Intersatellite measurement system and method for formation navigation microsatellites in lunar orbit

Abstract

The present invention provides an intersatellite measurement system and method for a lunar orbit formation navigation microsatellite, relating to the field of deep space exploration technology. The system comprises: a master satellite and a slave satellite, with a Ka intersatellite link established between the master satellite and the slave satellite; the master satellite and the slave satellite each transmit a timed intersatellite measurement signal and receive a timed intersatellite measurement signal from the other satellite, measure the time difference between the local timing signal and the received timing signal from the other satellite to obtain the local satellite pseudorange, and the two satellites exchange pseudoranges via the intersatellite link to calculate the intersatellite distance and time difference. The system does not require precise time synchronization between the two satellites; measurement results can be obtained directly onboard, eliminating the need for ground-based calculations and thus saving ground resources. The system also simplifies the satellite platform and antenna design of the slave satellite, reducing the satellite's weight and cost.

Description

Technical Field

[0001] The present invention relates to the field of deep space exploration technology, and in particular to an inter-satellite measurement system and method for a lunar orbit formation navigation microsatellite. Background Art

[0002] In recent years, deep space exploration has flourished globally. Major space powers have proposed and are gradually implementing deep space exploration missions, including lunar exploration, planetary exploration, and planetary defense. With the continued exploration of the lunar poles, the far side of the moon, and other areas invisible from Earth, as well as exploration of more distant planets and even the solar system, existing navigation systems are no longer sufficient for practical engineering needs. Deploying a network of navigation satellites around the moon and establishing a lunar navigation system, as part of cis-lunar space infrastructure, will expand reliable satellite navigation coverage and provide support for lunar and even deep space exploration missions.

[0003] If a navigation satellite's orbital determination accuracy is low, it cannot provide users with high-precision positioning and navigation services. To enable and enhance the autonomous orbit determination and navigation capabilities of navigation satellites, existing navigation satellite constellations have built inter-satellite links and equipped with inter-satellite measurement capabilities to serve autonomous orbit determination and joint satellite-ground orbit determination, thereby improving the orbit prediction accuracy of navigation satellites and further ensuring the long-term maintenance of satellite navigation and positioning performance without the support of ground stations.

[0004] Compared to large spacecraft, microsatellites are increasingly gaining attention in deep space exploration due to their small size, light weight, and ease of formation and networking. However, their hardware and software resources are relatively limited. Therefore, intersatellite measurements using microsatellites must meet precise measurement requirements while also requiring minimal hardware complexity and simplified computational processing.

[0005] A Chinese invention patent, publication number CN117318786A, proposes a method for measuring intersatellite links in Earth-Moon space with extremely high latency, based on the Beidou navigation system. The method calculates the intersatellite link distance based on the one-way ranging values obtained from Beidou navigation satellites and Earth-Moon spacecraft. This patent requires the use of Beidou satellite signals, which are difficult to utilize given the distance of satellites orbiting the moon.

[0006] Chinese invention patent publication number CN109283557A proposes a two-way pseudo-code-assisted carrier high-precision intersatellite ranging system and method. This system uses two-way pseudo-code regeneration or forwarding technology to assist with carrier coherent forwarding to obtain the absolute distance between the master and slave satellites. This patent requires the slave satellite to coherently forward the master satellite's carrier signal and regenerate or forward the master satellite's pseudo-code ranging signal. This results in complex hardware and algorithms, and it is not possible to achieve time synchronization between the master and slave satellites.

[0007] Chinese invention patent publication number CN110708754A proposes a method for allocating power between integrated ranging and communication signals within a navigation satellite constellation. This method calculates intersatellite link characteristics based on the relative distance between navigation satellites, adjusting the power ratio between communication and ranging signals. This patent does not cover the implementation of the intersatellite measurement system.

[0008] Chinese invention patent publication number CN113959431A proposes a high-precision method for combined inter-satellite distance and time difference measurement. This method calculates the distance and time difference between satellites using a multi-satellite measurement scheme based on a time-division system and the ADS TWR method. This invention primarily addresses the measurement principle and does not involve the onboard design and implementation of the inter-satellite measurement system. Summary of the Invention

[0009] In view of the defects in the prior art, the present invention provides a lunar orbit formation navigation microsatellite inter-satellite measurement system and method.

[0010] According to the present invention, a lunar orbit formation navigation microsatellite intersatellite measurement system and method are provided, and the scheme is as follows:

[0011] In a first aspect, a lunar orbit formation navigation microsatellite intersatellite measurement system is provided, the system comprising: a master satellite and a slave satellite, wherein a Ka intersatellite link is established between the master satellite and the slave satellite;

[0012] The master satellite and the slave satellite both send timing inter-satellite measurement signals and receive timing inter-satellite measurement signals from each other, measure the time difference between the local timing signal and the received timing signal of the other party to obtain the local satellite pseudo-range, and the two satellites exchange pseudo-ranges through the inter-satellite link to solve the inter-satellite distance and time difference.

[0013] Preferably, the master satellite includes: a high-gain Ka directional antenna, a master-satellite ranging payload, and a master-satellite platform; the slave satellite includes: a low-gain Ka wide-beam antenna, a slave-satellite ranging payload, and a slave-satellite platform;

[0014] The high-gain Ka directional antenna and the low-gain Ka wide-beam antenna complete the transmission and reception of inter-satellite measurement signals;

[0015] The master satellite ranging payload and the slave satellite ranging payload measure the inter-satellite distance and time difference;

[0016] The master satellite platform provides power, pulse-per-second signals, time broadcasting, and control instructions for the ranging payload, receives intersatellite measurement results and analog telemetry from the ranging payload, provides attitude adjustment and control for intersatellite measurements, and transmits measurement results to the ground.

[0017] The slave satellite platform provides power and control instructions for the ranging payload, receives inter-satellite measurement results and analog telemetry of the ranging payload, provides attitude adjustment and control for inter-satellite measurement, and transmits the measurement results to the ground.

[0018] Preferably, the master satellite adopts a high-gain Ka directional antenna. During inter-satellite measurement, the master satellite needs to adjust its attitude to align the antenna beam with the slave satellite.

[0019] The slave satellite adopts a low-gain Ka wide-beam antenna. During inter-satellite measurement, the slave satellite points the low-gain Ka wide-beam antenna in the direction of its velocity or in the opposite direction according to its relative position relationship with the master satellite.

[0020] Preferably, if the inter-satellite measurement signal cannot be locked, the master satellite platform adjusts the satellite attitude and uses a spiral scanning method to adjust the beam pointing of the high-gain Ka directional antenna.

[0021] Preferably, the master satellite is the initiator of the inter-satellite measurement, and the slave satellite synchronizes with the master satellite at the time of signal transmission;

[0022] The master satellite platform sends a pulse-second signal to the ranging payload. After the master satellite ranging payload receives the pulse-second signal and determines it is valid, it starts sending inter-satellite measurement signals at the falling edge of the pulse-second signal. After the slave satellite ranging payload receives the signal and successfully demodulates it, it starts sending inter-satellite measurement signals. After the master satellite ranging payload receives the slave satellite signal and successfully demodulates it, both parties start measuring using the two-way time comparison method. The slave satellite ranging payload corrects the sending time of the slave satellite signal based on the measurement results and sends time synchronization to the master satellite.

[0023] Preferably, the master satellite ranging payload and the slave satellite ranging payload both include: a Ka channel module and a digital baseband module;

[0024] The Ka channel module includes: a transmitting channel and a receiving channel, which support simultaneous transmission and reception. The transmitting channel up-converts, filters, and amplifies the central signal output by the digital baseband module and sends it to the antenna. The receiving channel amplifies, filters, and down-converts the radio frequency signal from the antenna into an intermediate frequency signal and outputs it to the digital baseband module. Both up-conversion and down-conversion adopt a single frequency conversion scheme.

[0025] The digital baseband module implements baseband signal processing and ranging algorithms, modulates the spread spectrum code sequence of inter-satellite measurement, digitally up-converts the frequency to generate an intermediate frequency signal, and outputs the signal to the Ka channel module; receives the intermediate frequency signal of the Ka channel module, performs pseudo-code despreading, pseudo-code synchronization, carrier synchronization, and frame synchronization after digital down-conversion, uses pseudo-code correlation operations to obtain the local satellite time difference measurement value required for the two-way time comparison method, analyzes the inter-satellite measurement frame to obtain the time measurement value of the opposite satellite; and calculates the inter-satellite distance and time difference.

[0026] Preferably, the digital baseband module includes: an intermediate frequency transceiver circuit, a digital signal processing circuit, and a clock generation circuit;

[0027] The intermediate frequency transceiver circuit uses an integrated transceiver chip to realize the conversion between baseband data and intermediate frequency signals, meeting the requirements of miniaturization, low power consumption and flexibility;

[0028] The digital signal processing circuit uses an FPGA chip to complete baseband data processing, and is equipped with an anti-fuse to refresh the FPGA chip and a watchdog reset circuit to improve the product's single-event resistance.

[0029] The clock generation circuit cascades a chip-level atomic clock and a disciplined constant-temperature crystal oscillator to provide a reference clock and a reference frequency for a digital baseband module and a Ka channel module.

[0030] Preferably, the inter-satellite measurement signal is a Ka-band radio frequency signal modulating a pseudo-code signal and an inter-satellite measurement frame;

[0031] The pseudo code signal is used to measure the time difference between the local timing signal and the received timing signal of the other party;

[0032] The inter-satellite measurement frame includes the local satellite time difference measurement result and the measurement timestamp. The master satellite and the slave satellite exchange the measurement results through the inter-satellite measurement frame, thereby completing the settlement of the inter-satellite distance and time difference on the local satellite.

[0033] In a second aspect, a method for inter-satellite measurement of a lunar orbit formation navigation microsatellite is provided, the method comprising:

[0034] Step 1: The ground selects the intersatellite measurement arc according to the orbit prediction and sends instructions to the satellite;

[0035] Step 2: The master satellite platform and the slave satellite platform adjust their attitudes;

[0036] Step 3: The ranging payloads of the master and slave satellites are powered on for a set threshold time.

[0037] Step 4: The master satellite and the slave satellite establish an inter-satellite link and lock the inter-satellite measurement signal;

[0038] Step 5: The slave satellite sends a synchronization signal to the master satellite;

[0039] Step 6: Obtain intersatellite measurement results;

[0040] Step 7: After the intersatellite measurement is completed, the master satellite and the slave satellite turn off the master satellite ranging payload and the slave satellite ranging payload, and adjust the master satellite and the slave satellite to the normal flight attitude towards the sun.

[0041] Preferably, step 4 includes:

[0042] The master satellite platform sends time broadcast and pulse-second signals to the ranging payload. The master satellite ranging payload starts sending timed inter-satellite measurement signals to the slave satellite at the falling edge of the pulse-second signal.

[0043] If the slave satellite cannot lock onto the master satellite signal, the master satellite platform adjusts the satellite attitude and uses a spiral scanning method to adjust the beam pointing of the high-gain Ka directional antenna;

[0044] After the slave satellite receives the master satellite signal and successfully demodulates it, it sends a timed inter-satellite measurement signal to the master satellite; the master satellite ranging payload receives the slave satellite signal and successfully demodulates it.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The present invention adopts a two-way comparison method to obtain the distance and time difference between satellites. The two satellites do not need precise time synchronization. The measurement results can be obtained directly on the satellite without the need for ground calculation, thus saving ground resources.

[0047] 2. The present invention simplifies the antenna design of the slave satellite, reduces the requirements for the attitude pointing accuracy and stability of the slave satellite, and is conducive to reducing the weight and cost of the entire slave satellite;

[0048] 3. The present invention adopts a combination of a high-gain Ka directional antenna and a low-gain Ka wide-beam antenna, which can improve the inter-satellite measurement distance and reduce the difficulty of inter-satellite beam alignment;

[0049] 4. The ranging payloads of the master and slave satellites of the present invention have the same hardware design except for the interchange of transmit and receive frequencies, which is conducive to the mass design of payloads and reduces the difficulty and cost of debugging.

[0050] 5. The ranging payload of the present invention adopts a chip-level atomic clock and a disciplined oven-controlled crystal oscillator cascade to provide a reference clock, which combines the high accuracy of the chip-level atomic clock and the low phase noise performance of the oven-controlled crystal oscillator, and is conducive to improving the accuracy of intersatellite measurements.

[0051] Other beneficial effects of the present invention will be explained through the introduction of specific technical features and technical solutions in the specific implementation methods. Those skilled in the art should be able to understand the beneficial technical effects brought about by the introduction of these technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0053] Figure 1 Schematic diagram of the intersatellite measurement system of the present invention;

[0054] Figure 2 This is the intersatellite measurement flow chart of the present invention. DETAILED DESCRIPTION

[0055] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0056] The embodiment of the present invention provides a lunar orbit formation navigation microsatellite inter-satellite measurement system, which realizes inter-satellite measurement within a range of 400km between the master satellite and the slave satellite. Figure 1 As shown, it includes: a master satellite and a slave satellite, and a Ka inter-satellite link is established between the master satellite and the slave satellite;

[0057] Both the master satellite and the slave satellite send timing inter-satellite measurement signals and receive timing inter-satellite measurement signals from each other. The time difference between the local timing signal and the received timing signal of the other party is measured to obtain the pseudo-range of the local satellite. The two satellites exchange pseudo-ranges through the inter-satellite link, that is, the inter-satellite distance and time difference are solved.

[0058] The master satellite includes a high-gain Ka directional antenna, a master ranging payload, and a master satellite platform. The slave satellite includes a low-gain Ka wide-beam antenna, a slave ranging payload, and a slave satellite platform. The master and slave ranging payloads have identical hardware designs, except for swapping transmit and receive frequencies. Both payloads include a Ka channel module and a digital baseband module. The Ka channel module includes transmit and receive channels, while the digital baseband module includes an intermediate frequency transceiver circuit, a digital signal processing circuit, and a clock generation circuit.

[0059] A high-gain Ka directional antenna and a low-gain Ka wide-beam antenna transmit and receive intersatellite measurement signals. The high-gain Ka directional antenna is a 0.6m Cassegrain antenna with a gain exceeding 36.8dBi (±0.2°), receiving left-hand circular polarization and transmitting right-hand circular polarization. The low-gain Ka wide-beam antenna is a waveguide antenna, including both a receiving and transmitting antennas, with a gain exceeding -6dBi (±60°), receiving right-hand circular polarization and transmitting left-hand circular polarization. This combination of the high-gain Ka directional antenna and the low-gain Ka wide-beam antenna balances improving intersatellite measurement range and reducing the difficulty of intersatellite beam alignment. The master and slave ranging payloads measure intersatellite range and time difference.

[0060] The main satellite platform provides power, pulse-per-second signals, time broadcast and control instructions for the main satellite ranging payload, receives the inter-satellite measurement results and analog telemetry of the main satellite ranging payload, provides attitude adjustment and control for inter-satellite measurement, and transmits the measurement results to the ground.

[0061] The slave satellite platform provides power and control instructions for the slave ranging payload, receives the inter-satellite measurement results and analog telemetry of the slave ranging payload, provides attitude adjustment and control for inter-satellite measurement, and transmits the measurement results to the ground.

[0062] The primary and secondary satellites fly in a large elliptical frozen orbit around the moon, with the inter-satellite distance oscillating in the range of 50km to 700km.

[0063] The intersatellite measurement signal is a Ka-band RF signal modulated with a pseudo-code signal and an intersatellite measurement frame. The modulation scheme is PCM-CDMA-BPSK, with a pseudo-code rate of 10.23 Mcps. The intersatellite measurement frame information stream and the pseudo-code sequence are XORed together to generate a spreading code sequence, which is then BPSK modulated. The pseudo-code signal is used to measure the time difference between the local timing signal and the received timing signal of the other party. The intersatellite measurement frame contains the local satellite's time difference measurement result and the measurement timestamp. The master and slave satellites exchange measurement results through the intersatellite measurement frame, completing the intersatellite distance and time difference settlement on the local satellite.

[0064] The master satellite and the slave satellite obtain the pseudo-range measurement results of their own satellites through pseudo-code correlation operations, and then obtain the pseudo-range measurement results of each other from the inter-satellite measurement frame, and complete the calculation of the inter-satellite distance and time difference on the local satellite.

[0065] Specifically, the Ka channel module includes a transmitting channel and a receiving channel, and supports simultaneous transmission and reception. The transmitting channel up-converts, filters, and amplifies the center signal output by the digital baseband module and sends it to the antenna with a transmission power of 0.5W. The receiving channel amplifies, filters, and down-converts the RF signal from the antenna into an intermediate frequency signal and outputs it to the digital baseband module; both up-conversion and down-conversion adopt a single frequency conversion scheme.

[0066] The digital baseband module implements baseband signal processing and ranging algorithms: it modulates the spread spectrum code sequence for inter-satellite measurement, digitally up-converts it to generate an intermediate frequency signal, and outputs it to the Ka channel module. It receives the intermediate frequency signal from the Ka channel module, performs pseudo-code despreading, pseudo-code synchronization, carrier synchronization, and frame synchronization after digital down-conversion. It uses pseudo-code correlation operations to obtain the local satellite time difference measurement value required for the two-way time comparison method, analyzes the inter-satellite measurement frame to obtain the time measurement value of the opposite satellite, and calculates the inter-satellite distance and time difference.

[0067] The intermediate frequency transceiver circuit of the digital baseband module uses an integrated transceiver chip to realize the conversion of baseband data and intermediate frequency signals, meeting the requirements of miniaturization, low power consumption and flexibility; the digital signal processing circuit adopts FPGA chip to complete baseband data processing, and is equipped with anti-fuse to refresh the FPGA chip and watchdog reset circuit to improve the product's single-particle resistance; the clock generation circuit cascades the chip-level atomic clock and the tamed constant temperature crystal oscillator to provide reference clock and reference frequency for the digital baseband module and Ka channel module.

[0068] Furthermore, the master satellite uses a high-gain Ka directional antenna to increase the distance of intersatellite measurements. During intersatellite measurements, the master satellite needs to adjust its attitude to align its antenna beam with the slave satellite, requiring the master satellite platform to have high attitude pointing accuracy and attitude stability. The slave satellite uses a low-gain Ka wide-beam antenna to reduce the difficulty of intersatellite pointing. During intersatellite measurements, the slave satellite points the low-gain Ka wide-beam antenna in the direction or opposite direction of its velocity based on its relative position to the master satellite. The slave satellite platform does not need high attitude pointing accuracy and attitude stability.

[0069] If the intersatellite measurement signal cannot be locked, the master satellite platform adjusts the satellite attitude and uses a spiral scanning method to adjust the beam pointing of the high-gain Ka directional antenna.

[0070] The master satellite is the initiator of intersatellite measurement, and the slave satellite synchronizes its signal sending time with the master satellite; the master satellite platform sends a second pulse signal to the ranging payload. After the master satellite ranging payload receives the second pulse signal and determines it is valid, it starts sending the intersatellite measurement signal at the falling edge of the second pulse. After the slave satellite ranging payload receives the signal and successfully demodulates it, it starts sending the intersatellite measurement signal. After the master satellite ranging payload receives the slave satellite signal and successfully demodulates it, both parties start measuring using the two-way time comparison method. The slave satellite ranging payload corrects the sending time of the slave satellite signal based on the measurement results and sends the time synchronization to the master satellite.

[0071] The present invention also provides a method for measuring the intersatellite formation navigation of a lunar orbit microsatellite, referring to Figure 2 As shown, the method includes:

[0072] Step 1: The ground selects the intersatellite measurement arc and injects commands to the satellite. Based on the orbit prediction, the ground calculates the arc where the master and slave satellites are less than 400 km apart. The ground injects the satellite's orbital data and intersatellite measurement commands to the master and slave satellites, including satellite attitude adjustment time, ranging payload power-on and power-off time, and intersatellite measurement time.

[0073] Step 2: The master and slave satellites adjust their attitudes. Based on the orbital data recorded on the ground, the master satellite platform adjusts its attitude, pointing its high-gain Ka directional antenna toward the slave satellite. Based on the positional relationship between the master and slave satellites, the slave satellite platform adjusts its attitude, pointing its low-gain Ka wide-beam antenna in the direction or opposite direction of their velocity.

[0074] Step 3: Power on the ranging payloads of the master and slave satellites for 20 minutes. The satellite platform sends a power-on command to the ranging payloads based on the ground-based instructions. This step is to wait for the output signal of the disciplined oven-controlled crystal oscillator in the channel module to stabilize.

[0075] Step 4: The master and slave satellites establish an intersatellite link and lock the intersatellite measurement signal. The master satellite platform sends a time broadcast and pulse-second signals to the ranging payload. The master satellite ranging payload starts sending a timed intersatellite measurement signal to the slave satellite at the falling edge of the pulse-second signal. If the slave satellite cannot lock the master satellite signal, the master satellite platform adjusts the satellite attitude and uses a spiral scanning method to adjust the beam pointing of the high-gain Ka directional antenna.

[0076] After the slave satellite receives the master satellite signal and successfully demodulates it, it sends a timed inter-satellite measurement signal to the master satellite; the master satellite ranging payload receives the slave satellite signal and successfully demodulates it.

[0077] Step 5: The slave satellite sends synchronization signals to the master satellite. The master and slave satellites begin to measure using the two-way time comparison method, filling the inter-satellite measurement frame with the local satellite's pseudo-range measurement results and measurement timestamp. The slave satellite ranging payload parses the master satellite timestamp in the inter-satellite measurement frame and regards this time as the starting time of the whole second of the slave satellite ranging payload's signal transmission.

[0078] Step 6: Obtain inter-satellite measurement results. The ranging payloads of the master and slave satellites respectively calculate the inter-satellite distance and time difference, and upload the measurement results and measurement timestamp to the local satellite platform; the satellite platform then transmits the measurement results to the ground.

[0079] Step 7: The master and slave satellites restore their solar attitude. After the intersatellite measurement is completed, the master and slave satellites turn off the ranging payloads and adjust their attitude to the normal flight solar attitude.

[0080] Next, the present invention will be described in more detail.

[0081] The present invention provides an intersatellite measurement system and method for formation navigation microsatellites in a lunar orbit. This system can establish an intersatellite measurement link within a range of 50km to 500km. It uses a two-way time comparison method to achieve ranging accuracy better than meter-level and nanosecond-level time synchronization. Before measurement, the two satellites do not require precise time synchronization or signal coherence; both satellites can autonomously calculate the intersatellite distance.

[0082] A Ka inter-satellite link is established between the navigation master and slave satellites, and the inter-satellite distance and time difference are obtained using a two-way time comparison method based on a spread spectrum system. The master and slave satellites operate in a large elliptical frozen orbit around the moon, and the inter-satellite distance oscillates. The master satellite includes a high-gain Ka directional antenna, a ranging payload, and a satellite platform, while the slave satellite includes a low-gain Ka wide-beam antenna, a ranging payload, and a satellite platform. The high-gain Ka directional antenna and the low-gain Ka wide-beam antenna transmit and receive inter-satellite measurement signals. The ranging payloads of the master and slave satellites use the two-way time comparison method to measure the inter-satellite distance and time difference. The master satellite platform provides power, pulse-second signals, time broadcast, and control commands to the ranging payload, receives inter-satellite measurement results and analog telemetry from the ranging payload, provides attitude adjustment and control for inter-satellite measurements, and transmits the measurement results to the ground. The slave satellite platform provides power and control commands to the ranging payload, receives inter-satellite measurement results and analog telemetry from the ranging payload, provides attitude adjustment and control for inter-satellite measurements, and transmits the measurement results to the ground.

[0083] The combination of high-gain Ka directional antenna and low-gain Ka wide-beam antenna can both improve the inter-satellite measurement distance and reduce the difficulty of inter-satellite beam alignment.

[0084] The master and slave ranging payloads have the same hardware design, including the Ka channel module and digital baseband module, except that the transmit and receive frequencies are interchanged.

[0085] The Ka channel module includes a transmitting channel and a receiving channel, supports simultaneous transmission and reception, up-converts, filters, and amplifies the center signal output by the digital baseband module and sends it to the Ka antenna, receives the RF signal from the Ka antenna, amplifies, filters, and down-converts it into an intermediate frequency signal, and outputs it to the digital baseband module; the up-conversion and down-conversion both adopt a single frequency conversion scheme.

[0086] The digital baseband module implements baseband signal processing and ranging algorithms: it modulates the spread spectrum code sequence for inter-satellite measurement, digitally up-converts it to generate an intermediate frequency signal, and outputs it to the Ka channel module. It receives the intermediate frequency signal from the Ka channel module, performs pseudo-code despreading, pseudo-code synchronization, carrier synchronization, and frame synchronization after digital down-conversion. It uses pseudo-code correlation operations to obtain the local satellite time difference measurement value required for the two-way time comparison method, and parses the inter-satellite measurement frame to obtain the time measurement value of the opposite satellite. It then calculates the inter-satellite distance and time difference.

[0087] The digital baseband module includes an intermediate frequency transceiver circuit, a digital signal processing circuit, and a clock generation circuit. The intermediate frequency transceiver circuit uses an integrated transceiver chip to convert baseband data and intermediate frequency signals, achieving the requirements of miniaturization, low power consumption, and flexibility. The digital signal processing circuit uses an FPGA chip to complete baseband data processing, and is equipped with an anti-fuse to refresh the FPGA chip and a watchdog reset circuit to improve the product's single-event resistance. The clock generation circuit cascades a chip-level atomic clock and a disciplined oven-controlled crystal oscillator to provide a reference clock and reference frequency for the digital baseband module and Ka channel module.

[0088] The difference between the master satellite and the slave satellite is that the master satellite uses a high-gain Ka directional antenna to increase the distance of inter-satellite measurement. During inter-satellite measurement, the master satellite needs to adjust its attitude to align the antenna beam with the slave satellite. If the inter-satellite measurement signal cannot be locked, the master satellite platform adjusts the satellite attitude and uses a spiral scanning method to adjust the beam pointing of the high-gain Ka directional antenna. The master satellite platform needs to have high attitude pointing accuracy and attitude stability. The slave satellite uses a low-gain Ka wide-beam antenna to reduce the difficulty of inter-satellite pointing. During inter-satellite measurement, the slave satellite points the low-gain Ka wide-beam antenna in the direction or opposite direction of its velocity based on its relative position to the master satellite. The slave satellite platform does not need high attitude pointing accuracy and attitude stability.

[0089] The difference between the master satellite and the slave satellite is that the master satellite is the initiator of intersatellite measurement, and the slave satellite's signal sending time is synchronized with the master satellite; the master satellite satellite platform sends a second pulse signal to the ranging payload. After the master satellite ranging payload receives the second pulse signal and determines it is valid, it starts sending intersatellite measurement signals at the falling edge of the second pulse. After the slave satellite ranging payload receives the signal and successfully demodulates it, it starts sending intersatellite measurement signals. After the master satellite ranging payload receives the slave satellite signal and successfully demodulates it, the two parties start measuring using the two-way time comparison method. The slave satellite ranging payload corrects the sending time of the slave satellite signal based on the measurement results and sends it to the master satellite for synchronization.

[0090] In the two-way time comparison method, both the master and slave satellites transmit timing signals and receive timing signals from each other, measuring the time difference between their local timing signals and the received timing signals from each other. The two satellites exchange the measured time difference via an inter-satellite link to calculate the inter-satellite distance and time difference. The distance measurement principle of the two-way comparison method does not fall within the scope of the present invention.

[0091] The inter-satellite measurement signal is a Ka-band radio frequency signal modulated with a pseudo-code signal and an inter-satellite measurement frame. The pseudo-code signal is used to measure the time difference between the local timing signal and the received timing signal of the other party. The inter-satellite measurement frame contains the time difference measurement result of the local satellite and the measurement timestamp. The master satellite and the slave satellite exchange measurement results through the inter-satellite measurement frame, thereby completing the settlement of the inter-satellite distance and time difference on the local satellite.

[0092] The embodiments of the present invention provide an inter-satellite measurement system and method for a lunar orbit formation navigation microsatellite. The system does not require precise time synchronization between the two satellites, and measurement results can be obtained directly on the satellite without ground calculation, thus saving ground resources. The system also simplifies the satellite platform and antenna design of the slave satellite, reducing the weight and cost of the satellite.

[0093] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0094] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A lunar orbit formation navigation microsatellite intersatellite measurement system, characterized by: include: A Ka inter-satellite link is established between the master satellite and the slave satellite; The master satellite and the slave satellite both send timing inter-satellite measurement signals and receive timing inter-satellite measurement signals from each other, measure the time difference between the local timing signal and the received timing signal of the other party to obtain the local satellite pseudo-range, and the two satellites exchange pseudo-ranges through the inter-satellite link to solve the inter-satellite distance and time difference; The primary satellite includes: a high-gain Ka directional antenna; The master satellite uses a high-gain Ka directional antenna. During inter-satellite measurement, the master satellite needs to adjust its attitude to align the antenna beam with the slave satellite. The slave satellite includes: a low-gain Ka wide-beam antenna; The slave satellite uses a low-gain Ka wide-beam antenna. During inter-satellite measurement, the slave satellite points the low-gain Ka wide-beam antenna in the direction of its velocity or in the opposite direction according to its relative position to the master satellite; The master satellite further includes: a master satellite ranging payload and a master satellite platform; the slave satellite further includes: a slave satellite ranging payload and a slave satellite platform; The high-gain Ka directional antenna and the low-gain Ka wide-beam antenna complete the transmission and reception of inter-satellite measurement signals; The master satellite ranging payload and the slave satellite ranging payload measure the inter-satellite distance and time difference; The primary satellite platform provides power, pulse-per-second signals, time broadcasting, and control instructions to the primary satellite ranging payload, receives intersatellite measurement results and analog telemetry from the primary satellite ranging payload, provides attitude adjustment and control for intersatellite measurement, and transmits measurement results to the ground. The slave satellite platform provides power and control instructions for the slave ranging payload, receives inter-satellite measurement results and analog telemetry from the slave ranging payload, provides attitude adjustment and control for inter-satellite measurement, and transmits the measurement results to the ground; The master satellite is the initiator of intersatellite measurement, and the slave satellite synchronizes with the master satellite at the time of signal transmission; The master satellite platform sends a pulse-second signal to the ranging payload. After the master satellite ranging payload receives the pulse-second signal and determines it is valid, it starts sending inter-satellite measurement signals at the falling edge of the pulse-second signal. After the slave satellite ranging payload receives the signal and successfully demodulates it, it starts sending inter-satellite measurement signals. After the master satellite ranging payload receives the slave satellite signal and successfully demodulates it, both parties start measuring using the two-way time comparison method. The slave satellite ranging payload corrects the sending time of the slave satellite signal based on the measurement results and sends time synchronization to the master satellite.

2. The lunar orbit formation navigation microsatellite intersatellite measurement system according to claim 1, characterized in that: If the intersatellite measurement signal cannot be locked, the master satellite platform adjusts the satellite attitude and uses a spiral scanning method to adjust the beam pointing of the high-gain Ka directional antenna.

3. The lunar orbit formation navigation microsatellite intersatellite measurement system according to claim 1, characterized in that: The master satellite ranging payload and the slave satellite ranging payload both include: a Ka channel module and a digital baseband module; The Ka channel module includes: a transmitting channel and a receiving channel, which support simultaneous transmission and reception. The transmitting channel up-converts, filters, and amplifies the central signal output by the digital baseband module and sends it to the antenna. The receiving channel amplifies, filters, and down-converts the radio frequency signal from the antenna into an intermediate frequency signal and outputs it to the digital baseband module. Both up-conversion and down-conversion adopt a single frequency conversion scheme. The digital baseband module implements baseband signal processing and ranging algorithms, modulates the spread spectrum code sequence of inter-satellite measurement, digitally up-converts the frequency to generate an intermediate frequency signal, and outputs the signal to the Ka channel module; receives the intermediate frequency signal of the Ka channel module, performs pseudo-code despreading, pseudo-code synchronization, carrier synchronization, and frame synchronization after digital down-conversion, uses pseudo-code correlation operations to obtain the local satellite time difference measurement value required for the two-way time comparison method, analyzes the inter-satellite measurement frame to obtain the time measurement value of the opposite satellite; and calculates the inter-satellite distance and time difference.

4. The lunar orbit formation navigation microsatellite intersatellite measurement system according to claim 3, characterized in that: The digital baseband module includes: an intermediate frequency transceiver circuit, a digital signal processing circuit and a clock generation circuit; The intermediate frequency transceiver circuit uses an integrated transceiver chip to realize the conversion between baseband data and intermediate frequency signals, meeting the requirements of miniaturization, low power consumption and flexibility; The digital signal processing circuit uses an FPGA chip to complete baseband data processing, and is equipped with an anti-fuse to refresh the FPGA chip and a watchdog reset circuit to improve the product's single-event resistance. The clock generation circuit cascades a chip-level atomic clock and a disciplined constant-temperature crystal oscillator to provide a reference clock and a reference frequency for a digital baseband module and a Ka channel module.

5. The lunar orbit formation navigation microsatellite intersatellite measurement system according to claim 1, characterized in that: The inter-satellite measurement signal is a Ka-band radio frequency signal modulating a pseudo-code signal and an inter-satellite measurement frame; The pseudo code signal is used to measure the time difference between the local timing signal and the received timing signal of the other party; The inter-satellite measurement frame includes the local satellite time difference measurement result and the measurement timestamp. The master satellite and the slave satellite exchange the measurement results through the inter-satellite measurement frame, thereby completing the settlement of the inter-satellite distance and time difference on the local satellite.

6. A lunar orbit formation navigation microsatellite inter-satellite measurement method, based on the lunar orbit formation navigation microsatellite inter-satellite measurement system according to any one of claims 1 to 5, characterized in that: include: Step 1: The ground selects the intersatellite measurement arc according to the orbit prediction and sends instructions to the satellite; Step 2: The master satellite platform and the slave satellite platform adjust their attitudes; Step 3: The ranging payloads of the master and slave satellites are powered on for a set threshold time. Step 4: The master satellite and the slave satellite establish an inter-satellite link and lock the inter-satellite measurement signal; Step 5: The slave satellite sends a synchronization signal to the master satellite; Step 6: Obtain intersatellite measurement results; Step 7: After the intersatellite measurement is completed, the master satellite and the slave satellite turn off the master satellite ranging payload and the slave satellite ranging payload, and adjust the master satellite and the slave satellite to the normal flight attitude towards the sun.

7. The inter-satellite measurement method for lunar orbit formation navigation microsatellites according to claim 6, characterized in that: The step 4 comprises: The master satellite platform sends time broadcast and pulse-second signals to the ranging payload. The master satellite ranging payload starts sending timed inter-satellite measurement signals to the slave satellite at the falling edge of the pulse-second signal. If the slave satellite cannot lock onto the master satellite signal, the master satellite platform adjusts the satellite attitude and uses a spiral scanning method to adjust the beam pointing of the high-gain Ka directional antenna; After the slave satellite receives the master satellite signal and successfully demodulates it, it sends a timed inter-satellite measurement signal to the master satellite; the master satellite ranging payload receives the slave satellite signal and successfully demodulates it.

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