A laser sail attitude measurement device based on Cavendish torsion balance

Abstract

The present invention belongs to the field of laser sail technology, specifically a laser sail attitude measurement device based on Cavendish torsion balance. The laser sail attitude measurement device comprises a vacuum box, a laser sail, a tungsten wire, a magnet sheet, an aluminum block, a positioning laser source, a driving laser source, a fan, an aluminum frame, and a scale; wherein the laser sail is connected to one end of the tungsten wire and is hung inside the vacuum box; the magnet sheet and two aluminum blocks form electromagnetic damping, which are arranged on both sides of the laser sail; the driving laser source is used to emit a driving laser to the laser sail, and the positioning laser source is used to emit a positioning laser to the laser sail; the other end of the tungsten wire is fixed on the aluminum frame; the scale is arranged on the reflected light path of the laser sail, and the fan is installed at the rear end of the driving laser for air cooling the driving laser. The present invention can accurately measure the deflection motion of the laser sail under the excitation of laser light pressure, and the addition of electromagnetic damping eliminates most of the noise in the experiment, and has good stability and repeatability.

Description

Technical Field

[0001] The invention belongs to the technical field of laser sails, and in particular relates to a laser sail attitude measurement device. Background Art

[0002] In the mid-19th century, Maxwell theoretically predicted the existence of light pressure. In the early 20th century, Lebedev first experimentally measured the value of light pressure, which triggered the scientific concept of light pressure-driven space travel. In 2010, the Japanese space agency JAXA successfully launched the IKAROS laser sail into space and successfully completed various experiments, further stimulating people's enthusiasm for research on laser sail spacecraft. In 2016, Hawking proposed the "Breakthrough Starshot" plan, which aims to use the huge light pressure generated by the ground-based laser array to accelerate the laser sail to 20% of the speed of light to achieve interstellar travel, aiming at the stars and the sea, to explore extraterrestrial civilizations, search for planets suitable for human habitation, and find scarce metal resources on Earth. In 2019, the research team of Rensselaer Polytechnic Institute in the United States has designed a prototype of this laser sail. In contrast, my country is still in its infancy in the overall design of thin-film structure spacecraft such as laser sails with the mission of deep space exploration. For the design scheme that is still in the demonstration stage, its key technology still needs sufficient theoretical analysis, numerical calculation, and guidance and support from physical or semi-physical simulation experiments. The precise measurement of the motion posture of the laser sail is a challenge, which directly affects the prediction and regulation of its performance such as navigation stability. The Cavendish torsion balance can be used for the precise experimental measurement of various tiny physical quantities, such as the gravitational constant. G and Coulomb's law, etc. The present invention designs a laser sail attitude measurement experimental device based on the Cavendish torsion balance, which can accurately measure the deflection motion of the laser sail under the excitation of laser light pressure, and eliminates most of the noise in the experiment by adding electromagnetic damping, and has good stability and repeatability. Summary of the invention

[0003] The purpose of the present invention is to design a laser sail motion attitude measurement device based on Cavendish torsion balance with good stability and repeatability.

[0004] The laser sail motion attitude measurement device designed by the present invention based on Cavendish torsion balance is as follows: Figure 1 As shown, the principle is: after the laser is irradiated onto one side of the laser sail, the light pressure will generate a tiny torque, causing the torsion balance system to deflect; after the positioning laser is irradiated onto the laser sail and reflected by it, the tiny deflection can be amplified into an observable light spot displacement. By measuring the light spot displacement, the deflection angle and displacement of the torsion balance can be inversely calculated.

[0005] The laser sail motion attitude measurement device designed by the present invention based on Cavendish torsion balance is as follows: Figure 1As shown, it includes: a vacuum box, a laser sail, a tungsten wire, a magnet sheet, an aluminum block, a positioning laser source, a driving laser source, a fan, an aluminum frame, and a scale; wherein:

[0006] The laser sail is connected to one end of the tungsten wire through a clamp and hung inside the vacuum box; the magnet sheet is attached to the lower end of the laser sail, and there are two aluminum blocks, which are vertically arranged on both sides of the laser sail at a close distance. The magnet sheet and the two aluminum blocks form electromagnetic damping; the positioning laser and the driving laser are arranged outside the vacuum box;

[0007] The driving laser source is used to emit driving laser to the laser sail to deflect the laser sail. The area of ​​the light spot irradiated on the laser sail is adjusted by adjusting the focal length of the driving laser source to avoid the laser sail being burned by concentrated energy due to a small irradiation area.

[0008] The positioning laser source is used to emit positioning laser to the laser sail, which can amplify the deflection of the laser sail after reflection;

[0009] A slot is designed inside the vacuum box, and the aluminum frame can be stably stuck inside the vacuum box through the slot.

[0010] One end of the tungsten wire is connected to the laser sail, and the other end is fixed to the aluminum frame by screws and nuts. This fixing method is more efficient and has a higher fault tolerance. The reason for using tungsten wire is that the raw material is easy to obtain and the torsional stiffness of tungsten wire is also lower, that is, a larger deflection can be observed.

[0011] The scale is set on the reflected light path of the laser sail, and the distance from the laser sail is W ; When the positioning laser is irradiated on the laser sail, the laser is reflected onto the scale and used to amplify the deflection of the laser sail.

[0012] The fan is installed at the rear end of the driving laser with screws and nuts, and is used for air cooling the driving laser.

[0013] In the present invention, the laser sail is preferably a square with a side length of 8-12 cm (for example, a square with a side length of 10 cm).

[0014] In the present invention, the vacuum box is made of acrylic material. The use of the vacuum box can eliminate the interference of air to the greatest extent and reduce the systematic error of the experiment.

[0015] In the present invention, the fixture is two thin sheets prepared by 3D printing, with a size of 1 cm*0.5 cm*0.1 cm, and the laser sail is connected to the tungsten wire by screws and nuts.

[0016] In the present invention, the surface of the laser sail has a PET aluminum film, and the reason for using the aluminum film is that the reflectivity is high and the reflectivity is insensitive to the laser wavelength. In order to provide structural support, the PET aluminum film is glued to the fork-shaped PVC film.

[0017] In the present invention, the magnet sheet on the laser sail and the aluminum blocks placed on both sides of the laser sail form electromagnetic damping, which can effectively curb disturbances caused by airflow and temperature unevenness. At the same time, electromagnetic damping can also make the entire system quickly stabilize after being subjected to slight vibrations, thereby improving the efficiency of the entire system.

[0018] In the present invention, the driving laser can be selected to have a wavelength of 450nm and a power of 10W. After being partially absorbed, reflected and refracted by the acrylic vacuum box, the actual power irradiated on the laser sail is about 8.48W. The laser cooling method is air cooling, and the slight vibration generated by the fan can be eliminated by placing a rubber pad at the bottom of the vacuum box and electromagnetic damping.

[0019] In the present invention, a camera with a delayed photography function is also used and placed in front of the scale to capture the process of the light spot moving.

[0020] The present invention can accurately measure the deflection motion of the laser sail produced by the excitation of laser light pressure, and eliminates most of the noise in the experiment by adding electromagnetic damping, and has good stability and repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the device principle.

[0022] Figure 2 Schematic diagram of the device structure.

[0023] Figure 3 Experimental results: the movement of the light spot on the scale when the laser is turned on and off.

[0024] Numbers in the figure: 1 is a vacuum box, 2 is an aluminum frame, 3 is a card slot, 4 is a tungsten wire, 5 is a laser sail, 6 is an aluminum block, 7 is a magnet, 8 is a driving laser source, 9 is a positioning laser source, 10 is a camera, and 11 is a scale. DETAILED DESCRIPTION

[0025] The present invention is further described by way of examples below.

[0026] Embodiment 1:

[0027] The materials used and their parameters are as follows: The suspension wire is tungsten wire, with a diameter of d 30μm, length L is 5.1cm, the torsion coefficient G The laser sail is a square with a side length of 10 cm and a PET aluminum-coated film on the surface. Its reflectivity is R About 0.9, equivalent force arm l3.5cm; the vacuum box is made of acrylic material, with an outer diameter of 36cm*36cm*36cm, an inner diameter of 30cm*30cm*30cm, a thickness of 3cm, and an ultimate vacuum of -29.5inhg; the driving laser power is 10w, and the effective power P is 8.48W, wavelength is 450nm, incident angle θ 90°; positioning laser power 20mw; reflection distance W It is 144.5cm.

[0028] The operating steps of the device are as follows:

[0029] (1) Adjust the distance between the aluminum block and the magnet so that it can better suppress the vibration of the laser sail and will not affect the deflection of the laser sail. Close the vacuum box and use a vacuum pump to draw a vacuum.

[0030] (2) Turn on the positioning laser and illuminate it on the reflective film of the laser sail. Adjust the focal length and irradiation position of the positioning laser so that the reflected spot area is as small as possible and falls on the center of the scale. Turn on the driving laser and make sure that the irradiation area of ​​the driving laser is large enough so as not to burn the laser sail. After completion, turn off the driving laser and adjust the position of the camera. The preparation work is complete.

[0031] (3) Turn on the driving laser and shine it on the left end of the laser sail. It can be observed that the light spot on the scale emits displacement, indicating that the laser sail has been deflected. After turning off the driving laser, the light spot returns to its initial position.

[0032] (4) After repeating step (3) three times, adjust the driving laser irradiation position so that it irradiates the right end of the laser sail. At this time, you can observe that the light spot on the scale moves in the opposite direction. Turn off the driving laser and the light spot returns to the initial position. After repeating three times, the experiment ends.

[0033] (5) Process the experimental video into experimental data graphs, such as Figure 3 As shown, the experimental measurement value is about 8.69 cm.

[0034] (6) The theoretical value calculation formula is: ,in Where W is the reflection distance, P To drive the effective power of the laser, R is the laser sail reflectivity, θ To drive the laser incident angle, l For the equivalent force arm, c is the speed of light, G is the torsion coefficient of the tungsten wire, d is the diameter of the tungsten wire, L is the length of the tungsten wire. The theoretical value calculated is 9.68 cm, which is close to the experimental measurement value with an error of 10.2%.

[0035] Embodiment 2:

[0036] The suspension wire is tungsten wire, diameter d 30μm, length L is 12.0cm, the torsion coefficient G is 36 GPa; the laser sail is a square with a side length of 10 cm and a PET aluminum-coated film on the surface. R About 0.9, equivalent force arm l 4.0 cm; the vacuum box is made of acrylic, with an outer diameter of 36cm*36cm*36cm, an inner diameter of 30cm*30cm*30cm, a thickness of 3cm, and an ultimate vacuum of -29.5inhg; the laser power is 10w, and the effective power is P is 8.48W, wavelength is 450 nm, incident angle θ 90°; positioning laser power 20mw; reflection distance W It is 284.5cm.

[0037] The operating steps of Example 1 were repeated to obtain an experimental value of the spot offset of about 44.8 cm, and a theoretical value calculated to be 51.3 cm, with an error of 12.7%.

Claims

1. A laser sail motion attitude measurement device based on Cavendish torsion balance, characterized in that: include: Vacuum box, laser sail, tungsten wire, magnet sheet, aluminum block, positioning laser source, driving laser source, fan, aluminum frame, scale; among which: The laser sail is connected to one end of the tungsten wire through a clamp and hung inside the vacuum box; the magnet sheet is attached to the lower end of the laser sail, and there are two aluminum blocks, which are vertically arranged on both sides of the laser sail at a close distance. The magnet sheet and the two aluminum blocks form electromagnetic damping; the positioning laser and the driving laser are arranged outside the vacuum box; The driving laser source is used to emit driving laser to the laser sail to deflect the laser sail; The area of ​​the light spot irradiated on the laser sail is adjusted by adjusting the focal length of the driving laser source to avoid the laser sail being burned due to the concentrated energy caused by the irradiation area being too small. The positioning laser source is used to emit positioning laser to the laser sail, which can amplify the deflection of the laser sail after reflection; The vacuum box is provided with a slot inside, and the aluminum frame is clamped inside the vacuum box through the slot; One end of the tungsten wire is connected to the laser sail, and the other end is fixed to the aluminum frame through screws and nuts; The scale is set on the reflected light path of the laser sail, and the distance from the laser sail is W ; When the positioning laser is irradiated on the laser sail, the laser is reflected onto the scale and used to amplify the deflection of the laser sail; The fan is installed at the rear end of the driving laser and is used to perform air cooling on the driving laser; The laser sail is a square with a side length of 8-12 cm; The surface of the laser sail is provided with a PET aluminum-plated film.

2. The laser sail motion attitude measurement device based on Cavendish torsion balance according to claim 1 is characterized in that: The driving laser has a wavelength of 450nm and a power of 10W.

3. The laser sail motion attitude measurement device based on Cavendish torsion balance according to claim 1 is characterized in that: A camera with time-lapse photography function is placed directly in front of the scale to capture the process of light spot movement.

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