Liquid carrier rocket first-stage shutdown condition satellite-rocket coupling analysis method

Abstract

The invention discloses a liquid carrier rocket first-stage shutdown condition satellite-rocket coupling analysis method, and the method comprises the steps: constructing a first-stage shutdown condition transverse external force function according to the after-thrust characteristics of a first-stage engine shutdown process and flight telemetry data fed back by a servo mechanism actuator through employing a liquid carrier rocket one-dimensional longitudinal and transverse torsion integrated model; and an attitude control loop is introduced, so that the problem that a satellite-rocket interface low-frequency vibration transverse response calculation result of a certain type of new-generation liquid carrier rocket under a first-stage shutdown condition is far smaller than a flight remote measurement result is solved, and the prediction precision of satellite-rocket coupling analysis is improved.

Description

Technical Field

[0001] The invention relates to the field of liquid launch vehicles, and in particular to a satellite-rocket coupling analysis method for a first-stage shutdown condition of a liquid launch vehicle. Background Art

[0002] The satellite-rocket coupling analysis generally selects the most severe load condition of the active flight phase of the launch vehicle. The first stage shutdown condition is the maximum axial overload condition, which must be calculated in the satellite-rocket coupling analysis of various types of liquid launch vehicles. In the past, the satellite-rocket coupling analysis of the first stage shutdown condition generally adopted the longitudinal spring-mass model. For the case where the first and second stages are separated by thermal separation, the external force is considered to be only the axial aftereffect thrust of the first stage engine shutdown and the axial ignition thrust of the second stage engine ignition. For the case where the first and second stages are separated by cold separation, the external force is considered to be only the axial aftereffect thrust of the first stage engine shutdown. At this time, there is only axial force transmission in the rocket body. When the first stage is shut down, this model meets the requirements when the rocket is only subjected to the axial force of the engine. When there is lateral external excitation, this model is not available, and the longitudinal, transverse and torsion integrated model needs to be used for calculation. In order to avoid the problem of excessive calculation amount when the virtual mass method is used to simulate the propellant in the tank, a one-dimensional longitudinal, transverse and torsion integrated model combining a one-dimensional beam model and a longitudinal spring-mass model can be used.

[0003] The flight telemetry results of a new generation of launch vehicle show that when the first stage is shut down, the lateral response at the low-frequency vibration measurement point of the satellite-rocket interface is large, and the value is equivalent to the axial response. In some launches, the lateral response even exceeds the axial response. At this time, the satellite-rocket coupling analysis uses the longitudinal spring-mass model and only considers the axial aftereffect thrust of the first-stage engine shutdown to obtain the lateral response of the satellite-rocket interface. The result is close to 0, which is very different from the telemetry result and cannot play a predictive role. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the present invention provides a satellite-rocket coupling analysis method for the shutdown condition of the first stage of a liquid carrier rocket, which solves the problem that the calculated result of the low-frequency vibration lateral response of the satellite-rocket interface in the shutdown condition of the first stage of a new generation of liquid carrier rocket is much smaller than the flight telemetry result, thereby improving the prediction accuracy of the satellite-rocket coupling analysis.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted to solve the technical problem is as follows:

[0006] A method for analyzing the satellite-rocket coupling of the first stage shutdown condition of a liquid launch vehicle, comprising:

[0007] Step 1: Establish a finite element dynamic analysis model of the first stage shutdown second of the launch vehicle based on the one-dimensional longitudinal, lateral and torsion integrated modeling method of the liquid launch vehicle;

[0008] Step 2: Convert the after-effect thrust data of the first-stage flight shutdown phase engine according to the ground test thrust data of the engine;

[0009] Step 3: According to the aftereffect thrust characteristics of the first-stage engine shutdown process and the feedback telemetry data of the servomechanism actuator of the rocket that has successfully flown, the mechanism of lateral external excitation generation during the first-stage shutdown process is analyzed, and the lateral external excitation is constructed;

[0010] Step 4: Obtain the transfer function of the attitude control system during the first-stage shutdown period. Under the action of lateral external excitation, the attitude angle and angular velocity will be generated at the inertial group and rate gyro of the rocket body. The swing angle of the engine can be solved through the control loop. The swing of the engine generates control force, thereby ensuring the dynamic balance of the rocket body;

[0011] Step 5: Apply the aftereffect thrust of the first-stage engine in step 2 and the lateral external excitation in step 3 to the connection between the engine and the rocket body in the rocket finite element model in step 1;

[0012] Step 6: Convert the transfer function of step 4 into the TF card of the commercial finite element analysis software MSC.NASTRAN, and establish the transfer relationship between the inertial group, the attitude angle and angular velocity of the rate gyro and the engine swing angle, as well as the transfer relationship between the engine swing angle and the lateral force generated by the engine swing;

[0013] Step 7: Use MSC.NASTRAN software to perform transient response analysis;

[0014] Step 8: Extract and analyze the results. Extract the time domain response at the low-frequency vibration measurement point of the satellite-rocket interface and calculate the impact response spectrum. Generally, the quality factor Q=10 is taken to extract the satellite-rocket interface force and convert it to the overload at the satellite's center of mass.

[0015] Furthermore, in the step one, the one-dimensional longitudinal, lateral and torsion integrated modeling method of the liquid carrier rocket is to model the tank using a one-dimensional beam model and a longitudinal spring-mass model combined with a one-dimensional beam model, to establish a three-dimensional finite element dynamic model for the complex configuration sections of the satellite fairing, satellite, satellite support structure, and first-stage engine, to establish a one-dimensional beam model for the semi-rigid shell structure of the inter-tank section, inter-stage section, transition section, and tail section, and to model the liquid part according to the mass of the liquid in each tank of the rocket at the moment of first-stage shutdown.

[0016] Furthermore, in step 2, the engine ground test thrust data is converted into the flight state engine thrust, and the conversion formula is:

[0017] P fx =P dm +S a *(p0-p)

[0018] Among them, P fx is the thrust value in flight state, P dm is the ground thrust value, S ais the engine nozzle area, p0 is the atmospheric pressure at sea level, and p is the atmospheric pressure at the flight altitude;

[0019] The altitude of the rocket at the moment of first-stage shutdown is obtained according to the ballistic data, thereby obtaining the atmospheric pressure at that location. The engine nozzle area and the ground test thrust curve of the first-stage engine shutdown process are obtained from the engine professional. These are substituted into the formula to calculate the first-stage engine shutdown after-effect thrust data for satellite-rocket coupling analysis.

[0020] Furthermore, in step 3, the lateral external excitation is obtained by the following analysis:

[0021] During the flight, the first-stage engine frame is compressed and deformed under the thrust of the first-stage engine. In order to keep the thrust direction pointing to the center of mass of the rocket, the servo mechanism will shrink by an angle α.

[0022] Before shutting down, the servo mechanism oscillates slightly at a low frequency near this angle;

[0023] At the moment of shutdown, as the thrust of the first-stage engine decreased rapidly, the compression deformation of the first-stage engine decreased rapidly to recovery. At this time, because the servo mechanism had not yet responded in time, the nozzle briefly swung to one side of the servo mechanism. Then the servo mechanism actuator responded. Telemetry data showed that the servo mechanism swing angle briefly oscillated at a frequency of fHz and then gradually returned to 0°.

[0024] Thus, a lateral external excitation caused by the swing of the engine nozzle is constructed and simulated by a fHz sine spectrum, with the amplitude taken as the thrust before the engine is shut down * sin(α).

[0025] Furthermore, in the step four, the transfer function of the attitude control system during the first-stage shutdown period mainly includes the inertial group transfer function, the rate gyro transfer function, the servo system transfer function, and the first-stage shutdown correction network. Since there is lateral external excitation in the first-stage shutdown condition, an attitude control loop is introduced to simulate the actual flight state.

[0026] Furthermore, in the step five, the after-effect thrust of the first-stage engine is the thrust data obtained in the step two, which is applied to the axial direction of the rocket. The lateral external excitation constructed in the step three acts on the pitch and yaw directions of the rocket, that is, lateral excitation acts in both lateral directions. In order to avoid impact response, the thrust of the first-stage engine gradually increases from 0N to the thrust in the working state before shutdown, and then the shutdown after-effect thrust data is connected. At this time, the lateral excitation is 0N at the beginning. When the first-stage engine is shut down and the thrust begins to decrease, sinusoidal lateral excitation is applied.

[0027] Furthermore, in step six, the transfer function is converted into a TF card, and according to the definition of the transfer function, ie, output / input, the coefficient value of the TF card in MSC.NASTRAN can be obtained.

[0028] Furthermore, in step seven, the transient response analysis is performed using the SOL 112 calculation module of MSC.NASTRAN, which extracts the node numbers of the nodes that need to output the acceleration response and the unit numbers of the unit forces that need to output from the finite element model, and the damping can be set according to the damping ratio measured by the full-arrow modal test.

[0029] Furthermore, in step eight, the overload coefficient at the satellite center of mass is obtained according to Q=ma and M=maL, where Q is the shear force at the satellite-rocket interface, M is the bending moment at the satellite-rocket interface, m is the satellite mass, L is the distance between the satellite center of mass and the satellite-rocket interface, a is the overload at the satellite center of mass, and the overloads in the pitch plane and the yaw plane need to be synthesized and given.

[0030] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0031] The invention discloses a satellite-rocket coupling analysis method for a liquid carrier rocket first stage shutdown condition, which improves the accuracy of satellite-rocket coupling analysis and can more accurately predict the low-frequency vibration lateral response of the satellite-rocket interface in the first stage shutdown condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0033] Figure 1 It is a flow chart of a method for analyzing satellite-rocket coupling of a liquid launch vehicle first stage shutdown condition according to the present invention;

[0034] Figure 2 It is a one-dimensional longitudinal, lateral and torsional integrated model for a new generation of liquid launch vehicle;

[0035] Figure 3 This is the axial aftereffect thrust curve of the first-stage engine shutdown process of a new generation liquid launch vehicle;

[0036] Figure 4 Feedback telemetry data for the post-vote actuator I of the servo mechanism of the first stage shutdown phase of a new generation liquid launch vehicle;

[0037] Figure 5 To construct a new generation of liquid launch vehicle with the first stage shutdown condition with lateral external excitation;

[0038] Figure 6 It is the attitude control loop for a new generation of liquid launch vehicle;

[0039] Figure 7 Comparison between the radial calculation results and the telemetry results of the lateral response of the low-frequency vibration of the rocket-satellite interface in a launch of a new generation of liquid carrier rocket;

[0040] Figure 8 The lateral response-tangential calculation results of the low-frequency vibration of the satellite-rocket interface of a certain new generation liquid carrier rocket are compared with the telemetry results. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] like Figure 1-8 As shown, this embodiment discloses a method for analyzing the satellite-rocket coupling of the first stage shutdown condition of a liquid launch vehicle, comprising the following steps:

[0043] Step 1: Establish a finite element dynamic analysis model of the first stage of the launch vehicle during shutdown seconds according to the one-dimensional longitudinal, lateral and torsion integrated modeling method for liquid launch vehicles. In this embodiment, the one-dimensional longitudinal, lateral and torsion integrated modeling method for liquid launch vehicles is to model the tank using a one-dimensional beam model combined with a longitudinal spring-mass model, establish a three-dimensional finite element dynamic model for the complex configuration sections of the satellite fairing, satellite, satellite support structure, and first-stage engine, establish a one-dimensional beam model for the semi-rigid shell structure of the inter-tank section, inter-stage section, transition section, and tail section, adopt a concentrated mass model for the second-stage engine, and adopt a longitudinal, lateral and torsion integrated model that combines a one-dimensional beam model with a longitudinal spring-mass model for the first and second stage tanks. The established rocket finite element model is as follows: Figure 2 shown.

[0044] Step 2: Convert the after-effect thrust data of the first-stage flight shutdown phase engine according to the engine ground test data, and obtain the after-effect thrust curve of the first-stage engine of a certain new generation launch vehicle as shown in the figure: Figure 3 As shown, in order to avoid impact response, the engine thrust is gradually loaded from 0 to the stable working state before shutdown, that is, the thrust curve needs to be intercepted from the stable working section before engine shutdown.

[0045] In the step 2, the engine ground test thrust data is converted into the flight state engine thrust, and the conversion formula is:

[0046] P fx =P dm +S a *(p0-p)

[0047] Among them, Pfx is the thrust value in flight state, P dm is the ground thrust value, S a is the engine nozzle area, p0 is the atmospheric pressure at sea level, and p is the atmospheric pressure at the flight altitude;

[0048] The altitude of the rocket at the moment of first-stage shutdown is obtained according to the ballistic data, thereby obtaining the atmospheric pressure at that location. The engine nozzle area and the ground test thrust curve of the first-stage engine shutdown process are obtained from the engine professional. These are substituted into the formula to calculate the first-stage engine shutdown after-effect thrust data for satellite-rocket coupling analysis.

[0049] Step 3: According to the aftereffect thrust characteristics of the first-stage engine shutdown process and the feedback telemetry data of the servomechanism actuator of the rocket that has successfully flown, the mechanism of lateral external excitation during the first-stage shutdown process is analyzed and lateral external excitation is constructed. During the flight, the first-stage engine frame is compressed and deformed under the action of the first-stage engine thrust. In order to keep the thrust direction pointing to the center of mass of the rocket, the servomechanism will shrink by an angle α. Before shutdown, the servomechanism oscillates at a low frequency near this angle. Figure 2 From the after-effect thrust curve of the first-stage engine, it can be seen that the thrust drops very quickly, and after dropping by more than half, it rises to a certain height, and then drops rapidly again, that is, there is a fluctuation in the thrust drop process, and the fluctuation frequency is about fHz. At the same time, when shutting down, as the thrust of the first-stage engine decreases rapidly, the compression deformation of the first-stage engine decreases rapidly. At this time, because the servo mechanism has not yet had time to feedback, the nozzle briefly swings to one side of the servo mechanism, thereby exerting a lateral force on the rocket body. Then, sensitive components such as the inertial group and rate gyro sense the change in the rocket's attitude, and the attitude control system takes effect, adjusting the engine swing angle through the servo mechanism to achieve the balance of the rocket. From the telemetry data of previous launches, it can be seen that the actuator feeds back this telemetry data after the servo mechanism votes (see Figure 4 ) The first stage is basically stable near α before shutdown, but oscillation occurs when shutdown, with an oscillation frequency of about fHz, and then gradually returns to 0°. Thus, a lateral external excitation caused by the swing of the engine nozzle is constructed, and a sine spectrum of fHz is used to simulate it. The amplitude is taken as the thrust before the engine is shut down * sin(α). The constructed lateral external excitation is as follows Figure 5 As shown, the moment when the sinusoidal excitation is applied coincides with the moment when the primary axial thrust begins to decrease.

[0050] Step 4: Obtain the transfer function of the attitude control system during the first shutdown period. Under the action of lateral external excitation, the attitude angle and angular velocity will be generated at the inertial group and rate gyro of the rocket body. The swing angle of the engine can be solved through the control loop. The swing of the engine generates control force, thereby ensuring the dynamic balance of the rocket body. The attitude control loop is as follows: Figure 6 shown.

[0051] In step four, the transfer function of the attitude control system during the first-stage shutdown period mainly includes the inertial group transfer function, the rate gyro transfer function, the servo system transfer function, and the first-stage shutdown correction network. Since there is lateral external excitation in the first-stage shutdown condition, an attitude control loop is introduced to simulate the actual flight state.

[0052] Step 5: Apply the axial aftereffect thrust of the first stage engine in step 2 to the connection between the engine and the rocket body (see Figure 3 ) and the lateral external excitation in step 3 (see Figure 5 ). Here, the thrust reduction time and the lateral excitation application time must be basically consistent. Since the first-stage engine is a bidirectional swing engine, the lateral external excitation acts on the two servo mechanism installation directions. The rotation angle of the inertial group and rate gyro installation position node enters the control system loop to obtain how much swing angle the node at the connection between the engine and the rocket body needs to generate to balance the rocket body.

[0053] Specifically, in step five, the after-effect thrust of the first-stage engine is the thrust data obtained in step two, which is applied to the axial direction of the rocket. The lateral external excitation constructed in step three acts on the pitch and yaw directions of the rocket, that is, lateral excitation acts in both lateral directions. In order to avoid impact response, the thrust of the first-stage engine gradually increases from 0N to the thrust in the working state before shutdown, and then the after-effect thrust data of shutdown is connected. At this time, the lateral excitation is 0N at the beginning. When the first-stage engine is shut down and the thrust begins to decrease, sinusoidal lateral excitation is applied.

[0054] Step 6: Convert the transfer function of step 4 into the TF card of the commercial finite element analysis software MSC.NASTRAN, and establish the transfer relationship between the attitude angle and angular velocity of the inertial group, rate gyro and the engine swing angle. The rotation angle of the node where the inertial group and rate gyro are installed enters the control system loop to obtain the swing angle required by the node where the engine and the rocket body are connected to balance the rocket body.

[0055] Specifically, in step six, the transfer function is converted into a TF card. According to the definition of the transfer function, ie, output / input, the coefficient value of the TF card in MSC.NASTRAN can be obtained.

[0056] Step 7: Use MSC.NASTRAN software to perform transient response analysis.

[0057] Specifically, in step seven, the transient response analysis is performed using the SOL 112 calculation module of MSC.NASTRAN. The node numbers for which the acceleration response output is required and the unit numbers for which the unit force output is required are extracted from the finite element model. The damping can be set according to the damping ratio measured by the full-arrow modal test. In this embodiment, the SOL 112 of MSC.NASTRAN software is used for analysis, and the damping of 0 to 20 Hz is set to 0.01, and the damping of above 20 Hz is set to 0.015.

[0058] Step 8: Extract and analyze the results. Extract the time domain response at the low-frequency vibration measurement point of the satellite-rocket interface and calculate the impact response spectrum. Generally, the quality factor Q=10 is taken to extract the satellite-rocket interface force and convert it to the overload at the satellite's center of mass.

[0059] Specifically, in step eight, the overload coefficient at the satellite center of mass is obtained according to Q=ma and M=maL, where Q is the shear force at the satellite-rocket interface, M is the bending moment at the satellite-rocket interface, m is the satellite mass, L is the distance between the satellite center of mass and the satellite-rocket interface, a is the overload at the satellite center of mass, and the overloads in the pitch plane and the yaw plane need to be synthesized and given.

[0060] In this embodiment, the lateral impact response spectrum at the low-frequency vibration measurement point of the satellite-rocket interface calculated by the present invention is compared with the telemetry result. Figure 7 and Figure 8 , Figure 7 For radial response comparison, Figure 8 This is a comparison of tangential responses. It can be seen that both the response peak and peak frequency have achieved high accuracy and played a good predictive role.

[0061] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for analyzing the satellite-rocket coupling of the first stage shutdown condition of a liquid launch vehicle, characterized in that: include: Step 1: Establish a finite element dynamic analysis model of the first stage shutdown second of the launch vehicle based on the one-dimensional longitudinal, lateral and torsion integrated modeling method of the liquid launch vehicle; Step 2: Convert the after-effect thrust data of the first-stage flight shutdown phase engine according to the ground test thrust data of the engine; Step 3: According to the aftereffect thrust characteristics of the first-stage engine shutdown process and the feedback telemetry data of the servomechanism actuator of the rocket that has successfully flown, the mechanism of lateral external excitation generation during the first-stage shutdown process is analyzed, and the lateral external excitation is constructed; Step 4: Obtain the transfer function of the attitude control system during the first-stage shutdown period. Under the action of lateral external excitation, the attitude angle and angular velocity will be generated at the inertial group and rate gyro of the rocket body. The swing angle of the engine can be solved through the control loop. The swing of the engine generates control force, thereby ensuring the dynamic balance of the rocket body; Step 5: Apply the aftereffect thrust of the first-stage engine in step 2 and the lateral external excitation in step 3 to the connection between the engine and the rocket body in the rocket finite element model in step 1; Step 6: Convert the transfer function of step 4 into the TF card of the commercial finite element analysis software MSC.NASTRAN, and establish the transfer relationship between the inertial group, the attitude angle and angular velocity of the rate gyro and the engine swing angle, as well as the transfer relationship between the engine swing angle and the lateral force generated by the engine swing; Step 7: Use MSC.NASTRAN software to perform transient response analysis; Step 8: Extract and analyze the results. Extract the time domain response at the low-frequency vibration measurement point of the satellite-rocket interface and calculate the impact response spectrum. Generally, the quality factor Q=10 is taken to extract the satellite-rocket interface force and convert it to the overload at the satellite's center of mass.

2. A method for analyzing the satellite-rocket coupling of a liquid launch vehicle's first stage shutdown condition as claimed in claim 1, characterized in that: In the step 1, the one-dimensional longitudinal, lateral and torsion integrated modeling method of the liquid carrier rocket is to model the tank using a one-dimensional beam model and a longitudinal spring-mass model combined with a one-dimensional longitudinal, lateral and torsion integrated modeling method, establish a three-dimensional finite element dynamic model for the complex configuration sections of the satellite fairing, satellite, satellite support structure, and first-stage engine, establish a one-dimensional beam model for the semi-rigid shell structure of the inter-tank section, inter-stage section, transition section, and tail section, and model the liquid part according to the mass of the liquid in each tank of the rocket at the moment of first-stage shutdown.

3. A method for analyzing the satellite-rocket coupling of a liquid launch vehicle's first stage shutdown condition as claimed in claim 1, characterized in that: In the step 2, the engine ground test thrust data is converted into the flight state engine thrust, and the conversion formula is: P fx =P dm +S a *(p0-p) Among them, P fx is the thrust value in flight state, P dm is the ground thrust value, S a is the engine nozzle area, p0 is the atmospheric pressure at sea level, and p is the atmospheric pressure at the flight altitude; The altitude of the rocket at the moment of first-stage shutdown is obtained according to the ballistic data, thereby obtaining the atmospheric pressure at that location. The engine nozzle area and the ground test thrust curve of the first-stage engine shutdown process are obtained from the engine professional. These are substituted into the formula to calculate the first-stage engine shutdown after-effect thrust data for satellite-rocket coupling analysis.

4. A method for analyzing the satellite-rocket coupling of a liquid launch vehicle first stage shutdown condition according to claim 1, characterized in that: In step 3, the lateral external excitation is obtained by the following analysis: During the flight, the first-stage engine frame is compressed and deformed under the thrust of the first-stage engine. In order to keep the thrust direction pointing to the center of mass of the rocket, the servo mechanism will shrink by an angle α. Before shutting down, the servo mechanism oscillates slightly at a low frequency near this angle; At the moment of shutdown, as the thrust of the first-stage engine decreased rapidly, the compression deformation of the first-stage engine decreased rapidly to recovery. At this time, because the servo mechanism had not yet responded in time, the nozzle briefly swung to one side of the servo mechanism. Then the servo mechanism actuator responded. Telemetry data showed that the servo mechanism swing angle briefly oscillated at a frequency of fHz and then gradually returned to 0°. Thus, a lateral external excitation caused by the swing of the engine nozzle is constructed and simulated by a fHz sinusoidal spectrum, with the amplitude taken as the thrust before the engine is shut down * sin(α).

5. The method for analyzing the satellite-rocket coupling of the first stage shutdown condition of a liquid launch vehicle according to claim 1, characterized in that: In the step 4, the transfer function of the attitude control system during the first-stage shutdown period mainly includes the inertial group transfer function, the rate gyro transfer function, the servo system transfer function, and the first-stage shutdown correction network. Since there is lateral external excitation in the first-stage shutdown condition, an attitude control loop is introduced to simulate the actual flight state.

6. A method for analyzing the satellite-rocket coupling of a liquid launch vehicle first stage shutdown condition according to claim 1, characterized in that: In the step 5, the after-effect thrust of the first-stage engine is the thrust data obtained in the step 2, which is applied to the axial direction of the rocket. The lateral external excitation constructed in the step 3 acts on the pitch and yaw directions of the rocket, that is, lateral excitation acts in both lateral directions. In order to avoid impact response, the thrust of the first-stage engine gradually increases from 0N to the thrust in the working state before shutdown, and then the shutdown after-effect thrust data is connected. At this time, the lateral excitation is 0N at the beginning. When the first-stage engine is shut down and the thrust begins to decrease, the sinusoidal lateral excitation is applied.

7. A method for analyzing the satellite-rocket coupling of a liquid launch vehicle first stage shutdown condition according to claim 1, characterized in that: In step six, the transfer function is converted into a TF card. According to the definition of the transfer function, ie, output / input, the coefficient value of the TF card in MSC.NASTRAN can be obtained.

8. The method for analyzing the satellite-rocket coupling of the first stage shutdown condition of a liquid launch vehicle according to claim 1, characterized in that: In step seven, the transient response analysis is performed using the SOL 112 calculation module of MSC.NASTRAN. The node numbers for which acceleration response output is required and the unit numbers for which unit force output is required are extracted from the finite element model. The damping can be set according to the damping ratio measured by the full-arrow modal test.

9. The method for analyzing the satellite-rocket coupling of the first stage shutdown condition of a liquid launch vehicle according to claim 1, characterized in that: In the step eight, the overload coefficient at the satellite center of mass is obtained according to Q=ma and M=maL, where Q is the shear force at the satellite-rocket interface, M is the bending moment at the satellite-rocket interface, m is the satellite mass, L is the distance between the satellite center of mass and the satellite-rocket interface, a is the overload at the satellite center of mass, and the overloads in the pitch plane and the yaw plane need to be synthesized and given.

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