A sun-synchronous orbit design method for remote sensing satellite based on revisit characteristics

Abstract

A method of sun-synchronous orbit design for remote sensing satellite based on revisit characteristics is proposed. The relationship between revisit and ground synchronization is established by Q value. The mathematical model of Q is established by node revisit sequence in a certain interval. Then the coverage rate is obtained by the mixed node access sequence and coverage area of orbit altitude and observation angle. Finally, the coverage rate of remote sensing satellite in sun-synchronous orbit is demonstrated from three aspects of time-varying coverage rate, minimum coverage time and minimum observation angle, which provides a reference for the design of sun-synchronous orbit of remote sensing satellite.

Description

Technical Field

[0001] This invention relates to a method for designing a sun-synchronous orbit for remote sensing satellites based on revisit characteristics, belonging to the field of sun-synchronous orbit satellite design. Background Technology

[0002] In recent years, Earth observation satellite technology, such as remote sensing satellites, has made great strides, achieving observation resolutions at the meter level or even below, and finding wide applications in military, civilian, and other fields. The payloads carried by remote sensing satellites, such as optical cameras, require stable lighting conditions; therefore, sun-synchronous orbits are frequently used as the design orbits for remote sensing satellites.

[0003] Global coverage is a crucial parameter for Earth observation satellites, and many scholars have conducted extensive research on coverage characteristics in sun-synchronous orbits. Casey and Way introduced the concepts of Q-value and geosynchronous orbit access order, and applied them to single repeat geosynchronous orbits (RGTs).

[0004] The Q value represents the number of times a satellite orbits the Earth within a single SSO orbital day. A PEO is defined as a solar day, and Pnod is the satellite's orbital period. The constraint expression for RGT is: DPEO = NPnod

[0005] Where D and N are irreducible integers, D is the number of days in a revisit orbit, and N is the number of orbital periods experienced by a satellite in one revisit. The definition of the Q value is given, where v is a positive integer:

[0006]

[0007] To ensure efficient coverage, Aorpimai and Palmer proposed an orbital control strategy for Earth observation satellites based on orbital elements, known as the "cyclic element" method. Constellation design and revisit orbit theory show that the orbits used by HJ-1A / 1B have achieved global coverage. However, this method cannot be directly applied to the design of sun-synchronous orbits for coverage performance. Currently, few studies have investigated the coverage characteristics of sun-synchronous orbits. Summary of the Invention

[0008] The technical problem solved by this invention is: addressing the lack of a design method in the existing technology that can directly study the coverage characteristics of sun-synchronous orbits, a design method for sun-synchronous orbits of remote sensing satellites based on revisit characteristics is proposed.

[0009] The present invention solves the above-mentioned technical problem through the following technical solution:

[0010] A method for designing a sun-synchronous orbit for remote sensing satellites based on revisit characteristics, comprising the following steps:

[0011] (1) Set the basic parameters of the remote sensing satellite orbit;

[0012] (2) Based on step (1), define network nodes and base nodes on the remote sensing satellite orbit;

[0013] (3) Establish a D-day repeated orbital access model;

[0014] (4) Establish a unitized orbital node access model;

[0015] (5) Calculate the relative coverage of Earth observation satellites on the equator based on the models established in steps (3) and (4);

[0016] (6) Calculate the satellite coverage using the data obtained in step (5), and perform global coverage characteristic analysis based on the calculated data.

[0017] In step (1), the basic parameters of the remote sensing satellite orbit include:

[0018] The number of orbits Q of a sun-synchronous orbit satellite around the Earth within a day, and the number of solar days P. EO Satellite orbital period P nod The number of days (D) for a return RGT orbit, the number of orbital periods (N) for a revisiting satellite, and the Earth's equatorial radius (R) are also included. e The remote sensing satellite camera angle α, the bottom roll angle β, and the observation angle γ are all given, where γ = β + 0.5α. v and d are calculated parameters, where v is a positive integer, and the calculation formula is:

[0019]

[0020] In step (2), the specific steps for defining network nodes and base nodes are as follows:

[0021] (2-1) Based on the number of orbits N completed by the remote sensing satellite within the number of days D in its return orbit, the Earth's equator N is divided into N ascending nodes, i.e., network nodes. The distance between adjacent nodes is calculated as the equatorial grid spacing δ. g :

[0022]

[0023] (2-2) Based on the number of times the remote sensing satellite orbits the Earth (Q) in one day, determine the base nodes to be visited. Two consecutive ascending nodes in chronological order are considered adjacent base nodes. Calculate the distance δ between adjacent base nodes. b :

[0024]

[0025] In the formula, ω EW is the Earth's rotational angular rate. Ω This is the long-term perturbation term of the right ascension of the ascending node.

[0026] In step (3), adjacent base nodes after the starting point are selected, the network nodes among them are marked, the node numbers from 0 to D are obtained, a D-day regression orbit access model is established, and the rising node position at the base interval on the k-th day is calculated:

[0027] y k = mod(kd, D) 0 < k < D

[0028] In the formula, k is the number of days, and d is the calculation parameter.

[0029] In step (4), the base distance of the RGT orbit is calculated based on the RGT orbit of the remote sensing satellite rotating around the equator. Using the obtained base distance as the unit length, the fractional part of the number of times the satellite orbits the Earth Q within one solar day is calculated:

[0030] f = Q - [Q]

[0031] In the formula, [Q] represents the floor function of Q, and f = d / D is used to calculate the position x of the node on the k-th day of the SSO orbit. k :

[0032] x k =k f -[k f ].

[0033] In step (5), the specific formula for calculating the relative coverage rate is as follows:

[0034]

[0035] γ = β + 0.5α;

[0036] In the formula, h is the altitude of the remote sensing satellite above the ground, W is the coverage rate (in L), and w is the relative coverage rate.

[0037] In step (6), the formula for calculating satellite coverage is: C k =C k-1 +ΔC k ;

[0038] In the formula, C k Let be the coverage rate on day k, and let w be the coverage rate on day 1, ΔC k This represents the coverage increment on day k.

[0039] If C k And C k-1 If there is no overlapping region, then ΔC k =w, otherwise ΔC k=x 1，k -x 1，k-1 =x 2，k -x 2，k-1 .

[0040] The advantages of this invention compared to the prior art are:

[0041] (1) This invention provides a method for designing a sun-synchronous orbit for remote sensing satellites based on revisit characteristics. The relationship between revisit and ground synchronization is established using the Q-value. A mathematical model of Q is established based on the node revisit sequence within a defined interval. The coverage rate is then obtained by combining the node revisit sequence and coverage area using orbital altitude and observation angle. Finally, the coverage rate of the remote sensing satellite in its sun-synchronous orbit is demonstrated through three aspects: time-varying coverage rate, minimum coverage time, and minimum observation angle, thus providing a reference for the design of sun-synchronous orbits for remote sensing satellites.

[0042] (2) This invention focuses on the global coverage characteristics at a specific time. Since the capabilities of satellite-borne cameras are limited by time, a detailed analysis of the coverage characteristics within a specified time period is conducted. The patterns of variables are intuitively illustrated through these coverage characteristics, providing significant guidance and practical value for the design of sun-synchronous orbit remote sensing satellites. It fills a theoretical gap in the understanding of sun-synchronous orbit coverage characteristics and is widely applicable. Verification of existing sun-synchronous orbit remote sensing satellite parameters demonstrates that the proposed method is simple, effective, and helps shorten the design time for sun-synchronous orbits. Attached Figure Description

[0043] Figure 1 A diagram of equatorial node numbers provided for the invention;

[0044] Figure 2 A diagram of the D-day repeating orbit access sequence provided for the invention;

[0045] Figure 3 A node access sequence diagram of the SSO track provided for the invention;

[0046] Figure 4 A schematic diagram of the satellite's observable range provided for the invention;

[0047] Figure 5 A schematic diagram of the first-day coverage provided for the invention;

[0048] Figure 6 A schematic diagram of the overlapping and separating regions between day k-1 and day k provided for the invention;

[0049] Figure 7 A schematic diagram of SSO orbital coverage provided for the invention;

[0050] Figure 8A diagram illustrating the time required for global coverage of the invention;

[0051] Figure 9 A schematic diagram illustrating the relationship between the Q value and the minimum observation angle for achieving global coverage over a specific duration, provided for the invention; Detailed Implementation

[0052] A design method for sun-synchronous orbits of remote sensing satellites based on revisit characteristics is proposed, applicable to the design of sun-synchronous orbit satellites sensitive to global coverage characteristics. First, the revisit sequence of the sun-synchronous orbit is given by analyzing the characteristics of the orbit. Then, considering the limitations of the camera capabilities carried by the satellite, an effective method to obtain coverage capability within a specific time period is proposed. Finally, the effectiveness of this method in providing global coverage performance under a specific observation angle is verified using existing satellite parameters.

[0053] The specific design method and steps are as follows:

[0054] (1) Set the basic parameters of the remote sensing satellite orbit;

[0055] The basic parameters of remote sensing satellite orbits include:

[0056] The number of orbits Q of a sun-synchronous orbit satellite around the Earth within a day, and the number of solar days P. EO Satellite orbital period P nod The number of days (D) for a return RGT orbit, the number of orbital periods (N) for a revisiting satellite, and the Earth's equatorial radius (R) are also included. e The remote sensing satellite camera angle α, the bottom roll angle β, and the observation angle γ are all given, where γ = β + 0.5α. v and d are calculated parameters, where v is a positive integer, and the calculation formula is:

[0057]

[0058] (2) Based on step (1), define network nodes and base nodes on the remote sensing satellite orbit;

[0059] The specific steps for defining network nodes and base nodes are as follows:

[0060] (2-1) Based on the number of orbits N completed by the remote sensing satellite within the number of days D in its return orbit, the Earth's equator N is divided into N ascending nodes, i.e., network nodes. The distance between adjacent nodes is calculated as the equatorial grid spacing δ. g :

[0061]

[0062] (2-2) Based on the number of times the remote sensing satellite orbits the Earth (Q) in one day, determine the base nodes to be visited. Two consecutive ascending nodes in chronological order are considered adjacent base nodes. Calculate the distance δ between adjacent base nodes. b :

[0063]

[0064] In the formula, ω E W is the Earth's rotational angular rate. Ω The long-term perturbation term of the right ascension of the ascending node;

[0065] (3) Establish a D-day repeated orbital access model;

[0066] In this process, adjacent base nodes after the starting point are selected, and the network nodes within them are marked to obtain node numbers from 0 to D. A D-day regression orbit access model is established, and the position of the ascending node at the base interval on the k-th day is calculated.

[0067] y k = mod(kd, D) 0 < k < D

[0068] In the formula, k is the number of days, and d is the calculation parameter;

[0069] (4) Establish a unitized orbital node access model;

[0070] Specifically, based on the RGT orbit of the remote sensing satellite revolving around the equator, the base distance of the RGT orbit is calculated. Using the obtained base distance as a unit length, the fractional part of the number of times the satellite orbits the Earth (Q) within one solar day is calculated:

[0071] f = Q - [Q]

[0072] In the formula, [Q] represents the floor function of Q, and f = d / D is used to calculate the position x of the node on the k-th day of the SSO orbit. k :

[0073] x k =k f -[k f ];

[0074] (5) Calculate the relative coverage of Earth observation satellites on the equator based on the models established in steps (3) and (4);

[0075] The specific formula for calculating relative coverage is as follows:

[0076]

[0077] γ = β + 0.5α;

[0078] In the formula, h is the altitude of the remote sensing satellite above the ground, W is the coverage rate (in L), and w is the relative coverage rate;

[0079] (6) Calculate the satellite coverage using the data obtained in step (5), and perform global coverage characteristic analysis based on the calculated data;

[0080] The formula for calculating satellite coverage is: C k =C k-1 +ΔC k ;

[0081] In the formula, C k Let be the coverage rate on day k, and let w be the coverage rate on day 1, ΔC k This represents the increase in coverage on day k.

[0082] If C k And C k-1 If there is no overlapping region, then ΔC k =w, otherwise ΔC k =x 1，k -x 1，k-1 =x 2，k -x 2，k-1 .

[0083] The following is a further explanation based on specific embodiments:

[0084] In the current embodiment, the design of a sun-synchronous orbit for a remote sensing satellite with revisit characteristics mainly includes the following steps:

[0085] (1) Set basic parameters;

[0086] The remote sensing satellite orbits in sun-synchronous circular orbits, considering only the influence of Earth's central gravity. The Q value represents the number of times a satellite in an SSO orbit orbits the Earth within a day, and P... EO A solar day is given, Pnod is the satellite's orbital period. D is the number of days in a return orbit, and N is the number of orbital periods the satellite goes through in one revisit. Re is the Earth's equatorial radius, taken as 6378.2 km. α is the camera's viewing angle, β is the satellite's bottom roll angle, and γ = β + 0.5α is defined as the satellite's observation angle.

[0087] A solar day P EO =86400s

[0088] Earth's equatorial radius R e =6378.2km

[0089] (2) Define network nodes and base nodes;

[0090] Define the network nodes and base nodes. The RGT orbit will complete N orbits around the Earth in D days. Therefore, N rising nodes divide the Earth's equator into N equal parts (the same applies to falling nodes). The distance between two nodes is defined as the grid spacing δ at the equator. g :

[0091] Network Nodes

[0092] Additionally, a satellite orbits the Earth Q times in a day, and the distance between two consecutively visited nodes is called the "equatorial unit interval," or base station distance.

[0093] base node

[0094] Where, ω E W is the Earth's rotational angular rate. Ω The long-term perturbation term is the right ascension of the ascending node. Q is the number of times the satellite orbits the Earth in one day;

[0095] Where ω E W is the Earth's rotational angular rate. Ω The long-term perturbation term of the right ascension of the ascending node;

[0096] Existence relation: δ b =Dδ g ;

[0097] N nodes distributed along the equator can be used to parameterize the access conditions (DPEO) within a single cycle. However, this method can lead to unnecessary data redundancy when the orbital period is long. Considering the characteristics of the RGT orbit, nodes in the base interval are used to describe the characteristics of the access orbit. Substituting into the above equation, we can obtain the relationship between the grid spacing and the base spacing, i.e., δ. b =Dδ g Therefore, one base spacing can be divided into D grid spacings;

[0098] (3) Establish a unitized orbital node access model.

[0099] For engineering solutions, there is no need to establish a D-day repeated orbital access model; a unitized orbital node access model can be established directly.

[0100] If the base spacing is defined as a unit length, then the fractional part of the Q value can be calculated by the following formula:

[0101] f = Q - [Q]

[0102] Where [Q] is the floor function of Q, then f = d / D. For the SSO orbit, the position of the node on day k is x. k =y k / D, therefore we can obtain:

[0103] x k =k f -[k f ]

[0104] like Figure 3 As shown, the normalized SSO orbital node access order is given. After obtaining the fractional form of the node access order expression, the coverage can be automatically calculated by computer.

[0105] Under normal circumstances, a D-day repeated orbital visit model is established. Taking a base distance after the starting point as an example, the number of nodes on the equator can be marked as follows: Figure 1 As shown. The numbers outside the arc (from N to ND) are the node numbers, and the corresponding numbers inside the arc (from 0 to D) are the numbers used in this paper. Additionally, Yk / yk is the position node on day k. Therefore, the position of the y-th node on day k can be obtained by the following formula:

[0106] y k = mod(kd, D) 0 < k < D

[0107] The resulting diagram illustrating the RGT orbit revisit sequence within D days is as follows: Figure 2 As shown;

[0108] (4) Calculate the relative coverage rate.

[0109] Define the camera's viewing angle α and the satellite's bottom roll angle β. The satellite's observation angle is defined as γ = β + 0.5α, as follows: Figure 4 The figure shows the coverage of Earth observation satellites along the equator, from which the formula for the coverage area is derived:

[0110]

[0111] Relative coverage is defined as coverage area W and inter-baseline distance δ. b The ratio of coverage to coverage. The formula for calculating relative coverage w is:

[0112]

[0113] (5) Calculate satellite coverage.

[0114] A base station can be selected to represent the coverage characteristics of a satellite. If a satellite can completely cover that base station for a period of time, then the satellite can achieve global coverage.

[0115] Based on the access order within each base interval, firstly, the coverage on the first day is as follows: Figure 5 As shown. Figure 5 Chinese x 11 and x 21 This is the boundary of the area covered on the first day. Clearly, x... 21 -x11 =w, therefore the coverage C1 on the first day is w.

[0116] And so on, calculate the coverage rate for k days:

[0117] C k =C k-1 +ΔC k

[0118] like Figure 6 As shown, the dividing and overlapping areas displayed in the slice diagram are caused by the nodes of the two days. Figure 6 As shown in a, if C k And C k-1 If there is no overlapping region, then ΔC k =w. Otherwise, then as Figure 6 As shown in b: ΔC k =x 1，k -x 1，k-1 =x 2，k -x 2，k-1 .

[0119] (6) Global coverage characteristics analysis.

[0120] Computer simulations yielded the following SSO orbital coverage data for different numbers of days at a given orbital altitude and satellite observation angle range: Figure 7 This allows us to obtain a map showing the number of days required to achieve global coverage at a given orbital altitude and satellite observation angle, as shown below. Figure 8 It is also possible to obtain the relationship between the Q value and the minimum observation angle for achieving global coverage within a specific number of days, as shown below. Figure 9 .

[0121] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0122] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A method for designing a sun-synchronous orbit for a remote sensing satellite based on revisit characteristics, characterized in that... The steps are as follows: (1) Set the basic parameters of the remote sensing satellite orbit; (2) Based on step (1), define network nodes and base nodes on the remote sensing satellite orbit; (3) Establish a D-day repeated orbital access model; (4) Establish a unitized orbital node access model; (5) Calculate the relative coverage of Earth observation satellites on the equator based on the models established in steps (3) and (4); (6) Calculate the satellite coverage using the data obtained in step (5), and perform global coverage characteristic analysis based on the calculated data; In step (2), the specific steps for defining network nodes and base nodes are as follows: (2-1) Based on the number of orbits N completed by the remote sensing satellite within the number of days D in its return orbit, the Earth's equator N is divided into N ascending nodes, i.e., network nodes. The distance between adjacent nodes is calculated as the equatorial grid spacing. : (2-2) Based on the number of times the remote sensing satellite orbits the Earth in one day, determine the base nodes to be visited. Two consecutive ascending nodes in chronological order are considered as adjacent base nodes. Calculate the distance between adjacent base nodes. : In the formula, This is the Earth's rotational angular rate. The long-term perturbation term of the right ascension of the ascending node; In step (3), adjacent base nodes after the starting point are selected, the network nodes are marked, the node numbers from 0 to D are obtained, a D-day regression orbit access model is established, and the rising node position at the base interval on day k is calculated: In the formula, k is the number of days, and d is the calculation parameter; In step (4), based on the RGT orbit of the remote sensing satellite revolving around the equator, the base distance of the RGT orbit is calculated. Using the obtained base distance as the unit length, the fractional part of the number of times the satellite orbits the Earth Q within one solar day is calculated: In the formula, [Q] represents the floor function of Q. Calculate the position of the node on day k in the SSO orbit. : ； Among them, by using the unitized SSO orbital node access order, the node access order expression in fractional form can be obtained, and then the coverage can be automatically obtained by computer calculation. Under normal circumstances, a D-day repeated orbital visit model is established. Taking a base distance after the starting point as an example, the number of nodes on the equator is marked. The numbers outside the arc from N to ND are the node numbers, and the corresponding numbers inside the arc from 0 to D are the current numbers. Yk / yk is the position node on the k-th day. The position of the y-th node on the k-th day can be obtained by the following formula: ： After calculation, the RGT orbit revisit order within D days is obtained and the relative coverage is calculated; In step (1), the basic parameters of the remote sensing satellite orbit include: The number of orbits Q of a sun-synchronous orbit satellite around the Earth within a day, and the number of solar days P. EO Satellite orbital period P nod The number of days (D) for a return RGT orbit, the number of orbital periods (N) for a revisiting satellite, and the Earth's equatorial radius (R) are also included. e Remote sensing satellite camera perspective The bottom roll angle of remote sensing satellites Remote sensing satellite observation angle ,in, v and d are both calculation parameters, where v is a positive integer, and the calculation formula is: ； In step (5), the specific formula for calculating the relative coverage rate is as follows: ； In the formula, h is the altitude of the remote sensing satellite above the ground, W is in the dimension of L, and w is the relative coverage. In step (6), the formula for calculating satellite coverage is: ; In the formula, C k Let w be the coverage rate on day k, and w be the coverage rate on day 1. C k This represents the increase in coverage on day k. like as well as If there is no overlapping area, then ,otherwise ; Among them, by obtaining a certain orbital altitude and satellite observation angle range through computer simulation, the SSO orbital coverage of different days can achieve the number of days required for global coverage and can achieve global coverage within a specific number of days, so that the relationship between Q value and minimum observation angle meets the requirements.

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