CN111366149B

CN111366149B - Method for extracting sun vector direction based on lunar phase

Info

Publication number: CN111366149B
Application number: CN202010218019.9A
Authority: CN
Inventors: 杨中光; 朱晓铖; 蔡志鸣; 陈雯; 余金培
Original assignee: Shanghai Engineering Center for Microsatellites; Innovation Academy for Microsatellites of CAS
Current assignee: Shanghai Zhongkechen New Satellite Technology Co ltd
Priority date: 2020-03-25
Filing date: 2020-03-25
Publication date: 2022-02-15
Anticipated expiration: 2040-03-25
Also published as: CN111366149A

Abstract

According to the lunar phase-based solar vector direction extraction method, in a lunar sensitive period coordinate system, the solar vector direction is obtained by utilizing the invariance of an included angle between the lunar edge direction and the solar vector direction and combining the least square method and lunar phase information calculation, and satellite navigation is carried out by using the solar vector direction, so that the application range is wide.

Description

Method for extracting sun vector direction based on lunar phase

Technical Field

The invention relates to the technical field of aerospace, in particular to a method for extracting a sun vector direction based on a lunar phase.

Background

With the development of aerospace technology, the autonomous navigation capability of the satellite becomes more and more important, wherein the astronomical navigation becomes a hot point of autonomous navigation with the advantages of high autonomy, strong anti-interference performance, no accumulated error and the like, and the satellite autonomous navigation can be quickly realized by taking an external celestial body as a reference. The moon is the brightest celestial body of the earth at night, and the change of the lunar phase reflects relative information among the sun, the moon and an observer, so that sun vector information can be extracted from the lunar phase.

The current lunar phase-based solar vector method has a narrow application range and large measurement errors. For example, the document "study of a three-axis attitude determination method in the lunar imaging sensor running segment [ C ]// academic conference of the professional committee of deep space exploration technology of the national space society of astronomy,", 2005 "discloses a method for extracting a sun vector by using a lunar phase. As shown in fig. 1, the method uses the ratio of the visible chord length of the short month part to the original chord length to calculate the included angle between the moon center vector and the sun vector, and further calculates the sun vector according to the moon center vector. However, the method of this document is suitable for a case where the sun is far from the moon, and the sun-missing moon edge caused by the sun is relatively blurred compared to the moon edge profile, and therefore the sun vector direction calculation accuracy is low.

Disclosure of Invention

Aiming at partial or all problems in the prior art, the invention provides a method for extracting a sun vector direction based on a lunar phase, which comprises the following steps:

selecting an edge point Q_i；

Calculating the moon center O_mPoint to the edge point Q_iDirection of vector (d)

The vector direction of the moon center pointing to the edge point is also called moon edge direction; and

according to the moon's heart O_mPoint to the edge point Q_iThe sun vector direction S ═ x is calculated_s y_s z_s)^TWherein, in the step (A),

further, the edge points include N, where N is a natural number greater than 1.

Further, the lunar phase is obtained by shooting the moon through a moon sensor.

Further, the moon edge direction and the sun vector direction are calculated based on the moon sensor coordinate system.

Further, the edge direction of the moon is obtained by calculation through a sine theorem, the mapping of the moon on an imaging focal plane and a geometric relation of a focus of the moon sensor.

Further, the sun vector direction is calculated according to a least square method.

Further, the method also includes using the sun vector direction for satellite navigation.

According to the method for extracting the sun vector direction based on the lunar phase, provided by the invention, the vector direction of the sun under the coordinate system of the lunar sensor is calculated by utilizing multi-pixel information of the lunar phase edge according to the lunar center vector direction measured value and the current lunar phase and combining a least square method, so that the influence of measurement errors is reduced. Compared with the prior art, the method is simple in calculation and wide in application range, and is suitable for the condition that any included angle exists between the moon center vector direction and the optical axis of the moon sensor and the condition that different distances exist between the moon center vector direction and the moon.

Drawings

To further clarify the above and other advantages and features of embodiments of the present invention, a more particular description of embodiments of the present invention will be rendered by reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. In the drawings, the same or corresponding parts will be denoted by the same or similar reference numerals for clarity.

FIG. 1 is a diagram illustrating the use of chord length ratio to calculate the direction of a sun vector in the prior art;

FIG. 2 is a flow chart of a method for extracting sun vector direction based on lunar phase according to an embodiment of the present invention; and

fig. 3 is a schematic diagram of a lunar phase obtained by photographing a moon using a moon sensor in a method for extracting a solar vector direction based on the lunar phase according to an embodiment of the present invention.

Detailed Description

In the following description, the present invention is described with reference to examples. One skilled in the relevant art will recognize, however, that the embodiments may be practiced without one or more of the specific details, or with other alternative and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. Similarly, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the embodiments of the invention. However, the invention is not limited to these specific details. Further, it should be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

Reference in the specification to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

It should be noted that the embodiment of the present invention describes the process steps in a specific order, however, this is only for the purpose of illustrating the specific embodiment, and does not limit the sequence of the steps. Rather, in various embodiments of the present invention, the order of the steps may be adjusted according to process adjustments.

In order to obtain the sun vector direction, the invention provides a method for extracting the sun vector direction based on the lunar phase obtained by shooting the moon through a moon sensor, and satellite navigation is carried out by using the sun vector direction. The method is further described with reference to the embodiment drawings.

The embodiment of the invention adopts a moon sensor coordinate system O_f'X_sY_sZ_sAnd (3) calculating the direction of the relevant vector, wherein a schematic diagram of the lunar phase is adopted as shown in fig. 3, a moon 301 forms a crescent moon-shaped lunar phase outline 302 in an imaging focal plane of a lunar sensor, and the field angle of the lunar sensor is alpha. Wherein, O_mRepresents the center of the moon 301, called the moon center; o is_m' represents the moon center O_mAt the imaging focal plane X_sO_f'Y_sA mapping position of (a); o is_fRepresenting the imaging focus, with coordinates of (00f)^TThen, then

Representing the orientation of the optical axis of the moon sensor, denoted f, the magnitude f of which is the focal length of said moon sensor, and

a position vector representing the direction of the observer from the center of the moon, noted

The vector can be obtained by measuring through the moon sensor, and an included angle between the vector R and the optical axis direction is marked as theta; and Q_iRepresenting a point on the outline of the lunar phase illuminated by the sun, called an edge point, whose mapping at the imaging focal plane is denoted as Q_i', called edge contour pixel, said edge contour pixel Q_iThe coordinate of' is (x)_i y_i 0)^T。

Fig. 2 is a flowchart illustrating a method for extracting a sun vector direction based on a lunar phase according to an embodiment of the present invention. As shown in fig. 2, a method for extracting a sun vector direction based on a lunar phase includes:

step 201, selecting edge points. According to the lunar phase as shown in fig. 3, N edge points Q are selected on the edge contour of the moon illuminated by the sun_iThere are N corresponding edge contour pixels Q in the focal plane_i', wherein i ═ 1, 2.., N;

step 202, calculating the vector direction of the moon center pointing to each edge point respectively. As shown in fig. 3, the moon center O_mPointing to edge point Q_iDirection of vector (d)

Comprises the following steps:

wherein the content of the first and second substances,

and according to the sine theorem have

Wherein according to the sine theorem:

and

and

step 203, calculating the sun vector direction. Assuming that the moon is an ideal sphere, the direction S is (x) based on the sun vector_sy_s z_s)^TVector direction pointing to edge point from moon center

The included angles between the two are always equal:

then for the N selected edge points, there are:

whereby the sun vector direction can be calculated, where c is a constant, and when O_m' when within the region of the lunar phase contour 302, z_sIs-1, otherwise z_sIs 1.

In one embodiment of the invention, the solution is performed by using a least square method, and the formula is simplified to be

Wherein:

then solve to get

And further obtaining the sun vector direction under the coordinate system of the moon sensor.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various combinations, modifications, and changes can be made thereto without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention disclosed herein should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A method for extracting sun vector direction based on lunar phase is characterized in that, assuming that the moon is an ideal sphere, the method comprises the following steps:

selecting an edge point Q_i；

And

wherein c is a constant.

2. The method of claim 1, wherein the edge points comprise N, where N is a natural number greater than 1.

3. The method of claim 1, wherein the lunar phase is obtained by photographing a moon with a moon sensor.

4. The method of claim 2, wherein the sun vector direction is calculated according to a least squares method.

5. The method of claim 3, wherein the moon center O_mPoint to the edge point Q_iThe vector direction of (2) and the sun vector direction are calculated based on the moon sensor coordinate system.

6. The method of claim 5, wherein the moon center O_mPoint to the edge point Q_iThe vector direction of the moon is obtained by calculation according to a sine theorem, the mapping of the moon on an imaging focal plane and the geometric relationship of the focus of the moon sensor.

7. The method of one of claims 1 to 5, further comprising:

and performing satellite navigation by using the sun vector direction.