Link time delay calibration method for differential interference measurement of double spacecrafts
By adding a calibration power source C observation arc and setting multiple sets of observation parameters in the differential interferometry of two spacecraft, and performing interferometric phase fitting, the problem of limited accuracy in the differential interferometry of two spacecraft was solved, and higher precision inter-spacecraft interference processing was achieved.
Patent Information
- Application Number
- CN202511552402.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-28
- Publication Date
- 2026-02-03
AI Technical Summary
In existing technologies, the differential interferometry method for two spacecraft has limited measurement accuracy when the angular distance is close, and is affected by the phase frequency nonlinearity of the actual receiving equipment, which causes the interference phase to deviate from the linear characteristics and produce large errors.
A link delay calibration method for differential interferometry between two spacecraft is adopted. By adding a calibration radio source C observation arc, setting multiple sets of observation parameters, performing interferometric processing and phase fitting, the differential interferometric delay between spacecraft is calculated, and the phase nonlinear delay error is reduced.
It improves the accuracy of differential interferometry between two spacecraft, enables higher precision inter-spacecraft interference processing, and supports deep space navigation and other tasks.
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Figure CN121454573A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of aerospace technology, specifically a link delay calibration method for differential interferometry of two spacecraft. Background Technology
[0002] In existing technologies, interferometry can provide sectional measurement constraints for probes along the perpendicular line-of-sight direction. Combined with ranging and velocity measurement results along the line-of-sight direction, three-dimensional constraints on the probe's orbit can be achieved. Therefore, starting with Chang'e-1, the lunar exploration program established a deep-space spacecraft orbit determination technology configuration of Unified S-Band (USB) / Unified X-Band (UXB) ranging and velocity measurement combined with Very Long Baseline Interferometry (VLBI) angle measurement. For two or more probes with a small observation angular distance, Same Beam Interferometry (SBI) can be implemented for simultaneous differential measurements.
[0003] From a signal design perspective, co-beam interferometry requires interferometric sidetone correlation design, with very close downlink frequencies between probes. This is also the design input for traditional co-beam interferometry, with the two spin satellites Rstar and Vstar of Japan's lunar orbiter SELENE as representative examples. The Shanghai Astronomical Observatory of the Chinese Academy of Sciences conducted co-beam observations of Rstar and Vstar, obtaining differential phase delays on the order of picoseconds, achieving ultra-high precision interferometry between lunar probes for the first time in China.
[0004] However, when different spacecraft are angularly close, even if their downlink signals or interferometric sidetones are independently designed, the same-beam interferometry processing method can still be applied to obtain the differential interferometric time delay of the two spacecraft, but the measurement accuracy is limited. NASA initially applied this technology to the observation of the Magellan and Pioneer 12 spacecraft, obtaining a relative position accuracy (averaged over 5 minutes) of 40–100 meters on the sky plane. The Beijing Aerospace Flight Control Center also obtained angular measurement observations of the microsatellite better than 1 ns from the SBI tracking of the Chang'e-4 relay satellite and microsatellites. The interferometric group time delay is calculated from the change in the interferometric phase of the broadband signal at different frequency points with frequency, i.e. This processing is based on the assumption that the interference phase at different frequencies is only affected by the interference delay and has a linear relationship with the signal frequency. However, the phase-frequency nonlinearity of actual receiving equipment will cause the interference phase to deviate from its linear characteristics, resulting in a phase nonlinear delay error, such as... Figure 2As shown, this results in significant errors in the co-beam interferometry measurements. Therefore, it is necessary to improve the dual-spacecraft differential interferometry method to enhance the accuracy of the interferometric time delay. Summary of the Invention
[0005] To address the aforementioned technical problems in the existing technology, this invention proposes a link delay calibration method for differential interferometry between two spacecraft, spacecraft A and spacecraft B, comprising the following steps: Step 1: Determine the observation time. Before or after observing spacecraft A and spacecraft B, add an observation arc for calibrating the radio source C. Step 2: Set the observation parameters. Spacecraft A sends M downlink side tone signals with frequencies of fam, where m = 1, 2, ..., M. When sending downlink broadband signals, each spectral line of the broadband signal spectrum is considered as one side tone signal, where M > 1. Spacecraft B sends down N side tone signals with frequencies of fbn, where n = 1, 2, ..., N. When sending down wideband signals, each spectral line of the wideband signal spectrum is considered as one side tone signal, where N > 1. The calibration radio source C has two sets of observation parameters, which are the same as those of spacecraft A and spacecraft B, respectively. Step 3: Track and calibrate the radio source C, spacecraft A and spacecraft B to obtain the raw data of the signals to be interferometrically processed from spacecraft A, spacecraft B and the radio source C; Step 4: Perform interferometric processing on the raw data of spacecraft A to obtain the interference phase θam corresponding to the side tone signal with frequency fam, m=1,2,…M; The raw data of spacecraft B is subjected to interferometry to obtain the interference phase θbn corresponding to the side tone signal with frequency fbn, n=1,2,…N; Step 5: Calculate the differential interference delay between the two spacecraft based on the type of calibration signal.
[0006] Furthermore, step 3 specifically involves: If a calibration power source C observation arc is added before observing spacecraft A and spacecraft B, then the calibration power source C is tracked first, and then spacecraft A and spacecraft B are tracked simultaneously. If a calibration power source C observation arc is added after observing spacecraft A and spacecraft B, then spacecraft A and spacecraft B are tracked simultaneously first, and then calibration power source C is tracked.
[0007] Furthermore, step 5 includes: If the calibration signal is a broadband signal, then the original data corresponding to the first set of observation parameters of the calibration radio source C are first subjected to interferometry, and the obtained interference phase θc1(f) is linearly fitted. The interference phase function θc1(fam) is obtained by interpolation at the frequency fam position, where f is the frequency of the broadband signal. The original data corresponding to the second set of observation parameters of the calibration source C are subjected to interferometry. The obtained interferometric phase θc2(f) is linearly fitted and interpolated at the frequency fbn to obtain the interferometric phase function θc2(fbn), where f is the frequency of the broadband signal. Subtract the calibration phase θc1(fam) corresponding to frequency fam from θam, i.e., θam-θc1(fam), and then solve for the slope of the θam-θc1(fam) sequence with respect to 2πfam. The slope is the interference delay τa of spacecraft A. Subtract the calibration phase θc2(fbn) corresponding to frequency fbn from θbn, i.e., θbn-θc2(fbn), and then solve for the slope of the θbn-θc2(fbn) sequence with respect to 2πfbn. The slope is the interference delay τb of spacecraft B. The differential interference delay between the two spacecraft is calculated as τsbi = τb - τa.
[0008] Furthermore, step 5 includes: If the calibration signal is a multi-tone signal, then the original data corresponding to the first set of observation parameters of the calibration radio source C are first subjected to interferometry to obtain the interferometric phase function θc1(fam); The original data corresponding to the second set of observation parameters of the calibration source C are subjected to interferometric processing to obtain the interferometric phase function θc2(fbn); Solve for the slope of the θam sequence with respect to 2πfam, where the slope is the initial interference delay τa of spacecraft A; Solve for the slope of the θc1(fam) sequence with respect to 2πfam, where the slope is the calibration interferometric delay τac of spacecraft A; Solve for the slope of the θbn sequence with respect to 2πfbn, where the slope is the initial interference delay τb of spacecraft B; Solve for the slope of the θc2(fbn) sequence with respect to 2πfbn, where the slope is the interferometric delay τbc of spacecraft B; The differential interference time delay between the two spacecraft is calculated as τsbi = τb - τbc - (τa - τac).
[0009] This invention addresses the problem that phase nonlinear delay errors generated by the actual receiving equipment in differential interferometric measurements with large differences in the interferometric side frequencies between two spacecraft, which limit the interferometric delay from achieving the expected accuracy of the same-beam interferometric delay. The invention proposes an error calibration method to reduce the impact of phase nonlinear delay errors.
[0010] This invention is mainly applied to the field of relative angle measurement between two spacecraft, specifically in the interferometric measurement of downlink signals between two spacecraft. For the case of differential interferometric measurement of downlink signal frequencies between two spacecraft without fine design, a link delay calibration method is designed to achieve high-precision interferometric processing between spacecraft, supporting more accurate deep space navigation and other tasks.
[0011] Unlike traditional co-beam interferometric beacon design, this invention is applicable to multi-detector differential interferometric measurements of different downlink signals, and can significantly improve measurement accuracy. Attached Figure Description
[0012] Figure 1 This is a flowchart of the data processing for differential interferometry between two spacecraft. Figure 2 An evaluation diagram of the interferometric time delay difference for different combinations of the same calibration power source; Figure 3 The interference fringe patterns of spacecraft A are shown, where (a) is the interference fringe of channel 1 of spacecraft A, (b) is the interference fringe of channel 2 of spacecraft A, (c) is the interference fringe of channel 3 of spacecraft A, and (d) is the interference fringe of channel 4 of spacecraft A. Figure 4 The interference fringe patterns for spacecraft B are shown below, where (a) is the interference fringe for channel 1 of spacecraft B, (b) is the interference fringe for channel 2 of spacecraft B, (c) is the interference fringe for channel 3 of spacecraft B, and (d) is the interference fringe for channel 4 of spacecraft B. Figure 5 The residual time delay diagram of co-beam interferometry between spacecraft A and spacecraft B using the traditional method; Figure 6 The interference fringe patterns of the calibration power source collected in spacecraft A are shown in the following diagrams: (a) is the interference fringe of the calibration power source in channel 1 of spacecraft A, (b) is the interference fringe of the calibration power source in channel 2 of spacecraft A, (c) is the interference fringe of the calibration power source in channel 3 of spacecraft A, and (d) is the interference fringe of the calibration power source in channel 4 of spacecraft A. Figure 7 The interference fringe patterns of the calibration power source collected by spacecraft B are shown in the following: (a) is the interference fringe of the calibration power source in channel 1 of spacecraft B, (b) is the interference fringe of the calibration power source in channel 2 of spacecraft B, (c) is the interference fringe of the calibration power source in channel 3 of spacecraft B, and (d) is the interference fringe of the calibration power source in channel 4 of spacecraft B. Figure 8 This is a differential interferometric time delay diagram of spacecraft A and spacecraft B in this invention. Detailed Implementation
[0013] To better understand the purpose, technical solution, and function of this invention, the invention will be described in further detail below with reference to the accompanying drawings. However, this invention can be implemented in many different ways as defined and covered by the claims. The accompanying drawings, which constitute a part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0014] The data processing flow of this invention is as follows: Figure 1 As shown, it specifically includes: Step 1: Determine the observation time and conduct on-orbit observations of a certain combined detector and calibration radio source.
[0015] In one specific embodiment, the combined detector includes spacecraft A and spacecraft B. Regarding the observation timing, the combined detector can be observed first, covering the period before and after the separation of spacecraft A and spacecraft B, followed by the observation of the calibration power source C. An additional observation arc of the calibration power source C can be added before or after the observation of the two spacecraft under test. Without loss of generality, it is assumed here that the calibration power source C is observed after the observation of spacecraft A and B under test.
[0016] Step 2: Set the observation parameters. Spacecraft A will send M downlink side tone signals with frequencies of fam, where m = 1, 2, ..., M, and a represents spacecraft A. When sending downlink broadband signals, each spectral line of the broadband signal spectrum will be considered as one side tone signal, and M > 1. Spacecraft B will send N downlink side tone signals with frequencies of fbn, where n = 1, 2, ..., N, and b represents spacecraft B. When sending downlink broadband signals, each spectral line of the broadband signal spectrum will be considered as one side tone signal, and N > 1. The calibration power source C has two sets of observation parameters, which are the same as those for spacecraft A and spacecraft B, respectively.
[0017] In one specific embodiment, two sets of observation parameters are set, each set including four acquisition channels, corresponding to the four downlink side tone signals of spacecraft A and spacecraft B, respectively. When acquiring the calibration power supply signal, two sets of observation parameters are used simultaneously, that is, the observation parameters of the calibration power supply C include two sets with a total of eight channels, which are the same as the observation parameters of spacecraft A and spacecraft B, respectively.
[0018] Step 3: Track the calibration source C according to the observation plan, and then simultaneously track spacecraft A and spacecraft B; or, simultaneously track spacecraft A and spacecraft B according to the observation plan, and then track the calibration source C. After the observation is completed, the raw data of the interferometric signals to be processed from spacecraft A, spacecraft B, and calibration source C are obtained.
[0019] In one specific embodiment, after the observation is completed, four channel signals from spacecraft A, four channel signals from spacecraft B, and eight channel signals from calibration power source C are obtained.
[0020] Step 4: Perform interferometric processing on the raw data of spacecraft A to obtain the interference phase θam corresponding to the sidetone signal with frequency fam, m=1,2,…M, as shown below. Figure 3 As shown; the raw data of spacecraft B is subjected to interferometric processing to obtain the interference phase θbn corresponding to the sidetone signal with frequency fbn, n=1,2,…N, as shown. Figure 4 As shown; The conventional co-beam interferometry time delay of spacecraft A and spacecraft B is as follows: Figure 5 As shown.
[0021] It can be seen that the theoretical value of the differential interference delay between spacecraft A and spacecraft B before separation is 0, while the actual delay obtained by traditional co-beam interferometry is not 0, with an RMS of 0.846 ns.
[0022] Step 5: Calculate the differential interference delay between the two spacecraft based on the type of calibration signal.
[0023] If the calibration signal is a broadband signal, firstly, the original data corresponding to the first set of observation parameters of the calibration radio source C are subjected to interferometry to obtain the interference phase θc1(f), as follows: Figure 6 As shown. A linear fit is performed on θc1(f), and interpolation is performed at the frequency fam to obtain the interference phase function θc1(fam), where f is the frequency of the broadband signal. Interference processing is then performed on the original data corresponding to the second set of observation parameters of the calibration power source C to obtain the interference phase θc2(f), as shown. Figure 7 As shown, a linear fit is performed on θc2(f), and the interference phase function θc2(fbn) is obtained by interpolation at the frequency fbn, where f is the frequency of the broadband signal.
[0024] Then, subtract the calibration phase θc1(fam) corresponding to frequency fam from θam, i.e., θam-θc1(fam), and then solve for the slope of the θam-θc1(fam) sequence with respect to 2πfam. This slope is the interference delay τa of spacecraft A; subtract the calibration phase θc2(fbn) corresponding to frequency fbn from θbn, i.e., θbn-θc2(fbn), and then solve for the slope of the θbn-θc2(fbn) sequence with respect to 2πfbn. This slope is the interference delay τb of spacecraft B; the differential interference delay of the two spacecraft is τsbi=τb-τa. For example... Figure 8 As shown.
[0025] In one specific embodiment, the theoretical value of the differential interference delay of spacecraft A and spacecraft B before separation is 0. The delay obtained by the differential interference processing of the present invention is basically close to 0, with an RMS of 0.038 ns, which improves the accuracy by an order of magnitude compared with the traditional co-beam interferometry.
[0026] If the calibration signal is a multi-tone signal, firstly, the raw data corresponding to the first set of observation parameters of the calibration source C are subjected to interferometry to obtain the interferometric phase function θc1(fam); then, the raw data corresponding to the second set of observation parameters of the calibration source C are subjected to interferometry to obtain the interferometric phase function θc2(fbn). Here, fam and fbn are design values; actual values will differ, so the actual processed multi-tone frequency values are used. Then, the slope of the θam sequence with respect to 2πfam is calculated, which is the initial interference delay τa of spacecraft A. The slope of the θc1(fam) sequence with respect to 2πfam is calculated, which is the calibration interference delay τac of spacecraft A. The slope of the θbn sequence with respect to 2πfbn is calculated, which is the initial interference delay τb of spacecraft B. The slope of the θc2(fbn) sequence with respect to 2πfbn is calculated, which is the interference delay τbc of spacecraft B. The differential interference delay between the two spacecraft is τsbi = τb - τbc - (τa - τac).
[0027] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various changes or modifications within the scope of the claims, all of which should be included within the protection scope of the present invention.
Claims
1. A link delay calibration method for differential interferometry between two spacecraft, wherein the two spacecraft are spacecraft A and spacecraft B, characterized in that, Includes the following steps: Step 1: Determine the observation time. Before or after observing spacecraft A and spacecraft B, add an observation arc for calibrating the radio source C. Step 2: Set the observation parameters. Spacecraft A sends M downlink side tone signals with frequencies of fam, where m = 1, 2, ..., M. When sending downlink broadband signals, each spectral line of the broadband signal spectrum is considered as one side tone signal, where M > 1. Spacecraft B sends down N side tone signals with frequencies of fbn, where n = 1, 2, ..., N. When sending down wideband signals, each spectral line of the wideband signal spectrum is considered as one side tone signal, where N > 1. The calibration radio source C has two sets of observation parameters, which are the same as those of spacecraft A and spacecraft B, respectively. Step 3: Track and calibrate the radio source C, spacecraft A and spacecraft B to obtain the raw data of the signals to be interferometrically processed from spacecraft A, spacecraft B and the radio source C; Step 4: Perform interferometric processing on the raw data of spacecraft A to obtain the interference phase θam corresponding to the side tone signal with frequency fam, m=1,2,…M; The raw data of spacecraft B is subjected to interferometry to obtain the interference phase θbn corresponding to the side tone signal with frequency fbn, n=1,2,…N; Step 5: Calculate the differential interference delay between the two spacecraft based on the type of calibration signal.
2. The method according to claim 1, characterized in that, Step 3 specifically involves: If a calibration power source C observation arc is added before observing spacecraft A and spacecraft B, then the calibration power source C is tracked first, and then spacecraft A and spacecraft B are tracked simultaneously. If a calibration power source C observation arc is added after observing spacecraft A and spacecraft B, then spacecraft A and spacecraft B are tracked simultaneously first, and then calibration power source C is tracked.
3. The method according to claim 1, characterized in that, Step 5 includes: If the calibration signal is a broadband signal, then the original data corresponding to the first set of observation parameters of the calibration radio source C are first subjected to interferometry, and the obtained interference phase θc1(f) is linearly fitted. The interference phase function θc1(fam) is obtained by interpolation at the frequency fam position, where f is the frequency of the broadband signal. The original data corresponding to the second set of observation parameters of the calibration source C are subjected to interferometry. The obtained interferometric phase θc2(f) is linearly fitted and interpolated at the frequency fbn to obtain the interferometric phase function θc2(fbn), where f is the frequency of the broadband signal. Subtract the calibration phase θc1(fam) corresponding to frequency fam from θam, i.e., θam-θc1(fam), and then solve for the slope of the θam-θc1(fam) sequence with respect to 2πfam. The slope is the interference delay τa of spacecraft A. Subtract the calibration phase θc2(fbn) corresponding to frequency fbn from θbn, i.e., θbn-θc2(fbn), and then solve for the slope of the θbn-θc2(fbn) sequence with respect to 2πfbn. The slope is the interference delay τb of spacecraft B. The differential interference delay between the two spacecraft is calculated as τsbi = τb - τa.
4. The method according to claim 1, characterized in that, Step 5 includes: If the calibration signal is a multi-tone signal, then the original data corresponding to the first set of observation parameters of the calibration radio source C are first subjected to interferometry to obtain the interferometric phase function θc1(fam); The original data corresponding to the second set of observation parameters of the calibration source C are subjected to interferometric processing to obtain the interferometric phase function θc2(fbn); Solve for the slope of the θam sequence with respect to 2πfam, where the slope is the initial interference delay τa of spacecraft A; Solve for the slope of the θc1(fam) sequence with respect to 2πfam, where the slope is the calibration interferometric delay τac of spacecraft A; Solve for the slope of the θbn sequence with respect to 2πfbn, where the slope is the initial interference delay τb of spacecraft B; Solve for the slope of the θc2(fbn) sequence with respect to 2πfbn, where the slope is the interferometric delay τbc of spacecraft B; The differential interference time delay between the two spacecraft is calculated as τsbi = τb - τbc - (τa - τac).