; when the speed of the target is less than or equal to At the speed of the parent star, the target and the parent star will not collide, and there is no need to adjust the position of the parent star. At the same time, the velocity components in the three directions of x, y, and z are monitored, and adjustments can be made according to the velocity changes of the individual direction components. There is no need to turn on all the thrusters every time, further saving the main star fuel.

The present invention will be described in detail below with reference to the accompanying drawings and examples.

As shown in Figure 1, it is a schematic diagram of the assembly model of the present invention. The tether system is an assembly composed of a parent star, space debris, and a tether connected between the parent star and the space debris.

During the process of decycling the target, that is, space debris, the speed of the target and the parent star is monitored. When the speed of the target is greater than the speed of the parent star, the position of the parent star is adjusted through the thruster to prevent the target from colliding with the parent star;

The speed of the target and the speed of the parent star include velocity components in the three directions of x, y, and z. When the component speed of the target in only one direction is greater than the component speed of the parent star in the corresponding direction, only the propulsion in the direction of the corresponding speed component is turned on. device to adjust the position of the parent star.

To monitor the speed of the target and the parent star and make adjustments to the parent star's position, you first need to establish a dynamic model. While controlling the attitude of the parent star, you can then adjust the parent star's position to ensure that the target does not phase with the parent star. Collision, including the following steps:

Step 1: Establish a dynamic model of the combination, including a tether dynamic model, a parent star dynamic model and a target dynamic model.

The tether dynamic model is expressed as:

Among them, m is the concentrated mass of the tether, r is the position vector of the tether, is the second derivative of the tether position vector r with respect to time; n is the number of nodes connected to point P; T _j is the pulling force of the corresponding tether on point P, G is the spatial microgravity vector of point P, F _k are other external forces on point P, p is the number of external forces on point P, and point P is the connection point between the main rope and the sub-rope in the tether, as shown in Figure 1.

Since the rope unit can only bear tension and not pressure, the rope mechanics model is

In the formula, l ₀ and l are the original length and current length of the tether respectively; k is the tensile stiffness of the tether, c is the tensile damping coefficient of the tether, r _j is the distance between point P and each connection point, Then it is the unit direction vector from point P to each connection point.

The main star, that is, the parent star and the target are regarded as rigid bodies. Since the main star can control its own posture under the action of the momentum wheel and thruster, the parent star dynamic model is expressed as:

m _S a _S ＝F _S +F _thru , (3)

Among them, m _S is the mass of the main star, a _S is the acceleration of the main star, F _S is the tether tension experienced by the main star, F _thru is the thrust of the propeller, J _S is the inertia matrix of the main star, ω _S is the rotation angular velocity of the main star, τ _S is the torque produced by the tether tension and torsion on the main star, τ _c is the control torque produced by the momentum wheel of the main star, is the first derivative of the main star's rotation angular velocity ω _S with respect to time.

The dynamic equation of the target has a similar form to that of the host star. The target dynamic model is expressed as:

m _T a _T = F _T , (4)

Among them, m _T is the mass of the target, a _T is the acceleration of the target, F _T is the tether tension exerted by the target, J _T is the inertia matrix of the target in its body coordinate system, ω _T is the target rotation angular velocity, and τ _T is The moment caused by the pulling force of the sub-rope on the target, is the first derivative of the target rotation angular velocity ω _T with respect to time.

in,

Step 2: According to the dynamic model of the parent star, use the PD control algorithm to solve the output control torque of the momentum wheel of the parent star to control the attitude of the parent star.

In order to prevent the solar panel and antenna pointing of the parent star from being affected by the target acquisition process, the attitude of the parent star should be controlled to be consistent before and after the target is captured. The attitude of the parent star is described by the Euler angle Φ _S = [α, β, γ] ^T. The corresponding Euler angles according to the zxz rotation method are α, β, and γ respectively. Then the relationship between the Euler angle change rate and the angular velocity is:

In the formula, ω _x , ω _y , and ω _z are the components of the parent star’s angular velocity around the coordinate axis in the body coordinate system.

Assume that the initial value of the satellite Euler angle is set to Φ _S0 = [90°, 90°, 90°] ^T , and the satellite attitude and angular velocity change range is very small. Linearize the above equation to obtain the Euler angle change rate and angular velocity. The corresponding relationship is,

The parent star attitude dynamics equation in equation (3) is expanded and written into component form as,

Substituting equation (7) into equation (8) and ignoring the quadratic term, the simplified attitude dynamics control equation can be obtained as,

Using the traditional PD control algorithm, the momentum wheel output control torque can be obtained as follows:

Among them, α _Sd , β _Sd , γ _Sd represent the expected Euler angle of the parent star, Represents the first derivative of the Euler angle of the parent star with respect to time,/> Represents the first derivative of the Euler angle of the expected parent star with respect to time,/> Represents the second derivative of the expected parent star Euler angle with respect to time, the parameter k _p > 0 represents the proportional control gain, k _d > 0 represents the differential control gain, τ _cx , τ _cy , τ _cz represents the momentum wheel control torque in x, y , the components in the three directions of z, J _Sx , J _Sy , J _Sz represent the components of the main star inertia matrix in the three directions of x, y, and z, τ _Sx , τ _Sy , τ _Sz are the torque generated by the tether on the main star in x , components in the three directions of y and z.

Step 3: Control the position of the mother star through the thruster according to the monitored speed. The thrust F _thru of the thruster is determined based on the speed difference ΔV between the target and the mother star and the time Δt expected to adjust the speed difference. .

Assume that after the main star successfully captures the target, the relative speed between the main star and the target along the tether direction is zero. The target will inevitably pull the tether during the rotation process, causing tension in the tether. This pulling force will cause the main star's acceleration along the tether direction to decrease and the target's acceleration along the tether direction to increase, so the target's speed along the tether direction must be greater than the main star's. It is necessary to control the home star in this configuration to prevent the target from colliding with the host star.

Design the following control conditions and control laws:

Control condition: v _T > v _S , that is, the speed of the target is greater than the speed of the parent star

Control law:

ΔV＝[v _Tx -v _Sx ,v _Ty -v _Sy ,v _Tz -v _Sz ]

The speed difference between the target and the parent star is expressed as: ΔV = [v _Tx -v _Sx , v _Ty - v _Sy , v _Tz - v _Sz ], where v _Tx , v _Ty , and v _Tz respectively represent the target speed in x, y, The velocity components in the three directions of z, v _Sx , v _Sy , and v _Sz respectively represent the velocity components of the parent star's velocity in the three directions of x, y, and z;

The thrust of the propeller:

Among them, m _S is the mass of the parent star.

In a specific embodiment, as shown in Figure 1, the target is considered to be a symmetrical cube, and the tensile force it receives is also symmetrical. There are four sub-ropes of the tether, which are symmetrically connected to the target. At this time, the target receives the force from the tether. The pulling force can be automatically offset in the z-direction, and due to the reciprocating swing of the target, only a small amount of fine-tuning is required in the y-direction. Therefore, when only considering the velocity component of the target and the parent star along the tether direction, that is, the x-axis direction, ΔV = [v _Tx -v _Sx ,0,0]. At this time, you only need to turn on the thruster corresponding to the x-axis direction That’s it.

At this time, the control condition is v _Tx > v _Sx ,

The control law is:

ΔV＝[v _Tx -v _Sx ,0,0],

In this configuration, the tether is in a relaxed state, but the target angular velocity is not zero, and the racemization process has not yet ended. This control law calculates the speed difference between the parent star and the target, and expects the parent star to reach the target's linear velocity along the x-axis within Δt time, thereby obtaining the required propeller thrust. Under the action of this thrust, the tether will be tightened and can exert a despin torque on the target, thereby despinating the target.

As shown in Figure 2, it is the swing state of the target during the racemization process, where the small cube represents the target, the large cube represents the parent star, and the tether is in between. Figure 2(a) shows the initial state, the target does not swing, and the tether is in a tight state. Figure 2(b) shows that the target swings in the clockwise direction and the tether is relaxed. At this time, the speed of the target is greater than the speed of the parent star. The thruster needs to be triggered to generate a certain thrust to straighten the tether. The straightened tether generates pulling force. , the target will reduce its rotation speed to zero and rotate counterclockwise under the action of this pulling force. Figure 2(c) shows that the parent star decelerates the target when it rotates counterclockwise. When the target's speed rotates counterclockwise after the previous deracination process, and the target speed exceeds the speed of the parent star again, the thruster rotates according to the control rate. It triggers and generates corresponding propulsion force, and performs a second racecycling process on the target. This is repeated until the target's rotational speed reduces to a certain range and the speed difference between the target and the main star is reduced to 0 or close to 0, and the system returns to stability.

The target single-axis rotation racemization is simulated according to the simulation parameters in Table 1.

Table 1 Simulation parameters

The initial angular velocity of the target is 0.3rad/s around the z-axis. The target angular velocity change process diagram shown in Figure 3 is obtained through derotation simulation, in which the angular velocity in the x and y directions does not change, and the two lines coincide with 0, and the z direction Each time the angular velocity crosses the straight line x=0, it means that the thruster is triggered and the direction of the target's angular velocity is switched. As can be seen from Figure 3, four deceleration actions are performed within 150 seconds. Each time the target undergoes a deceleration action, its angular velocity Lower it a little until it drops to near 0, and the system returns to a stable state. It can be seen that the system only needs 4 thruster triggering actions to reduce the target from 0.3rad/s to near 0, which greatly saves fuel.

A space debris despin control method of the present invention is based on a combination of a parent star, space debris, and a tether connected between the parent star and the space debris, that is, a tether system. As shown in Figure 1, the tether system also includes a tether ejection device and a spring damping unit; the tether ejection device is installed on the main satellite, and the tether and spring damping unit are stored inside the tether ejection device when space debris needs to be captured. , triggering the tether ejection device, and the tether and spring damping unit eject together.

The tether includes a main rope and a sub-tether, the main rope is connected to the main star, and the sub-tether is connected to the space debris; the spring damping unit is provided on the main rope and the sub-tether.

The number of sub-ropes is n, and n sub-ropes are connected to the same point P as the main rope; where n is a positive integer greater than or equal to 2; as shown in Figure 1, the number of sub-ropes is 4, and the number of sub-ropes is related to the space It depends on the shape of the debris. Try to ensure that the pulling force received by the space debris from the sub-rope is even and symmetrical.

Multiple spring damping units are provided on the main rope, and one spring damping unit is provided on each sub-rope. In the specific implementation process, if necessary, multiple spring damping units can also be provided on the sub-ropes. As shown in Figure 1, three spring damping units are provided on the main rope. During the specific implementation process, any integer number can also be provided.

The above specific embodiments only describe the design principles of the present invention. The shapes and names of the components in this description can be different and are not limited. Therefore, those skilled in the field of the present invention can make modifications or equivalent substitutions to the technical solutions described in the foregoing embodiments; and these modifications and substitutions do not deviate from the creative purpose and technical solutions of the present invention, and should all fall within the protection scope of the present invention.

Claims (5)

1. A space debris racemization control method is characterized by being used for capturing space debris by a rope system, wherein the rope system is an assembly consisting of a parent star, space debris and a tether connected between the parent star and the space debris; in the racemization process of the target, namely the space debris, the speed of the target and the speed of the mother star are monitored, and when the speed of the target is greater than the speed of the mother star, the position of the mother star is adjusted through the propeller so as to prevent the target from colliding with the mother star; when the speed of the target is smaller than or equal to that of the parent star, the target and the parent star cannot collide, and the position of the parent star does not need to be adjusted;

the speed of the target and the speed of the parent star both comprise speed components in the directions of x, y and z, when the component speed of the target in only one direction is greater than the component speed of the parent star in the corresponding direction, only the propeller in the direction corresponding to the speed component is turned on, and the position of the parent star is adjusted;

the method for adjusting the position of the parent star by monitoring the speed of the target and the parent star comprises the following steps:

step one, establishing a combined body dynamic model which comprises a tether dynamics model, a parent star dynamics model and a target dynamics model;

step two, according to a parent star dynamics model, solving a momentum wheel output control moment of the parent star by using a PD control algorithm, and controlling the attitude of the parent star;

step three, controlling the position of the parent star through the propeller according to the monitored speed condition, wherein the thrust F of the propeller is determined according to the speed difference DeltaV between the target and the parent star and the expected time Deltat for adjusting the speed difference _thru Is of a size of (2);

the tether dynamics model is expressed as:

where m is the mass of the tether in focus, r is the position vector of the tether,a second derivative of tether position vector r with respect to time; n is the number of nodes connected with the P point; t (T) _j G is the space microgravity vector of the P point, F _k The P points are the number of other external forces applied to the P points, and the P points are the connection points of the main ropes and the sub ropes in the tether;

the parent star dynamics model is expressed as:

m _S a _S ＝F _S +F _thru ,

wherein m is _S The mass of the main star, a _S Acceleration of the main star F _S Is the tether tension applied by the main star, F _thru For propulsion, J _S Is the inertia of the main starQuantity matrix omega _S As the principal star rotational angular velocity, τ _S For the moment generated by the pulling force and the torsion of the tether to the main star, tau _c For the control moment generated by the main star momentum wheel,is the principal star rotational angular velocity omega _S First derivative with respect to time;

the target dynamics model is expressed as:

m _T a _T ＝F _T ,

wherein m is _T For the target mass, a _T For acceleration of the object, F _T Tether tension applied to the target, J _T For the inertia matrix of the target in the body coordinate system, omega _T For the target rotational angular velocity τ _T For the moment generated by the sub-rope tension on the target,for the target rotation angular velocity omega _T First derivative with respect to time;

euler angle phi for female star gesture _S ＝[α,β,γ] ^T The Euler angles corresponding to the rotation mode of z-x-z are alpha, beta and gamma respectively;

the momentum wheel output control moment is expressed as:

wherein alpha is _Sd ,β _Sd ,γ _Sd Representing the desired parent star euler angle,representing the first derivative of the parent star euler angle with respect to time,representing the first derivative of the expected parent Euler angle with respect to time, < >>Representing the second derivative of the expected parent Euler angle with respect to time, parameter k _p >0 represents the proportional control gain, k _d >0 represents differential control gain, τ _cx ,τ _cy ,τ _cz Representing components of momentum wheel control moment in three directions of x, y and z, J _Sx ,J _Sy ,J _Sz Representing the components of the principal moment of inertia matrix in the x, y and z directions, τ _Sx ,τ _Sy ,τ _Sz The components of the moment generated for the tether to the main star in the x, y and z directions.

2. The control method according to claim 1, wherein the thrust force F of the propeller is determined based on the speed difference DeltaV between the target and the parent satellite and the time Deltat for which the speed difference is adjusted _thru Specifically, the size of (3) is:

the speed difference between the target and the parent star is expressed as: deltaV= [ V _Tx -v _Sx ,v _Ty -v _Sy ,v _Tz -v _Sz ]Wherein v is _Tx ，v _Ty ，v _Tz Representing the velocity components of the target velocity in the x, y and z directions, v _Sx ,v _Sy ,v _Sz The velocity components of the parent star velocity in the x, y and z directions are respectively represented;

thrust of the propeller:

wherein m is _S Is the mass of the parent star.

3. A control method according to claim 2, wherein Δv= [ V ] when only the velocity component of the target and the parent star in the tether direction, i.e., the x-axis direction, is considered _Tx -v _Sx ,0,0]At this time, the propeller at the position corresponding to the x-axis direction is only required to be turned on.

4. The control method of claim 1, wherein the tether system further comprises a tether ejection device and a spring dampening unit; the tether ejection device is arranged on the main star; the tether and the spring damping unit are stored in the tether ejection device, and when the space debris needs to be captured, the tether ejection device is triggered, and the tether and the spring damping unit are ejected together;

the tether comprises a main rope and a sub rope; the main ropes are connected with the main star, and the sub ropes are connected with the space debris;

the spring damping unit is arranged on the main rope and the sub rope.

5. The control method according to claim 4, wherein the number of the sub-ropes is n, and n sub-ropes are connected with the main rope at the same point P; wherein n is a positive integer of 2 or more; the main rope is provided with a plurality of spring damping units, and each sub rope is provided with a spring damping unit.