Multiple control mode hybrid entry guidance method for mars lander

Abstract

The application discloses a Mars lander multi-control mode hybrid entry guidance method, and belongs to the field of aircraft guidance control. The method is realized by the following steps: combining a terminal height penalty function, a distance penalty factor and a traditional target function to form a comprehensive target function, and making the Mars lander meet the parachute opening requirement of the terminal height being above the minimum boundary and the terminal flight distance being minimum through the comprehensive target function. A mapping relationship between a comprehensive target function sequence and an inflation Mach number sequence is established, the mapping relationship between the two sequence functions is used as a judgment basis for the inflation decelerator opening time, the inflation decelerator opening Mach number is taken as a controlled variable to be added to the guidance process to form a Mach number control loop, a double-loop predictive correction guidance strategy is formed based on the Mach number control loop and a control aerodynamic angle guidance loop, the multi-control mode hybrid entry guidance is realized by using the double-loop predictive correction guidance strategy, the terminal height of the large-mass Mars lander is improved, and the terminal precision of the lander is ensured.

Description

Technical Field

[0001] This invention relates to an entry guidance method, and more particularly to a hybrid entry guidance method for a Mars lander with multiple control modes, belonging to the field of spacecraft guidance and control. Background Technology

[0002] Mars landing exploration is one of the most important areas of deep space exploration today. The Mars landing process generally consists of three phases: atmospheric entry, parachute deceleration, and landing. The atmospheric entry phase, with its vast airspace and harsh aerodynamic environment, is the critical stage of Mars landing. This phase requires using aerodynamic forces to reduce the velocity from 5000-7000 m / s to around 400 m / s, posing a significant technical challenge. Although the United States and my country have both achieved successful landings on the Martian surface, the largest payload mass in the implemented Mars landing missions was 1043 kg (US's "Perseverance" rover). For future Mars sample return and manned landing missions, the landing payload mass will reach 2 tons or even higher. However, due to the limitation of the launch vehicle diameter, the effective area of ​​the lander will not increase significantly, which means that the lander's ballistic coefficient will increase substantially. With a higher ballistic coefficient, the trajectory during atmospheric entry will be lower, and aerodynamic disturbances will have a greater impact, ultimately affecting the accuracy of the terminal parachute deployment.

[0003] Supersonic inflatable aerodynamic decelerators are an effective way to reduce the ballistic coefficient. After the lander's speed decreases to Mach 5, the aerodynamic decelerator is inflated and deployed, thereby increasing the effective area. However, the deployment of the inflatable aerodynamic decelerator causes a sudden change in drag characteristics, introducing complexity to guidance. Therefore, conventional guidance schemes are no longer applicable, and a new multi-control mode hybrid entry guidance method for Mars landers needs to be designed. For Mars entry missions with small payloads, the tilt angle is generally used as the controlled variable in the guidance scheme design. However, for large-mass Mars landers, the deployment of the inflatable decelerator affects the terminal guidance results; under the same conditions, the earlier the deployment, the higher the subsequent flight trajectory. Therefore, to improve the accuracy of the parachute deployment point, it is necessary to combine tilt angle control with inflatable Mach number control to establish a multi-control mode hybrid entry guidance method. Summary of the Invention

[0004] To address the issue that traditional tilt angle control methods are insufficient for achieving the required accuracy of terminal guidance for large-mass Mars landers, this invention primarily aims to provide a hybrid multi-control mode entry guidance method for Mars landers. This method constructs a terminal altitude penalty function and a range penalty factor, and combines these with a traditional objective function to form a comprehensive objective function. This comprehensive objective function ensures that the Mars lander meets the parachute deployment requirements of achieving a terminal altitude above the minimum boundary and minimizing the terminal flight range. A mapping relationship is established between the comprehensive objective function sequence and the inflation Mach number sequence. This mapping relationship is used to determine the inflator decelerator activation time. The inflator decelerator activation Mach number is incorporated as a controlled variable into the guidance process to form a Mach number control loop. Based on the Mach number control loop and the aerodynamic angle control guidance loop, a dual-loop predictive correction guidance strategy is formed. This dual-loop predictive correction guidance method enables hybrid multi-control mode entry guidance for Mars landers, improving the terminal altitude of large-mass Mars landers and ensuring their terminal accuracy.

[0005] The present invention is achieved through the following technical solution.

[0006] This invention discloses a hybrid entry guidance method for a Mars lander with multiple control modes. To meet the constraints of terminal altitude and flight range, a terminal altitude penalty function and a terminal range penalty coefficient are designed and weighted with a traditional objective function to obtain a comprehensive objective function. The value of this objective function is obtained by numerical integration of the dynamic model. This value can be used to search for the corrected quantity to achieve the correction process. Given different inflatable decelerator activation Mach numbers, a sequence is formed. Through numerical integration, a sequence of the rate of change of the comprehensive objective function value is obtained. The two sequences are fitted to obtain the mathematical relationship between the inflatable decelerator activation Mach number and the comprehensive objective function value. The inflatable decelerator activation Mach number is used as one of the corrected quantities in the predictive correction guidance process, forming a dual-loop predictive correction guidance strategy together with guidance that uses the tilt angle as the corrected quantity. The inflatable decelerator activation time follows a relationship with the comprehensive objective function value during correction, and a criterion for determining the inflatable decelerator activation time is designed based on this relationship. The dual-loop predictive correction guidance process is used as the output basis for issuing guidance commands to achieve hybrid entry guidance for the Mars lander with multiple control modes.

[0007] The invention discloses a hybrid entry guidance method for a Mars lander with multiple control modes, used for hybrid entry guidance of a large-mass Mars lander with multiple control modes, comprising the following steps:

[0008] Step 1: Establish altitude penalty function and range penalty function. Smooth and differentiable the penalty function to construct altitude penalty function and range penalty coefficient. Combine the terminal altitude penalty function and range penalty coefficient with the traditional objective function to form a comprehensive objective function. Through the comprehensive objective function, the Mars lander meets the terminal constraints on parachute deployment altitude and waiting flight range of the guidance problem. The terminal parachute deployment altitude constraint refers to the parachute deployment requirement above the minimum boundary of the terminal altitude, and the waiting flight range constraint refers to the parachute deployment requirement with the minimum waiting flight range of the terminal.

[0009] The term "massive Mars lander" refers to a Mars lander with a mass greater than 2 tons. "Traditional Mars lander" refers to a Mars lander with a mass less than 2 tons.

[0010] The specific implementation method of step 1 is as follows:

[0011] To meet the constraints on parachute deployment altitude and flight range of the traditional Mars lander guidance problem terminal, i.e., the guidance target is to make the Mars lander terminal altitude as high as possible and the flight range as short as possible, the objective function of the traditional Mars lander adopts the form shown in equation (1):

[0012]

[0013] Where J0 is the traditional objective function, h f It is the terminal height, S togo It is the flight path before takeoff.

[0014] The addition of an inflatable decelerator results in a lower trajectory for the massive Mars lander, leading to a faster descent speed and a more challenging aerodynamic environment. This results in a lower terminal altitude compared to traditional Mars lander missions, potentially failing to meet the minimum terminal altitude requirements and causing parachute deployment failure. Furthermore, the coupling effects of various state variables in the Mars lander's dynamic model increase the pre-flight range error, degrading terminal guidance accuracy and thus failing to meet the mission's requirements. Therefore, simply using the aforementioned traditional objective function is no longer sufficient for massive Mars landing missions.

[0015] In the guidance mission for a massive Mars lander, the terminal parachute deployment altitude constraint is h. min -h f ≤0, h min This is the terminal's minimum altitude. The range constraint is S. togo -S max ≤0, S max This represents the maximum permissible waiting flight range. Therefore, the terminal altitude constraint for parachute deployment corresponds to the terminal altitude constraint penalty function P. h The range constraint corresponds to the penalty function P for the flight range. s :

[0016]

[0017] By combining the terminal altitude penalty function and range penalty factor shown in equation (2) with the traditional objective function, the comprehensive objective function of the massive Mars lander is constructed as shown in equation (3):

[0018] J = f(J0, P) h ,P s (3)

[0019] Where J is the overall objective function with added penalty function. However, due to the terminal height constraint penalty function P... h Penalty function P for flight range s Since it is not differentiable, the comprehensive objective function J is also not differentiable. Therefore, the comprehensive objective function J cannot be solved based on the gradient iterative formula.

[0020] The above terminal height constraint penalty function P h Perform the smoothing process as shown in equation (4):

[0021]

[0022] Here, ε is the smoothness factor. It is continuous and first-order differentiable for any small quantity.

[0023] The above-mentioned penalty function P for the waiting flight range s Perform the smoothing process as shown in equation (5):

[0024]

[0025] Where w is the flight range constraint w(σ)=S togo -S max ≤0. ε is the smoothness factor. It is continuous and first-order differentiable for any small quantity. To prevent excessive altitude and long flight range, the flight range penalty coefficient h in equation (6) is constructed. x As a coefficient of the height term in the objective function.

[0026]

[0027] Where k1 is a coefficient. Combining the altitude penalty function and the waiting flight range penalty coefficient with the traditional objective function, we obtain the comprehensive objective function J.

[0028] According to equations (5) and (6), the comprehensive objective function J of the massive Mars lander is obtained as follows:

[0029]

[0030] Here, k2 is the coefficient of the height penalty term, which is used to determine whether the height penalty term takes effect.

[0031] By using the comprehensive objective function J, the terminal altitude is guaranteed to be above the minimum altitude, and the flight range is smaller compared to traditional objective functions.

[0032] Step 2: Set the Mach number sequence for the inflatable decelerator, calculate the rate of change of the comprehensive objective function at each point in the sequence, and obtain the sensitivity sequence of the comprehensive objective function to the inflatable Mach number. Establish a mapping relationship between the comprehensive objective function sequence and the inflatable Mach number sequence. Based on the mapping relationship, construct a criterion for determining the inflatable decelerator's start time. Determine whether the inflatable Mach number should be corrected at the current moment based on the inflatable decelerator's start time criterion. If not, retain the result of the Mach number control loop guidance correction at the previous moment, and use the result of whether the inflatable Mach number should be corrected as the Mach number guidance time criterion in Step 3.

[0033] The specific implementation method of step 2 is as follows:

[0034] An increase in the lander's ballistic coefficient can cause a lower trajectory during the approach phase and greater aerodynamic disturbances, thus affecting the lander's control capabilities. Deploying the inflatable decelerator increases the aircraft's lift, improving the subsequent flight trajectory and ultimately impacting terminal accuracy. The timing of the inflatable decelerator deployment affects terminal accuracy differently. Therefore, to quantitatively assess the sensitivity of terminal accuracy to the timing of inflatable decelerator deployment, the comprehensive objective function constructed in step 1 is used as a measure of terminal accuracy, with the inflatable Mach number at deployment time replacing the deployment time. Given an inflatable Mach number sequence of length i: [M] s,1 M s,2 M s,3 ···M s,i ]. M s,i It is the Mach number of the air-filled decelerator at different times.

[0035] Based on the above Mach number sequence, the corresponding comprehensive objective function value J is obtained after numerical integration of the dynamic model. i According to equation (8), the rate of change η of the comprehensive objective function value sequence is obtained. i

[0036]

[0037] Where ΔM is the Mach number increment. J i It is the Mach number M for air filling. si The corresponding comprehensive objective function value.

[0038] The earlier the air-inflated decelerator is deployed, the higher the terminal height, and the greater the change in the comprehensive objective function value. Preliminary assessment indicates a linear relationship between the inflation Mach number and the sensitivity of the comprehensive objective function. The rate of change of the comprehensive objective function value is normalized and used as the sensitivity η of the comprehensive objective function value to the inflation Mach number.m :

[0039]

[0040] Where, η max It is the largest rate of change in the sequence, η min It is the smallest rate of change in the sequence.

[0041] The sensitivity of the comprehensive objective function value to the inflation Mach number exhibits a regular change, indicating that the inflation Mach number can also be used as a controlled variable affecting flight status. By incorporating the inflation decelerator activation Mach number as a controlled variable into the guidance process to form a Mach number control loop, the optimal inflation Mach number is found through a one-dimensional search. The sensitivity η of the comprehensive objective function value to the inflation Mach number is obtained by interpolating the inflation Mach number sequence and the comprehensive objective function sensitivity sequence. m Value. When sensitivity η m The larger the value, the shorter the guidance time of the inflation Mach number control loop. Based on the mapping relationship between the inflation Mach number sequence and the sensitivity of the comprehensive objective function, the inflation Mach number guidance time interval t is established. s The pattern is shown in equation (10).

[0042] t s =b0+b1J m (10)

[0043] Where b0 and b1 are the coefficients to be designed. The start time T of the next Mach number control loop guidance is determined according to the pattern shown in equation (10). next for:

[0044] T next =T last +t s (11)

[0045] Among them, T last It is the time when the inflation Mach number was last corrected. If the current time is equal to T... next If the current time is correct, it is determined that the inflation Mach number should be corrected at the current moment; otherwise, the result of the guidance correction of the control loop at the previous time is retained.

[0046] Step 3: Form a dual-loop predictive correction guidance strategy based on the Mach number control loop and the aerodynamic angle control guidance loop. According to the Mach number guidance time judgment criteria in Step 2, either the Mach number control loop or the aerodynamic angle control guidance loop is selected for guiding the massive Mars lander. This dual-loop predictive correction guidance achieves multi-control mode hybrid entry guidance for the Mars lander, increasing the terminal altitude of the massive Mars lander and ensuring its terminal accuracy.

[0047] The specific implementation method of step 3 is as follows:

[0048] The analysis in step 2 shows that the opening of the air-filled decelerator has a regular impact on the comprehensive objective function value. Therefore, the Mach number at which the air-filled decelerator is opened is used as the controlled variable for the guidance mission, thus affecting the terminal guidance accuracy. Simultaneously, to further improve controllability, a dual-loop predictive correction guidance strategy is designed, combining the conventional guidance scheme where the tilt angle is the controlled variable in conventional guidance missions, with the tilt angle and the air-filled Mach number as the corrected variables.

[0049] Step 3.1: The dual-loop predictive correction guidance strategy involves the simultaneous action of two controlled variables: the tilt angle and the inflation Mach number. However, due to the limited computing power of the onboard computer, it is impossible to correct both variables simultaneously. Therefore, the tilt angle and inflation Mach number act alternately in time. That is, while correcting one variable, the other retains the previous prediction result. The predictive correction loops for the tilt angle and inflation Mach number are constructed separately.

[0050] Step 3.2: The method for constructing the control loop for the tilt angle is as follows: Given the value of the tilt angle, the value of the comprehensive objective function is obtained by integrating the dynamic model. Then, the tilt angle is corrected using equation (12):

[0051]

[0052] Where σ is the roll angle, n represents the nth position, and λ is the iteration factor. The corrected roll angle is returned to the flight state at the next time step.

[0053] Step 3.3: Construct the control loop for the inflation Mach number. The specific implementation method is as follows:

[0054] Step 3.3.1: Based on the current actual Mach number and the inflation Mach number activation judgment criteria constructed in Step 2, determine whether to enter guidance mode.

[0055] The minimum inflation Mach number is preset. The predicted inflation Mach number, the actual Mach number, and the Mach number guidance time are obtained.

[0056] The system determines whether the current time is equal to the Mach number guidance time; whether the flight Mach number is greater than the previously predicted inflation Mach number; and whether the inflation Mach number is greater than the minimum inflation Mach number time. If all three conditions are met, the system enters the inflation Mach number prediction and correction guidance loop.

[0057] Step 3.3.2 provides the predicted and corrected Mach number result. The next guidance time is then determined using the inflation time criterion from step 2 above.

[0058] Step 3.3.2: Based on the given prediction and correction Mach number results.

[0059] Step 3.3.2.1: Obtain the value of the previously predicted inflation Mach number, and increase or decrease the inflation Mach number value by a preset small amount to obtain two comprehensive objective function values. Keep the Mach number value with the smaller result.

[0060] Step 3.3.2.2: Further increase or decrease the Mach number value obtained in the previous step by a preset small amount. This yields two combined objective function values, and the Mach number value corresponding to the smaller combined objective function value is retained.

[0061] Step 3.3.2.3: Repeat step 3.3.2.2 until the maximum number of times is set. Output the Mach number result of the prediction correction.

[0062] Step 3.4: Based on Step 3.3.1, determine whether the current time is equal to the Mach number guidance time; whether the flight Mach number is greater than the previously predicted inflation Mach number; and whether the inflation Mach number is greater than the minimum inflation Mach number time. If all three conditions are met, proceed to Step 3.3 for inflation Mach number prediction and correction guidance. If the current time is not equal to the Mach number guidance time; or the flight Mach number is not greater than the previously predicted inflation Mach number; or the inflation Mach number is not greater than the minimum inflation Mach number time; or any one of the above three conditions is met, proceed to Step 3.2 for tilt angle control loop prediction and correction guidance. Either the Mach number control loop or the aerodynamic angle control guidance loop is selected for the guidance of the large-mass Mars lander. Utilizing dual-loop prediction and correction guidance enables multi-control mode hybrid entry guidance for the Mars lander, improving the terminal altitude of the large-mass Mars lander and ensuring its terminal accuracy.

[0063] Beneficial effects:

[0064] 1. The multi-control mode hybrid entry guidance method for Mars landers disclosed in this invention, to meet the errors of terminal altitude and pre-flight range, designs a terminal altitude penalty function and a terminal pre-flight range penalty coefficient, which are weighted with a conventional objective function to obtain a comprehensive objective function. The value of this objective function is obtained and used to search for the quantities to be corrected, thereby correcting the roll angle and inflation Mach number. The addition of the terminal altitude penalty function and the pre-flight range penalty coefficient further improves the terminal accuracy of the guidance mission.

[0065] 2. The hybrid entry guidance method for a Mars lander disclosed in this invention constructs a criterion for determining the activation time of the inflation Mach number based on the influence of the inflation Mach number on the comprehensive objective function value. Based on this criterion, a guidance loop for the Mach number is designed, and combined with a guidance loop for the tilt angle, forming a dual-loop predictive correction guidance strategy to enhance the controllability of the guidance mission. The addition of an inflatable decelerator solves the problem of a lower landing trajectory caused by the increased mass of the lander. Simultaneously, the designed dual-loop predictive correction guidance strategy ensures guidance accuracy, enabling hybrid entry guidance for a large-mass Mars lander using multiple control modes. Attached Figure Description

[0066] Figure 1 Flowchart of the hybrid entry guidance method for the Mars lander with multiple control modes;

[0067] Figure 2 Curve showing the relationship between inflation Mach number and rate of change of the comprehensive objective function;

[0068] Figure 3 Inflation Mach number correction time interval curve;

[0069] Figure 4 Tilt angle-time curve

[0070] Figure 5 Inflation Mach Number Adjustment Curve

[0071] Figure 6 Altitude-Flight Range Curve Detailed Implementation

[0072] To better illustrate the purpose and advantages of this invention, the following description, in conjunction with an example and corresponding drawings, explains the invention.

[0073] To verify the feasibility and advantages of the trajectory optimization method, a large-mass Mars lander was used for simulation. The lander's mass m = 4000 kg, and its surface area S1 = 15.9043 m² before the inflatable decelerator was deployed. 2 The area of ​​the inflatable reducer after unfolding is S2 = 28.2743 m². 2 Initial conditions for the entry phase: Altitude h0 = 123 km, velocity v0 = 5505 m / s, longitude θ0 = -90.072°, latitude φ0 = -43.898°, heading angle ψ0 = 85.01°, trajectory inclination angle γ0 = -14.15°. Terminal conditions for the entry phase: Longitude θ0 = -90.072°, latitude φ ... heading angle ψ0 = 85.01°, trajectory inclination angle γ0 = -90.072°. T = -73.26°, latitude φ T = -41.45°. Upper limit of the tilt angle σ max =90°, lower limit of tilt angle σ min =10°.

[0074] like Figure 1As shown in the example, the specific implementation steps of the multi-control mode hybrid entry guidance method for Mars landers disclosed in this example are as follows:

[0075] Step 1: Establish altitude penalty function and range penalty function. Smooth and differentiable the penalty function to construct altitude penalty function and range penalty coefficient. Combine the terminal altitude penalty function and range penalty coefficient with the traditional objective function to form a comprehensive objective function. Through the comprehensive objective function, the Mars lander meets the terminal constraints on parachute deployment altitude and waiting flight range of the guidance problem. The terminal parachute deployment altitude constraint refers to the parachute deployment requirement above the minimum boundary of the terminal altitude, and the waiting flight range constraint refers to the parachute deployment requirement with the minimum waiting flight range of the terminal.

[0076] The term "massive Mars lander" refers to a Mars lander with a mass greater than 2 tons. "Traditional Mars lander" refers to a Mars lander with a mass less than 2 tons.

[0077] The specific implementation method of step 1 is as follows:

[0078] To meet the constraints on parachute deployment altitude and flight range of the traditional Mars lander guidance problem terminal, i.e., the guidance target is that the Mars lander terminal altitude should be as high as possible and the flight range should be as short as possible, the objective function of the traditional Mars lander adopts the form shown in equation (13):

[0079]

[0080] Where J0 is the conventional objective function, h f It is the terminal height, S togo The flight path is the distance to be flown, and all three are obtained by numerical integration of the dynamic model.

[0081] Where J0 is the traditional objective function, h f It is the terminal height, S togo It is the flight path before takeoff.

[0082] The addition of an inflatable decelerator results in a lower trajectory for the massive Mars lander, leading to a faster descent speed and a more challenging aerodynamic environment. This results in a lower terminal altitude compared to traditional Mars lander missions, potentially failing to meet the minimum terminal altitude requirements and causing parachute deployment failure. Furthermore, the coupling effects of various state variables in the Mars lander's dynamic model increase the pre-flight range error, degrading terminal guidance accuracy and thus failing to meet the mission's requirements. Therefore, simply using the aforementioned traditional objective function is no longer sufficient for massive Mars landing missions.

[0083] In the guidance mission of a massive Mars lander, the terminal altitude, in addition to satisfying the constraint of minimizing J0, also needs to satisfy the minimum altitude constraint, which is h. min -h f ≤0, hmin =6km, which is the minimum altitude at the terminal. Similarly, the range constraint must also satisfy the maximum ready-to-fly range constraint S. togo -S max ≤0, S max =5km, which is the maximum permissible waiting range. Therefore, the above constraints can be written as the terminal altitude constraint penalty function P. h And the penalty function P for the flight range s :

[0084]

[0085] By combining the terminal altitude penalty function and range penalty factor shown in equation (14) with the traditional objective function, the comprehensive objective function of the massive Mars lander is constructed as shown in equation (15):

[0086] J = f(J0, P) h ,P s (15)

[0087] Where J is the overall objective function with added penalty function. However, due to the terminal height constraint penalty function P... h Penalty function P for flight range s Since it is not differentiable, the comprehensive objective function J is also not differentiable. Therefore, the comprehensive objective function J cannot be solved based on the gradient iterative formula.

[0088] The above terminal height constraint penalty function P h Perform the smoothing process as shown in equation (16):

[0089]

[0090] Here, ε is set to 0.1, a small positive parameter representing the smoothness factor. It is continuous and first-order differentiable for any small quantity.

[0091] The above-mentioned penalty function P for the waiting flight range s Perform the smoothing process as shown in equation (17):

[0092]

[0093] Where w is the flight range constraint w(σ)=S togo -S max ≤0. To prevent excessive altitude and long waiting range, the waiting range penalty coefficient h in formula (18) is constructed. x As a coefficient of the height term in the objective function.

[0094]

[0095] Where k1 is a coefficient, set to 1000000. Combining the altitude penalty function and the waiting flight range penalty coefficient with the traditional objective function, we obtain the comprehensive objective function J.

[0096] According to equations (17) and (18), the comprehensive objective function J of the massive Mars lander is obtained as follows:

[0097]

[0098] The coefficient k2 is set to 1000000.

[0099] By using the comprehensive objective function J, the terminal altitude is guaranteed to be above the minimum altitude, and the flight range is smaller compared to traditional objective functions.

[0100] Step 2: Set the Mach number sequence for the inflatable decelerator, calculate the rate of change of the comprehensive objective function at each point in the sequence, and obtain the sensitivity sequence of the comprehensive objective function to the inflatable Mach number. Establish a mapping relationship between the comprehensive objective function sequence and the inflatable Mach number sequence. Based on the mapping relationship, construct a criterion for determining the inflatable decelerator's start time. Determine whether the inflatable Mach number should be corrected at the current moment based on the inflatable decelerator's start time criterion. If not, retain the result of the Mach number control loop guidance correction at the previous moment, and use the result of whether the inflatable Mach number should be corrected as the Mach number guidance time criterion in Step 3.

[0101] The specific implementation method of step 2 is as follows:

[0102] An increase in the lander's ballistic coefficient can cause a lower trajectory during the approach phase and greater aerodynamic disturbances, thus affecting the lander's control capabilities. Conversely, the deployment of the inflatable decelerator increases the aircraft's lift, improving the subsequent flight trajectory and ultimately impacting terminal accuracy. The deployment time of the inflatable decelerator has varying effects on terminal accuracy. Therefore, to quantitatively assess the sensitivity of terminal accuracy to the timing of inflatable decelerator deployment, the comprehensive objective function constructed in step 1 is used as the metric for terminal accuracy, with the inflatable Mach number at deployment time replacing the deployment time. A sequence of inflatable Mach numbers of length 12 is given: [3.4 3.5 3.6…4.6]. The numbers in the sequence represent the Mach numbers at different deployment times of the inflatable decelerator.

[0103] Based on the above Mach number sequence, after numerical integration of the dynamic model, the corresponding comprehensive objective function value J can be obtained. i According to equation (20), the rate of change η of the comprehensive objective function value sequence can be obtained. i Plotting the inflation Mach number as the independent variable and the rate of change of the objective function value as the dependent variable yielded the following results: Figure 2 The curve showing the relationship between the inflation Mach number and the rate of change of the comprehensive objective function.

[0104]

[0105] Where ΔM is the Mach number increment, set to 0.02. J i It is the Mach number M for air filling. s,i The corresponding comprehensive objective function value.

[0106] The earlier the air-inflated decelerator is deployed, the higher the terminal height, and the greater the change in the comprehensive objective function value. Preliminary assessment indicates a linear relationship between the inflation Mach number and the sensitivity of the comprehensive objective function. The rate of change of the comprehensive objective function value is normalized and used as the sensitivity η of the comprehensive objective function value to the inflation Mach number. m :

[0107]

[0108] Where, η max It is the largest rate of change in the sequence, η min It is the smallest rate of change in the sequence.

[0109] The sensitivity of the comprehensive objective function value to the inflation Mach number exhibits a regular change, indicating that the inflation Mach number can also be used as a controlled variable affecting flight status. By incorporating the inflation decelerator activation Mach number as a controlled variable into the guidance process to form a Mach number control loop, the optimal inflation Mach number is found through a one-dimensional search. The sensitivity η of the comprehensive objective function value to the inflation Mach number is obtained by interpolating the inflation Mach number sequence and the comprehensive objective function sensitivity sequence. m Value. When sensitivity η m The larger the value, the shorter the guidance time of the inflation Mach number control loop. Based on the mapping relationship between the inflation Mach number sequence and the sensitivity of the comprehensive objective function, the inflation Mach number guidance time interval t is established. s The pattern is shown in equation (22).

[0110] t s =b0+b1J m (twenty two)

[0111] Where b0 and b1 are the coefficients to be designed, set to 10 and –9 / 2 respectively. To more intuitively illustrate the selection rule for the guidance time interval, the following is given: Figure 3 The inflation Mach number correction time interval curve. Based on this pattern, the timing T of the next guidance can be determined. next for:

[0112] T next =T last +t s (twenty three)

[0113] Among them, T lastIt is the moment when the inflation Mach number was last corrected, if the current moment is exactly equal to T. next If so, determine that the inflation Mach number should be corrected at the current moment; otherwise, retain the result of the correction at the previous moment.

[0114] Step 3: Considering the impact of opening the air-filled decelerator on the overall objective function, a dual-loop predictive correction guidance strategy is designed, with the tilt angle and the air-filled Mach number as the corrected quantities. Based on the Mach number guidance time judgment criteria in Step 3, an air-filled Mach number guidance scheme is designed, and when performing predictive correction on the air-filled Mach number, the current tilt angle is obtained from the previous correction value.

[0115] The specific implementation method of step 3 is as follows:

[0116] The analysis in step 2 shows that the opening of the air-filled decelerator has a regular impact on the comprehensive objective function value. Therefore, the Mach number at which the air-filled decelerator is opened is used as the controlled variable for the guidance mission, thus affecting the terminal guidance accuracy. Simultaneously, to further improve controllability, a dual-loop predictive correction guidance strategy is designed, combining the conventional guidance scheme where the tilt angle is the controlled variable in conventional guidance missions, with the tilt angle and the air-filled Mach number as the corrected variables.

[0117] Step 3.1: The dual-loop predictive correction guidance strategy involves the simultaneous action of two controlled variables: the tilt angle and the inflation Mach number. However, due to the limited computing power of the onboard computer, it is impossible to correct both variables simultaneously. Therefore, the tilt angle and inflation Mach number act alternately in time. That is, while correcting one variable, the other retains the previous prediction result. The predictive correction loops for the tilt angle and inflation Mach number are constructed separately.

[0118] Step 3.2: The method for constructing the control loop for the tilt angle is as follows: Given the value of the tilt angle, the value of the comprehensive objective function is obtained by integrating the dynamic model. Then, the tilt angle is corrected using equation (24):

[0119]

[0120] Where σ is the roll angle, n represents the nth position, and λ is 0.7. The corrected roll angle is returned to the flight state at the next moment.

[0121] Step 3.3: Construct the control loop for the inflation Mach number. The specific implementation method is as follows:

[0122] Step 3.3.1: Based on the current actual Mach number and the inflation Mach number activation judgment criteria constructed in Step 2, determine whether to enter guidance mode.

[0123] The minimum inflation Mach number is preset. The predicted inflation Mach number, the actual Mach number, and the Mach number guidance time are obtained.

[0124] The system determines whether the current time is equal to the Mach number guidance time; whether the flight Mach number is greater than the previously predicted inflation Mach number; and whether the inflation Mach number is greater than the minimum inflation Mach number time. If all three conditions are met, the system enters the inflation Mach number prediction and correction guidance loop.

[0125] Step 3.3.2 provides the predicted and corrected Mach number result. The next guidance time is then determined using the inflation time criterion from step 2 above.

[0126] Step 3.3.2: Based on the given prediction and correction Mach number results.

[0127] Step 3.3.2.1: Obtain the value of the previously predicted inflation Mach number, and increase or decrease the inflation Mach number value by a preset small amount to obtain two comprehensive objective function values. Keep the Mach number value with the smaller result.

[0128] Step 3.3.2.2: Further increase or decrease the Mach number value obtained in the previous step by a preset small amount. This yields two combined objective function values, and the Mach number value corresponding to the smaller combined objective function value is retained.

[0129] Step 3.3.2.3: Repeat step 3.3.2.2 until the maximum number of times is set. Output the Mach number result of the prediction correction.

[0130] Step 3.4: Based on Step 3.3.1, determine whether the current time is equal to the Mach number guidance time; whether the flight Mach number is greater than the previously predicted inflation Mach number; and whether the inflation Mach number is greater than the minimum inflation Mach number time. If all three conditions are met, proceed to Step 3.3 for inflation Mach number prediction and correction guidance. If the current time is not equal to the Mach number guidance time; or the flight Mach number is not greater than the previously predicted inflation Mach number; or the inflation Mach number is not greater than the minimum inflation Mach number time; or any one of the above three conditions is met, proceed to Step 3.2 for tilt angle control loop prediction and correction guidance. Either the Mach number control loop or the aerodynamic angle control guidance loop is selected for the guidance of the large-mass Mars lander. Utilizing dual-loop prediction and correction guidance enables multi-control mode hybrid entry guidance for the Mars lander, improving the terminal altitude of the large-mass Mars lander and ensuring its terminal accuracy.

[0131] Therefore, by combining the dynamic model with time as the independent variable with the aforementioned guidance scheme, a hybrid entry guidance method for the Mars lander with multiple control modes can be obtained. Simulation results show... Figure 4 The curve of the change in the tilt angle and Figure 5 The inflation Mach number adjustment curve. Figure 4The tilt angles shown are all within the upper and lower limits, which meets the requirements. Figure 5 As can be seen, the predicted inflation Mach number was continuously revised, finally deploying when the Mach number dropped to 3.8. The altitude-range curve for the entire flight is shown below. Figure 6 As shown, the terminal height is above the minimum height of 6km, thus meeting the terminal height requirement.

[0132] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hybrid entry guidance method for a Mars lander with multiple control modes, used for the hybrid entry guidance of a large-mass Mars lander with multiple control modes, characterized in that: Includes the following steps, Step 1: Establish altitude penalty function and range penalty function, smooth and differentiate the penalty function, construct altitude penalty function and range penalty coefficient, and combine terminal altitude penalty function, range penalty coefficient and traditional objective function to form comprehensive objective function. Through comprehensive objective function, the Mars lander meets the terminal constraints of parachute opening altitude and waiting flight range in the guidance problem. The terminal parachute opening altitude constraint refers to the parachute opening requirement above the minimum boundary of terminal altitude, and the waiting flight range constraint refers to the parachute opening requirement with the minimum waiting flight range of terminal altitude. Step 2: Set the Mach number sequence for the inflatable reducer, calculate the rate of change of the comprehensive objective function at each point in the sequence, and obtain the sensitivity sequence of the comprehensive objective function to the inflatable Mach number; establish a mapping relationship between the comprehensive objective function sequence and the inflatable Mach number sequence, construct the inflatable reducer start-up time judgment criterion based on the two sequence function mapping relationship, determine whether the inflatable Mach number should be corrected at the current moment based on the inflatable reducer start-up time judgment criterion, otherwise retain the result of the Mach number control loop guidance correction at the previous moment, and use the result of whether the inflatable Mach number should be corrected as the Mach number guidance time judgment criterion in Step 3; The specific implementation method of step 2 is as follows: Based on the Mach number sequence, the corresponding comprehensive objective function value J is obtained by numerical integration of the dynamic model. i According to equation (8), the rate of change ŋ of the comprehensive objective function value sequence is obtained. i Where ΔM is the Mach number increment; J i It is the Mach number M for air filling. si The corresponding comprehensive objective function value; The rate of change of the comprehensive objective function value is normalized and used as the sensitivity of the comprehensive objective function value to the inflation Mach number. m : Among them, ŋ max It is the largest rate of change in the sequence, ŋ min It is the smallest rate of change in the sequence; The sensitivity of the comprehensive objective function value to the inflation Mach number exhibits a regular change, indicating that the inflation Mach number can also be used as a controlled variable affecting flight status. Incorporating the inflation decelerator activation Mach number as a controlled variable into the guidance process forms a Mach number control loop. The optimal inflation Mach number is found through a one-dimensional search. The sensitivity of the comprehensive objective function value to the inflation Mach number is obtained by interpolating the inflation Mach number sequence and the comprehensive objective function sensitivity sequence. m Value; when sensitivity ŋ m The larger the value, the shorter the guidance time of the inflation Mach number control loop; based on the mapping relationship between the inflation Mach number sequence and the sensitivity of the comprehensive objective function, the inflation Mach number guidance time interval t is established. s The pattern is shown in equation (10); Where b0 and b1 are the coefficients to be designed; the start time T of the next Mach number control loop guidance is determined according to the rule shown in equation (10). next for: Among them, T last It is the time when the inflation Mach number was last corrected. If the current time is equal to T... next If the current time is determined, the inflation Mach number should be corrected; otherwise, the guidance correction result of the control loop of the previous time is retained. Step 3: Form a dual-loop predictive correction guidance strategy based on the Mach number control loop and the control aerodynamic angle guidance loop; according to the Mach number guidance time judgment criteria in Step 2, select either the Mach number control loop or the control aerodynamic angle guidance loop for the guidance of the massive Mars lander. That is, use dual-loop predictive correction guidance to realize the mixed entry guidance of multiple control modes of the Mars lander, improve the terminal altitude of the massive Mars lander, and ensure the terminal accuracy of the massive Mars lander.

2. The Mars lander multi-control mode hybrid entry guidance method as described in claim 1, characterized in that: The term "massive Mars lander" refers to a Mars lander with a mass greater than 2 tons; "traditional Mars lander" refers to a Mars lander with a mass less than 2 tons.

3. The Mars lander multi-control mode hybrid entry guidance method as described in claim 1 or 2, characterized in that: The specific implementation method of step 1 is as follows: The objective function of a traditional Mars lander takes the form shown in equation (1): Where J0 is the traditional objective function, h f It is the terminal height, S togo It is the flight path before takeoff; In the guidance mission for a massive Mars lander, the terminal parachute deployment altitude constraint is h. min -h f ≤0, h min It is the terminal's minimum altitude; the range constraint is S. togo -S max ≤0, S max To determine the maximum permissible waiting range; therefore, the terminal altitude constraint penalty function P corresponds to the terminal altitude constraint condition for parachute deployment altitude. h The range constraint corresponds to the penalty function P for the flight range. s : By combining the terminal altitude penalty function and range penalty factor shown in equation (2) with the traditional objective function, the comprehensive objective function of the massive Mars lander is constructed as shown in equation (3): Where J is the overall objective function with added penalty function; however, due to the terminal height constraint penalty function P h Penalty function P for flight range s Since it is not differentiable, the comprehensive objective function J is also not differentiable. Therefore, the comprehensive objective function J cannot be solved based on the gradient iterative formula. The above terminal height constraint penalty function P h Perform the smoothing process as shown in equation (4): Where ε is the smoothness factor; it is continuous and first-order differentiable for any small quantity; The above-mentioned penalty function P for the waiting flight range s Perform the smoothing process as shown in equation (5): Where w is the flight range constraint w(σ) = S togo -S max ≤ 0; ε is a smoothing factor; it is continuous and first-order differentiable for any small quantity; to prevent excessive altitude and long flight range, the long flight range penalty coefficient h of formula (6) is constructed. x As the coefficient of the height term in the objective function; Where k1 is a coefficient; combining the altitude penalty function and the waiting flight range penalty coefficient with the traditional objective function, we obtain the comprehensive objective function J; Based on equations (5) and (6), the comprehensive objective function J of the massive Mars lander is obtained as follows: Where k2 is the coefficient of the height penalty term; The objective function J is used to ensure that the terminal height is above the minimum height.

4. The Mars lander multi-control mode hybrid entry guidance method as described in claim 3, characterized in that: The specific implementation method of step 3 is as follows: Step 3.1: The dual-loop prediction correction guidance strategy is a guidance strategy in which two controlled variables, the tilt angle and the inflation Mach number, act together. Therefore, the two controlled variables, the tilt angle and the inflation Mach number, act alternately in time; that is, when correcting one variable, the other variable retains the previous prediction result; the prediction correction loops for the two controlled variables, the tilt angle and the inflation Mach number, are constructed separately. Step 3.2: The method for constructing the prediction and correction guidance loop for the tilt angle is as follows: Given the value of the tilt angle, the value of the comprehensive objective function is obtained by integrating the dynamic model; then, the tilt angle is corrected using equation (12): Where σ is the tilt angle, n represents the nth position, and λ is the iteration factor; the corrected tilt angle is returned to the flight state at the next moment; Step 3.3: Construct the prediction and correction guidance loop for the inflation Mach number. The specific implementation method is as follows: Step 3.3.1: Based on the current actual Mach number and the inflation Mach number activation judgment criteria constructed in Step 2, determine whether to enter guidance mode; The minimum inflation Mach number is preset; the previously predicted inflation Mach number, the actual Mach number, and the Mach number guidance time are obtained. Determine if the current time is equal to the Mach number guidance time; at the same time, determine if the flight Mach number is greater than the previously predicted inflation Mach number; and whether the inflation Mach number is greater than the minimum inflation Mach number time; if all three conditions are met, then enter the inflation Mach number prediction and correction guidance loop. Step 3.3.1 provides the predicted and corrected Mach number result; and the next guidance time is given based on the inflation time judgment in step 2 above. Step 3.3.2: Based on the given Mach number prediction and correction results; Step 3.3.2.1: Obtain the value of the inflation Mach number predicted in the previous step, and increase or decrease the inflation Mach number value by a preset small amount to obtain two comprehensive objective function values. Keep the Mach number value that yields the smaller result. Step 3.3.2.2: Further increase or decrease the Mach number value obtained in the previous step by a preset small amount; obtain two comprehensive objective function values ​​respectively, and retain the Mach number value corresponding to the smaller comprehensive objective function value; Step 3.3.2.3: Repeat step 3.3.2.2 until the maximum number of times is set; output the Mach number result of the prediction correction; Step 3.4: Based on Step 3.3.1, determine whether the current time is equal to the Mach number guidance time; whether the flight Mach number is greater than the previously predicted inflation Mach number; and whether the inflation Mach number is greater than the minimum inflation Mach number time. If all three conditions are met, proceed to Step 3.3 for inflation Mach number prediction and correction guidance. If the current time is not equal to the Mach number guidance time; or the flight Mach number is not greater than the previously predicted inflation Mach number; or the inflation Mach number is not greater than the minimum inflation Mach number time; or any one of the above three conditions is met, proceed to Step 3.2 for tilt angle control loop prediction and correction guidance. Select either the Mach number control loop or the aerodynamic angle control loop for guidance of the massive Mars lander. Utilize dual-loop prediction and correction guidance to achieve multi-control mode hybrid entry guidance for the Mars lander, improve the terminal altitude of the massive Mars lander, and ensure the terminal accuracy of the massive Mars lander.

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