A method for designing a constellation of extremely low earth orbit satellites for point-to-point continuous coverage

Abstract

The application discloses a kind of fixed point continuous coverage's extremely low orbit constellation design method, including the orbit inclination of given satellite, based on the desired time that desired first star appears in the zenith of target place, determine the corresponding right ascension and declination of first star at desired time, and based on the corresponding right ascension and declination of first star at desired time, determine the latitude argument and right ascension of ascending node of first star;Determine the semi-major axis of the orbit where constellation is located;Based on the continuous communication time length of target place, determine the number of satellites of constellation;Based on the latitude argument and right ascension of ascending node of first star in constellation, the right ascension of ascending node and latitude argument of all satellites in constellation are sequentially determined;The constellation provided by the application can sequentially, fixedly pass through the overhead of target area at fixed time period every day, to form continuous communication coverage, while retaining the low delay, high speed communication advantage brought by extremely low orbit.

Description

Technical Field

[0001] This invention relates to the field of very low Earth orbit (VLEO) constellation technology, and more specifically to a method for designing a VLEO constellation with fixed-point continuous coverage. Background Technology

[0002] In disaster emergency response, continuous and stable emergency communication to the disaster area is the lifeline for effective rescue operations. Although low-Earth orbit satellites are considered ideal communication relay platforms due to their advantages of low communication latency and low link loss, there are inherent limitations to the revisiting of a specific ground location by a single satellite: due to their short orbital period, the time they spend passing over the target area is extremely short, usually only providing a communication window of a few minutes, which is difficult to meet the uninterrupted communication requirements of tasks such as real-time disaster information transmission and continuous rescue scheduling.

[0003] While multi-satellite networking can extend coverage time, the current mainstream satellite constellation configuration is typically the Walker constellation, which achieves global or wide-area signal coverage by adjusting the number and orbital positions of satellites. This approach excels in overall coverage, but exhibits significant shortcomings when used for directional communication targeting specific areas. Firstly, the complex calculation of satellite ground paths makes it difficult to accurately obtain parameters such as visibility windows and observation azimuth. Secondly, the utilization efficiency of satellite coverage time is low; conventional layouts aim for uniform global coverage, resulting in insufficient continuous coverage time for specific locations (such as disaster monitoring areas), easily leading to communication interruptions. Summary of the Invention

[0004] The purpose of this invention is to provide a design method for a fixed-point continuous coverage ultra-low orbit constellation, in order to solve the technical problem that in the prior art, the revisit of a single satellite to a specific ground is difficult to meet the uninterrupted communication requirements of tasks such as real-time disaster information transmission and continuous rescue scheduling, while multi-satellite networking requires the deployment of a large number of satellites, resulting in high construction and operation and maintenance costs.

[0005] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0006] A method for designing a fixed-point continuous coverage VLEO constellation includes the following steps:

[0007] Given the orbital inclination i of the VLEO constellation, the desired time when the first star of the VLEO constellation appears directly overhead at the target location. Determine the first satellite at the expected time. Corresponding right ascension and declination And based on the first star at the expected time Corresponding right ascension and declination Determine the latitude and argument of the first star. Right ascension of ascending node ;

[0008] Determine the semi-major axis of the orbit containing the extremely low Earth orbit constellation;

[0009] The number of satellites in the very low Earth orbit constellation is determined based on the duration of continuous communication requirements at the target location.

[0010] Based on the latitude argument of the first star in the aforementioned very low Earth orbit constellation Right ascension of ascending node The ascending node right ascension and latitudinal argument of all satellites in the VLEO constellation are determined sequentially, based on the orbital inclination of the VLEO constellation. Latitude radii of all satellites Right ascension of ascending node The semi-major axis of the orbit and the number of satellites determine the distribution pattern of the very low Earth orbit constellation.

[0011] Furthermore, the horizontal angle between the orbit of the VLEO constellation and the equator is taken as the orbital inclination i of the VLEO constellation, which is between 0 and 180°, based on the right ascension of the VLEO constellation's orbit at the 0° meridian. And the expected time t when the first star of the VLEO constellation appears directly above the target location, to determine the position of the first star in the VLEO constellation. Right ascension of time and declination ;

[0012] Here, we assume the longitude of the target location is... Latitude is The right ascension of the first star of the extremely low orbit constellation when it is directly overhead at the target location at the desired time t. = + Declination is Based on the right ascension and declination of the first satellite in the ultra-low Earth orbit constellation at the desired time t, determine the latitudinal argument of the first satellite. Right ascension of ascending node ;in:

[0013] ;

[0014] is the latitude of the target location; i is the orbital inclination of the orbit containing the VLEO constellation; The right ascension is the right ascension of the first star of the aforementioned low Earth orbit constellation when it is directly overhead at the target location at the desired time t.

[0015] Furthermore, the semi-major axis of the orbit is the sum of the Earth's radius and the orbital altitude. The formula for calculating the semi-major axis of the orbit containing the aforementioned low Earth orbit constellation is as follows:

[0016] ;

[0017] Where μ is the Earth's gravitational constant, μ = 398600.4418 × 10⁻⁶ 9 m³ / s²; For the Earth's radius, =6378.1km, J2 is the first-order nonspherical perturbation coefficient of the Earth, which is 1.08 × 10⁻³. This is the Earth's rotational angular velocity. =7.292×10^-5 rad / s;

[0018] i is the orbital inclination angle of the very low Earth orbit constellation, which is a known selected value;

[0019] N is the number of times a near-Earth orbit satellite orbits the Earth in one day; N is set to 16.

[0020] Using the initial semi-major axis of the orbit of the aforementioned very low orbit constellation The initial value is input into the calculation formula for the semi-major axis of the orbit of the aforementioned extremely low orbit constellation, and the calculation is performed iteratively. ;

[0021] Until the accuracy requirements are met Stop iteration, where the precision satisfies 1e -3 Stop iteration when the time is right;

[0022] Will n As the semi-major axis of the track The calculation results.

[0023] Furthermore, a target location is considered successfully observed if it is within the sensor coverage area of ​​any satellite.

[0024] Furthermore, let the semi-cone angle of the satellite sensor's field of view be denoted as... Field of view radius ,in, For the Earth's radius, =6378.1km, To obtain the semi-major axis of the orbit;

[0025] according to Sure ,in, For the semi-major axis of the track; The difference in latitudinal argument between two adjacent satellites in the VLEO constellation corresponding to the desired time t is given by r, which is the field of view radius of the satellite sensor.

[0026] Assuming the actual duration of continuous communication at the target location is not less than the required duration of continuous communication tc, the number of satellites n in the constellation is determined according to the following formula;

[0027] ;

[0028] in, Indicates rounding up;

[0029] The continuous communication duration is defined as the time required from the first satellite of the very low Earth orbit constellation entering the coverage area to the last satellite leaving the coverage area.

[0030] Furthermore, the method for sequentially determining the right ascension of the ascending node and the argument of latitude for all satellites in the aforementioned very low Earth orbit constellation is as follows:

[0031] Determine the orbital period of the satellites in the aforementioned very low Earth orbit constellation;

[0032] ;

[0033] in, Let μ be the semi-major axis of the extremely low Earth orbit constellation, and μ be the Earth's gravitational constant, μ = 398600.4418 × 10⁻⁶. 9 m³ / s²;

[0034] Based on the orbital periods of the satellites in the aforementioned VLEO constellation, the time difference between the successive passage of two adjacent satellites through the ascending node in the VLEO constellation is determined as follows: ;

[0035] pnod is the difference in latitudinal argument between two adjacent satellites in the EPR constellation corresponding to the desired time t, and pnod is the orbital period of the satellites in the EPR constellation.

[0036] Based on the time difference between the successive passage of two adjacent satellites through the ascending node in the aforementioned VLEO constellation, the right ascension of the ascending node of all satellites in the VLEO constellation at the desired time t is determined. And determine the latitudinal argument of all satellites at the desired time t. .

[0037] Furthermore, the right ascension of the ascending node of all satellites in the aforementioned very low Earth orbit constellation at the desired time t. The calculation formula is:

[0038] ;

[0039] in, The right ascension of the ascending node of the first star in the constellation. The difference in latitudinal argument between two adjacent satellites in the aforementioned very low Earth orbit constellation corresponding to the desired time t. ω represents the Earth's rotational angular velocity, and pnod represents the satellite's orbital period.

[0040] Furthermore, the latitude argument of all satellites in the aforementioned very low Earth orbit constellation at the desired time t. The calculation formula is:

[0041] ;

[0042] in, The latitude argument of the first satellite in the aforementioned very low Earth orbit constellation. It represents the difference in latitude argument between adjacent satellites in the constellation at the desired time t.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] The constellation provided by this invention can pass over the target area sequentially and at fixed points during fixed time periods each day, thereby forming continuous communication coverage, while retaining the advantages of low latency and high-speed communication brought by extremely low orbit. Attached Figure Description

[0045] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0046] Figure 1 This is a flowchart illustrating the ultra-low orbit constellation design method according to an embodiment of the present invention.

[0047] Figure 2 This is a schematic diagram of the distribution pattern of the ultra-low orbit constellation according to an embodiment of the present invention; Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] like Figure 1 As shown, this invention provides a method for designing a fixed-point continuous coverage ultra-low orbit constellation, comprising the following steps:

[0050] (i) Given the orbital inclination i of the VLEO constellation, the desired time when the first star of the VLEO constellation appears directly above the target location. Determine the first satellite at the expected time. Corresponding right ascension and declination And based on the first star at the expected time Corresponding right ascension and declination Determine the latitude and argument of the first star. Right ascension of ascending node .

[0051] The horizontal angle between the orbit of the VLEO constellation and the equator is taken as the orbital inclination i of the VLEO constellation, and is taken between 0 and 180°. This is based on the right ascension of the VLEO constellation's orbit at the 0° meridian. And the expected time t when the first star of the VLEO constellation appears directly above the target location, to determine the position of the first star in the VLEO constellation. Right ascension of time and declination ;

[0052] Here, we assume the longitude of the target location is... Latitude is The right ascension of the first star of the extremely low orbit constellation when it is directly overhead at the target location at the desired time t. = + Declination is Based on the right ascension and declination of the first satellite in the ultra-low Earth orbit constellation at the desired time t, determine the latitudinal argument of the first satellite. Right ascension of ascending node ;in:

[0053] ;

[0054] is the latitude of the target location; i is the orbital inclination of the orbit containing the VLEO constellation; The right ascension is the right ascension of the first star of the aforementioned low Earth orbit constellation when it is directly overhead at the target location at the desired time t.

[0055] like Figure 2 As shown, the first satellite in the VLEO constellation needs to appear at point K directly above the target location T at the desired time t. The longitude of the target location T is... Latitude is Latitude Argument Right ascension of ascending node The meaning is as follows Figure 2 As shown.

[0056] (ii) Determine the semi-major axis of the orbit in which the extremely low orbit constellation is located.

[0057] The formula for calculating the semi-major axis of the orbit containing the aforementioned very low Earth orbit constellation is as follows:

[0058] ;

[0059] Where μ is the Earth's gravitational constant, μ = 398600.4418 × 10⁻⁶ 9 m³ / s²; For the Earth's radius, =6378.1km, J2 is the first-order nonspherical perturbation coefficient of the Earth, which is 1.08 × 10⁻⁶. -3 , This is the Earth's rotational angular velocity. =7.292×10^-5 rad / s;

[0060] i is the orbital inclination angle of the very low Earth orbit constellation, which is a known selected value;

[0061] N is the number of times a near-Earth orbit satellite orbits the Earth in one day. N is usually set to 16, but is generally between 15 and 17.

[0062] Using the initial semi-major axis of the orbit of the aforementioned very low orbit constellation The initial value is input into the calculation formula for the semi-major axis of the orbit of the aforementioned extremely low orbit constellation, and the calculation is performed iteratively. ;

[0063] Until the accuracy requirements are met Stop iteration, where the precision satisfies 1e -3 Stop iteration when the time is right;

[0064] Will n As the semi-major axis of the track The calculation results.

[0065] (iii) Determine the number of satellites in the ultra-low orbit constellation based on the duration of continuous communication requirements at the target location.

[0066] Let the half-cone angle of the satellite sensor's field of view be . Field of view radius A target location is considered successfully observed if it falls within the sensor coverage area of ​​any satellite, and the half-cone angle of the satellite sensor's field of view... It needs to be determined based on the data from satellite sensors during the actual mission.

[0067] in, For the Earth's radius, =6378.1km, To obtain the semi-major axis of the orbit;

[0068] according to Sure ,in, For the semi-major axis of the track; The difference in latitudinal argument between two adjacent satellites in the VLEO constellation corresponding to the desired time t is given by r, which is the field of view radius of the satellite sensor.

[0069] Assume that the actual duration of continuous communication at the target location is not less than the required duration t of continuous communication. c The number of satellites n in the constellation is determined according to the following formula;

[0070] ;

[0071] in, Indicates rounding up;

[0072] The continuous communication duration is defined as the time required from the first satellite of the very low Earth orbit constellation entering the coverage area to the last satellite leaving the coverage area.

[0073] This implementation method can be based on satellite sensor parameters (field of view radius r) and the minimum continuous communication duration required. The minimum number of satellites n for the constellation configuration is determined, and the duration of continuous communication requirements that change in real time is based on flexibly adjusting the number of satellites n for the constellation configuration.

[0074] (iv) Based on the latitudinal argument of the first star in the aforementioned low Earth orbit constellation Right ascension of ascending node The ascending node right ascension and latitudinal argument of all satellites in the VLEO constellation are determined sequentially, based on the orbital inclination of the VLEO constellation. Latitude radii of all satellites Right ascension of ascending node The semi-major axis of the orbit and the number of satellites determine the distribution pattern of the very low Earth orbit constellation.

[0075] Determine the orbital period of the satellites in the aforementioned very low Earth orbit constellation;

[0076] ;

[0077] in, Let μ be the semi-major axis of the extremely low Earth orbit constellation, and μ be the Earth's gravitational constant, μ = 398600.4418 × 10⁻⁶. 9 m³ / s²;

[0078] Based on the orbital periods of the satellites in the aforementioned VLEO constellation, the time difference between the successive passage of two adjacent satellites through the ascending node in the VLEO constellation is determined as follows: ;

[0079] p is the difference in latitudinal argument between two adjacent satellites in the aforementioned very low Earth orbit constellation corresponding to the desired time t. nod The orbital period of the satellites in the aforementioned very low Earth orbit constellation;

[0080] Based on the time difference between the successive passage of two adjacent satellites through the ascending node in the aforementioned VLEO constellation, the right ascension of the ascending node of all satellites in the VLEO constellation at the desired time t is determined. And determine the latitudinal argument of all satellites at the desired time t. .

[0081] The right ascension of the ascending node of all satellites in the very low Earth orbit constellation at the desired time t. The calculation formula is:

[0082] ;

[0083] in, The right ascension of the ascending node of the first star in the constellation. The difference in latitudinal argument between two adjacent satellites in the aforementioned very low Earth orbit constellation corresponding to the desired time t. p is the Earth's rotational angular velocity. nod This is the satellite's orbital period.

[0084] The latitude argument of all satellites in the aforementioned very low Earth orbit constellation at the desired time t. The calculation formula is:

[0085] ;

[0086] in, The latitude argument of the first satellite in the aforementioned very low Earth orbit constellation. It represents the difference in latitude argument between adjacent satellites in the constellation at the desired time t.

[0087] For the first satellite, its right ascension of the ascending node and its latitudinal argument are... and For the second satellite, these are Ω1 and u1, and so on. The orbital semi-major axis, orbital inclination, and other parameters determined by this implementation method can be used to determine the unique position of a satellite in inertial space. For all satellites in the Earth orbit constellation designed by this method, all parameters are the same except for the right ascension of the ascending node and the argument of latitude at the desired time t. The sorting rule can be regarded as the satellite that passes over the target location first having the sequence number 0, and the satellite that passes over the target location last having the sequence number n-1.

[0088] Therefore, the sub-satellite points of the constellation designed according to this implementation method naturally coincide. As long as the orbital inclination, the semi-major axis of the orbit, the right ascension of the ascending node and the argument of latitude at a given desired time are calculated, the satellite will have a unique position in inertial space. It is not necessary to focus on parameters such as the position of its orbital plane and the number of planes to express the position of the satellite.

[0089] This embodiment proposes a novel satellite constellation orbit design scheme that ensures a designated area receives stable and uninterrupted communication services for a predetermined duration each day. Specifically, this embodiment abandons the idea of ​​global coverage and focuses on achieving efficient, fixed-point, continuous coverage of key areas. The constellation passes over the target area sequentially and at fixed points during fixed time periods each day, thus forming continuous communication coverage while retaining the low-latency, high-speed communication advantages of extremely low orbits.

[0090] The constellation designed in this embodiment passes over a fixed position above a ground target at a fixed time each day. With an orbital altitude not exceeding 300km, it has higher communication speed and shorter latency, lower construction costs, and the constellation configuration can be flexibly adjusted according to satellite sensor parameters and communication duration requirements.

[0091] A low-Earth orbit (LEO) communication constellation with continuous coverage is designed with Beijing (39.9°N, 116.4°E) as the target coverage location. Communication begins daily at noon and lasts for 1000 seconds. The formula for calculating the semi-major axis of the constellation's orbit is as follows:

[0092] ;

[0093] Based on the orbital inclination of a given satellite ,by Iterative calculation as initial value until the accuracy requirements are met. ;Will As the semi-major axis of the track The calculation results can determine the semi-major axis of the satellite's orbit. .

[0094] Based on the field of view semi-cone angle of ground-based satellite sensors ,according to Sure , ,in, For the Earth's radius, Given the semi-major axis of the orbit, we can obtain ,Pick .

[0095] The duration of continuous communication at the target location is not less than The number of satellites n in the constellation is determined according to the following formula;

[0096] ;

[0097] Therefore, a total of 27 satellites are needed.

[0098] Based on the formula: ;

[0099] Calculate the right ascension of the ascending node of the first star. Latitude Argument difference in right ascension of ascending nodes .

[0100] It can be seen that the nadir trajectories of all satellites coincide and recur periodically. Simulations show that the effective communication duration per day is 1019.5 seconds, which meets the design requirements.

[0101] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A method for designing a fixed-point continuous coverage VLEO constellation, characterized in that, Includes the following steps: Given the orbital inclination i of the VLEO constellation, the desired time when the first star of the VLEO constellation appears directly overhead at the target location. Determine the first satellite at the desired time. Corresponding right ascension and declination And based on the first star at the expected time Corresponding right ascension and declination Determine the latitude and argument of the first star. Right ascension of ascending node ; Determine the semi-major axis of the orbit containing the extremely low Earth orbit constellation; The number of satellites in the very low Earth orbit constellation is determined based on the duration of continuous communication requirements at the target location. Based on the latitude argument of the first star in the aforementioned very low Earth orbit constellation Right ascension of ascending node The ascending node right ascension and latitudinal argument of all satellites in the VLEO constellation are determined sequentially, based on the orbital inclination of the VLEO constellation. Latitude radii of all satellites Right ascension of ascending node The semi-major axis of the orbit and the number of satellites determine the distribution pattern of the very low Earth orbit constellation.

2. The method for designing a fixed-point continuous coverage ultra-low orbit constellation according to claim 1, characterized in that, The horizontal angle between the orbit of the VLEO constellation and the equator is taken as the orbital inclination i of the VLEO constellation, and is taken between 0 and 180°. This is based on the right ascension of the VLEO constellation's orbit at the 0° meridian. And the expected time t when the first star of the VLEO constellation appears directly above the target location, to determine the position of the first star in the VLEO constellation. Right Ascension of Time and declination ; Here, we assume the longitude of the target location is... Latitude is The right ascension of the first star of the extremely low orbit constellation when it is directly overhead at the target location at the desired time t. = + Declination is Based on the right ascension and declination of the first satellite in the ultra-low Earth orbit constellation at the desired time t, determine the latitudinal argument of the first satellite. Right ascension of ascending node ;in: ； is the latitude of the target location; i is the orbital inclination of the orbit containing the VLEO constellation; The right ascension is the right ascension of the first star of the aforementioned low Earth orbit constellation when it is directly overhead at the target location at the desired time t.

3. The method for designing a fixed-point continuous coverage ultra-low orbit constellation according to claim 1, characterized in that, The semi-major axis of the orbit is the sum of the Earth's radius and the orbital altitude. The formula for calculating the semi-major axis of the orbit containing the aforementioned low Earth orbit constellation is as follows: ； Where μ is the Earth's gravitational constant, μ = 398600.4418 × 10⁻⁶ 9 m³ / s²; For the Earth's radius, =6378.1km, J2 is the first-order nonspherical perturbation coefficient of the Earth, which is 1.08 × 10⁻⁶. -3 , This is the Earth's rotational angular velocity. =7.292×10^-5 rad / s; i is the orbital inclination angle of the very low Earth orbit constellation, which is a known selected value; N is the number of times a near-Earth orbit satellite orbits the Earth in one day; N is set to 16. Using the initial semi-major axis of the orbit of the aforementioned very low orbit constellation The initial value is input into the calculation formula for the semi-major axis of the orbit of the aforementioned extremely low orbit constellation, and the calculation is performed iteratively. ; Until the accuracy requirements are met Stop iteration, where the precision satisfies 1e -3 Stop iteration when the time is right; Will n As the semi-major axis of the track The calculation results.

4. The method for designing a fixed-point continuous coverage ultra-low orbit constellation according to claim 1, characterized in that, The target location is considered successfully observed if it is within the sensor coverage area of ​​any satellite.

5. The method for designing a fixed-point continuous coverage ultra-low orbit constellation according to claim 3, characterized in that, Let the half-cone angle of the satellite sensor's field of view be . Field of view radius ,in, For the Earth's radius, =6378.1km, To obtain the semi-major axis of the orbit; according to Sure ,in, For the semi-major axis of the track; The difference in latitudinal argument between two adjacent satellites in the VLEO constellation corresponding to the desired time t is given by r, which is the field of view radius of the satellite sensor. Assume that the actual duration of continuous communication at the target location is not less than the required duration t of continuous communication. c The number of satellites n in the constellation is determined according to the following formula; ； in, Indicates rounding up; The continuous communication duration is defined as the time required from the first satellite of the very low Earth orbit constellation entering the coverage area to the last satellite leaving the coverage area.

6. The method for designing a fixed-point continuous coverage ultra-low orbit constellation according to claim 1, characterized in that, The method for sequentially determining the right ascension of the ascending node and the argument of latitude of all satellites in the aforementioned very low Earth orbit constellation is as follows: Determine the orbital period of the satellites in the aforementioned very low Earth orbit constellation; ； in, Let μ be the semi-major axis of the extremely low Earth orbit constellation, and μ be the Earth's gravitational constant, μ = 398600.4418 × 10⁻⁶. 9 m³ / s²; Based on the orbital periods of the satellites in the aforementioned VLEO constellation, the time difference between the successive passage of two adjacent satellites through the ascending node in the VLEO constellation is determined as follows: ; p is the difference in latitudinal argument between two adjacent satellites in the aforementioned very low Earth orbit constellation corresponding to the desired time t. nod The orbital period of the satellites in the aforementioned very low Earth orbit constellation; Based on the time difference between the successive passage of two adjacent satellites through the ascending node in the aforementioned VLEO constellation, the right ascension of the ascending node of all satellites in the VLEO constellation at the desired time t is determined. And determine the latitudinal argument of all satellites at the desired time t. .

7. The method for designing a fixed-point continuous coverage ultra-low orbit constellation according to claim 5, characterized in that, The right ascension of the ascending node of all satellites in the very low Earth orbit constellation at the desired time t. The calculation formula is: ； in, The right ascension of the ascending node of the first star in the constellation. The difference in latitudinal argument between two adjacent satellites in the aforementioned very low Earth orbit constellation corresponding to the desired time t. p is the Earth's rotational angular velocity. nod This is the satellite's orbital period.

8. The method for designing a fixed-point continuous coverage ultra-low orbit constellation according to claim 5, characterized in that, The latitude argument of all satellites in the aforementioned very low Earth orbit constellation at the desired time t. The calculation formula is: ； in, The latitude argument of the first satellite in the aforementioned very low Earth orbit constellation. It represents the difference in latitude argument between adjacent satellites in the constellation at the desired time t.

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