A hierarchical fast search method for high-precision lunar satellite laser ranging echo signals

Abstract

The present invention discloses a hierarchical rapid search method for high-precision lunar-orbit satellite laser ranging echo signals, which belongs to the field of deep-space laser ranging technology. The method comprises: a ground-side laser emission system tracks and points to a target position according to a guidance file; emitting a long-pulse-width laser signal, and if no tracking target point echo is detected, performing a target point airspace search based on an Archimedean spiral search model; after receiving the tracking target point echo signal at the current position, stopping the Archimedean spiral search, and continuing to track the trend of the predicted orbit guidance file with the current position as the correction origin; if the tracking target point echo signal quality reaches a predetermined recognition threshold, emitting a narrow-pulse-width laser signal, entering a precision measurement mode, and acquiring high-precision laser measurement data. The present invention can effectively shorten the search time for lunar-orbit satellite angular reflection echoes, and improve the success rate of capturing satellite angular reflection laser echo signals in a complex and far-reaching Earth-Moon space environment.

Description

Technical Field

[0001] The invention belongs to the technical field of laser ranging, and in particular relates to a high-precision lunar orbit satellite laser ranging echo signal hierarchical rapid search method. Background Art

[0002] Laser corner reflector lunar ranging is a high-tech method used to accurately measure the Earth-Moon distance and study lunar dynamics. By emitting laser pulses to laser corner reflectors on the lunar surface and receiving the reflected light, the distance between the Earth and the Moon can be calculated. This technology is of great significance for verifying general relativity and studying the physical properties and motion of the Moon. Extrapolating lunar surface angles to lunar-orbiting satellites for laser ranging is crucial for precise orbit determination of Earth-Moon spacecraft and the development of Earth-Moon communication and navigation systems.

[0003] The operating principle of a laser corner reflector is based on the reflective properties of light: incident light, after being reflected by the corner reflector's three mutually perpendicular reflective surfaces, returns along its original path. Laser lunar measurement, due to the vast distance between the Earth and the Moon, produces extremely weak signals compared to those from near-Earth satellites. This requires extremely high laser pointing accuracy and is significantly affected by weather, atmospheric disturbances, and the position of celestial bodies, resulting in a very low probability of success. In particular, to obtain high-precision data, the laser pulse width must be limited, making the reflected signal even weaker.

[0004] To this extent, if the measurement target position changes from the lunar surface to a lunar orbit satellite, the difficulty of ranging will increase further, mainly reflected in the pointing error caused by the pointing orbit error and the decrease in the laser angle index caused by the satellite platform.

[0005] Traditional laser telescope systems used for space object ranging have fixed laser sources. Theoretically, the success rate of Earth-Moon laser ranging is positively correlated with the strength of the return signal. The greater the energy of a single laser pulse, the stronger the return signal, and the greater the probability of receiving the return signal. However, in practical applications, due to the inherent limitations of laser technology, it is impossible to achieve both narrow pulse width and high energy. Larger single laser pulses also tend to widen the pulse width, resulting in reduced ranging accuracy. Due to the low pulse energy of narrow-pulse lasers, it is difficult to ensure accurate pointing and obtain a valid return signal.

[0006] Unlike corner reflectors on the lunar surface, which are relatively fixed in position, tracking and ranging using laser angle reflectors on lunar-orbiting satellites currently relies heavily on long-term orbit determination by ground stations. This can lead to significant pointing errors when tracking and control resources are insufficient. Ranging laser beams typically operate in the fundamental mode, also known as the 00 mode, with energy exhibiting a quasi-Gaussian distribution, concentrated primarily at the beam center. If the laser telescope continues to measure distance only toward the intended target, pointing errors are likely to further reduce the probability of successful ranging.

[0007] Traditional laser ranging for lunar-orbiting spacecraft typically involves generating a pointing guidance file based on orbital measurements and predictions. This guidance file then guides the telescope's pointing direction. Inspectors manually adjust for pointing errors, searching for errors based on the deviation between the predicted and actual pointing directions. This method relies heavily on subjective judgment by the operator. When pointing errors or orbital prediction errors exist, it is impossible to accurately search the area covered by the error ellipsoid near the target point.

[0008] Therefore, how to improve the success rate of laser ranging from the Earth to the Moon orbit spacecraft corner reflector has become an important technical problem that needs to be solved urgently in this technical field. Summary of the Invention

[0009] To solve the above technical problems, the present invention provides a high-precision lunar satellite laser ranging echo signal hierarchical rapid search method. By improving the laser signal search method, the capture success rate of the Earth-Moon laser ranging echo signal is significantly improved.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A high-precision lunar satellite laser ranging echo signal hierarchical rapid search method comprises the following steps:

[0012] Step 1: The ground-side laser launch system tracks and points to the target location according to the guidance file;

[0013] Step 2: Enter the coarse measurement search phase and switch the laser light source of the ground laser transmission system to emit long-pulse laser signals;

[0014] Step 3: During the coarse search phase, if no echo of the tracking target point is detected, a spatial search for the target point is performed based on the Archimedean spiral search model.

[0015] Step 4: After receiving the tracking target point echo signal at the current position, stop the Archimedean spiral search and continue tracking the predicted orbit guidance file trend with the current position as the origin;

[0016] Step 5: If the quality of the echo signal of the tracking target point reaches the predetermined threshold, the control system switches to emitting a narrow pulse width laser signal, enters the precision measurement mode, and obtains high-precision laser measurement data.

[0017] In a second aspect, the present invention provides an electronic device comprising: one or more processors; a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned high-precision lunar satellite laser ranging echo signal hierarchical rapid search method.

[0018] In a third aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enables the processor to implement the aforementioned high-precision lunar satellite laser ranging echo signal hierarchical rapid search method.

[0019] The beneficial effects of the present invention are:

[0020] The present invention switches between laser light sources with multiple different pulse widths on the ground end, preferentially adopting long-pulse-width, high-energy laser signals in the early target search stage, and combining them with the Archimedean spiral search method to enhance the intensity of the transmitted and reflected signals and the laser search coverage range, thereby improving the success rate of signal capture in the complex and far-reaching Earth-Moon space environment.

[0021] After successfully capturing the target echo, the system switches to a narrow pulse width, high-precision laser signal to improve ranging accuracy. This pulse width switching mechanism enables the system to search for the correct laser direction more quickly and efficiently.

[0022] The Archimedean spiral method is used to search the target point airspace. This spiral search mode can systematically cover the target area, reduce search blind spots, and optimize search efficiency.

[0023] In summary, this invention can effectively improve the success rate of ground-based laser ranging of lunar-orbiting satellites, particularly in the complex and deep cis-lunar space environment. By switching between multi-pulse-width laser light sources and applying an Archimedean spiral search mode, the system can more efficiently capture target signals, providing more reliable ranging support for cis-lunar space exploration. This search method is not only applicable to lunar-orbiting satellite laser ranging but can also be extended to spacecraft orbiting deep space, including those on the lunar surface, in cis-lunar space, or elsewhere at significant distances from Earth. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of a high-precision lunar satellite laser ranging echo signal hierarchical rapid search method of the present invention;

[0025] Figure 2 This is the optical path diagram of the dual laser ranging transmission under the condition of dual laser switching through the beam splitter prism;

[0026] Figure 3 This is the optical path diagram of the dual laser ranging transmission under the condition of dual laser switching achieved by rotating the fast mirror;

[0027] Figure 4 This is a diagram of the laser ranging transmission optical path for achieving laser switching by Q-switching a single laser;

[0028] Figure 5 Schematic diagram of Archimedean spiral. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and examples.

[0030] like Figure 1 As shown, the present invention provides a high-precision, hierarchical, rapid search method for lunar satellite laser ranging echo signals. This method divides the search process into two phases: a coarse search and a fine search. By switching between laser light sources with multiple pulse widths on the ground, the laser pulse energy, pulse width, and frequency are adjusted. Its primary purpose is to use a long-pulse-width laser for the coarse search in the early stages of the experiment. This single-pulse laser has high energy, but a relatively low pulse frequency and long pulse duration, which reduces relative ranging accuracy. However, due to the increased signal energy, the echo signal is relatively enhanced, increasing the probability of echo capture. To avoid errors caused by inaccurate pointing and guidance files, an Archimedean spiral method is used to search the target point space to improve the success rate of signal capture. After successfully capturing the coarse search target signal, it can be confirmed that the current laser pointing is accurate. At this point, the method transitions to the fine search phase. While maintaining pointing, it switches to a narrow-pulse-width laser. This single-pulse laser has low energy, but a relatively high pulse frequency and short pulse duration, maintaining a high relative ranging accuracy. The specific steps are as follows:

[0031] Step 1: The ground-based laser launch system tracks and points to the target location according to the guidance file.

[0032] Step 2: Enter the coarse search phase and switch the ground laser launch system's laser light source to emit long-pulse, high-energy laser signals. Typically, the energy of a long-pulse single pulse is no less than 3J, the pulse width is no more than 10ns, and the pulse frequency is no less than 1Hz.

[0033] Step 3: During the coarse search phase, if no clear return signal is detected from the target point, an Archimedean spiral search is performed, and parameters are set. The ground-based laser control system adjusts the laser emission direction according to the preset Archimedean spiral model to conduct a spatial search for the target point. The Archimedean spiral model is designed based on the laser's divergence angle and orbital projection parameters. If no return signal is found, the Archimedean spiral is adjusted using the current predicted position as the origin and, combined with the theoretical orbit determination error from the guidance file, parameters such as pitch, number of scan revolutions, and rotation period are adjusted. Ensure that the scanning range covers the pointing error range.

[0034] Step 4: Monitor the return signal. Once the wide-beam laser echo is received at the current position, stop the Archimedean spiral search and continue tracking the predicted trajectory using the current position as the origin. Ranging accuracy is lower at this point, but accurate pointing can be quickly acquired.

[0035] Step 5: Pulse width switching: Once the signal quality reaches the predetermined threshold, the control system switches to a narrow-pulse-width, high-precision laser signal and enters precision measurement mode. This allows for acquisition of high-precision laser signals. The energy of a narrow-pulse-width laser pulse is typically no less than 300mJ, the pulse width no more than 100ps, and the pulse frequency no less than 100Hz.

[0036] Furthermore, during the coarse search phase, a long-pulse, high-energy laser is used as the primary light source to enhance signal energy and improve the probability of capture. After the ground receiving device receives the echo signal and successfully captures the target echo, it switches to a narrow-pulse, high-precision laser signal to improve ranging accuracy.

[0037] In step 2, two laser light sources with different pulse widths are used, including a long pulse width (selected wavelength of 562 nm, single pulse energy of 3 J, pulse frequency of 10 Hz, and pulse width of 7 ns) and a narrow pulse width laser (selected wavelength of 1064 nm, single pulse energy of 300 mJ, pulse frequency of 1000 Hz, and pulse width of 75 ps).

[0038] like Figure 2 As shown in the figure, two groups of lasers with long pulse width and narrow pulse width are used to realize the dual laser laser common path through the beam splitter prism, and the light source switching is realized by controlling the lasers to emit light at different times. Figure 3 As shown, light source switching is achieved through a fast-reflection mirror. A fast-reflection mirror is a lens that can quickly and precisely change the direction of a reflected light beam. It typically consists of a high-precision reflective mirror and a fast-response drive mechanism. The drive mechanism controls the mirror's rotation about one or two axes, enabling rapid adjustment of the beam's direction. By adjusting the fast-reflection mirror's rotational position, lasers with different pulse widths can be introduced into the telescope's optical path, enabling rapid switching between different lasers.

[0039] Preferably, a single laser can be used to adjust the pulse width and pulse energy of the single laser through the acousto-optic or electro-optic Q-switching technology generated by the modulator, so as to achieve the effect of switching between different pulse widths and energies of dual lasers. Figure 4 shown.

[0040] The laser echo signal reflected from the moon is detected using a signal receiving system, which includes a highly sensitive photoelectric detector and a signal processing unit, such as a superconducting nanowire detector.

[0041] For Archimedean spiral search, a mathematical model is used to generate an Archimedean spiral path, which can systematically cover the target airspace, reduce search blind spots, and improve search efficiency and measurement accuracy. Archimedean spiral is a spiral with special properties, such as Figure 5As shown. Assume that point A starts at point O, the center of the cross, and moves at a constant speed along the line OA while also rotating around point O at a constant angular velocity. When viewed from above, point A's trajectory is a spiral. This type of spiral is named an "Archimedes spiral." Because it moves at a constant speed, it can also be defined as a "constant velocity spiral." The equation for the Archimedean spiral in polar coordinates is:

[0042] r(θ)=a+b(θ)

[0043] Where: b is the spiral coefficient, in km / °, which represents the change in the curve diameter when the curve changes by 1°; θ is the rotation angle, in degrees, which represents the total number of degrees the curve rotates; a is the polar diameter when θ = 0°, in km.

[0044] The Archimedean spiral search path is generated based on pre-set parameters, such as pitch and starting radius. During the actual search, these parameters can be dynamically adjusted, such as in areas suspected of echoes or areas of focus. The Archimedean spiral parameters are selected to match the orbit determination error and laser divergence. Assuming a 1-meter laser aperture, a laser divergence of 0.6 arc seconds (half-degree), and a satellite-to-earth distance of approximately 380,000 kilometers, the diameter of the light spot upon reaching the lunar-orbiting satellite is approximately 2.2 kilometers. Assuming an orbit determination error of 10 kilometers using the guidance file obtained through radio orbit determination, the number of scan revolutions is set to 5, with a pitch of 0.01 arc minute, resulting in a total scan radius of 0.05 arc minutes and a coverage range of approximately 11 kilometers. This provides complete coverage of the target airspace.

[0045] By increasing the laser pulse energy and pulse width, combined with an Archimedean spiral search method, the probability of successful ranging from a ground-based laser station to a lunar-orbiting satellite's laser corner reflector can be effectively increased. This search method is applicable not only to lunar orbit laser corner reflectors but also to spacecraft on the lunar surface, in cislunar space, and in other deep-space orbits far from Earth.

[0046] In a second aspect, the present invention provides an electronic device comprising: one or more processors; a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned high-precision lunar satellite laser ranging echo signal hierarchical rapid search method.

[0047] In a third aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enables the processor to implement the aforementioned high-precision lunar satellite laser ranging echo signal hierarchical rapid search method.

[0048] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-precision lunar satellite laser ranging echo signal hierarchical rapid search method, characterized in that: The steps are as follows: Step 1: The ground-side laser launch system tracks and points to the target location according to the guidance file; Step 2: Enter the coarse measurement search phase and switch the laser light source of the ground laser transmission system to emit long-pulse laser signals; Step 3: During the coarse search phase, if no echo of the tracking target point is detected, a spatial search for the target point is performed based on the Archimedean spiral search model. Step 4: After receiving the tracking target point echo signal at the current position, stop the Archimedean spiral search and continue tracking the predicted orbit guidance file trend with the current position as the origin; Step 5: If the quality of the echo signal of the tracking target point reaches the predetermined recognition threshold, the control system switches to emitting a narrow pulse width laser signal and enters the precision measurement mode, at which time high-precision laser measurement data can be obtained.

2. The high-precision lunar satellite laser ranging echo signal hierarchical rapid search method according to claim 1 is characterized in that: In step 2, two lasers with different pulse widths are used as the laser light sources of the emission system.

3. The high-precision lunar satellite laser ranging echo signal hierarchical rapid search method according to claim 2 is characterized in that: The two lasers with different pulse widths are switched through a beam splitter prism or a fast-reflecting mirror.

4. The high-precision lunar satellite laser ranging echo signal hierarchical rapid search method according to claim 1 is characterized in that: A single laser can also be used to switch between long-pulse-width laser signals and narrow-pulse-width laser signals through acousto-optic modulation or electro-optical Q-switching technology.

5. The high-precision lunar satellite laser ranging echo signal hierarchical rapid search method according to claim 2, characterized in that: The two lasers with different pulse widths include a long pulse width laser and a narrow pulse width laser. The single pulse energy of the long pulse width laser is not less than 3J, the pulse width is not greater than 10ns, and the pulse frequency is not less than 1Hz; the single pulse energy of the narrow pulse width laser is not less than 300mJ, the pulse width is not greater than 100ps, and the pulse frequency is not less than 100Hz.

6. The high-precision lunar satellite laser ranging echo signal hierarchical rapid search method according to claim 1, characterized in that: In step 3, if the tracking target point echo is still not detected, the Archimedean spiral is adjusted with the current predicted position as the origin and combined with the theoretical orbit determination error of the guidance file to ensure that the scanning range covers the pointing error range.

7. The high-precision lunar satellite laser ranging echo signal hierarchical rapid search method according to claim 6, characterized in that: The adjustment of the Archimedean spiral includes the pitch, the number of scanning turns, and the rotation period.

8. The high-precision lunar satellite laser ranging echo signal hierarchical rapid search method according to claim 1, characterized in that: During the search process, the laser is pointed to an Archimedean spiral, and the curve equation of the Archimedean spiral in plane polar coordinates is: r(θ)=a+b(θ), Where b is the spiral coefficient, in km / °, which represents the change in the curve diameter when the curve changes by 1°; θ is the rotation angle, in degrees, which represents the total number of degrees the curve rotates; and a is the polar diameter when θ = 0°, in km.

9. An electronic device, characterized in that: include: one or more processors; a memory for storing one or more programs; Among them, when one or more programs are executed by the one or more processors, the one or more processors implement a high-precision lunar satellite laser ranging echo signal hierarchical rapid search method as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that Executable instructions are stored thereon, which, when executed by a processor, enable the processor to implement a high-precision lunar-orbit satellite laser ranging echo signal hierarchical rapid search method as described in any one of claims 1-8.

Images