Midnight sunlight avoidance method for geostationary satellites while taking into account effective imaging

Abstract

This invention discloses a midnight sun avoidance method for geostationary satellites that ensures effective imaging. This method not only prevents sunlight from entering the beveled sunshade, but also ensures that satellite camera imaging quality meets operational requirements during the midnight sun avoidance period, reducing the satellite's daily detection blind time to minutes. Furthermore, the camera's optical axis autonomously returns to pointing toward the Earth's center before and after midnight sun avoidance. Three avoidance strategies are designed based on the annual change in the angle between the sun vector and the satellite's orbital plane to optimize the avoidance trajectory and improve coverage of key observation areas.

Description

Technical Field

[0001] The present invention relates to a midnight sunlight avoidance method for a geostationary orbit satellite taking effective imaging into consideration, and belongs to the technical field of spacecraft overall design and attitude orbit control. Background Art

[0002] To protect the main payload camera lenses from sunlight damage, geostationary remote sensing satellites employ beveled sunshades and autonomous maneuvers for sunlight avoidance. Existing methods for geostationary satellites with beveled sunshades include midday and midnight avoidance, with the latter typically lasting three to four hours. During the midnight avoidance period, the satellite maneuvers in real time as the solar angle of incidence changes. This maneuvering results in poor camera image quality, making the image data unusable for operational purposes. This reduces the satellite's effective daily observation time by three to four hours. To fully utilize the camera's observation period and extend the satellite's daily observation time, a new midnight avoidance method is needed to ensure that the satellite camera captures as much high-quality image data as possible during the midnight avoidance period. Summary of the Invention

[0003] The technical problem addressed by this invention is to overcome the shortcomings of existing technologies and provide a midnight sun avoidance method for geostationary satellites that ensures effective imaging. This method not only prevents sunlight from entering the beveled sunshade, but also ensures that satellite camera imaging quality meets operational requirements during the midnight sun avoidance period, reducing the satellite's daily detection blind time to minutes. Furthermore, the camera's optical axis autonomously returns to pointing toward the Earth's center before and after midnight sun avoidance. Three avoidance strategies have been designed to optimize the avoidance trajectory based on the annual change in the angle between the sun vector and the satellite's orbital plane.

[0004] The technical solution of the present invention is:

[0005] The present invention discloses a method for avoiding midnight sunlight of a geostationary satellite while taking into account effective imaging, comprising the following steps:

[0006] S1. Calculate the angle α between the projection of the sun vector on the XOZ plane of the satellite system and the Z axis;

[0007] S2. If the angle α is less than or equal to the sunlight avoidance safety threshold angle α f , then go to step S3, otherwise exit the midnight sun avoidance;

[0008] S3, calculating the β angle thresholds for different avoidance strategies;

[0009] S4, calculate the angle β between the sun vector and the satellite orbit plane;

[0010] S5. Calculate the pointing bias angle P when the satellite points to the key detection area based on the satellite's fixed position and the key detection area.β ;

[0011] S6, according to the angle β, the β angle threshold and the pointing offset angle P β , adopt different sunlight avoidance strategies.

[0012] Furthermore, in the above avoidance method, the calculation of the β angle thresholds for different avoidance strategies is specifically as follows:

[0013] Calculate the β angle threshold β1 of midnight sunlight avoidance strategy 1 according to the satellite midnight earth shadow time;

[0014] The β angle threshold β2 of strategy 2 is calculated based on the satellite key detection area.

[0015] Furthermore, in the above avoidance method, the β angle threshold β1 of the midnight sunlight avoidance strategy 1 is calculated based on the satellite midnight earth shadow time, specifically:

[0016] According to the orbital characteristics of the satellite, the length of the satellite's true earth shadow at different β angles is calculated;

[0017] According to the satellite's maneuverability and the satellite's payload detection field of view, the minimum β angle corresponding to the satellite's true earth shadow duration being greater than 30 minutes is selected as the threshold β1 of strategy 1.

[0018] Furthermore, in the above avoidance method, the β angle threshold β2 of the calculation strategy 2 based on the satellite key detection area is specifically:

[0019] Calculate the maximum roll direction deviation angle of the satellite when observing the key detection area based on the boundary of the key detection area is the maximum value of the set {roll1, roll2, roll3, roll4}, where roll1, roll2, roll3, and roll4 are the angles between the four boundary points of the key observation area and the equatorial plane;

[0020] According to the maximum offset angle Calculate the β angle threshold β2 for sunlight avoidance strategy 2,

[0021] Furthermore, in the above avoidance method, according to the angle β, the β angle threshold and the pointing offset angle P β , using different sunlight avoidance strategies, specifically:

[0022] If -β1+P β ≤β≤β1, the satellite experiences the Earth's shadow for a longer period of time, and the satellite adopts sunlight avoidance strategy 1;

[0023] If β1<β<β2, the satellite experiences the Earth's shadow for a short time or there is no Earth's shadow, and the satellite adopts sunlight avoidance strategy 2;

[0024] If β<-β1+P β or β ≥ β 2, the satellite adopts sunlight avoidance strategy 3;

[0025] Among them, β1 is the threshold of strategy 1, β2 is the threshold of strategy 2, P β It is the pointing offset angle of the satellite when it points to the key detection area, calculated based on the satellite's fixed position.

[0026] Furthermore, in the above avoidance method, the satellite adopts sunlight avoidance strategy 1, specifically:

[0027] The satellite performed five maneuvers, four of which were roll, pitch, and yaw joint maneuvers with an angular velocity of V sun Or V1, to ensure that the satellite camera can effectively image during the maneuver; one is a 180° turn and rapid maneuver, the maximum angular velocity of the maneuver is V2, during which the satellite cannot effectively image; the satellite performs conventional imaging during the five maneuver intervals, of which V sun is the rate of change of the angle between the projection of the sun on the orbital plane and the Z-axis of the orbital system, V1 is the maximum constraint of the camera payload imaging angular velocity, and V2 is the maximum maneuvering angular velocity of the yaw axis of the star.

[0028] Furthermore, in the above avoidance method, the satellite adopts sunlight avoidance strategy 2, specifically: the satellite performs a total of five maneuvers; wherein,

[0029] Three roll, pitch, and yaw joint maneuvers, with an angular velocity of V sun or V1, to ensure effective imaging by the satellite camera during maneuvers;

[0030] A rapid maneuver of 90 degrees in yaw and a small pitch angle, with a maximum angular velocity of V3. The satellite cannot effectively image during the rapid maneuver;

[0031] A rapid maneuver of 90 degrees in yaw and a small roll angle, with a maximum angular velocity of V4. The satellite cannot effectively image during the rapid maneuver;

[0032] Among them, V sun is the rate of change of the angle between the projection of the sun on the orbital plane and the Z-axis of the orbital system, V1 is the maximum constraint of the camera payload imaging angular velocity, V3 is the synthesis of the maximum maneuvering angular velocity of the star's yaw axis and the maximum maneuvering angular velocity of the pitch axis, and V4 is the synthesis of the maximum maneuvering angular velocity of the star's yaw axis and the maximum maneuvering angular velocity of the roll axis.

[0033] Furthermore, in the above avoidance method, the satellite adopts sunlight avoidance strategy 3, specifically: the satellite performs two maneuvers in total; wherein,

[0034] The first maneuver is to rotate the satellite around the yaw axis by ±90°. If the solar altitude angle is positive, the deflection is negative 90 degrees, otherwise it is positive 90 degrees. At the same time, the pitch axis is offset by M degrees, and the maximum angular velocity of the maneuver is V3.

[0035] The second maneuver involves a ±90° rotation of the satellite around the yaw axis. If the solar altitude angle is positive, the deflection is negative 90 degrees, otherwise it is positive 90 degrees. Simultaneously, the satellite rotates –M degrees around the roll axis, with a maximum angular velocity of V4. The satellite cannot effectively image during the two maneuvers, and conventional imaging is performed during the interval between the two maneuvers.

[0036] Where M = (α f -|β|), α f is the sunlight avoidance safety threshold angle; β is the angle between the sun vector and the satellite orbit plane during the satellite's working life; V3 is the synthesis of the maximum maneuvering angular velocity of the satellite's yaw axis and the maximum maneuvering angular velocity of the pitch axis; V4 is the synthesis of the maximum maneuvering angular velocity of the satellite's yaw axis and the maximum maneuvering angular velocity of the roll axis.

[0037] Furthermore, in the above avoidance method, the calculation of the satellite true earth shadow duration at different β angles is specifically as follows:

[0038]

[0039] Among them, t s The length of the earth's shadow.

[0040] Furthermore, in the above avoidance method, the angle β between the sun vector and the satellite orbit plane is calculated as follows:

[0041] β=arcsin S oy

[0042] Among them, S oy Represents the Y-axis component of the sun vector in the orbital system.

[0043] The beneficial effects of the present invention and the prior art are:

[0044] (1) The present invention solves the problem that the imaging quality of geostationary remote sensing satellites cannot be guaranteed during the midnight sunlight avoidance period. The present invention adopts a design scheme of small-angle uniform slow maneuvering combined with large-angle rapid maneuvering. The maximum angular velocity during the small-angle maneuvering process can ensure that the imaging quality of the satellite camera during the small-angle uniform slow maneuvering process meets business requirements.

[0045] (2) This invention designs three different midnight sunlight avoidance strategies based on the annual variation in the solar altitude relative to the orbital plane, and fully utilizes conditions such as the Earth's shadow period to perform conventional imaging during maneuver intervals. Furthermore, this method is adapted to actuators such as high-torque flywheels and control-torque gyroscopes to maximize the camera's effective imaging time during the midnight sunlight avoidance period.

[0046] (3) The present invention can autonomously select corresponding midnight sun avoidance strategies in real time according to the movement of the sun in different seasons of the year, and does not require ground personnel to operate, thereby reducing the difficulty and risk of ground personnel's business operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a flow chart for implementing the present invention;

[0048] Figure 2 It is a schematic diagram of the longitude and latitude of the boundary points of the key detection area of ​​the present invention. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0050] The present invention discloses a method for avoiding midnight sunlight of a geostationary satellite while taking into account effective imaging, comprising the following steps:

[0051] Step S1, calculating the angle α between the projection of the sun vector on the XOZ plane of the satellite system and the Z axis;

[0052] Step S2: If the angle α is less than or equal to the sunlight avoidance safety threshold angle α f , then go to step S3, otherwise exit the midnight sun avoidance;

[0053] Step S3, calculating the β angle thresholds for different avoidance strategies;

[0054] Step S4, calculating the angle β between the sun vector and the satellite orbit plane;

[0055] Step S5: Calculate the pointing bias angle P when the satellite points to the key detection area based on the satellite's fixed position and the key detection area. β ;

[0056] Step S6: According to the angle β, the β angle threshold and the pointing offset angle P β , adopt different sunlight avoidance strategies.

[0057] Preferably, in step S3, the β angle thresholds for different avoidance strategies are calculated as follows:

[0058] Calculate the β angle threshold β1 of midnight sunlight avoidance strategy 1 according to the satellite midnight earth shadow time;

[0059] The β angle threshold β2 of strategy 2 is calculated based on the satellite key detection area.

[0060] Preferably, the β angle threshold β1 of the midnight sunlight avoidance strategy 1 is calculated according to the satellite midnight earth shadow time, specifically:

[0061] According to the orbital characteristics of the satellite, the length of the satellite's true earth shadow at different β angles is calculated as follows: Among them, t s The length of the earth's shadow.

[0062] According to the satellite's maneuverability and the satellite's payload detection field of view, the minimum β angle corresponding to the satellite's true earth shadow duration exceeding 30 minutes is selected as the threshold β1 of strategy 1.

[0063] Preferably, the β angle threshold β2 of strategy 2 is calculated based on the satellite key detection area, specifically:

[0064] Calculate the maximum roll direction deviation angle of the satellite when observing the key detection area based on the boundary of the key detection area is the maximum value of the set {roll1, roll2, roll3, roll4}, where roll1, roll2, roll3, and roll4 are the angles between the four boundary points of the key observation area and the equatorial plane;

[0065] According to the maximum offset angle Calculate the β angle threshold β2 for sunlight avoidance strategy 2,

[0066] Preferably, in step S6, according to the angle β, the β angle threshold and the pointing offset angle P β , using different sunlight avoidance strategies, specifically:

[0067] If -β1+P β ≤β≤β1, the satellite experiences the Earth's shadow for a longer period of time, and the satellite adopts sunlight avoidance strategy 1;

[0068] If β1<β<β2, the satellite experiences the Earth's shadow for a short time or there is no Earth's shadow, and the satellite adopts sunlight avoidance strategy 2;

[0069] If β<-β1+P β or β ≥ β 2, the satellite adopts sunlight avoidance strategy 3;

[0070] Among them, β1 is the threshold of strategy 1, β2 is the threshold of strategy 2, P β It is the pointing offset angle of the satellite when it points to the key detection area, calculated based on the satellite's fixed position.

[0071] Preferably, the satellite adopts sunlight avoidance strategy 1, specifically:

[0072] The satellite performed five maneuvers, four of which were roll, pitch, and yaw joint maneuvers with an angular velocity of V sunOr V1, to ensure that the satellite camera can effectively image during the maneuver; one is a 180° turn and rapid maneuver, the maximum angular velocity of the maneuver is V2, during which the satellite cannot effectively image; the satellite performs conventional imaging during the five maneuver intervals, of which V sun is the rate of change of the angle between the projection of the sun on the orbital plane and the Z-axis of the orbital system, V1 is the maximum constraint of the camera payload imaging angular velocity, and V2 is the maximum maneuvering angular velocity of the yaw axis of the star.

[0073] Preferably, the satellite adopts sunlight avoidance strategy 2, specifically: the satellite performs a total of five maneuvers; wherein,

[0074] Three roll, pitch, and yaw joint maneuvers, with an angular velocity of V sun or V1, to ensure effective imaging by the satellite camera during maneuvers;

[0075] A rapid maneuver of 90 degrees in yaw and a small pitch angle, with a maximum angular velocity of V3. The satellite cannot effectively image during the rapid maneuver;

[0076] A rapid maneuver of 90 degrees in yaw and a small roll angle, with a maximum angular velocity of V4. The satellite cannot effectively image during the rapid maneuver;

[0077] Among them, V sun is the rate of change of the angle between the projection of the sun on the orbital plane and the Z-axis of the orbital system, V1 is the maximum constraint of the camera payload imaging angular velocity, V3 is the synthesis of the maximum maneuvering angular velocity of the star's yaw axis and the maximum maneuvering angular velocity of the pitch axis, and V4 is the synthesis of the maximum maneuvering angular velocity of the star's yaw axis and the maximum maneuvering angular velocity of the roll axis.

[0078] Preferably, the satellite adopts sunlight avoidance strategy 3, specifically: the satellite performs two maneuvers in total; wherein,

[0079] The first maneuver is to rotate the satellite around the yaw axis by ±90°. If the solar altitude angle is positive, the deflection is negative 90 degrees, otherwise it is positive 90 degrees. At the same time, the pitch axis is offset by M degrees, and the maximum angular velocity of the maneuver is V3.

[0080] The second maneuver involves a ±90° rotation of the satellite around the yaw axis. If the solar altitude angle is positive, the deflection is negative 90 degrees, otherwise it is positive 90 degrees. Simultaneously, the satellite rotates –M degrees around the roll axis, with a maximum angular velocity of V4. The satellite cannot effectively image during the two maneuvers, and conventional imaging is performed during the interval between the two maneuvers.

[0081] Where M = (α f -β), α fis the sunlight avoidance safety threshold angle; β is the angle between the sun vector and the satellite orbit plane during the satellite's working life; V3 is the synthesis of the maximum maneuvering angular velocity of the satellite's yaw axis and the maximum maneuvering angular velocity of the pitch axis; V4 is the synthesis of the maximum maneuvering angular velocity of the satellite's yaw axis and the maximum maneuvering angular velocity of the roll axis.

[0082] Preferably, in step S4, the angle β between the sun vector and the satellite orbit plane is calculated as follows:

[0083] β=arcsinS oy

[0084] Among them, S oy Represents the Y-axis component of the sun vector in the orbital system.

[0085] Example

[0086] Three avoidance strategies have been designed, tailored to the solar altitude. Strategy 1 addresses situations with relatively small absolute solar altitudes. In these situations, the Earth's shadow lasts longer per orbit, allowing the satellite to fully utilize the Earth's shadow to complete a 180-degree yaw maneuver while simultaneously avoiding the sun. Strategy 3 addresses situations with relatively large absolute solar altitudes. Sun avoidance can be achieved through two simple, rapid, large-angle maneuvers. Strategy 2 addresses situations with positive solar altitudes and short or no Earth's shadow. Compared to Strategy 3, this strategy effectively improves coverage of key areas.

[0087] like Figure 1 As shown, the present invention provides a method for avoiding midnight sunlight on a geostationary satellite while taking into account effective imaging, comprising the following steps:

[0088] (1) Determine whether to enter midnight sunlight avoidance based on the angle α between the projection of the sun vector on the satellite's own system and the Z axis of the satellite's own system.

[0089] The calculation method of 1.1α is as follows:

[0090]

[0091] Among them S bx 、S bz They represent the X-axis component and Z-axis component of the sun vector in the attitude control system respectively. The calculation method is as follows:

[0092] S b =C bo S o

[0093] Among them, S b =[S bx ,S by ,S bz ] T and S o =[Sox ,S oy ,S oz ] T are the projection components of the sun vector in the attitude control system and the orbit system, respectively, C bo is the direction cosine matrix of the attitude control system relative to the orbital system. o and C bo All are obtained through the attitude and orbit control subsystem.

[0094] 1.2 If α is greater than the sunlight avoidance safety threshold α f Angle, the satellite performs conventional imaging or position keeping operation; if α is less than or equal to the sunlight avoidance safety threshold angle α f Then go to step (2).

[0095] (2) Calculate the threshold angles of different avoidance strategies based on the satellite's key detection areas.

[0096] 2.1 Calculate the threshold angle β1 for midnight sun avoidance strategy 1.

[0097] Select the shadow duration t s Greater than l t The minimum β angle corresponding to the minute is used as the threshold β1 of strategy 1. The calculation formula for the earth shadow duration is:

[0098]

[0099] In the above formula, t s is the length of the Earth's shadow, and β is in radians.

[0100] 2.2 Calculate the threshold angle β2 of strategy 2 based on the satellite key detection area.

[0101] Assume that the center point of the key detection area is (γ0, δ0), and its width in the longitude direction is 2γ and in the latitude direction is 2δ. Figure 2 It can be seen that the longitude and latitude of the four boundary points of the sensitive working area are (γ0-γ, δ0+δ), (γ0-γ, δ0-δ), (γ0+γ, δ0-δ), and (γ0+γ, δ0+δ). Therefore, under the ground-fixed system, the coordinates of the four boundary points of the sensitive working area are:

[0102] A:[A x ,A y ,A z ]=[Recos(γ0-γ),Re sin(γ0-γ),Re sin(δ0+δ)]

[0103] B:[B x ,B y ,B z]=[Recos(γ0-γ),Re sin(γ0-γ),Re sin(δ0-δ)]

[0104] C:[C x ,C y ,C z ]=[Recos(γ0+γ),Re sin(γ0+γ),Re sin(δ0-δ)]

[0105] D:[D x ,D y ,D z ]=[Recos(γ0+γ),Re sin(γ0+γ),Re sin(δ0+δ)]

[0106] For geostationary satellites, the satellite is on the equatorial plane, so the angles between SA, SB, SC, and SD and the equatorial plane can be calculated as follows:

[0107]

[0108] The maximum value of the set {roll1, roll2, rol3l, rol4l} is the maximum roll direction deviation angle when the satellite observes the key detection area. Let the β angle threshold of sunlight avoidance strategy 2

[0109] (3) Select a midnight sun avoidance strategy based on the β angle.

[0110] 3.1 Calculate the angle β between the sun vector and the satellite orbit plane during the satellite's working life:

[0111] β=arcsin S oy

[0112] Among them, S oy Represents the Y-axis component of the sun vector in the orbital system.

[0113] 3.2 Selecting a midnight sun avoidance strategy based on β angle, if -β1+P β ≤β≤β1, the satellite experiences the Earth's shadow for a long time, and the process goes to step (4); if β1<β<β2, the satellite experiences the Earth's shadow for a short time or no Earth's shadow, and the process goes to step (5); if β<-β1+P β Or β≥β2, go to step (6);

[0114] Among them, P β It is the pointing offset angle of the satellite when pointing to the key detection area, and is defined as follows:

[0115]

[0116] Among them, O z is the Z-axis coordinate of the center point O of the key detection area in the ground-fixed system, and SO is the distance between the satellite position S and the center point O of the key detection area in the ground-fixed system.

[0117] (4) The satellite avoids sunlight according to midnight sunlight avoidance strategy 1.

[0118] 4.1 The satellite performs the first maneuver. During this process, the satellite performs a uniform, slow, and small-angle maneuver around the pitch axis of the attitude control system. The maneuvering angular velocity is V sun (The rate of change of the angle between the sun's projection on the orbital plane and the Z axis of the orbital system). The maneuvering direction is away from the sun, and the maneuvering process ends in the earth's shadow. At the end of the maneuvering process, the maximum pitch angle is recorded.

[0119] 4.2 After the satellite enters the Earth's shadow, the maximum maneuver angle is related to the solar altitude angle. Perform the reverse uniform slow maneuver in step 4.1. The satellite camera effectively images during the maneuver. After the maneuver is completed, the satellite's Z axis (also known as the camera's optical axis) returns to pointing toward the Earth's center. V1 is the maximum angular velocity constraint for the camera payload's imaging.

[0120] 4.3 The satellite performs a large-angle rapid maneuver, i.e., a 180° rotation around the Z axis of the attitude control system. The maximum angular velocity of the maneuver is V2. During the maneuver, the satellite cannot effectively image. After the maneuver is completed, the satellite performs conventional non-maneuverable imaging. V2 is the maximum angular velocity of the maneuver on the satellite's yaw axis.

[0121] 4.4 Satellite performs reverse uniform slow maneuver around the pitch axis The maneuvering direction is the same as step 4.2, ensuring that the angle between the sun vector and the satellite earth vector is equal to the safety threshold angle α when leaving the earth's shadow. f The maneuvering angular velocity is V1, during which the satellite camera effectively images. V1 is the maximum angular velocity constraint for the camera payload imaging.

[0122] 4.5 After leaving the Earth's shadow, perform the reverse uniform slow maneuver in step 4.4 The maneuvering angular velocity is V sun During the maneuver, the satellite camera effectively captured images. After the maneuver was completed, the satellite camera's optical axis returned to pointing to the center of the earth, and the midnight sun avoidance ended.

[0123] (5) The satellite avoids sunlight according to midnight sunlight avoidance strategy 2.

[0124] 5.1 The satellite performs the first maneuver. The satellite performs a uniform slow and small angle maneuver around the pitch axis of the attitude control system. The maneuvering angular velocity is V sunThe maneuvering direction is away from the sun. When the satellite enters the virtual shadow area, it ends and goes to step 5.2. At the end of the maneuvering process, record the maximum pitch angle Note: The virtual Earth shadow is the orbital interval extending 34.8 minutes before and after midnight. Note: 34.8 minutes corresponds to the time it takes for a GEO satellite to pass through the Earth's half-angle of 8.7 degrees.

[0125] 5.2 The satellite performs a large-angle rapid maneuver, rotating ±90 degrees around the Z axis of the system and with a Y axis offset (α f -|β|) degrees. The rule for positive or negative rotation about the system's Z axis is as follows: if the solar altitude angle is positive, the deflection is negative -90 degrees; otherwise, it is positive 90 degrees. The maximum angular velocity of the maneuver is V3. During the maneuver, the satellite camera cannot effectively image. After the maneuver is completed, proceed to step 5.3. V3 is the sum of the maximum maneuvering angular velocity of the satellite's yaw axis and the maximum maneuvering angular velocity of its pitch axis.

[0126] 5.3 The satellite performs the reverse uniform slow maneuver of step 5.1 The maneuver angular velocity is V1. During the maneuver, the satellite camera effectively captures images. The maneuver ends when the satellite exits the virtual shadow area, and the process proceeds to step 5.4. V1 is the maximum angular velocity constraint for the camera payload imaging.

[0127] 5.4 The satellite performs a large, rapid maneuver, rotating ±90 degrees around its own Z axis and returning the Y axis to 0 degrees. The rules for determining whether the Z axis rotation is positive or negative are as follows: if the solar altitude is positive, the deflection is negative -90 degrees; otherwise, it is positive 90 degrees. The maximum angular velocity of the maneuver is V4. During this maneuver, the satellite camera cannot effectively image. Once the maneuver is complete, proceed to step 5.5. V4 is the composite of the maximum angular velocity of the satellite's yaw and roll axes.

[0128] 5.6 The satellite performs a uniform slow small angle maneuver along the Y axis of the attitude control system with an angular velocity of V1. The maneuver direction is consistent with the direction of the sun's motion. This process is carried out until the angle between the sun vector and the satellite-earth vector is greater than the safety threshold angle α. f When , midnight sun avoidance ends. V1 is the maximum constraint on the camera payload imaging angular velocity.

[0129] (6) The satellite avoids sunlight according to midnight sunlight avoidance strategy 3.

[0130] 6.1 The satellite performs a large-angle maneuver, rotating ±90 degrees around the Z axis of the system and offsetting the Y axis (α f-|β|) degrees. The rules for positive or negative rotation about the system's Z axis are as follows: if the solar altitude angle is positive, the deflection is negative -90 degrees; otherwise, it is positive 90 degrees. The maximum angular velocity of the maneuver is V3. During the maneuver, the satellite camera cannot effectively image. After the maneuver is completed, the satellite performs conventional, non-maneuverable imaging. V3 is the composite of the maximum maneuvering angular velocity of the satellite's yaw axis and the maximum maneuvering angular velocity of its pitch axis.

[0131] 6.2 When α is close to α f When the satellite performs a large-angle maneuver, it rotates ±90 degrees around the Z axis of the system, and the Y axis is offset (|β|-α f ) degrees. The rule for determining whether to rotate positively or negatively about the system's Z axis is as follows: if the solar altitude is positive, the deflection is negative -90 degrees; otherwise, it is positive 90 degrees. The maximum angular velocity for the maneuver is V4. During this maneuver, the satellite camera cannot effectively image. Once the maneuver is completed, midnight sun avoidance is complete. V4 is the composite of the maximum maneuvering angular velocity of the satellite's yaw and roll axes.

[0132] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

[0133] The contents not described in detail in the specification of the present invention belong to the common knowledge of professionals in this field.

Claims

1. A method for avoiding midnight sunlight on a geostationary satellite while taking into account effective imaging, characterized in that: include: S1. Calculate the angle α between the projection of the sun vector on the XOZ plane of the satellite system and the Z axis; S2. If the angle α is less than or equal to the sunlight avoidance safety threshold angle α f , then go to step S3, otherwise exit the midnight sun avoidance; S3, calculating the β angle thresholds for different avoidance strategies; S4, calculate the angle β between the sun vector and the satellite orbit plane; S5. Calculate the pointing bias angle P when the satellite points to the key detection area based on the satellite's fixed position and the key detection area. β ; S6, according to the angle β, the β angle threshold and the pointing offset angle P β , using different sunlight avoidance strategies; The satellite adopts sunlight avoidance strategy 1, specifically: The satellite performed five maneuvers, four of which were roll, pitch, and yaw joint maneuvers with an angular velocity of V sun Or V1, to ensure that the satellite camera can effectively image during the maneuver; one is a 180° turn and rapid maneuver, the maximum angular velocity of the maneuver is V2, during which the satellite cannot effectively image; the satellite performs conventional imaging during the five maneuver intervals, of which V sun is the rate of change of the angle between the projection of the sun on the orbital plane and the Z axis of the orbital system, V1 is the maximum constraint of the imaging angular velocity of the camera payload, and V2 is the maximum maneuvering angular velocity of the yaw axis of the star; The satellite adopts sunlight avoidance strategy 2, specifically: the satellite performs five maneuvers in total; among them, Three roll, pitch, and yaw joint maneuvers, with an angular velocity of V sun or V1, to ensure effective imaging by the satellite camera during maneuvers; A rapid maneuver of 90 degrees in yaw and a small pitch angle, with a maximum angular velocity of V3. The satellite cannot effectively image during the rapid maneuver; A rapid maneuver of 90 degrees in yaw and a small roll angle, with a maximum angular velocity of V4. The satellite cannot effectively image during the rapid maneuver; Among them, V sun is the rate of change of the angle between the projection of the sun on the orbital plane and the Z axis of the orbital system, V1 is the maximum constraint of the camera payload imaging angular velocity, V3 is the composite of the maximum maneuvering angular velocity of the yaw axis and the maximum maneuvering angular velocity of the pitch axis, and V4 is the composite of the maximum maneuvering angular velocity of the yaw axis and the maximum maneuvering angular velocity of the roll axis; The satellite adopts sunlight avoidance strategy 3, specifically: the satellite performs two maneuvers; wherein, The first maneuver is to rotate the satellite around the yaw axis by ±90°. If the solar altitude angle is positive, the deflection is negative 90 degrees, otherwise it is positive 90 degrees. At the same time, the pitch axis is offset by M degrees, and the maximum angular velocity of the maneuver is V3. The second maneuver involves a ±90° rotation of the satellite around the yaw axis. If the solar altitude angle is positive, the deflection is negative 90 degrees, otherwise it is positive 90 degrees. Simultaneously, the satellite rotates –M degrees around the roll axis, with a maximum angular velocity of V4. The satellite cannot effectively image during the two maneuvers, and conventional imaging is performed during the interval between the two maneuvers. Where M = (α f -|β|), α f is the sunlight avoidance safety threshold angle; β is the angle between the sun vector and the satellite orbit plane during the satellite's working life; V3 is the synthesis of the maximum maneuvering angular velocity of the satellite's yaw axis and the maximum maneuvering angular velocity of the pitch axis; V4 is the synthesis of the maximum maneuvering angular velocity of the satellite's yaw axis and the maximum maneuvering angular velocity of the roll axis.

2. The method for avoiding midnight sunlight on a geostationary satellite while taking into account effective imaging according to claim 1, characterized in that: The calculation of the β angle thresholds for different avoidance strategies is specifically as follows: According to the satellite midnight earth shadow time, calculate the β angle threshold β1 of midnight sunlight avoidance strategy 1; The β angle threshold β2 of strategy 2 is calculated based on the satellite key detection area.

3. The method for avoiding midnight sunlight on a geostationary satellite while taking into account effective imaging according to claim 2, characterized in that: The β angle threshold β1 of the midnight sunlight avoidance strategy 1 is calculated based on the satellite midnight earth shadow time as follows: According to the orbital characteristics of the satellite, the length of the satellite's true earth shadow at different β angles is calculated; According to the satellite's maneuverability and the satellite's payload detection field of view, the minimum β angle corresponding to the satellite's true earth shadow duration being greater than 30 minutes is selected as the threshold β1 of strategy 1.

4. The method for avoiding midnight sunlight on a geostationary satellite while taking into account effective imaging according to claim 2, characterized in that: The β angle threshold β2 of the calculation strategy 2 according to the satellite key detection area is specifically: Calculate the maximum roll direction deviation angle of the satellite when observing the key detection area based on the boundary of the key detection area is the maximum value of the set {roll1, roll2, roll3, roll4}, where roll1, roll2, roll3, and roll4 are the angles between the four boundary points of the key observation area and the equatorial plane; According to the maximum offset angle Calculate the β angle threshold β2 for sunlight avoidance strategy 2, 5. The method for avoiding midnight sunlight on a geostationary satellite while taking into account effective imaging according to claim 1, characterized in that: According to the included angle β, β angle threshold and pointing offset angle P β , using different sunlight avoidance strategies, specifically: If -β1+P β ≤β≤β1, the satellite experiences the Earth's shadow for a longer period of time, and the satellite adopts sunlight avoidance strategy 1; If β1<β<β2, the satellite experiences the Earth's shadow for a short time or there is no Earth's shadow, and the satellite adopts sunlight avoidance strategy 2; If β<-β1+P β or β ≥ β 2, the satellite adopts sunlight avoidance strategy 3; Among them, β1 is the threshold of strategy 1, β2 is the threshold of strategy 2, P β It is the pointing offset angle of the satellite when it points to the key detection area, calculated based on the satellite's fixed position.

6. The method for avoiding midnight sunlight on a geostationary satellite while taking into account effective imaging according to claim 3, characterized in that: The calculation of the true earth shadow duration of the satellite at different β angles is specifically as follows: Among them, t s The length of the earth's shadow.

7. The method for avoiding midnight sunlight on a geostationary satellite while taking into account effective imaging according to claim 1, characterized in that: The angle β between the sun vector and the satellite orbit plane is calculated as follows: β=arcsinS oy Among them, S oy Represents the Y-axis component of the sun vector in the orbital system.

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