阅读说明：本技术 一种低轨卫星大幅宽探测垂轨摆扫方法 (Low-orbit satellite large-width detection vertical orbit swinging scanning method ) 是由 曹永奎 倪淑燕 廖育荣 李兆铭 李磊 于 2019-12-25 设计创作，主要内容包括：本发明提供一种低轨卫星大幅宽探测垂轨摆扫方法,具体过程为：(一)计算卫星的角速度；(二)计算卫星扫描过程中图像的中心位置；(三)基于所述卫星角速度,计算指向图像中心位置时卫星的位置；(四)根据所述卫星的位置,计算指向图像中心位置时卫星的期望姿态；根据所述期望姿态对卫星进行控制,实现大幅宽探测垂轨摆扫。该方法能够实现卫星的垂轨摆扫,充分利用过顶时间,提升敏捷成像的效率。(The invention provides a low-orbit satellite large-width detection vertical orbit swinging scanning method, which comprises the following specific processes: calculating the angular velocity of the satellite; (II) calculating the central position of the image in the satellite scanning process; (III) calculating the position of the satellite when the satellite points to the central position of the image based on the angular velocity of the satellite; fourthly, calculating an expected attitude of the satellite when the satellite points to the central position of the image according to the position of the satellite; and controlling the satellite according to the expected attitude to realize large-width detection vertical orbit swinging. The method can realize vertical orbit swing scanning of the satellite, fully utilizes the overhead time and improves the agile imaging efficiency.)

1. A low-orbit satellite large-width detection vertical orbit swinging method is characterized by comprising the following specific processes:

calculating the angular velocity of the satellite;

(II) calculating the central position of the image in the satellite scanning process;

(III) calculating the position of the satellite when the satellite points to the central position of the image based on the angular velocity of the satellite;

fourthly, calculating an expected attitude of the satellite when the satellite points to the central position of the image according to the position of the satellite; and controlling the satellite according to the expected attitude to realize large-width detection vertical orbit swinging.

2. The method for wide-range detection of vertical sweep of low earth orbit satellite according to claim 1, wherein the calculation process of the step (two) is as follows:

calculating the number m of imaging strips and the number n of times of imaging required in each strip according to the width of the camera and the size of a target area;

the longitude and latitude coordinates of four vertexes of the target area are assumed to be respectively: (Lo)_E,La_E)、(Lo_F,La_F)、(Lo_G,La_G) And (Lo)_H,La_H) In the case of the p (p.ltoreq.m) th and q (q.ltoreq.n) th images, the optical axis of the camera on the satellite should point to the point (Lo)_p,q,La_p,q)

When p is an odd number, the calculation formula is as follows:

when p is an even number, the calculation formula is as follows:

the satellite camera optical axis should point to a point (Lo)_p,q,La_p,q) Namely the central position of the image in the satellite scanning process.

3. The method for detecting the vertical swing of the low-earth-orbit satellite with the large width according to claim 2, wherein the step (three) is as follows:

suppose that the field angle at the time of the first imaging is γ₀The elevation point and the geocentric angle gamma of the satellite_p,qShowing the position of the satellite at the p-th strip and the q-th image,

γ_p,q＝γ₀+ω[(p-1)m+q]。

Technical Field

The invention relates to a low-orbit satellite large-width detection vertical orbit swinging scanning method, and belongs to the technical field of spacecraft control.

Background

The space-based platform detection is utilized to continuously observe the ground environment, the regional safety and the like, and the method has the advantages of strong sustainability, wide reachable range and the like. The low-orbit satellite platform can achieve higher resolution, and the formed constellation can achieve very high revisitation rate, so that the low-orbit satellite platform is the first choice for a plurality of earth observation satellites. However, the low orbit satellite earth observation field of view is limited, and the detection range needs to be widened, so that the detection capability of a large-range area is improved.

The wide-range imaging can image a wider area when the satellite passes by one time, the imaging efficiency of the satellite is improved, the satellite top-passing time is effectively utilized, and the cost is reduced. The satellite attitude change is utilized to adjust the sensor pointing direction, and the realization of satellite agile imaging is an effective way for expanding the imaging width. The posture change tracks in the agile imaging process are different, and the influence on the imaging performance is obvious. The method is characterized in that a proper posture track is designed, so that limited overhead time is fully utilized, the target area is subjected to wide imaging greatly, and the method is one of the problems to be solved for further improving the imaging efficiency.

Currently, the way for realizing large-width imaging by a low-orbit agile satellite adopts multi-strip scanning along the track direction: in the overhead time, a strip is formed by scanning in a posture maneuvering mode, the posture is adjusted after the scanning is finished, the next strip is scanned, and finally the large-width imaging is realized by splicing. This approach requires allocating a portion of the time for the satellite attitude maneuver during the over-the-top time, which reduces the detection capability of the agile satellite.

Disclosure of Invention

In view of the above, the invention provides a large-width detection vertical orbit swinging method for a low-orbit satellite, which can realize vertical orbit swinging of the satellite, fully utilize the overhead time and improve the efficiency of agile imaging, so that the limited time can be fully utilized in the overhead time of the agile satellite.

The technical scheme for realizing the invention is as follows:

a low-orbit satellite large-width detection vertical orbit swinging method comprises the following specific processes:

calculating the angular velocity of the satellite;

(II) calculating the central position of the image in the satellite scanning process;

(III) calculating the position of the satellite when the satellite points to the central position of the image based on the angular velocity of the satellite;

fourthly, calculating an expected attitude of the satellite when the satellite points to the central position of the image according to the position of the satellite; and controlling the satellite according to the expected attitude to realize large-width detection vertical orbit swinging.

Further, the calculation process of the step (two) of the present invention is:

calculating the number m of imaging strips and the number n of times of imaging required in each strip according to the width of the camera and the size of a target area;

the longitude and latitude coordinates of four vertexes of the target area are assumed to be respectively: (Lo)_E,La_E)、(Lo_F,La_F)、(Lo_G,La_G) And (Lo)_H,La_H) In the case of the p (p.ltoreq.m) th and q (q.ltoreq.n) th images, the optical axis of the camera on the satellite should point to the point (Lo)_p,q,La_p,q)

When p is an odd number, the calculation formula is as follows:

when p is an even number, the calculation formula is as follows:

the satellite camera optical axis should point to a point (Lo)_p,q,La_p,q) Namely the central position of the image in the satellite scanning process.

Further, the step (three) of the present invention is:

suppose that the field angle at the time of the first imaging is γ₀The elevation point and the geocentric angle gamma of the satellite_p,qShowing the position of the satellite at the p-th strip and the q-th image,

γ_p,q＝γ₀+ω[(p-1)m+q]。

advantageous effects

The invention can realize vertical rail swinging, thereby fully utilizing the overhead time, improving the agile imaging efficiency, fully exerting the capability of the satellite on-orbit task and improving the benefit.

Drawings

FIG. 1 is a schematic diagram of vertical swing scanning for large width detection.

FIG. 2 is a geometrical relationship analysis of satellite side-sway imaging.

Fig. 3 is a schematic diagram of roll and pitch angle calculations.

FIG. 4 shows a view stitching approach for vertical sweep.

FIG. 5 shows a schematic view of along-rail swipe imaging.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.

As shown in fig. 1, when the satellite reaches the upper part of the target area, the satellite starts to detect from one corner of the area, and after the detection is completed, the field of view is adjusted to move for the next detection, so that two detection fields can be spliced into a larger field of view, and thus a vertical rail strip-shaped area is formed repeatedly; the process is then repeated in reverse until the entire area is covered. In the process, the satellite controls the load direction through the attitude, and the whole process is realized.

Firstly, the height of a satellite orbit is assumed to be h km, and the single detection width of a satellite point under a carrying detector is s-a × b km²The maximum allowable inclination angle of the camera is α rad, and the size of a detection target area is S-l × wkm²Where l represents the along-rail length and w represents the perpendicular rail width; the radius of the earth is R.

Calculating satellite velocity and angular velocity

When the satellite passes by once, according to the load imaging capacity, the load points to the target area to start imaging scanning by adjusting the pitch angle when the target area is not reached. When leaving the area, imaging can be achieved within a certain range.

If the complete coverage of the specified area is ensured in the large-width swinging detection of the satellite, the imaging is started from the corner of the specified range, and the highest imaging efficiency can be ensured. In FIG. 2, A is the position of the satellite, C is the position of the sub-satellite point of A, B is the center position of the first image, and D is the first imageThe central point position of the sweep period is located in the track of the point under the satellite. A. the₁，A₂The orbit height is h km, O represents the geocentric, and R represents the radius of the earth.

From the sine theorem we can derive:

so that:

due to the fact that the & lt OBA & gt is & lt pi-alpha

This is B, C point-to-ground opening angle.

When calculating the roll angle phi, similar to the above process, see the left diagram of fig. 3, where the known condition is BD ═ w km, governed by the cosine theorem:

the roll angle value is therefore:

for the pitch axis, see the right diagram of fig. 3, it can be obtained by the cosine theorem of the triangle:

wherein the introduction of the beta is the change of the angle representation caused by the change of the orbit coordinate system, and the pitch angle can be calculated as follows:

substituting the specific numerical value to calculate the size of the product.

The computed satellite may advance the geocentric angle:

in one transit, the opening angle of the track section around the geocentric, which can allow the load to work, is as follows:

according to the satellite motion law, the satellite velocity and the angular velocity of the satellite at the height of h km can be calculated as follows:

wherein G is_E＝GM_E＝3.986×10¹⁴m³/s²And is the gravitational constant.

In the step, the maximum task time t of one transit can be further calculated_m：

Secondly, calculating the central position of the image in the scanning process

I.e. the center of the image at each scout imaging is calculated. As shown in fig. 4, EFGH is the four vertices of an area with known latitude and longitude, and the area is parallel to the locus of the sub-satellite points. The number (p, q) in the figure indicates the q-th image on the p-th band.

Calculating the number of imaging strips at least as follows according to the width of the camera and the size of the target area:

wherein w represents the vertical rail width and a represents the field of view width of the camera;

ceil (×) in the formula represents rounding up, and similarly, the number of images required in each band is:

wherein, l represents the length along the track, b represents the length of the field of view of the camera;

therefore, m × n imaging is required, and the images are uniformly distributed in the region. As shown in fig. 4, p denotes the imaging order of the bands, and q denotes the imaging order in the bands. The coordinates of the center point at each imaging can be obtained by calculation. And in the low-latitude area, the longitude and latitude are approximately calculated through the interpolation difference.

The longitude and latitude coordinates of four vertexes of the target area are assumed to be respectively: (Lo)_E,La_E)、(Lo_F,La_F)、(Lo_G,La_G) And (Lo)_H,La_H). In the p (p ≦ m) th band, q (q ≦ n) th image, the satellite camera optical axis should point to the point (Lo)_p,q,La_p,q) I.e., the center position of the image, the scanning directions are different when p is odd and even.

When p is an odd number, the calculation formula is as follows:

when p is an even number, the calculation formula is as follows:

thirdly, calculating the position of the satellite when pointing to the central point of the image

Assuming that the orbit parameters of the satellite are known, the earth center corresponding to the position of the satellite at the lifting point along the running direction of the satellite in the orbit plane is usedOpening angle gamma_p,qThe position of the satellite in the p (p is less than or equal to m) th strip and the q (q is less than or equal to n) th image is shown, and the field angle in the first imaging is assumed to be gamma₀Then, there are:

γ_p,q＝γ₀+ω[(p-1)m+q](17)

in the formula, ω is calculated from formula (11).

Fourthly, calculating the expected attitude of the satellite pointing to the central position

And transforming longitude and latitude coordinates in a geographic coordinate system into a representation under an orbit coordinate system through a typical coordinate transformation relation:

wherein i₀For orbital inclination, gamma-gamma_p,qFrom the coordinates (x)_o,y_o,z_o) Obtaining an expected attitude angle phi_p,q，θ_p,q，The calculation method is as follows:

through the four steps, the change condition of the expected value of the satellite attitude angle in the whole imaging task process can be calculated, and the satellite attitude control is completed according to the expected attitude given by the formula (19), so that the satellite can realize vertical-orbit wide scanning and large-range imaging.

In a traditional agile imaging mode of pushing and sweeping along a track, as shown in fig. 5, the distance between the end point of the previous strip and the start point of the next strip is far, large-angle attitude maneuver needs to be performed between imaging strips, and a large amount of time is occupied for attitude adjustment. The invention adopts a vertical rail swinging mode, the distance between the end point of the previous strip and the start point of the next strip is short, large-angle maneuvering is not needed between the strips, the overhead time can be fully utilized, the efficiency of agile imaging is improved, the capability of the satellite on-orbit task is fully exerted, and the benefit is improved.

Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, it will be apparent to those skilled in the art that various modifications may be made without departing from the principles of the invention and these are considered to fall within the scope of the invention.