CN112389683B - Method for maintaining prestress of film of solar sail spacecraft - Google Patents

Abstract

The invention discloses a method for maintaining the membrane prestress of a solar sail spacecraft, and aims to solve the problem that the membrane prestress is changed due to a high-temperature and low-temperature alternating environment. The invention is realized by the following steps: s1, determining the tension mode of the film; s2, establishing a thermal analysis model and a mechanical analysis model of the film and the supporting rod; s3, calculating the temperature fields of the film and the supporting rod under the high-temperature working condition and the low-temperature working condition; s4, calculating the thermal deformation of the film and the supporting rod under high-temperature and low-temperature fields; and S5, determining the parameters of the connecting device of the film and the supporting rod according to the difference of the deformation of the film and the deformation of the supporting rod under the two working conditions. The method provided by the invention can keep the membrane prestress basically constant and the membrane profile does not change when the solar sail spacecraft is subjected to high-low temperature alternation.

Description

A method for maintaining prestressed film of solar sail spacecraft

technical field

The invention relates to the field of spacecraft design and research, in particular to a solar sail spacecraft, and provides a thin-film prestress maintaining method.

Background technique

The solar sail spacecraft uses the solar light pressure as the driving force to achieve space navigation. It is an advanced non-working substance propulsion spacecraft, which has significant advantages in deep space exploration and other missions with long endurance characteristics.

The solar sail spacecraft uses the momentum obtained by the reflection of solar photons on the sail surface to accelerate the spacecraft. In order to obtain as large an acceleration as possible, the sail surface uses a lightweight film, and at the same time, it needs to be as large as possible to improve the surface-to-mass ratio of the spacecraft. Due to the limitation of the rocket envelope during launch, two types of solar sail spacecraft have been proposed and developed at home and abroad. One is to use a lightweight support rod to support a large-area film, and to drive the support rod to expand through a motor, inflation or strain energy when in orbit to form the flight configuration of the spacecraft. One type is spin deployment, in which a concentrated mass is arranged at the top of the film, and centrifugal force is used to pull the film to unfold, and the spacecraft maintains a plane through spin when in orbit.

In order to obtain as large a light pressure as possible, the film needs to avoid deformation such as wrinkles as much as possible, so a certain prestress is required inside the film after unfolding. However, for the support rod type solar sail, when the orbit experiences high and low temperature changes, the prestress inside the film will change due to the inconsistency of thermal expansion coefficient between the film and the support rod. On the one hand, the shape of the film will be displaced, resulting in light pressure On the other hand, it may lead to film relaxation or excessive internal prestress, resulting in film tearing, buckling of support rods and other results that endanger the life of the spacecraft.

At present, the membrane structures in the existing solar sail spacecraft are mostly connected by Kevlar strings, and the influence of temperature changes on the prestress is not considered. Therefore, the method of maintaining the prestress of the solar sail spacecraft film under the high and low temperature interactive load has become an urgent problem to be solved in this field.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a method for maintaining the prestress of the thin film of a solar sail spacecraft, which aims to solve the technical problem of the change of the prestress of the thin film caused by the alternating high and low temperature environment.

The object of the present invention is achieved through the following technical solutions: a method for maintaining the prestressed film of a solar sail spacecraft, comprising the following steps:

S1, determine the tensioning mode of the film, the root of the film is fixed with a constant force spring, and the top of the film is connected with a support rod by a shape memory alloy spring;

S2, establishing a thermal analysis model and a mechanical analysis model of the film and the support rod based on the finite volume method and the finite element method, respectively;

S3, determine the high temperature working condition and the low temperature working condition of the spacecraft, and calculate the temperature field under the high and low temperature working conditions based on the thermal analysis model;

S4, calculating the thermal deformation of the film and the support rod under high temperature and low temperature temperature fields based on the mechanical analysis model;

S5, according to the difference between the thermal deformation of the film and the support rod under the two working conditions of high and low temperature, determine the parameters of the connecting device of the film and the support rod, the parameters include the parameters of the shape memory alloy spring and the constant force spring.

Optionally, in the step S1, the length of the constant force spring used for the root of the film is variable and the tension force is constant.

Optionally, the shape memory alloy spring used at the top of the film in the step S1 increases in stiffness and shortens in length at high temperature, but decreases in stiffness and elongates in length at low temperature.

Optionally, the step S3 includes the following sub-steps:

S31: Determine the high temperature working condition and the low temperature working condition;

For the solar sail spacecraft running in the earth orbit, when the solar sail spacecraft is in the light area and the solar incident angle of the thin film array is 0°, it is a high temperature condition; when the solar sail spacecraft is in the shadow area, and the thin film array When the solar incident angle of the surface is 90°, it is a low temperature condition;

S32: Calculate the temperature field of the membrane and support rod under high temperature and low temperature conditions;

Based on the established thermal analysis model, thermal loads are applied to the film and the support rod structure, including solar thermal radiation, earth thermal radiation, earth albedo radiation, and thermal radiation of the space environment. The temperature field of the membrane and support rod.

Optionally, the step S5 includes the following sub-steps:

S51, determine the configuration of the shape memory alloy spring, and use the shear modulus of elasticity method to determine the parameters of the shape memory alloy spring: the shape memory alloy spring is a metal spring wire and a shape memory alloy spring wire connected in parallel, and packaged with a shell obtained after

S52: Determine the parameters of the constant force spring: determine the constant force of the constant force spring according to the size of the film prestress and the critical buckling load of the support rod; after the value of the constant force is determined, determine the size of the constant force spring , diameter and stroke parameters.

Further, the detailed steps of determining the parameters of the shape memory alloy spring in the step S51 are as follows:

Determine the elastic modulus of the shape memory alloy material under high and low temperature conditions, record the high temperature elastic modulus of the shape memory alloy material as _GH , and the low temperature elastic modulus as _GL ;

According to the static analysis results of the film, determine the tensile force P of the shape memory alloy spring; according to the thermal deformation analysis results of the support rod and the film, determine the stroke difference of the shape memory alloy spring wire under high temperature and low temperature conditions δ;

According to the design life, the maximum shear strain under low temperature conditions is taken as γ _L , and the maximum shear strain γ _H under high temperature conditions is obtained as:

γ _H =γ _L G _L / _GH ,

The maximum shear stress τ _H under high temperature conditions is:

τ _H =γ _H · _GH ,

The diameter d of the design shape memory alloy spring wire is:

In the above formula, C is the spring wire index used to describe the ratio of the middle diameter to the wire diameter of the shape memory alloy spring wire;

The diameter D of the shape memory alloy spring wire is:

D=πτ _H d ³ /(8Pk),

In the above formula, k is the curvature coefficient of the shape memory alloy spring wire, which is:

The number of turns n of the shape memory alloy spring wire is:

n=δd/πD(γ _L -γ _H ),

In the above formula, δ is the stroke difference of the shape memory alloy spring wire under high temperature and low temperature conditions;

The stiffness coefficients of the shape memory alloy spring wire under high temperature and low temperature conditions are:

In the above formula, K _H is the stiffness coefficient of the shape memory alloy spring wire at high temperature, and K _L is the stiffness coefficient of the shape memory alloy spring wire at low temperature.

Compared with the prior art, the present invention has the following beneficial effects: when the solar sail spacecraft undergoes alternating high and low temperatures, the prestress of the thin film structure designed based on the present invention remains basically constant, and the thin film surface does not change.

Description of drawings

Fig. 1 is the flow chart of the method of the present invention;

Fig. 2 is the schematic diagram of film tensioning mode;

Figure 3 is a schematic diagram of the shape memory alloy spring configuration and loading: a) spring configuration; b) loading schematic diagram;

Figure 4 is a schematic diagram of the configuration and installation of the constant force spring: a) the constant force spring; b) the installation method of the constant force spring;

Figure 5 is an analysis model of the membrane and support rod;

Figure 6 is a schematic diagram of the on-orbit operation of the solar sail spacecraft;

Figure 7 is a schematic diagram of the attitude of the solar sail spacecraft;

Figure 8 is the temperature cloud diagram of the film and support rod: a) high temperature condition; b) low temperature condition;

9 is a schematic diagram of thermal deformation of the film;

Figure 10 is a schematic diagram of thermal deformation of the support rod: a) high temperature condition; b) low temperature condition;

Figure 11 is a cloud diagram of the internal prestress of the film: a) high temperature condition; b) low temperature condition.

The reference numerals in the present invention are as follows:

1--solar sail spacecraft body; 11--support rod fixing structure; 2--support rod; 3--film; 31--metal buckle; 4--Kevlar rope; 5--constant force spring; 6-- - shape memory alloy spring; 61 - metal spring wire; 62 - shape memory alloy spring wire; 7 - fixing ring mechanism.

Detailed ways

Specific embodiments will be described below with reference to the accompanying drawings.

The steps of the design method of the present invention mainly include five steps, and its process is shown in Figure 1:

Step S1: determine the tensioning method of the film 3, use a constant force spring 5 to fix at the root, and use a shape memory alloy spring 6 to connect to the support rod 2 at the top;

Please refer to FIG. 2 , which is a schematic diagram of the film tensioning method proposed by the present invention. The figure shows the situation of two support rods 2 and a film 3 , and the film 3 is an isosceles trapezoid structure, which can also be considered as a topless Triangular structure. In Fig. 2, the body side of the solar sail spacecraft body 1 is connected with a support rod 2 through a support rod fixing structure 11. The top of the support rod 2 is also provided with a fixing ring mechanism 7 for firmly clamping the support rod 2. The film 3 needs to pass through It is connected to the support rod fixing structure 11 and the fixing ring mechanism 7 in a certain tensioning manner. At the four corners A, B, C and D of the film 3 , there are also four metal buckles 31 , where A and D are located at the root of the film 3 , and B and C are located at the top of the film 3 .

In this embodiment, at points A and D at the root of the film 3, the connecting device composed of the Kevlar rope 4 and the constant force spring 5 is connected to the support rod fixing structure 11 on the solar sail spacecraft body 1; at the top B of the film 3 Point and point C are connected with the fixing ring mechanism 7 on the support rod 2 through the connecting device composed of the Kevlar rope 4 and the shape memory alloy spring 6 .

Since the thermal expansion coefficients of the film 3 and the support rod 2 are inconsistent, when the film 3 goes from a low temperature to a high temperature, the gap between the film 3 and the support rod 2 is reduced.

The shape memory alloy spring 6 has nonlinear characteristics, and its configuration and loading schematic diagram are shown in FIG. 3 . The shape memory alloy spring 6 includes two core components, a metal spring wire 61 and a shape memory alloy spring wire 62 . Under high temperature (when exposed to the sun), the stiffness coefficient of the shape memory alloy spring wire 62 increases, and the compression amount decreases. At low temperature, the stiffness coefficient of the shape memory alloy spring wire 62 decreases, and the compression amount increases. Due to the nonlinearity of the shape memory alloy spring 6 , the gap between the membrane 3 and the support rod 2 can be effectively compensated.

For the configuration and installation method of the constant force spring 5, please refer to Figure 4a and Figure 4b, respectively. It has two functions: First, when the film 3 experiences high and low temperature changes, the temperature change rate of the shape memory alloy spring 6 is slow, resulting in the temperature The change is slow, and the change of the gap between the support rod 2 and the film 3 cannot be compensated in time, while the constant force spring 5 can effectively balance the inconsistency of thermal expansion between the support rod 2 and the film 3; Buckling occurs due to excessive pressure. The Kevlar rope 4 is mainly used to realize the high-strength connection between the constant force spring 5 and the membrane 3, and is used to compensate the length of the connection device.

Step S2: establish a thermal analysis model and a mechanical analysis model of the membrane 3 and the support rod 2 based on the finite volume method and the finite element method respectively;

To conduct thermal and mechanical analysis of the structure, the thermal analysis model of the membrane 3 and the support rod 2 in the solar sail spacecraft should be established first.

Sub-step S21: establish a thermal analysis model of the membrane 3 and the support rod 2;

The finite element analysis model of membrane 3 and support rod 2 is established by finite element software, as shown in Figure 5, the element type is linear triangular element, with a total of 7871 nodes and 9433 elements.

Sub-step S22: establishing a mechanical analysis model of the membrane 3 and the support rod 2;

The mechanical analysis model of the structure is established with quadrilateral shell elements, with a total of 941 nodes and 876 elements.

Step S3: According to the configuration and orbital attitude characteristics of the solar sail spacecraft, determine the high temperature working condition and the low temperature working condition of the spacecraft, and calculate the temperature field under the two working conditions based on the thermal analysis model;

Sub-step S31: determine the high temperature working condition and the low temperature working condition;

Taking the solar sail spacecraft running in the earth's orbit as an example, the spacecraft can be divided into a lighted area and a shadowed area during the orbital operation, as shown in Figure 6. The solar incident angle of the film 3 front is in the range of 0 to 90°. When the solar incident angle is 0°, the film 3 always maintains the state of facing the sun, that is, the Z _i direction points to the sun, as shown in Figure 7; the solar incident angle is 90° When , the normal of the film 3 front is perpendicular to the direction of sunlight. Therefore, when the solar sail spacecraft is in the light area, and the solar incidence angle of the 3-film front is 0°, it is a high temperature condition; when the solar sail spacecraft is in the shadow area, and the solar incidence angle of the 3-film front is 90° at low temperature.

Sub-step S32: Calculate the temperature fields of the membrane 3 and the support rod 2 under high temperature conditions and low temperature conditions;

Based on the established thermal analysis model, apply thermal loads to the structure, including solar thermal radiation, earth thermal radiation, earth albedo radiation, and space environmental thermal radiation, and the temperatures of film 3 and support rod 2 under high temperature and low temperature conditions can be obtained. field, as shown in Figure 8. The temperature of film 3 under high temperature condition is -14.75℃, and the temperature range of support rod 2 is -52.4℃～34.9℃; under low temperature condition, the temperature of film 3 is -224.42℃, and the temperature range of support rod 2 is -183.0℃～-186.2 °C.

Step S4: Calculate the thermal deformation of the film 3 and the support rod 2 under high temperature and low temperature temperature fields based on the mechanical analysis model;

Sub-step S41: Calculate the thermal deformation of the film 3 under high temperature and low temperature conditions;

The film 3 enters the illuminated area (high temperature condition) from the shadow area (low temperature condition), and the in-plane displacement of the corner point of the film 3 reaches 42.58 mm, as shown in FIG. 9 .

Sub-step S42: Calculate the thermal deformation of the support rod 2 under low temperature and high temperature conditions;

Under the low temperature condition, the support rod 2 is shortened by 9.1mm, and the top lateral displacement is 3.6mm; under the high temperature condition, the support rod 2 is shortened by 2.8mm, and the top lateral displacement is 94.3mm, as shown in Figure 10.

Step S5 : According to the difference between the deformations of the membrane 3 and the support rod 2 under the two working conditions, determine the parameters of the connection device of the membrane 3 and the support rod 2 , including the parameters of the shape memory alloy spring 6 and the constant force spring 5 .

Sub-step S51: determine the configuration of the shape memory alloy spring 6, and use the shear elastic modulus method to determine the parameters of the shape memory alloy spring 6;

In the shape memory alloy spring 6, a metal spring wire 61 and a shape memory alloy spring wire 62 are connected in parallel, and are packaged with a casing. The shape memory alloy spring 6 utilizes the compression performance of the shape memory alloy spring wire 62 to delay the hysteresis effect of the shape memory alloy and increase the service life. The casing is used for packaging mainly to limit the position, to avoid structural damage caused by the breakage of the metal spring wire 61, and also to protect the metal spring wire 61 and the shape memory alloy spring wire 62 from the influence of space effects.

Determining the parameters of the shape memory alloy spring 6 mainly refers to determining the parameters of the shape memory alloy spring wire 62 in the shape memory alloy spring 6. Here, the cutting elastic modulus method is adopted, and the detailed steps are as follows:

1) Determine the elastic modulus of the shape memory alloy material under high and low temperature conditions, record the high temperature elastic modulus of the shape memory alloy material as _GH , and the low temperature elastic modulus as _GL ;

2) According to the static analysis results of the film, determine the tensile force P that the shape memory alloy spring 6 bears; according to the thermal deformation analysis results of the support rod 2 and the film 3, determine the shape memory alloy under high temperature and low temperature conditions. The stroke difference δ of the spring wire 62;

3) According to the design life, the maximum shear strain under low temperature conditions is taken as γ _L , and the maximum shear strain γ _H under high temperature conditions is obtained as:

γ _H =γ _L G _L / _GH ,

The maximum shear stress τ _H under high temperature conditions is:

τ _H =γ _H · _GH ,

4) The diameter d of the design shape memory alloy spring wire 62 is:

In the above formula, C is the spring wire index used to describe the ratio of the middle diameter to the wire diameter of the shape memory alloy spring wire 62;

The center diameter D of the shape memory alloy spring wire 62 is:

D=πτ _H d ³ /(8Pk),

In the above formula, k is the curvature coefficient of the shape memory alloy spring wire 62, there are:

The number of turns n of the shape memory alloy spring wire 62 is:

n=δd/πD(γ _L -γ _H ),

In the above formula, δ is the stroke difference of the shape memory alloy spring wire 62 under high temperature and low temperature conditions;

The stiffness coefficients of the shape memory alloy spring wire 62 under high temperature and low temperature conditions are:

In the above formula, K _H is the stiffness coefficient of the shape memory alloy spring wire 62 at high temperature, and _KL is the stiffness coefficient of the shape memory alloy spring wire 62 at low temperature.

So far, all parameters of the shape memory alloy spring 6 are obtained.

Sub-step S52: determine the parameters of the constant force spring 5;

The configuration of the constant force spring 5 is shown in Figure 4, and it is installed on the star in a box type. According to the size of the prestress of the membrane 3 and the critical buckling load of the support rod 2, the constant tension of the constant force spring 5 is determined. In general, the constant tension value of the constant force spring 5 is designed according to the critical load when the support rod 2 reaches buckling, and the design safety margin is 2. After the constant tension value is determined, the size, diameter and travel parameters of the spring can be determined.

As shown in FIG. 11 , after adopting the method for maintaining a constant prestress of the film 3 according to the present invention, the prestress distribution of the film 3 under high temperature working conditions and low temperature working conditions changes little, which can effectively solve the high and low temperature alternating The technical problem that the prestress of the membrane 3 changes due to the environment.

Although the content of the present invention is described in detail through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be based on the scope defined by the claims.

Claims (6)

1. A method for maintaining the membrane prestress of a solar sail spacecraft is characterized by comprising the following steps:

s1, determining a tensioning mode of the film (3), fixing the root of the film (3) by using a constant force spring (5), and connecting the top end of the film (3) with the support rod (2) by using a shape memory alloy spring (6);

s2, establishing a thermal analysis model and a mechanical analysis model of the film (3) and the supporting rod (2) based on a finite volume method and a finite element method respectively;

s3, determining the high-temperature working condition and the low-temperature working condition of the spacecraft, and calculating the temperature fields under the high-temperature working condition and the low-temperature working condition based on the thermal analysis model;

s4, calculating the thermal deformation of the film (3) and the supporting rod (2) under high-temperature and low-temperature fields based on the mechanical analysis model;

s5, determining parameters of a connecting device of the film (3) and the support rod (2) according to the difference of thermal deformation of the film (3) and the support rod (2) under high and low temperature working conditions, wherein the parameters comprise parameters of a shape memory alloy spring (6) and a constant force spring (5), and the shape memory alloy spring (6) comprises a metal spring wire (61) and a shape memory alloy spring wire (62) which are connected in parallel.

2. The method for maintaining the membrane prestress of the solar sail spacecraft as claimed in claim 1, wherein the constant force spring (5) used for the root of the membrane (3) in the step S1 has a variable length and a constant tension.

3. The method for maintaining the membrane prestress of the solar sail spacecraft as claimed in claim 1, wherein the shape memory alloy wire (62) of the shape memory alloy spring (6) used at the top end of the membrane (3) in the step S1 has a higher stiffness coefficient and a lower compression amount at high temperature and a lower stiffness coefficient and an higher compression amount at low temperature.

4. The method for maintaining the membrane prestress of a solar sail spacecraft as claimed in claim 1, wherein said step S3 comprises the following substeps:

s31: determining a high-temperature working condition and a low-temperature working condition;

for a solar sail spacecraft running on an earth orbit, when the solar sail spacecraft is in an illumination area and the sun incident angle of a film array surface is 0 degree, the high-temperature working condition is adopted; when the solar sail spacecraft is in a ground shadow area, the low-temperature working condition is that the solar incident angle of the film array surface is 90 degrees;

s32: calculating the temperature fields of the film and the supporting rod under the high-temperature working condition and the low-temperature working condition;

and applying thermal load to the film (3) and the support rod (2) structure based on the established thermal analysis model, wherein the thermal load comprises solar thermal radiation, earth albedo radiation and space environment thermal radiation, and obtaining the temperature fields of the film (3) and the support rod (2) under high-temperature working conditions and low-temperature working conditions.

5. The method for maintaining the membrane prestress of a solar sail spacecraft as claimed in claim 1, wherein said step S5 includes the following sub-steps:

s51, determining the configuration of the shape memory alloy spring (6), and determining the parameters of the shape memory alloy spring by using a tangential elastic modulus method: the shape memory alloy spring (6) is obtained by connecting a metal spring wire (61) and a shape memory alloy spring wire (62) in parallel and packaging the metal spring wire and the shape memory alloy spring wire by using a shell;

s52: determining the parameters of the constant force spring (5): determining the constant tension of the constant force spring (5) according to the magnitude of the membrane prestress and the critical buckling load of the support rod; after the numerical value of the constant tension is determined, the size, the diameter and the stroke parameters of the constant tension spring (5) are determined and obtained.

6. The method for maintaining the membrane prestress of a solar sail spacecraft of claim 5, wherein the step S51 for determining the parameters of the shape memory alloy spring (6) is detailed as follows:

determining shape memoryThe elastic modulus of the alloy material under the high and low temperature working conditions is recorded as G_HLow-temperature modulus of elasticity of G_L；

Determining the tensile force P borne by the shape memory alloy spring (6) according to the result of the static analysis of the film; determining the stroke difference delta of the shape memory alloy spring wire (62) under the conditions of high temperature and low temperature according to the thermal deformation analysis results of the support rod (2) and the film (3);

taking the maximum shear strain gamma under the working condition of low temperature according to the design life_LObtaining the maximum shear strain gamma under the high-temperature working condition_HComprises the following steps:

γ_H＝γ_LG_L/G_H，

maximum shear stress tau under high temperature conditions_HComprises the following steps:

τ_H＝γ_H·G_H，

the diameter d of the shape memory alloy spring wire (62) is designed as follows:

in the above formula, C is a spring wire index for describing the ratio of the pitch diameter to the wire diameter of the shape memory alloy spring wire (62);

the pitch diameter D of the shape memory alloy spring wire (62) is as follows:

D＝πτ_Hd³/(8Pk)，

in the above formula, k is the curvature coefficient of the shape memory alloy wire (62) and has:

the number n of turns of the shape memory alloy spring wire (62) is as follows:

n＝δd/πD(γ_L-γ_H)，

in the above formula, δ is the stroke difference of the shape memory alloy spring wire (62) under the conditions of high temperature and low temperature;

the rigidity coefficients of the shape memory alloy spring wire (62) under the working conditions of high temperature and low temperature are respectively as follows:

in the above formula, K_HIs the stiffness coefficient, K, of the shape memory alloy wire (62) at high temperature_LIs the stiffness coefficient of the shape memory alloy spring wire (62) at low temperature.

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