JP2017150834A - Artificial satellite, satellite system, and method for confirming internal time of artificial satellite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable internal satellite time to be corrected inside a satellite system with high accuracy.SOLUTION: An artificial satellite is provided with: a crystal oscillator for sending out a base clock; a GPS receiver for sending out a reference clock; an onboard computer for clocking an internal satellite time on the basis of the base clock or reference clock, and outputting the internal satellite time and an internal clock; clock correction data acquisition means for acquiring clock correction data for identifying a change in the base clock; an internal satellite apparatus; and a telemetry communication unit. The onboard computer monitors the soundness of the reference clock while having its internal clock synchronized with the reference clock, and periodically notifies the telemetry communication unit of the clock correction data while also outputting the internal satellite time and/or operation timing to the internal satellite apparatus, and further clocks the internal satellite time on the basis of the base clock and stops synchronization in a case of abnormality in the soundness of the reference clock, and outputs the internal satellite time and/or operation timing to the internal satellite apparatus.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an artificial satellite that manages internal time, a satellite system, and a method for determining the internal time of the artificial satellite.

  Many artificial satellites have a clock inside. Many artificial satellites use the time recorded by the clock. As this timepiece, a device according to the accuracy required in the satellite system is appropriately employed.

  Clocks mounted on the satellite include clocks using atomic clocks and crystal oscillators, clocks synchronized with GPS (Global Positioning System) signals, and clocks combining these.

  For example, a satellite using a highly accurate time, such as a GNSS (Global Navigation Satellite System) satellite, uses an atomic clock. On the other hand, many orbiting satellites such as medium-orbit satellites and low-orbit satellites use GPS radio waves to realize accurate clocks.

  Technologies related to the internal time of the satellite are disclosed in, for example, the following documents.

  Patent Document 1 and Patent Document 2 disclose an internal time system of an artificial satellite including a satellite internal oscillator (reference clock generation circuit) that generates a clock signal.

  The internal time system of Patent Document 1 is a satellite internal oscillator, a GPS receiver, and a synchronization means (retiming circuit) that supplies time information received by the GPS receiver to an internal device in synchronization with a clock signal of the satellite internal oscillator. Is included. By including this synchronization means, this internal time system can provide the time information received by the GPS receiver to each element inside the satellite with the generation resolution of the clock signal of the satellite internal oscillator.

  On the other hand, the 1-second signal acquisition device of Patent Document 2 is generated by an in-device reference oscillator (1-second clock generator), a GPS receiver, and a 1-second signal (pulse train) received from the GPS receiver. Switching means (timing acquisition circuit) for switching to a 1 second signal and supplying it to the internal device is included. In addition, this 1-second signal acquisition device includes a 1PPS validity determination unit and a state determination unit, and activates the switching unit when determining the failure of the 1-second signal received from the GPS receiver. For this reason, the 1-second signal acquisition device can switch the source of the 1-second signal from the GPS receiver to the in-device reference oscillator when determining a malfunction in the 1-second signal output from the GPS receiver. .

  A mechanism for determining the soundness of a GPS receiver is also described in Patent Document 3. The time management device of Patent Document 3 includes a determination unit that compares a pulse train from a GPS receiver with a pulse train engraved by an internal clock and identifies the deviation.

Japanese Patent Laid-Open No. 10-177081 Japanese Patent Laid-Open No. 08-105984 JP 2009-294007 A

  When operating a satellite, we want to know the internal time with higher accuracy in the satellite system in order to give accurate information at the intended timing and time information closer to the true observation time.

  Many of today's low-medium-orbit satellites specify the system time (time information, timekeeping clock) used in the satellite using a reference clock obtained from a GPS receiver.

  On the other hand, when the reference clock becomes unusable due to GPS invisible or a GPS receiver failure, the system time must be maintained in the artificial satellite.

  Many current satellites for medium and low orbits implement TCXO (Temperature Compensated Crystal Oscillator) and OCXO (Oven Controlled Crystal Oscillator) to maintain high system time accuracy. On the other hand, few use atomic clocks.

  Further, in the mechanism for maintaining the system time described in Patent Document 1 and Patent Document 2, the time is recorded with the accuracy of the oscillator or the internal reference oscillator (1 second clock generator) when the GPS receiver fails. Is possible. The reference clock from the oscillator or the internal reference oscillator can maintain a certain degree of accuracy in the short term, but cannot maintain the accuracy permanently like the reference clock output from the GPS receiver.

  In other words, during the period in which the reference clock output from the GPS receiver cannot be used, the accuracy of the system time depends on the frequency accuracy of the crystal oscillator (element). For this reason, the clock accuracy of the oscillator is relatively lowered as compared with the section in which the reference clock can be normally used from the GPS receiver. As a result, there are subtle effects on the operation of the artificial satellite and the grant time.

  In order to minimize this effect, a crystal oscillator having a compensation function such as TCXO or OCXO, which are high-precision crystal oscillators, is often adopted as an oscillator mounted on a satellite.

  The time given to the operation of the artificial satellite, the observation data, etc. always requires high accuracy equivalent to the accuracy using the reference clock output from the GPS receiver. Therefore, the inventor examined a mechanism that can ensure the accuracy of the time of observation data and the like while maintaining the accuracy of the time in the satellite system when an abnormality occurs in the reference clock or the like of the GPS receiver.

  Based on the above background, the present invention provides an artificial satellite, a satellite system, and a satellite system that operate so as to maintain the accuracy of the time ticked by the satellite in the satellite system when an abnormality occurs in the reference clock transmitted from the GPS receiver. And it aims at providing the internal time determination method of an artificial satellite.

  An artificial satellite according to an embodiment of the present invention transmits a crystal oscillator that transmits a reference clock, a GPS receiver that transmits at least a reference clock, a reference clock that is transmitted from the crystal oscillator, and a GPS receiver that transmits the reference clock. An on-board computer that receives a reference clock, records the time in the satellite based on the reference clock or the reference clock, and outputs the time in the satellite and the internal clock, and clock correction data that identifies a change in the reference clock A clock correction data acquisition means for acquiring a satellite internal device for receiving an operation timing corresponding to the satellite time and / or internal clock from the on-board computer, and a telemetry communication unit for communicating with a counterpart station, The on-board computer receives from the GPS receiver. While the internal clock generated to the attached reference clock is constantly synchronized, the soundness of the reference clock transmitted from the GPS receiver is monitored, and the operation time corresponding to the time in the satellite and / or the internal clock is determined. While outputting to the in-satellite equipment, in addition, periodically notifies the telemetry communication unit of the clock correction data obtained from the clock correction data acquisition means, and the on-board computer is abnormal in the soundness of the reference clock. If there is, the time in the satellite is ticked based on the reference clock from the crystal oscillator, and the synchronization process between the internal clock and the reference clock is stopped, and the operation timing corresponding to the time in the satellite and / or the internal clock is set. It outputs to the said in-satellite apparatus.

  A satellite system according to an embodiment of the present invention includes a crystal oscillator that transmits a reference clock, a GPS receiver that transmits at least a reference clock, a reference clock that is transmitted from the crystal oscillator, and a GPS receiver that transmits the reference clock. An on-board computer that receives a reference clock, records the time in the satellite based on the reference clock or the reference clock, and outputs the time in the satellite and the internal clock, and clock correction data that identifies a change in the reference clock A clock correction data acquisition means for acquiring a satellite internal device for receiving an operation timing corresponding to the satellite time and / or internal clock from the on-board computer, and a telemetry communication unit for communicating with a counterpart station, The on-board computer is connected to the GPS receiver While constantly synchronizing the generated internal clock with the received reference clock, the health of the reference clock transmitted from the GPS receiver is monitored, and the operation time corresponding to the time in the satellite and / or the internal clock is determined. While outputting to the in-satellite equipment, in addition, periodically notifies the telemetry communication unit of the clock correction data obtained from the clock correction data acquisition means, and the on-board computer is abnormal in the soundness of the reference clock. If there is, the time in the satellite is ticked based on the reference clock from the crystal oscillator, and the synchronization process between the internal clock and the reference clock is stopped, and the operation timing corresponding to the time in the satellite and / or the internal clock is set. An artificial satellite output to the in-satellite device and clock correction data transmitted from the artificial satellite are acquired. A lock correction data collection unit, and a satellite clock timing correction unit that performs offline correction processing of the satellite internal time and / or operation timing associated with the internal clock used in the internal processing of the artificial satellite based on the clock correction data; , And a correction station.

  According to an embodiment of the present invention, an internal time determination method using an artificial satellite built-in computer receives a reference clock sent from a crystal oscillator and a reference clock sent from a GPS receiver, and uses the reference clock or the reference clock as the reference clock. Based on the time of the satellite, and generating the time of the satellite and the internal clock, while constantly synchronizing the internal clock output to the reference clock received from the GPS receiver, Monitors the soundness of the reference clock that is sent out, outputs the operation time corresponding to the time in the satellite and / or the internal clock to the in-satellite equipment, and periodically adds clock correction data that identifies changes in the reference clock. If the telemetry communication unit is notified and the soundness of the reference clock is abnormal, the crystal oscillator The time in the satellite is recorded based on the reference clock, and the synchronization process between the internal clock and the reference clock is stopped, and the operation time corresponding to the internal time and / or the internal clock is output to the in-satellite device. It is characterized by that.

  According to the present invention, when an abnormality occurs in a reference clock transmitted from a GPS receiver, an artificial satellite, a satellite system, and an artificial satellite that operate so as to maintain the accuracy of the time that the satellite ticks in the satellite system can be maintained. An internal time determination method can be provided.

It is a block diagram which shows the internal structure of the artificial satellite 1 of one Embodiment concerning this invention. It is a flowchart which shows the example of a control sequence of a satellite system. It is a block diagram which shows the satellite system which concerns on one structural example. It is the timing chart which showed the example of the synchronous flow which synchronizes OBC_1Mpps with REF_1Mpps (OBC_1Mpps side phase lag processing). It is the timing chart which showed the example of the synchronous flow which synchronizes OBC_1Mpps with REF_1Mpps (OBC_1Mpps side phase advance processing). It is a timing chart showing an example of a synchronization flow for synchronizing OBC_1pps with REF_1pps (synchronization processing by fine tracking processing after coarse tracking processing). It is explanatory drawing which shows the stability of the reference clock on the basis of REF_1pps.

  Embodiments of the present invention will be described with reference to the drawings. Each figure is a diagram schematically showing components and control timing according to the invention.

[Embodiment]
FIG. 1 is a block diagram showing the internal structure of an artificial satellite 1 according to an embodiment.

  As shown in the figure, the artificial satellite 1 includes an on-board computer 10, a GPS receiver 20, a crystal oscillator 30, a clock correction data acquisition means 40, a satellite internal device 50, and a telemetry / telecommand communication unit 60. . The artificial satellite 1 is also equipped with a satellite power supply device (not shown) as necessary.

  The on-board computer 10 includes a time measuring means for the time in the satellite, a clock switching means for switching the clock that is the reference of the internal clock, a clock synchronizing means for synchronizing the internal clock with the reference clock, and a soundness determining means for determining the soundness of the reference clock. To work. The on-board computer 10 includes a general counter circuit and the like, and can detect a phase difference between clocks, count up / down, and the like.

  The on-board computer 10 is configured to constantly receive the reference clock sent from the GPS receiver 20 and the reference clock sent from the crystal oscillator 30. Further, the on-board computer 10 is configured to clock the time in the satellite based on the reference clock at the normal time and based on the reference clock when the reference clock is abnormal by using the time measuring means. This intra-satellite time is used for linking to the intra-satellite device 50 and clock correction data described later.

  The on-board computer 10 sends the internal clock using the clock synchronization means to the reference clock sent from the GPS receiver 20 during normal times, and from the crystal oscillator 30 switched by the clock switching means when the reference clock is abnormal. The reference clock is configured to be synchronized with the reference clock.

  The on-board computer 10 is configured to always determine the soundness of the reference clock using soundness determination means. Any method for determining the soundness of the reference clock may be used. An example of a method for determining soundness will be described later using one configuration example.

  The on-board computer 10 associates the soundness information indicating the soundness of the reference clock determined using the soundness determination unit with the clock correction data obtained from the clock correction data acquisition unit 40, and the soundness information corresponds. The attached clock correction data may be notified to the telemetry / telecommand communication unit 60.

  Similarly, the on-board computer 10 associates the synchronization information indicating the synchronization state between the reference clock and the internal clock with the clock correction data obtained from the clock correction data acquisition means 40, and obtains the clock correction data associated with the synchronization information. You may make it notify to the telemetry / telecommand communication part 60. FIG.

  Similarly, the on-board computer 10 associates the counter value of the reference clock indicating the internal clock period with the clock correction data obtained from the clock correction data acquisition unit 40, and converts the clock correction data associated with this counter value to the telemetry / You may make it notify to the telecommand communication part 60. FIG.

  The on-board computer 10 associates any one or combination of the soundness information, the synchronization information, and the counter value with each clock correction data so that the satellite (on-board computer) is synchronized with the reference clock by offline processing. Therefore, it is possible to identify the period of time that is ticked and correct it more accurately.

  The GPS receiver 20 acquires a navigation signal and transmits at least a reference clock. From a recent GPS receiver 20, a pulse train having a 1-second cycle and a pulse sequence having a 1-microsecond cycle can be acquired together with GPS time (time information).

  The crystal oscillator 30 is an oscillation source of a reference clock, and transmits a reference clock. As the crystal oscillator 30, for example, SPXO can be used.

  The clock correction data acquisition means 40 constantly acquires the state and stability of the crystal oscillator 30 as clock correction data. The clock correction data desirably includes both the temperature of the crystal oscillator 30 and the stability of the output pulse train of the crystal oscillator 30. By referring to the clock correction data, it is possible to identify a change in the reference clock. If the crystal oscillator 30 is VCXO, it is desirable to include a control voltage value. As the clock correction data acquisition means 40, a sensor or a microcomputer matched to desired information (temperature or the like) may be mounted to acquire desired information.

  The satellite internal device 50 is, for example, a broadcast device, a communication device, an observation device, or the like, and is provided according to the use of the satellite. Time information, time code, and the like are appropriately added to signals (for example, satellite transmission signals) and information (for example, observation data) generated by these devices. Some of these devices operate at a specific timing specified by the on-board computer 10. The satellite internal device 50 according to the present embodiment receives at least one of the operation time corresponding to the time in the satellite or the internal clock, and uses it according to the application.

  The telemetry / telecommand communication unit 60 receives a telecommand from a communication device outside the satellite (communication partner station: ground station, spacecraft, other satellite, etc.), and transmits telemetry to other communication devices. A sending unit (not shown) for sending is included.

  With the above configuration, the artificial satellite 1 operates so as to maintain the accuracy of the time ticked by the satellite in the satellite system when an abnormality occurs in the reference clock transmitted from the GPS receiver 20.

  By mounting the above configuration on the satellite, the satellite system can perform offline correction of the signals and information generated by the artificial satellite 1 with high accuracy outside the satellite, so that even when an abnormality occurs in the reference clock, for example, The time system can be accurately synchronized with other time systems. Further, for example, when the abnormality of the reference clock does not recover in the satellite, it becomes possible to finally instruct the time adjustment feedback amount to the artificial satellite 1 by the telecommand in units of the reference clock based on the clock correction data. .

  Next, operations related to the offline correction operation of the satellite system will be described.

  In this description, a sector that uses clock correction data generated by an artificial satellite will be described as a correction station. This correction station can communicate with the artificial satellite 1 and constantly acquires and manages clock correction data by telemetry. The correction station may be configured to collect the clock correction data by a method other than telemetry.

  In a specific configuration example, the ground station may be provided with a clock correction data collection unit and a satellite clock timing correction unit to form a correction station. The clock correction data collection unit is configured to acquire clock correction data transmitted from the artificial satellite 1. The satellite clock timing correction unit is configured to perform offline correction processing on the internal time and / or operation timing associated with the internal clock used in the internal processing of the artificial satellite 1 based on the clock correction data. . If necessary, the ground station may be provided with a mechanism for feeding back the correction result to the artificial satellite 1 by a telecommand. Further, the ground station may be provided with a mechanism for providing complementary information for providing the correction result to the user terminal using the generated signal / information of the artificial satellite 1 via the communication line. Further, the ground station may be provided with a mechanism for providing the correction result itself via a communication line to a user terminal that uses the generated signal / information of the artificial satellite 1.

  FIG. 2 is a flowchart showing an example of a control sequence related to the offline correction operation of the satellite system.

  The offline correction operation includes an operation process of the artificial satellite 1 and a correction process of the correction station using the clock correction information generated by the artificial satellite 1.

  In the operation process of the artificial satellite 1, the on-board computer 10 and its peripheral circuits (such as the GPS receiver 20) use the reference clock from the GPS receiver 20 during normal operation during operation suitable for the purpose of the artificial satellite 1. The satellite internal time and the internal clock are supplied (S11).

  In the operation process of the satellite 1, in parallel operation, the on-board computer 10 and its peripheral circuits (clock correction data acquisition unit 40, etc.) acquire clock correction data and transmit the clock correction data to the ground station by telemetry communication. Notification is made constantly (S21). For this notification, it is desirable to notify the soundness information, the synchronization information, and the counter value in association with the clock correction data.

  The frequency of this notification may be determined as appropriate for each configuration and application of the satellite system and the type of correction target signal / data. For example, if the satellite scans the ground surface every second, the telemetry frequency for notifying clock correction data may be set to 1 second. In addition, if the observation satellite does not require real-time property, a certain amount of clock correction data may be notified collectively.

  In the operation process of the artificial satellite 1, the on-board computer 10 monitors the soundness of the reference clock from the GPS receiver 20 (S12), and when the reference clock is abnormal, the on-board computer 10 and the internal clock are based on the reference clock. Is supplied (S13). This state (S13) proceeds to S11 if the soundness of the reference clock returns to normal.

  As a result of the transition to this state (S13), the time information / internal clock given to the various signals / information generated by the satellite internal device 50 and the operation of the satellite internal device 50 are slightly less than the state of S11. Accuracy is reduced. In particular, when the state of S13 continues, generally, the deviation in accuracy tends to increase.

  In the correction station correction process, the ground station collects the clock correction information generated by the artificial satellite 1 and the signal / data to be corrected (B11).

  Next, the ground station performs off-line correction of the signal / data to be corrected using the clock correction information (B12).

  In the offline correction, more accurate time and timing can be corrected by using the characteristic parameter, soundness information, synchronization information, and counter value of the crystal oscillator 30.

  By operating each unit in this way, it is possible to determine the exact time and acquisition timing of the signal / data acquired without obtaining the reference clock obtained from the GPS receiver.

  As a result, when an abnormality occurs in the reference clock transmitted from the GPS receiver, it is possible to maintain the accuracy of the time ticked by the satellite in the satellite system.

  Next, the present invention will be described by showing a configuration that further embodies the above embodiment.

[Configuration example]
FIG. 3 is a block diagram showing a satellite system according to one configuration example. FIG. 3 shows the observation satellite and the ground station together. Note that explanations related to observation equipment of observation satellites are omitted.

  Part A in the figure is a GPS receiver 20. The GPS receiver 20 outputs reference clocks (REF_1pps, REF_1Mpps) and time information (reference time data). This time information includes status information indicating the soundness of the time data.

  B in the figure is a satellite management system on-board computer 10 (OBC) that manages the entire satellite. The onboard computer 10 of this configuration example generates, maintains, and manages satellite time, and distributes the time to each device in the satellite. This realizes highly accurate satellite orbit and attitude control, observation sensor tagging, and so on.

  The part C (HCE: Heater Control Electronics), the part D (observation equipment), and the part E (telemetry / telecommand part) in the figure are the same as the general configuration of the observation satellite. The C part, the D part, and the E part correspond to the clock correction data acquisition unit 40, the satellite internal device 50, and the telemetry / telecommand communication unit 60, respectively.

  The on-board computer 10 includes a time synchronization unit (B-1) that performs time synchronization processing as the main logic of an ASIC (Application Specific Integrated Circuit) mounted therein. The on-board computer 10 is mounted with a 50 MHz crystal oscillator 30 (B-2) as a source clock for operating the ASIC. Further, the on-board computer 10 is mounted with a platinum sensor (B-3) for temperature monitoring disposed in the vicinity of the crystal oscillator 30 as the clock correction data acquisition means 40. This platinum sensor (B-3) is connected to the HCE outside the on-board computer in this configuration example. In this configuration example, the temperature information of the platinum sensor (B-3) is sent to the telemetry / telecommand processing unit (B-) via the satellite internal device I / F unit (B-5) along with other temperature telemetry collected by the HCE. Collected in 6) and sent to the telemetry / telecommand communicator 60. The satellite internal device I / F unit (B-5) supplies 64 Hz Tick to the observation device (D unit) and the like via the SpaceWire (general-purpose communication standard in the satellite system: SpW) network. Tick of 64 Hz is a time code generated by the time synchronizer (B-1) and assigned a number from 0 to 63 to each pulse in one cycle. Each device on the SpW network determines the timing for executing each process by this time code. The on-board computer 10 is equipped with a processor (B-4), and runs software for controlling the satellite internal devices and setting the time synchronization processing on the processor (B-4).

  The on-board computer 10 includes a circuit for generating a 1 microsecond periodic pulse signal (OBC_1Mpps) based on a reference clock output from a built-in crystal oscillator 30 (50 MHz) in the ASIC. The on-board computer 10 is equipped with a circuit that generates a 1-second period pulse signal (OBC_1pps) and a 64 Hz pulse signal (Tick) based on OBC_1Mpps. Tick is a signal for notifying operation timing to each installed software and circuit.

  Further, the internal time of the observation satellite is synchronized with the GPS system time with high accuracy. For this purpose, the on-board computer 10 receives the reference clock (1 second pulse signal, 1 microsecond pulse signal) and time information (time code) generated by the GPS receiver 20 as the source timing of the internal time.

  The on-board computer 10 synchronizes by reducing the phase difference between the reference clock obtained from the GPS receiver 20 and the internal clock that records the internal time in the time synchronization unit (B-1). The processor (B-4) synchronizes both clocks by the following method when the measured result detects a difference greater than or equal to a predetermined value. By using this synchronization method, the phase difference between the reference clock of the GPS receiver 20 and the internal clock can be brought close with high accuracy at an early stage.

The time synchronization performed by the time synchronization unit (B-1) may be performed in the following order: REF_1Mpps and OBC_1Mpps, REF_1pps and OBC_1pps.
4 and 5 are timing charts showing a synchronization flow for synchronizing OBC_1Mpps with REF_1Mpps. FIG. 6 is a timing chart showing a synchronization flow for synchronizing OBC_1pps with REF_1pps.

(1) First, the processor (B-4) confirms the soundness of the GPS receiver 20 (clock signal). The soundness check by the processor (B-4) can be performed by monitoring both reference clock signals if the time information, 1 microsecond periodic pulse signal (REF_1Mpps), and 1 second periodic pulse signal (REF_1pps) can all be judged healthy. The synchronization processing of the time synchronization unit is executed while operating.
The soundness of the reference clock is determined according to the following conditions, and it is determined that the reference clock can be used when all the conditions are satisfied.
-The status included in the reference time data is "Normal".
-The value measured for the REF_1pps cycle by the REF_1Mpps count is within the judgment value.
-The value measured for the REF_1pps cycle by the OBC_1Mpps count is within the judgment value.

(2) Next, REF_1Mpps and OBC_1Mpps are synchronized in the following flow (see FIGS. 4 and 5).
(2-1) The phase difference between REF_1Mpps and OBC_1Mpps is measured with the crystal oscillator original oscillation (50 MHz) (the number of clocks is counted).
(2-2) Based on the phase difference between the two clocks, the number of 50 MHz clocks included in one cycle of OBC_1Mpps is increased or decreased to bring the phase difference closer to zero. At this time, the period is adjusted within the range of 45 to 55 clocks so that the period of OBC_1Mpps does not greatly collapse.
(2-3) The above processing is repeated until the phase difference becomes 0, and REF_1Mpps and OBC_1Mpps are synchronized with the accuracy of the clock time of the source oscillation.

(3) Next, REF_1pps and OBC_1pps are synchronized in the following flow (see FIG. 6). At this time, in order to minimize the influence on the software operation, in order to prevent rapid time fluctuations, synchronization is performed according to the following flow.
(3-1) The phase difference between REF_1pps and OBC_1pps is measured by OBC_1Mpps (the number of clocks is counted).
(3-2) If the phase difference is 64 microseconds or more, as a rough tracking process, the Tick cycle is increased or decreased by n clocks (n microseconds). By using this process, the coarse tracking process changes the OBC_1pps cycle to 1 second ± 64 × n microseconds and brings the phase difference closer to zero.
(3-3) When the phase difference is less than 64 microseconds, the interval from Tick (Tick0) output at the same time as the OBC_1pps pulse to the output of the next Tick (Tick1) is set to m clocks as a fine tracking process. Increase or decrease by (microseconds). By using this process, the fine tracking process changes the OBC_1pps cycle to 1 second ± m microseconds, and brings the phase difference closer to 0.
(3-4) The above processing is repeated to synchronize REF_1pps and OBC_1pps.

  By performing the above synchronization processing, the internal time of the satellite can be synchronized with the time information (GPS reference time) with high accuracy. As a result, it can be indirectly synchronized with an atomic clock mounted on a GPS satellite, and a stable operation clock can be obtained in a permanent period.

(4) On the other hand, when the reference clock or the like is interrupted due to GPS invisible or GPS receiver failure, the observation satellite (OBC10) detects the disruption and autonomously uses the crystal oscillator 30 as a reference time. Transition to management. At this time, in order to maintain the accuracy of the satellite time, the number of clocks included in one cycle of OBC_1pps is maintained at the value immediately before the interruption (the clock value of the source oscillation).

(5) In addition to the time synchronization processing described above, in order to perform high-accuracy offline correction of the satellite internal time in the satellite system, the observation satellite periodically includes clock correction data in the telemetry. Send to the station. Note that it is desirable that the observation satellite notifies the ground station of information (eg, VCXO control voltage value) for identifying the change of the reference clock as clock correction data.
(5-1) Temperature information of the crystal oscillator 30. This temperature information is measured by a temperature sensor (platinum sensor B-3) mounted in the vicinity of the crystal oscillator 30 and acquired via the HCT.
(5-2) Frequency stability information of the crystal oscillator 30. In this frequency stability information, the number of source clocks of the crystal oscillator 30 is counted while the REF_1pps is input a predetermined number of times (predetermined time), and the change rate of the error amount from the theoretical value is set as the stability value. it can. For example, the source clock count value of the crystal oscillator 30 may be continuously collected while REF_1pps is counted 16 times (4 bits), and the error variation in each section may be referred to by offline processing (see FIG. 7).

  By collecting the clock correction data at the ground station for a long time and evaluating its temperature trend and aging trend, it is possible to synchronize with GPS time even if only a general crystal oscillator is used without using TCXO etc. It is possible to correct the satellite internal time off-line with high accuracy when it collapses. Further, it is desirable that the on-board computer 10 notifies the soundness information, the synchronization information, and the source clock count value in association with each clock correction data. By using this information, it becomes possible to determine with high accuracy at which timing the synchronization with the reference clock has been removed or synchronized (recovered) in the offline processing.

  Briefly explaining the above operation, the observation satellite normally synchronizes the time in the satellite with the GPS reference time with high accuracy by the operation of the time synchronization circuit provided in the on-board computer 10, and for clock correction. Send data periodically to the ground station. In addition, in the event of an abnormality in which the time in the satellite cannot be synchronized with the GPS reference time with high accuracy, the observation satellite autonomously releases the synchronization and continues the high-accuracy time management with the internal crystal oscillator. Continue until you can get. The ground station corrects the time recorded by the satellite to a more accurate time by referring to the clock correction data notified from the observation satellite and the like regarding the operation executed during this time and the obtained observation result. In other words, the difference between the system time and the GPS reference time that are recorded when the observation satellite cannot acquire the GPS reference time is corrected to indirectly synchronize with the more accurate GPS system time.

  Thus, even if the observation satellite is equipped with SPXO instead of the general OCXO, for example, it maintains its own satellite time using the SPXO reference clock even after the GPS reference time is disrupted. As a satellite system, it becomes possible to grasp the satellite time with high accuracy.

  By these processes, when an abnormality occurs in the GPS receiver, an artificial satellite that operates so as to maintain the accuracy of the time that the satellite ticks in the satellite system can be obtained. Further, it is possible to obtain a method for accurately determining the internal time of the on-board computer with an artificial satellite while an abnormality occurs in the GPS receiver.

  In this configuration example, the observation satellite is exemplified, but the communication satellite or the like may realize a similar mechanism so that the internal time can be grasped more accurately.

  Note that each unit of the on-board computer may be realized as appropriate using a combination of hardware and software. The hardware can be composed of FPGA or LSI. In the form of a combination of hardware and software, a satellite main program and subprogram are expanded in the memory, and hardware such as a processor is operated based on these programs. Further, this program may be recorded non-temporarily on a recording medium and distributed.

  Although the embodiments and configuration examples have been illustrated and described above, the specific internal configuration of the satellite of the present invention is not limited to the above-described embodiments and configuration examples, and changes within a scope that does not depart from the gist of the present invention. Is included in the present invention.

  As described above, according to the present invention, when an abnormality occurs in the reference clock transmitted from the GPS receiver, an artificial satellite or satellite that operates so as to maintain the accuracy of the time ticked by the satellite in the satellite system. A system and a method for determining the internal time of an artificial satellite can be provided.

In addition, a part or all of the above-described embodiments can be described as follows. Note that the following supplementary notes do not limit the present invention.
[Appendix 1]
A crystal oscillator that sends out a reference clock; and
A GPS receiver that transmits at least a reference clock; and
A reference clock sent from the crystal oscillator and a reference clock sent from the GPS receiver are received, and the time in the satellite is ticked based on the reference clock or the reference clock, and the time in the satellite and the internal clock are An on-board computer to output,
Clock correction data acquisition means for acquiring clock correction data for identifying a change in the reference clock;
A satellite internal device that receives an operation timing corresponding to the satellite time and / or internal clock from the on-board computer;
A telemetry communication unit that communicates with the other station;
With
The on-board computer monitors the soundness of the reference clock transmitted from the GPS receiver while constantly synchronizing the internal clock generated to the reference clock received from the GPS receiver, and the time in the satellite. In addition, while outputting the operation timing corresponding to the internal clock to the in-satellite device, in addition, periodically notifies the telemetry communication unit of the clock correction data obtained from the clock correction data acquisition means,
Furthermore, if the on-board computer has an abnormality in the soundness of the reference clock, the in-satellite time is ticked based on the reference clock from the crystal oscillator, and the synchronization process between the internal clock and the reference clock is stopped, An artificial satellite characterized in that an operation timing corresponding to the intra-satellite time and / or internal clock is output to the intra-satellite device.

[Appendix 2]
The artificial satellite according to the above supplementary note, wherein the clock correction data acquisition means uses the temperature of the crystal oscillator for clock correction data.

[Appendix 3]
The artificial satellite according to the above supplementary note, wherein the clock correction data acquisition means uses the stability of the output pulse train of the crystal oscillator for the clock correction data.

[Appendix 4]
The on-board computer communicates the health information indicating the health of the reference clock with the clock correction data obtained from the clock correction data acquisition unit, and communicates with the counterpart station via the telemetry communication unit. The artificial satellite described in the above supplementary note.

[Appendix 5]
The on-board computer associates synchronization information indicating a synchronization state between the reference clock and the internal clock with the clock correction data obtained from the clock correction data acquisition unit, and communicates with the counterpart station via the telemetry communication unit. An artificial satellite as described in the above supplementary note.

[Appendix 6]
The GPS receiver sends time information and a reference clock on the order of at least 1 ms,
The on-board computer always synchronizes the internal clock with a reference clock on the order of at least 1 ms, and if there is an abnormality in the soundness of the reference clock, the synchronization processing between the internal clock and the reference clock is stopped, and the internal clock is The artificial satellite according to the above supplementary note, wherein the artificial satellite is engraved with an internal clock cycle based on the number of reference clocks when synchronization is stopped.

[Appendix 7]
When the on-board computer synchronizes the internal clock generated with the reference clock received from the GPS receiver, the on-board computer calculates the phase difference between the reference clock and the internal clock and the number of reference clocks sent from the crystal oscillator. The artificial satellite according to the above-mentioned supplementary note, characterized in that, based on the measurement result, the period of the internal clock is increased / decreased by adjusting the number of reference clocks and synchronized.

[Appendix 8]
The on-board computer measures the phase difference between the reference clock and the internal clock using the generated internal clock when synchronizing the internal clock to be generated with the reference clock received from the GPS receiver. Based on the phase difference amount of the measurement result, after determining whether the phase difference is reduced by coarse tracking processing or fine tracking processing, the internal clock cycle is brought closer to the reference clock,
This coarse tracking process aligns the phase difference in units of clock pulses, and the fine tracking process aligns the phase difference in units of clock pulses.
An artificial satellite as described in the above supplementary note.

[Appendix 9]
An artificial satellite as described above, and
A clock correction data collection unit that acquires clock correction data transmitted from the artificial satellite, and an operation corresponding to the satellite internal time and / or internal clock used in the internal processing of the artificial satellite based on the clock correction data A correction station comprising a satellite clock timing correction unit that performs offline correction processing of the timing;
Including satellite system.

[Appendix 10]
The correction station further includes a feedback unit that feeds back the satellite internal time and / or operation timing of the artificial satellite corrected offline by the satellite clock timing correction unit to the artificial satellite. Satellite system.

[Appendix 11]
The correction station further includes a feedback unit that feeds back a satellite internal time and / or operation timing of the artificial satellite that has been offline-corrected by the satellite clock timing correction unit to a user terminal of the artificial satellite. The satellite system described.

[Appendix 12]
The correction station further includes the satellite internal time and / or the operation timing of the generated signal or generated information output from the artificial satellite corrected offline by the satellite clock timing correction unit. Alternatively, the satellite system according to the above supplementary note, further comprising a feedback unit that transmits complementary information for complementation to the operation terminal at the operation timing.

[Appendix 13]
A reference clock sent from a crystal oscillator and a reference clock sent from a GPS receiver are received, and the time in the satellite is ticked based on the reference clock or the reference clock, and the time in the satellite and the internal clock are generated. While
While constantly synchronizing the internal clock output to the reference clock received from the GPS receiver, the health of the reference clock transmitted from the GPS receiver is monitored, and the time in the satellite and / or the internal clock is monitored. In addition to outputting the corresponding operation timing to the in-satellite device, in addition, periodically notifies the telemetry communication unit of the clock correction data that identifies the change of the reference clock,
If the soundness of the reference clock is abnormal, the time in the satellite is ticked based on the reference clock from the crystal oscillator, and the synchronization process between the internal clock and the reference clock is stopped, and the time in the satellite and / or the internal clock is stopped. An internal time determination method using a built-in computer of an artificial satellite, wherein an operation timing corresponding to a clock is output to the in-satellite device.

[Appendix 14]
The internal time determination method according to the above supplementary note, wherein the clock correction data uses a temperature of the crystal oscillator.

[Appendix 15]
The internal time determination method according to the above supplementary note, wherein the clock correction data uses stability of an output pulse train of the crystal oscillator.

[Appendix 16]
The internal time determination method according to the above supplementary note, wherein soundness information indicating soundness of a reference clock is associated with the clock correction data and communicated to the other station via the telemetry communication unit.

[Appendix 17]
The internal time determination method according to the above supplementary note, wherein synchronization information indicating a synchronization state between a reference clock and an internal clock is associated with the clock correction data and communicated to a partner station via the telemetry communication unit.

[Appendix 18]
Accept time information and a reference clock on the order of at least 1 ms from the GPS receiver,
Always synchronize the internal clock with the reference clock on the order of at least 1 ms, and if there is an abnormality in the soundness of the reference clock, stop the synchronization process between the internal clock and the reference clock and use the internal clock as the reference clock The internal time determination method as described in the above supplementary note, wherein the internal clock period is based on an internal clock period.

[Appendix 19]
When synchronizing the internal clock generated with the reference clock received from the GPS receiver, the phase difference between the reference clock and the internal clock is measured using the number of reference clocks sent from the crystal oscillator. The internal time determination method according to the above supplementary note, wherein based on the measurement result, the period of the internal clock is increased / decreased by adjusting the number of reference clocks to be synchronized.

[Appendix 20]
When synchronizing the internal clock generated to the reference clock received from the GPS receiver, the phase difference between the reference clock and the internal clock is measured using the generated internal clock, and the phase difference amount of the measurement result Based on the above, after determining whether the phase difference is to be reduced by coarse tracking processing or fine tracking processing, the internal clock cycle is brought closer to the reference clock,
This coarse tracking process aligns the phase difference in units of clock pulses, and the fine tracking process aligns the phase difference in units of clock pulses.
An internal time determination method as described in the above supplementary note.

DESCRIPTION OF SYMBOLS 1 Artificial satellite 10 On-board computer 20 GPS receiver 30 Crystal oscillator 40 Clock correction data acquisition means 50 Satellite internal equipment 60 Telemetry / telecommand communication part

Claims (10)

A crystal oscillator that sends out a reference clock; and
A GPS receiver that transmits at least a reference clock; and
A reference clock sent from the crystal oscillator and a reference clock sent from the GPS receiver are received, and the time in the satellite is ticked based on the reference clock or the reference clock, and the time in the satellite and the internal clock are An on-board computer to output,
Clock correction data acquisition means for acquiring clock correction data for identifying a change in the reference clock;
A satellite internal device that receives an operation timing corresponding to the satellite time and / or internal clock from the on-board computer;
A telemetry communication unit that communicates with the other station;
With
The on-board computer monitors the soundness of the reference clock transmitted from the GPS receiver while constantly synchronizing the internal clock generated to the reference clock received from the GPS receiver, and the time in the satellite. In addition, while outputting the operation timing corresponding to the internal clock to the in-satellite device, in addition, periodically notifies the telemetry communication unit of the clock correction data obtained from the clock correction data acquisition means,
Furthermore, if the on-board computer has an abnormality in the soundness of the reference clock, the in-satellite time is ticked based on the reference clock from the crystal oscillator, and the synchronization process between the internal clock and the reference clock is stopped, An artificial satellite characterized in that an operation timing corresponding to the intra-satellite time and / or internal clock is output to the intra-satellite device.   2. The artificial satellite according to claim 1, wherein the clock correction data acquisition means uses the temperature of the crystal oscillator for clock correction data.   The artificial satellite according to claim 1 or 2, wherein the clock correction data acquisition means uses the stability of the output pulse train of the crystal oscillator for the clock correction data.   The on-board computer communicates the health information indicating the health of the reference clock with the clock correction data obtained from the clock correction data acquisition unit, and communicates with the counterpart station via the telemetry communication unit. The artificial satellite according to any one of claims 1 to 3.   The on-board computer associates synchronization information indicating a synchronization state between the reference clock and the internal clock with the clock correction data obtained from the clock correction data acquisition unit, and communicates with the counterpart station via the telemetry communication unit. The artificial satellite according to any one of claims 1 to 4, characterized in that: The GPS receiver sends time information and a reference clock on the order of at least 1 ms,
The on-board computer always synchronizes the internal clock with a reference clock on the order of at least 1 ms, and if there is an abnormality in the soundness of the reference clock, the synchronization processing between the internal clock and the reference clock is stopped, and the internal clock is The artificial satellite according to any one of claims 1 to 5, wherein the artificial satellite is engraved with an internal clock period based on the number of reference clocks when synchronization is stopped.   When the on-board computer synchronizes the internal clock generated with the reference clock received from the GPS receiver, the on-board computer calculates the phase difference between the reference clock and the internal clock and the number of reference clocks sent from the crystal oscillator. 7. The method according to claim 1, wherein the internal clock period is increased / decreased by adjusting the number of reference clocks and synchronized based on the measurement result. Satellite. The on-board computer measures the phase difference between the reference clock and the internal clock using the generated internal clock when synchronizing the internal clock to be generated with the reference clock received from the GPS receiver. Based on the phase difference amount of the measurement result, after determining whether the phase difference is reduced by coarse tracking processing or fine tracking processing, the internal clock cycle is brought closer to the reference clock,
This coarse tracking process aligns the phase difference in units of clock pulses, and the fine tracking process aligns the phase difference in units of clock pulses.
The artificial satellite according to any one of claims 1 to 7, characterized in that: A crystal oscillator that transmits a reference clock; a GPS receiver that transmits at least a reference clock; a reference clock that is transmitted from the crystal oscillator; and a reference clock that is transmitted from the GPS receiver; and the reference clock or the reference An on-board computer that clocks the time in the satellite based on the clock and outputs the time in the satellite and the internal clock; clock correction data acquisition means for acquiring clock correction data for identifying a change in the reference clock; and A satellite internal device that receives an operation timing corresponding to the satellite time and / or internal clock from a board computer, and a telemetry communication unit that communicates with a partner station,
The on-board computer monitors the soundness of the reference clock transmitted from the GPS receiver while constantly synchronizing the internal clock generated to the reference clock received from the GPS receiver, and the time in the satellite. In addition, while outputting the operation timing corresponding to the internal clock to the in-satellite device, in addition, periodically notifies the telemetry communication unit of the clock correction data obtained from the clock correction data acquisition means,
Furthermore, if the on-board computer has an abnormality in the soundness of the reference clock, the in-satellite time is ticked based on the reference clock from the crystal oscillator, and the synchronization process between the internal clock and the reference clock is stopped, An artificial satellite that outputs to the in-satellite device operation timing corresponding to the in-satellite time and / or internal clock;
A clock correction data collection unit that acquires clock correction data transmitted from the artificial satellite, and an operation corresponding to the satellite internal time and / or internal clock used in the internal processing of the artificial satellite based on the clock correction data A correction station comprising a satellite clock timing correction unit that performs offline correction processing of the timing;
A satellite system comprising: A reference clock sent from a crystal oscillator and a reference clock sent from a GPS receiver are received, and the time in the satellite is ticked based on the reference clock or the reference clock, and the time in the satellite and the internal clock are generated. While
While constantly synchronizing the internal clock output to the reference clock received from the GPS receiver, the health of the reference clock transmitted from the GPS receiver is monitored, and the time in the satellite and / or the internal clock is monitored. In addition to outputting the corresponding operation timing to the in-satellite device, in addition, periodically notifies the telemetry communication unit of the clock correction data that identifies the change of the reference clock,
If the soundness of the reference clock is abnormal, the time in the satellite is ticked based on the reference clock from the crystal oscillator, and the synchronization process between the internal clock and the reference clock is stopped, and the time in the satellite and / or the internal clock is stopped. An internal time determination method using a built-in computer of an artificial satellite, wherein an operation timing corresponding to a clock is output to the in-satellite device.

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