Ground simulation system and method for tethered satellite long-distance release and recovery process

Abstract

The invention discloses a tethered satellite long-distance release and recovery process ground simulation system and a tethered satellite long-distance release and recovery process ground simulation method, and belongs to the tethered satellite mechanism testing field. A ground simulation experiment system is built, a method based on energy loss is adopted, and energy consumption caused by speed attenuation in a wheel type mechanism coiling process is measured; calculating friction force values of the tether and the tether mechanism under various working conditions of different speeds, different angles and the like in the releasing process; an optimal release and recovery curve is designed based on the magnitude of the friction force of the mechanism, and then the motion planning and control method in the release and recovery process of the tethered satellite system is examined and verified through a physical simulation experiment, so that a scientific basis is provided for evaluating the maximum ejection distance of a child satellite.

Description

Technical Field

[0001] The invention belongs to the field of tethered satellite mechanism testing, and in particular relates to a ground simulation system and method for a tethered satellite long-distance release and recovery process. Background Art

[0002] As a new type of space vehicle, tethered satellites have attracted extensive attention. The in-orbit flight of tethered satellites mainly includes three stages: release, retention, and recovery. The most critical issue is the release and recovery of the satellite. The ground simulation experiment technology of tethered satellites is an important ground simulation test method, which is widely used in the dynamic performance evaluation of satellite structures and control algorithms before launch.

[0003] For a non-propulsive sub-satellite system, during the ejection process, the friction between the tether and the mechanism will cause energy loss in the sub-satellite, thus affecting the sub-satellite's accurate arrival at the predetermined ejection position. Therefore, the precise measurement and evaluation of friction is crucial to ensure the accuracy of the sub-satellite's motion trajectory and the overall performance of the system. At present, the existing ground-based experimental research on tethered satellites basically adopts the air flotation platform solution. The air flotation experiment is used to simulate the free movement of the sub-satellite in a low-friction environment, verify the attitude control and stability during the release and recovery process, and play an important role in the release and recovery of tethered satellites. However, the supporting experimental equipment for the air flotation experiment includes gas cylinders, air cushions, etc. The experimental steps are complicated and the available space is limited. It is impossible to fully reproduce the real operating environment and simulate the release and recovery of long-distance tethered satellites. Summary of the invention

[0004] The present invention provides a ground simulation system and method for the long-distance release and recovery process of a tethered satellite, which adopts a low-friction wheel mechanism with friction compensation and can realize a long-distance tethered satellite retracting and releasing line simulation test in a low-friction environment.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] A ground simulation system for the long-distance release and recovery process of a tethered satellite, comprising a tethered satellite, a wheeled mechanism, and a measurement and control system;

[0007] The tethered satellite has a tethered cable connected to a wheeled mechanism, and the tethered cable can be wound / recovered on the wheeled mechanism;

[0008] A blower is installed next to the wheeled mechanism, and the wind speed of the blower is adjustable to make the wheeled mechanism rotate;

[0009] Two centrally symmetrical marking points are arranged on the wheeled mechanism; the measurement and control system is used to monitor and track the marking points on the wheeled mechanism; the monitoring system comprises a motion capture camera and a workstation, the motion capture camera captures the motion trajectory of the marking points and transmits the captured data to the workstation;

[0010] The rotational inertia of the wheel mechanism is consistent with the mass of the satellite.

[0011] The method for using the above system for ground simulation of the long-distance release and recovery process of a tethered satellite comprises the following steps:

[0012] S1: Set the tethered satellite to release the tether at a constant speed, so that the initial speed of the wheel of the wheel mechanism is the same as the release speed, and use a motion capture camera to record the deceleration of the wheel;

[0013] S2: Adjust the initial release velocity and the tether swing angle, repeat S1 and record the data;

[0014] S3: Calculate the friction level under various working conditions based on the loss energy; design the optimal release / recovery curve based on the friction level;

[0015] S4: Adjust the wind force of the air blowing device to make the wheel of the wheel mechanism rotate at a constant speed slightly lower than the maximum pay-off speed to offset the wheel friction during the long-distance pay-off test;

[0016] S5: Perform the reeling and releasing action according to the optimal release / recovery curve. During the release process of the mechanism, artificial interference is imposed on the rotating wheel so that the passive winding speed of the rotating wheel is lower than the release speed of the mechanism, thereby causing a large amount of tether to accumulate in the mechanism, which in turn leads to tether entanglement. The maximum length of the tether that can be accumulated in the mechanism is evaluated. During the subsequent mission execution, when the accumulated tether length is close to the threshold, a feedback control strategy is adopted to reduce the tether accumulation length, thereby reducing the risk of mission failure due to tether entanglement.

[0017] Beneficial effects: The present invention provides a ground simulation system and method for the long-distance release and recovery process of a tethered satellite. The constructed ground simulation experimental system adopts an energy-based method to measure the energy consumption caused by the speed decay during the winding process of the wheeled mechanism, and calculates the friction value between the tether and the tethered mechanism under various working conditions such as different speeds and different angles during the release process; the optimal release and recovery curve is designed based on the friction force level of the mechanism, and then the motion planning and control method of the release and recovery process of the tethered satellite system are evaluated and verified through physical simulation experiments. During the experiment, the wheeled mechanism simulates the sub-satellite tracking open-loop trajectory, and the optical target position is obtained by using the global optical tracking system. The tether release distance at any time during the experiment can be solved, and the tether release state of the mechanism can be evaluated by comparing it with the nominal trajectory. In addition, the present invention adopts an energy-based method to measure the energy consumption caused by the speed decay during the winding process of the wheeled mechanism, and can calculate the friction value between the tether and the tethered mechanism under various working conditions such as different speeds and different angles during the release process, which provides a scientific basis for evaluating the maximum ejection distance of the sub-satellite. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of a simulation system in an embodiment of the present invention;

[0019] Figure 2 It is a schematic diagram of the calculation results of the wire laying test data in the simulation system in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments:

[0021] In order to carry out ground simulation experiments to verify the long-distance release and recovery process of tethered satellites, a Figure 1 The simulation experiment system shown in the figure, the following embodiments only consider the one-dimensional dynamic characteristics of the system in the direction of satellite ejection release; the constructed simulation experiment system mainly includes a rope retracting and releasing mechanism, a wheeled mechanism, a blower, a motion capture camera, and a workstation; the tether of the rope retracting and releasing mechanism is connected to the wheeled mechanism, the tether can be wound / recovered on the wheeled mechanism, and two centrally symmetrical fluorescent marking points are set on the wheeled mechanism; the motion capture camera is used to monitor and track the fluorescent marking points on the wheeled mechanism; the motion capture camera captures the motion trajectory of the marking points and transmits the captured data to the workstation;

[0022] The moment of inertia of the wheeled mechanism is designed to be consistent with the mass of the sub-satellite. The wheeled mechanism simulates the sub-satellite tracking open-loop trajectory, and uses the global optical tracking system to obtain the position of the optical target (the mark point on the wheeled mechanism). The energy equivalence method is used to ensure that the dynamic characteristics of the ground test and the on-orbit system are similar, so that the wheeled mechanism can reflect the translational characteristics of the sub-satellite by rotation as much as possible; the wind speed of the air blowing mechanism is adjustable, and the wind force is calibrated before the experiment so that the wheeled mechanism can maintain a uniform idling speed to construct a low-friction environment.

[0023] During the experiment, the wheeled mechanism simulates the satellite tracking open-loop trajectory, uses the motion capture camera to obtain the position of the fluorescent marker point, and solves the tether release distance at any time during the experiment. By comparing it with the nominal trajectory, the tether release state can be evaluated; the energy-based method is used to measure the energy consumption caused by the speed attenuation during the winding process of the wheeled mechanism, and the friction value between the tether and the rope mechanism under various working conditions such as different speeds and angles during the release process can be calculated. The experiment is carried out according to the following process:

[0024] 1. Place and fix the rope mechanism in a suitable position so that it is in the field of view of the motion compensation system;

[0025] 2. Adjust the wind speed of the blast equipment so that the wheel can maintain a stable rotation speed slightly lower than the pay-off speed;

[0026] 3. Adjust the swing angle of the tether and the rope mechanism;

[0027] 4. Set the rope mechanism to release the line at a uniform speed, make the initial speed of the wheel the same as the release speed, and use the motion capture system to record the deceleration of the wheel;

[0028] 5. Adjust the initial release velocity and the tether swing angle, repeat steps 2-4 and record the data;

[0029] 6. Calculate the friction level under various working conditions based on the loss energy, and calculate the average friction between the tether and the mechanism in the process through the kinetic energy lost during the motion of the runner. The specific process is:

[0030] The motion capture system can provide the original position information of the fluorescent marker. During the long-distance ground retraction and release test of the tethered satellite, the original data needs to be processed to obtain the required physical information such as the rotor motion angle, angular velocity, and rotation distance. The original data processing process is as follows:

[0031] The motion capture camera obtains the position information of the fluorescent marker point, where x, y, and z correspond to the three-dimensional spatial positions of the marker points respectively. The three-dimensional spatial coordinates of the two marker points are:

[0032]

[0033] The marking point is fixed to the rotating wheel, d 1 d 2 d 3 The three-axis components of the corresponding wheel position vector:

[0034] V=position 1 -position 2 =[v 1 v 2 v 3 ] T

[0035] When the wheel moves, the wheel position vector rotates accordingly, and the corresponding wheel polar coordinate angle θ at time t is:

[0036]

[0037] The sampling frequency of the motion capture camera is 60Hz, that is, the position information of 60 pairs of markers is recorded every minute. During the data processing, if some data is lost due to interference from environmental factors such as occlusion, the position coordinates at this moment are replaced by the previous set of normal data;

[0038] All angle data are judged, the accumulated number of circles is considered, and the angle data is converted from [-π,π] to [0,+∞) to ensure the stability of the angular velocity solution.

[0039] Use the difference method to solve the angular velocity based on the angle information:

[0040]

[0041] The winding speed of the rotating wheel is:

[0042] V=ωR

[0043] According to the law of conservation of energy, the work done by friction on the runner is equal to the kinetic energy consumed by the runner. During the experiment, the initial angular velocity of the runner is ω 1 , after a period of time under the action of friction, the angular velocity is ω 2 , V is the linear velocity of the wheel during the pay-off process, which is a time-related function; J is the moment of inertia of the wheel; is the average friction.

[0044] System 1 Initial energy at the moment:

[0045]

[0046] t 2 System energy after releasing the line for a certain distance:

[0047]

[0048] Pay-off distance:

[0049]

[0050] According to the functional relationship:

[0051]

[0052] Right now:

[0053]

[0054] 7. Design the optimal release recovery curve according to the friction force level;

[0055] 8. Adjust the wind force of the air blowing equipment so that the rotor can maintain a uniform rotation speed slightly lower than the maximum pay-off speed to offset the friction of the rotor during the long-distance pay-off test;

[0056] 9. Set the control parameters of the rope mechanism motor so that it can retract and release the line according to the predetermined trajectory;

[0057] 10. Turn on the indoor motion capture system to record data, start the rope-tethering mechanism, and complete a line release;

[0058] 11. Save the data recorded by the indoor motion capture system and reverse the tether for recovery;

[0059] 12. Repeat steps 10 and 11 for many times. During the release process, observe and record the accumulation of the tether in the mechanism and the release of the tether. By comparing the tether accumulation lengths during the release process under different pre-treated tethers, different parameter curves, and different motor settings, the comprehensive performance of the mechanism, tether, and optimal release curve can be evaluated.

[0060] 13. Repeat steps 10 and 11 many times, and artificially interfere with the rotating wheel during the mechanism's wire-releasing process, so that the passive winding speed of the rotating wheel is lower than the mechanism's wire-releasing speed, thereby causing a large amount of tethers to accumulate in the mechanism, which in turn causes the tethers to be entangled;

[0061] 14. The difference between the wheel movement distance measured by the motion capture system and the release distance of the motor tracking curve is the accumulated tether length in the mechanism. According to the data in step 13, the maximum length of the tether that can be accumulated in the mechanism is evaluated. During the subsequent task execution, when the accumulated tether length is close to the threshold, a feedback control strategy is adopted to reduce the accumulated tether length, thereby reducing the risk of task failure due to tether entanglement;

[0062] The Gauss-pseudospectral method is used to calculate the optimal open-loop trajectory, and the two-body tethered satellite dumbbell model is used as the dynamic model. ξ are the swing angle and length of the two-degree-of-freedom tether respectively, and the objective function is:

[0063]

[0064] The final state of the release phase is:

[0065] ξ 1 =1,ξ 1 ′=0,ξ 3 =0.05

[0066] The release phase path constraints are:

[0067]

[0068] Based on GPOS to solve the optimal trajectory, considering the influence of tether friction, the minimum acceleration during the release process is the acceleration of the satellite when only friction acts. Taking comprehensive considerations, the velocity during the rope release process is fitted into a sixth-order polynomial form:

[0069]

[0070] During the release process, V is the winding speed of the rotating wheel, and the length of the accumulated tether in the mechanism is:

[0071] l err =∫V a -Vdt.

[0072] The calculation result of a certain laying-out test data is as follows Figure 2 As shown, the left figure is the speed-time curve of the wheel movement process, and the right figure is the wheel winding length-time curve.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A ground simulation system for the long-distance release and recovery process of a tethered satellite, characterized in that: It includes a tethered satellite, a wheeled mechanism, and a measurement and control system; the tether of the tethered satellite is connected to the wheeled mechanism, and the tether can be wound / recovered on the wheeled mechanism; two centrally symmetrical marking points are set on the wheeled mechanism; the measurement and control system is used to monitor and track the marking points on the wheeled mechanism.

2. The ground simulation system for the long-distance release and recovery process of a tethered satellite according to claim 1 is characterized in that: A blower is installed beside the wheeled mechanism, and the rotation speed of the wheeled mechanism is adjusted by the wind speed of the blower.

3. The ground simulation system for the long-distance release and recovery process of a tethered satellite according to claim 1 or 2, characterized in that: The monitoring system includes a motion capture camera and a workstation. The motion capture camera captures the motion trajectory of the marker point and transmits the captured data to the workstation.

4. The ground simulation system for the long-distance release and recovery process of a tethered satellite according to claim 1, characterized in that: The rotational inertia of the wheel mechanism is consistent with the mass of the satellite.

5. A ground simulation method for the long-distance release and recovery process of a tethered satellite, characterized in that: The following steps are involved: S1: Set the tethered satellite to release the tether at a constant speed, so that the initial speed of the wheel of the wheel mechanism is the same as the release speed, and use a motion capture camera to record the deceleration of the wheel; S2: Adjust the initial release velocity and the tether swing angle, repeat S1 and record the data; S3: Calculate the friction level under various working conditions based on the loss energy; design the optimal release / recovery curve based on the friction level; S4: Adjust the wind force of the air blowing device to make the wheel of the wheel mechanism rotate at a constant speed slightly lower than the maximum pay-off speed to offset the wheel friction during the long-distance pay-off test; S5: Perform the reeling and unwinding actions according to the optimal release / recovery curve. During the unwinding process of the mechanism, artificial interference is imposed on the reel so that the passive winding speed of the reel is lower than the unwinding speed of the mechanism, thereby causing a large amount of tether to accumulate in the mechanism, which in turn leads to tangle of the tether. The maximum length of the tether that can be accumulated in the mechanism is evaluated.

6. The ground simulation method for the long-distance release and recovery process of a tethered satellite according to claim 5, characterized in that: The motion capture camera records the original position information of the fluorescent marker point. During the long-distance ground retraction and deployment test experiment of the tethered satellite, the original data is processed to obtain the wheel movement angle, angular velocity and speed.

7. The ground simulation method for the long-distance release and recovery process of a tethered satellite according to claim 6, characterized in that: The process of processing the original data is as follows: The motion capture camera obtains the position information of the fluorescent marker point, where x, y, and z correspond to the three-dimensional spatial positions of the marker points respectively. The three-dimensional spatial coordinates of the two marker points are: position1=[x1 y1 z1] T position2=[x2 y2 z2] T The marked point is fixed to the wheel, and d1, d2, and d3 correspond to the three-axis components of the wheel position vector: V=position1-position2=[d1 d2 d3] T When the wheel moves, the wheel position vector rotates accordingly, and the corresponding wheel polar coordinate angle θ at time t is: Use the difference method to solve the angular velocity based on the angle information: The winding speed of the rotating wheel is: V=ωR.

8. The ground simulation method for the long-distance release and recovery process of a tethered satellite according to claim 6 or 7, characterized in that: In S3, the friction level under various working conditions is calculated based on the loss energy, which specifically includes the following steps: According to the law of conservation of energy, the work done by friction on the runner is equal to the kinetic energy consumed by the runner. The initial angular velocity of the runner is ω1, and the angular velocity after a period of time under the action of friction is ω2. V is the linear velocity of the runner during the release process; J is the moment of inertia of the runner; is the average friction; The initial energy of the system at time t1 is After releasing the wire for a certain distance at time t2, the system energy is Pay-off distance According to functional relationship The average friction is obtained as:

9. The ground simulation method for the long-distance release and recovery process of a tethered satellite according to claim 8, characterized in that: The release phase path constraint in the optimal release / recovery curve is: The objective function is: Among them, θ, ξ are the swing angle and rope length of the two-degree-of-freedom tether respectively.

10. The ground simulation method for the long-distance release and recovery process of a tethered satellite according to claim 9, characterized in that: The length of the stacking tether in the mechanism is: L err =∫V a -Vdt.

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