A method and system for on-orbit testing of a space telescope structural stability

Abstract

The application provides a kind of space telescope structure stability on-orbit test method and system, according to the measurement accuracy requirement of space task and the stability requirement of telescope, a kind of high-precision space telescope structure stability on-orbit test method combining heterodyne interferometry, differential wavefront phase detection (DWS) is proposed.Through intercepting part of the outgoing light for interference, the structural stability change of the space telescope is obtained without affecting the measurement task.The interferometer structure adopted by the method and system of the application is stable and compact, has the characteristics of small volume, light weight and high precision, and meets the test requirements of the structural stability of the satellite-borne telescope.

Description

Technical Field

[0001] This invention relates to a system and method for on-orbit testing of the structural stability of space telescopes, belonging to the field of space testing. Background Technology

[0002] To meet the requirements of space missions, spaceborne optical components must possess excellent structural stability to cope with changes in the surrounding environment during on-orbit operation and achieve the expected measurement requirements. Therefore, pre-testing of the structural stability of key components is crucial to ensure the smooth execution of measurement missions. Furthermore, to monitor the actual on-orbit performance of spaceborne optical components, a small, lightweight, and highly accurate auxiliary measurement device is needed, without affecting the normal operation of the satellite. This device would measure the interference caused by structural changes in key components and compensate accordingly in the results. Current testing methods suffer from limitations such as low accuracy and structural complexity; therefore, a compact and high-precision on-orbit structural stability testing scheme is required. Summary of the Invention

[0003] The technical problem solved by this invention is to address the issues of insufficient accuracy and complex structure in common structural stability testing methods in the existing technology. This invention optimizes existing solutions and proposes a high-precision, simple, and efficient on-orbit telescope testing system and method.

[0004] The present invention solves the above-mentioned technical problem by means of the following technical solution: an on-orbit testing method for the structural stability of a space telescope, comprising:

[0005] The beam emitted from the spaceborne optical platform is split by beam splitter BS3. Its reflected component is sent to the space telescope, and its transmitted component is sent to beam splitter BS4. The reflected and transmitted components of the light after passing through beam splitter BS4 are received by photodetector PD1 and photodetector PD2, respectively.

[0006] Using local light as reference light, the reference light is incident on beam splitter BS2. After passing through beam splitter BS2, its reflected component is incident on beam splitter BS4. The transmitted and reflected components of the light passing through beam splitter BS4 are received by photodetectors PD1 and PD2, respectively. The component of the reference light transmitted through beam splitter BS2 is reflected by plane mirror M1 to the structural stability measurement device.

[0007] The two beams incident on photodetector PD1 interfere to form a reference beam, which is received by detector PD1; the two beams incident on photodetector PD2 interfere to form a reference beam, which is received by detector PD2.

[0008] The light emitted from the space telescope is partially intercepted by the structural stability measurement device. The intercepted beam and the beam reflected by the plane mirror M1 interfere in the structural stability measurement device to form a measurement beat, which is received by the four-quadrant detector in the structural stability measurement device.

[0009] The signals output by photodetectors PD1, PD2 and four-quadrant detector QPD are filtered and converted from analog to digital before being input to a digital phase meter. After processing, the axial signal and differential wavefront phase detection (DWS) signal are obtained.

[0010] Data processing was performed on the obtained axial signal LPS and differential wavefront phase detection (DWS) signal to obtain the axial variation Δz of the space telescope structure, as well as the variations θ in the azimuth and elevation directions. y θ x .

[0011] Furthermore, the structural stability measuring device includes a plane mirror M2, a lens L, a beam splitter BS5, and a four-quadrant detector.

[0012] The captured beam is reflected by the plane mirror M2 to the lens L, and the beam focused by the lens L is incident on the beam splitter BS5. Its transmitted component is received by the four-quadrant detector QPD. The beam reflected by the plane mirror M1 is incident on the beam splitter BS5, and after being reflected by the beam splitter BS5, it is received by the four-quadrant detector QPD. The two beams incident on the four-quadrant detector QPD interfere to form a measurement frame, which is received by the four-quadrant detector.

[0013] Furthermore, the structural stability measuring device is placed at multiple points to measure the structural stability changes of each part of the space telescope; or different parts of the outgoing light passing through the space telescope are intercepted to obtain the influence of the space telescope on the outgoing light wavefront of the space telescope.

[0014] Furthermore, beam splitters BS2, BS3, BS4 and BS5 are all non-polarizing beam splitters with a transmission-to-reflection ratio of 50:50.

[0015] Furthermore, the axial signal LPS is:

[0016]

[0017] Among them, the phase result obtained by the four-quadrant detector in each quadrant is Φ. A Φ B Φ C and Φ D .

[0018] Furthermore, the differential wavefront phase detection (DWS) signal is used to measure the wavefront deviation angle of the two beams, and is divided into a horizontal DWS signal.h and vertical DWS signal DWS v They are respectively:

[0019]

[0020]

[0021] in, The average phase of the left two quadrants of the four-quadrant detector; The average phase of the two right quadrants of the four-quadrant detector; The average phase of the upper two quadrants of the four-quadrant detector; It represents the average phase of the two lower quadrants of the four-quadrant detector.

[0022] Furthermore, the axial variation Δz of the space telescope structure is determined by the reference signal output by the detector PD. Measurement signals output by the four-quadrant detector QPD The calculation formula is as follows:

[0023]

[0024] Furthermore, the variation θ of the space telescope structure in the azimuth and elevation directions... y θ x The differential wavefront phase detection (DWS) signal output from the four-quadrant detector is obtained as follows:

[0025] DWS h =C h θ y ,

[0026] DWS v =C v θ x ,

[0027] The four-quadrant detector is calibrated in advance to obtain the proportional coefficient C. h proportionality coefficient C v Using the obtained differential wavefront phase detection signal, the changes θ of the space telescope structure in the azimuth and elevation directions are calculated. y θ x .

[0028] An on-orbit testing system for the structural stability of a space telescope includes: a structural stability measuring device, a beam splitter BS2, a beam splitter BS3, a beam splitter BS4, a reflector M1, a photodetector PD1, and a photodetector PD2.

[0029] The beam emitted from the spaceborne optical platform is split by beam splitter BS3. Its reflected component is sent to the space telescope, and its transmitted component is sent to beam splitter BS4. The reflected and transmitted components of the light after passing through beam splitter BS4 are received by photodetector PD1 and photodetector PD2, respectively.

[0030] Using local light as reference light, the reference light is incident on beam splitter BS2. After passing through beam splitter BS2, its reflected component is incident on beam splitter BS4. The transmitted and reflected components of the light passing through beam splitter BS4 are received by photodetectors PD1 and PD2, respectively. The component of the reference light transmitted through beam splitter BS2 is reflected by plane mirror M1 to the structural stability measurement device.

[0031] The two beams incident on photodetector PD1 interfere to form a reference beam, which is received by detector PD1; the two beams incident on photodetector PD2 interfere to form a reference beam, which is received by detector PD2.

[0032] The light emitted from the space telescope is partially intercepted by the structural stability measurement device. The intercepted beam and the beam reflected by the plane mirror M1 interfere in the structural stability measurement device, forming a measurement beat, which is received by the four-quadrant detector in the structural stability measurement device.

[0033] Furthermore, the structural stability measuring device includes a plane mirror M2, a lens L, a beam splitter BS5, and a four-quadrant detector.

[0034] The captured beam is reflected by the plane mirror M2 to the lens L, and the beam focused by the lens L is incident on the beam splitter BS5. Its transmitted component is received by the four-quadrant detector QPD. The beam reflected by the plane mirror M1 is incident on the beam splitter BS5, and after being reflected by the beam splitter BS5, it is received by the four-quadrant detector QPD. The two beams incident on the four-quadrant detector QPD interfere to form a measurement frame, which is received by the four-quadrant detector.

[0035] The advantages of this invention compared to the prior art are:

[0036] (1) This invention provides a high-precision on-orbit structural stability testing method, which employs a combination of a reflector, lens, beam splitter, and four-quadrant detector to capture and measure portions of the light beam at various points on the sample under test, thereby obtaining the influence of each part of the sample on the optical path. Compared with existing solutions, this method uses fewer components, is smaller in size, has a more flexible measurement method, and does not affect satellite measurement missions.

[0037] (2) The structural stability testing method provided by the present invention is different from the previous method of treating the sample to be tested as a rigid body. The beam will pass through the entire system to be tested and then be emitted. Therefore, by taking multiple points of the emitted light for measurement, the influence of the sample on the wavefront of the beam can be measured. Attached Figure Description

[0038] Figure 1 This is a flowchart of the method of the present invention;

[0039] Figure 2 This is a schematic diagram of the optical path for ground testing;

[0040] Figure 3 This is a schematic diagram of the optical path for on-orbit testing of the present invention. Specific implementation methods

[0041] This invention proposes an on-orbit stability testing method based on heterodyne interferometry. By interfering a portion of the outgoing light after passing through the sample under test, the structural changes of the sample can be obtained. Since the reference light for interference is output from a local light source and interferes with the measurement light after propagating in free space, the measurement results can better reflect the influence of the sample under test on the optical path. By combining differential wavefront phase detection signals and axial signals, the structural changes of the sample under test in each degree of freedom can be accurately measured. Furthermore, by using a combination of mirrors, lenses, beam splitters, and four-quadrant detectors, multiple measurements can be performed on the sample under test, or multiple sets can be used simultaneously to measure the wavefront changes of the beam after passing through the sample. The interferometer used in this testing method is compact, small in size, and lightweight, effectively reducing the satellite's load and well meeting the requirements for device structural stability testing, ensuring effective measurement.

[0042] like Figure 3 As shown, an on-orbit testing system for the structural stability of a space telescope includes: a structural stability measuring device, a beam splitter BS2, a beam splitter BS3, a beam splitter BS4, a reflector M1, a photodetector PD1, and a photodetector PD2.

[0043] The beam emitted from the spaceborne optical platform is split by beam splitter BS3. Its reflected component is sent to the space telescope, and its transmitted component is sent to beam splitter BS4. The reflected and transmitted components of the light after passing through beam splitter BS4 are received by photodetector PD1 and photodetector PD2, respectively.

[0044] Using local light as reference light, the reference light is incident on beam splitter BS2. After passing through beam splitter BS2, its reflected component is incident on beam splitter BS4. The transmitted and reflected components of the light passing through beam splitter BS4 are received by photodetectors PD1 and PD2, respectively. The component of the reference light transmitted through beam splitter BS2 is reflected by plane mirror M1 to the structural stability measurement device.

[0045] The two beams incident on photodetector PD1 interfere to form a reference beam, which is received by detector PD1; the two beams incident on photodetector PD2 interfere to form a reference beam, which is received by detector PD2.

[0046] The light emitted from the space telescope is partially intercepted by the structural stability measurement device. The intercepted beam and the beam reflected by the plane mirror M1 interfere in the structural stability measurement device, forming a measurement beat, which is received by the four-quadrant detector in the structural stability measurement device.

[0047] The structural stability measurement device includes a plane mirror M2, a lens L, a beam splitter BS5, and a four-quadrant detector.

[0048] The captured beam is reflected by the plane mirror M2 to the lens L, and the beam focused by the lens L is incident on the beam splitter BS5. Its transmitted component is received by the four-quadrant detector QPD. The beam reflected by the plane mirror M1 is incident on the beam splitter BS5, and after being reflected by the beam splitter BS5, it is received by the four-quadrant detector QPD. The two beams incident on the four-quadrant detector QPD interfere to form a measurement frame, which is received by the four-quadrant detector.

[0049] like Figure 1 As shown, the specific steps of the method of the present invention are as follows:

[0050] (1) As Figure 2 As shown, for ground testing, a laser with a wavelength of 1064 nm is first output from the laser. The beam is then split by beam splitter 1 (BS1), and the two beams pass through acousto-optic modulators (AOMs) 1 and 2 respectively, resulting in a measurement light with frequency f1 and a reference light with frequency f2. Δf = f1 - f2 = 1 MHz, and the resulting beat frequency signal frequency f is... het f het =Δf.

[0051] (2) In step (1), the measurement light is modulated by the acousto-optic modulator 1 and then enters the beam splitter 3 (BS3). After passing through the beam splitter 3, its reflected component enters the beam splitter 4 (BS4), and thereafter the reflected and transmitted components are received by the photodetector 1 (PD1) and the photodetector 2 (PD2), respectively. Then, the sample to be tested is placed in the sample placement area, and the transmitted component of the measurement light after passing through the beam splitter 3 will pass through the sample to be tested. After that, the outgoing light will be partially intercepted. The intercepted beam is reflected by the plane mirror 2 (M2) to the lens L, and then the beam focused by the lens L enters the beam splitter 5 (BS5), and its transmitted component is received by the quadrant detector (QPD).

[0052] In step (1), the reference light is modulated by the acousto-optic modulator 2 and then enters the beam splitter 2 (BS2). After passing through the beam splitter 2, its reflected component enters the beam splitter 4. Thereafter, the transmitted and reflected components are received by the photodetectors 1 and 2, respectively. The component of the reference light transmitted through the beam splitter 2 will be reflected by the plane mirror 1 (M1) to the beam splitter 5. After being reflected by the beam splitter 5, it is received by the four-quadrant detector.

[0053] like Figure 3As shown, for the on-orbit telescope structural stability test, beam splitter 1 and acousto-optic modulators 1 and 2 are removed. The measurement light is the output light from the spaceborne optical platform, and the test sample is the on-orbit telescope. The beam is then split by beam splitter 3, with its reflected component partially intercepted after passing through the telescope for stability testing, and its transmitted component entering beam splitter BS4. Additionally, a local light beam is used as the reference light, split by beam splitter 2, and then incident on plane mirror M1 and beam splitter BS4 respectively, before being used for structural stability testing.

[0054] (3) The beam incident on photodetector 1 will interfere, forming a reference beam, which is received by detector 1; the two beams incident on photodetector 2 will also interfere, forming a reference beam, which is received by detector 2. By comparing the signals obtained from photodetectors 1 and 2, the system error can be reduced;

[0055] (4) A portion of the outgoing light from the sample is intercepted by the structural stability measurement device. The intercepted beam is reflected by the plane mirror 2 (M2) to the lens L, and then focused by the lens L before entering the beam splitter 5 (BS5). Its transmitted component is received by the quadrant detector (QPD). The beam reflected by the plane mirror 1 enters the beam splitter 5, and is then reflected by the beam splitter 5 and received by the quadrant detector. The two beams entering the quadrant detector interfere to form a measurement beat, which is then received by the quadrant detector.

[0056] The structural stability measurement device includes a plane mirror, a lens, a beam splitter, and a four-quadrant detector, corresponding to the plane mirror 2, lens L, beam splitter 5, and four-quadrant detector in the actual optical path. The beam emitted after passing through the sample is intercepted by a small hole below the plane mirror 2 and then enters the mirror; this is the measurement beam. The reference beam is reflected by the plane mirror 1, propagates through free space, and then enters the beam splitter 5 through a light-transmitting hole below the beam splitter 5. Thereafter, it interferes with the measurement beam to obtain the beat frequency signal.

[0057] Because a portion of the emitted light interferes with the reference light, the portion being intercepted may be the edge of the emitted laser beam, resulting in a weaker beam intensity. For the heterodyne interference efficiency η, we have:

[0058]

[0059] Among them, a i (r,t) represents the amplitude of the electric field component of the interfering beam, where r is the spatial position and t is the time. Let S be the phase and S be the photosensitive area of ​​the detector surface. It is evident that the interference efficiency is related to factors such as beat frequency intensity and wavefront error, where i = 1, 2. Therefore, using a lens L to converge the beam results in higher optical power received by the detector surface, which is beneficial for improving interference efficiency.

[0060] The structural stability measurement device can be placed at multiple points to measure the changes in structural stability of each part of the sample; or different parts of the emitted light after passing through the telescope can be intercepted to obtain the influence of the sample on the wavefront of the emitted light.

[0061] The beam splitters BS2, BS3, BS4, and BS5 are all non-polarizing beam splitters with a transmission-to-reflection ratio of 50:50. (5) The signals output from the photodetector and the four-quadrant detector are filtered and converted from analog to digital before being input into the digital phase meter. After processing, the axial signal and the differential wavefront phase detection (DWS) signal can be obtained. The axial signal (LPS) is defined as:

[0062]

[0063] The phase result obtained by the four-quadrant detector in each quadrant is Φ. A Φ B Φ C and Φ D ;

[0064] Differential wavefront phase detection signals are used to measure the wavefront deviation angle of two beams, and are divided into horizontal DWS signals and DWS signals. h and vertical DWS signal DWS v They are defined as follows:

[0065]

[0066]

[0067] in The average phase of the left two quadrants of the four-quadrant detector; The average phase of the two right quadrants of the four-quadrant detector; The average phase of the upper two quadrants of the four-quadrant detector; The average phase of the lower two quadrants of the four-quadrant detector;

[0068] (6) By processing the axial signal and differential wavefront phase detection (DWS) signal obtained in step (5), the variation Δz of the sample structure along the axial direction and the variation θ in the azimuth and pitch directions can be obtained. y θ x This allows for multi-degree-of-freedom, high-precision structural stability measurements of the sample under test.

[0069] The axial variation Δz can be obtained from the reference signal output by the detector PD. Measurement signals output by the four-quadrant detector QPD The calculation method is as follows:

[0070] λ is the wavelength, λ = 1064 nm;

[0071] Variations θ of the structure of the sample under test in the azimuth and pitch directions y θ x It can be obtained from the differential wavefront phase detection (DWS) signal output by the four-quadrant detector. For small offsets between the interfering beams, it is proportional to the obtained differential wavefront phase detection signal:

[0072] DWS h =C h θ y ,

[0073] DWS v =C v θ x ,

[0074] The proportional relationship between the two is related to the devices and beams used, and can be obtained by calibrating the four-quadrant detector in advance, thereby obtaining the proportionality coefficient C. h C v Subsequently, the changes θ of the sample structure under test in the azimuth and pitch directions can be calculated using the obtained differential wavefront phase detection signal. y θ x .

[0075] The parts of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for on-orbit testing of the structural stability of a space telescope, characterized in that, include: The beam emitted from the spaceborne optical platform is split by beam splitter BS3. Its reflected component is sent to the space telescope, and its transmitted component is sent to beam splitter BS4. The reflected and transmitted components of the light after passing through beam splitter BS4 are received by photodetector PD1 and photodetector PD2, respectively. Using local light as reference light, the reference light is incident on beam splitter BS2. After passing through beam splitter BS2, its reflected component is incident on beam splitter BS4. The transmitted and reflected components of the light passing through beam splitter BS4 are received by photodetectors PD1 and PD2, respectively. The component of the reference light transmitted through beam splitter BS2 is reflected by plane mirror M1 to the structural stability measurement device. The two beams incident on photodetector PD1 interfere to form a reference beam, which is received by detector PD1; the two beams incident on photodetector PD2 interfere to form a reference beam, which is received by detector PD2. The light emitted from the space telescope is partially intercepted by the structural stability measurement device. The intercepted beam and the beam reflected by the plane mirror M1 interfere in the structural stability measurement device to form a measurement beat, which is received by the four-quadrant detector in the structural stability measurement device. The signals output by photodetectors PD1, PD2 and four-quadrant detector QPD are filtered and converted from analog to digital before being input to a digital phase meter. After processing, the axial signal and differential wavefront phase detection (DWS) signal are obtained. Data processing was performed on the obtained axial signal LPS and differential wavefront phase detection (DWS) signal to obtain the axial variation Δz of the space telescope structure, as well as the variations θ in the azimuth and elevation directions. y θ x .

2. The method for on-orbit testing of the structural stability of a space telescope according to claim 1, characterized in that: The structural stability measurement device includes a plane mirror M2, a lens L, a beam splitter BS5, and a four-quadrant detector. The captured beam is reflected by the plane mirror M2 to the lens L, and the beam focused by the lens L is incident on the beam splitter BS5. Its transmitted component is received by the four-quadrant detector QPD. The beam reflected by the plane mirror M1 is incident on the beam splitter BS5, and after being reflected by the beam splitter BS5, it is received by the four-quadrant detector QPD. The two beams incident on the four-quadrant detector QPD interfere to form a measurement frame, which is received by the four-quadrant detector.

3. The method for on-orbit testing of the structural stability of a space telescope according to claim 2, characterized in that: The structural stability measuring device is placed at multiple points to measure the changes in structural stability of various parts of the space telescope; or to capture different parts of the outgoing light passing through the space telescope, thereby obtaining the influence of the space telescope on the outgoing light wavefront of the space telescope.

4. The method for on-orbit testing of the structural stability of a space telescope according to claim 3, characterized in that: The beam splitters BS2, BS3, BS4 and BS5 are all non-polarizing beam splitters with a transmission-to-reflection ratio of 50:

50.

5. The method for on-orbit testing of the structural stability of a space telescope according to claim 1, characterized in that: The axial signal LPS is: Among them, the phase result obtained by the four-quadrant detector in each quadrant is Φ. A Φ B Φ C and Φ D .

6. The method for on-orbit testing of the structural stability of a space telescope according to claim 5, characterized in that: The differential wavefront phase detection (DWS) signal is used to measure the wavefront deviation angle of the two beams, and is divided into a horizontal DWS signal. h and vertical DWS signal DWS v They are respectively: in, The average phase of the left two quadrants of the four-quadrant detector; The average phase of the two right quadrants of the four-quadrant detector; The average phase of the upper two quadrants of the four-quadrant detector; It represents the average phase of the two lower quadrants of the four-quadrant detector.

7. The method for on-orbit testing of the structural stability of a space telescope according to claim 1, characterized in that: The axial variation Δz of the space telescope structure is determined by a reference signal output from the detector PD. Measurement signals output by the four-quadrant detector QPD The calculation formula is as follows:

8. The method for on-orbit testing of the structural stability of a space telescope according to claim 1, characterized in that: The variation θ of the space telescope structure in azimuth and elevation directions y θ x The differential wavefront phase detection (DWS) signal output from the four-quadrant detector is obtained as follows: DWS h =C h i y , DWS v =C v i x , The four-quadrant detector is calibrated in advance to obtain the proportional coefficient C. h proportionality coefficient C v Using the obtained differential wavefront phase detection signal, the changes θ of the space telescope structure in the azimuth and elevation directions are calculated. y θ x .

9. An on-orbit testing system for the structural stability of a space telescope, characterized in that, include: Structural stability measurement device, beam splitter BS2, beam splitter BS3, beam splitter BS4, reflector M1, photodetector PD1 and photodetector PD2; The beam emitted from the spaceborne optical platform is split by beam splitter BS3. Its reflected component is sent to the space telescope, and its transmitted component is sent to beam splitter BS4. The reflected and transmitted components of the light after passing through beam splitter BS4 are received by photodetector PD1 and photodetector PD2, respectively. Using local light as reference light, the reference light is incident on beam splitter BS2. After passing through beam splitter BS2, its reflected component is incident on beam splitter BS4. The transmitted and reflected components of the light passing through beam splitter BS4 are received by photodetectors PD1 and PD2, respectively. The component of the reference light transmitted through beam splitter BS2 is reflected by plane mirror M1 to the structural stability measurement device. The two beams incident on photodetector PD1 interfere to form a reference beam, which is received by detector PD1; the two beams incident on photodetector PD2 interfere to form a reference beam, which is received by detector PD2. The light emitted from the space telescope is partially intercepted by the structural stability measurement device. The intercepted beam and the beam reflected by the plane mirror M1 interfere in the structural stability measurement device, forming a measurement beat, which is received by the four-quadrant detector in the structural stability measurement device.

10. The on-orbit testing system for the structural stability of a space telescope according to claim 9, characterized in that: The structural stability measurement device includes a plane mirror M2, a lens L, a beam splitter BS5, and a four-quadrant detector. The captured beam is reflected by the plane mirror M2 to the lens L, and the beam focused by the lens L is incident on the beam splitter BS5. Its transmitted component is received by the four-quadrant detector QPD. The beam reflected by the plane mirror M1 is incident on the beam splitter BS5, and after being reflected by the beam splitter BS5, it is received by the four-quadrant detector QPD. The two beams incident on the four-quadrant detector QPD interfere to form a measurement frame, which is received by the four-quadrant detector.

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