A Method for Target Attitude Planning of a Multi-Field-of-View Star Observation Satellite

Abstract

A method for target attitude planning of a multi-field-of-view star observation satellite, comprising: Step 1, obtaining the season or month when the satellite conducts star observation, the satellite orbit altitude, and the stray light suppression angle of the imaging optical device; Step 2, giving the optional sky areas of each optical device according to the projection relationship between the optional fields of view of the optical device and the observable sky area; Step 3, selecting a set of observation points according to the star distribution in the optional sky area, obtaining the pointing of each optical device in the celestial coordinate system under this observation point, judging whether it is in its available sky area, and deleting the unavailable observation points; Step 4, counting the number of stars in the camera field of view under the available observation points and optimizing the available observation points; Step 5, repeating Steps 3 and 4 until a satisfactory set of observation points is found, and outputting the right ascension and declination of the optimal observation point and the satellite attitude transformation matrix. The present invention provides an ideal observation sky area and target attitude for remote sensing satellites and astronomical observation satellites when performing multi-field-of-view star imaging.

Description

Technical Field

[0001] The present invention relates to a method for target attitude planning of a multi-field-of-view star observation satellite, belonging to the field of satellite target attitude planning, and is applied to the selection of imaging areas and attitude planning during multi-field-of-view star imaging of remote sensing satellites and astronomical observation satellites. Background Art

[0002] When the payload of a remote sensing satellite is a camera, radiometric calibration or geometric calibration can be performed by imaging stars, and multiple cameras or star sensors are required to image the starry sky simultaneously.

[0003] Since remote sensing satellites are designed for ground imaging requirements, there are some problems when imaging the starry sky. For example, the small field of view of the camera results in a limited number of observable celestial bodies, and optical devices (cameras, star sensors, etc.) may be unavailable due to sunlight or earth atmosphere light. Currently, there is a lack of corresponding observation sky areas and target attitude planning methods in the related field.

[0004] In addition to remote sensing satellites imaging the starry sky, some space science satellites for astronomical observation need to image specific sky areas due to detection tasks. In the current literature on mission planning for astronomical observation satellites, more attention is paid to issues such as increasing the number of fixed-point target visits, extending the observation time, minimizing energy consumption, and sky coverage, and rarely involves the attitude planning problem of multiple-field-of-view cameras imaging the starry sky simultaneously. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: overcoming the deficiencies of the prior art, providing a method for target attitude planning of a multi-field-of-view star observation satellite, providing an ideal observation sky area and target attitude for remote sensing satellites and astronomical observation satellites during multi-field-of-view star imaging, so that all imaging optical devices (such as cameras, star cameras, and star sensors, with a quantity greater than or equal to 1, i.e., multi-field-of-view) during the observation process are not interfered by sunlight and earth atmosphere light, and the number of stars entering the camera's field of view is as large as possible, ensuring the effectiveness of the observation and improving the observation quality.

[0006] The technical solution of the present invention is as follows:

[0007] A method for target attitude planning of a multi-field-of-view star observation satellite, the steps are as follows:

[0008] Step 1, obtain the season or month when the satellite conducts star observation, the satellite orbit altitude, and the stray light suppression angle of the imaging optical device;

[0009] Step 2, according to the projection relationship between the optional field of view of the optical device and the observable sky area, give the optional sky areas of each optical device;

[0010] Step 3: According to the distribution of stars in the optional sky area, select a set of observation points, obtain the pointing of each optical device in the celestial coordinate system under this observation point, determine whether it is within its available sky area, and delete the unavailable observation points;

[0011] Step 4: Count the number of stars in the camera's field of view under the available observation points, and optimize the available observation points;

[0012] Step 5: Repeat Steps 3 and 4 until a satisfactory set of observation points is found, and output the right ascension, declination of the optimal observation point and the satellite attitude transformation matrix.

[0013] Further, the stray light suppression angle specifically refers to: when the optical device is affected by external stray light, the imaging effect deteriorates or even fails. There is a constraint of the stray light suppression angle during the imaging of the optical device. When the stray light rays are outside the stray light suppression angle, the optical device works normally. Otherwise, the imaging effect of the optical device deteriorates or it cannot work properly; the stray light includes sunlight and earth atmosphere light.

[0014] Further, according to the mission plan of the satellite, select the month or specific date for starry sky imaging, and select to perform multi-field-of-view starry sky imaging in the shadow area. Obtain the satellite orbit data through satellite-ground measurement and control, and extrapolate to obtain the satellite orbit altitude on the starry sky observation day. When the satellite is in a circular orbit, the satellite orbit altitude directly uses the nominal orbit altitude.

[0015] Further, in Step 2, according to the projection relationship between the optional field of view of the optical device and the observable sky area, the optional sky area of each optical device is given, specifically as follows:

[0016] After obtaining the satellite orbit altitude H and the stray light suppression angle B of the imaging optical device, the included angle A between the XOY plane of the orbit coordinate system and the edge of the earth atmosphere is

[0017]

[0018] The available cone C of the optical device's field of view is

[0019]

[0020] where p is the thickness of the atmosphere and R e is the radius of the earth;

[0021] Perform the analysis of the observable sky area in the celestial coordinate system. Denote the projection of the available cone field of view of the optical device on the celestial sphere as the optional sky area of this optical device. When the optical axis pointing of this optical device is within any direction within the cone range with R Z as the generatrix, it will not be interfered by the earth atmosphere light. α 0 is the right ascension center point of the optional sky area of the optical device, and α 0It is related to the specific season / month of the observation; the optional celestial region observation center points during the vernal equinox, summer solstice, autumnal equinox, and winter solstice are respectively

[0022] Vernal equinox α 0 = 180°

[0023] Summer solstice α 0 = 270°

[0024] Autumnal equinox α 0 = 0°

[0025] Winter solstice α 0 = 90°

[0026] The set of optional celestial regions is

[0027] S = {α, δ: cos 2 (α - α 0 ) cos 2 δ + sin 2 δ ≤ sin 2 C}

[0028] If B > A, then C < 90°, δ e ∈ (-C, C), and the coordinates (α e , δ e ) describing the edge of the optional celestial region are obtained by the following formula

[0029]

[0030] If B < A, then C > 90°, δ e ∈ [-90°, 90°], and the coordinates (α e , δ e ) describing the edge of the optional celestial region are obtained by the following formula

[0031]

[0032] Furthermore, in the third step, the set of observation points is selected as follows:

[0033] When selecting an observation point, each observation point contains two celestial sphere coordinate points. One coordinate point is the satellite +Z-axis pointing point, and the coordinate is recorded as (α 1 , δ 1 ), and the other coordinate point is the pointing point of a vector located in the satellite's body system XOZ plane and having a certain positive angle with both the +X-axis and the +Z-axis, and the coordinate is recorded as (α 2 , δ 2 );

[0034] When selecting the set of observation points, follow the principle from broad to narrow and from sparse to dense. When selecting the set of observation points for the first time, cover the largest available sky area of the optical equipment, with sparse density. After one calculation, when selecting the set of observation points for the second time, select the observation points near the available observation points in the first time, with the density encrypted compared with the previous time, and so on.

[0035] According to the conversion relationship between the celestial coordinate system and the inertial coordinate system, the attitude transformation matrix C from the J2000 inertial coordinate system of the satellite to the body coordinate system of the satellite ib is calculated through the following formula

[0036]

[0037] where

[0038] X T = Y T ×Z T

[0039] According to the installation directions of each optical equipment on the satellite, calculate the directions of each optical equipment in the celestial coordinate system; assume the installation matrix of the optical equipment in the body coordinate system of the satellite is C bCam , then the attitude matrix of this optical equipment in the J2000 inertial coordinate system is:

[0040]

[0041] where is the vector representation of the optical axis of the optical equipment in the inertial coordinate system, and z 1 , z 2 , z 3 are the three components of the vector;

[0042] The coordinate (α, δ) of the optical axis of this optical equipment in the celestial coordinate system is

[0043] δ = arcsin(z 3 ),

[0044] Next, judge whether the coordinate (α, δ) of this optical equipment in the celestial coordinate system is within the available sky area obtained in Step 2:

[0045] When all optical equipment are within their respective available sky areas, then this observation point is available;

[0046] When the optical axes of one or two optical equipment are not pointing within the available sky area and cannot meet the mission requirements, this observation point is unavailable;

[0047] Delete the unavailable observation points to obtain the available observation points.

[0048] Further, in Step 4, the number of stars in the camera's field of view at available observation points is counted, and the available observation points are optimized. Specifically:

[0049] First, according to the camera installation matrix, field of view shape, and coordinate system definition, an array of pointing vectors at the edges of the camera's field of view in the satellite's body frame is established as

[0050]

[0051] where n is the number of edge points of the field of view, and [z 1i z 2i z 3i T is the pointing of the i-th edge vector in the satellite's body frame, where i = 1, …, n;

[0052] The coordinate array Cam of the camera's field of view edge vectors in the celestial sphere frame ball is obtained by the method described in Step 3;

[0053]

[0054] According to the camera detector's field of view, it is determined whether a certain star point is within the detector's field of view of the optical device, the number of star points in the camera's field of view is calculated, and the observation point with the largest number of star points is selected as the preferred observation point.

[0055] Further, when determining whether a certain star point is within the detector's field of view of the optical device, if the detector's field of view is a circular detector field of view, it is performed in the following manner:

[0056] Calculate the angle Star ,δ Star ) between the star point coordinates (α Cam ,δ Cam ) and the camera optical axis coordinates (α

[0057] Ang = arccos(Z Star ·Z Cam )

[0058] where the star point coordinates are from known star catalog information;

[0059]

[0060] The semi-apex angle of the camera's circular field of view is D r , then there is

[0061] If Ang ≥ D r , then the star point is not within the camera detector's field of view;

[0062] If Ang < D r ​, then the star point is within the field of view of the camera detector.

[0063] Further, when determining whether a certain star point is within the field of view of the detector of an optical device, if the detector field of view is a circular detector field of view, it can also be determined by using the directionality of the cross product to determine whether a certain star point is within a rectangular field of view:

[0064] The coordinates of the star point are (α Star , δ Star ), and the coordinates of the four points of the camera detector are (α 1 , δ 1 ), (α 2 , δ 2 ), (α 3 , δ 3 ), (α 4 , δ 4 ). Construct vectors p 12 (α 2 - α 1 , δ 2 - δ 1 ), p 23 (α 3 - α 2 , δ 3 - δ 2 ), p 34 (α 4 - α 3 , δ 4 - δ 3 ), p 41 (α 1 - α 4 , δ 1 - δ 4 ), p Star1 (α 1 - α Star , δ 1 - δ Star ), p Star2 (α 2 - α Star , δ 2 - δ Star ), p Star3 (α 3 - α Star , δ 3 - δ Star ), p Star4 (α 4 - α Star , δ 4 - δ Star );

[0065] If (p 12 × p Star1 ) * (p34 ×p Star3 ) ≥ 0 and (p 23 ×p Star2 ) * (p 41 ×p Star4 ) ≥ 0, then the star point is within the field of view of the camera detector; otherwise, the star point is not within the field of view of the camera detector.

[0066] Furthermore, when determining whether a certain star point is within the field of view of the detector of an optical device, if the detector field of view is a rectangular detector field of view, it is carried out in the following manner:

[0067] Calculate the area of the rectangular field of view. The star point and the four points of the rectangular field of view form four spherical triangles. The sum of the areas of the four spherical triangles is compared with the rectangular area. If they are equal, the star point is within the field of view; if it is larger, the star point is outside the field of view.

[0068] The specific method for calculating the area of a spherical triangle is as follows: For a spherical triangle P A P B P C with a radius of 1, the area is

[0069] S = P A + P B + P C - π

[0070] where P A , P B , P C are spherical angles. The spherical angle is measured by the plane angle formed by two planes. That is, the spherical angle P A is the angle between the plane P A OP B and the plane P A OP C . and are respectively the perpendiculars from point P B and point P C to the line OP A . Then the spherical angle P A is the angle between the vectors and . Then

[0071]

[0072]

[0073] where are respectively the vectors from point O to point P A , point P B , point P C . Then

[0074]

[0075] Denote the function for calculating the area of the spherical triangle formed by the vectors inside the sphere as Then there is Then

[0076]

[0077] The star point coordinates are (α Star , δ Star ), and the coordinates of the four points of the camera detector are (α 1 , δ 1 ), (α 2 , δ 2 ), (α 3 , δ 3 ), (α 4 , δ 4 ). The corresponding vector coordinates in the inertial system are Z star , Z 1 , Z 2 , Z 3 , Z 4 . Then

[0078] The area projected by the detector's field of view in celestial coordinates is

[0079] S 0 = S 123 + S 134 = f(Z 1 , Z 2 , Z 3 ) + f(Z 1 , Z 3 , Z 4 )

[0080] The sum of the areas of the four spherical triangles formed by the star point and the four points of the rectangular field of view is

[0081] S Star = S 12Star + S 23Star + S 34Star + S 14Star

[0082] = f(Z 1 , Z 2 , Z Star ) + f(Z 2 , Z 3 , Z Star ) + f(Z 3 , Z 4 , Z Star ) + f(Z 1 , Z 4 , Z Star )

[0083] Then there is

[0084] If S Star > S 0 , then the star point is not within the field of view of the camera detector;

[0085] If S Star = S 0 , then the star point is within the field of view of the camera detector.

[0086] Furthermore, continue to select denser new observation points near the preferred observation points obtained in step four. Combine the selected new observation points with the preferred observation points obtained in step three to form a new set of observation points. Repeat step three and step four to obtain the optimal set of observation points. Output the right ascension and declination (α j , δ j ) of the optimal observation points, j = 1, …, m, and the attitude transformation matrix C ib (j), j = 1, …, m from the satellite J2000 inertial system to the local system, where m is the number of optimal observation points.

[0087] The beneficial effects of the present invention compared with the prior art are as follows:

[0088] (1) The present invention provides a target attitude planning method for multi-field-of-view star imaging scenarios of remote sensing satellites and astronomical observation satellites, enabling all imaging optical devices during the observation process to be free from the interference of sunlight and earth atmosphere light, and maximizing the number of stars entering the camera's field of view, ensuring the effectiveness of the observation and improving the observation quality;

[0089] (2) The present invention provides an analysis model for the observable sky area of optical devices, which can assist in the mission analysis of remote sensing satellites and astronomical observation satellites and the pointing layout design of optical observation devices, providing a technical means for quantitative analysis in satellite scheme design;

[0090] (3) The present invention also gives a specific algorithm for calculating the number of stars in the detector's field of view for the optical payload for star imaging, making the method more feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 is a schematic diagram of the system composition of the embodiment;

[0092] Figure 2 is a flowchart of the method implementation of the present invention;

[0093] Figure 3 is a schematic diagram of the relationship between the optional field of view of the optical device and the projection of the optional sky area;

[0094] Figure 4 is a schematic diagram of the influence of different seasons on the optional sky area;

[0095] Figure 5 It is a schematic diagram of the calculation method for the area of a spherical triangle. Specific implementation manners

[0096] The following further describes in detail the specific implementation manners of the present invention in conjunction with the accompanying drawings.

[0097] As Figure 2 shown, a method for target attitude planning of a multi-field-of-view star observation satellite proposed by the present invention includes the following steps:

[0098] Step 1, obtain the season or month for the satellite to conduct star observation, the satellite orbit altitude, and the stray light suppression angle of the imaging optical device;

[0099] The stray light suppression angle specifically refers to: when the optical device is affected by external stray light, the imaging effect deteriorates or even fails. There is a constraint on the stray light suppression angle during the imaging of the optical device. When the stray light rays are outside the stray light suppression angle, the optical device works normally. Otherwise, the imaging effect of the optical device deteriorates or it cannot work normally; the stray light includes sunlight and earth atmosphere light.

[0100] According to the mission plan of the satellite, select the month or specific date for star imaging, and select to conduct multi-field-of-view star imaging in the shadow area. Obtain the satellite orbit data through satellite-ground measurement and control, and extrapolate to obtain the satellite orbit altitude on the star observation day. When the satellite is in a circular orbit, the satellite orbit altitude directly uses the nominal orbit altitude.

[0101] Step 2, give the optional sky areas of each optical device according to the projection relationship between the optional fields of view of the optical device and the observable sky areas; specifically:

[0102] After obtaining the satellite orbit altitude H and the stray light suppression angle B of the imaging optical device, the included angle A between the XOY plane of the orbital coordinate system and the edge of the earth atmosphere is

[0103]

[0104] The available cone C of the field of view of the optical device is

[0105]

[0106] where p is the thickness of the atmosphere and R e is the radius of the earth;

[0107] Conduct an analysis of the observable sky area in the celestial coordinate system, and record the projection of the available cone of the field of view of the optical device on the celestial sphere as the optional sky area of this optical device. When the optical axis direction of this optical device points to any direction within the cone range with R Z as the generatrix, it will not be interfered by the earth atmosphere light, α 0α is the right ascension center point of the optional sky area for the optical device 0 It is related to the specific season / month when the observation is carried out; the observation center points of the optional sky area during the vernal equinox, summer solstice, autumnal equinox, and winter solstice are respectively

[0108] α at the vernal equinox 0 = 180°

[0109] α at the summer solstice 0 = 270°

[0110] α at the autumnal equinox 0 = 0°

[0111] α at the winter solstice 0 = 90°

[0112] The set of optional sky areas is

[0113] S = {α,δ: cos 2 (α - α 0 ) cos 2 δ + sin 2 δ ≤ sin 2 C}

[0114] If B > A, then C < 90°, δ e ∈ (-C, C), and the coordinates (α e , δ e ) describing the edge of the optional sky area are obtained from the following formula

[0115]

[0116] If B < A, then C > 90°, δ e ∈ [-90°, 90°], and the coordinates (α e , δ e ) describing the edge of the optional sky area are obtained from the following formula

[0117]

[0118] Step 3: According to the distribution of stars in the optional sky area, select a set of observation points, obtain the pointing directions of each optical device in the celestial coordinate system at this observation point, and determine whether it is within its available sky area, and delete the unavailable observation points;

[0119] Select a set of observation points, specifically:

[0120] When selecting an observation point, each observation point contains two celestial coordinate system points. One coordinate point is the satellite +Z axis pointing point, and the coordinate is recorded as (α 1 , δ 1 ), and the other coordinate point is the pointing point of a vector located in the satellite's body coordinate system XOZ plane and having a certain positive angle with both the +X axis and the +Z axis, and the coordinate is recorded as (α2 , δ 2 );

[0121] When selecting the set of observation points, follow the principle from wide to narrow and from sparse to dense. When selecting the set of observation points for the first time, cover the largest available sky area of the optical equipment, with sparse density. After one calculation, when selecting the set of observation points for the second time, select the observation points near the available observation points in the first time, with the density encrypted compared with the previous time, and so on;

[0122] According to the conversion relationship between the celestial coordinate system and the inertial coordinate system, the attitude conversion matrix C from the satellite J2000 inertial coordinate system to the satellite body coordinate system ib is calculated through the following formula

[0123]

[0124] where

[0125] X T = Y T × Z T

[0126] According to the installation directions of each optical equipment on the satellite, calculate the directions of each optical equipment in the celestial coordinate system; assume the installation matrix of the optical equipment in the satellite body coordinate system is C bCam , then the attitude matrix of this optical equipment in the J2000 inertial coordinate system is:

[0127]

[0128] where is the vector representation of the optical axis of the optical equipment in the inertial coordinate system, and z 1 , z 2 , z 3 are the three components of the vector;

[0129] The coordinate (α, δ) of the optical axis of this optical equipment in the celestial coordinate system is

[0130]

[0131] Next, judge whether the coordinate (α, δ) of this optical equipment in the celestial coordinate system is within the available sky area obtained in step two:

[0132] When all optical equipment are within their respective available sky areas, then this observation point is available;

[0133] When the optical axes of one or two optical equipment point outside the available sky area and cannot meet the mission requirements, this observation point is unavailable;

[0134] Delete the unavailable observation points to obtain the available observation points.

[0135] Step 4: Count the number of stars in the camera's field of view at the available observation points and optimize the available observation points;

[0136] Specifically:

[0137] First, according to the camera installation matrix, field of view shape, and coordinate system definition, establish an array of the pointing vectors of the camera's field of view edges in the satellite's body frame as

[0138]

[0139] where n is the number of field of view edge points, and [z 1i z 2i z 3i T is the pointing of the i-th edge vector in the satellite's body frame, i = 1,..., n;

[0140] The coordinate array Cam of the camera's field of view edge vectors in the celestial sphere frame ball is obtained by the method described in Step 3;

[0141]

[0142] According to the camera detector's field of view, determine whether a certain star point is within the detector's field of view of the optical device, calculate the number of star points in the camera's field of view, and select the observation point with the largest number of star points as the preferred observation point.

[0143] Specifically:

[0144] When determining whether a certain star point is within the detector's field of view of the optical device, if the detector's field of view is a circular detector's field of view, it is carried out in the following manner:

[0145] Calculate the angle Star ,δ Star ) between the star point coordinates (α Cam ,δ Cam ) and the camera optical axis coordinates (α

[0146] Ang = arccos(Z Star ·Z Cam )

[0147] where the star point coordinates are from the known star catalog information;

[0148]

[0149] The semi-apex angle of the camera's circular field of view is D r , then there is

[0150] If Ang ≥ D​r , then the star point is not within the field of view of the camera detector;

[0151] If Ang < D r , then the star point is within the field of view of the camera detector.

[0152] When determining whether a certain star point is within the field of view of the detector of an optical device, if the detector field of view is a circular detector field of view, it can also be determined by the method of using the directionality of cross product to determine whether a certain star point is within a rectangular field of view:

[0153] The coordinates of the star point are (α Star , δ Star ), and the coordinates of the four points of the camera detector are (α 1 , δ 1 ), (α 2 , δ 2 ), (α 3 , δ 3 ), (α 4 , δ 4 ). Construct vectors p 12 (α 2 - α 1 , δ 2 - δ 1 ), p 23 (α 3 - α 2 , δ 3 - δ 2 ), p 34 (α 4 - α 3 , δ 4 - δ 3 ), p 41 (α 1 - α 4 , δ 1 - δ 4 ), p Star1 (α 1 - α Star , δ 1 - δ Star ), p Star2 (α 2 - α Star , δ 2 - δ Star ), p Star3 (α 3 - α Star , δ 3 - δ Star ), p Star4 (α 4 - α Star , δ 4 - δ Star );

[0154] If (p 12 × p Star1 ) * (p 34 × p Star3 ) ≥ 0 and (p 23 × p Star2 ) * (p 41 × p Star4 ) ≥ 0, then the star point is within the field of view of the camera detector; otherwise, the star point is not within the field of view of the camera detector.

[0155] When determining whether a certain star point is within the field of view of the detector of an optical device, if the detector field of view is a rectangular detector field of view, it is carried out in the following manner:

[0156] Calculate the area of the rectangular field of view. The star point and the four points of the rectangular field of view form four spherical triangles. The sum of the areas of the four spherical triangles is compared with the rectangular area. If they are equal, the star point is within the field of view; if it is larger, the star point is outside the field of view;

[0157] The specific method for calculating the area of a spherical triangle is as follows: For a spherical triangle P A P B P C with a radius of 1, the area is

[0158] S = P A + P B + P C - π

[0159] where P A , P B , P C are spherical angles. The spherical angle is measured by the plane angle formed by two planes. That is, the spherical angle P A is the angle between the plane P A OP B and the plane P A OP C . and are respectively the perpendiculars from point P B and point P C to the straight line OP A . Then the spherical angle P A is the angle between the vectors and . Then

[0160]

[0161]

[0162] where are respectively the distances from point O to point P A 、point PB , the vector of point P C ; then

[0163]

[0164] Denote the function that calculates the area of the spherical triangle formed by the vectors inside the sphere as Then there is Then

[0165]

[0166] The star point coordinates are (α Star , δ Star ), and the coordinates of the four points of the camera detector are (α 1 , δ 1 ), (α 2 , δ 2 ), (α 3 , δ 3 ), (α 4 , δ 4 ). The corresponding vector coordinates in the inertial system are Z star , Z 1 , Z 2 , Z 3 , Z 4 ; then

[0167] The area of the projection of the detector's field of view in celestial coordinates is

[0168] S 0 = S 123 + S 134 = f(Z 1 , Z 2 , Z 3 ) + f(Z 1 , Z 3 , Z 4 )

[0169] The sum of the areas of the four spherical triangles formed by the star point and the four points of the rectangular field of view is

[0170] S Star = S 12Star + S 23Star + S 34Star + S 14Star

[0171] = f(Z 1 , Z 2 , Z Star ) + f(Z 2 , Z 3 , Z Star ) + f(Z 3 , Z 4 , ZStar ) + f(Z 1 , Z 4 , Z Star )

[0172] Then there is

[0173] If S Star > S 0 , then the star point is not within the field of view of the camera detector;

[0174] If S Star = S 0 , then the star point is within the field of view of the camera detector.

[0175] Step Five, repeat Step Three and Four until a satisfactory set of observation points is found, and output the right ascension and declination of the optimal observation point and the satellite attitude transformation matrix.

[0176] Embodiment:

[0177] In this embodiment, the satellite is equipped with an imaging camera, a star camera, and two star sensors. It should be noted that in practical applications, the number of cameras and star sensors can be configured arbitrarily. Figure 1 The schematic diagram of the system composition of this embodiment is given, Figure 2 The flowchart of the method implementation of the present invention is given. The specific implementation manners of the present invention will be described in detail below with reference to the accompanying drawings.

[0178] In Step One, according to the mission plan of the satellite, select the month or specific date for starry sky imaging, and select to perform multi-field-of-view starry sky imaging in the shadow area. Obtain the satellite orbit data through space-ground TT&C, and extrapolate to obtain the satellite orbit altitude on the starry sky observation day. For simplicity of calculation, when the satellite is in a circular orbit, the satellite orbit altitude can be directly approximated by using the nominal orbit altitude.

[0179] In Step Two, after obtaining the satellite orbit altitude H and the stray light suppression angle B of the imaging optical device, the included angle A between the XOY plane of the orbital coordinate system and the edge of the earth's atmosphere is

[0180]

[0181] The available cone C of the field of view of an optical device is

[0182]

[0183] where p is the thickness of the atmosphere and R e is the radius of the earth.

[0184] Perform the analysis of the observation sky area in the celestial coordinate system, and record the projection of the available cone of the field of view of the optical device on the celestial sphere as the optional sky area of the optical device, Figure 3 , 4The projection relationship between the optional conical field of view and the optional sky area of an optical device is given. When the optical axis of the optical device points in any direction within the cone range with R Z as the generatrix, it will not be interfered by the ground-air light. α 0 is the right ascension center point of the optional sky area of the optical device, and α 0 is related to the specific season / month when the observation is carried out. In particular, when observing at the spring equinox, summer solstice, autumn equinox, and winter solstice, the observation center points of the optional sky area are respectively

[0185] Spring equinox α 0 = 180°

[0186] Summer solstice α 0 = 270°

[0187] Autumn equinox α 0 = 0°

[0188] Winter solstice α 0 = 90°

[0189] The set of the optional sky area is

[0190] S = {α, δ: cos 2 (α - α 0 ) cos 2 δ + sin 2 δ ≤ sin 2 C}

[0191] If B > A, then C < 90°, and δ e ∈ (-C, C). The coordinates (α e , δ e ) describing the edge of the optional sky area are obtained by the following formula

[0192]

[0193] If B < A, then C > 90°, and δ e ∈ [-90°, 90°]. The coordinates (α e , δ e ) describing the edge of the optional sky area are obtained by the following formula

[0194]

[0195] Similarly, the optional sky areas of the imaging camera, star camera, and two star sensors can be obtained as S CAM 、S SC 、S STSA 、S STSB . The available sky areas of optical devices with different stray light suppression angles are different, with both overlapping and non-overlapping regions.

[0196] In step 3, when selecting the observation points, each observation point contains two celestial coordinate points. One point is the satellite +Z axis pointing point, and the coordinates are recorded as (α 1 , δ 1 ), and the other point is the pointing point of the vector located in the XOZ plane of the satellite's body system and having a certain positive angle with both the +X axis and the +Z axis, and the coordinates are recorded as (α 2 , δ 2 ).

[0197] When selecting the set of observation points, the principle of from wide to narrow and from sparse to dense should be followed. When selecting the set of observation points for the first time, the largest available sky area of the optical equipment should be covered, and the density is sparse; after one calculation, the second observation points should be selected near the first available observation points, and the density can be appropriately increased compared with the previous time, and so on.

[0198] According to the conversion relationship between the celestial coordinate system and the inertial system, the attitude conversion matrix C ib from the satellite J2000 inertial system to the body system can be calculated by the following formula

[0199]

[0200] where,

[0201] X T = Y T ×Z T

[0202] Then, according to the installation pointing of each optical equipment on the satellite, calculate the pointing of each optical equipment in the celestial coordinate system. The installation matrix of a certain optical equipment in the satellite's body system is C bCam , then the attitude matrix of this optical equipment in the J2000 inertial system is

[0203]

[0204] The coordinates (α, δ) of the optical axis of this optical equipment in the celestial coordinate system are

[0205]

[0206] Next, judge whether the pointing coordinates (α, δ) of the optical axis of a certain optical equipment are within the available sky area obtained in step 2:

[0207] When all the optical equipment are within their respective available sky areas, then this observation point is available;

[0208] When the pointing of one or two optical equipment axes is not within the available sky area and cannot meet the mission requirements, this observation point is not available;

[0209] Delete the unavailable observation points to obtain the available observation points.

[0210] In step 4, for the available observation points obtained in step 3, calculate the number of stars in the camera's field of view. First, according to the camera installation matrix, the shape of the field of view, and the coordinate system definition, establish an array of the pointing vectors of the edges of the camera's field of view in the satellite's body coordinate system as

[0211]

[0212] where n is the number of edge points of the field of view, and [z 1i z 2i z 3i T is the pointing of the i-th edge vector in the satellite's body coordinate system, and i = 1,..., n.

[0213] The coordinate array Cam of the camera's field of view edge vector in the celestial coordinate system ball can be obtained by the method described in step 3 of this step.

[0214]

[0215] According to the camera detector's field of view, determine whether a certain star point is within the detector's field of view of the optical device, calculate the number of star points in the camera's field of view, and select the observation point with the largest number of star points as the preferred observation point.

[0216] The present invention provides a specific method for determining whether a certain star point is within the detector's field of view of the optical device. The determination methods for common camera circular detector fields of view and rectangular detector fields of view are as follows.

[0217] · Circular field of view determination method 1: Calculate the angle Star , δ Star ) between the star point coordinates (α Cam , δ Cam ) and the camera optical axis coordinates (α

[0218] Ang = arccos(Z Star · Z Cam )

[0219] where the star point coordinates are from the known star catalog information.

[0220]

[0221] The semi-cone angle of the camera's circular field of view is D r , then there is

[0222] If Ang ≥ D r , then the star point is not within the camera detector's field of view;​

[0223] If Ang < D r , then the star point is within the camera detector's field of view.

[0224] · Method 1 for judging the rectangular field of view: Calculate the area of the rectangular field of view. The star point and the four points of the rectangular field of view can form four spherical triangles. Compare the sum of the areas of the four spherical triangles with the area of the rectangle. If they are equal, the star point is within the field of view; if it is larger, the star point is outside the field of view.

[0225] First, the calculation method of the area of a spherical triangle is given. As Figure 5 shown, for a spherical triangle P A P B P C with a radius of 1, the area is

[0226] S = P A + P B + P C - π

[0227] where P A , P B , P C are spherical angles. The spherical angle is measured by the plane angle formed by two planes. That is, the spherical angle P A is the angle between the plane P A OP B and the plane P A OP C . and are the perpendiculars from point P B and point P C to the line OP A respectively. Then the spherical angle P A is the angle between the vectors and . Then

[0228]

[0229]

[0230] where are the vectors from point O to point P A , point P B , and point P C respectively. Then

[0231]

[0232] Denote the function for calculating the area of the spherical triangle formed by the vectors within the sphere as Then there is

[0233]

[0234] The star point coordinates are (α Star , δ Star ), and the coordinates of the four points of the camera detector are (α 1 , δ 1 ), (α 2 , δ 2 ), (α 3 , δ 3 ), (α 4 , δ 4 ). The vector coordinates in the corresponding inertial system are Z star , Z 1 , Z 2 , Z 3 , Z 4 . Then

[0235] The area of the projection of the detector's field of view in celestial coordinates is

[0236] S 0 = S 123 + S 134 = f(Z 1 , Z 2 , Z 3 ) + f(Z 1 , Z 3 , Z 4 )

[0237] The sum of the areas of the four spherical triangles formed by the star point and the four points of the rectangular field of view is

[0238] S Star = S 12Star + S 23Star + S 34Star + S 14Star

[0239] = f(Z 1 , Z 2 , Z Star ) + f(Z 2 , Z 3 , Z Star ) + f(Z 3 , Z 4 , Z Star ) + f(Z 1 , Z 4 , Z Star )

[0240] Then

[0241] If S Star > S 0, then the star point is not within the field of view of the camera detector;

[0242] If S Star = S 0 , then the star point is within the field of view of the camera detector.

[0243] · Method two for judging the rectangular field of view: Use the directionality of cross product to judge whether a certain star point is within the rectangular field of view. The coordinates of the star point are (α Star , δ Star ), and the coordinates of the four points of the camera detector are (α 1 , δ 1 ), (α 2 , δ 2 ), (α 3 , δ 3 ), (α 4 , δ 4 ). Construct vectors p 12 (α 2 - α 1 , δ 2 - δ 1 ), p 23 (α 3 - α 2 , δ 3 - δ 2 ), p 34 (α 4 - α 3 , δ 4 - δ 3 ), p 41 (α 1 - α 4 , δ 1 - δ 4 ), p Star1 (α 1 - α Star , δ 1 - δ Star ), p Star2 (α 2 - α Star , δ 2 - δ Star ), p Star3 (α 3 - α Star , δ 3 - δ Star ), p Star4 (α 4 - α Star , δ 4 - δ Star ).

[0244] Then there is

[0245] If (p 12 × p Star1 ) * (p 34 × p Star3 ) ≥ 0 and (p 23 × p Star2 ) * (p 41 × p Star4 ) ≥ 0, then the star point is within the field of view of the camera detector;

[0246] Otherwise, the star point is not within the field of view of the camera detector.

[0247] It should be noted that due to the curvature of the spherical surface, there will be a certain error in judging the star points located at the edge of the field of view using this method.

[0248] In step five, repeat steps three and four until a satisfactory set of observation points is found, and output the right ascension and declination of the optimal observation points and the satellite attitude transformation matrix.

[0249] Continue to select denser new observation points near the preferred observation points obtained in step four. The selected new observation points and the preferred observation points obtained in step three are put together to form a new set of observation points. Repeat steps three and four to obtain the optimal set of observation points. Output the right ascension and declination (α j , δ j ), j = 1, …, m and the attitude transformation matrix C ib (j), j = 1, …, m from the satellite J2000 inertial system to the local system, where m is the number of optimal observation points.

[0250] Steps three, four, and five can be repeated multiple times according to the mission requirements and the tolerance of the computational workload to achieve the required optimization result.

[0251] The content not described in detail in the specification of the present invention belongs to the well-known technology in the art.

Claims

1. A method for target attitude planning of a multi-field-of-view star observation satellite, characterized in that the steps are as follows: Step 1, obtain the season or month when the satellite conducts star observation, the satellite orbit altitude, and the stray light suppression angle of the imaging optical device; Step 2, according to the projection relationship between the optional field of view of the optical device and the observable celestial area, give the optional celestial areas of each optical device; Step 3, according to the star distribution in the optional celestial area, select a set of observation points, obtain the pointing of each optical device in the celestial coordinate system under this observation point, judge whether it is in its available celestial area, and delete the unavailable observation points; Step 4, count the number of stars in the camera field of view under the available observation points, and optimize the available observation points; Step 5, repeat Steps 3 and 4 until a satisfactory set of observation points is found, and output the right ascension, declination of the optimal observation point and the satellite attitude transformation matrix; The specific method for giving the optional celestial areas of each optical device in Step 2 according to the projection relationship between the optional field of view of the optical device and the observable celestial area is as follows: After obtaining the satellite orbit altitude H and the stray light suppression angle B of the imaging optical device, the included angle A between the XOY plane of the orbital coordinate system and the edge of the earth's atmosphere is The available cone C of the optical device field of view is where p is the thickness of the atmosphere and R e is the radius of the Earth; Perform the analysis of the observable sky area in the celestial coordinate system. Denote the projection of the available conical field of view of the optical device on the celestial sphere as the optional sky area of the optical device. When the optical axis of the optical device points to any direction within the cone with R Z as the generatrix, it will not be interfered by the earth's atmospheric light. α 0 is the right ascension center point of the optional sky area of the optical device, and α 0 is related to the specific season / month when the observation is carried out; the observation center points of the optional sky area during the vernal equinox, summer solstice, autumnal equinox, and winter solstice are respectively Spring equinox α 0 = 180° Summer Solstice α 0 = 270° Autumnal Equinox α 0 = 0° Winter Solstice α 0 = 90° The set of optional celestial areas is S = {α, δ : cos 2 (α - α 0 )cos 2 δ + sin 2 δ ≤ sin 2 C} If B > A, then C < 90°, δ e ∈(-C, C), describing the coordinates (α e , δ e ) of the edge of the optional sky area are obtained by the following formula If B < A, then C > 90°, δ e ∈[-90°, 90°], describing the coordinates (α e , δ e ) of the edge of the optional sky area are obtained by the following formula 2. A method for target attitude planning of a multi-field-of-view star observation satellite according to claim 1, characterized in that: The stray light suppression angle specifically refers to: when the optical device is affected by external stray light, the imaging effect deteriorates or even fails. When the optical device images, there is a constraint on the stray light suppression angle. When the stray light rays are outside the stray light suppression angle, the optical device works normally. Otherwise, the imaging effect of the optical device deteriorates or it cannot work normally; the stray light includes sunlight and earth's atmosphere light.

3. A method for target attitude planning of a multi-field-of-view star observation satellite according to claim 1, characterized in that: According to the mission plan of the satellite, select the month or specific date for star imaging, and select to conduct multi-field-of-view star imaging in the shadow area. Obtain the satellite orbit data through satellite-ground measurement and control, and extrapolate to obtain the satellite orbit altitude on the star observation day. When the satellite is in a circular orbit, the satellite orbit altitude directly uses the nominal orbit altitude.

4. A method for target attitude planning of a multi-field-of-view star observation satellite according to claim 1, characterized in that: The specific method for selecting a set of observation points in Step 3 is as follows: When selecting the observation points, each observation point contains two celestial coordinate points. One coordinate point is the satellite +Z axis pointing point, and the coordinates are recorded as (α 1 , δ 1 ). The other coordinate point is the pointing point of the vector located in the satellite's body XOZ plane and having a certain positive angle with both the +X axis and the +Z axis, and the coordinates are recorded as (α 2 , δ 2 ); When selecting a set of observation points, follow the principle of from wide to narrow and from sparse to dense. When selecting the set of observation points for the first time, cover the largest optional celestial area of the optical device, and the density is sparse; After one calculation, when selecting the set of observation points for the second time, select the observation points near the first available observation points, and the density is encrypted compared with the previous time, and so on; According to the conversion relationship between the celestial coordinate system and the inertial coordinate system, the attitude conversion matrix C from the J2000 inertial coordinate system of the satellite to the body coordinate system of the satellite ib is calculated by the following formula Among them, X T = Y T × Z T According to the installation directions of each optical device on the satellite, calculate the directions of each optical device in the celestial coordinate system; assume that the installation matrix of the optical device in the satellite body system is C bCAM , then the attitude matrix of this optical device in the J2000 inertial system is as follows: Among them, is the vector representation of the optical axis of the optical device in the inertial system, and z 1 , z 2 , z 3 are the three components of the vector; The coordinates (α CAM , δ CAM ) of the optical axis of the optical device in the celestial coordinate system are δ CAM = arcsin(z 3 ), Next, determine whether the coordinates (α CAM , δ CAM ) of the optical axis of the optical device in the celestial coordinate system are within the available sky area obtained in Step 2: when the optical axes of all optical devices are in their respective optional celestial areas, then this observation point is available; when the optical axes of one or two optical devices do not point in the optional celestial area and cannot meet the mission requirements, this observation point is unavailable; Delete the unavailable observation points to obtain the available observation points.

5. A method for target attitude planning of a multi-field-of-view star observation satellite according to claim 4, characterized in that: The specific method for counting the number of stars in the camera field of view under the available observation points in Step 4 and optimizing the available observation points is as follows: First, according to the camera installation matrix, field of view shape, and coordinate system definition, establish an array of camera field of view edge pointing vectors in the satellite body coordinate system as where n is the number of field-of-view edge points, [z 1i z 2i z 3i T is the direction of the i-th edge vector in the satellite body frame, i = 1, …, n;​ Coordinate array Cam of the camera field-of-view edge vector in the celestial coordinate system ball Obtained by the method described in step 3 Based on the camera detector's field of view, determine whether a certain star point is within the detector's field of view of the optical device, calculate the number of star points in the camera's field of view, and select the observation point with the largest number of star points as the preferred observation point.

6. A method for target attitude planning of a multi-field-of-view star observation satellite according to claim 5, Characterized in that: When determining whether a certain star point is within the detector's field of view of the optical device, if the detector's field of view is a circular detector's field of view, it is carried out in the following manner: Calculate the angle between the star point coordinates (α Star , δ Star ) and the camera optical axis coordinates (α CAM , δ CAM ) Ang = arccos(Z Star ·Z CAM ) Among them, the star point coordinates are from known star catalog information; The half cone angle of the circular field of view of the camera is D r , then there is If Ang≥D r , then the star point is not within the field of view of the camera detector; If Ang < D r , then this star point is within the field of view of the camera detector.

7. A method for target attitude planning of a multi-field-of-view star observation satellite according to claim 5, Characterized in that: When determining whether a certain star point is within the detector's field of view of the optical device, if the detector's field of view is a circular detector's field of view, it can also be carried out by using the directionality of the cross product to determine whether a certain star point is within the rectangular field of view: The star point coordinates are (α Star , δ Star ), and the coordinates of the four points of the camera detector are (α 1 , δ 1 ), (α 2 , δ 2 ), (α 3 , δ 3 ), (α 4 , δ 4 ). Vectors p 12 (α 2 - α 1 , δ 2 - δ 1 ), p 23 (α 3 - α 2 , δ 3 - δ 2 ), p 34 (α 4 - α 3 , δ 4 - δ 3 ), p 41 (α 1 - α 4 , δ 1 - δ 4 ), p Star1 (α 1 - α Star , δ 1 - δ Star ), p Star2 (α 2 - α Star , δ 2 - δ Star ), p Star3 (α 3 -α Star ,δ 3 -δ Star )、p Star4 (α 4 -α Star ,δ 4 -δ Star ); If (p 12 × p Star1 ) * (p 34 × p Star3 ) ≥ 0 and (p 23 × p Star2 ) * (p 41 × p Star4 ) ≥ 0, then the star point is within the field of view of the camera detector; Conversely, then the star point is not within the camera detector's field of view.

8. A method for target attitude planning of a multi-field-of-view star observation satellite according to claim 5, Characterized in that: When determining whether a certain star point is within the detector's field of view of the optical device, if the detector's field of view is a rectangular detector's field of view, it is carried out in the following manner: Calculate the area of the rectangular field of view. The star point and the four points of the rectangular field of view form four spherical triangles. Compare the sum of the areas of the four spherical triangles with the rectangular area. If they are equal, the star point is within the field of view; if it is larger, the star point is outside the field of view; The specific calculation method for the area of a spherical triangle is as follows: For a spherical triangle P with a radius of 1 A P B P C the area is S = P A +P B +P C -π Among them, P A , P B , P C are spherical angles, and the spherical angle is measured by the plane angle formed by two planes. That is, the spherical angle P A is the angle between the plane P A OP B and the plane P A OP C . and are the perpendiculars from the point P B and the point P C to the straight line OP A respectively. Then the spherical angle P A is the angle between the vectors and . Then Among them, then are respectively the vectors from point O to point P A , point P B , point P C ; then Denote the vector within the sphere The function for calculating the area of the spherical triangle formed by it is Then there is The star point coordinates are (α Star , δ Star ), and the coordinates of the four points of the camera detector are (α 1 , δ 1 ), (α 2 , δ 2 ), (α 3 , δ 3 ), (α 4 , δ 4 ). The corresponding vector coordinates in the inertial system are Z star , Z 1 , Z 2 , Z 3 , Z 4 . Then The area projected by the detector's field of view in the celestial coordinate system is S 0 = S 123 + S 134 = f(Z 1 , Z 2 , Z 3 ) + f(Z 1 , Z 3 , Z 4 ) The sum of the areas of the four spherical triangles formed by the star point and the four points of the rectangular field of view is S Star = S 12Star + S 23Star + S 34Star + S 14Star = f(Z 1 , Z 2 , Z Star ) + f(Z 2 , Z 3 , Z Star ) + f(Z 3 , Z 4 , Z Star ) + f(Z 1 , Z 4 , Z Star ) Then there is If S Star > S 0 , then the star point is not within the field of view of the camera detector; If S Star = S 0 , then the star point is within the field of view of the camera detector.

9. A method for target attitude planning of a multi-field-of-view star observation satellite according to claim 5, Characterized in that: Continue to select denser new observation points near the preferred observation points obtained in Step 4. Combine the selected new observation points with the preferred observation points obtained in Step 3 to form a new set of observation points. Repeat Step 3 and Step 4 to obtain the optimal set of observation points. Output the right ascension and declination (α j , δ j ) of the optimal observation points, j = 1, …, m, and the attitude transformation matrix C ib (j) from the satellite J2000 inertial system to the local system, j = 1, …, m, where m is the number of optimal observation points.

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