System and method for on-satellite time maintenance and time format conversion

Abstract

The invention provides an on-satellite time maintenance and time format conversion system and method. The system comprises a satellite service computer, a satellite-borne GNSS module, a first load and a second load, and the satellite service computer is connected with the first load, the second load and the satellite-borne GNSS module; the first load is connected with the satellite-borne GNSS module; the second load is connected with the satellite-borne GNSS module; the satellite service computer carries out satellite service computer local time (namely whole satellite system time) maintenance by receiving GNSS whole second time from the satellite-borne GNSS module or receiving a time service instruction injected on the ground; the first load has local time maintenance and time format conversion functions and outputs first load data; the second load has local time maintenance and time format conversion functions and outputs second load data. According to the method, on-satellite time unification is realized, and on-satellite time format conversion based on the FPGA is realized.

Description

Technical Field

[0001] The present invention relates to satellite time maintenance, and in particular to a system and method for satellite time maintenance and time format conversion. Background Art

[0002] In today's aerospace industry, satellite time maintenance is crucial for satellite-ground mission coordination and task timing coordination between onboard subsystems. Currently, satellites usually have ground-controllable time synchronization and time calibration functions, and achieve time unification between onboard systems through timing pulses. However, existing technologies have obvious defects.

[0003] In satellite system time maintenance, when using GNSS time, abnormal situations are usually not judged and handled. This may lead to time errors and affect the accuracy and reliability of satellite missions. For example, when the GNSS signal is interfered or fails, if it cannot be judged and handled in time, it may cause confusion in the satellite time.

[0004] At the same time, for situations where there are specific requirements for timestamps in payload data, the existing technology has deficiencies in time format conversion, especially the function of completing payload time format conversion based on FPGA, which cannot meet complex time format conversion requirements.

[0005] In addition, the existing public technology only involves the time system of the satellite computer, and does not involve the judgment and processing of abnormal situations when using GNSS time, nor does it involve the function of completing the payload time format conversion based on FPGA.

[0006] In summary, it is of great significance to study a new system and method for on-board time maintenance and time format conversion. Summary of the invention

[0007] In view of the defects in the prior art, the purpose of the present invention is to study a system and method for on-board time maintenance and time format conversion. In the process of realizing on-board time unification, the abnormal situation of GNSS time can be judged and processed, and the function of payload time format conversion can be completed based on FPGA.

[0008] A system for on-board time maintenance and time format conversion provided by the present invention includes: a satellite service computer, a satellite-borne GNSS module, a first payload and a second payload;

[0009] The satellite service computer is connected to the satellite-borne GNSS module, the first payload and the second payload; the first payload is connected to the satellite-borne GNSS module; and the second payload is connected to the satellite-borne GNSS module.

[0010] Preferably, the main control chip of the satellite service computer is an ARM processor, which maintains the local time of the satellite service computer, that is, the system time of the entire satellite, by receiving the GNSS whole second time and GNSS second pulse from the onboard GNSS module, or receiving the timing instructions injected on the ground; at the same time, the satellite service computer performs time system maintenance for the entire satellite through system time broadcasting and GNSS second pulse.

[0011] Preferably, the main control chip of the first payload is FPGA, which realizes synchronization of the local time of the first payload with the system time of the entire satellite by receiving the system time broadcast and GNSS second pulse. By receiving the GNSS whole second time forwarded by the satellite service computer, the first payload realizes the FPGA-based time format conversion function and outputs the first payload data containing a timestamp.

[0012] Preferably, the main control chip of the second payload is FPGA, which realizes synchronization of the local time of the second payload with the system time of the whole satellite by receiving the system time broadcast and GNSS second pulse. By receiving the GNSS whole second time forwarded by the satellite service computer, the second payload realizes the time format conversion function based on FPGA and outputs the second payload data containing timestamp.

[0013] The present invention also provides a method for on-board time maintenance and time format conversion, comprising the following steps:

[0014] Local time maintenance steps: The satellite computer receives GNSS full second time and GNSS second pulse to maintain the local time of the satellite computer;

[0015] Time system maintenance steps: The satellite computer receives the timing instructions from the ground to maintain the time system of the entire satellite;

[0016] Carrier-to-carrier synchronization step: The first payload receives the system time broadcast and GNSS second pulse to synchronize the local time of the first payload with the entire satellite system time;

[0017] The second payload synchronization step: The second payload receives the system time broadcast and GNSS second pulse to synchronize the local time of the second payload with the entire satellite system time;

[0018] The first payload conversion step: The first payload receives the GNSS full second time forwarded by the satellite service computer and implements the time format conversion function based on FPGA;

[0019] The second payload conversion step: The second payload receives the GNSS whole second time forwarded by the satellite service computer and implements the FPGA-based time format conversion function.

[0020] Preferably, the local time maintenance step includes:

[0021] After the GNSS time adjustment permission is set by the command, the local time of the star service computer is latched after receiving the GNSS full second pulse, which is counted as T0, and the received GNSS full second time is counted as T1. If it is judged that the deviation between T0 and T1 exceeds the threshold, the GNSS time is considered to be wrong, and the time adjustment is not performed, and the deviation value is returned through telemetry; if it is judged that the deviation between T0 and T1 does not exceed the threshold, Δt=T1-T0 is calculated, and Δt is superimposed on the local time of the star service computer for time adjustment.

[0022] After the GNSS timing permission is set by the command, the local time of the satellite computer is latched after the satellite computer receives the GNSS full second pulse, which is counted as T0. The received GNSS full second time is counted as T1, and Δt=T1-T0 is calculated. Δt is added to the local time of the satellite computer for time calibration;

[0023] The time system maintenance steps include:

[0024] After the ground timing permission of the satellite computer is set through instructions, the timing instruction containing time data is entered on the ground. The satellite computer receives and parses the timing instruction and changes the local time of the satellite computer to the time in the timing instruction.

[0025] Preferably, the carrier-to-carrier synchronization step includes: after the first payload is allowed to be time-calibrated by an instruction, after the first payload receives the GNSS full second pulse, the first payload local time is latched and counted as TZ1_0, and the received GNSS full second time is counted as TZ1_1; if it is determined that the deviation between TZ1_0 and TZ1_1 exceeds a threshold, it is considered that the GNSS time is wrong, and time calibration is not performed, and the deviation value is returned through telemetry; if it is determined that the deviation between TZ1_0 and TZ1_1 does not exceed the threshold, Δtz1=TZ1_1-TZ1_0 is calculated, and Δtz1 is superimposed on the local time of the first payload for time calibration;

[0026] After the first payload timing permission is set through the instruction, the first payload receives the GNSS full second pulse and latches the first payload local time, which is counted as TZ1_0. The received GNSS full second time is counted as TZ1_1. Δtz1=TZ1_1-TZ1_0 is calculated, and Δtz1 is superimposed on the first payload local time for time calibration.

[0027] Preferably, the step of synchronizing the second payload includes: after the second payload is allowed to calibrate the time through an instruction, after the second payload receives the GNSS full second pulse, the local time of the second payload is latched and counted as TZ2_0, and the received GNSS full second time is counted as TZ2_1; if it is determined that the deviation between TZ2_0 and TZ2_1 exceeds a threshold, it is considered that the GNSS time is wrong, and no calibration is performed, and the deviation value is returned through telemetry; if it is determined that the deviation between TZ2_0 and TZ2_1 does not exceed the threshold, Δtz2=TZ2_1-TZ2_0 is calculated, and Δtz2 is superimposed on the local time of the second payload for calibration;

[0028] After the second payload timing permission is set through the instruction, the second payload latches the local time of the second payload after receiving the GNSS full second pulse, which is counted as TZ2_0. The received GNSS full second time is counted as TZ2_1. Δtz2=TZ2_1-TZ2_0 is calculated, and Δtz2 is added to the local time of the second payload for time calibration.

[0029] Preferably, the load-conversion step comprises:

[0030] Set the local time count of the first payload to A1, where A1 is a 48-bit 0.1ms count.

[0031] Set the GNSS whole second time count received by the first payload to B1, where B1 is a 32-bit whole second count;

[0032] Set the integer second count of the timestamp in the first payload data to C 1， C1 is the 32-bit full second count, the microsecond time count within a second is D1, and D1 is the 32-bit microsecond count within a second.

[0033] Preferably, the carrier conversion step comprises:

[0034] Set the local time count of the second device to A 2， A2 is a 48-bit 0.1ms count;

[0035] Set the GNSS whole second time count received by the second carrier to B 2， B2 is a 2-bit full second count;

[0036] Set the integer second time count of the timestamp in the second payload data to C 2， C2 is the 32-bit full second count, the microsecond time count within a second is D2, and D2 is the 32-bit microsecond count within a second.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1) The present invention performs satellite system time maintenance through the GNSS module or ground timing instructions, and heterogeneous redundant backup to avoid the inability to maintain the satellite system time due to GNSS module abnormalities;

[0039] 2) The present invention uses a GNSS module to maintain satellite system time, can judge GNSS time anomalies, the judgment threshold can be modified by instructions, and can choose whether to use abnormal GNSS time for time maintenance through instructions; can remotely measure and output the deviation value between GNSS time and satellite system time;

[0040] 3) The payload can synchronize with the entire satellite system time by receiving system time broadcast and GNSS second pulses; the deviation between the local time of the payload and the system time of the entire satellite can be calculated and judged. The judgment threshold can be modified through instructions, and the instruction can be used to select whether to perform time maintenance when the deviation exceeds the threshold; the deviation between the local time of the payload and the system time of the entire satellite can be output by telemetry;

[0041] 4) The present invention realizes the load time format conversion based on an FPGA without floating point computing capability, and converts the 48-bit 0.1ms count into a 32-bit full second + 32-bit microsecond count. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0043] Figure 1 A schematic diagram of an on-board time maintenance and time format conversion method in an embodiment of the present invention;

[0044] Figure 2 This is a flow chart of a method for converting the time format of the first load based on FPGA in an embodiment of the present invention;

[0045] Figure 3 This is a flow chart of a method for converting the time format of the second load based on FPGA in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In the process of realizing on-board time unification, the present invention judges and processes the abnormal situation of GNSS time, and completes the function of payload time format conversion based on FPGA.

[0047] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments 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 of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0048] Embodiment 1:

[0049] An embodiment of the present invention provides a system for on-board time maintenance and time format conversion, including: a satellite service computer, an on-board GNSS module, a first payload and a second payload.

[0050] In this embodiment, the main control chip of the satellite service computer is an ARM processor, which maintains the local time of the satellite service computer, that is, the system time of the entire satellite, by receiving the GNSS whole second time and GNSS second pulse from the onboard GNSS module, or receiving the timing instructions injected on the ground. At the same time, the satellite service computer performs time system maintenance for the entire satellite through system time broadcasts and GNSS second pulses.

[0051] In this embodiment, the main control chip of the first payload is FPGA. By receiving the system time broadcast and GNSS second pulse, the local time of the first payload is synchronized with the system time of the entire satellite. By receiving the GNSS whole second time forwarded by the satellite service computer, the first payload implements the time format conversion function based on FPGA and outputs the first payload data containing a timestamp.

[0052] In this embodiment, the main control chip of the second payload is FPGA. By receiving the system time broadcast and GNSS second pulse, the local time of the second payload is synchronized with the system time of the entire satellite. By receiving the GNSS whole second time forwarded by the satellite computer, the second payload implements the FPGA-based time format conversion function and outputs the second payload data containing a timestamp.

[0053] The satellite service computer is connected to the satellite-borne GNSS module, the first payload and the second payload; the first payload is connected to the satellite-borne GNSS module; and the second payload is connected to the satellite-borne GNSS module.

[0054] Specifically, the onboard GNSS module outputs a set of high-precision synchronized GNSS second pulses at every whole second, and within 0.5s after the pulse output, outputs the GNSS whole second time data of the moment corresponding to the GNSS second pulse. The format of the GNSS whole second time is a 32-bit whole second count, with 00:00:00 Beijing time on January 1, 2000 as the time starting point. An increase of 1 in the whole second count means that the GNSS whole second time increases by 1 second.

[0055] The time format of the whole satellite system time is 48-bit 0.1ms count, with 00:00:00 on January 1, 2000 Beijing time as the time starting point. Every time the 0.1ms count is accumulated by 1, the whole satellite system time increases by 0.1ms. The format of the system time broadcast time, the first load local time and the second load local time is the same as the time format of the whole satellite system time.

[0056] The format of the timestamp in the first payload data is 32-bit full seconds + 32-bit microseconds, with 00:00:00 Beijing time, January 1, 2000, as the time starting point. The format of the timestamp in the second payload data is the same as that of the timestamp in the first payload data.

[0057] The GNSS second pulse is an RS422 differential pulse signal, and the falling edge is valid. The GNSS whole second time realizes data transmission through the asynchronous RS422 communication interface. The system time broadcast and GNSS whole second forwarding realize data transmission through the asynchronous RS422 communication interface, and the transmission frequency is 1Hz.

[0058] Embodiment 2:

[0059] The embodiment of the present invention provides a method for on-board time maintenance and time format conversion, comprising the following steps:

[0060] Local time maintenance steps: The satellite computer receives GNSS full second time and GNSS second pulse to maintain the local time of the satellite computer, including: after setting the satellite computer GNSS time adjustment permission through instructions, the satellite computer receives the GNSS full second pulse, latches the local time of the satellite computer, counts it as T0, and counts the received GNSS full second time as T1. If it is judged that the deviation between T0 and T1 exceeds the threshold, it is considered that the GNSS time is wrong, and the time adjustment is not performed, and the deviation value is returned through telemetry; if it is judged that the deviation between T0 and T1 does not exceed the threshold, Δt=T1-T0 is calculated, and Δt is superimposed on the local time of the satellite computer for time adjustment.

[0061] After the GNSS timing permission is set for the star service computer through instructions, the star service computer latches the local time of the star service computer after receiving the GNSS full second pulse, which is counted as T0. The received GNSS full second time is counted as T1, and Δt=T1-T0 is calculated. Δt is added to the local time of the star service computer for time calibration.

[0062] In this embodiment, the threshold value defaults to 0.2s and can be modified by an injection instruction.

[0063] Time system maintenance steps: The satellite computer receives the timing instructions entered on the ground to implement time system maintenance for the entire satellite, including: after setting the ground timing permission for the satellite computer through instructions, the ground enters the timing instructions containing time data, the satellite computer receives and parses the timing instructions, and changes the local time of the satellite computer to the time in the timing instructions.

[0064] The time in the timing instructions takes into account the delays of ground equipment output, space transmission delay, and satellite computer analysis.

[0065] The first payload synchronization step: the first payload receives the system time broadcast and the GNSS second pulse to synchronize the local time of the first payload with the whole satellite system time, including: after the first payload is allowed to synchronize time through instructions, after the first payload receives the GNSS whole second pulse, the first payload local time is latched and counted as TZ1_0, and the received GNSS whole second time is counted as TZ1_1. If it is determined that the deviation between TZ1_0 and TZ1_1 exceeds the threshold, it is considered that the GNSS time is wrong, and no time synchronization is performed, and the deviation value is returned through telemetry; if it is determined that the deviation between TZ1_0 and TZ1_1 does not exceed the threshold, Δtz1=TZ1_1-TZ1_0 is calculated, and Δtz1 is superimposed on the local time of the first payload for time synchronization.

[0066] After the first payload timing permission is set through the instruction, the first payload receives the GNSS full second pulse and latches the first payload local time, which is counted as TZ1_0. The received GNSS full second time is counted as TZ1_1. Δtz1=TZ1_1-TZ1_0 is calculated, and Δtz1 is superimposed on the first payload local time for time calibration.

[0067] The second payload synchronization step: the second payload receives the system time broadcast and GNSS second pulse to synchronize the second payload local time with the whole satellite system time, including: after the second payload is allowed to synchronize time through the instruction, after the second payload receives the GNSS full second pulse, the second payload local time is latched and counted as TZ2_0, and the received GNSS full second time is counted as TZ2_1. If it is determined that the deviation between TZ2_0 and TZ2_1 exceeds the threshold, it is considered that the GNSS time is wrong, and no time synchronization is performed, and the deviation value is returned through telemetry; if it is determined that the deviation between TZ2_0 and TZ2_1 does not exceed the threshold, Δtz2=TZ2_1-TZ2_0 is calculated, and Δtz2 is superimposed on the second payload local time for time synchronization;

[0068] After the second payload timing permission is set through the instruction, the second payload latches the local time of the second payload after receiving the GNSS full second pulse, which is counted as TZ2_0. The received GNSS full second time is counted as TZ2_1. Δtz2=TZ2_1-TZ2_0 is calculated, and Δtz2 is added to the local time of the second payload for time calibration.

[0069] Figure 2 This is a flow chart of a method for converting the time format of the first load based on FPGA in an embodiment of the present invention.

[0070] like Figure 2As shown, the deviation between the local time of the first payload and the GNSS whole second time received by the first payload is compared through FPGA. When the local time of the first payload lags behind the GNSS whole second time received by the first payload, the GNSS whole second time is decremented by 1 second until the local time of the first payload does not lag behind the GNSS whole second time; when the local time of the first payload is ahead of the GNSS whole second time received by the first payload by more than or equal to 1 second, the GNSS whole second time is increased by 1 second until the local time of the first payload is ahead of the GNSS whole second time by less than 1 second.

[0071] After the above calculation and processing, the local time of the first payload will be equal to the calculated GNSS full second time or less than 1 second ahead of the calculated GNSS full second time. The calculated GNSS full second time is taken as the full second time of the timestamp in the first payload data. The difference between the local time of the first payload and the calculated GNSS full second time (resolution 0.1ms) is multiplied by 100, which is the microsecond in the second of the timestamp in the first payload data.

[0072] Specifically, the first payload receives the GNSS full second time forwarded by the satellite service computer and implements the time format conversion function based on FPGA, including:

[0073] Set the local time count of the first payload to A1, where A1 is a 48-bit 0.1ms count.

[0074] Set the GNSS whole second time count received by the first payload to B1, where B1 is a 32-bit whole second count;

[0075] The whole second time count of the timestamp in the first payload data is set to C1, where C1 is a 32-bit whole second count, and the microsecond time count in a second is set to D1, where D1 is a 32-bit microsecond count in a second.

[0076] Figure 3 This is a flow chart of a method for converting the time format of the second load based on FPGA in an embodiment of the present invention.

[0077] like Figure 3 As shown, the deviation between the local time of the second payload and the GNSS whole second time received by the second payload is compared through FPGA. When the local time of the second payload lags behind the GNSS whole second time received by the second payload, the GNSS whole second time is decremented by 1 second until the local time of the second payload does not lag behind the GNSS whole second time; when the local time of the second payload is ahead of the GNSS whole second time received by the second payload by more than or equal to 1 second, the GNSS whole second time is increased by 1 second until the local time of the second payload is ahead of the GNSS whole second time by less than 1 second.

[0078] After the above calculation and processing, the local time of the second payload will be equal to the GNSS full second time after calculation and processing or be less than 1 second ahead of the GNSS full second time after calculation and processing. The GNSS full second time after calculation and processing is taken as the full second time of the timestamp in the second payload data. The difference between the local time of the second payload and the GNSS full second time after calculation and processing (resolution 0.1ms) is multiplied by 100, which is the microsecond within the second of the timestamp in the second payload data.

[0079] Specifically, the second payload receives the GNSS full second time forwarded by the satellite service computer and implements the time format conversion function based on FPGA, including:

[0080] Set the local time count of the second payload to A 2， A2 is a 48-bit 0.1ms count;

[0081] Set the GNSS whole second time count received by the second payload to B 2， B2 is a 2-bit full second count;

[0082] Set the integer second time count of the timestamp in the second payload data to C 2， C2 is the 32-bit full second count, the microsecond time count within a second is D2, and D2 is the 32-bit microsecond count within a second.

[0083] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions 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 as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0084] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A system for on-board time maintenance and time format conversion, characterized in that: include: Satellite computer, satellite GNSS module, first payload and second payload; The satellite service computer is connected to the onboard GNSS module, the first payload and the second payload; The first payload is connected to the onboard GNSS module; the second payload is connected to the onboard GNSS module.

2. The system for on-board time maintenance and time format conversion according to claim 1, characterized in that: The main control chip of the satellite service computer is an ARM processor, which maintains the local time of the satellite service computer, that is, the system time of the entire satellite, by receiving the GNSS whole second time and GNSS second pulse from the onboard GNSS module, or receiving the timing instructions injected on the ground; at the same time, the satellite service computer maintains the time system of the entire satellite through system time broadcasting and GNSS second pulse.

3. The system for on-board time maintenance and time format conversion according to claim 1, characterized in that: The main control chip of the first payload is FPGA. By receiving system time broadcast and GNSS second pulse, the local time of the first payload is synchronized with the system time of the entire satellite. By receiving the GNSS whole second time forwarded by the satellite service computer, the first payload implements the FPGA-based time format conversion function and outputs the first payload data containing a timestamp.

4. The system for on-board time maintenance and time format conversion according to claim 1, characterized in that: The main control chip of the second payload is FPGA. By receiving system time broadcast and GNSS second pulse, the local time of the second payload is synchronized with the system time of the entire satellite. By receiving the GNSS whole second time forwarded by the satellite service computer, the second payload implements the FPGA-based time format conversion function and outputs the second payload data containing a timestamp.

5. A method for on-board time maintenance and time format conversion, characterized in that: The steps include: Local time maintenance steps: The satellite computer receives GNSS full second time and GNSS second pulse to maintain the local time of the satellite computer; Time system maintenance steps: The satellite computer receives the timing instructions from the ground to maintain the time system of the entire satellite; Carrier-to-carrier synchronization step: The first payload receives the system time broadcast and GNSS second pulse to synchronize the local time of the first payload with the entire satellite system time; The second payload synchronization step: The second payload receives the system time broadcast and GNSS second pulse to synchronize the local time of the second payload with the entire satellite system time; A conversion step: the first payload receives the GNSS full second time forwarded by the satellite service computer to implement a time format conversion function based on FPGA; Carrier 2 conversion step: The second payload receives the GNSS whole second time forwarded by the satellite service computer to implement the FPGA-based time format conversion function.

6. The method for on-board time maintenance and time format conversion according to claim 5, characterized in that: The local time maintenance step includes: After the GNSS time adjustment permission is set by the command, the local time of the star service computer is latched after receiving the GNSS full second pulse, which is counted as T0, and the received GNSS full second time is counted as T1. If it is judged that the deviation between T0 and T1 exceeds the threshold, the GNSS time is considered to be wrong, and the time adjustment is not performed, and the deviation value is returned through telemetry; if it is judged that the deviation between T0 and T1 does not exceed the threshold, Δt=T1-T0 is calculated, and Δt is superimposed on the local time of the star service computer for time adjustment. After the GNSS timing permission is set by the command, the local time of the satellite computer is latched after the satellite computer receives the GNSS full second pulse, which is counted as T0. The received GNSS full second time is counted as T1, and Δt=T1-T0 is calculated. Δt is added to the local time of the satellite computer for time calibration; The time system maintenance steps include: After the ground timing permission of the satellite computer is set through instructions, the timing instruction containing time data is entered on the ground. The satellite computer receives and parses the timing instruction and changes the local time of the satellite computer to the time in the timing instruction.

7. The method for on-board time maintenance and time format conversion according to claim 5, characterized in that: The load-one synchronization step includes: after setting the first load time calibration permission through an instruction, after the first load receives the GNSS full second pulse, latching the first load local time, counting it as TZ1_0, and counting the received GNSS full second time as TZ1_1; if it is determined that the deviation between TZ1_0 and TZ1_1 exceeds the threshold, it is considered that the GNSS time is wrong, and the time calibration is not performed, and the deviation value is returned through telemetry; if it is determined that the deviation between TZ1_0 and TZ1_1 does not exceed the threshold, Δtz1=TZ1_1-TZ1_0 is calculated, and Δtz1 is superimposed on the first load local time for time calibration; After the first payload timing permission is set through the instruction, the first payload receives the GNSS full second pulse and latches the first payload local time, which is counted as TZ1_0. The received GNSS full second time is counted as TZ1_1. Δtz1=TZ1_1-TZ1_0 is calculated, and Δtz1 is superimposed on the first payload local time for time calibration.

8. The method for on-board time maintenance and time format conversion according to claim 5, characterized in that: The carrier-two synchronization step includes: after the second payload is set to allow time calibration through an instruction, after the second payload receives the GNSS full second pulse, the second payload local time is latched and counted as TZ2_0, and the received GNSS full second time is counted as TZ2_1. If it is determined that the deviation between TZ2_0 and TZ2_1 exceeds the threshold, it is considered that the GNSS time is wrong, and time calibration is not performed, and the deviation value is returned through telemetry; if it is determined that the deviation between TZ2_0 and TZ2_1 does not exceed the threshold, Δtz2=TZ2_1-TZ2_0 is calculated, and Δtz2 is superimposed on the local time of the second payload for time calibration; After the second payload timing permission is set through the instruction, the second payload latches the local time of the second payload after receiving the GNSS full second pulse, which is counted as TZ2_0. The received GNSS full second time is counted as TZ2_1. Δtz2=TZ2_1-TZ2_0 is calculated, and Δtz2 is added to the local time of the second payload for time calibration.

9. The method for on-board time maintenance and time format conversion according to claim 5, characterized in that: The carrier-conversion step comprises: Set the local time count of the first payload to A1, where A1 is a 48-bit 0.1ms count; Set the GNSS whole second time count received by the first payload to B1, where B1 is a 32-bit whole second count; Set the whole second time count of the timestamp in the first payload data to C 1， C1 is the 32-bit full second count, the microsecond time count within a second is D1, and D1 is the 32-bit microsecond count within a second.

10. The method for on-board time maintenance and time format conversion according to claim 5, characterized in that: The second payload receiving and utilizing the payload conversion step comprises: Set the local time count of the second payload to A 2， A2 is a 48-bit 0.1ms count; Set the GNSS whole second time count received by the second payload to B 2， B2 is a 2-bit full second count; Set the integer second time count of the timestamp in the second payload data to C 2， C2 is the 32-bit full second count, the microsecond time count within a second is D2, and D2 is the 32-bit microsecond count within a second.

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