A Global Search Method for Visible Windows of Space Targets Based on Coverage Feature Analysis

Abstract

The present invention discloses a global search method for visible windows of space targets based on coverage characteristic analysis, which relates to the field of aerospace technology and includes: designing a model and its parameters for observing space targets; analyzing the coverage characteristics of an observation satellite for the Earth according to the model of observing space targets and deriving a function of coverage annulus parameters; using geometric relationships to reversely search for visible observation satellites centered on the space target; designing a planning time according to the positioning and tracking convergence situation of the observation satellite for the space target; and completing the global search for visible windows of space targets. The global search method for visible windows of space targets provided by the present invention can quickly judge the visible relationship between the target and multiple satellites, without traversing the time windows of the target and multiple satellites, greatly reducing the time interval for searching visible windows and the sampling points for which the visible relationship needs to be judged, and being beneficial to the rapid response of the input of the observation task window.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerospace, and particularly relates to a global search method for visible windows of space targets based on coverage characteristic analysis. Background Art

[0002] Space target observation tasks have characteristics different from those of ground target observation, such as task randomness, spatio-temporal constraints, logical constraints, completion timeliness, environmental constraints, etc. Therefore, their task planning is more complex. In the face of sudden task requirements, it is necessary to quickly search for satellites that can perform observation tasks for observation.

[0003] Most of the existing research focuses on the task planning and allocation of multi-satellite observation. The window time is default input by the traversal tracking propagation method, and the visible relationship between the target sampling points and the satellites is searched by judging one by one. Although this algorithm has high accuracy and is simple and easy to implement, the calculation amount is too large and the efficiency is too low. The prior literature "Zhang Shengyu. Research on the On-orbit Cooperative Observation Technology of Agile Satellite Multi-targets [D]. Beijing: University of Chinese Academy of Sciences, 2021." discloses an emergency scheduling method for infrared low-earth orbit constellation tasks based on multiple strategies. This method can achieve fast search response for window time, but the accuracy is too dependent on the relative motion analysis between the target and the satellite, and the search efficiency has been improved but still has great limitations. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a global search method for visible windows of space targets based on coverage characteristic analysis to solve the problem of the lack of fast search for time windows in the observation of space targets in the existing technologies; the method of the present invention is used for the fast input of time windows for space target observation events and can achieve fast response to space target observation events.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A global search method for visible windows of space targets based on coverage characteristic analysis of the present invention comprises the following steps:

[0007] S1. Design a model and its parameters for space target observation;

[0008] S2. Analyze the coverage characteristics of the observation satellite on the earth according to the model of the space target observation to deduce the coverage annulus parameter function;

[0009] S3. Use geometric relationships to search for visible observation satellites in reverse with the space target as the center;

[0010] S4. Design the planning time according to the positioning and tracking convergence situation of the observation satellite on the space target;

[0011] S5. Complete the global search of the visible window of the space target.

[0012] Furthermore, the parameters of the space target observation model in S1 include:

[0013] Earth's radius R e , edge height H a 、Space target height H tar , Satellite height H sat , satellite payload maximum detection range L and actual detection range D, limb observation angle θ a and target observation angle θ tar ; When the space object is visible from the satellite, the relationship is expressed as:

[0014] θ tar ≥θ a ,D≤L (1)

[0015] The calculation formula of the limb observation angle is:

[0016]

[0017] The maximum detection distance L of the satellite payload is determined according to the actual situation. Under the model of space target observation, the transmittance can be set to 1 and the background intensity to 0 to obtain the maximum detection distance.

[0018] Furthermore, the S2 specifically includes:

[0019] When the position of the space target has been captured, the visibility of the space target to the satellite is determined; the coverage of the satellite is projected onto the surface of the earth to form a coverage ring centered on the sub-satellite point;

[0020] The inner radius of the ring is R b , the outer radius is R t , the corresponding angle with the center of the earth is θ b and θ t , the width of the covering ring is R d ;in,

[0021] The calculation formula for the inner circle radius is:

[0022]

[0023] The calculation formula for the outer circle radius is:

[0024]

[0025] Where H l Satisfies the following relationship:

[0026]

[0027] The width of the coverage annulus is:

[0028] R d = R t - R b (6)

[0029] From the derivation of the above formula, it can be seen that the width of the coverage annulus is determined by the satellite altitude H sat and the target altitude H tar jointly, and other parameters are regarded as constants; for the circular orbit of constellation satellites, the satellite altitude H sat is set as a constant, while the target altitude H tar is a function that changes with time. Therefore, the width of the coverage annulus, the inner circle radius, and the outer circle radius are only related to the value of H tar ;

[0030] A coverage annulus projected onto the Earth's surface is formed by the model constraints of space target observation.

[0031] Furthermore, the specific content of S3 includes:

[0032] Utilize the characteristic that the sizes of the coverage annuli generated by satellites due to each space target are the same, project a coverage annulus identical to that of the satellite with the sub-satellite point of the target as the center. According to geometric relationships, if the satellite falls into this coverage annulus at this time, it means that the satellite and the space target have visibility, that is, reversely utilize the coverage annulus of the space target to monitor the visibility of constellation satellites to the space target;

[0033] Judge the visibility relationship between the space target and the observation satellite: when the sub-satellite point of the space target falls within the coverage annulus, it means that the relationship between the satellite and the space target is visible; when the sub-satellite point of the space target falls within the inner circle or outside of the coverage annulus, it means that the relationship between the satellite and the space target is invisible.

[0034] Furthermore, the content of S4 includes:

[0035] The minimum observation time T s,min is the shortest duration for the satellite to complete positioning and tracking convergence during observation. When the observation duration of the space target is less than this minimum observation time, it is regarded as an observation failure, and the minimum observation time is set according to the satellite payload capacity; the planning period T s needs to be greater than or equal to the minimum observation time, and the planning period is the minimum step size of mission planning; considering the maneuvering time of the satellite during observation, the minimum observation time, and the re-search for positioning and tracking caused by satellite switching, design a judgment factor E; if the observation and positioning tracking of the space target were achieved in the previous planning period, then E = 1.0, and if no observation was carried out, then take E = 2.0; therefore, the calculation formula for the planning period is:

[0036] T s = E·T s,min (7).

[0037] Further, the S5 specifically includes:

[0038] Use the reverse search algorithm to complete the global visible window search problem of space targets: at the initial moment, calculate and screen out all the satellites that are visible to the space target to form a satellite observation group of the target. Set a certain update planning period, calculate the visible time window of the satellites for the space target within this update planning period until the window time of all the targets to be observed within this update planning period is calculated. After completion, calculate the satellite observation group at the start time of the next period, and so on, to keep the dynamic update of the satellite observation group and the target, so as to achieve the global visible window search.

[0039] In actual calculation, considering the phenomenon that there are satellites that are not visible to the space target at the update grouping moment but have a visible time window for the space target within the planning period, the outer circle radius of the coverage annulus can be appropriately enlarged to achieve the effect of less or even no omission of the window.

[0040] Advantages of the present invention:

[0041] The method of the present invention can quickly judge the visible relationship between space targets and multiple satellites, without traversing the time windows of space targets and multiple satellites, greatly reducing the time interval of visible window search and the sampling points for judging visible relationships, which is beneficial to the rapid response of the input of the observation task window. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the target observation model in the present invention;

[0043] Figure 2 It is a schematic diagram of the reverse monitoring of the target coverage annulus in the present invention;

[0044] Figure 3 It is a flowchart of the global visible window search algorithm obtained in the present invention;

[0045] Figure 4a It is a schematic diagram of the comparison between the visible time window of the present invention and the global visible time window in the example of Target 1;

[0046] Figure 4b It is a schematic diagram of the comparison between the visible time window of the present invention and the global visible time window in the example of Target 2;

[0047] Figure 4c It is a schematic diagram of the comparison between the visible time window of the present invention and the global visible time window in the example of Target 3. DETAILED DESCRIPTION OF THE INVENTION

[0048] For the convenience of those skilled in the art, the present invention will be further described below in conjunction with embodiments and the accompanying drawings. The content mentioned in the embodiments does not limit the present invention.

[0049] A global search method for the visible window of space targets based on coverage characteristic analysis according to the present invention, taking three space targets to be observed as an example, the steps are as follows:

[0050] S1. Design the model and its parameters for observing space targets;

[0051] The parameters of the model for observing space targets include:

[0052] The radius of the earth R e , the limb height H a , the height of the space target H tar , the height of the satellite H sat , the maximum detection distance L and the actual detection distance D of the satellite payload, the limb observation angle θ a and the target observation angle θ tar ; Considering that the observation satellite is an infrared low-earth orbit agile satellite with omnidirectional maneuvering ability, the conditions restricting the observation of space targets are the infrared space background and the maximum detection distance, as Figure 1 shown; When the space target is visible to the satellite, the relationship is expressed as:

[0053] θ tar ≥θ a , D≤L (1)

[0054] Among them, the calculation formula for the limb observation angle is:

[0055]

[0056] The maximum detection distance L of the satellite payload is determined according to the actual situation. Under the model of observing this space target, the transmittance can be set to 1 and the background intensity can be set to 0 to obtain the maximum detection distance.

[0057] Set the orbital parameters of the satellite and the target to be observed; Use a Walker satellite constellation configuration with 32 satellites, 4 orbital planes, and a phase factor of 1 for mission observation. The initial satellite orbital height is 1600 km, the orbital inclination is 60°, and the other orbital elements are all 0. This constellation is only for the convenience of detailed description and analysis of the numerical example, and the satellite orbital parameters can be arbitrarily designed to apply the method of the present invention; The initial orbital parameters of the three targets to be observed are shown in Table 1;

[0058] Table 1

[0059]

[0060]

[0061] The initial time is UTCG 1 May 2022 08:00:00.000, and the minimum observation period T s,min is set to 100 s, and the target appearance duration is set to 1 hour.

[0062] The radius of the Earth R e is 6378.14 km, and the limb height H a is set to 80 km, the maximum detection distance of the payload is 6000 km, the satellite orbit height is 1600 km, and the heights of the three targets are given in Table 1.

[0063] S2. Analyze the coverage characteristics of the observation satellite for the Earth according to the model of the space target observation to derive the coverage annulus parameter function;

[0064] When the position where the space target appears has been captured, the visibility of the space target for the satellite is determined; project the coverage range of the satellite onto the Earth's surface to form a coverage annulus centered on the sub-satellite point;

[0065] Denote the inner radius of the annulus as R b , the outer radius as R t , and the corresponding angles with the Earth's center as θ b and θ t , and the width of the coverage annulus is R d ; where,

[0066] The calculation formula for the inner radius is:

[0067]

[0068] The calculation formula for the outer radius is:

[0069]

[0070] In the formula, H l satisfies the following relationship:

[0071]

[0072] Then the width of the coverage annulus is:

[0073] R d =R t -R b (6)

[0074] From the derivation of the above formula, it can be seen that the width of the coverage annulus is jointly determined by the satellite height H sat and the target height H tar ; for the circular orbit of the constellation satellite, the satellite height H sat is set as a constant, while the target height Htar is a function that changes over time. Therefore, the width of the coverage annulus, the radius of the inner circle, and the radius of the outer circle are only related to the value of H tar ;

[0075] A coverage annulus projected onto the Earth's surface is formed by the model constraints of space target observation.

[0076] S3. Use geometric relationships to search backward for visible observation satellites centered on the space target;

[0077] Utilize the characteristic that the coverage annulus sizes generated by each space target for the satellite are the same. Project a coverage annulus identical to that of the satellite centered on the sub-satellite point of the target. According to geometric relationships, if the satellite falls within this coverage annulus at this time, it means that the satellite has visibility with the space target, that is, inversely use the coverage annulus of the space target to monitor the visibility of constellation satellites to the space target, see Figure 2 ;

[0078] Judge the visibility relationship between the space target and the observation satellite: When the sub-satellite point of the space target falls within the coverage annulus, it means that the relationship between the satellite and the space target is visible; when the sub-satellite point of the space target falls within the inner circle or outside of the coverage annulus, it means that the relationship between the satellite and the space target is invisible.

[0079] Utilize the characteristic that the coverage annulus sizes generated by each space target for the satellite are the same. Project a coverage annulus identical to that of the satellite centered on the sub-satellite point of the space target. According to geometric relationships, if the satellite falls within this coverage annulus at this time, it means that the satellite has visibility with the space target. Taking the initial moment of the numerical example as an example, the satellite numbers visible to Target 1 are 9, 16, 28, the satellite numbers visible to Target 2 are 4, 9, 10, 24, 28, 29, and the satellite numbers visible to Target 3 are 3, 10, 11, 18, 19, 26, 27, see Figure 4a - Figure 4c ;

[0080] S4. Design and plan the time according to the positioning and tracking convergence situation of the observation satellite to the space target;

[0081] The minimum observation time T s,min is the shortest duration for the satellite to complete positioning and tracking convergence during observation. When the observation duration of the space target is less than this minimum observation time, it is regarded as an observation failure. The minimum observation time is set according to the satellite payload capacity; the planning period T sIt is necessary to be greater than or equal to the minimum observation time, and the planning period is the minimum step size of mission planning; considering the maneuvering time of the satellite when observing the target, the minimum observation time and the re-search for positioning and tracking caused by satellite handover, a judgment factor E is designed; if the observation and positioning tracking of the space target were achieved in the previous planning period, then E = 1.0, and if no observation was carried out, E = 2.0 is taken; therefore, the calculation formula for the planning period is:

[0082] T s = E·T s,min (7)

[0083] In the numerical example, the satellite numbered 19 visible to target 1 did not observe this target at the initial moment. At this time, the calculated planning period according to the formula was 200 s. After that, the observation and positioning tracking of the target were achieved, and the planning period became 100 s.

[0084] S5. Complete the global search for the visible window of the space target;

[0085] Use the reverse search algorithm to complete the global visible window search problem of the space target: At the initial moment, calculate and screen out all the satellites visible to the space target to form the satellite observation group of the target. Set a certain updated planning period, and calculate the visible time window of the satellite for the space target within this updated planning period until the window time of all the targets to be observed within this updated planning period is calculated. After completion, calculate the satellite observation group at the start time of the next period, and so on, to keep the dynamic update of the satellite observation group and the target, so as to achieve the global visible window search. The algorithm flow is as Figure 3 shown.

[0086] In actual calculation, considering the phenomenon that there are satellites that are not visible to the space target at the moment of updated grouping but have a visible time window for the space target within the planning period, the outer circle radius of the coverage annulus can be appropriately enlarged to achieve the effect of less or even no omission of the window.

[0087] There are many specific application ways of the present invention. The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements can be made, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. A global search method for the visible window of space targets based on coverage characteristic analysis, characterized in that The steps are as follows: S1: Design the model and its parameters for space target observation; S2: Analyze the coverage characteristics of the observation satellite for the Earth according to the model of the space target observation, so as to deduce the coverage annulus parameter function; S3: Use geometric relationships to search for visible observation satellites centered on the space target in reverse; S4: Design the planning time according to the positioning and tracking convergence of the observation satellite for the space target; S5: Complete the global search for the visible window of the space target; The specific content of S2 includes: When the position where the space target appears has been captured, the visibility of the space target for the satellite is determined; project the coverage range of the satellite onto the Earth's surface to form a coverage annulus centered on the sub-satellite point of the satellite; Let the inner radius of the annulus be \(R\). b and the outer radius be \(R'\). t The corresponding angles with the center of the earth are \(\theta\). b and \(\theta'\). t The width of the covered annulus is \(R''\). d Wherein, The calculation formula for the inner circle radius is: The calculation formula for the outer circle radius is: where H l satisfies the following relationship: Then the width of the coverage annulus is: R d = R t - R b (6) The width of the coverage annulus is determined jointly by the satellite altitude H sat and the target altitude H tar with other parameters regarded as constants; for the circular orbits of constellation satellites, the satellite altitude H sat is set as a constant and the target altitude H tar is a function that varies with time; the width of the coverage annulus, the inner circle radius, and the outer circle radius are only related to the value of H tar ; R e is the radius of the Earth, H a is the limb height, and L is the maximum detection distance of the satellite payload; A coverage annulus projected onto the Earth's surface is formed by the constraints of the space target observation model; The specific content of S3 includes: Utilize the characteristic that the coverage annulus sizes caused by each space target for the satellite are the same, project a coverage annulus identical to that of the satellite centered on the sub-satellite point of the target. According to geometric relationships, if the satellite falls into this coverage annulus at this time, it means that the satellite and the space target have visibility, that is, reversely use the coverage annulus of the space target to monitor the visibility of the constellation satellites for the space target; Judge the visibility relationship between the space target and the observation satellite: when the sub-satellite point of the space target falls within the coverage annulus, it means that the relationship between the satellite and the space target is visible; when the sub-satellite point of the space target falls within the inner circle or outside of the coverage annulus, it means that the relationship between the satellite and the space target is invisible.

2. The global search method for the visible window of a space target based on coverage characteristic analysis according to claim 1, wherein The parameters of the space target observation model in S1 include: The radius of the earth R e , the limb height H a , the height of the space target H tar , the height of the satellite H sat , the maximum detection distance L and the actual detection distance D of the satellite payload, the limb observation angle θ a and the target observation angle θ tar ; When the space target is visible to the satellite, the relationship is expressed as: θ tar ≥ θ a , D ≤ L (1) Among them, the calculation formula for the limb observation angle is: The maximum detection distance L of the satellite payload is determined according to the actual situation. Under this space target observation model, the transmittance can be set to 1 and the background intensity can be set to 0 to obtain the maximum detection distance.

3. The global search method for the visible window of a space target based on coverage characteristic analysis according to claim 1, wherein S4 includes: Minimum Observation Time T s,min It is the shortest duration for the satellite to complete positioning and tracking convergence during observation. When the observation duration of a space target is less than this minimum observation time, it is regarded as an observation failure. The minimum observation time is set according to the satellite payload capacity; Planning Period T s should be greater than or equal to the minimum observation time. The planning period is the minimum step size of mission planning; Considering the maneuvering time of the satellite during observation of the target, the minimum observation time, and the re-search for positioning and tracking caused by satellite switching, a judgment factor E is designed; If the observation and positioning tracking of the space target were achieved in the previous planning period, then E = 1.

0. If no observation was carried out, then E = 2.0; Therefore, the calculation formula for the planning period is as follows: T s = E·T s,min (7).

4. The global search method for the visible window of a space target based on coverage characteristic analysis according to claim 1, characterized in that The specific content of S5 includes: Use the reverse search algorithm to complete the global visible window search problem for the space target: at the initial moment, calculate and screen out all the satellites that are visible to the space target to form a satellite observation group of the target, set a certain update planning period, calculate the visible time window of the satellite for the space target within this update planning period until the window times of all the targets to be observed within this update planning period are calculated. After completion, calculate the satellite observation group at the start moment of the next period, and so on, maintaining the dynamic update of the satellite observation group and the target, so as to realize the global visible window search.

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