A method for processing Mars atmosphere entry path constraints based on drag prediction

Abstract

The method for processing the path constraint for entering the Martian atmosphere based on resistance prediction belongs to the technical field of guidance law design. The present invention is to solve the problem in the prior art that the high-precision tracking reference trajectory of the probe cannot be taken into account at the same time as the safety state. It includes: obtaining the path constraint control quantity according to the physical parameters and path constraint conditions of the probe; obtaining the expected tracking trajectory of the probe according to the expected entry position and terminal position of the probe entering the Martian atmosphere; obtaining the tracking guidance law according to the expected tracking trajectory of the probe, outputting the expected control quantity, performing limiting calculation on the expected control quantity, and obtaining the actual control quantity of the probe; obtaining the dynamic equation of the probe according to the actual control quantity of the probe, and constraining the entry path of the probe into the Martian atmosphere. The present invention is used to perform online correction of the path constraint of the Martian atmosphere entry process.

Description

Technical Field

[0001] The invention relates to a Mars atmosphere entry path constraint processing method, belonging to the technical field of guidance law design. Background Art

[0002] The atmospheric entry phase of Mars starts from the probe entering the boundary of the Martian atmosphere (at an altitude of about 125km) and ends with the probe opening the parachute. During this process, the probe's speed decays from 4 to 7km / s to about 400m / s, which meets the conditions for opening the parachute. During this period, the probe faces overload, dynamic pressure and heat flow constraints. In addition, this process occupies most of the journey of the entry, descent, and landing (EDL) process on Mars and is a key link in determining the landing accuracy of the probe. Therefore, the process of entering the Martian atmosphere is an important technology for the precise landing of the Mars probe.

[0003] During the Martian atmosphere entry process, there are the following problems:

[0004] 1. There is a certain degree of uncertainty in the atmospheric density and atmospheric model of Mars;

[0005] 2. The aerodynamic parameters in the nominal model (such as lift-to-drag ratio, ballistic coefficient, etc.) are different from the actual ones;

[0006] 3. The entry point state of the detector is uncertain;

[0007] The above uncertainties require the detector to constantly correct its own trajectory during the entry process. In the existing technology, overload, dynamic pressure and thermal flow constraints are usually only processed as path constraints during the offline nominal trajectory design. When the uncertainty is too large, the flight trajectory of the detector will seriously deviate from the nominal trajectory. When correcting its own running trajectory, the detector state will inevitably break through the path constraint. At this time, the detector will face a series of risks such as disintegration.

[0008] Therefore, how to ensure that the detector is in a safe state while meeting the requirements of high-precision tracking of the reference trajectory is a problem that urgently needs to be solved in the existing technology. Summary of the invention

[0009] The purpose of the present invention is to solve the problem in the prior art that the high-precision tracking reference trajectory of the detector cannot be taken into account at the same time as the safety status, and a method for processing the Mars atmosphere entry path constraints based on resistance prediction is provided.

[0010] The method for processing the Mars atmosphere entry path constraint based on resistance prediction of the present invention comprises:

[0011] S1. Obtaining a path constraint control quantity according to the physical parameters of the detector and the path constraint conditions;

[0012] S2. obtaining an expected tracking trajectory of the probe according to an expected entry position and terminal position of the probe into the Martian atmosphere;

[0013] S3. According to the expected tracking trajectory of the detector, the tracking guidance law is obtained, the expected control amount is output, and the expected control amount is limited and calculated to obtain the actual control amount of the detector;

[0014] S4. Based on the actual control quantity of the probe, the dynamic equation of the probe is obtained to constrain the entry path of the probe into the Martian atmosphere.

[0015] Preferably, the specific method of obtaining the path constraint control amount according to the physical parameters of the detector and the path constraint conditions in S1 includes:

[0016] S1-1, taking the detector as a particle, obtain the three-degree-of-freedom dynamic equation of the detector;

[0017] S1-2. Obtain the path constraints of the probe during its entry into the Martian atmosphere;

[0018] S1-3, converting the path constraint of the detector into a constraint on the resistance, and obtaining the maximum resistance value allowed by the detector;

[0019] S1-4, ignoring the remainder, obtain the Taylor expansion of the drag acceleration;

[0020] S1-5, combining the maximum allowed resistance value of the detector obtained in S1-3 and the Taylor expansion of the resistance acceleration obtained in S1-4, to obtain the path constraint condition of the detector state;

[0021] S1-6. Regulate the path constraint conditions so that the detector meets the path constraint during operation.

[0022] Preferably, the path constraints of the detector include overload constraints, dynamic pressure constraints and heat flow constraints.

[0023] Preferably, the specific method for obtaining the three-degree-of-freedom dynamic equation of the detector in S1-1 includes:

[0024] Taking the detector as a particle, the three-degree-of-freedom dynamic equation of the detector is:

[0025]

[0026] Among them, r represents the radial distance from the center of mass probe to the center of Mars, that is, the distance from the center of Mars, V represents the relative speed between the probe and the Martian atmosphere, γ represents the flight track angle, ψ represents the flight heading angle, θ and φ represent the longitude and latitude respectively, and g mrepresents the Martian gravitational acceleration at the location of the probe, L and D represent the lift acceleration and drag acceleration respectively, and d v Indicates the interference of the speed channel, d γ represents the interference of the track angle channel, d ψ represents the interference of the heading angle channel, σ represents the detector's tilt angle;

[0027] Among them, g m =μ / r 2 , μ represents the Martian gravitational constant;

[0028] L=ρV 2 C L S r / (2m);

[0029] D=ρV 2 C D S r / (2m);

[0030] m represents the detector mass, S r Indicates the aerodynamic area of ​​the detector, C D , C L They represent the drag coefficient and lift coefficient of the Martian atmosphere respectively, and ρ represents the density of the Martian atmosphere.

[0031] Preferably, the specific method of obtaining the path constraint conditions during the probe entering the Martian atmosphere in S1-2 includes:

[0032] During the entry into the Martian atmosphere, the constraints on the probe's path include overload constraints, dynamic pressure constraints, and heat flow constraints, which are:

[0033]

[0034] in, represents the heat flux density at the detector stagnation point, q represents the dynamic pressure, n represents the overload, q max 、n max They represent the maximum allowable heat flux, maximum dynamic pressure and maximum overload respectively, k Q represents the constant coefficient, and g0 represents the gravitational acceleration on the surface of Mars.

[0035] Preferably, the specific method of converting the path constraint of the detector into a constraint on the resistance in S1-3 to obtain the maximum resistance value allowed by the detector includes:

[0036] Combining the lift acceleration L and the drag acceleration D, the path constraint is converted to:

[0037]

[0038] D Q , D q , D n They represent the resistance constraint corresponding to the heat flux, the resistance constraint corresponding to the dynamic pressure, and the constraint corresponding to the overload respectively;

[0039] Convert the thermal flow constraint, dynamic pressure constraint and overload constraint into the resistance constraint to obtain the maximum resistance value D allowed by the detector. max :

[0040] D max =min(D Q ,D q ,D n ).

[0041] Preferably, the specific method of obtaining the Taylor expansion of the drag acceleration described in S1-4 includes:

[0042] Rewrite the density of Mars atmosphere ρ as Among them, β ρ is the intermediate variable, β ρ =1 / r s , r s represents the reference height of the Martian atmospheric density, ρ0 represents the standard atmospheric density of Mars, and h represents the height of the probe from the surface of Mars;

[0043] Taking the first and second derivatives of the drag acceleration D, we obtain:

[0044]

[0045]

[0046] Where u represents the control quantity of the detector guidance system, g D is the intermediate variable, f D For the intermediate variable:

[0047]

[0048]

[0049] u=cosσ

[0050] The amplitude range of the control variable u of the detector guidance system is [u minphy ,u maxphy ],u minphy 、u maxphy They represent the lower and upper bounds of the control quantity respectively;

[0051] When the remainder is ignored, the Taylor expansion of the drag acceleration D is obtained:

[0052]

[0053] Where D0 represents the initial value of the drag acceleration D, and Δt represents the gain coefficient of the path constraint processing part;

[0054] Will Substituting in, we get:

[0055]

[0056] Preferably, the specific method of obtaining the path constraint condition of the detector state in S1-5 includes:

[0057] The maximum resistance D allowed by the combined detector max , get the path constraints of the detector state:

[0058]

[0059] Preferably, the specific method for regulating the path constraint conditions described in S1-6 includes:

[0060] Since the flight path angle γ during the Mars entry process is small, cosγ>0, so g D <0, so we get:

[0061] u≥u temp

[0062] u temp represents the control lower bound generated by the path constraint processing part,

[0063]

[0064] Further obtain the lower limit u of the detector control constraint min :

[0065]

[0066] The control constraint lower limit u is affected by the partial gain coefficient Δt through the path constraint processing min To regulate.

[0067] Advantages of the present invention: The present invention proposes a method for processing the path constraints for entering the Martian atmosphere based on resistance prediction, and proposes an online processing method for path constraints (heat flux density, overload and dynamic pressure constraints). Based on the principle of resistance acceleration prediction, the path constraints are converted into control constraints, and the online processing of the path constraints during the Martian atmosphere entry process is realized, which can effectively prevent the probe from breaking through the path constraints during the trajectory correction process. The calculation amount is small, practical, and effective, and the final accuracy of the probe's atmospheric entry process is slightly affected, and it can be combined with other most widely used trajectory tracking and guidance methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is a principle block diagram of the Mars atmosphere entry path constraint processing method based on resistance prediction according to the present invention;

[0069] Figure 2 It is a curve diagram of the change of the control input of the detector atmosphere entry process over time when there is no additional path constraint processing module and no initial error;

[0070] Figure 3 It is a curve chart showing the change of the height error of the detector during the atmospheric entry process over time when the path constraint processing module is not added and there is no initial error;

[0071] Figure 4 It is a curve chart showing the change of the velocity error of the detector during the atmospheric entry process over time when there is no additional path constraint processing module and no initial error;

[0072] Figure 5 It is a curve diagram of the dynamic pressure variation with time during the process of the detector entering the atmosphere when the path constraint processing module is not added and there is no initial error;

[0073] Figure 6 It is a curve diagram of the change of overload of the detector during the atmospheric entry process with time when no path constraint processing module is added and there is no initial error;

[0074] Figure 7 It is a curve diagram of the heat flux density of the detector entering the atmosphere changing with time when there is no additional path constraint processing module and no initial error;

[0075] Figure 8 It is a curve diagram of the change of the control input of the detector atmosphere entry process over time when there is no additional path constraint processing module and there is an initial error;

[0076] Fig. 9 It is a curve chart showing the change of the height error of the detector during the atmospheric entry process over time when the path constraint processing module is not added and there is an initial error;

[0077] Fig.10 It is a curve diagram of the velocity error of the detector during the atmospheric entry process changing with time when the path constraint processing module is not added and there is an initial error;

[0078] Fig.11 It is a curve diagram of the dynamic pressure variation with time during the atmospheric entry process of the detector when the path constraint processing module is not added and there is an initial error;

[0079] Fig.12 It is a curve diagram of the change of overload of the detector during the atmospheric entry process with time when the path constraint processing module is not added and there is an initial error;

[0080] Fig.13It is a curve diagram of the heat flux density of the detector entering the atmosphere changing with time when there is no additional path constraint processing module and initial error;

[0081] Fig.14 It is a graph showing the change of the control input of the detector atmosphere entry process over time when the path constraint processing module is added and there is an initial error;

[0082] Fig.15 It is a curve chart showing the change of the height error of the detector during the atmospheric entry process with the additional path constraint processing module and the initial error;

[0083] Fig.16 It is a curve diagram of the velocity error of the detector during the atmospheric entry process changing with time when the path constraint processing module is added and there is an initial error;

[0084] Fig.17 It is a curve diagram of the dynamic pressure variation with time during the atmospheric entry process of the detector when the path constraint processing module is added and there is an initial error;

[0085] Fig.18 It is a curve diagram of the change of overload of the detector during atmospheric entry with time when the path constraint processing module is added and there is an initial error;

[0086] Fig.19 This is a graph showing the change of heat flux density over time during the detector's atmospheric entry process when a path constraint processing module is added and there is an initial error. DETAILED DESCRIPTION

[0087] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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.

[0088] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0089] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0090] Embodiment 1:

[0091] Combine the following Figure 1 This embodiment is described. The Mars atmosphere entry path constraint processing method based on resistance prediction described in this embodiment includes:

[0092] S1. Obtaining a path constraint control quantity according to the physical parameters of the detector and the path constraint conditions;

[0093] S2. obtaining an expected tracking trajectory of the probe according to an expected entry position and terminal position of the probe into the Martian atmosphere;

[0094] S3. According to the expected tracking trajectory of the detector, the tracking guidance law is obtained, the expected control amount is output, and the expected control amount is limited and calculated to obtain the actual control amount of the detector;

[0095] S4. Based on the actual control quantity of the probe, the dynamic equation of the probe is obtained to constrain the entry path of the probe into the Martian atmosphere.

[0096] Furthermore, the specific method of obtaining the path constraint control amount according to the physical parameters of the detector and the path constraint conditions in S1 includes:

[0097] S1-1, taking the detector as a particle, obtain the three-degree-of-freedom dynamic equation of the detector;

[0098] S1-2. Obtain the path constraints of the probe during its entry into the Martian atmosphere;

[0099] S1-3, converting the path constraint of the detector into a constraint on the resistance, and obtaining the maximum resistance value allowed by the detector;

[0100] S1-4, ignoring the remainder, obtain the Taylor expansion of the drag acceleration;

[0101] S1-5, combining the maximum allowed resistance value of the detector obtained in S1-3 and the Taylor expansion of the resistance acceleration obtained in S1-4, to obtain the path constraint condition of the detector state;

[0102] S1-6. Regulate the path constraint conditions so that the detector meets the path constraint during operation.

[0103] Furthermore, the path constraints of the detector include overload constraints, dynamic pressure constraints and heat flow constraints.

[0104] Furthermore, the specific method of obtaining the three-degree-of-freedom dynamic equation of the detector in S1-1 includes:

[0105] Taking the detector as a particle, the three-degree-of-freedom dynamic equation of the detector is:

[0106]

[0107] Among them, r represents the radial distance from the center of mass probe to the center of Mars, that is, the distance from the center of Mars, V represents the relative speed between the probe and the Martian atmosphere, γ represents the flight track angle, ψ represents the flight heading angle, θ and φ represent the longitude and latitude respectively, and g mrepresents the Martian gravitational acceleration at the location of the probe, L and D represent the lift acceleration and drag acceleration respectively, and d v Indicates the interference of the speed channel, d γ represents the interference of the track angle channel, d ψ represents the interference of the heading angle channel, σ represents the detector's tilt angle;

[0108] Among them, g m =μ / r 2 , μ represents the Martian gravitational constant;

[0109] L=ρV 2 C L S r / (2m);

[0110] D=ρV 2 C D S r / (2m);

[0111] m represents the detector mass, S r Indicates the aerodynamic area of ​​the detector, C D , C L They represent the drag coefficient and lift coefficient of the Martian atmosphere respectively, and ρ represents the density of the Martian atmosphere.

[0112] Furthermore, the specific method of obtaining the path constraint conditions of the probe entering the Martian atmosphere in S1-2 includes:

[0113] During the entry into the Martian atmosphere, the constraints on the probe's path include overload constraints, dynamic pressure constraints, and heat flow constraints, which are:

[0114]

[0115] in, represents the heat flux density at the detector stagnation point, q represents the dynamic pressure, n represents the overload, q max 、n max They represent the maximum allowable heat flux, maximum dynamic pressure and maximum overload respectively, k Q represents the constant coefficient, and g0 represents the gravitational acceleration on the surface of Mars.

[0116] Furthermore, the specific method of converting the path constraint of the detector into a constraint on the resistance in S1-3 to obtain the maximum resistance value allowed by the detector includes:

[0117] Combining the lift acceleration L and the drag acceleration D, the path constraint is converted to:

[0118]

[0119] D Q , D q , D n They represent the resistance constraint corresponding to the heat flux, the resistance constraint corresponding to the dynamic pressure, and the constraint corresponding to the overload respectively;

[0120] Convert the thermal flow constraint, dynamic pressure constraint and overload constraint into the resistance constraint to obtain the maximum resistance value D allowed by the detector. max :

[0121] D max =min(D Q ,D q ,D n ).

[0122] Furthermore, the specific method of obtaining the Taylor expansion of the drag acceleration described in S1-4 includes:

[0123] Rewrite the density of Mars atmosphere ρ as Among them, β ρ is the intermediate variable, β ρ =1 / r s , r s represents the reference height of the Martian atmospheric density, ρ0 represents the standard atmospheric density of Mars, and h represents the height of the probe from the surface of Mars;

[0124] Taking the first and second derivatives of the drag acceleration D, we obtain:

[0125]

[0126]

[0127] Where u represents the control quantity of the detector guidance system, g D is the intermediate variable, f D For the intermediate variable:

[0128]

[0129]

[0130] u=cosσ

[0131] The amplitude range of the control variable u of the detector guidance system is [u minphy ,u maxphy ],u minphy 、u maxphy They represent the lower and upper bounds of the control quantity respectively;

[0132] When the remainder is ignored, the Taylor expansion of the drag acceleration D is obtained:

[0133]

[0134] Where D0 represents the initial value of the drag acceleration D, and Δt represents the gain coefficient of the path constraint processing part;

[0135] Will Substituting in, we get:

[0136]

[0137] Furthermore, the specific method of obtaining the path constraint condition of the detector state in S1-5 includes:

[0138] The maximum resistance D allowed by the combined detector max , get the path constraints of the detector state:

[0139]

[0140] Furthermore, the specific method for regulating the path constraint conditions described in S1-6 includes:

[0141] Since the flight path angle γ during the Mars entry process is small, cosγ>0, so g D <0, so we get:

[0142] u≥u temp

[0143] u temp represents the control lower bound generated by the path constraint processing part,

[0144]

[0145] Further obtain the lower limit u of the detector control constraint min :

[0146]

[0147] The control constraint lower limit u is affected by the partial gain coefficient Δt through the path constraint processing min To regulate.

[0148] In this embodiment, the probe is considered as a point mass and the rotation of Mars is ignored. Then the three-degree-of-freedom dynamic equation of the probe can be expressed as:

[0149]

[0150] Where r is the radial distance from the probe's mass center to the center of Mars, referred to as the distance from the center of Mars, V is the relative speed between the probe and the Martian atmosphere, γ is the flight track angle (the angle between the velocity and the local horizontal plane), ψ is the flight heading angle (the angle between the projection of the velocity on the local horizontal plane and the true north direction), θ and φ represent longitude and latitude respectively, and g ... velocity and the true north direction), θ and φ represent longitude and latitude respectively, and g is the relative speed between the probe and the Mar m =μ / r 2 is the gravitational acceleration of Mars, μ is the gravitational constant of Mars, L = ρV 2 C L S r / (2m) and D=ρV 2 C D S r / (2m) represent lift acceleration and drag acceleration respectively, m is the mass of the probe, S r is the aerodynamic area of ​​the detector, C D , C L are the drag coefficient and lift coefficient of the Martian atmosphere, respectively. ρ is the density of the Martian atmosphere, which can be expressed as follows if the French National Space Center model is used:

[0151]

[0152] In the formula, ρ0, h = r-R0 represent the standard atmospheric density of Mars and the height of the probe from the surface of Mars, R0 is the radius of Mars, r s is the reference altitude of the Martian atmosphere.

[0153] During the Martian atmosphere entry process, the probe's path should satisfy the overload, dynamic pressure and heat flow constraints, namely

[0154]

[0155] In the formula, is the heat flux density at the detector stagnation point, where q is the dynamic pressure, n is the overload, q max 、n max Respectively represent the allowable heat flux density, dynamic pressure, and overload maximum value, k Q is a constant coefficient, and g0 is the gravitational acceleration on the surface of Mars.

[0156] Combining the L and D expressions with equation (1), the path constraint can be converted to

[0157]

[0158] The three different path constraints are uniformly converted into constraints on resistance. The maximum resistance allowed by the detector is:

[0159] D max =min(D Q ,D q ,Dn ) (2)

[0160] Furthermore, in order to convert the drag constraint into the control quantity constraint, the relationship between the drag and the control quantity should be sought, and the atmospheric density can be rewritten as where β ρ =1 / r s , taking the first and second order derivatives of the resistance D, we can get:

[0161]

[0162]

[0163] In the formula

[0164]

[0165]

[0166] u=cosσ

[0167] Taking into account the actual physical limitations, the amplitude of the detector's tilt angle is limited to a certain range, that is, the amplitude of the control variable u = cosσ is limited to [u minphy ,u maxphy ], u minphy ,u maxphy They are the lower and upper bounds of the control volume caused by physical limitations.

[0168] When the remainder is ignored, the resistance D can be Taylor expanded as follows:

[0169]

[0170] Substituting formula (3) into formula (4), we can obtain:

[0171]

[0172] Combining formula (2), we can see that if we want the detector state to meet the path constraint, we should have

[0173]

[0174] Considering that the angle γ is small during the atmospheric entry process, it can be guaranteed that cosγ>0, so g D <0, then formula (5) can be rewritten as:

[0175] u≥u temp

[0176] Where:

[0177]

[0178] Furthermore, combined with the performance constraints of the actuator, the actual control constraint lower limit u of the detector can be given: min ,Right now:

[0179]

[0180] This formula provides a path constraint processing solution based on resistance prediction. Δt is regarded as a gain coefficient. By appropriately selecting the value of Δt, a lower bound of the control quantity can be obtained. When the control quantity meets the constraint, it can effectively ensure that the path constraint is not exceeded during the operation of the detector.

[0181] In the present invention, Figure 2 As shown in the figure, during the Mars atmosphere entry process, the probe usually adopts a blunt body design. By adding a mass block, its center of mass can be offset so that it maintains a non-zero constant angle of attack during flight and has a certain lift. The atmospheric entry process of the probe is an unpowered flight process. The only thing that can be performed and adjusted is the probe's roll angle σ. By adjusting σ, the direction of the lift received by the probe can be controlled, thereby adjusting the probe's flight trajectory.

[0182] Since only the roll angle σ can be controlled during the probe's atmospheric entry, if its longitudinal and lateral motions are to be controlled simultaneously, it will become a complex underactuated control problem. The usual approach is to decouple the longitudinal and lateral motions and design their control separately.

[0183] Consider its dynamic equation as:

[0184]

[0185] Under the premise of ignoring the rotation and flattening of Mars, considering that the change of the heading angle ψ during the atmospheric entry process is small, it is reasonable to assume that it remains unchanged at the initial value when studying the longitudinal motion of the probe. At this time, the lateral and longitudinal motions of the probe can be decoupled, and θ, φ and ψ are used to describe the lateral motion of the probe, while r, V and γ are used to describe the longitudinal motion. The longitudinal dynamics of the probe can be written as:

[0186]

[0187] The high-precision Mars landing mission requires that the probe can accurately reach the preset terminal state (altitude, speed, range, etc.) after the atmospheric entry process is completed. Among them, the terminal altitude is the most critical, which directly determines the time and space margin of subsequent flight missions. Therefore, the probe altitude is usually selected for tracking and control.

[0188] Define the height tracking error e = hh r , where h r As the reference height, taking the derivative of e, we can get:

[0189]

[0190]

[0191] in:

[0192] Comprehensive formula It can be seen that during the atmospheric entry process, if the path constraint processing module is added, the actual constraint imposed on the control amount is u∈[u min ,u max ], where: u min =u D ,u max =1.

[0193] Equation (6) is the longitudinal trajectory error dynamics of the Mars atmosphere entry process and is a reference for the guidance law design work.

[0194] The design of the trajectory tracking guidance law during Mars atmosphere entry is to design u in equation (1) so that the trajectory error e can converge to 0.

[0195] Taking a simple PD controller as an example, u is designed as:

[0196]

[0197] Formula (1) is rewritten as:

[0198]

[0199] In d e In the bounded case, equation (8) is asymptotically stable.

[0200] According to the task requirements, the path constraints and the physical parameters of the detector are substituted to determine the calculation formula of the path constraint online processing method, and the minimum control amount u that can ensure that the detector does not break the path constraint is calculated in real time. temp .

[0201] The upper bound of the control quantity acting on the control system is consistent with the upper bound given by the physical constraint; the lower bound of the control quantity acting on the control system is given by the following steps: temp The minimum control quantity u limited by the physical conditions of the detector minphy Compare and take the maximum value, and then compare it with the maximum control quantity u limited by physical conditions maxphy Compare and take the minimum value. That is:

[0202]

[0203] u max =u maxphy

[0204] When r0, V0, θ0, φ0, γ0, ψ0 and r f ,V f ,θ f ,φ f ,γ f ,ψ f After determination, the reference trajectory tracked by the detector can be determined according to certain principles, such as maximizing the terminal height, that is, obtaining the expected detector state quantity at each moment.

[0205] The guidance law is designed to drive the detector to track the desired trajectory. The PD guidance law shown in equation (7) is used for guidance. The output of the guidance law is the desired control variable u cal , the expected control amount needs to go through the limiting link to obtain the actual control amount acting on the detector, that is:

[0206]

[0207] After adding the online path processing scheme, the guidance system structure of the detector is as follows: Figure 1 shown.

[0208] The nominal Martian environmental parameters used in the simulation are shown in Table 1:

[0209] Table 1

[0210] parameter Value unit <![CDATA[g0]]> 3.734246 <![CDATA[m / s -2 ]]> <![CDATA[R0]]> <![CDATA[3386.6×10 3 ]]> m <![CDATA[r s ]]> 9354 m <![CDATA[ρ0]]> <![CDATA[1.58×10 -2 ]]> <![CDATA[kg / m 3 ]]>

[0211] The nominal detector physical parameters are shown in Table 2:

[0212] Table 2

[0213]

[0214]

[0215] The nominal detector initial state and terminal state used to generate the reference trajectory are shown in Table 3:

[0216] Table 3

[0217] State variables Initial state Terminal State unit h <![CDATA[125×10 3 ]]> <![CDATA[11.8766×10 3 ]]> m V 4695 550 m / s γ -11.0891 - ° ψ 73.6804 - ° θ -65 -45.0769 ° φ -50 -44.3250 °

[0218] The control parameter values ​​are shown in Table 4:

[0219] Table 4

[0220] parameter Value <![CDATA[K p ]]> 0.1 <![CDATA[K d ]]> 0.5 Δt 10

[0221] The reference trajectory of the tracking process is planned using Gpops software, and the goal is to maximize the terminal height. During the planning process, in order to leave a control margin to deal with interference and uncertainty in the process, the roll angle amplitude is limited to [20°, 70°].

[0222] The simulation conditions are as follows:

[0223] Condition 1: The atmospheric density, aerodynamic coefficient, initial speed, initial track angle, and initial altitude are consistent with the nominal values. The PD guidance law is used to track the reference altitude trajectory. The guidance framework does not contain a path constraint processing module.

[0224] Condition 2: The atmospheric density, aerodynamic coefficient, initial speed, and initial track angle are consistent with the nominal values. The initial altitude error is 2 km. The reference altitude trajectory is tracked using the PD guidance law. The guidance framework does not contain a path constraint processing module.

[0225] Condition 3: The atmospheric density, aerodynamic coefficient, initial speed, and initial track angle are consistent with the nominal values. The initial altitude error is 2 km. The PD guidance law is used to track the reference altitude trajectory. The guidance framework contains a path constraint processing module.

[0226] The termination condition of the simulation is V<550m / s or h<11.8766km.

[0227] The simulation results of working condition 1 are as follows: Figure 2-Figure 7 As shown, it represents the state change curve of the detector atmosphere entry process when there is no additional path constraint processing module and no initial error. Figure 2 is a graph of the control input versus time, Figure 3 is a graph of height error versus time, Figure 4 is a graph of velocity error versus time, Figure 5 is a graph of dynamic pressure changing with time, Figure 6 is a graph of overload versus time. Figure 7 It is a graph of heat flux density changing with time. It can be seen that when the parameters involved in the atmospheric entry process are consistent with the nominal, the detector can track the reference trajectory well during the atmospheric entry process, and the heat flux, dynamic pressure and overload during the entry process all meet the path constraint requirements.

[0228] The simulation results of working condition 2 are as follows: Figure 8-Figure 13 As shown, it represents the state change curve of the detector atmosphere entry process when there is no additional path constraint processing module and there is an initial error. Figure 8 is a graph of the control input versus time, Fig. 9 is a graph of height error versus time, Fig.10 is a graph of velocity error versus time, Fig.11 is a graph of dynamic pressure changing with time, Fig.12 is a graph of overload versus time. Fig.13It is a graph of heat flux density changing with time. It can be seen that when there is an initial height deviation during the atmospheric entry process, the detector can track the reference trajectory under the guidance law, and the height error can converge asymptotically. However, in the process of eliminating the tracking error, the detector overload breaks through the path constraint, which makes the detector at risk of disintegration.

[0229] The simulation results of working condition 3 are as follows: Figure 14-Figure 19 As shown, it represents the state change curve of the detector atmosphere entry process when the path constraint processing module is added and there is an initial error. Fig.14 is a graph of the control input versus time, Fig.15 is a graph of height error versus time, Fig.16 is a graph of velocity error versus time, Fig.17 is a graph of dynamic pressure changing with time, Fig.18 is a graph of overload versus time. Fig.19 It is a curve graph of heat flux density changing with time. It can be seen that if the path constraint online processing scheme of the present invention is added to the guidance framework, when the height deviation of the entry point is 2km, the detector can also track the reference trajectory under the guidance law, and the height error can converge asymptotically. At the same time, in the process of eliminating the tracking error, the path constraint processing module effectively ensures that the detector state meets the path constraint.

[0230] Therefore, the path constraint processing scheme of the present invention can be effectively combined with the guidance law. When performing trajectory tracking and guidance for entering the Martian atmosphere, it can ensure the safe operation of the probe without affecting the tracking accuracy of the probe.

[0231] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A method for processing Mars atmosphere entry path constraints based on drag prediction, characterized in that: It includes: S1. Obtaining a path constraint control quantity according to the physical parameters of the detector and the path constraint conditions; S2. obtaining an expected tracking trajectory of the probe according to an expected entry position and terminal position of the probe into the Martian atmosphere; S3. According to the expected tracking trajectory of the detector, the tracking guidance law is obtained, the expected control amount is output, and the expected control amount is limited and calculated to obtain the actual control amount of the detector; S4. According to the actual control amount of the probe, the dynamic equation of the probe is obtained to constrain the entry path of the probe into the Martian atmosphere; The specific method of obtaining the path constraint control quantity according to the physical parameters of the detector and the path constraint conditions in S1 includes: S1-1, taking the detector as a particle, obtain the three-degree-of-freedom dynamic equation of the detector; S1-2. Obtain the path constraints of the probe during its entry into the Martian atmosphere; S1-3, converting the path constraint of the detector into a constraint on the resistance, and obtaining the maximum resistance value allowed by the detector; S1-4, ignoring the remainder, obtain the Taylor expansion of the drag acceleration; S1-5, combining the maximum allowed resistance value of the detector obtained in S1-3 and the Taylor expansion of the resistance acceleration obtained in S1-4, to obtain the path constraint condition of the detector state; S1-6, regulating the path constraint conditions so that the detector meets the path constraint during operation; The path constraints of the detector include overload constraints, dynamic pressure constraints and thermal flow constraints; The specific method for obtaining the three-degree-of-freedom dynamic equation of the detector described in S1-1 includes: Taking the detector as a particle, the three-degree-of-freedom dynamic equation of the detector is: Among them, r represents the radial distance from the center of mass probe to the center of Mars, that is, the distance from the center of Mars, V represents the relative speed between the probe and the Martian atmosphere, γ represents the flight track angle, ψ represents the flight heading angle, θ and φ represent the longitude and latitude respectively, and g m represents the Martian gravitational acceleration at the location of the probe, L and D represent the lift acceleration and drag acceleration respectively, and d v Indicates the interference of the speed channel, d γ represents the interference of the track angle channel, d ψ represents the interference of the heading angle channel, σ represents the detector's tilt angle; Among them, g m =μ / r 2 , μ represents the Martian gravitational constant; L=ρV 2 C L S r / (2m); D=ρV 2 C D S r / (2m); m represents the detector mass, S r Indicates the aerodynamic area of ​​the detector, C D , C L represent the drag coefficient and lift coefficient of the Martian atmosphere, respectively, and ρ represents the density of the Martian atmosphere; The specific method for obtaining the path constraint conditions during the process of the probe entering the Martian atmosphere in S1-2 includes: During the entry into the Martian atmosphere, the constraints on the probe's path include overload constraints, dynamic pressure constraints, and heat flow constraints, which are: in, represents the heat flux density at the detector stagnation point, q represents the dynamic pressure, n represents the overload, q max 、n max They represent the maximum allowable heat flux, maximum dynamic pressure and maximum overload respectively, k Q represents the constant coefficient, and g0 represents the gravitational acceleration on the surface of Mars.

2. The Mars atmosphere entry path constraint processing method based on resistance prediction according to claim 1 is characterized in that: The specific method of converting the path constraint of the detector into the constraint on the resistance and obtaining the maximum resistance value allowed by the detector in S1-3 includes: Combining the lift acceleration L and the drag acceleration D, the path constraint is converted to: D Q , D q , D n They represent the resistance constraint corresponding to the heat flux, the resistance constraint corresponding to the dynamic pressure, and the constraint corresponding to the overload respectively; Convert the thermal flow constraint, dynamic pressure constraint and overload constraint into the resistance constraint to obtain the maximum resistance value D allowed by the detector. max : D max =min(D Q ,D q ,D n )。 3. The Mars atmosphere entry path constraint processing method based on resistance prediction according to claim 2 is characterized in that: The specific method of obtaining the Taylor expansion of the drag acceleration described in S1-4 includes: Rewrite the Martian atmospheric density ρ as Among them, β ρ is the intermediate variable, β ρ =1 / r s , r s represents the reference height of the Martian atmospheric density, ρ0 represents the standard atmospheric density of Mars, and h represents the height of the probe from the surface of Mars; Taking the first and second derivatives of the drag acceleration D, we obtain: Where u represents the control quantity of the detector guidance system, g D is the intermediate variable, f D For the intermediate variable: u=cosσ The amplitude range of the control variable u of the detector guidance system is [u minphy ,u maxphy ],u minphy 、u maxphy They represent the lower and upper bounds of the control quantity respectively; When the remainder is ignored, the Taylor expansion of the drag acceleration D is obtained: Where D0 represents the initial value of the drag acceleration D, and Δt represents the gain coefficient of the path constraint processing part; Will Substituting in, we get:

4. The Mars atmosphere entry path constraint processing method based on resistance prediction according to claim 3 is characterized in that: The specific method of obtaining the path constraint condition of the detector state described in S1-5 includes: The maximum resistance D allowed by the combined detector max , get the path constraints of the detector state:

5. The Mars atmosphere entry path constraint processing method based on resistance prediction according to claim 4 is characterized in that: The specific method for regulating the path constraint conditions described in S1-6 includes: Since the flight path angle γ during the Mars entry process is small, cosγ>0, so g D <0, so we get: u≥u temp u temp represents the control lower bound generated by the path constraint processing part, Further obtain the lower limit u of the detector control constraint min : The control constraint lower limit u is affected by the partial gain coefficient Δt through the path constraint processing min To regulate.

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