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

Abstract

This invention provides a system and method for onboard time maintenance and time format conversion, comprising a satellite computer, an onboard GNSS module, a first payload, and a second payload. The satellite computer is connected to the first payload, the second payload, and the onboard GNSS module. The first payload is connected to the onboard GNSS module; the second payload is connected to the onboard GNSS module. The satellite computer maintains its local time (i.e., the whole satellite system time) by receiving GNSS whole-second time from the onboard GNSS module or by receiving time synchronization commands from the ground. The first payload has local time maintenance and time format conversion functions and outputs first payload data; the second payload has local time maintenance and time format conversion functions and outputs second payload data. This invention achieves unified onboard time and realizes onboard time format conversion based on FPGA.

Description

Technical Field

[0001] This invention relates to satellite timekeeping maintenance, specifically to a system and method for onboard time maintenance and time format conversion. Background Technology

[0002] In today's aerospace field, satellite time maintenance is crucial for space-ground mission coordination and the timing synchronization of tasks among various onboard subsystems. Currently, satellites typically possess ground-controlled time synchronization and calibration functions, achieving time unification among onboard systems through time synchronization pulses. However, existing technologies have significant shortcomings.

[0003] In satellite system time maintenance, anomalies in GNSS time usage are typically not assessed or addressed. This can lead to time errors, affecting the accuracy and reliability of satellite missions. For example, if GNSS signals are interfered with or malfunction, failure to promptly identify and address the issue can result in inaccurate onboard time.

[0004] Meanwhile, existing technologies fall short in time format conversion for situations where there are specific requirements for timestamps in payload data. In particular, they lack the functionality to perform payload time format conversion based on FPGA, thus failing to meet complex time format conversion needs.

[0005] Furthermore, the existing publicly available technologies only involve the time system of the satellite computer, and do not involve the judgment and handling of abnormal situations when using GNSS time, nor do they involve the function of completing the payload time format conversion based on FPGA.

[0006] In conclusion, it is of great significance to study a new system and method for onboard time maintenance and time format conversion. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to research a system and method for on-board time maintenance and time format conversion. This system can identify and handle anomalies in GNSS time during the process of achieving on-board time unification, and can also perform payload time format conversion based on an FPGA.

[0008] A system for onboard time maintenance and time format conversion according to the present invention includes: a satellite computer, an onboard GNSS module, a first payload, and a second payload;

[0009] The satellite 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; and the second payload is connected to the onboard GNSS module.

[0010] Preferably, the main control chip of the satellite computer is an ARM processor. It maintains the local time of the satellite computer, i.e. the whole satellite system time, by receiving GNSS whole second time and GNSS second pulse from the onboard GNSS module or by receiving time synchronization instructions from the ground. At the same time, the satellite computer performs time system maintenance for the whole satellite through system time broadcast and GNSS second pulse.

[0011] Preferably, the main control chip of the first payload is an 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 relayed by the satellite computer, the first payload realizes the time format conversion function based on the FPGA and outputs the first payload data containing the timestamp.

[0012] Preferably, the main control chip of the second payload is an 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 relayed by the satellite computer, the second payload realizes the time format conversion function based on the FPGA and outputs the second payload data containing the timestamp.

[0013] This 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 whole 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 time synchronization command from the ground and performs time system maintenance for the entire satellite;

[0016] The first payload synchronization step is as follows: The first payload receives the system time broadcast and GNSS second pulse to synchronize the local time of the first payload with the time of the entire satellite system.

[0017] The second payload synchronization process involves receiving the system time broadcast and GNSS second pulse to synchronize the local time of the second payload with the overall satellite system time.

[0018] The first payload conversion step is to receive the GNSS whole second time relayed by the satellite computer and realize the time format conversion function based on FPGA.

[0019] The second payload conversion process involves receiving GNSS whole-second times relayed by the satellite computer and implementing FPGA-based time format conversion.

[0020] Preferably, the local time maintenance steps include:

[0021] After enabling GNSS time synchronization on the satellite computer via command, upon receiving a GNSS integer second pulse, the satellite computer latches its local time, designated as T0, and the received GNSS integer second time, designated as T1. If the deviation between T0 and T1 exceeds a threshold, the GNSS time is considered incorrect, and no time synchronization is performed; the deviation value is returned via telemetry. If the deviation between T0 and T1 does not exceed the threshold, Δt = T1 - T0 is calculated, and Δt is added to the satellite computer's local time for time synchronization.

[0022] After setting GNSS timing permission on the satellite computer via command, the satellite computer latches its local time after receiving a GNSS integer second pulse, which is recorded as T0. The received GNSS integer second time is recorded as T1. Δt = T1 - T0 is calculated, and Δt is superimposed on the satellite computer's local time for time synchronization.

[0023] The time system maintenance steps include:

[0024] After the satellite computer is set to allow ground time synchronization via command, a time synchronization command containing time data is sent from the ground. The satellite computer receives and parses the time synchronization command and changes its local time to the time in the time synchronization command.

[0025] Preferably, the first-load synchronization step includes: after setting the first load time synchronization permission via command, after the first load receives a GNSS integer second pulse, it latches the first load local time, denoted as TZ1_0, and the received GNSS integer second time, denoted as TZ1_1. If the deviation between TZ1_0 and TZ1_1 exceeds a threshold, it is considered that the GNSS time is incorrect, and no time synchronization is performed, and the deviation value is returned via telemetry; if the deviation between TZ1_0 and TZ1_1 does not exceed the threshold, it calculates Δtz1 = TZ1_1 - TZ1_0, and adds Δtz1 to the first load local time for time synchronization.

[0026] After the first load is set to enable time synchronization via command, the first load latches its local time after receiving a GNSS integer second pulse, which is recorded as TZ1_0. The received GNSS integer second time is recorded as TZ1_1. Δtz1 = TZ1_1 - TZ1_0 is calculated, and Δtz1 is superimposed on the first load's local time for time synchronization.

[0027] Preferably, the second-load synchronization step includes: after setting the second load time synchronization permission via command, after the second load receives a GNSS integer second pulse, it latches the local time of the second load, which is recorded as TZ2_0, and the received GNSS integer second time is recorded 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 incorrect, 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 added to the local time of the second load for time synchronization.

[0028] After the second payload is set to enable time synchronization via command, the second payload latches its local time after receiving a GNSS integer second pulse, which is recorded as TZ2_0. The received GNSS integer second time is recorded as TZ2_1. Δtz2 = TZ2_1 - TZ2_0 is calculated, and Δtz2 is superimposed on the second payload's local time for time synchronization.

[0029] Preferably, the carrier conversion step includes:

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

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

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

[0033] Preferably, the load-to-conversion step includes:

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

[0035] Set the received GNSS integer time count to B. 2， B2 is a 2-bit integer second counter;

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

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

[0038] 1) This invention maintains satellite system time through GNSS modules or ground timing commands, with heterogeneous redundancy backup, to avoid satellite system time maintenance failure due to GNSS module malfunction;

[0039] 2) This invention uses a GNSS module for satellite system time maintenance, which can detect GNSS time anomalies. The threshold for detection can be modified by command, and the option to use abnormal GNSS time for time maintenance can be selected by command. It can also remotely measure and output the deviation between GNSS time and satellite system time.

[0040] 3) The payload can synchronize with the entire satellite system time by receiving system time broadcasts and GNSS second pulses; it can calculate the deviation between the payload's local time and the entire satellite system time, judge the deviation value, and the judgment threshold can be modified by command. It can also select whether to perform time maintenance when the deviation exceeds the threshold by command; it can remotely output the deviation value between the payload's local time and the entire satellite system time.

[0041] 4) This invention implements payload time format conversion based on FPGA without floating-point arithmetic capability, converting 48-bit 0.1ms count into 32-bit whole second count + 32-bit microsecond count within second. Attached Figure Description

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

[0043] Figure 1 This is a schematic diagram of an on-board time maintenance and time format conversion method according to an embodiment of the present invention;

[0044] Figure 2 This is a flowchart of the time format conversion method for the first payload based on FPGA in an embodiment of the present invention;

[0045] Figure 3 This is a flowchart of the second payload time format conversion method based on FPGA in an embodiment of the present invention. Detailed Implementation

[0046] In the process of achieving unified on-board time, this invention judges and handles abnormal GNSS time conditions, and at the same time completes the payload time format conversion function based on FPGA.

[0047] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0048] Example 1:

[0049] This invention provides a system for onboard time maintenance and time format conversion, comprising: a satellite computer, an onboard GNSS module, a first payload, and a second payload.

[0050] In this embodiment, the main control chip of the satellite computer is an ARM processor. It maintains the local time of the satellite computer, i.e. the whole satellite system time, by receiving the GNSS whole second time and GNSS second pulse from the onboard GNSS module or by receiving the time synchronization command from the ground. At the same time, the satellite computer performs time system maintenance for the whole satellite through system time broadcast and GNSS second pulse.

[0051] In this embodiment, the main control chip of the first payload is an 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 relayed by the satellite computer, the first payload implements the time format conversion function based on the FPGA and outputs the first payload data containing the timestamp.

[0052] In this embodiment, the main control chip of the second payload is an 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 whole satellite. By receiving the GNSS whole second time relayed by the satellite computer, the second payload realizes the time format conversion function based on the FPGA and outputs the second payload data containing the timestamp.

[0053] The satellite 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; and the second payload is connected to the onboard GNSS module.

[0054] Specifically, the spaceborne GNSS module outputs a set of high-precision synchronized GNSS second pulses at every whole second. Within 0.5 seconds after the pulse output, it outputs the GNSS whole second time data corresponding to the GNSS second pulse. The format of the GNSS whole second time is a 32-bit whole second count, with Beijing time January 1, 2000 00:00:00 as the time starting point. Incrementing the whole second count by 1 indicates that the GNSS whole second time increases by 1 second.

[0055] The system time format is a 48-bit 0.1ms counter, with Beijing time January 1, 2000 00:00:00 as the starting point. Each increment of the 0.1ms counter represents an increase of 0.1ms in the system time. The broadcast time, the local time of the first payload, and the local time of the second payload all have the same format as the system time.

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

[0057] The GNSS second pulse is an RS422 differential pulse signal, valid on the falling edge; the GNSS whole second time is transmitted via an asynchronous RS422 communication interface; system time broadcasting and GNSS whole second forwarding are transmitted via an asynchronous RS422 communication interface at a frequency of 1Hz.

[0058] Example 2:

[0059] This 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 integer second times and GNSS second pulses to maintain its local time. This includes: after enabling GNSS time synchronization via command, upon receiving a GNSS integer second pulse, the satellite computer latches its local time as T0 and records the received GNSS integer second time as T1. If the deviation between T0 and T1 exceeds a threshold, the GNSS time is considered incorrect, and no time synchronization is performed; the deviation value is returned via telemetry. If the deviation between T0 and T1 does not exceed the threshold, Δt = T1 - T0 is calculated, and Δt is added to the satellite computer's local time for time synchronization.

[0061] After the GNSS timing permission is enabled by setting the satellite computer via command, the satellite computer latches its local time after receiving a GNSS integer second pulse, which is recorded as T0. The received GNSS integer second time is recorded as T1. Δt = T1 - T0 is calculated, and Δt is superimposed on the satellite computer's local time for time synchronization.

[0062] In this embodiment, the threshold is set to 0.2s by default, but can be modified using the betting command.

[0063] Time maintenance steps: The satellite computer receives the time synchronization command from the ground and performs time synchronization maintenance for the entire satellite. This includes: after the satellite computer is enabled for ground time synchronization by setting the command, the ground sends a time synchronization command containing time data. The satellite computer receives and parses the time synchronization command and changes the satellite computer's local time to the time in the time synchronization command.

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

[0065] The synchronization steps for the first payload are as follows: The first payload receives the system time broadcast and the GNSS second pulse to synchronize the local time of the first payload with the system time of the entire satellite. This includes: After setting the first payload to allow time synchronization via command, after the first payload receives the GNSS second pulse, it latches the local time of the first payload and records it as TZ1_0. The received GNSS second time is recorded as TZ1_1. If the deviation between TZ1_0 and TZ1_1 exceeds the threshold, the GNSS time is considered to be incorrect, and no time synchronization is performed. The deviation value is returned via telemetry. If the deviation between TZ1_0 and TZ1_1 does not exceed the threshold, Δtz1 = TZ1_1 - TZ1_0 is calculated, and Δtz1 is added to the local time of the first payload for time synchronization.

[0066] After the first load is set to enable time synchronization via command, the first load latches its local time after receiving a GNSS integer second pulse, which is recorded as TZ1_0. The received GNSS integer second time is recorded as TZ1_1. Δtz1 = TZ1_1 - TZ1_0 is calculated, and Δtz1 is superimposed on the first load's local time for time synchronization.

[0067] The synchronization steps for the second payload are as follows: The second payload receives the system time broadcast and GNSS second pulse to synchronize its local time with the full satellite system time. This includes: after setting the second payload time synchronization permission via command, upon receiving the GNSS full second pulse, the second payload latches its local time, denoted as TZ2_0, and the received GNSS full second time, denoted as TZ2_1. If the deviation between TZ2_0 and TZ2_1 exceeds a threshold, the GNSS time is considered incorrect, and no time synchronization is performed. The deviation value is then returned via telemetry. If the deviation between TZ2_0 and TZ2_1 does not exceed the threshold, Δtz2 = TZ2_1 - TZ2_0 is calculated, and Δtz2 is added to the second payload's local time for time synchronization.

[0068] After the second payload is set to enable time synchronization via command, the second payload latches its local time after receiving a GNSS integer second pulse, which is recorded as TZ2_0. The received GNSS integer second time is recorded as TZ2_1. Δtz2 = TZ2_1 - TZ2_0 is calculated, and Δtz2 is superimposed on the second payload's local time for time synchronization.

[0069] Figure 2 This is a flowchart of the time format conversion method for the first payload 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 integer second time received by the first payload is compared by the FPGA. When the local time of the first payload lags behind the GNSS integer second time received by the first payload, the GNSS integer second time is decreased in units of 1 second until the local time of the first payload is no longer lagging behind the GNSS integer second time. When the local time of the first payload leads the GNSS integer second time received by the first payload by more than or equal to 1 second, the GNSS integer second time is increased in units of 1 second until the local time of the first payload leads the GNSS integer second time by less than 1 second.

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

[0072] Specifically, the first payload conversion step involves receiving GNSS whole-second times relayed by the satellite computer and implementing FPGA-based time format conversion, including:

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

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

[0075] Set the integer second count of the timestamp in the first payload data to C1, where C1 is a 32-bit integer second count, and the microsecond count within the second to D1, where D1 is a 32-bit microsecond count within the second.

[0076] Figure 3 This is a flowchart of the second payload time format conversion method 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 integer second time of the GNSS received by the second payload is compared by the FPGA. When the local time of the second payload lags behind the integer second time of the GNSS received by the second payload, the integer second time of the GNSS is decreased in units of 1 second until the local time of the second payload is no longer lagging behind the integer second time of the GNSS. When the local time of the second payload leads the integer second time of the GNSS received by the second payload by more than or equal to 1 second, the integer second time of the GNSS is increased in units of 1 second until the local time of the second payload leads the integer second time of the GNSS by less than 1 second.

[0078] After the above calculations, the local time of the second payload will be equal to the calculated GNSS whole second time or lead the calculated GNSS whole second time by less than 1 second. The calculated GNSS positive second time is taken as the whole second time of the timestamp in the second payload data. The difference between the local time of the second payload and the calculated GNSS whole second time (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 conversion steps are as follows: The second payload receives the GNSS whole-second time relayed by the satellite computer and implements the FPGA-based time format conversion function, including:

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

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

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

[0083] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as 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; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0084] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method of on-board time maintenance and time format conversion, characterized in that, The method comprises the following steps: The local time maintenance step: the star computer receives the GNSS second time and the GNSS second pulse, and realizes the maintenance of the local time of the star computer; The time system maintenance step: the star computer receives the timing instruction injected from the ground, and realizes the time system maintenance of the whole satellite; The first payload synchronization step: the first payload receives the system time broadcast and the GNSS second pulse, and realizes the synchronization of the local time of the first payload and the system time of the whole satellite; The second payload synchronization step: the second payload receives the system time broadcast and the GNSS second pulse, and realizes the synchronization of the local time of the second payload and the system time of the whole satellite; The first payload conversion step: the first payload receives the GNSS second time forwarded by the star computer, and realizes the time format conversion function based on FPGA. The second payload conversion step: the second payload receives the GNSS second time forwarded by the star computer, and realizes the time format conversion function based on FPGA. The local time maintenance step comprises: After the star computer is allowed to set the GNSS time by the instruction, the star computer latches the local time of the star computer as T0 after receiving the GNSS whole-second pulse, and receives the GNSS whole-second time as T1. If it is judged that the deviation of T0 and T1 exceeds a threshold value, it is considered that the GNSS time is wrong, and no time correction is performed, and the deviation value is returned through telemetry. If it is judged that the deviation of T0 and T1 does not exceed the threshold value, the time correction is performed by superimposing the GNSS time onto the local time of the star computer. , and , After the star service computer is allowed to set GNSS time service by the instruction, the star service computer latches the local time of the star service computer after receiving the GNSS whole-second pulse, and the local time of the star service computer is counted as T0, the whole-second time of the GNSS is counted as T1, and the time difference between T0 and T1 is calculated , which is counted as T is superimposed to the local time of the star service computer for time correction. The time system maintenance step comprises: After the ground sets the timing instruction containing the time data through the instruction setting, the star computer receives and analyzes the timing instruction, and changes the local time of the star computer to the time in the timing instruction. The step of loading and synchronizing comprises: after the first load receives the GNSS whole-second pulse, the first load local time is latched as TZ1_0, the GNSS whole-second time is received as TZ1_1, if it is judged that the deviation of TZ1_0 and TZ1_1 exceeds a threshold value, it is considered that the GNSS time is wrong, no time correction is performed, and the deviation value is returned through telemetry; if it is judged that the deviation of TZ1_0 and TZ1_1 does not exceed the threshold value, the first load local time is corrected by superimposing , to the first load local time to correct the time. After the first payload receives the GNSS second pulse, the first payload local time is latched, which is TZ1_0, and the GNSS second time is received, which is TZ1_1, and the time difference is calculated , which is superimposed on the first payload local time for time correction; The step of loading the second synchronization includes: after the second load receives the GNSS whole-second pulse, locking the second load local time as TZ2_0, receiving the GNSS whole-second time as TZ2_1, if it is judged that the deviation of TZ2_0 and TZ2_1 exceeds a threshold value, it is considered that the GNSS time is wrong, time correction is not performed, and the deviation value is returned through telemetry; if it is judged that the deviation of TZ2_0 and TZ2_1 does not exceed the threshold value, the second load local time is corrected by superimposing , to the second load local time . After the second payload receives the GNSS second pulse, the second payload local time is latched, denoted as TZ2_0, and the GNSS second time is received, denoted as TZ2_1. The time difference between the two is calculated as , which is added to the second payload local time to correct the time. , which is added to the second payload local time to correct the time.

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

3. The method for on-board time maintenance and time format conversion according to claim 1, characterized in that, The second payload conversion step comprises: set the local time count of the second load to A 2， A2 is a 48-bit 0.1 ms count; The second load receives the GNSS second time count as B 2， B2 is a 2-bit second count; Set the whole second time count of the timestamp in the second load data to C 2， C2 is a 32-bit whole second count, and D2 is a 32-bit microsecond count within a second.

4. A system for on-board time maintenance and time format conversion, characterized in that, The method for realizing the on-satellite time maintenance and time format conversion in claim 1 comprises: a star computer, a star-borne GNSS module, a first payload and a second payload. The star computer is connected with the star-borne GNSS module, the first payload and the second payload; the first payload is connected with the star-borne GNSS module; and the second payload is connected with the star-borne GNSS module. The main control chip of the star computer is an ARM type processor, which maintains the local time of the star computer, i.e. the system time of the whole satellite, by receiving the GNSS second time and the GNSS second pulse from the star-borne GNSS module or receiving the timing instruction injected from the ground.

5. The system for on-board time maintenance and time format conversion according to claim 4, characterized in that, The main control chip of the first payload is FPGA, which realizes the synchronization of the local time of the first payload and the system time of the whole satellite by receiving the system time broadcast and the GNSS second pulse, and realizes the time format conversion function based on FPGA by receiving the GNSS second time forwarded by the star computer, and outputs the first payload data containing the time stamp.

6. The system for on-board time maintenance and time format conversion according to claim 4, characterized in that, The master chip of the second load is FPGA, and the local time of the second load is synchronized with the system time of the whole satellite by receiving system time broadcast and GNSS second pulse. The second load realizes the time format conversion function based on FPGA by receiving the GNSS whole second time forwarded by the satellite computer, and outputs the second load data containing time stamp.

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