A multi-head fusion star sensor system and a method of using the same

Abstract

The application relates to a multi-head fusion star sensor system use method, and relates to the technical field of satellite attitude measurement and determination. Three star sensor probes are arranged on a satellite, and each star sensor is provided with a matrix; four groups of attitude quaternions output by the star sensor correspond to three probes and fusion star sensors respectively; a reference probe is selected to set a mark, and the attitude reference of the attitude quaternions output by the fusion star sensor is adjusted to be consistent with the matrix of the probe; the angles between the three probes and stray light including sunlight and earth light are calculated in real time; the effectiveness flags of the three probes are judged to be effective or ineffective; if the three probes are all effective, the current reference probe is not switched; if two probes are effective or one probe is effective, the reference probe is switched to the effective probe; if the reference probe is effective, the reference probe is not switched. The application has the advantages that the reference probe is ensured to be in an effective state, the output of the fusion star sensor can be corrected in real time, and the star sensor output precision is ensured.

Description

Technical Field

[0001] This invention relates to the field of satellite attitude measurement and determination technology, and in particular to a method for using a multi-head fusion star sensor system. Background Technology

[0002] The star sensor output quaternion is actually the attitude quaternion of the star sensor's body coordinate system relative to the inertial coordinate system. The star sensor output is characterized by high accuracy on the optical axis and low accuracy on the horizontal axis.

[0003] The multi-head fusion star sensor can output the attitude quaternions corresponding to the three probes in real time, and can also output the fused quaternions calculated based on the reference probe and the other two probes. According to the internal fusion algorithm of the star sensor, the output accuracy of the fusion star sensor can be further improved based on the single probe, especially the horizontal axis pointing accuracy of the star sensor.

[0004] The core idea of ​​the star sensor's internal fusion algorithm is as follows: First, a reference star sensor is specified. Then, the fused quaternion output data is the attitude quaternion of the reference sensor's coordinate system relative to the inertial coordinate system. When the reference star sensor is valid, the star sensor software estimates the transformation matrix of other sensor coordinate systems relative to the reference sensor coordinate system in real time. At the same time, the output information of the reference sensor and other valid sensors is fused to improve the star sensor output accuracy. When the reference star sensor is invalid, the star sensor no longer estimates the real-time transformation matrix of other sensor coordinate systems relative to the reference sensor coordinate system. It can only use the estimated transformation matrix that was valid in the last frame, and the fusion calculation only uses other valid sensors. Due to various factors such as different satellite orbits, different star sensor installation layouts, and satellite attitude maneuvers based on user missions, each probe of the star sensor is inevitably subject to interference from stray light such as sunlight and atmospheric light. As the satellite operates in orbit, its external heat flux changes in real time, affecting and altering the satellite's structure, which in turn causes changes in the relative transformation relationships between the various probes of the star sensor. When the reference probe becomes invalid due to interference from stray light such as sunlight and atmospheric light, the star sensor no longer estimates the real-time transformation matrix of the coordinate systems of other probes relative to the reference probe coordinate system, and only uses the last valid estimated transformation matrix. If the reference probe is not switched, the fusion algorithm cannot compensate for the real-time changes in the relative relationships between the probes, which will lead to fluctuations or even a decrease in the output accuracy of the fused star sensor.

[0005] Therefore, to address the above shortcomings, a method for using a multi-head fusion star sensor system is needed. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] The technical problem to be solved by this invention is to address the issue of star sensor probes being susceptible to stray light, which leads to a decrease in accuracy.

[0008] (II) Technical Solution

[0009] To address the aforementioned technical problems, this invention provides a method for using a multi-head fusion star sensor system, comprising the following steps:

[0010] I. Three star sensor probes are mounted on the satellite, and each star sensor is equipped with a matrix to transform the star sensor measurement coordinate system and the satellite body coordinate system;

[0011] II. The star sensor outputs four sets of attitude quaternions Q1, Q2, Q3 and Q4, which correspond to the three probes and the fused star sensor respectively; at the same time, one of the three probes is selected as the reference probe setting flag, and the attitude reference of the attitude quaternion Q4 output by the fused star sensor is adjusted to be consistent with the matrix of that probe.

[0012] Ⅲ. Calculate the angles between the three probes and stray light, including sunlight and ground-level light, in real time, and determine whether the output validity flags of the three probes are valid or invalid;

[0013] VI. If all three probes are valid, the current reference probe will not be switched. If two probes or one probe is valid, the reference probe will be switched to the valid probe. If the reference probe is valid, the probe will not be switched.

[0014] As a further explanation of the present invention, preferably, when the angle between the probe optical axis and the stray light is less than 30°, the probe outputs an invalid validity flag; when the angle between the probe optical axis and the stray light is greater than or equal to 30°, the probe outputs an valid validity flag.

[0015] As a further explanation of the present invention, preferably, the angle between the probe's optical axis and the sunlight... The calculation satisfies:

[0016]

[0017] in,

[0018] The angle between the probe and the satellite's pointing vector towards the Earth's center;

[0019] This is the half-angle of Earth at the satellite's position.

[0020] As a further explanation of the present invention, preferably, the angle between the probe and the satellite pointing to the geocentric vector... satisfy:

[0021]

[0022] in,

[0023] The vector in the third row of the probe mounting matrix represents the direction of the Z-axis of the body coordinate system in the star sensor measurement coordinate system;

[0024] It is the unit vector of the satellite's body coordinate system.

[0025] As a further explanation of the present invention, preferably, the unit vector of the satellite body coordinate system satisfy:

[0026]

[0027] in,

[0028] Calculate the transformation matrix corresponding to the satellite's inertial attitude for each control cycle;

[0029] This is the unit vector of the satellite in the geocentric equatorial inertial coordinate system.

[0030] As a further explanation of the present invention, preferably, the angle between the probe's optical axis and the sunlight... The calculation satisfies:

[0031]

[0032] in This is the unit vector of the Sun in the satellite's body coordinate system.

[0033] As a further explanation of the present invention, preferably, the unit vector of the sun in the satellite body coordinate system is... satisfy:

[0034]

[0035] in It is the unit vector of the Sun in the geocentric equatorial inertial coordinate system.

[0036] As a further explanation of the present invention, preferably, the conversion matrix of the three star sensor probes satisfies:

[0037]

[0038] in This represents the number of probes.

[0039] (III) Beneficial Effects

[0040] The above-described technical solution of the present invention has the following advantages:

[0041] This invention autonomously calculates the effectiveness of the reference probe and autonomously removes invalid probes, ensuring that the reference probe of the fused star sensor is in an effective state, guaranteeing the accuracy of the real-time output of the fused attitude, and improving the autonomy of satellite attitude measurement and determination; it also has good versatility and can be extended to other models that use multi-head fused star sensors. Attached Figure Description

[0042] Figure 1 This is a flowchart of the multi-head fusion star sensor system of the present invention.

[0043] Figure 2 This is a flowchart of the probe setup process of the present invention;

[0044] Figure 3 This is a flowchart of the probe switching process of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] A method for using a multi-head fusion star sensor system, the system comprising one circuit and three sensor probes. A matrix is ​​installed on the satellite for the three sensor probes, representing the transformation relationship from the star sensor measurement coordinate system to the satellite's body coordinate system. , , These correspond to probe 1, probe 2, and probe 3, respectively. For example... Figure 1 As shown, the method specifically includes the following steps:

[0047] I. Pre-binding and installation matrix , , Within the satellite control system application software, the star sensor can output four sets of attitude quaternions. , , , These correspond to Probe 1, Probe 2, Probe 3, and the fused star sensor, respectively. The fused star sensor is the result of the algorithm within the star sensor and is not a physical probe.

[0048] II. Star-sensor output fused with star-sensor attitude quaternion Simultaneously, the "Reference Probe Setting Flag" needs to be output. When the "Reference Probe Setting Flag" is Probe 1, the star sensor outputs a fused star sensor quaternion. The attitude reference is consistent with probe 1, which is When the "Reference Probe Setting Flag" is set to Probe 2, the star sensor outputs a fused star sensor quaternion. The attitude reference is consistent with probe 2, which is When the "Reference Probe Setting Flag" is set to Probe 3, the star sensor outputs a fused star sensor quaternion. The attitude reference is consistent with probe 3, which is .

[0049] III. The satellite control system application software uses fused star-aware quaternions by default in orbit. During attitude determination, it is necessary to acquire the "reference probe setting flag" output by the star sensor in real time to switch the attitude reference, i.e., to fuse the star sensor quaternions. Switching the mounting matrix. If the reference probe returned by the star sensor is probe 1, then set the mounting matrix of the fused star sensor quaternion Q4 to be the same as that of probe 1. If the reference probe is probe 2, then set the fusion star-sensor quaternion. The mounting matrix is ​​the same as that of probe 2, which is... If the reference probe is probe 3, then set the fusion star-sensor quaternion. The installation matrix is ​​the same as that of probe 3, which is .

[0050] VI. The control system application software calculates the angles between the three probes and stray light such as sunlight and atmospheric radiation in real time on orbit, and sets the validity flags for probe 1, probe 2, and probe 3 outputs. Based on the "probe output validity flags" and the "reference probe setting flags" returned by the current star sensor, the control system application software sets the star sensor reference probes, where:

[0051] Each control cycle of the satellite calculates the unit vector of the sun in the geocentric equatorial inertial coordinate system. Simultaneously, the satellite calculates its inertial attitude during each control cycle, and its corresponding conversion array... Specifically:

[0052]

[0053] in These represent the number of probes, which are 1, 2, and 3 respectively.

[0054] It can calculate the unit vector of the sun in the satellite's body coordinate system. Specifically:

[0055]

[0056] The angles between star sensor probes 1, 2, and 3 and sunlight are respectively:

[0057]

[0058]

[0059]

[0060] in, , and These are the vectors in the third row of the three probe installation matrices, representing the direction of the Z-axis of the body coordinate system in the star sensor measurement coordinate system. The satellite's position vector in the geocentric equatorial inertial coordinate system is calculated for each control cycle. The unit vector is Then the unit vector of the satellite pointing to the Earth's center in the geocentric equatorial inertial coordinate system is: It can calculate the unit vector of the satellite pointing to the Earth's center in the satellite's body coordinate system. for:

[0061]

[0062] The angles between star sensor probes 1, 2, and 3 and the satellite's geocentric vector are respectively:

[0063]

[0064]

[0065]

[0066] The half-angle of Earth at the satellite's position can be calculated based on the satellite's orbit. And the angles between star sensor probes 1, 2, and 3 and sunlight are obtained to satisfy:

[0067]

[0068]

[0069]

[0070] When the angle between the probe's optical axis and sunlight or ground-to-ground light is less than 30 degrees, the star-sensor is considered to be potentially seeing stray light, and the probe's output validity flag is set to invalid. Only when both the angle between the probe's optical axis and sunlight, and the angle between the probe's optical axis and ground-to-ground light are greater than or equal to 30 degrees, is the probe's output validity flag set to valid.

[0071] V. The control system application software sets the star sensor reference probe based on the "probe output validity flag" and the "reference probe setting flag" returned by the current star sensor, specifically as follows:

[0072] 1. When all three output validity flags of probes 1, 2, and 3 are valid, keep the current reference probe settings unchanged.

[0073] 2. When only one of the probes in the "Probe 1, 2, 3 Output Validity Flags" is invalid, if the invalid probe is not the reference probe, the current reference probe setting remains unchanged; if the invalid probe is the reference probe, the control system application software automatically sends a command to the star sensor to switch the reference probe to another probe that does not show stray light; if probe 1 is the reference probe and is invalid, then the reference probe is switched to probe 2; if probe 2 is the reference probe and is invalid, then the reference probe is switched to probe 3; if probe 3 is the reference probe and is invalid, then the reference probe is switched to probe 1.

[0074] 3. When two probes in the “Probe 1, 2, 3 Output Validity Flags” are invalid, the control system application software will automatically send a command to the star sensor to switch the reference probe to the valid probe.

[0075] 4. When all "output validity flags of probes 1, 2, and 3" are invalid, keep the current reference probe settings unchanged.

[0076] In summary, this invention calculates in real time the angles between the three probes of the multi-head fusion star sensor and stray light such as sunlight and atmospheric light. When the angle is less than 30 degrees (parameter adjustable), the star sensor probe is considered to be seeing stray light. If the reference probe sees stray light, the reference probe is switched according to a predetermined logic to ensure that the reference probe is effective in real time and to guarantee the star sensor output accuracy under all attitude conditions. At the same time, the onboard software judges the selection status of the star sensor reference probe in real time. After the star sensor reference probe is switched, the attitude reference of the fusion star sensor quaternion is switched in a timely manner to ensure a smooth transition of the satellite attitude.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for using a multi-head fusion star sensor system, characterized in that: Includes the following steps: I. Three star sensor probes are mounted on the satellite, and each star sensor is equipped with a matrix to transform the star sensor measurement coordinate system and the satellite body coordinate system; II. The star sensor outputs four sets of attitude quaternions Q1, Q2, Q3 and Q4, which correspond to the three probes and the fused star sensor respectively; at the same time, one of the three probes is selected as the reference probe setting flag, and the attitude reference of the attitude quaternion Q4 output by the fused star sensor is adjusted to be consistent with the matrix of that probe. III. Calculate in real-time the angles between the three probes and stray light, including sunlight and atmospheric light. If the angle between the probe's optical axis and the stray light is less than 30°, the probe outputs an invalid validity flag; if the angle is greater than or equal to 30°, the probe outputs an valid validity flag. Determine whether the validity flags of the three probes are valid or invalid. The angle between the probe's optical axis and sunlight is... The calculation satisfies: in This is the unit vector of the Sun in the satellite's body coordinate system; Unit vector of satellite body coordinate system satisfy: in, Calculate the transformation matrix corresponding to the satellite's inertial attitude for each control cycle; This is the unit vector of the satellite in the geocentric equatorial inertial coordinate system; The angle between the probe and the satellite pointing to the Earth's center vector satisfy: in, The vector in the third row of the probe mounting matrix represents the direction of the Z-axis of the body coordinate system in the star sensor measurement coordinate system; This is the unit vector in the satellite's body coordinate system; The angle between the probe's optical axis and sunlight The calculation satisfies: in, The angle between the probe and the satellite's pointing vector towards the Earth's center; The half-angle of Earth's surface relative to the satellite's position; VI. If all three probes are valid, the current reference probe will not be switched. If two probes or one probe is valid, the reference probe will be switched to the valid probe. If the reference probe is valid, the probe will not be switched.

2. The method of using a multi-head fusion star sensor system according to claim 1, characterized in that: The unit vector of the sun in the satellite's body coordinate system satisfy: in It is the unit vector of the Sun in the geocentric equatorial inertial coordinate system.

3. The method of using a multi-head fusion star sensor system according to claim 2, characterized in that: The conversion matrix of the three star sensor probes satisfies: in This represents the number of probes.

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