On-orbit xenon residual amount evaluation method and device

Abstract

The method comprises the following steps: constructing a xenon density measurement light path by taking laser which is in frequency resonance with xenon molecules as a light source, dividing the laser output by the light source into a beam of horizontal line polarized light and a beam of vertical line polarized light through a half-wave plate HWP1 and a polarization splitting prism PBS1, wherein the horizontal line polarized light continuously passes through the half-wave plate HWP2 and the polarization splitting prism PBS2 to obtain two beams of low-power vertical line polarized light and high-power horizontal line polarized light which are perpendicular to each other in polarization direction, the low-power vertical line polarized light enters the xenon chamber as a detection field, and the high-power horizontal line polarized light enters the xenon chamber as a pumping field; the directions of the detection field and the pumping field entering the xenon chamber are opposite and collinear, and the density of xenon to be measured is indirectly measured by acquiring the xenon absorption spectrum in the xenon chamber, so that the on-orbit xenon residual amount is obtained.

Description

Technical Field

[0001] The present invention relates to the field of space electric propulsion systems, and in particular to a method and device for evaluating the remaining amount of xenon gas on orbit. Background Art

[0002] Electric propulsion systems generally use xenon as a propellant. As electric propulsion systems are increasingly used on-orbit, real-time assessment of the remaining xenon in electric propulsion systems has become an important parameter for system applications. This is used for tasks such as long-term on-orbit electric propulsion system operating status monitoring, satellite life-expiration assessment and processing, and on-orbit refueling of electric propellants. Electric propulsion propellants are stored at high pressure in a supercritical state, such as xenon. Its pressure and density curve is shown in the figure below. It is a non-ideal gas. Figure 1 As shown, in the commonly used xenon gas density range of 0.5 to 1.6 kg / L, a slight change in pressure will cause a drastic change in density, making it impossible to accurately calculate the density using pressure sensors and temperature sensors. Summary of the Invention

[0003] The technical problem solved by the present invention is to overcome the shortcomings of the existing technology and solve the problem that under on-orbit conditions, pressure and temperature sensors cannot be used to accurately obtain the xenon density in the xenon chamber due to non-ideal gas characteristics. A method and device for evaluating the remaining amount of xenon gas on-orbit are provided to evaluate the remaining amount of xenon gas on-orbit.

[0004] The technical solution of the present invention is to provide a method for evaluating the remaining amount of on-orbit xenon gas, wherein the on-orbit xenon gas is a non-ideal gas stored in a supercritical state, and the steps include:

[0005] A laser that resonates with the frequency of xenon molecules is selected as the light source to construct an optical path for measuring xenon density.

[0006] The xenon absorption spectrum is obtained using the xenon density measurement optical path to indirectly measure the density of the xenon gas to be measured and obtain the remaining amount of xenon gas on orbit.

[0007] Furthermore, the xenon density measurement optical path includes: the laser output by the light source passes through the half-wave plate HWP1 to adjust the total power of the optical path, and then passes through the polarization beam splitter prism PBS1 to be divided into a first horizontally polarized light and a first vertically polarized light. The first vertically polarized light is used for wavelength measurement. The first horizontally polarized light continues to pass through the half-wave plate HWP2 to adjust the power of the optical path entering the xenon chamber, and then passes through the polarization beam splitter prism PBS2 to obtain two beams of second vertically polarized light and second horizontally polarized light with mutually perpendicular polarization directions. The power of the second horizontally polarized light is greater than that of the second vertically polarized light. The second vertically polarized light enters the xenon chamber as a detection field, and the second horizontally polarized light enters the xenon chamber as a pump field. The directions in which the detection field and the pump field enter the xenon chamber are opposite and collinear.

[0008] Furthermore, the pump field passes through three reflectors M1, M2, and M3 in sequence, and then vertically passes through the polarization beam splitter prism PBS3 to enter the xenon chamber; a photodetector is provided at the polarization beam splitter prism PBS3.

[0009] Furthermore, the xenon absorption spectrum is obtained using the xenon density measurement optical path to indirectly measure the density of the xenon gas to be measured, and the remaining amount of xenon gas on orbit is obtained, including:

[0010] The xenon chamber is filled with xenon gas of standard density, and the absorption spectrum of the xenon gas of standard density characterized by optical thickness OD is obtained based on the xenon gas density measurement optical path;

[0011] When used on-orbit, the absorption spectrum of the xenon gas to be measured, represented by the optical thickness (OD), is obtained based on the xenon gas density measurement optical path.

[0012] By comparing the two absorption spectra, the density of the xenon gas to be measured is obtained, and thus the remaining amount of xenon gas on orbit is obtained.

[0013] Furthermore, the absorption spectrum of the standard density xenon gas or the xenon gas to be measured characterized by the optical thickness OD is obtained, specifically:

[0014] A light screen is placed between the reflectors M1 and M2 to block the pump field, the laser frequency is tuned, and the absorption spectrum of xenon gas is obtained through a photodetector. When the pump field is turned on, the pump field propagates in the xenon chamber in the opposite direction to the detection field, and the saturation absorption spectrum of xenon gas is obtained through a photodetector.

[0015] The saturated absorption spectrum is used to determine the resonance frequency range of the laser and the xenon molecules, and then the absorption spectrum characterized by the absorption intensity is obtained; the absorption spectrum characterized by the absorption intensity is deducted from the background light intensity to obtain the absorption spectrum characterized by the optical thickness OD.

[0016] Furthermore, the laser output by the light source passes through the optical isolator OI and then enters the half-wave plate HWP1.

[0017] The present invention also provides a device for measuring the remaining amount of on-orbit xenon gas, comprising: a light source, a half-wave plate HWP1, a polarization beam splitter prism PBS1, a half-wave plate HWP2, a polarization beam splitter prism PBS2, and a xenon chamber; the light source uses a laser that resonates with the frequency of xenon gas molecules; the laser output by the light source passes through the half-wave plate HWP1 to adjust the total power of the optical path; then passes through the polarization beam splitter prism PBS1 to be divided into a first horizontally polarized light and a first vertically polarized light, the first vertically polarized light being used for wavelength measurement; the first horizontally polarized light continues to pass through the half-wave plate HWP2 to adjust the laser power entering the xenon chamber; and then passes through the polarization beam splitter prism PBS2 to obtain two beams of second vertically polarized light and second horizontally polarized light having mutually perpendicular polarization directions, the power of the second horizontally polarized light being greater than that of the second vertically polarized light; the second vertically polarized light enters the xenon chamber as a detection field, and the second horizontally polarized light enters the xenon chamber as a pump field, with the detection field and the pump field entering the xenon chamber in opposite and collinear directions.

[0018] Furthermore, it includes reflectors M1, M2, M3 and a polarization beam splitter prism PBS3; the pump field passes through the three reflectors M1, M2, M3 in sequence and then vertically passes through the polarization beam splitter prism PBS3 to enter the xenon chamber; a photodetector is provided at the polarization beam splitter prism PBS3.

[0019] Furthermore, an optical isolator OI is provided between the light source and the half-wave plate HWP1; the output light of the light source passes through the optical isolator OI and then enters the half-wave plate HWP1.

[0020] The advantages of the present invention compared with the prior art are:

[0021] The present invention innovatively proposes a xenon density measurement optical path, which uses a spectral absorption method to measure the xenon density in the xenon chamber of the on-orbit electric propulsion system in real time, thereby calculating the remaining xenon amount, solving the problem of on-orbit xenon remaining amount assessment caused by non-ideal gas characteristics; the xenon measurement accuracy obtained by the technical solution proposed in the present invention is independent of the xenon pressure, and can maintain a fixed measurement accuracy throughout the entire life cycle; this method can also be extended to the measurement of other on-orbit propellants in addition to xenon, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The xenon pressure and density change curve at 20°C in the prior art;

[0023] Figure 2 This is a density measurement optical path diagram according to an embodiment of the present invention;

[0024] Figure 3 is the absorption spectrum characterized by absorption intensity of the standard and test gases in the embodiment of the present invention;

[0025] Figure 4OD is the absorption spectrum of the standard gas and the gas to be measured characterized by the optical thickness OD in the embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to better understand the technical solution of the present invention, the specific implementation methods of the present invention are described in detail below with reference to the accompanying drawings.

[0027] This embodiment uses xenon as an example to describe in detail the method for estimating the remaining amount of xenon gas on orbit proposed by the present invention, which specifically includes the following steps:

[0028] (1) A laser that resonates with the frequency of xenon molecules is selected as the light source to construct an optical path for measuring xenon density.

[0029] In the measurement of xenon gas concentration, a laser frequency that resonates with xenon molecules is selected as the detection light source.

[0030] Specifically, the xenon density measurement optical path diagram is as follows: Figure 2 As shown in the figure, Laser is the light source, OI is the optical isolator, HWP1 and HWP2 are half-wave plates, PBS1, PBS2, and PBS3 are polarization beam splitters, PD is the photodetector, M1, M2, and M3 are reflectors, wavemeter is the wavelength meter (the wavelength meter can be omitted in the on-orbit measurement scheme), and Xe cell is the high-pressure xenon gas cylinder.

[0031] In this embodiment, an external cavity semiconductor laser is used as the light source, and the central wavelength of the output light is controlled to be 834nm. The output light of the laser passes through the optical isolator OI to eliminate the influence of optical feedback on the laser mode. The outgoing laser passes through the half-wave plate HWP1 to adjust the total power of the incident annular light path. After passing through the polarization beam splitter prism PBS1, the laser is divided into a beam of horizontal linear polarized light and a beam of vertical linear polarized light. The horizontal linear polarized light passes through the half-wave plate HWP2 and the polarization beam splitter prism PBS2. HWP2 can adjust the power of the two laser beams entering the xenon chamber. PBS2 can be used to obtain two beams of linear polarized light with mutually perpendicular polarization directions. A beam of vertical linear polarized light with weak power is used as the detection field, and another beam of horizontal linear polarized light with stronger power is used as the pump field. The pump field passes through three reflectors M1, M2, and M3 in sequence, and then vertically passes through the beam splitter prism PBS3 to enter the Xe-Cell in the high-pressure xenon gas bottle.

[0032] (2) Obtain the xenon absorption spectrum, indirectly measure the density of the xenon gas to be measured, and obtain the remaining amount of xenon gas on orbit. The absorption capacity of xenon gas for monochromatic laser is characterized by optical thickness OD, which can be expressed as:

[0033] OD=ln(It / I0)

[0034] Among them, It is the residual light intensity of the light beam after it is absorbed by the xenon medium, and I0 is the initial light intensity of the light beam before it is incident.

[0035] The relative intensity of the light field can be measured using a photodetector, and the OD of the xenon medium can be calculated. In the physical model, the OD of the medium is determined by the atomic concentration ρ, the atomic absorption cross section σ, and the length l of the medium in the direction of light propagation. It is usually the product of these three parameters, namely:

[0036]

[0037] Therefore, by measuring the absorption degree of the monochromatic light field, the xenon concentration can be indirectly measured.

[0038] It should be noted that when the xenon gas concentration is high, its OD is also large, and the light field will be completely absorbed, resulting in inaccurate measurement results. In this case, it is necessary to slightly adjust the frequency of the monochromatic light field to detune it to reduce the absorption of xenon photons. Since the absorption of light interacting with atoms follows a Lorentz curve, a correction formula can be used when calculating the OD at resonance:

[0039]

[0040] Where Δ is the detuning amount of the light field, OD Δ is the optical thickness when the detuning amount of the light field is Δ, and γ is the excited state decay rate.

[0041] Specifically, the steps for calculating the remaining amount of xenon gas on orbit are as follows:

[0042] 1) Set as Figure 2 The measurement optical path shown is used to measure the density of xenon gas in the gas cylinder (volume B);

[0043] 2) Fill the cylinder with xenon gas of standard density ρ1, and based on the measurement light path, obtain Figure 3 The black absorption curve shown is the absorption spectrum of standard density xenon characterized by absorption intensity. The black absorption curve is further processed and the background light intensity is deducted during the processing to obtain the following Figure 4 The black absorption curve shown (the absorption spectrum of standard density xenon characterized by optical thickness OD) is used to calculate its absorption area A1;

[0044] 3) When actually used on-orbit, the absorption curve of the xenon gas in the current gas cylinder is measured based on the measurement optical path, such as Figure 3 The red absorption curve shown (the absorption spectrum of the xenon gas to be measured characterized by absorption intensity) is further processed, and the background light intensity is deducted during the processing to obtain the following Figure 4 The red absorption curve shown (the absorption spectrum of the xenon gas to be measured characterized by optical thickness OD) is used to calculate its absorption area A2;

[0045] 4) By comparing the two absorption spectra, the density of the xenon gas to be measured is obtained, and thus the remaining amount of xenon gas on track is obtained, that is, the remaining amount of xenon gas in the current gas cylinder is m = B*A2 / A1*ρ1.

[0046] Specifically, during the measurement process, a light screen is placed between the reflectors M1 and M2 to block the pump field, and the frequency of the laser is scanned to allow the output detection laser to interact with the xenon atoms. At this time, the signal received by the photodetector PD is the absorption spectrum of xenon. When the light screen is removed and the pump field is turned on, Figure 2 As shown, the pump light and the probe light propagate in opposite directions and collinearly. Since the pump light and the probe light interact with the xenon atoms together, the signal received by the photodetector at this time is the saturation absorption spectrum of the xenon gas. By analyzing the saturation absorption spectrum, the position where the laser frequency resonates with the xenon molecules can be determined.

[0047] Outside the resonant frequency range, the probe light is hardly absorbed; within the resonant frequency range, the probe light will be absorbed to a large extent. By adjusting the laser frequency within a small range, the probe light absorption spectrum characterized by the absorption intensity can be obtained; by comparing and analyzing the intensity of the absorption spectra in the two cases and calculating according to the theoretical model of xenon density, the xenon density to be measured can be obtained.

[0048] This embodiment also provides an on-orbit xenon gas remaining amount measurement device, comprising: a light source, a half-wave plate HWP1, a polarization beam splitter prism PBS1, a half-wave plate HWP2, a polarization beam splitter prism PBS2, and a xenon chamber. The light source uses a laser that resonates with the frequency of xenon gas molecules. The laser output by the light source passes through the half-wave plate HWP1 to adjust the total power of the optical path. The laser then passes through the polarization beam splitter prism PBS1 to be split into a first horizontally polarized light and a first vertically polarized light. The first vertically polarized light is used for wavelength measurement. The first horizontally polarized light further passes through the half-wave plate HWP2 to adjust the laser power entering the xenon chamber. The first horizontally polarized light then passes through the polarization beam splitter prism PBS2 to obtain two beams of second vertically polarized light and second horizontally polarized light with mutually perpendicular polarization directions. The power of the second horizontally polarized light is greater than that of the second vertically polarized light. The second vertically polarized light enters the xenon chamber as a detection field, and the second horizontally polarized light enters the xenon chamber as a pump field. The detection field and the pump field enter the xenon chamber in opposite and collinear directions.

[0049] Preferably, the measuring device further comprises reflectors M1, M2, M3 and a polarization beam splitter prism PBS3; the pump field passes through the three reflectors M1, M2, M3 in sequence and then vertically passes through the polarization beam splitter prism PBS3 to enter the xenon chamber; a photodetector is provided at the polarization beam splitter prism PBS3.

[0050] Preferably, an optical isolator OI is provided between the light source and the half-wave plate HWP1; the output light of the light source passes through the optical isolator OI and then enters the half-wave plate HWP1.

[0051] It will be understood that the present invention is described by way of example, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and any embodiment that falls within the scope of the claims of this application is intended to be within the scope of protection of the present invention.

[0052] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for evaluating the remaining amount of xenon gas on orbit, characterized in that: The on-orbit xenon gas is a non-ideal gas stored in a supercritical state, and the steps include: A laser that resonates with the frequency of xenon molecules is selected as the light source to construct an optical path for measuring xenon density. The xenon absorption spectrum is obtained using the xenon density measurement optical path to indirectly measure the density of the xenon gas to be measured and obtain the remaining amount of xenon gas on orbit.

2. The method for estimating the remaining amount of xenon gas on-orbit according to claim 1, wherein: The xenon density measurement optical path includes: laser light output by a light source passes through a half-wave plate HWP1 to adjust the total optical path power, then passes through a polarization beam splitter prism PBS1 to be divided into a first horizontally polarized light and a first vertically polarized light. The first vertically polarized light is used for wavelength measurement. The first horizontally polarized light continues to pass through a half-wave plate HWP2 to adjust the optical path power before entering a xenon chamber. Then, the first horizontally polarized light passes through a polarization beam splitter prism PBS2 to obtain two beams of second vertically polarized light and second horizontally polarized light with mutually perpendicular polarization directions. The power of the second horizontally polarized light is greater than that of the second vertically polarized light. The second vertically polarized light enters the xenon chamber as a detection field, and the second horizontally polarized light enters the xenon chamber as a pump field. The detection field and the pump field enter the xenon chamber in opposite and collinear directions.

3. The method for estimating the remaining amount of xenon gas on-orbit according to claim 2, wherein: The pump field passes through three reflectors M1, M2, and M3 in sequence, then vertically passes through the polarization beam splitter prism PBS3 and enters the xenon chamber; a photodetector is provided at the polarization beam splitter prism PBS3.

4. The method for estimating the remaining amount of xenon gas on-orbit according to claim 3, wherein: The xenon absorption spectrum is obtained by using the xenon density measurement optical path to indirectly measure the density of the xenon gas to be measured and obtain the remaining amount of xenon gas on orbit, including: The xenon chamber is filled with xenon gas of standard density, and the absorption spectrum of the xenon gas of standard density characterized by optical thickness OD is obtained based on the xenon gas density measurement optical path; When used on-orbit, the absorption spectrum of the xenon gas to be measured, represented by the optical thickness (OD), is obtained based on the xenon gas density measurement optical path. By comparing the two absorption spectra, the density of the xenon gas to be measured is obtained, and thus the remaining amount of xenon gas on orbit is obtained.

5. The method for estimating the remaining amount of xenon gas on-orbit according to claim 4, characterized in that: Obtain the absorption spectrum of standard density xenon gas or xenon gas to be measured characterized by optical thickness OD, specifically: A light screen is placed between the reflectors M1 and M2 to block the pump field, the laser frequency is tuned, and the absorption spectrum of xenon gas is obtained through a photodetector. When the pump field is turned on, the pump field propagates in the xenon chamber in the opposite direction to the detection field, and the saturation absorption spectrum of xenon gas is obtained through a photodetector. The saturated absorption spectrum is used to determine the resonance frequency range of the laser and the xenon molecules, and then the absorption spectrum characterized by the absorption intensity is obtained; the absorption spectrum characterized by the absorption intensity is deducted from the background light intensity to obtain the absorption spectrum characterized by the optical thickness OD.

6. The method for estimating the remaining amount of xenon gas on-orbit according to claim 2, wherein: The laser output by the light source passes through the optical isolator OI and then enters the half-wave plate HWP1.

7. A device for measuring the remaining amount of xenon gas on track, characterized in that: include: A light source, a half-wave plate HWP1, a polarization beam splitter prism PBS1, a half-wave plate HWP2, a polarization beam splitter prism PBS2, and a xenon chamber; the light source uses a laser that resonates with the frequency of xenon gas molecules; the laser output by the light source passes through the half-wave plate HWP1 to adjust the total power of the optical path; then passes through the polarization beam splitter prism PBS1 to be divided into a first horizontally polarized light and a first vertically polarized light, the first vertically polarized light being used for wavelength measurement; the first horizontally polarized light continues to pass through the half-wave plate HWP2 to adjust the laser power entering the xenon chamber; and then passes through the polarization beam splitter prism PBS2 to obtain two beams of second vertically polarized light and second horizontally polarized light with mutually perpendicular polarization directions, the power of the second horizontally polarized light being greater than that of the second vertically polarized light. The second vertically polarized light enters the xenon chamber as a detection field, and the second horizontally polarized light enters the xenon chamber as a pump field, with the detection field and the pump field entering the xenon chamber in opposite and collinear directions.

8. The device for measuring the remaining amount of xenon gas on-orbit according to claim 7, characterized in that: It also includes reflectors M1, M2, M3 and a polarization beam splitter prism PBS3; the pump field passes through the three reflectors M1, M2, M3 in sequence and then vertically passes through the polarization beam splitter prism PBS3 to enter the xenon chamber; a photodetector is provided at the polarization beam splitter prism PBS3.

9. The device for measuring the remaining amount of xenon gas on-orbit according to claim 7, characterized in that: An optical isolator OI is provided between the light source and the half-wave plate HWP1; the output light of the light source passes through the optical isolator OI and then enters the half-wave plate HWP1.

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