Target satellite assignment device, target satellite assignment method, and program

Abstract

A target satellite assignment device (1) comprises: a target satellite assignment unit (13) for assigning a second satellite and a third satellite to a first satellite as target satellites, the second satellite and the third satellite being from among satellites (2) that are present in the same orbital plane and that are provided with a free-space optical communication device, and the assigning being performed on the basis of orbital information indicating the orbits of the satellites (2); and a target satellite information output unit (14) for outputting, to the first satellite, target satellite information indicating the target satellites assigned to the first satellite. The target satellite assignment unit (13) performs target satellite assignment processing to assign to the first satellite, as target satellites, a second satellite and a third satellite that satisfy a first condition that the angle formed by a pointing direction from the first satellite to the second satellite and a pointing direction from the first satellite to the third satellite is greater than 2θ and less than (180°-2θ), where θ is a prohibited light-receiving angle for sunlight relative to the pointing direction of the satellite.

Description

Target Satellite Allocation Device, Target Satellite Allocation Method, and Program

[0001] The present disclosure relates to a target satellite allocation device, a target satellite allocation method, and a program.

[0002] In order to construct an inter-satellite network in a satellite constellation, the use of free space optical communication with high confidentiality and capable of realizing large-capacity communication is being considered. Free space optical communication is one-to-one communication, and it is necessary to select satellites that can be communicatively connected and assign target satellites to each satellite.

[0003] Patent Document 1 discloses a communication device existing on the ground, comprising one or more communication means configured to be able to transmit and receive a directional communication medium, and a determination means for determining one or more communication partners by the one or more communication means. When the determination means determines to communicate with a plurality of communication partners, the communication device selects a communication partner such that the angle between the plurality of communication partners as seen from the communication device is an angle that minimizes the influence of sunlight.

[0004] Patent Document 2 discloses a spacecraft comprising an attitude control actuator for controlling the attitude of the spacecraft, an imaging device for receiving an optical communication signal from another spacecraft, and an attitude controller for controlling the attitude control actuator based on the position of the optical communication signal in the image obtained by the imaging device. The attitude controller can capture or track an optical communication signal by controlling the attitude of the spacecraft itself, and determines a satellite with the highest space navigation light intensity as a communication partner.

[0005] International Publication No. 2022 / 209801, Japanese Patent Application Laid-Open No. 2021-103820

[0006] In inter-satellite communication within the orbital plane using free-space optical communication equipment, communication is disconnected if the angle between the direction of the communication terminal and sunlight is within the no-reception angle. In particular, in constellations with asynchronous solar orbits, the relative positions of the satellite's orbital plane and the sun change over time, causing the presence and duration of disconnections of inter-satellite communication links within the orbital plane to vary. Therefore, there is a possibility that satellites may become isolated from the inter-satellite network within the orbital plane. Hereafter, communication links will simply be referred to as links. The technology described in Patent Document 1 concerns communication between arbitrary communication devices, and it is unclear whether it can be applied to inter-satellite communication within the orbital plane. Furthermore, the technology described in Patent Document 2 does not take into account the effects of sunlight, and therefore cannot prevent satellites from becoming isolated from the inter-satellite network within the orbital plane.

[0007] This disclosure is made to solve the problems described above, and aims to suppress the isolation of satellites due to solar interference from the inter-satellite network within the orbital plane in inter-satellite communication in solar asynchronous orbits using free-space optical communication equipment.

[0008] To achieve the above objective, the target satellite assignment device according to this disclosure comprises a target satellite assignment unit and a target satellite information output unit. The target satellite assignment unit assigns the second and third satellites to the first satellite as target satellites based on orbital information indicating the orbits of satellites that are located in the same orbital plane and equipped with free-space optical communication devices. The target satellite information output unit outputs target satellite information indicating the target satellites assigned to the first satellite to the first satellite. The target satellite assignment unit performs target satellite assignment processing to assign the second and third satellites to the first satellite as target satellites, which satisfy a first condition in which, if θ is the angle at which sunlight reception is prohibited with respect to the direction of the satellite's orientation, the angle between the direction of orientation from the first satellite to the second satellite and the direction of orientation from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ).

[0009] According to this disclosure, in inter-satellite communication within the same orbital plane of a solar asynchronous orbit using a free-space optical communication device, by assigning target satellites such that the direction of directional signals to at least one of the second and third satellites communicating with the first satellite does not fall within the no-go angle for sunlight reception, it becomes possible to suppress isolation of satellites from the inter-satellite network due to solar interference.

[0010] A diagram showing an example of the functional configuration of the target satellite allocation device according to Embodiment 1. A diagram showing the no-sunlight angle for receiving sunlight according to Embodiment 1. A diagram showing the target satellite allocation method according to Embodiment 1. A flowchart showing an example of the target satellite allocation process according to Embodiment 1. A flowchart showing another example of the target satellite allocation process according to Embodiment 1. A diagram showing the second condition for selecting another satellite as a target satellite for the own satellite according to Embodiment 3. A diagram showing an inter-satellite network that satisfies the third condition for selecting another satellite as a target satellite for the own satellite according to Embodiment 4. A diagram showing an inter-satellite network forming a circular topology. A diagram showing the target satellite allocation method according to Embodiment 5. A diagram showing an example of the hardware configuration of the target satellite allocation device according to Embodiments 1 to 5.

[0011] The target satellite allocation device, target satellite allocation method, and program according to this embodiment will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

[0012] (Embodiment 1) The configuration of the target satellite assignment device 1 according to Embodiment 1 will be explained with reference to Figure 1. Figure 1 is a diagram showing an example of the functional configuration of the target satellite assignment device 1 according to this embodiment. The target satellite assignment device 1 is located on the ground and assigns other satellites 2 as target satellites to satellites 2 that are located in the same orbital plane in outer space. In Figure 1, three satellites 2 are shown as representative examples: the first satellite to which the target satellite is assigned, and the second and third satellites which are target satellites assigned to the first satellite. However, in reality, there are many satellites 2 in the same orbital plane.

[0013] As shown in Figure 1, the target satellite assignment device 1 includes an orbital information acquisition unit 11 that acquires orbital information indicating the orbits of satellites 2 located in the same orbital plane, an orbital information storage unit 12 that stores the orbital information, a target satellite assignment unit 13 that assigns the second and third satellites to the first satellite as target satellites among the satellites 2 located in the same orbital plane, and assigns the first satellite to the second and third satellites as target satellites, respectively, and a target satellite information output unit 14 that outputs target satellite information indicating the target satellites assigned to the first, second, and third satellites to the first, second, and third satellites, respectively.

[0014] The first satellite is equipped with at least two free-space optical communication devices (LCTs: Laser Communication Terminals). This allows the first satellite to connect with at least two other satellites 2 in the same orbital plane. The LCTs point in the direction of the target satellite as seen from themselves. Hereinafter, the pointing direction of the LCTs will be simply referred to as the pointing direction. The second and third satellites are equipped with at least one LCT each. In the example in Figure 1, satellite 2 is equipped with a target direction calculation unit 21 that calculates the direction of the target satellite based on target satellite information, and a pointing direction control unit 22 that controls the pointing direction to the direction of the target satellite.

[0015] The orbital information acquisition unit 11 acquires orbital information of satellites 2 located within the same orbital plane and stores it in the orbital information storage unit 12. The orbital information may include, for example, the orbital altitude and the phase of satellite 2 within the orbital plane. Alternatively, the orbital information may include the time history of the position and velocity of each satellite 2, the orbital elements of each satellite 2, orbital elements common to all satellites 2 and terms unique to each satellite 2, orbital information of a specific satellite 2, and changes in the orbits of other satellites 2 relative to that specific satellite 2. The orbital information may be acquired from satellite 2, from an external device or system, or input by the user.

[0016] The target satellite assignment unit 13 assigns the second and third satellites to the first satellite as target satellites based on the orbital information stored in the orbital information storage unit 12. Hereafter, let θ be the no-reception angle for sunlight with respect to the direction of satellite 2's orientation. The no-reception angle for sunlight θ will be explained using Figure 2. Since communication is disconnected if the angle between the direction of sunlight and the direction of orientation is within the no-reception angle θ, the range of θ + θ = 2θ is the no-reception range, as shown in Figure 2.

[0017] Next, the method for assigning target satellites will be explained using Figure 3. As shown in Figure 3, when the target satellite assignment unit 13 selects the second satellite as the first target satellite for the first satellite, it selects the third satellite as the second target satellite such that the angle α between the direction of directional movement from the first satellite to the second satellite and the direction of directional movement from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ). In the example in Figure 3, the range of 2θ + 2θ = 4θ relative to the direction of directional movement from the first satellite to the second satellite is the range in which the direction of directional movement from the first satellite to the third satellite should not be included, that is, the range in which the assignment of the third satellite is prohibited.

[0018] For example, the target satellite allocation unit 13 selects a satellite 2 adjacent to the first satellite in the orbital plane as the second satellite, and selects the closest satellite 2 as the third satellite from among the satellites 2 whose angle α between the direction of directional movement from the first satellite to the second satellite and the direction of directional movement from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ).

[0019] Alternatively, the target satellite assignment unit 13 may, based on the orbital information stored in the orbital information storage unit 12, list candidate combinations of the second and third satellites such that the angle α between the directional direction from the first satellite to the second satellite and the directional direction from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ), and select a combination of the second and third satellites from the list as the target satellite for the first satellite.

[0020] For example, the target satellite allocation unit 13 selects a combination of second and third satellites from among candidate combinations of second and third satellites in which the sum of the distance from the first satellite to the second satellite and the distance from the first satellite to the third satellite is the shortest, from among the angle α between the direction of directional movement from the first satellite to the second satellite and the direction of directional movement from the first satellite to the third satellite that is greater than 2θ and less than (180° - 2θ).

[0021] The target satellite assignment unit 13 assigns the second and third satellites as target satellites to the first satellite, and then assigns the first satellite as a target satellite to the second and third satellites, respectively. A link is established by aligning the target satellites between the first satellite and the second and third satellites.

[0022] By assigning the second and third satellites as target satellites for the first satellite, such that the angle α between the direction of directional movement from the first satellite to the second satellite and the direction of directional movement from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ), and by assigning the first satellite as a target satellite to the second and third satellites respectively, it is possible to avoid the simultaneous severance of both links from the first satellite to the second and third satellites due to solar interference at the worst-case timing when the orbital plane in which satellite 2 is located is parallel to the direction of sunlight and the link severance time and range are maximum. Therefore, the first satellite can maintain at least one communicable link at any given time, and the isolation of the first satellite due to solar interference can be suppressed.

[0023] Returning to Figure 1, the target satellite information output unit 14 outputs target satellite information indicating the assigned target satellites to the first, second, and third satellites to the first, second, and third satellites. The target direction calculation unit 21 of the first satellite calculates the directions of the second and third satellites based on the target satellite information received from the target satellite information output unit 14. The direction control unit 22 controls one LCT to align its direction to the direction of the second satellite, and controls the other LCT to align its direction to the direction of the third satellite. The target direction calculation unit 21 of the second satellite calculates the direction of the first satellite based on the target satellite information received from the target satellite information output unit 14. The direction control unit 22 controls one LCT to align its direction to the direction of the first satellite. The target direction calculation unit 21 of the third satellite calculates the direction of the first satellite based on the target satellite information received from the target satellite information output unit 14. The direction control unit 22 controls one LCT to align its direction to the direction of the first satellite.

[0024] The target satellite information output unit 14 may be configured not only to output target satellite information to the first, second, and third satellites, but also to display the target satellite information on a screen or transmit it to a terminal used by the user.

[0025] Here, the flow of the target satellite assignment process performed by the target satellite assignment device 1 will be explained using Figure 4. The target satellite assignment process shown in Figure 4 starts, for example, when power is turned on to the target satellite assignment device 1. If the orbit information acquisition unit 11 of the target satellite assignment device 1 does not acquire orbit information (step S11; NO), the process moves to step S19. If the orbit information acquisition unit 11 acquires orbit information (step S11; YES), it stores the orbit information in the orbit information storage unit 12 (step S12). Based on the orbit information, the target satellite assignment unit 13 selects a second satellite to assign to the first satellite (step S13). Based on the orbit information, the target satellite assignment unit 13 extracts satellites 2 in which the angle α between the direction of direction from the first satellite to the second satellite and the direction of direction from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ) (step S14), and selects the third satellite as the second target satellite from among the extracted satellites 2 (step S15).

[0026] The target satellite allocation unit 13 assigns the second and third satellites as target satellites to the first satellite (step S16), and assigns the first satellite as a target satellite to the second and third satellites, respectively (step S17).

[0027] The target satellite information output unit 14 outputs target satellite information indicating the target satellite assigned to the first satellite, second satellite, and third satellite to the first satellite, second satellite, and third satellite (step S18). Based on the received target satellite information, the first satellite, second satellite, and third satellite calculate the direction of the target satellite and control the LCT to align their aiming direction with that of the target satellite.

[0028] If the power to the target satellite assignment device 1 is not turned OFF (step S19; NO), the process returns to step S11 and steps S11 to S19 are repeated. When the power to the target satellite assignment device 1 is turned OFF (step S19; YES), the process ends.

[0029] Next, using Figure 5, we will explain the flow of the target satellite allocation process in the case where the target satellite allocation unit 13 selects a combination of the second and third satellites as the target satellite for the first satellite from a list of candidate combinations of the second and third satellites. Steps S21, S22, and S25 to S28 of the target satellite allocation process shown in Figure 5 are the same as steps S11, S12, and S16 to S19, respectively, so we will omit their explanation.

[0030] The target satellite assignment unit 13, based on orbital information, lists candidate combinations of the second and third satellites such that the angle α between the direction of directional movement from the first satellite to the second satellite and the direction of directional movement from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ) (step S23), and selects a combination of the second and third satellites from the list as the target satellite for the first satellite (step S24).

[0031] According to the target satellite assignment device 1 of Embodiment 1, in inter-satellite communication within the orbital plane of a solar asynchronous orbit using a free-space optical communication device, by assigning a target satellite such that the direction of directional signals to at least one of the second and third satellites communicating with the first satellite does not fall within the no-receiving angle of sunlight, it becomes possible to suppress isolation of the first satellite from the inter-satellite network due to solar interference.

[0032] (Embodiment 2) In Embodiment 1, the second and third satellites were assigned to the first satellite located in the same orbital plane. In Embodiment 2, however, for all satellites 2 located in the same orbital plane, the satellite 2 to which the target satellite is assigned is designated as the first satellite, and the other satellites 2 are treated as candidates for the second and third satellites, and the target satellite assignment process is performed to constitute an inter-satellite network. The differences between Embodiment 2 and Embodiment 1 will be described below. In the following description, the first satellite will be referred to as the own satellite, and the second and third satellites as other satellites.

[0033] Each satellite 2 is equipped with at least two LCTs. This allows each satellite 2 to connect with at least two other satellites 2 in the same orbital plane.

[0034] The orbital information acquisition unit 11 acquires orbital information of all satellites 2 that are in the same orbital plane and stores it in the orbital information storage unit 12. Based on the orbital information stored in the orbital information storage unit 12, the target satellite assignment unit 13 assigns target satellites to all satellites 2 such that the connected component is 1 in a graph in which satellites 2 on the same orbital plane are nodes and links connecting two satellites 2 are edges. At this time, if θ is the angle at which sunlight reception is prohibited with respect to the direction of orientation of the satellite 2, the target satellite assignment unit 13 assigns as target satellites to at least two LCTs of each satellite 23 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2 satellites 2

[0035] According to the target satellite assignment device 1 of Embodiment 2, in inter-satellite communication within the orbital plane of a solar asynchronous orbit using a free-space optical communication device, by assigning target satellites to all satellites 2 such that the direction of their directional gaze toward at least one of the two other satellites communicating with their own satellite is not included in the no-angle for receiving sunlight, isolation of any of the satellites 2 from the inter-satellite network within the orbital plane can be suppressed.

[0036] (Embodiment 3) In Embodiments 1 and 2, the condition for selecting the second and third satellites as target satellites for the first satellite was that the angle α between the direction of directional observation from the first satellite to the second satellite and the direction of directional observation from the first satellite to the third satellite was greater than 2θ and less than (180° - 2θ). In Embodiment 3, this is used as the first condition, and a second condition is added: the inter-satellite distance between the first and second satellites and the inter-satellite distance between the first and third satellites are both shorter than the maximum communication range of the LCT, and the closest approach distance between the line segment connecting the first and second satellites and the Earth surface and the closest approach distance between the line segment connecting the first and third satellites and the Earth surface are both greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored. The target satellite assignment process is then performed. Other functions of the target satellite assignment device 1 are the same as in Embodiments 1 and 2. In the following description, the first satellite is referred to as the own satellite, and the second and third satellites are referred to as other satellites.

[0037] The second condition will be explained using Figure 6. As shown in Figure 6, the second condition is that the inter-satellite distance L between your satellite and the other satellite, and the closest approach distance d between the line segment connecting your satellite and the other satellite and the Earth's surface, must be such that L < maximum communication range of the LCT, and d > atmospheric altitude where the influence on free-space optical communication cannot be ignored. By adding this second condition to the conditions for selecting another satellite as a target satellite for your own satellite, it is possible to avoid situations where communication is impossible due to a lack of line of sight between satellites.

[0038] According to the target satellite assignment device 1 of Embodiment 3, in inter-satellite communication within the orbital plane of a solar asynchronous orbit using a free-space optical communication device, by assigning a target satellite that satisfies the first and second conditions to satellite 2, it is possible to always satisfy the line-of-sight constraint in addition to the solar interference constraint, and to suppress links that do not contribute to communication.

[0039] (Embodiment 4) In Embodiment 4, similar to Embodiment 2, two other satellites 2 are assigned as target satellites to all satellites 2 that exist in the same orbital plane. In Embodiment 4, as a condition for selecting the second and third satellites as target satellites for the first satellite, a third condition is added to the first and second conditions: at least one of the second and third satellites connected to the first satellite is not a satellite 2 adjacent to the first satellite in the same orbital plane, and the target satellite assignment process is performed. The other functions of the target satellite assignment device 1 are the same as in Embodiment 2. In the following description, the first satellite is referred to as the own satellite, and the second and third satellites are referred to as other satellites.

[0040] The third condition will be explained using Figures 7A and 7B. As shown in Figure 7A, the third condition is that multiple satellites 2 exist on the same orbital plane, and at least one of the two other satellites connected to the self-satellite is not a satellite 2 adjacent to the self-satellite on the same orbital plane. By adding the third condition to the conditions for selecting other satellites as target satellites for the self-satellite, it is possible to avoid the inter-satellite network becoming a ring topology. As a result, compared to the case where a ring topology as shown in Figure 7B is formed, latency can be reduced by shortening the geometric distance of the links and reducing the number of communication hops.

[0041] Furthermore, a third condition may be that the geometric time and number of communication hops for transmitting the inter-satellite distance are simulated, and the values ​​used to evaluate these are minimized. In this case, for example, an optimization algorithm can be used. When an optimization algorithm is used, the third condition is to minimize the latency evaluation function represented by the following equation 1.

[0042]

[0043] In Equation 1, for a complete graph with satellites as nodes and the distance between satellites as the edge weight, let the edge be L(i, j), the speed of light be c, the fixed delay time T_delay by the satellite, and the binary variable x(i, j) representing the satellites in the path. Let the binary variable matrix of the adjacency matrix representing the assignment as the search variable be E ∈ {0, 1}(NS×NS).

[0044] When the target satellite assignment unit 13 sets the latency W(i, j) between each pair of satellites 2 to L(i, j) / c + T_delay from the coefficients of each path defined above, it enters 1 when the sunlight interference and the visibility constraint between satellites are satisfied, and 0 when the sunlight interference or the visibility constraint between satellites is not satisfied and a link cannot be formed. The connectivity matrix between each pair of satellites is V(i, j) ∈ {0, 1}(NS×NS), and a graph is created with an adjacency matrix including E*W*V as the edge weight. The target satellite assignment unit 13 calculates the evaluation function of the latency represented by Equation 1 with the shortest path for each pair of satellites 2 in this graph as x. The target satellite assignment unit 13 calculates the optimal assignment of the target satellite to all satellites 2 by an optimization algorithm that minimizes the evaluation function of the latency. Note that the evaluation function is not limited to the evaluation function of the latency, and other evaluation functions of indicators may be used as long as they are indicators for evaluating the geometric time for transmitting the satellite - to - satellite distance and the number of communication hops. Also, the target satellite assignment unit 13 may calculate the optimal assignment of the target satellite to all satellites 2 by a black - box optimization algorithm.

[0045] According to the target satellite assignment device 1 according to Embodiment 4, in the inter - satellite communication within the orbital plane of the sun - synchronous orbit using a free - space optical communication device, by assigning a target satellite that satisfies the first condition and the third condition to the satellite 2, in addition to enabling all satellites 2 to always communicate using the inter - satellite network within the orbital plane regardless of the time, the latency can be reduced.

[0046] (Embodiment 5) In Embodiment 1, the first satellite had at least two LCTs and could be connected to at least two other satellites 2 in the same orbital plane. However, in Embodiment 5, the first satellite has at least three LCTs and can be connected to at least three other satellites 2 in the same orbital plane. The other satellites 2 each have at least one LCT. Hereinafter, the differences from Embodiment 1 of Embodiment 5 will be described.

[0047] The method for allocating target satellites according to Embodiment 5 will be described with reference to FIG. 8. As shown in FIG. 8, when the target satellite allocation unit 13 selects the second satellite as the first target satellite of the first satellite, it selects two satellites 3 whose angle α formed by the direction from the first satellite to the second satellite and the direction from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ) as the second target satellite, and selects two satellites 4 whose angle β formed by the direction from the first satellite to the second satellite and the direction from the first satellite to the fourth satellite is greater than 2θ and less than (180° - 2θ) as the third target satellite.

[0048] For example, the target satellite allocation unit 13 selects the satellite 2 adjacent to the first satellite in the orbital plane as the second satellite, and selects the closest satellite 2 from the satellites 2 whose angle α formed by the direction from the first satellite to the second satellite and the direction from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ) as the third satellite, and selects the closest satellite 2 from the satellites 2 whose angle β formed by the direction from the first satellite to the second satellite and the direction from the first satellite to the fourth satellite is greater than 2θ and less than (180° - 2θ) as the fourth satellite.

[0049] Further, based on the orbital information stored in the orbital information storage unit 12, the target satellite allocation unit 13 lists candidates for combinations of the second satellite, the third satellite, and the fourth satellite whose angle α formed by the direction from the first satellite to the second satellite and the direction from the first satellite to the third satellite and whose angle β formed by the direction from the first satellite to the second satellite and the direction from the first satellite to the fourth satellite are greater than 2θ and less than (180° - 2θ), and may select a combination of the second satellite, the third satellite, and the fourth satellite as the target satellite of the first satellite from the list.

[0050] For example, the target satellite allocation unit 13 selects a combination of second, third, and fourth satellites from among candidate combinations of second, third, and fourth satellites in which the sum of the distance from the first to second satellite, the distance from the first to third satellite, and the distance from the first to fourth satellite is shortest, from among the candidate combinations of second, third, and fourth satellites in which the angle α between the direction of directional movement from the first to second satellite and the direction of directional movement from the first to third satellite, and the angle β between the direction of directional movement from the first to second satellite and the direction of directional movement from the first to fourth satellite is greater than 2θ and less than (180° - 2θ).

[0051] The target satellite assignment unit 13 assigns the second, third, and fourth satellites as target satellites to the first satellite, and then assigns the first satellite as a target satellite to the second, third, and fourth satellites, respectively. A link is established by aligning the target satellites of the first satellite with those of the second, third, and fourth satellites.

[0052] By assigning the second, third, and fourth satellites as target satellites for the first satellite, such that the angle α between the direction of directional movement from the first satellite to the second satellite and the direction of directional movement from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ), and the angle β between the direction of directional movement from the first satellite to the second satellite and the direction of directional movement from the first satellite to the fourth satellite is greater than 2θ and less than (180° - 2θ), two of the three links from the first satellite to the second, third, and fourth satellites can be maintained in a communicative state while avoiding solar interference, even under the worst-case conditions where the orbital plane in which satellite 2 is located is parallel to the direction of sunlight and the link disconnection time and range are maximum.

[0053] The same applies when the first satellite is equipped with four or more LCTs. Based on the orbital information stored in the orbital information storage unit 12, the target satellite assignment unit 13 assigns as the first satellite the other satellite 2 in three or more combinations of pairs of the first satellite and the other satellite 2 in which the angle between the directional direction from the first satellite to the other satellite 2 is greater than 2θ and less than (180° - 2θ).

[0054] According to the target satellite assignment device 1 of Embodiment 5, in inter-satellite communication within the orbital plane of a solar asynchronous orbit using a free-space optical communication device, at least two of the three or more links from the first satellite to other satellites 2 can be maintained in a communicative state while avoiding solar interference. By applying this target satellite assignment method and assigning three or more other satellites 2 as target satellites to all satellites 2 existing in the same orbital plane, each satellite 2 can construct a loop in the network topology graph, thereby improving the redundancy of the inter-satellite network.

[0055] The hardware configuration of the target satellite allocation device 1 will be explained using Figure 9. As shown in Figure 9, the target satellite allocation device 1 includes a temporary storage unit 301, a storage unit 302, a calculation unit 303, an input unit 304, a transmitting / receiving unit 305, and a display unit 306. The temporary storage unit 301, storage unit 302, input unit 304, transmitting / receiving unit 305, and display unit 306 are all connected to the calculation unit 303 via a BUS.

[0056] The calculation unit 303 is, for example, a CPU (Central Processing Unit). The calculation unit 303 executes the processing of the target satellite allocation unit 13 according to the control program stored in the memory unit 302.

[0057] The temporary storage unit 301 is, for example, RAM (Random-Access Memory). The temporary storage unit 301 loads the control program stored in the storage unit 302 and uses it as a work area for the calculation unit 303.

[0058] The memory unit 302 is a non-volatile memory such as flash memory, hard disk, DVD-RAM (Digital Versatile Disc - Random Access Memory), or DVD-RW (Digital Versatile Disc - ReWritable). The memory unit 302 pre-stores a program for causing the calculation unit 303 to process the target satellite assignment device 1, and also supplies the information stored in this program to the calculation unit 303 according to the instructions of the calculation unit 303, and stores the information supplied from the calculation unit 303. The orbital information storage unit 12 is configured in the memory unit 302.

[0059] The input unit 304 is an interface device that connects input devices such as a keyboard, pointing device, and voice input device to the BUS. Information entered by the user is supplied to the calculation unit 303 via the input unit 304. In a configuration where the user inputs trajectory information to the trajectory information acquisition unit 11, the input unit 304 functions as the trajectory information acquisition unit 11.

[0060] The transmitting / receiving unit 305 is a communication device that communicates with satellite 2. Alternatively, it may be a network termination device or wireless communication device that connects to a network including a communication device that communicates with satellite 2, and a serial interface or LAN (Local Area Network) interface that connects to them. The transmitting / receiving unit 305 functions as a target satellite information output unit 14.

[0061] The display unit 306 is a display device such as an LCD (Liquid Crystal Display) or an organic EL (electroluminescence) display. When the target satellite information output unit 14 is configured to display target satellite information on the screen, the display unit 306 functions as the target satellite information output unit 14.

[0062] The processing of the orbital information acquisition unit 11, orbital information storage unit 12, target satellite allocation unit 13, and target satellite information output unit 14 of the target satellite allocation device 1 shown in Figure 1 is performed by a control program that uses resources such as the temporary storage unit 301, calculation unit 303, storage unit 302, input unit 304, transmission / reception unit 305, and display unit 306 for processing.

[0063] Furthermore, the aforementioned hardware configuration and flowchart are examples only and can be changed and modified as needed.

[0064] The core components of the target satellite allocation device 1, such as the calculation unit 303, temporary storage unit 301, storage unit 302, input unit 304, transmission / reception unit 305, and display unit 306, can be implemented using a standard computer system, rather than a dedicated system. For example, the target satellite allocation device 1 can be configured by distributing a computer-readable recording medium such as a flexible disk, CD-ROM (Compact Disc - Read Only Memory), or DVD-ROM (Digital Versatile Disc - Read Only Memory) containing a computer program for performing the aforementioned operations, and then installing the computer program on a computer. Alternatively, the target satellite allocation device 1 can be configured by storing the computer program on a storage device of a server on a communication network such as the Internet, and then downloading it from a standard computer system.

[0065] Furthermore, if the functions of the target satellite assignment device 1 are realized through a division of labor between the OS (Operating System) and the application program, or through cooperation between the OS and the application program, then only the application program portion may be stored in the recording medium or storage device.

[0066] Furthermore, it is possible to superimpose a computer program onto the carrier wave and provide it via a communication network. For example, the computer program may be posted on a bulletin board system (BBS) on the communication network and provided via the communication network. The system may then be configured to execute the aforementioned processing by starting this computer program and running it under the control of the OS, just like other application programs.

[0067] In embodiments 1 to 5 described above, the target satellite assignment device 1 is located on the ground, but the invention is not limited to this, and the target satellite assignment device 1 may be provided on the satellite 2.

[0068] In embodiments 1 to 5 described above, the target satellite assignment unit 13 assigns the second and third satellites as target satellites to the first satellite, and then assigns the first satellite as a target satellite to the second and third satellites, respectively, but is not limited to this. For example, if the first satellite is a satellite 2 that uses beacon light to acquire another target satellite 2 instead of satellite communication, or if the first satellite is a satellite 2 that acts as a space interferometer to detect changes in the other target satellite 2, the first satellite performs processing independently, so it is not necessary to assign the first satellite as a target satellite to the second and third satellites, respectively. In this case, the target satellite information output unit 14 only needs to output target satellite information indicating the target satellite assigned to the first satellite to the first satellite.

[0069] In the embodiments 1 to 5 described above, the target satellite assignment device 1 includes an orbital information acquisition unit 11 and an orbital information storage unit 12, but the orbital information acquisition unit 11 and the orbital information storage unit 12 may be provided by an external device or system.

[0070] Although embodiments 2 to 5 described above have been explained separately, these embodiments may be combined. For example, embodiment 3 and embodiment 4 may be combined, embodiment 3 and embodiment 5 may be combined, embodiment 2 and embodiment 5 may be combined, or embodiment 4 and embodiment 5 may be combined.

[0071] Although a preferred embodiment 1 has been described in detail above, the invention is not limited to the embodiment described above, and various modifications and substitutions can be made to the above-described embodiment 1 without departing from the scope of the claims.

[0072] Furthermore, this disclosure allows for various embodiments and modifications without departing from its broad spirit and scope. The embodiments described above are for illustrative purposes only and do not limit the scope of this disclosure. That is, the scope of this disclosure is indicated by the claims, not by the embodiments. Various modifications made within the scope of the claims and the equivalent significance of the disclosure are considered to be within the scope of this disclosure.

[0073] This application is based on Japanese Patent Application No. 2025-14116, filed on 30 January 2025. The entire specification, claims, and drawings of Japanese Patent Application No. 2025-14116 are incorporated herein by reference.

[0074] 1 Target satellite assignment device, 2 Satellite, 11 Orbit information acquisition unit, 12 Orbit information storage unit, 13 Target satellite assignment unit, 14 Target satellite information output unit, 21 Target direction calculation unit, 22 Direction control unit, 301 Temporary storage unit, 302 Storage unit, 303 Calculation unit, 304 Input unit, 305 Transmit / receive unit, 306 Display unit, d Closest approach distance, L Inter-satellite distance.

Claims

1. A target satellite assignment device comprising: a target satellite assignment unit that assigns a second satellite and a third satellite to a first satellite as target satellites based on orbital information indicating the orbits of satellites that are located in the same orbital plane and equipped with free-space optical communication devices; and a target satellite information output unit that outputs target satellite information indicating the target satellites assigned to the first satellite to the first satellite, wherein the target satellite assignment unit performs a target satellite assignment process to assign the second satellite and the third satellite to the first satellite as target satellites, provided that θ is the forbidden angle for receiving sunlight with respect to the direction of the satellite's orientation, and the angle between the direction of orientation from the first satellite to the second satellite and the direction of orientation from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ).

2. The target satellite assignment device according to claim 1, wherein the free-space optical communication device performs one-to-one inter-satellite communication, and the target satellite assignment unit performs the target satellite assignment process to assign the second satellite and the third satellite to the first satellite as target satellites, satisfying, in addition to the first condition, the inter-satellite distance between the first satellite and the second satellite and the inter-satellite distance between the first satellite and the third satellite, respectively, shorter than the maximum communication range of the free-space optical communication device, and the closest approach distance between the line segment connecting the first satellite and the second satellite and the Earth's surface and the closest approach distance between the line segment connecting the first satellite and the third satellite and the Earth's surface, respectively, greater than the atmospheric altitude at which the influence on free-space optical communication cannot be ignored.

3. The target satellite assignment device according to claim 1 or 2, wherein the target satellite assignment unit assigns the first satellite to the second satellite as a target satellite, assigns the first satellite to the third satellite as a target satellite, establishes a communication link between the first satellite and the second satellite and a communication link between the first satellite and the third satellite, and the target satellite information output unit outputs the target satellite information indicating the target satellites assigned to the first satellite, the second satellite and the third satellite to the first satellite, the second satellite and the third satellite, respectively.

4. The target satellite allocation device according to claim 3, wherein the target satellite allocation unit performs the target satellite allocation process on all of the satellites, designating the satellite to which the target satellite is allocated as the first satellite, and the other satellites as candidates for the second and third satellites, thereby forming an inter-satellite network.

5. The target satellite allocation device according to claim 4, wherein the target satellite allocation unit performs the target satellite allocation process to allocate the second satellite and the third satellite to the first satellite as target satellites, wherein, in addition to the first condition, at least one of the second satellite and the third satellite connected to the first satellite is not a satellite adjacent to the first satellite on the same orbital plane.

6. The target satellite allocation device according to claim 5, wherein the third condition is set such that the geometric time and number of communication hops for transmitting the inter-satellite distance of the satellites are simulated and the values ​​for evaluating these are minimized, and an optimization algorithm is used for the target satellite allocation process.

7. The target satellite assignment device according to any one of claims 4 to 6, wherein the target satellite assignment unit performs the target satellite assignment process to assign, in three or more combinations of pairs of the first satellite and other satellites, other satellites that satisfy the first condition such that the angle between the directional direction from the first satellite to the other satellite is greater than 2θ and less than (180° - 2θ), as the target satellite of the first satellite.

8. A target satellite assignment method, which is performed by a target satellite assignment device and is based on orbital information indicating the orbits of satellites that are in the same orbital plane and equipped with free-space optical communication devices, wherein the second and third satellites are assigned to the first satellite as target satellites, wherein, if θ is the angle at which sunlight reception is prohibited with respect to the direction of the satellite's orientation, the second and third satellites are assigned to the first satellite as target satellites if the angle between the direction of orientation from the first satellite to the second satellite and the direction of orientation from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ).

9. A program that causes a computer to function as a target satellite assignment unit that assigns the second and third satellites to the first satellite as target satellites based on orbital information indicating the orbits of satellites that exist in the same orbital plane and are equipped with free-space optical communication devices, wherein the target satellite assignment unit performs a target satellite assignment process that assigns the first satellite the second and third satellites as target satellites, where θ is the angle at which sunlight reception is prohibited with respect to the direction of the satellite's orientation, and the angle between the direction of orientation from the first satellite to the second satellite and the direction of orientation from the first satellite to the third satellite is greater than 2θ and less than (180° - 2θ).

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