A rolling torque measurement device for electric thrusters based on laser induced fluorescence

Abstract

The present application relates to the field of thruster measurement technology, and specifically, to a rolling torque measurement device of an electric thruster based on laser induced fluorescence, including a laser emitting device, a fluorescence receiving device and a control system arranged inside an air floating platform, and an electric thruster and a modulating mirror group arranged inside a vacuum chamber, wherein: the laser emitting device includes a tunable laser, a signal source, a beam splitter, a laser wavelength monitoring device and a laser incident device; the fluorescence receiving device includes a monochromator, a photomultiplier tube and a phase-locked amplifier connected in sequence; the laser wavelength monitoring device and the phase-locked amplifier are both connected to the control system; the modulating mirror group includes a three-dimensional moving mechanism, an incident mirror group and a receiving mirror group; the incident mirror group is connected to the laser incident device; and the receiving mirror group is connected to the monochromator. The present application adopts a stable sub-picometer solid-state laser source, which will not affect the working characteristics of the electric thruster, realizes non-invasive measurement, and improves the accuracy of the test.

Description

Technical Field

[0001] The present application relates to the technical field of thruster measurement, and in particular to a rolling torque measurement device for an electric thruster based on laser induced fluorescence. Background Art

[0002] In the field of deep space exploration, spacecraft need to fly for a long time, which requires the electric thrusters to work in orbit for tens of thousands of hours. When the electric thrusters are working, while generating thrust, due to factors such as the effect of the grid on neutrality, the magnetic field on the beam, and the influence of the neutralizer position on the beam, a rolling torque will be generated along the thrust direction. Long-term operation will cause abnormal rotation of the satellite; because the torque is in the same direction as the thrust, it is impossible to offset the reverse torque through the satellite's vector adjustment mechanism, so it can only be offset by the torque generated by chemical propulsion or momentum wheels, which requires the measurement of the rolling torque, and based on the measurement results, requirements for the propellant carrying capacity of the chemical propulsion system or the operation of the momentum wheel are proposed.

[0003] The rolling moment generated by the electric thruster is in the order of hundreds of micro-newton meters. To use direct force measurement, the electric thruster needs to be suspended in the working state (vacuum conditions), and the interference of the thruster power supply and air supply pipelines must be eliminated, as well as the influence of the thermal environment and plasma environment under the working state of the thruster. Under the above constraints, the current force measurement technology cannot achieve accurate measurement of small thrusts below 1 micro-newton. Therefore, only indirect measurement can be used. The traditional Mach probe measurement method is an invasive measurement method. After the probe body enters the measurement area, it will cause serious interference to the object being measured. This interference will cause a large deviation in the measurement result when measuring small quantities such as rolling moment. Summary of the invention

[0004] The present application provides an electric thruster rolling torque measurement device based on laser induced fluorescence, which can measure the rolling torque of the electric thruster in a non-invasive manner and using the principle of laser induced fluorescence when the ion thruster is in working condition.

[0005] In order to achieve the above-mentioned purpose, the present application provides an electric thruster rolling torque measurement device based on laser induced fluorescence, comprising a laser emitting device, a fluorescence receiving device and a control system arranged inside an air floating platform, and an electric thruster and a modulation mirror group arranged inside a vacuum chamber, wherein: the laser emitting device comprises a tunable laser, a signal source, a beam splitter, a laser wavelength monitoring device and a laser incident device, the signal source is connected to the tunable laser, the laser emitted by the tunable laser passes through the beam splitter, a part of the laser energy enters the laser wavelength monitoring device, and the other part of the laser energy enters the laser incident device; the fluorescence receiving device comprises a monochromator, a photomultiplier tube and a phase-locked amplifier connected in sequence; the laser wavelength monitoring device and the phase-locked amplifier are both connected to the control system; the modulation mirror group comprises a three-dimensional moving mechanism, an incident mirror group and a receiving mirror group; the incident mirror group is connected to the laser incident device through an incident optical fiber; the receiving mirror group is connected to the monochromator through a receiving optical fiber.

[0006] Furthermore, the tunable laser includes a solid-state laser and a tapered controller for generating sub-picometer laser light.

[0007] Furthermore, the central wavelength of the solid-state laser is selected according to the energy level transition rule in the monovalent ion excitation strategy of the electric thruster working fluid.

[0008] Furthermore, the laser wavelength monitoring device includes a fiber coupling head and a wavelength meter. The fiber coupling head is used to receive a portion of the laser energy reflected by the beam splitter and transmit it to the wavelength meter. The wavelength meter is used to monitor the laser wavelength and is connected to the control system.

[0009] Furthermore, the laser incident device includes a chopper, a first reflector, a second reflector and a five-dimensional coupler, wherein: the chopper is used to receive another part of the laser energy reflected by the beam splitter, and to reflect the laser energy twice by the first reflector and the second reflector into the five-dimensional coupler; the five-dimensional coupler is connected to the incident optical fiber, and is used to transmit the laser energy to the incident mirror group inside the vacuum chamber through the incident optical fiber.

[0010] Furthermore, the incident mirror group and the receiving mirror group are both arranged on a three-dimensional moving mechanism. Driven by the three-dimensional moving mechanism, the incident mirror group and the receiving mirror group can cover all positions of the plasma area generated by the electric thruster in the measurement area.

[0011] Furthermore, the laser energy enters the plasma region generated by the electric thruster through the incident mirror group, generating a fluorescence signal, and the receiving mirror group transmits the fluorescence signal to the monochromator through the receiving optical fiber.

[0012] Furthermore, the coupling efficiency between the incident optical fiber and the five-dimensional coupler is ≥50%, and the power loss of the laser energy after passing through the incident mirror group is ≤10%.

[0013] Furthermore, a through-cabin flange is provided on the vacuum chamber, and both the incident optical fiber and the receiving optical fiber pass through the through-cabin flange and the modulation mirror group for incident and reception of laser energy; the incident optical fiber adopts single-mode optical fiber, and the receiving optical fiber adopts multi-mode optical fiber.

[0014] Furthermore, the spatial resolution of the fluorescent signal received by the receiving mirror group is φ4mm×1mm under coarse adjustment and is φ1mm×1mm under fine adjustment.

[0015] The present invention provides a rolling torque measuring device for an electric thruster based on laser induced fluorescence, which has the following beneficial effects:

[0016] The present application adopts a stable sub-picometer solid-state laser source, and the entire three-dimensional moving mechanism, the incident mirror group, and the receiving mirror group are all outside the beam area of ​​the electric thruster, and will not affect the working characteristics of the electric thruster; at the same time, the laser energy is incident near the object to be measured, and will not interfere with the object to be measured, thereby realizing non-invasive measurement and improving the accuracy of the test. In addition, the control system realizes the automatic coordination of key components such as the solid-state laser, wavelength meter, three-dimensional moving mechanism, monochromator, and phase-locked amplifier during the measurement process, thereby avoiding measurement errors caused by operational differences among personnel during the measurement process and improving the reliability of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of this application are used to provide a further understanding of this application, so that other features, purposes and advantages of this application become more obvious. The schematic embodiment drawings and their descriptions of this application are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0018] Figure 1 It is a structural schematic diagram of a rolling torque measurement device for an electric thruster based on laser induced fluorescence provided in an embodiment of the present application;

[0019] In the figure: 1-solid-state laser, 2-conical controller, 3-signal source, 4-wavelength meter, 5-beam splitter, 6-fiber coupling head, 7-chopper, 8-first reflector, 9-second reflector, 10-five-dimensional coupler, 11-incident optical fiber, 12-cabin flange, 13-three-dimensional moving mechanism, 14-electric thruster, 15-receiving optical fiber, 16-monochromator, 17-photomultiplier tube, 18-phase-locked amplifier, 19-control system, 20-air floating platform, 21-incident mirror group, 22-receiving mirror group, 23-vacuum cabin. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0021] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0022] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0023] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0024] In addition, the term "plurality" shall mean two or more.

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0026] like Figure 1As shown, the present application provides an electric thruster rolling torque measurement device based on laser induced fluorescence, including a laser emitting device, a fluorescence receiving device and a control system 19 arranged inside an air floating platform 20, and an electric thruster 14 and a modulation mirror group arranged inside a vacuum chamber 23, wherein: the laser emitting device includes a tunable laser, a signal source 3, a beam splitter 5, a laser wavelength monitoring device and a laser incident device, the signal source 3 is connected to the tunable laser, the laser emitted by the tunable laser passes through the beam splitter 5, a part of the laser energy enters the laser wavelength monitoring device, and the other part of the laser energy enters the laser incident device; the fluorescence receiving device includes a monochromator 16, a photomultiplier tube 17 and a phase-locked amplifier 18 connected in sequence; the laser wavelength monitoring device and the phase-locked amplifier 18 are both connected to the control system 19; the modulation mirror group includes a three-dimensional moving mechanism 13, an incident mirror group 21 and a receiving mirror group 22; the incident mirror group 21 is connected to the laser incident device through an incident optical fiber 11; the receiving mirror group 22 is connected to the monochromator 16 through a receiving optical fiber 15.

[0027] Specifically, when the electric thruster 14 is working, while generating thrust, due to factors such as the grid neutrality, the effect of the magnetic field on the beam, and the influence of the neutralizer position on the beam, a rolling torque will be generated along the thrust direction. Long-term operation will cause abnormal rotation of the satellite. The electric thruster rolling torque measurement device based on laser induced fluorescence provided in the embodiment of the present application can use a non-invasive method and the principle of laser induced fluorescence to achieve the measurement of the rolling torque of the electric thruster 14 when the electric thruster 14 is working. Among them, the laser emitting device, the fluorescence receiving device and the control system 19 are all arranged inside the air floating platform 20 to ensure that the wavelength and direction of the incident laser are in a stable state. The electric thruster 14 and the modulation mirror group are installed inside the vacuum cabin 23 to simulate the actual working environment of the electric thruster 14. During the measurement process, the laser emitting device is used to emit laser energy, and the laser energy enters the incident mirror group 21 through the incident optical fiber 11. The incident mirror group 21 allows the laser energy to enter the plasma region generated by the electric thruster 14, thereby exciting the monovalent ions of the working fluid. The fluorescence signal of a fixed wavelength generated after the excited monovalent ions are de-excited enters the receiving optical fiber 15 through the receiving mirror group 22, and then enters the fluorescence receiving device through the receiving optical fiber 15, passes through the monochromator 16, the photomultiplier tube 17 and the phase-locked amplifier 18 in sequence, and is finally collected by the control system 19, and the collected results are analyzed and processed to obtain the rolling torque measurement result of the electric thruster 14. The monochromator 16 is mainly used to separate the optical signal of the required fixed wavelength, the photomultiplier tube 17 converts the optical signal into a current signal, the phase-locked amplifier 18 is used to separate and amplify the current signal, and the control system 19 is mainly used to coordinate the tunable laser, the signal source 3, the laser wavelength monitoring device, the three-dimensional moving mechanism 13, the receiving optical fiber 15, the monochromator 16, the photomultiplier tube 17, the phase-locked amplifier 18 and other devices to work synchronously to achieve automatic collection, and realize real-time calculation of the rolling torque based on the collected laser induced fluorescence signal.

[0028] Furthermore, the tunable laser includes a solid-state laser 1 and a conical controller 2, which are used to generate sub-picometer laser light. The solid-state laser 1 generates seed light, and the conical controller 2 is used to modulate the laser seed light. The combination of the two can generate sub-picometer laser light of the required wavelength and power, and the wavelength is suitable for a certain excited state of monovalent ions in the plasma generated by the electric thruster 14.

[0029] Furthermore, the central wavelength of the solid-state laser 1 is selected according to the transition rule from energy level 1 to 2 in a certain excitation strategy of the monovalent ions of the working fluid of the electric thruster 14, wherein the line width is better than 500kHz, the output power is ≥200mW, and the wavelength stability is better than 2pm / h.

[0030] Furthermore, the laser wavelength monitoring device includes a fiber coupling head 6 and a wavelength meter 4. The fiber coupling head 6 is used to receive a portion of the laser energy reflected by the beam splitter 5 and transmit it to the wavelength meter 4. The wavelength meter 4 is used to monitor the laser wavelength and is connected to the control system 19. During the measurement process, a portion of the energy (10%) is reflected by the beam splitter 5 into the wavelength meter 4 for monitoring the laser wavelength, and according to the laser wavelength displayed by the wavelength meter 4, the laser wavelength is fine-tuned to the central wavelength required for measurement through the tapered controller 2.

[0031] Furthermore, the laser incident device includes a chopper 7, a first reflector 8, a second reflector 9 and a five-dimensional coupler 10, wherein: the chopper 7 is used to receive another part of the laser energy reflected by the beam splitter 5, and the laser energy enters the five-dimensional coupler 10 through two reflections of the first reflector 8 and the second reflector 9; the five-dimensional coupler 10 is connected to the incident optical fiber 11, and is used to transmit the laser energy to the incident mirror group 21 inside the vacuum chamber 23 through the incident optical fiber 11. The chopper 7 is mainly used to pulse modulate the laser signal, the first reflector 8 and the second reflector 9 together form an optical path, so that the laser energy reaches the five-dimensional coupler 10 stably after two reflections, and the chopping process and the incident process are separated and designed to facilitate the adjustment of the optical path. The five-dimensional coupler 10 is mainly used to couple the spatial laser reflected by the reflector to the incident optical fiber 11. The five-dimensional design can realize the adjustment in five directions, which greatly improves the coupling efficiency.

[0032] Furthermore, the incident mirror group 21 and the receiving mirror group 22 are both arranged on the three-dimensional moving mechanism 13. Driven by the three-dimensional moving mechanism 13, the incident mirror group 21 and the receiving mirror group 22 can cover all positions of the plasma area generated by the electric thruster 14 in the measurement area. The incident mirror group 21 is installed on the x-axis of the three-dimensional moving mechanism, and the receiving mirror group 22 is installed on the y-axis of the three-dimensional moving mechanism. The entire three-dimensional moving mechanism 13 is outside the plasma area and maintains a fixed positional relationship with the electric thruster 14 to be measured. In addition, the stroke of the three-dimensional moving mechanism 13 needs to cover all the measured areas according to different product requirements. At the same time, the necessary moving parts such as the lead screw are vacuum lubricated, and the power supply and control cables should use high temperature resistant wires and have a device to prevent plasma sputtering.

[0033] Furthermore, the laser energy enters the plasma region generated by the electric thruster 14 through the incident mirror group 21, generates a fluorescence signal, and the receiving mirror group 22 transmits the fluorescence signal to the monochromator 16 through the receiving optical fiber 15. The laser energy is reflected by the incident mirror group 21 and injected into the plasma region generated by the electric thruster 14, exciting the monovalent ions of the working fluid, and the fluorescence signal of a fixed wavelength generated after the excited monovalent ions are de-excited will directly enter the receiving mirror group 22, and then be transmitted to the monochromator 16 through the receiving mirror group 22 in the form of optical fiber coupling.

[0034] Furthermore, the coupling efficiency between the incident optical fiber 11 and the five-dimensional coupler 10 is ≥50%, and the power loss of the laser energy after passing through the incident mirror assembly 21 is ≤10%.

[0035] Furthermore, a through-cabin flange 12 is provided on the vacuum chamber 23, and both the incident optical fiber 11 and the receiving optical fiber 15 pass through the through-cabin flange 12 and the modulation mirror group for incident and receiving laser energy; the incident optical fiber 11 adopts a single-mode optical fiber, and the receiving optical fiber 15 adopts a multi-mode optical fiber. The optical path entering and exiting the vacuum chamber 23 adopts a whole optical fiber, and no switching is performed at the through-cabin flange 12.

[0036] Furthermore, the spatial resolution of the fluorescence signal received by the receiving mirror group 22 is φ4mm×1mm under coarse adjustment, and the spatial resolution is φ1mm×1mm under fine adjustment. During the fluorescence signal acquisition process, the receiving mirror group 22 should ensure that the measurement has high spatial resolution. The spatial resolution refers to the diameter of the laser spot reflected by the receiving mirror group 22, which can be adjusted by the coupler in the receiving mirror group 22. The spatial resolution reaches φ4mm×1mm (along the laser incident direction×vertical laser direction) under coarse adjustment, and the spatial resolution reaches φ1mm×1mm (along the laser incident direction×vertical laser direction) under fine adjustment.

[0037] Specifically, when the rolling torque measuring device of the electric thruster based on laser induced fluorescence provided in the embodiment of the present application is used for measurement, the solid-state laser 1 and the conical controller 2 form a tunable laser for generating sub-picometer laser light. The laser light is divided into two branches by the beam splitter 5. A part of the energy (10%) is reflected by the beam splitter 5 and enters the wavelength meter 4 for monitoring the laser wavelength. The remaining energy is modulated by the frequency 1KHz chopper 7, and passes through the optical path composed of the first reflector 8 and the second reflector 9, and enters the incident optical fiber 11 through the five-dimensional coupler 10. The incident optical fiber 11 transmits the laser energy through the cabin flange 12 into the vacuum cabin 23. Inside the vacuum cabin 23, the three-dimensional moving mechanism 13 is adjusted, and the incident optical fiber 11 transmits the laser energy through the cabin flange 12 into the vacuum cabin 23. The emitting mirror group 21 injects laser energy into the plasma area generated by the electric thruster 14 to excite the monovalent ions of the working fluid. The excited monovalent ions generate a fluorescence signal of a fixed wavelength after de-excitation, which enters the receiving optical fiber 15 through the receiving mirror group 22 in the form of fiber coupling, and is transmitted to the monochromator 16 through the receiving optical fiber 15. The energy of the target wavelength is separated by the grating and converted into a current signal by the photomultiplier tube 17. The signal is respectively input to the phase-locked amplifier 18 with the frequency of the two choppers 7 for phase-sensitive detection, and is collected in real time by the control system 19 to separate the laser-induced fluorescence signal with sub-picometer accuracy. The data is then processed in real time through the relevant software and algorithms of the control system 19 to finally obtain the rolling torque measurement result.

[0038] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A rolling torque measuring device for an electric thruster based on laser induced fluorescence, characterized in that: It includes a laser emitting device, a fluorescence receiving device and a control system arranged inside the air floating platform, and an electric thruster and a modulation mirror group arranged inside the vacuum chamber, wherein: The laser emitting device comprises a tunable laser, a signal source, a beam splitter, a laser wavelength monitoring device and a laser incident device, wherein the signal source is connected to the tunable laser, and the laser emitted by the tunable laser passes through the beam splitter, a part of the laser energy enters the laser wavelength monitoring device, and another part of the laser energy enters the laser incident device; The fluorescence receiving device comprises a monochromator, a photomultiplier tube and a lock-in amplifier connected in sequence; The laser wavelength monitoring device and the lock-in amplifier are both connected to the control system; The modulation mirror group includes a three-dimensional moving mechanism, an incident mirror group and a receiving mirror group; The incident mirror group is connected to the laser incident device via an incident optical fiber; The receiving mirror assembly is connected to the monochromator via a receiving optical fiber; The tunable laser comprises a solid-state laser and a tapered controller, and is used to generate sub-picometer laser light; The central wavelength of the solid-state laser is selected according to the energy level transition rule in the monovalent ion excitation strategy of the electric thruster working fluid; The laser incident device includes a chopper, a first reflector, a second reflector and a five-dimensional coupler, wherein: The chopper is used to receive another part of the laser energy reflected by the beam splitter, and to reflect the laser energy twice by the first reflector and the second reflector into the five-dimensional coupler; The five-dimensional coupler is connected to the incident optical fiber and is used to transmit the laser energy to the incident mirror group inside the vacuum chamber through the incident optical fiber. The five-dimensional design is adopted to achieve adjustment in five directions, thereby improving the coupling efficiency. The incident mirror group and the receiving mirror group are both arranged on the three-dimensional moving mechanism. Driven by the three-dimensional moving mechanism, the incident mirror group and the receiving mirror group can cover all positions of the plasma area generated by the electric thruster in the measurement area; The coupling efficiency between the incident optical fiber and the five-dimensional coupler is ≥50%, and the power loss of the laser energy after passing through the incident mirror group is ≤10%; The spatial resolution of the fluorescent signal received by the receiving mirror group is Φ4mm×1mm under coarse adjustment and is Φ1mm×1mm under fine adjustment.

2. The rolling torque measuring device of electric thruster based on laser induced fluorescence according to claim 1 is characterized in that: The laser wavelength monitoring device includes an optical fiber coupling head and a wavelength meter. The optical fiber coupling head is used to receive a portion of the laser energy reflected by the beam splitter and transmit it to the wavelength meter. The wavelength meter is used to monitor the laser wavelength and is connected to the control system.

3. The rolling torque measuring device of electric thruster based on laser induced fluorescence according to claim 1, characterized in that: The laser energy enters the plasma region generated by the electric thruster through the incident mirror group to generate a fluorescent signal, and the receiving mirror group transmits the fluorescent signal to the monochromator through the receiving optical fiber.

4. The rolling torque measuring device of electric thruster based on laser induced fluorescence according to claim 3 is characterized in that: The vacuum chamber is provided with a through-chamber flange, and the incident optical fiber and the receiving optical fiber both pass through the through-chamber flange and the modulating mirror group for incident and receiving laser energy; the incident optical fiber is a single-mode optical fiber, and the receiving optical fiber is a multi-mode optical fiber.

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