Low-orbit atmospheric density measuring device and method in parallel with orbit removal and measurement

Abstract

The application discloses a low-orbit atmospheric density measuring device and method in parallel with orbit departure, and belongs to the field of low-orbit spacecraft measurement and control. The application comprises a device shell, a film ball, an inflation system, a patch type pressure sensor, a pressing unlocking mechanism and a communication module B. The application adopts a spherical film device to inflate and expand to increase the windward area of constellation satellites, and improve the orbit departure efficiency of the constellation satellites. Meanwhile, the patch type pressure sensor is used to measure the resultant force borne by the orbit departure-measuring system. The real-time low-orbit atmospheric density is calculated in combination with the orbit data, the shape structure and the resistance coefficient of the orbit departure-measuring system. The folding method of the film ball is a combination of plane spiral bonding and z-type folding. The multiple plane petals of the film ball are sequentially spiral bonded and then z-type folded to form a cubic shape, so that the film ball is conveniently packaged. The application realizes the atmospheric density measurement of the area passed by the constellation satellites during the orbit departure based on the patch type pressure sensor, and has the advantages of low cost and real-time measurement.

Description

Technical Field

[0001] This invention relates to a low-Earth orbit atmospheric density measurement device and method that combines deorbiting and measurement, specifically for a low-Earth orbit atmospheric density measurement device and method configured on low-Earth orbit constellation satellites, and belongs to the field of low-Earth orbit spacecraft telemetry and control. Background Technology

[0002] In recent years, large-scale low-Earth orbit (LEO) constellations have flourished. Equipping these satellites with active deorbiting devices is crucial to preventing them from becoming space debris and impacting space environment safety and sustainable development. Thin-film sphere payloads, which reduce spacecraft orbital altitude through atmospheric drag, are one type of active deorbiting device. They are characterized by high deorbiting efficiency and good attitude stability, showing great application potential. A thin-film sphere is a drag-enhancing deorbiting device. It is formed by using a high-strength thin-film material to generate internal pre-stress, thus increasing the satellite's frontal area in all directions. Thin-film sphere devices possess excellent omnidirectional drag characteristics, are highly adaptable, and their installation surface on the satellite is unrestricted, making them a promising deorbiting method in the context of large constellations. After completing their missions, constellation satellites often do not completely deplete their fuel, and their components remain relatively intact, retaining some attitude control and communication capabilities. Furthermore, since current constellation satellite deployments rely on multi-satellite launches, the deorbiting process is also characterized by large-scale, batch-based operations. This characteristic can be utilized to rationally allocate tasks during deorbiting, achieving resource conservation and improving constellation operational efficiency.

[0003] The low Earth orbit (LEO) atmosphere is a crucial medium for understanding space science and geophysics, and an essential pathway for human travel to and from space. The LEO atmosphere is a complex result of factors such as Earth's gravity, solar activity, and geomagnetic activity. Obtaining a sufficiently accurate LEO atmospheric model and continuously calibrating and refining it using extensive satellite measurement data are pressing challenges. Therefore, there is an urgent need for devices capable of repeated verification and correction to conduct global surveys of the real LEO space atmosphere.

[0004] Traditional low-Earth orbit (LEO) atmospheric satellites suffer from high costs and long development cycles, and the measurement results from a single satellite are often inaccurate and lack precision. Developing a constellation specifically for atmospheric measurement would lead to resource waste. In recent years, electronic devices have been gradually miniaturized and reduced in cost, and sensor detection accuracy has been further improved. Utilizing sensors for scientific missions has gradually become a hot topic in space science exploration. Therefore, it is necessary to design measurement devices and methods for LEO atmospheric density based on sensor working principles and existing satellite constellations, to achieve low-cost, high-precision atmospheric measurement. Summary of the Invention

[0005] Addressing the deorbiting and measurement requirements of satellites deployed in low Earth orbit constellations, the main objective of this invention is to provide a low Earth orbit atmospheric density measurement device and method that combines deorbiting and measurement. Based on a patch-type pressure sensor, it measures the atmospheric density of the area traversed by the constellation satellites during deorbiting, offering advantages such as low cost and real-time measurement of multiple satellites. Furthermore, by inflating and deploying a spherical thin-film device, the windward area of ​​the constellation satellites is increased, thereby increasing atmospheric drag during deorbiting and improving the deorbiting efficiency.

[0006] The objective of this invention is achieved through the following technical solutions.

[0007] This invention discloses a low-Earth orbit atmospheric density measurement device that combines deorbiting and measurement. Mounted on the edge of a constellation satellite, the device's bottom is fixed to the satellite, while its top is exposed and connected to the satellite via circuitry and a communication network. After the constellation satellite completes its primary mission, this device improves deorbiting efficiency and allows for the measurement of atmospheric density in the areas traversed during deorbiting. The constellation satellite includes an onboard computer, solar panels, a GNSS module, an attitude control module, a communication module A, and a satellite outer shell.

[0008] The onboard computer performs the following functions: First, it controls the folding and unfolding states of the solar panels and controls the angle of the solar panels relative to the constellation satellites based on the position data obtained by the GNSS module and the position data of the sun. Second, it controls the frequency of data acquisition by the GNSS module and reads the position data obtained by the GNSS module. Third, it controls the attitude control module to realize the maneuvering of the constellation satellites and maintain the stability of the constellation satellites' attitude, while reading the current angular momentum state of the attitude control module and unloading momentum when it is about to reach the limit of angular momentum. Fourth, it controls the communication module A to communicate with the ground base station, adjacent constellation satellites, and the communication module B of the low-orbit atmospheric density measurement device, and processes the returned atmospheric density value, orbit, attitude, and command execution status information. Fifth, it reads and processes the data from the patch pressure sensor of the atmospheric density measurement device and calculates the atmospheric density value. Sixth, it controls the pressure unlocking mechanism of the atmospheric density measurement device to switch from the locked state to the unlocked state, thereby controlling the start of the inflation system of the atmospheric density measurement device.

[0009] The solar panel features a folding structure with solar cells attached to both sides. It is fixed to the outside of the constellation's satellites. The panel absorbs solar energy and converts it into electricity, providing power to the satellites and the low-Earth orbit atmospheric density measurement device.

[0010] The GNSS module is fixed inside the outer shell of the constellation satellites. The GNSS module is used to acquire the current position and velocity data of the constellation satellites and transmit the data to the onboard computer.

[0011] The attitude control module employs a control moment gyroscope assembly, which is fixed to the inside of the constellation satellite's outer shell. The attitude control module adjusts the constellation satellite's three-axis attitude angles and angular velocities by changing the control moment gyroscope assembly's own three-axis angular momentum, while simultaneously transmitting its own three-axis angular momentum, the constellation satellite's three-axis attitude angles, and angular velocities back to the onboard computer.

[0012] Communication module A is fixed inside the outer shell of the constellation satellite. Communication module A communicates with ground base stations, adjacent constellation satellites, and communication module B in the low-Earth orbit atmospheric density measurement device, and transmits data bidirectionally.

[0013] The main body of the constellation satellite's outer shell is rectangular. All components of the constellation satellite, except for the outer shell itself, are secured by bolts and internal partitions. This process isolates the components, reducing environmental factors and interference between them, thus providing fixation, isolation, and protection. The outer shell is made of alloy structural materials.

[0014] The present invention discloses a low-orbit atmospheric density measurement device that combines deorbiting and measurement, comprising a device housing, a diaphragm sphere, an inflation system, a patch pressure sensor, a clamping and unlocking mechanism, and a communication module B.

[0015] The main body of the device is a hollow cuboid with one open side and a partition in the middle. All components of the low-orbit atmospheric density measurement device, except for the outer shell, are secured by a clamping and unlocking mechanism, bolts, and the internal partition. This also isolates the components, reducing environmental factors and interference between them, thus providing fixation, isolation, and protection. The outer shell is made of an alloy structural material. The surface of the outer shell that secures the inflation system is called the bottom, which is fixed to the constellation satellites; the surface that secures the thin-film sphere is called the top.

[0016] The diaphragm sphere is folded and sealed using a clamping and unlocking mechanism, and is fixed inside the device housing. The sphere is connected to an inflation system. The sphere inflates and unfolds into a spherical shape, increasing the drag effect of environmental perturbations on the constellation satellites. Simultaneously, a patch-type pressure sensor on the surface of the sphere measures the forces acting on the satellites. Based on these forces, the atmospheric density of the regions traversed by the satellites during their deorbiting process is measured.

[0017] The inflation system incorporates gas-generating material and a perforated plate throttling component. Connected to the membrane sphere via piping, the inflation speed is controlled by the perforated plate throttling component. The inflation system inflates the membrane sphere, causing the folded sphere to unfold into a spherical shape.

[0018] The patch-type pressure sensor employs a thin-film structure. It connects to the satellite's onboard computer via communication module B. Distributed on the surface of a thin-film sphere, the sensor measures the force acting on each sensor at its current position and time by measuring the resistance change caused by the sphere's deformation under stress. The patch-type pressure sensors are grouped together on the sphere's surface. Vector calculations are performed based on the data and layout of all sensors to determine the force acting on the constellation satellites. This force is then used to measure the atmospheric density of the regions the satellites pass through during their deorbiting process.

[0019] The clamping and unlocking mechanism includes explosive bolts and a top cover. The explosive bolts are located at the four corners inside the top cover, fixing it to the top of the device housing. The top cover is a rectangular alloy sheet with the same dimensions as the device housing. In the locked state, the top cover clamps the folded membrane ball. The explosive bolts contain explosives and an igniter. In the unlocked state, the explosives are detonated, causing the shear lock to shear or break along the bolt's weakening groove, thus separating and unlocking the device housing and the top cover, releasing the clamping force on the membrane ball, and allowing the membrane ball to inflate and unfold.

[0020] Communication module B is fixed to the inside of the device housing. Communication module B communicates with communication module A and the onboard computer, and transmits data bidirectionally.

[0021] This invention discloses a method for measuring low-Earth orbit atmospheric density in parallel with deorbiting and measurement. Based on the aforementioned low-Earth orbit atmospheric density measuring device, the method includes the following steps:

[0022] Step 1: Based on the parallel off-orbit measurement mission indicators, determine the size, number of folds, and folding depth of the thin-film sphere in the low-orbit atmospheric density measurement device for parallel off-orbit measurement. Then, determine the pressure sensor patch layout on the surface of the thin-film sphere based on its size, number of folds, and folding depth. The parallel off-orbit measurement mission indicators include off-orbit time, folding efficiency, folding stress, and measurement accuracy.

[0023] Step 1.1: Calculate the dimensions of the membrane sphere based on the mass, size, orbital altitude, initial deorbit date, and deorbit time of the constellation satellites.

[0024] The rate of change of the orbital state vector of a constellation satellite is defined as

[0025]

[0026] In the formula, r is the position vector of the constellation satellites, and v is the velocity vector of the constellation satellites. These represent the accelerations caused by atmospheric drag, solar radiation pressure, central gravitational force considering J2 perturbation, and lunar perturbation, respectively.

[0027] The drag on the constellation satellites is calculated based on the orbital dynamics model. The relationship between the average force and the surface-to-mass ratio, orbital altitude, and initial deorbit date within one orbital period is analyzed. Based on the deorbit mission requirements, the size of the membrane sphere is obtained through iterative calculations.

[0028] Step 1.2: A folding method combining planar spiral bonding and Z-shaped folding was used to determine the number of folds and the amount of material folded per fold for the low-orbit atmospheric density measurement device operating in parallel with off-orbit measurement. The specific folding method is as follows: multiple planar single lobes of the film sphere are sequentially spirally bonded together and then Z-shaped folded, ultimately folded into a cubic shape for easy encapsulation. This folding method offers advantages such as low damage and high density.

[0029] Step 1.2.1: Sequentially spirally bond the multiple planar lobes of the membrane sphere together.

[0030] The diameter of the membrane spheres varies, and the number of lobes (j) is selected based on the premise that the maximum width of each lobe is less than 50cm. The lobes are arranged vertically, with increasing numbers from bottom to top. Planar spiral bonding is a figurative description of the lobe bonding scheme; viewed from the side, the completed planar structure resembles the spiral structure of a snail shell. The planar spiral bonding method differs depending on whether j / 2 is odd or even.

[0031] ① When j / 2 is an even number, the steps for planar spiral bonding are as follows:

[0032] Step 1: Glue the right boundary of the j / 2-1 and j / 2th single lobes;

[0033] Step 2: Attach the left edges of the j / 2 and j / 2+1th lobes; and the left edges of the j / 2-1 and j / 2+2th lobes.

[0034] Step 3: Glue the right boundary of the j / 2+1 and j / 2-2 lobes; glue the right boundary of the j / 2+2 and j / 2-3 lobes.

[0035] ...

[0036] By doing so, the left and right boundaries of the single petals are bonded together to form a spiral structure;

[0037] Final step: Bond the right boundary of the (j-1)th and jth single lobes to complete the planar spiral bonding.

[0038] ②When j / 2 is an odd number, the steps for planar spiral bonding are as follows:

[0039] Step 1: Glue the left boundaries of the j / 2th and j / 2+1th single lobes;

[0040] Step 2: Attach the right boundary of the j / 2th and j / 2-1th lobes; and the left boundary of the j / 2+1th and j / 2-2th lobes;

[0041] Step 3: Glue the left edges of the j / 2-1 and j / 2+2 lobes; the left edges of the j / 2-2 and j / 2+3 lobes.

[0042] ...

[0043] By doing so, the left and right boundaries of the single petals are bonded together to form a spiral structure;

[0044] Final step: Bond the right boundary of the (j-1)th and jth single lobes to complete the planar spiral bonding.

[0045] Step 1.2.2: The model formed by sequentially spirally bonding multiple planar single lobes of the thin film sphere is folded in a Z-shape, and finally folded into a cube shape for easy encapsulation.

[0046] The Z-folding method, similar to the letter "Z," is divided into axial and circumferential Z-folds. The axial fold runs along the longest axis of a single lobe, while the circumferential fold runs perpendicular to the axial direction. Z-folding increases axial height, reduces circumferential area, and improves folding efficiency. Its main folding parameters are as follows:

[0047]

[0048]

[0049] Where C z Let l be the number of folds, l be the amount of folding per fold, D be the diameter of the sphere, and d be the side length after folding.

[0050] Step 1: Circumferential Z-fold. Fold upwards along the circumferential axis according to the selected folding amount each time, and so on, continuously folding to reduce the circumferential length.

[0051] Step 2: Axial Z-fold. Similar to the circumferential fold, fold in a "Z" shape according to the selected folding amount each time.

[0052] Step 1.3: Based on the diaphragm sphere size determined in Step 1.1 and the number of folds and the amount of each fold determined in Step 1.2, arrange the patch pressure sensors on the surface of the diaphragm sphere.

[0053] The layout of the patch pressure sensor meets the following constraints: the patch of the patch pressure sensor is axially symmetrically distributed on the surface of the thin film sphere. This axial symmetry facilitates the measurement of the force on the thin film sphere and subsequent atmospheric density inversion calculations. The patch pressure sensor layout includes multiple arrays, one array per lobe. The measurement range of the patch pressure sensor layout covers the surface of the thin film sphere, improving the accuracy and redundancy of the force measurement. The patch pressure sensor layout avoids being located at the folds or ends of the lobes of the thin film sphere to prevent interference from the folding and retraction of the thin film sphere. The size of the patch pressure sensor is determined according to the curvature of the thin film sphere, ensuring that the size of the patch pressure sensor is compatible with the curvature of the thin film sphere, and that the ratio of the perpendicular distance between the edge of the patch pressure sensor and the surface of the thin film sphere to the size of the patch pressure sensor does not exceed 0.2. The shape of the patch pressure sensor should not produce sharp corners to avoid damaging the thin film of the thin film sphere.

[0054] Step Two: Based on the dimensions, number of folds, fold amount per fold, and pressure sensor patch layout of the thin-film sphere of the parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device determined in Step One, the parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device is packaged into an independent module and mounted on a constellation satellite. The parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device described in this invention is mounted on the edge of the constellation satellite, with its bottom fixed to the satellite and its top exposed, connected to the constellation satellite via circuitry and a communication network.

[0055] Step 3: After completing its primary mission, the constellation satellites execute a parallel deorbiting and measurement mission. After receiving ground signals, communication module A sends a command to the onboard computer to activate a low-Earth orbit atmospheric density measurement device that performs both deorbiting and measurement concurrently. This command is received by communication module B. First, the explosive bolts are detonated, causing the shear lock to break or disengage along the bolt's weakening groove, thus separating and unlocking the device's outer shell and top cover, releasing the pressure on the membrane sphere. Then, the inflation system begins supplying gas, and the membrane sphere unfolds in a controlled manner. The satellite is subjected to environmental perturbations, primarily atmospheric drag, causing its orbital altitude to decrease, achieving the deorbiting effect.

[0056] Step Four: The attitude control module adjusts the primary satellite's three-axis attitude angles and angular velocities by changing the three-axis angular momentum of the control moment gyroscope assembly. This maneuvers the deorbit-measurement system to a stable equilibrium position with the sphere in front and the satellite behind, while simultaneously transmitting its own three-axis angular momentum, the primary satellite's three-axis attitude angles, and angular velocities back to the onboard computer. The patch-type pressure sensors then begin operating, measuring the force at the current position and moment by detecting changes in resistance caused by deformation under stress. The net force acting on the deorbit-measurement system is then obtained through patch-type pressure sensors positioned on the sphere's surface. The deorbit-measurement system comprises two parts: a constellation of satellites and a parallel low-Earth orbit atmospheric density measurement device.

[0057] Step 4.1: An attitude control method based on sliding mode control is adopted. In sliding mode control, feedforward control is used to counteract the influence of aerodynamic torque and improve the response rate of attitude control. Based on this control method, the attitude control module maneuvers the deorbit-measurement system attitude maneuver to a balanced position with the sphere in front and the satellite behind and maintains stability.

[0058] To describe the attitude and trajectory of the off-track measurement system, a spherical coordinate system, a velocity coordinate system, and a body coordinate system are established. The spherical coordinate system is established with the center of the thin-film sphere as the origin, with the Y-axis coinciding with the velocity direction of the off-track measurement system; the X-axis lies in the orbital plane and is perpendicular to the Y-axis, with the direction from the Earth's center to the origin of the coordinate system being positive; the Z-axis conforms to the right-hand rule. The origin of the velocity coordinate system is the center of mass of the off-track measurement system; y o The axis and the off-track measurement system have the same velocity direction; x o The axis lies in the orbital plane and is perpendicular to y. o The z-axis, with the positive direction pointing from the Earth's center to the origin of the coordinate system; o The axes conform to the right-hand rule. The origin of the body coordinate system is the centroid of the off-track measurement system, where y... b The axis coincides with the central axis of the deorbit-measurement system, pointing from the satellite toward the sphere, which conforms to the right-hand rule.

[0059] The attitude of the off-track measurement system is controlled using a sliding mode control law. Based on the selection method of the sliding mode surface, an appropriate sliding mode surface is selected, and the sliding mode switching surface function is as follows:

[0060] s=ω e +kq ve (4)

[0061] Where k is the controller parameter.

[0062] The current attitude angular velocity of the deorbit-measurement system is ω, and the desired attitude angular velocity is ω. d ,but

[0063] ω e =ω-ω r (5)

[0064] Where, ω r =C bo ω d C bo This is the transformation matrix from the orbital coordinate system to the body coordinate system.

[0065] The presence of the diaphragm sphere in the off-track measurement system increases its windward area and centroid-to-center distance, resulting in a much larger influence of aerodynamic torque compared to other torques. This aerodynamic torque becomes the primary factor affecting the attitude of the off-track measurement system. To ensure smoother and more stable control, feedforward control is employed to counteract the influence of the aerodynamic torque. With feedforward control, before the controlled variable changes after a disturbance occurs, control is applied based on the magnitude of the disturbance to compensate for its impact on the controlled variable. This direct control is lag-free and improves the response rate of the off-track measurement system. The feedforward control term is shown in formula (6).

[0066] u0=ρ P ×F A_b (6)

[0067] The designed sliding mode variable structure control law is

[0068]

[0069] Where I is the moment of inertia of the off-track measurement system. Let I3 be the error quaternion, I3 be the third-order identity matrix, and ρ be the error quaternion. P F is the position vector of the center of gravity of the off-track-measuring system in the body coordinate system. A_b Let sgn(s) be the aerodynamic torque experienced by the off-track measurement system in the body coordinate system. i Let F(s) be a symbolic function, and its expression is:

[0070] F(s)={sgn(s

[0071] Step 4.2: Based on the strain effect of resistance, the magnitude of the force acting on the patch pressure sensor is obtained, and the direction of the force is obtained according to the patch layout. The force vectors of all patch pressure sensors are added together to obtain the resultant force acting on the off-track measurement system.

[0072] The number of patch pressure sensors is N, and the coordinates of patch pressure sensor i in the spherical coordinate system are [x...]. i y i z i ] T The force it experiences is F i The radius of the thin film sphere is R. The resultant force on the off-track measurement system is obtained as follows:

[0073]

[0074] In the formula, C lN This is the transformation matrix from the spherical coordinate system to the inertial system.

[0075] Step 5: Based on the resultant force on the deorbit-measurement system obtained in Step 4, perturbation factors unrelated to atmospheric drag, including solar radiation pressure, higher-order Earth gravity, and lunar gravity, are removed through high-precision theoretical calculations. Then, combined with the orbital data, shape and structure, and drag coefficient of the deorbit-measurement system, the atmospheric density of the area it passes through is calculated in real time.

[0076] Step 5.1: Add the influence of the Earth's shadow model, represented by the solar visibility coefficient, to the basic solar radiation pressure perturbation model, and add the real-time solar position correction composed of the actual date and the obliquity of the ecliptic, to obtain a solar radiation pressure perturbation model that considers the Earth's shadow and real-time influence, thereby improving the accuracy of the solar radiation pressure perturbation force on the off-orbit-measurement system.

[0077] The solar radiation pressure perturbation force is expressed as follows:

[0078]

[0079] In the formula, r is the position vector of the off-track measurement system, and K S The solar visibility coefficient at the location of the off-orbit measurement system is represented by R; R is the radius of the thin film sphere; p SR η is the solar pressure at 1 astronomical unit (AU), ε is the reflection coefficient, λ is the obliquity of the ecliptic, floor(X) represents the largest integer not greater than X, and the current year, month, and day are represented as year, month, and day.

[0080]

[0081] Step 5.2: Add a higher-order Earth gravity field model characterized by geocentric distance, geographic latitude and longitude, associated Legendre polynomial, and Earth gravitational potential coefficient to the basic central gravity model, thereby improving the accuracy of the off-orbit-measurement system under Earth's gravity.

[0082] The expression for the component of gravity acting on the off-orbit measurement system is:

[0083]

[0084]

[0085]

[0086] In the formula, θ e denoted as latitude and longitude of the off-orbit measurement system; m as mass of the off-orbit measurement system; μ as the Earth's gravitational constant; n and k as the order and degree of the Earth's gravity field model, respectively. The Earth's gravitational potential coefficient is determined by the Earth's mass distribution. For fully normalized associative Legendre polynomials, R eIt is the Earth's average equatorial radius.

[0087]

[0088]

[0089]

[0090]

[0091] Step 5.3: Calculate the gravitational forces exerted on the off-orbit-measurement system by the Sun and Moon based on the position vector and mass of the off-orbit-measurement system.

[0092] The sun and moon exert gravitational pull on the off-orbit measurement system.

[0093]

[0094] In the formula, μ sun μ moon The gravitational constants of the Sun and the Moon, respectively; r sun r moon These are the position vectors of the Sun and the Moon in the inertial coordinate system, respectively.

[0095] Step 5.4: Based on the resultant force on the deorbit-measurement system obtained in Step 4, the solar radiation perturbation force on the deorbit-measurement system obtained in Step 5.1, the higher-order Earth gravity on the deorbit-measurement system obtained in Step 5.2, and the gravitational forces of the Sun and Moon on the deorbit-measurement system obtained in Step 5.2, calculate the atmospheric drag on the deorbit-measurement system.

[0096] F A =F B -F U -F S -F T (20)

[0097] Step 5.5: Based on the atmospheric drag on the deorbit-measurement system obtained in Step 5.4, calculate the real-time atmospheric density according to the atmospheric drag expression, combined with the orbital data, shape and structure of the deorbit-measurement system, and drag coefficient.

[0098] The expression for atmospheric drag on the off-orbit measurement system is:

[0099]

[0100] In the formula, Q is the molecular velocity ratio, σ n The adjustment coefficient is ρ, where ρ is the atmospheric density, v is the velocity vector of the off-orbit-measurement system, and ω is the velocity vector. e denoted as ω, where ω is the Earth's rotational angular velocity, and α is the semi-major axis of the off-orbit-measurement system orbit.

[0101] Step Six: Based on Steps Four and Five, use patch-type pressure sensors to measure the atmospheric density of the area the constellation satellites pass through during their deorbiting process; based on Step Three, use a spherical thin-film device to inflate and deploy, increasing the windward area of ​​the constellation satellites and improving their deorbiting efficiency. After achieving the deorbiting of the constellation satellites, measure the atmospheric density of the area they pass through.

[0102] Step 7: Train a self-attention neural network using the existing atmospheric drag model and the real spatial atmospheric density information of the area traversed obtained in Step 5. Construct an agent based on the trained self-attention neural network, enabling the agent to accurately predict the real atmospheric density based on the output of the existing atmospheric drag model, thus achieving accurate prediction of atmospheric density at any time and any location.

[0103] Developing high-precision atmospheric prediction models is of great significance for spacecraft orbit determination, orbit prediction, reentry prediction, and space security.

[0104] Beneficial effects:

[0105] 1. This invention discloses a method for measuring low-Earth orbit atmospheric density in parallel with deorbiting. It employs a spherical thin-film device that expands with inflation to increase the windward area of ​​the constellation satellites, thereby improving deorbiting efficiency. Simultaneously, it measures the resultant force on the deorbiting-measurement system based on a patch-type pressure sensor. High-precision theoretical calculations are used to remove perturbation factors unrelated to atmospheric drag. Finally, the real-time low-Earth orbit atmospheric density is calculated by combining the orbital data, shape, and drag coefficient of the deorbiting-measurement system. This invention innovatively combines atmospheric density measurement with the drag-enhancing deorbiting of constellation satellites. Compared to satellites specifically designed for atmospheric density measurement, this method fully utilizes constellation satellite resources, achieving a wide measurement range while maintaining low cost.

[0106] 2. This invention discloses a method for measuring low-orbit atmospheric density in parallel with deorbiting and measurement. The folding method for the thin-film sphere combines planar spiral bonding and Z-shaped folding. Multiple planar lobes of the thin-film sphere are sequentially spirally bonded and then Z-shaped folded, ultimately forming a cubic shape for easy encapsulation. Its core advantage lies in using planar bonding for the lobes of the thin-film sphere, eliminating the need for direct Z-axis folding, thus avoiding numerous creases, reducing damage to the thin-film material, and achieving high folding efficiency.

[0107] 3. This invention discloses a low-Earth orbit atmospheric density measurement device that combines deorbiting and measurement, comprising a device housing, a thin-film sphere, an inflation system, a patch-type pressure sensor, a clamping and unlocking mechanism, and a communication module B. This low-Earth orbit atmospheric density measurement device is mounted on the edge of a constellation satellite, with its bottom fixed to the satellite and its top exposed, connected to the satellite via circuitry and a communication network. After the constellation satellite completes its main mission, this device improves the deorbiting efficiency of the satellite and enables the measurement of atmospheric density in the areas traversed during the deorbiting process. Attached Figure Description

[0108] Figure 1 This is a flowchart of a low-orbit atmospheric density measurement method that combines deorbiting and measurement, as disclosed in this invention.

[0109] Figure 2 This relates the surface-to-mass ratio to the track height and the required off-track time.

[0110] Figure 3 This is a schematic diagram of a thin-film sphere folding method. Figure 3 (a) is a schematic diagram of planar spiral bonding. Figure 3 (b) is a schematic diagram of the Z-shaped fold;

[0111] Figure 4 A schematic diagram of the layout of a thin-film sphere single-lobe patch pressure sensor;

[0112] Figure 5 This is a schematic diagram of a low-orbit atmospheric density measurement device that combines deorbiting and measurement. Figure 5 (a) is the inflated and deployed state. Figure 5 (b) is in the folded packaging state;

[0113] Figure 6 Simulation diagram of the inflation and deployment process of the membrane sphere;

[0114] Figure 7 The curve showing the Euler angle variation of the off-track measurement system under the action of the attitude control system;

[0115] Figure 8 The derailment-measurement system is used to measure the acceleration under multi-source perturbation.

[0116] Wherein: 1—Patch-type pressure sensor, 2—Thin film ball, 3—Pressure unlocking mechanism, 4—Device housing, 5—Communication module B, 6—Inflation system. Detailed Implementation

[0117] To better illustrate the technical details of the present invention, a specific embodiment of the low-orbit atmospheric density measurement device and method of the present invention, which combines deorbiting and measurement, is described in further detail below.

[0118] Example 1

[0119] The constellation satellites are known to be cube satellites with sides of 0.1m and a mass of 3kg. The initial orbital elements of the constellation satellites are: The spherical density of the thin film is 13.2 g / m³. 2 The initial angular velocity is 0, and the initial attitude Euler angles are [60°60°60°]; take σ. n =0.8; the resultant force data measured by the pressure sensor is [-0.0374-2.8672×10] -4 -1.7067×10 -6 ]N.

[0120] This invention discloses a low-Earth orbit atmospheric density measurement device that combines deorbiting and measurement. Mounted on the edge of a constellation satellite, the device's bottom is fixed to the satellite, while its top is exposed and connected to the satellite via circuitry and a communication network. After the constellation satellite completes its primary mission, this device improves deorbiting efficiency and allows for the measurement of atmospheric density in the areas traversed during deorbiting. The constellation satellite includes an onboard computer, solar panels, a GNSS module, an attitude control module, a communication module A, and a satellite outer shell.

[0121] The onboard computer performs the following functions: First, it controls the folding and unfolding states of the solar panels and controls the angle of the solar panels relative to the constellation satellites based on the position data obtained by the GNSS module and the position data of the sun. Second, it controls the frequency of data acquisition by the GNSS module and reads the position data obtained by the GNSS module. Third, it controls the attitude control module to realize the maneuvering of the constellation satellites and maintain the stability of the constellation satellites' attitude, while reading the current angular momentum state of the attitude control module and unloading momentum when it is about to reach the limit of angular momentum. Fourth, it controls the communication module A to communicate with the ground base station, adjacent constellation satellites, and the communication module B of the low-orbit atmospheric density measurement device, and processes the returned atmospheric density value, orbit, attitude, and command execution status information. Fifth, it reads and processes the data from the patch pressure sensor of the atmospheric density measurement device and calculates the atmospheric density value. Sixth, it controls the pressure unlocking mechanism of the atmospheric density measurement device to switch from the locked state to the unlocked state, thereby controlling the start of the inflation system of the atmospheric density measurement device.

[0122] The solar panel features a folding structure with solar cells attached to both sides. It is fixed to the outside of the constellation's satellites. The panel absorbs solar energy and converts it into electricity, providing power to the satellites and the low-Earth orbit atmospheric density measurement device.

[0123] The GNSS module is fixed inside the outer shell of the constellation satellites. The GNSS module is used to acquire the current position and velocity data of the constellation satellites and transmit the data to the onboard computer.

[0124] The attitude control module employs a control moment gyroscope assembly, which is fixed to the inside of the constellation satellite's outer shell. The attitude control module adjusts the constellation satellite's three-axis attitude angles and angular velocities by changing the control moment gyroscope assembly's own three-axis angular momentum, while simultaneously transmitting its own three-axis angular momentum, the constellation satellite's three-axis attitude angles, and angular velocities back to the onboard computer.

[0125] Communication module A is fixed inside the outer shell of the constellation satellite. Communication module A communicates with ground base stations, adjacent constellation satellites, and communication module B in the low-Earth orbit atmospheric density measurement device, and transmits data bidirectionally.

[0126] The main body of the constellation satellite's outer shell is rectangular. All components of the constellation satellite, except for the outer shell itself, are secured by bolts and internal partitions. This process isolates the components, reducing environmental factors and interference between them, thus providing fixation, isolation, and protection. The outer shell is made of alloy structural materials.

[0127] This invention discloses a low-orbit atmospheric density measurement device that combines deorbiting and measurement, comprising a device housing, a diaphragm sphere, an inflation system, a patch-type pressure sensor, a clamping and unlocking mechanism, and a communication module B, as shown below. Figure 5 As shown. Figure 5 As shown, one type of low-orbit atmospheric density measurement device that combines deorbiting and measurement includes: 1—pattern-type pressure sensor, 2—thin film ball, 3—pressing and unlocking mechanism, 4—device housing, 5—communication module B, and 6—inflation system.

[0128] 4. The main body of the device casing is a hollow cuboid with one open side and a partition in the middle. All components of the low-orbit atmospheric density measuring device, except for the casing, are secured by a clamping and unlocking mechanism, bolts, and the internal partition. This also isolates the components, reducing environmental factors and interference between them, thus providing fixation, isolation, and protection. The casing is made of alloy structural material. The surface of the casing that secures the inflation system is called the bottom end, which is fixed to the constellation satellites; the surface that secures the membrane sphere is called the top end.

[0129] 2. The diaphragm sphere is folded and sealed using a clamping and unlocking mechanism, and is fixed inside the device housing. The diaphragm sphere is connected to the inflation system. The diaphragm sphere is inflated and unfolds into a spherical shape by the inflation system, increasing the drag effect of environmental perturbations on the constellation satellites. Simultaneously, a patch-type pressure sensor on the surface of the diaphragm sphere measures the force acting on the constellation satellites. Based on the force acting on the constellation satellites, the atmospheric density of the area traversed by the constellation satellites during deorbiting is measured.

[0130] 6. The inflation system incorporates gas-generating material and a perforated plate throttling component. The inflation system connects to the membrane sphere via piping, and the perforated plate throttling component controls the inflation speed. The inflation system inflates the membrane sphere, causing the folded membrane sphere to unfold into a spherical shape.

[0131] 1. The patch-type pressure sensor adopts a thin-film structure. The patch-type pressure sensor is connected to the satellite's onboard computer via communication module B. The patch-type pressure sensors are distributed on the surface of a thin-film sphere. When the thin-film sphere is fully deployed, the force experienced by the patch-type pressure sensor at the current position and time is measured by the change in resistance caused by force deformation. The patch-type pressure sensors are arranged in groups on the surface of the thin-film sphere. Based on the data and arrangement of all patch-type pressure sensors, vector calculations are performed to obtain the force experienced by the constellation satellites. Based on the force experienced by the constellation satellites, the atmospheric density of the area traversed by the constellation satellites during deorbiting is measured.

[0132] The clamping and unlocking mechanism includes explosive bolts and a top cover. The explosive bolts are located at the four corners inside the top cover, fixing it to the top of the device housing. The top cover is a rectangular alloy sheet with the same dimensions as the device housing. In the locked state, the top cover clamps the folded membrane ball. The explosive bolts contain explosives and an igniter. In the unlocked state, the explosives are detonated, causing the shear lock to shear or break along the bolt's weakening groove, thus separating and unlocking the device housing and the top cover, releasing the clamping force on the membrane ball, and allowing the membrane ball to inflate and unfold.

[0133] 5. Communication module B is fixed to the inside of the device housing. Communication module B communicates with communication module A and the onboard computer, and transmits data bidirectionally.

[0134] A low-Earth orbit atmospheric density measurement method that combines deorbiting and measurement is adopted, specifically implemented as follows:

[0135] Step 1: Based on the parallel off-orbit measurement task indicators, determine the size, number of folds, and folding depth of the thin-film sphere in the low-orbit atmospheric density measurement device for parallel off-orbit measurement, and determine the pressure sensor patch layout on the surface of the thin-film sphere according to the size, number of folds, and folding depth. The parallel off-orbit measurement task indicators include off-orbit time, folding efficiency, folding stress, and measurement accuracy;

[0136] First, based on the mass, size, orbital altitude, initial deorbit date, and deorbit time of the constellation satellites, calculate the dimensions of the membrane sphere, such as... Figure 2 As shown; then, using a folding method combining planar spiral bonding and Z-shaped folding, the number of folds and the amount of each fold for the thin film sphere of the low-orbit atmospheric density measurement device, which operates in parallel with off-orbit measurement, were determined, as shown. Figure 3 As shown; finally, based on the size of the thin-film sphere, the number of folds, and the amount of each fold, the layout of the patch-type pressure sensor on the surface of the thin-film sphere is determined, as follows. Figure 4 As shown.

[0137] Figure 1 This is a flowchart of a low-orbit atmospheric density measurement method that combines deorbiting and measurement, as disclosed in this invention. Figure 2To determine the relationship between the surface-to-mass ratio, the track height, and the required off-track time, the radius of the membrane sphere is chosen to be 1m. Figure 3 This is a schematic diagram of a thin film sphere folding method; Figure 4 This is a schematic diagram of the layout of a thin-film sphere single-lobe patch pressure sensor.

[0138] Step Two: Based on the dimensions, number of folds, fold amount per fold, and pressure sensor patch layout of the thin-film sphere of the parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device determined in Step One, the parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device is packaged into an independent module and mounted on a constellation satellite. The parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device of this invention is mounted on the edge of the constellation satellite, with its bottom fixed to the constellation satellite and its top exposed, connected to the constellation satellite via circuitry and a communication network.

[0139] Figure 5 This is a schematic diagram of a low-orbit atmospheric density measurement device that combines deorbiting and measurement.

[0140] Step 3: After completing its main mission, the constellation satellites execute a parallel deorbiting and measurement mission. After receiving ground signals, communication module A sends a command to the onboard computer to activate a low-Earth orbit atmospheric density measurement device that performs both deorbiting and measurement concurrently. This command is received by communication module B. First, the explosive bolts are detonated, causing the shear lock to break or disengage along the bolt's weakening groove, thus separating and unlocking the device's outer shell and top cover, releasing the pressure on the membrane sphere. Then, the inflation system begins supplying gas, and the membrane sphere unfolds in a controlled manner. The satellite is subjected to environmental perturbations, primarily atmospheric drag, causing its orbital altitude to decrease, achieving the deorbiting effect.

[0141] Figure 6 Simulation diagram of the inflation and deployment process of the membrane sphere. The deployment process of the folded model is divided into three stages. From 0-35ms, the model mainly unfolds circumferentially. Due to the negative pressure inside the sphere, the injected gas can expand rapidly. However, due to the obstruction of the folds, the nitrogen gas is mainly concentrated in the gap between the first and second layers, while the unfolding speed of the remaining layers is slow. From 35-60ms, the membrane sphere mainly unfolds axially. In this stage, gas flows from the folds into the gaps between the remaining layers, gradually opening up the folds. By 50ms, the gas has completely entered the model, and the folds are completely unfolded by 65ms. In the 60ms-stabilization stage, inflation has ended, and the membrane sphere is in an oscillation phase, gradually stabilizing after 160ms. During the deployment process, stress is mainly concentrated at the folds. After unfolding, stress is concentrated at the single-lobe bonding position. After the membrane sphere is fully stabilized, the error compared with the theoretical 1m sphere is less than 5%, proving the accuracy of this folding modeling scheme.

[0142] Step Four: The attitude control module adjusts the primary satellite's three-axis attitude angles and angular velocities by changing the three-axis angular momentum of the control moment gyroscope assembly. This maneuvers the deorbit-measurement system's attitude to a stable equilibrium position with the sphere in front and the satellite behind. Simultaneously, it transmits its own three-axis angular momentum, the primary satellite's three-axis attitude angles, and angular velocities back to the onboard computer. Figure 7 As shown. The patch-type pressure sensor starts working, measuring the force at the current position and time by the change in resistance caused by force deformation, and then obtaining the resultant force on the deorbit-measurement system through the patch-type pressure sensors arranged on the surface of the sphere. The deorbit-measurement system includes two parts: a constellation of satellites and a low-Earth orbit atmospheric density measurement device that performs deorbit-measurement in parallel.

[0143] Figure 7 The curves showing the Euler angle changes of the off-track-measurement system under the action of the attitude control system.

[0144] Step 5: Based on the resultant force on the deorbit-measurement system obtained in Step 4, perturbation factors unrelated to atmospheric drag, including solar radiation pressure, higher-order Earth gravity, and lunar gravity, are removed through high-precision theoretical calculations. Then, combined with the orbital data, shape and structure, and drag coefficient of the deorbit-measurement system, the atmospheric density of the area it passes through is calculated in real time.

[0145] Figure 8 The deorbit-measurement system perturbation acceleration is calculated under multi-source perturbation. The initial perturbation force is calculated; the solar radiation pressure perturbation force is [-2.5296 × 10⁻⁶]. -5 -4.588×10 -6 -1.9949×10 -6 The higher-order non-spherical gravitational force of Earth is [-0.03749.1621×10 N]. -18 0]N, the gravitational pull of the Sun and Moon is [-2.9376×10] -7 -5.3247×10 -7 2.8819×10 -7 ]N. The atmospheric drag experienced by the off-orbit-measurement system, calculated using equation (19), is [1.4133 × 10⁻⁶]. -6 -2.8267×10 -4 Substituting 0]N into equation (20), the initial atmospheric density is 4.682 × 10⁻⁶. -13 kg / m 3 .

[0146] Step Six: Based on Steps Four and Five, use patch-type pressure sensors to measure the atmospheric density of the area the constellation satellites pass through during their deorbiting process; based on Step Three, use a spherical thin-film device to inflate and deploy, increasing the windward area of ​​the constellation satellites and improving their deorbiting efficiency; and after achieving the deorbiting of the constellation satellites, measure the atmospheric density of the area they pass through.

[0147] Step 7: Using the existing atmospheric drag model and the real atmospheric density information of the area traversed obtained in Step 5, a self-attention neural network is trained, enabling the agent to accurately predict the real atmospheric density based on the output of the existing atmospheric drag model. This achieves accurate prediction of atmospheric density at any time and any location, constructing a high-precision atmospheric prediction model, which is of great significance for spacecraft orbit determination, orbit prediction, reentry prediction, and space safety.

[0148] Through the technical details and algorithms described above, a device and method for parallel deorbiting and measurement tasks of constellation satellites were finally realized, enabling the measurement of atmospheric density in the areas traversed by constellation satellites during deorbiting. It has the core advantages of low cost, real-time measurement of multiple satellites, and a win-win situation for both deorbiting and detection.

[0149] In summary, the above are merely preferred embodiments of the present invention and are 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 low-Earth orbit atmospheric density measurement device that combines deorbiting and measurement, mounted on the edge of a constellation satellite, wherein the bottom end is fixed to the constellation satellite and the top end is exposed, and connected to the constellation satellite through circuits and a communication network; after the constellation satellite completes its main mission, the device improves the deorbiting efficiency of the constellation satellite and is capable of measuring the atmospheric density of the area traversed by the constellation satellite during the deorbiting process; the constellation satellite includes an onboard computer, a solar panel, a GNSS module, an attitude control module, a communication module A, and a constellation satellite outer shell; The onboard computer is used to perform the following functions: first, to control the folding and unfolding state of the solar panels and to control the angle of the solar panels relative to the constellation satellites based on the position data obtained by the GNSS module and the position data of the sun; second, to control the frequency of data acquisition by the GNSS module and to read the position data obtained by the GNSS module. Third, the attitude control module controls the maneuvering of the constellation satellites and maintains their stability. It also reads the current angular momentum state of the attitude control module and unloads momentum when the satellites are about to reach their limit. Fourth, the communication module A communicates with the ground base station, adjacent constellation satellites, and the communication module B of the low-Earth orbit atmospheric density measurement device, and processes the returned atmospheric density values, orbit, attitude, and command execution status information. Fifth, it reads and processes the data from the patch-type pressure sensor of the atmospheric density measurement device to calculate the atmospheric density value. Sixth, it controls the pressure unlocking mechanism of the atmospheric density measurement device to switch from locked to unlocked, thereby controlling the start of the inflation system of the atmospheric density measurement device. The solar panel adopts a folding structure, with solar cells attached to both sides of the panel. The solar panel is fixed to the outside of the constellation satellites. The solar panel absorbs solar energy and converts it into electrical energy to provide power to the constellation satellites and the low-Earth orbit atmospheric density measurement device. The GNSS module is fixed inside the outer shell of the constellation satellites; the GNSS module is used to acquire the current position and velocity data of the constellation satellites and transmit the data to the onboard computer. The attitude control module uses a control torque gyroscope assembly, and the attitude control module is fixed to the inside of the constellation satellite shell; The attitude control module adjusts the three-axis attitude angles and angular velocities of the constellation satellites by changing the three-axis angular momentum of the control torque gyroscope assembly, and at the same time transmits its own three-axis angular momentum, the three-axis attitude angles and angular velocities of the constellation satellites back to the onboard computer. Communication module A is fixed to the inside of the satellite's outer shell; communication module A communicates with ground base stations, adjacent satellites in the constellation, and communication module B in the low-orbit atmospheric density measurement device, and transmits data bidirectionally. The main body of the constellation satellite shell is rectangular, and all components of the constellation satellite except the constellation satellite shell are fixed by bolts and internal partitions; The device is characterized in that: the low-orbit atmospheric density measuring device that combines deorbiting and measurement includes a device shell, a diaphragm sphere, an inflation system, a patch-type pressure sensor, a clamping and unlocking mechanism, and a communication module B; The main body of the device shell is a hollow cuboid with one open side and a partition in the middle. All components of the low-orbit atmospheric density measuring device except the device shell are fixed by a clamping and unlocking mechanism, bolts and internal partitions, while isolating each component. The shell is made of alloy structural material. The side of the device shell that fixes the inflation system is called the bottom end, which is fixed to the constellation satellites. The side of the device shell that fixes the thin film sphere is called the top end. The membrane sphere is folded and sealed by a pressing and unlocking mechanism, and is fixed inside the device housing. The membrane sphere is connected to the inflation system. The membrane sphere is inflated and unfolds into a spherical shape by the inflation system, which increases the drag effect of environmental perturbations on the constellation satellites. At the same time, the patch-type pressure sensor on the surface of the membrane sphere measures the force on the constellation satellites. Based on the force on the constellation satellites, the atmospheric density of the area passed through by the constellation satellites during the deorbiting process is measured. The inflation system has built-in gas-generating material and a perforated plate throttling component. The inflation system is connected to the membrane sphere through a pipeline and uses the perforated plate throttling component to control the inflation speed. The inflation system inflates the membrane sphere, causing the folded membrane sphere to expand into a spherical shape. The patch pressure sensor adopts a thin-film structure; the patch pressure sensor is connected to the satellite's onboard computer via communication module B; the patch pressure sensor is distributed on the surface of the thin-film sphere, and when the thin-film sphere is fully expanded, the force on the patch pressure sensor at the current position and time is measured by the resistance change caused by the force deformation; the patch pressure sensors are arranged in groups on the surface of the thin-film sphere, and vector calculations are performed based on the data and layout of all patch pressure sensors to obtain the force on the constellation satellites, and the atmospheric density of the area traversed by the constellation satellites during deorbiting is measured based on the force on the constellation satellites; The clamping and unlocking mechanism includes explosive bolts and a top cover. The explosive bolts are distributed at the four corners inside the top cover, fixing the top cover to the top of the device housing. The top cover is a rectangular alloy sheet with the same size as the device housing. In the locked state, the top cover clamps the folded membrane ball. The explosive bolts contain explosives and an igniter. In the unlocked state, the explosives are detonated, causing the shear lock to shear or break along the bolt weakening groove, thus separating and unlocking the device housing and the top cover, releasing the clamping on the membrane ball, and allowing the membrane ball to inflate and unfold. Communication module B is fixed to the inside of the device housing; communication module B communicates with communication module A and the onboard computer, and transmits data bidirectionally.

2. A method for measuring low-orbit atmospheric density in parallel with deorbiting, implemented based on the low-orbit atmospheric density measuring device for parallel deorbiting and measurement as described in claim 1, characterized in that: Includes the following steps, Step 1: Based on the parallel off-orbit measurement task indicators, determine the size, number of folds, and folding amount per fold in the low-orbit atmospheric density measurement device for parallel off-orbit measurement, and determine the pressure sensor patch layout on the surface of the thin film sphere according to the size, number of folds, and folding amount per fold; the parallel off-orbit measurement task indicators include off-orbit time, folding efficiency, folding stress, and measurement accuracy; Step 2: Based on the dimensions, number of folds, fold amount per fold, and pressure sensor patch layout of the thin-film sphere of the parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device determined in Step 1, the parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device is packaged into an independent module and mounted on the constellation satellite; the parallel deorbiting-measurement low-Earth orbit atmospheric density measurement device is mounted on the edge of the constellation satellite, with the bottom end fixed to the constellation satellite and the top end exposed, and connected to the constellation satellite through circuits and communication networks; Step 3: After the constellation satellites complete their main mission, they execute a parallel deorbiting and measurement mission. After receiving ground signals, the onboard computer issues instructions to activate a low-orbit atmospheric density measurement device that combines deorbiting and measurement, which is received by the communication module B. First, the explosive bolts of the pyrotechnic device are detonated, causing the shear lock to break or disconnect along the bolt weakening groove, thus separating and unlocking the device's outer shell and top cover, releasing the pressure on the membrane sphere. Then, the inflation system begins to supply gas, and the membrane sphere unfolds in a controlled manner. Step 4: The attitude control module adjusts the three-axis attitude angle and angular velocity of the primary satellite by changing the three-axis angular momentum of the control torque gyroscope assembly, maneuvering the deorbit-measurement system to a stable equilibrium position with the sphere in front and the satellite behind. Simultaneously, it transmits its own three-axis angular momentum, the primary satellite's three-axis attitude angle, and angular velocity back to the onboard computer. The patch-type pressure sensor begins operation, measuring the force at the current position and moment through resistance changes caused by force deformation. The resultant force on the deorbit-measurement system is obtained through patch-type pressure sensors positioned on the sphere's surface. The deorbit-measurement system comprises two parts: constellation satellites and a parallel low-Earth orbit atmospheric density measurement device. Step 5: Based on the resultant force on the deorbit-measurement system obtained in Step 4, perturbation factors unrelated to atmospheric drag, including solar radiation pressure, higher-order Earth gravity, and lunar gravity, are removed through high-precision theoretical calculations. Then, combined with the orbital data, shape and structure, and drag coefficient of the deorbit-measurement system, the atmospheric density of the area it passes through is calculated in real time. Step Six: Based on Steps Four and Five, use patch-type pressure sensors to measure the atmospheric density of the area the constellation satellites pass through during their deorbiting process; based on Step Three, use a spherical thin-film device to inflate and deploy, increasing the windward area of ​​the constellation satellites and improving their deorbiting efficiency. After achieving the deorbiting of the constellation satellites, measure the atmospheric density of the area they pass through.

3. The low-orbit atmospheric density measurement method as described in claim 2, characterized in that: The implementation method for step one is as follows: Step 1.1: Calculate the dimensions of the membrane sphere based on the mass, size, orbital altitude, initial deorbit date, and deorbit time of the constellation satellites; The rate of change of the orbital state vector of a constellation satellite is defined as In the formula, r is the position vector of the constellation satellites, and v is the velocity vector of the constellation satellites. These represent the accelerations caused by atmospheric drag, solar radiation pressure, central gravitational force considering J2 perturbation, and lunar perturbation, respectively. The drag on the constellation satellites is calculated based on the orbital dynamics model. The relationship between the average force and the surface-to-mass ratio, orbital altitude, and initial deorbit date within one orbital period is analyzed. Based on the deorbit mission requirements, the size of the membrane sphere is obtained through iterative calculations. Step 1.2: Using a folding method combining planar spiral bonding and Z-shaped folding, determine the number of folds and the amount of each fold for the thin film sphere of the low-orbit atmospheric density measurement device that operates in parallel with off-orbit measurement; the specific folding method is as follows: after sequentially spiral bonding multiple planar single lobes of the thin film sphere, Z-shaped folding is performed to fold it into a cubic shape; Step 1.2.1: Sequentially spirally bond the multiple planar lobes of the membrane sphere; The diameter of the film spheres varies, and the number of lobes j is selected based on the premise that the maximum width of each lobe is less than 50cm. The lobes are arranged vertically and numbered gradually from bottom to top. Planar spiral bonding is a vivid description of the lobe bonding scheme. From the side, the shape of the bonded planar structure is similar to the spiral structure of a snail shell. The planar spiral bonding method is different when j / 2 is odd or even. ① When j / 2 is an even number, the steps for planar spiral bonding are as follows: Step 1: Glue the right boundary of the j / 2-1 and j / 2th single lobes; Step 2: Attach the left edges of the j / 2 and j / 2+1th lobes; and the left edges of the j / 2-1 and j / 2+2th lobes. Step 3: Glue the right boundary of the j / 2+1 and j / 2-2 lobes; glue the right boundary of the j / 2+2 and j / 2-3 lobes. …… By doing so, the left and right boundaries of the single petals are bonded together to form a spiral structure; Final step: Bond the right boundary of the (j-1)th and jth single lobes to complete the planar spiral bonding; ②When j / 2 is an odd number, the steps for planar spiral bonding are as follows: Step 1: Glue the left boundaries of the j / 2th and j / 2+1th single lobes; Step 2: Attach the right boundary of the j / 2th and j / 2-1th lobes; and the left boundary of the j / 2+1th and j / 2-2th lobes; Step 3: Glue the left edges of the j / 2-1 and j / 2+2 lobes; the left edges of the j / 2-2 and j / 2+3 lobes. …… By doing so, the left and right boundaries of the single petals are bonded together to form a spiral structure; Final step: Bond the right boundary of the (j-1)th and jth single lobes to complete the planar spiral bonding; Step 1.2.2: The model formed by sequentially spirally bonding multiple planar single lobes of the thin film sphere is folded in a Z-shape, and finally folded into a cube shape for easy encapsulation; The Z-folding method is similar to the letter "Z," and is divided into axial and circumferential Z-folds. The axial fold is along the longest axis of a single lobe, and the circumferential fold is along the direction perpendicular to the axial direction. Z-folding can increase the axial height, reduce the circumferential area, and improve folding efficiency. Its main folding parameters are as follows: Where C z Let l be the number of folds, l be the amount of folding each time, D be the diameter of the sphere, and d be the side length after folding. Step 1: Circumferential Z-shaped folding. Fold upwards along the circumferential axis according to the selected folding amount each time, and so on, continuously folding to reduce the circumferential length; Step 2: Axial Z-shaped folding. Similar to the circumferential folding, fold in a "Z" shape according to the selected folding amount each time. Step 1.3: Based on the diaphragm sphere size determined in Step 1.1 and the number of folds and the amount of each fold determined in Step 1.2, arrange the patch pressure sensors on the surface of the diaphragm sphere; The layout of the patch pressure sensor meets the following constraints: the patch of the patch pressure sensor is axially symmetrically distributed on the surface of the thin film sphere. Due to the axial symmetry, it is convenient to measure the force on the thin film sphere and facilitate subsequent atmospheric density inversion calculations; the patch pressure sensor layout includes multiple arrays, with one array on each lobe, and the measurement range of the patch pressure sensor layout covers the surface of the thin film sphere; the patch pressure sensor layout avoids being located at the creases of the thin film sphere and the ends of the lobes; the size of the patch pressure sensor is determined according to the curvature of the thin film sphere, so that the size of the patch pressure sensor is adapted to the curvature of the thin film sphere, and the ratio of the perpendicular distance between the edge of the patch pressure sensor and the surface of the thin film sphere to the size of the patch pressure sensor does not exceed 0.2; the shape of the patch pressure sensor should not produce sharp corners.

4. The low-orbit atmospheric density measurement method as described in claim 3, characterized in that: Step four is implemented as follows: Step 4.1: An attitude control method based on sliding mode control is adopted. In sliding mode control, feedforward control is used to counteract the influence of aerodynamic torque and improve the response rate of attitude control. Based on this control method, the attitude control module maneuvers the attitude of the deorbit-measurement system to a balanced position with "sphere in front and satellite behind" and maintains stability. To describe the attitude and trajectory of the off-track measurement system, a spherical coordinate system, a velocity coordinate system, and a body coordinate system are established. The spherical coordinate system is established with the center of the thin-film sphere as the origin, and the Y-axis coincides with the velocity direction of the off-track measurement system. The X-axis lies in the orbital plane and is perpendicular to the Y-axis, with the direction from the Earth's center to the origin of the coordinate system being positive. The Z-axis conforms to the right-hand rule. The origin of the velocity coordinate system is the center of mass of the off-track measurement system. o The axis and the off-track measurement system have the same velocity direction; x o The axis lies in the orbital plane and is perpendicular to y. o The z-axis, with the positive direction pointing from the Earth's center to the origin of the coordinate system; o The axes conform to the right-hand rule; the origin of the body coordinate system is the centroid of the off-track-measurement system, where y b The axis coincides with the central axis of the deorbit-measurement system, pointing from the satellite toward the sphere, which conforms to the right-hand rule; The attitude of the off-track measurement system is controlled using a sliding mode control law; based on the selection method of the sliding mode surface, an appropriate sliding mode surface is selected, and the sliding mode switching surface function is: s=ω e +kq ve (4) Where k is the controller parameter; The current attitude angular velocity of the deorbit-measurement system is ω, and the desired attitude angular velocity is ω. d ,but oh e =oh-oh r (5) Where, ω r =C bo ω d C bo This is the transformation matrix from the orbital coordinate system to the body coordinate system; Due to the presence of the diaphragm sphere in the off-track measurement system, the windward area and center-of-mass distance of the off-track measurement system increase, resulting in the influence of aerodynamic torque being much greater than other torques, becoming the main factor affecting the attitude of the off-track measurement system. In order to make the control smoother and more stable, feedforward control is used to counteract the influence of aerodynamic torque. With feedforward control, when the controlled variable has not changed after the disturbance is generated, the control is performed according to the magnitude of the disturbance to compensate for the influence of the disturbance on the controlled variable. Direct control has no lag and improves the response rate of the off-track measurement system. The feedforward control term is shown in formula (6). u0=ρ P ×F A_b (6) The designed sliding mode variable structure control law is Where I is the moment of inertia of the off-track measurement system. Let I3 be the error quaternion, I3 be the third-order identity matrix, and ρ be the error quaternion. P F is the position vector of the center of gravity of the off-track-measuring system in the body coordinate system. A_b Let sgn(s) be the aerodynamic torque experienced by the off-track measurement system in the body coordinate system. i Let F(s) be a symbolic function, and its expression is: F(s)={sgn(s1),sgn(s2),sgn(s3)} T (8) Step 4.2: Based on the strain effect of resistance, the magnitude of the force acting on the patch pressure sensor is obtained, and the direction of the force is obtained according to the patch layout. The force vectors of all patch pressure sensors are added together to obtain the resultant force acting on the off-track measurement system. The number of patch pressure sensors is N, and the coordinates of patch pressure sensor i in the spherical coordinate system are [x...]. i y i z i ] T The force it experiences is F i The radius of the thin film sphere is R; the resultant force on the off-track measurement system is obtained as follows: In the formula, C lN This is the transformation matrix from the spherical coordinate system to the inertial system.

5. The low-orbit atmospheric density measurement method as described in claim 4, characterized in that: Step five is implemented as follows: Step 5.1: Add the influence of the Earth's shadow model, represented by the solar visibility coefficient, to the basic solar radiation pressure perturbation model, and add the real-time solar position correction composed of the actual date and the obliquity of the ecliptic to obtain a solar radiation pressure perturbation model that considers the Earth's shadow and real-time influence, thereby improving the accuracy of the solar radiation pressure perturbation force on the off-orbit-measurement system; The solar radiation pressure perturbation force is expressed as follows: In the formula, r is the position vector of the off-track measurement system, and K S The solar visibility coefficient at the location of the off-orbit measurement system is represented by R; R is the radius of the thin film sphere; p SR η is the solar pressure in 1 astronomical unit (AU), and η is the reflection coefficient. ε is the obliquity of the ecliptic, λ is the solar longitude; floor(X) represents the largest integer not greater than X; the current year, month, and day are represented as year, month, and day; Step 5.2: Add a higher-order Earth gravity field model characterized by geocentric distance, geographic latitude and longitude, associated Legendre polynomial, and Earth gravitational potential coefficient to the basic central gravity model, thereby improving the accuracy of the off-orbit-measurement system under Earth's gravity. The expression for the component of gravity acting on the off-orbit measurement system is: In the formula, θ e denoted as latitude and longitude of the off-orbit measurement system; m as mass of the off-orbit measurement system; μ as the Earth's gravitational constant; n and k as the order and degree of the Earth's gravity field model, respectively. The Earth's gravitational potential coefficient is determined by the Earth's mass distribution. For fully normalized associative Legendre polynomials, R e It is the Earth's average equatorial radius; Step 5.3: Calculate the gravitational forces exerted on the off-orbit-measurement system by the Sun and Moon based on the position vector and mass of the off-orbit-measurement system; The sun and moon exert gravitational pull on the off-orbit measurement system. In the formula, μ sun μ moon The gravitational constants of the Sun and the Moon, respectively; r sun r moon These are the position vectors of the Sun and the Moon in the inertial coordinate system, respectively. Step 5.4: Based on the resultant force on the deorbit-measurement system obtained in Step 4, the solar radiation perturbation force on the deorbit-measurement system obtained in Step 5.1, the higher-order Earth gravity on the deorbit-measurement system obtained in Step 5.2, and the gravitational forces of the Sun and Moon on the deorbit-measurement system obtained in Step 5.2, calculate the atmospheric drag on the deorbit-measurement system. F A =F B -F U -F S -F T (20) Step 5.5: Based on the atmospheric drag on the deorbit-measurement system obtained in Step 5.4, calculate the real-time atmospheric density according to the atmospheric drag expression, combined with the orbital data, shape and structure of the deorbit-measurement system, and drag coefficient. The expression for atmospheric drag on the off-orbit measurement system is: In the formula, Q is the molecular velocity ratio, σ n The adjustment coefficient is ρ, where ρ is the atmospheric density, v is the velocity vector of the off-orbit-measurement system, and ω is the velocity vector. e denoted as ω, where ω is the Earth's rotational angular velocity, and α is the semi-major axis of the off-orbit-measurement system orbit.

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