Lunar in-situ probe timing method based on relay communication

Abstract

The invention provides a lunar in-situ probe timing method based on relay communication, which comprises the following steps that: a relay satellite performs framing on the basis of a probe telemetering frame format, inserts a relay satellite punctuality time code, and forwards a relay satellite data transmission frame through an earth data transmission link; establishing a ground test system; the ground test system is used for finishing time calibration on the detector, so that the detector time is synchronized with the ground standard time; a ground test system is used for completing time calibration on the relay satellite, so that the time of the relay satellite is synchronized with the ground standard time; by means of the detector punctuality time code and the relay satellite punctuality time code, time delay delta T device star links from the time when any telemetering frame time code of the detector is generated to the time when the relay satellite completes decoding and the relay satellite time code is printed are obtained through a ground system, and an engineering constant value C is obtained through calculation according to the multiple sets of time delay delta T device star links; calculating the standard time difference between the detector and the ground by using the engineering constant value C, namely the timing amount; and finishing the time correction of the detector according to the time correction amount.

Description

Technical Field

[0001] The present invention relates to a method for calibrating the time of a lunar in-situ detector based on relay communication. Specifically, the error of on-board transmission time caused by a relay satellite can be avoided. After the relay satellite time is synchronized with the ground time, the lunar in-situ detector is calibrated based on the relay satellite time system to ensure that the time difference between the detector and the ground is in the order of tens of ms. Background Art

[0002] The computer of a deep space probe cannot obtain GPS satellite signals like near-Earth satellites to achieve accurate time synchronization between the probe and the Earth. The traditional method of time synchronization for deep space probes is: the computer of the probe calculates the time code T on the generator at the moment of framing any telemetry frame. 器 After passing through the computer and test equipment, the telemetry frame is transmitted to the ground telemetry demodulation equipment through the space link or coaxial cable. The ground telemetry demodulation equipment down-converts, demodulates and decodes the received telemetry signal, and then obtains the GPS standard time T GPS , and parse and obtain the on-device time code T from the corresponding telemetry frame 器 . Thus, the time difference ΔT is obtained. 器地 =T GPS -T 器 .

[0003] It should be noted that the telemetry frame has experienced T in Table 1 since the generation time. 器上延时 , T 器-地 , T 地面 The ground telemetry demodulation equipment demodulates the baseband data after a delay and locks the GPS standard time T GPS , this delay is called the link delay ΔT 链路 . ΔT 链路 This includes the delay caused by the onboard equipment software / hardware, the space link between the device and the ground, and the ground measurement and control equipment. In order to accurately calibrate the time and keep the time between the device and the ground synchronized, it is necessary to apply the time difference T 校时 =ΔT 器地 -ΔT 链路 Prepare the time calibration instruction and input it to the computer on the digital tube. The time calibration instruction here is relative time calibration. Figure 3 T 上行时延 Can be ignored. The test principle of the detector-to-ground link delay in the detector AIT and large system docking test phase is based on the pulse recording time, and the detector-to-ground link delay ΔT is measured by the difference between the previous and next times. 链路 , the measurement principle is as follows Figure 2 shown.

[0004] Table 1 Time mark description

[0005]

[0006]

[0007] Since the lunar in-situ probe landed in certain areas of the moon, the probe is blocked by the moon and cannot be seen by the earth. The uplink and downlink data cannot be transmitted directly to the earth. It needs to communicate with the earth tracking station through the lunar relay satellite, and the link delay ΔT of the probe to the earth cannot be accurately measured. 链路 , so it is impossible to use the traditional time calibration methods of deep space probes to complete the time calibration.

[0008] In the past, the lunar in-situ probe used relay satellites to calibrate time, with an error of less than 10 seconds. Due to the time accuracy requirements of the on-orbit probe mission navigation and guidance, the time difference between the lunar in-situ probe and the ground is required to be within ±60ms. Therefore, it is urgent to design an effective high-precision time calibration method to ensure the time calibration accuracy of the probe during operation. This is of great significance for ensuring the performance of the lunar in-situ probe's on-orbit evaluation time system and meeting the time accuracy requirements of the exploration mission. Summary of the invention

[0009] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, and to propose a time synchronization method based on lunar surface relay communication, which solves the problem of time synchronization accuracy when the detector communicates with the ground through a relay satellite.

[0010] The technical solution of the present invention is: a lunar in-situ detector timing method based on relay communication, comprising:

[0011] Insert the detector punctual time code into the telemetry frame format that complies with the CCSDS protocol;

[0012] The relay satellite forms frames based on the detector telemetry frame format and inserts the relay satellite timekeeping code. The relay satellite forwards the relay satellite digital transmission frame through the ground digital transmission link.

[0013] Establishing a ground test system;

[0014] Use the ground test system to calibrate the detector so that the detector time is synchronized with the ground standard time;

[0015] Use the ground test system to calibrate the relay satellite so that the relay satellite time is synchronized with the ground standard time;

[0016] Using the detector time code and the relay satellite time code, the ground system obtains the time delay ΔT from the time when the detector's telemetry frame time code is generated to the time when the relay satellite completes decoding and marks the relay satellite time code. 器星链路 , according to multiple groups of time delay ΔT 器星链路 The engineering constant C is calculated;

[0017] The engineering constant C is used to calculate the time difference between the detector and the ground standard time, that is, the calibration value; the detector is calibrated based on the calibration value.

[0018] The ground test system comprises a communication link between the detector and the ground test system, a communication link between the relay satellite and the ground test system, and a forward return link between the detector and the relay satellite.

[0019] The establishment of the ground test system comprises:

[0020] Use radio frequency cables to connect the detector to ground measurement and control equipment to establish a detector-ground remote control and telemetry link;

[0021] Use radio frequency cables to connect the relay satellite and ground measurement and control equipment to establish a relay satellite-ground remote control and telemetry link;

[0022] Use radio frequency cables to connect the relay satellite and the detector's measurement and control equipment to establish a forward and return link between the detector and the relay satellite.

[0023] According to the multiple groups of time delay ΔT 器星链路 The engineering constant C is calculated, including: obtaining the detector time code and the relay satellite time code in the relay satellite data transmission frame multiple times to obtain multiple groups of delays ΔT 器星链路 , and take the average value to get the engineering constant C.

[0024] The time delay ΔT 器星时延 =T 星 -T 器 ; Among them, T 星 The relay satellite time code inserted at the end of the frame when the relay satellite forwards the detector telemetry frame; T 器 The probe time code is inserted into the field for the probe telemetry frame.

[0025] The time difference between the detector and the ground standard time is calculated by using the engineering constant C, that is, the time calibration quantity includes:

[0026] Considering the relay satellite as a ground station, calculate the time calibration value T of the lunar in-situ detector 校时 In actual engineering, the errors caused by software time quantization and interruption factors in detector design are ignored, and the time difference between the detector and the ground standard time is obtained, that is, the calibration time T 校时-工程 .

[0027] The calculation of the time calibration value T of the lunar surface in-situ detector 校时 :

[0028] T 校时 =T 星 -T 器 -ΔT 器星时延 -T 空间链路 +ΔT 星地 +T 器-量化 +T 星-量化 +T 器-int +T 星-int

[0029] Where, ΔT 器星 ΔT is the time difference calculated between the detector and the relay satellite in the same relay satellite data transmission frame; 星地 ΔT is the time difference between the relay star and the ground; 器星链路 T is the time delay from the time when the telemetry frame time code of any detector is generated to the time when the relay satellite completes decoding and marks the relay satellite time code; 空间链路 The space link information transmission distance delay, that is, the return transmission delay from the detector to the relay satellite; ΔT 器-量化 When writing the time code for the detector downlink telemetry group frame, the time error caused by millisecond time quantization; ΔT 星-量化 When writing the time code for the relay satellite downlink telemetry frame, the time error caused by millisecond time quantization; ΔT 器-int is the time error caused when the detector telemetry framing interrupt is closed by other events; ΔT 星-int It is the time error caused when the relay satellite telemetry framing interrupt is closed by other events.

[0030] The T 校时-工程 =T 星 -T 器 -CT 空间链路 .

[0031] The advantages of the present invention compared with the prior art are:

[0032] (1) When the lunar surface in-situ detector cannot communicate directly with the ground station, the detector is calibrated based on the time system on the relay satellite, which can ensure that the time accuracy of the detector is within the specification range when it is working on the lunar surface, and ensure that the orbit control, lunar surface operation and other processes will not produce unacceptable errors due to time deviation;

[0033] (2) The engineering constants required for on-orbit calibration are obtained through the joint test of the detector and relay satellite. There is no need for the relay satellite system and the detector system to participate in the large system docking test at the same time, which reduces the coupling degree in the development process of the detector system, relay satellite system, and measurement and control system.

[0034] (3) This timing method can realize the unified design of timing modes for subsequent lunar probes and be applied to subsequent lunar exploration missions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The figure is a flow chart of the method of the present invention.

[0036] Figure 2 This is a schematic diagram of the traditional centralized time calibration principle and the instrument-to-ground time delay measurement system for lunar probes;

[0037] Figure 3 This is a schematic diagram of the traditional time calculation method for lunar probes;

[0038] Figure 4 This is a schematic diagram of the ideal timing system of the probe, relay satellite and ground station;

[0039] Figure 5 The telemetry frame format of the relay satellite forwarding detector proposed by the present invention;

[0040] Figure 6 This is a schematic diagram of the ground test system for detector timing based on relay communication proposed by the present invention;

[0041] Figure 7 The time curve of the detector and the relay satellite before and after the time calibration of the present invention (the vertical axis is the accumulated seconds of the time code, including partial magnification)

[0042] Figure 8 This is the difference curve between the detector time and GPS after the time calibration of the present invention. DETAILED DESCRIPTION

[0043] When the probe is working in orbit, in order to keep the time of the probe and the ground synchronous, the ground station needs to calibrate the probe. The calibration time difference T in the calibration instruction noted by the ground station is 校时 =ΔT 器地 -ΔT 链路 , where ΔT 链路 It is an important factor affecting the accuracy of time calibration.

[0044] During the communication between the lunar in-situ probe and the ground station via the relay satellite, Figure 3 The system adds a relay satellite, and the timing system architecture is as follows Figure 4 When a relay satellite is added to the system, ΔT 链路 =T 器上时延 +T 器-星 +ΔT 星 +T 星-地 +T 地面 , where T 器上时延 、T 地面 The meaning is the same as Table 1, T 器-星 T is the space link delay from the detector sending out the RF signal to the relay satellite receiving the RF signal. 星-地 ΔT is the space link delay from the relay satellite sending out the RF signal to the ground station receiving the RF signal. 星 It is the forwarding delay from the time when the detector telemetry RF signal enters the relay satellite to the time when the relay satellite forwards the telemetry RF signal to the ground station.

[0045] The relay satellite is not designed with a pulse output mechanism for the time code insertion moment. In addition, due to the inconsistent development progress and design habits of the lunar in-situ probe and relay satellite, the probe and relay satellite equipment cannot simultaneously obtain the link delay between the probe and the ground in the large system measurement and control docking test, and cannot directly measure the link delay ΔT between the probe and the ground. 链路The relay satellite uses a regenerative forwarding mechanism to demodulate and decode the detector telemetry signal and perform data layer operations, and uses traditional methods to measure ΔT 链路 There is a pulse matching ambiguity problem, so the ΔT 链路 The impact requires a lot of analysis and experimental work; at the same time, considering that subsequent lunar probes will not be able to communicate directly with ground stations, it is necessary to design a high-precision time calibration method for lunar in-situ probes based on relay satellites to meet the time calibration accuracy requirements of subsequent deep space missions.

[0046] like Figure 1 As shown, the present invention proposes a lunar in-situ detector timing method based on relay communication, the steps are as follows:

[0047] (1) Design of detector telemetry format, inserting detector time code into the telemetry frame format that complies with the CCSDS protocol;

[0048] The detector complies with the CVCDU format of the telemetry frame of the CCSDS space data link protocol. The insertion field format is detailed in Table 2, including multiple bytes of detector on-board time, which is the on-board time when the telemetry frame is generated. The detector transmits the telemetry frame to the relay satellite through the return link.

[0049] Table 2 Insert field format definition

[0050] Parameter code Parameter name Telemetry mode code Telemetry Mode Instruction Count Instruction execution status -- Device time

[0051] (2) The relay satellite forwards the detector telemetry format to the ground station. The frame is assembled based on the detector telemetry frame format, and the relay satellite time code is inserted. The relay satellite forwards the relay satellite digital transmission frame through the ground digital transmission link;

[0052] When the relay satellite receives the telemetry frame data returned by the detector, completes demodulation and decoding, and inserts the telemetry frame tail into the relay satellite at the forwarding time. The relay satellite forwards the relay satellite data transmission frame format through the ground data transmission link. Figure 5 shown.

[0053] (3) Design a ground test system to establish communication links between the detector and the ground, between the relay satellite and the ground, and between the detector and the relay satellite. Use the ground verification system to verify the feasibility and correctness of the detector's time calibration based on the relay satellite time system. Figure 6 shown.

[0054] (4) Complete the time calibration of the detector to synchronize the detector time with the ground standard time;

[0055] (5) Complete the time calibration of the relay satellite to synchronize the relay satellite time with the ground standard time;

[0056] (6) Using the detector time code and the relay satellite time code, the ground system obtains the time delay ΔT from the time when the detector's telemetry frame time code is generated to the time when the relay satellite completes decoding and marks the relay satellite time code. 器星链路 , repeatedly obtain the detector time code and the relay satellite time code in the relay satellite data transmission frame, obtain multiple groups of time delays, and calculate the average value to obtain the engineering constant C;

[0057] (7) The engineering constant C is used to calculate the time difference between the detector and the ground standard time, i.e., the calibration value. Based on this calibration value, the relay satellite forward link completes the calibration of the detector.

[0058] The step (3) of establishing a ground test system is specifically as follows:

[0059] (3.1) Use radio frequency cables to connect the detector to the ground measurement and control equipment to establish a detector-ground remote control telemetry link;

[0060] (3.2) Use radio frequency cables to connect the relay satellite and ground measurement and control equipment to establish a relay satellite-ground remote control and telemetry link;

[0061] (3.3) Use radio frequency cables to connect the relay satellite and the detector’s measurement and control equipment to establish a forward return link between the detector and the relay satellite;

[0062] (3.4) The ground test system can complete the timing of detectors and relay satellites.

[0063] The step (6) uses the detector time code and the relay satellite time code to obtain the time delay ΔT from the time when the detector's arbitrary telemetry frame time code is generated to the time when the relay satellite completes decoding and marks the relay satellite time code through the ground system. 器星链路 , repeatedly obtain the detector time code and the relay satellite time code in the relay satellite data transmission frame, obtain multiple groups of delays, and calculate the average value to obtain the engineering constant C, which is:

[0064] (6.1) The detector and relay satellite are calibrated based on the ground time to ensure that the time on the detector and the time on the relay satellite are within the allowable error range of the ground time. After the two devices are calibrated, the time on the detector and the time on the relay satellite can be approximately equal in a short period of time;

[0065] (6.2) The relay satellite and ground equipment are usually connected by high-frequency cables, and the signal is transmitted at approximately the speed of light. In the experiment, the transmission path distance is short and the delay can be ignored.

[0066] (6.3) The detector telemetry source package is transmitted to the ground test equipment through the relay satellite. After the relay satellite and the detector are time-calibrated, ΔT can be obtained through the ground equipment 器星时延 =T 星 -T 器 Where T星 and T 器 It is the relay satellite time code and the detector time code in the relay satellite data transmission frame.

[0067] (6.4) When the relay satellite is in the time calibration mode, after calibrating the detector and the relay satellite, multiple sets of ΔT are obtained. 器星时延 , average the data to get ΔT 器星时延 =C (engineering constant), C is used as the engineering constant in the calibration time calculation process.

[0068] The step (7) uses the engineering constant C to calculate the time difference between the detector and the ground standard time, i.e., the calibration time; specifically, it is:

[0069] (7.1) The relay satellite uses GPS to provide the current Beijing time of the test: the detector time is the time after power-on, which has a large deviation from the current Beijing time of the test;

[0070] (7.2) The ground verification system decodes the detector time code T in the relay satellite data transmission frame 器 And the corresponding relay satellite time code T 星 , through the formula ΔT 器星时延 =T 星 -T 器 -T 校时-工程 -T 空间链路 The calibration time T can be obtained 校时 =T 星 -T 器 -T 空间链路 -C, and use the calibration value to calibrate the detector. Calibration value T 校时 =T 星 -T 器 -T 空间链路 -C, T in a relay satellite data transmission frame 星 , T 器 , multiple groups of T are used in engineering applications 星 -T 器 The data is averaged as the calibration time;

[0071] (7.3) The detector is timed through the relay satellite channel. The time curves of the relay satellite and the detector before and after the time calibration are as follows: Figure 7 As shown in the figure, after the time calibration, the relay satellite transmits the telemetry frame T 星 -T 器 Restore to the time when the two devices are approximately equal ΔT 器星时延 , restored to the engineering constant value C, indicating that the detector time is approximately equal to the relay satellite time;

[0072] After the detector is time-calibrated, the time code in the telemetry frame transmitted to its own ground verification equipment is compared with the GPS time. Figure 8The maximum deviation of the detector timing is 8ms, which meets the requirement that after the detector is timed by the relay satellite, the detector and the ground standard time are ±60ms.

Claims

1. A lunar in-situ detector timing method based on relay communication, characterized in that: include: Insert the detector punctual time code into the telemetry frame format that complies with the CCSDS protocol; The relay satellite forms frames based on the detector telemetry frame format and inserts the relay satellite timekeeping code. The relay satellite forwards the relay satellite digital transmission frame through the ground digital transmission link. Establishing a ground test system; Use the ground test system to calibrate the detector so that the detector time is synchronized with the ground standard time; Use the ground test system to calibrate the relay satellite so that the relay satellite time is synchronized with the ground standard time; Using the detector time code and the relay satellite time code, the ground system obtains the time delay ΔT from the time when the detector's telemetry frame time code is generated to the time when the relay satellite completes decoding and marks the relay satellite time code. 器星链路 , according to multiple groups of time delay ΔT 器星链路 The engineering constant C is calculated; The engineering constant C is used to calculate the time difference between the detector and the ground standard time, that is, the calibration value; the detector is calibrated based on the calibration value.

2. According to claim 1, a lunar in-situ detector timing method based on relay communication is characterized in that: The ground test system comprises a communication link between the detector and the ground test system, a communication link between the relay satellite and the ground test system, and a forward return link between the detector and the relay satellite.

3. According to claim 2, a lunar in-situ detector timing method based on relay communication is characterized in that: The establishment of the ground test system comprises: Use radio frequency cables to connect the detector to ground measurement and control equipment to establish a detector-ground remote control and telemetry link; Use radio frequency cables to connect the relay satellite and ground measurement and control equipment to establish a relay satellite-ground remote control and telemetry link; Use radio frequency cables to connect the relay satellite and the detector's measurement and control equipment to establish a forward and return link between the detector and the relay satellite.

4. According to the method of claim 1, the timing of the lunar in-situ detector based on relay communication is characterized in that: According to the multiple groups of time delay ΔT 器星链路 The engineering constant C is calculated, including: obtaining the detector time code and the relay satellite time code in the relay satellite data transmission frame multiple times to obtain multiple groups of delays ΔT 器星链路 , and take the average value to get the engineering constant C.

5. The method for calibrating the time of a lunar in-situ detector based on relay communication according to claim 1, characterized in that: The time delay ΔT 器星时延 =T 星 -T 器 ; Among them, T 星 The relay satellite time code inserted at the end of the frame when the relay satellite forwards the detector telemetry frame; T 器 The probe time code is inserted into the field for the probe telemetry frame.

6. The method for calibrating the time of a lunar in-situ detector based on relay communication according to claim 1, characterized in that: The time difference between the detector and the ground standard time is calculated by using the engineering constant C, that is, the time calibration quantity includes: Considering the relay satellite as a ground station, calculate the time calibration value T of the lunar in-situ detector 校时 In actual engineering, the errors caused by software time quantization and interruption factors in detector design are ignored, and the time difference between the detector and the ground standard time is obtained, that is, the calibration time T 校时-工程 .

7. The method for calibrating the time of a lunar in-situ detector based on relay communication according to claim 6, characterized in that: The calculation of the time calibration value T of the lunar surface in-situ detector 校时 : T 校时 =T 星 -T 器 -ΔT 器星时延 -T 空间链路 +ΔT 星地 +T 器-量化 +T 星-量化 +T 器-int +T 星-int Where, ΔT 器星 ΔT is the time difference calculated between the detector and the relay satellite in the same relay satellite data transmission frame; 星地 ΔT is the time difference between the relay star and the ground; 器星链路 T is the time delay from the time when the telemetry frame time code of any detector is generated to the time when the relay satellite completes decoding and marks the relay satellite time code; 空间链路 The space link information transmission distance delay, that is, the return transmission delay from the detector to the relay satellite; ΔT 器-量化 When writing the time code for the detector downlink telemetry group frame, the time error caused by millisecond time quantization; ΔT 星-量化 When writing the time code for the relay satellite downlink telemetry frame, the time error caused by millisecond time quantization; ΔT 器-int is the time error caused when the detector telemetry framing interrupt is closed by other events; ΔT 星-int It is the time error caused when the relay satellite telemetry framing interrupt is closed by other events.

8. The method for calibrating the time of a lunar in-situ detector based on relay communication according to claim 7, characterized in that: The T 校时-工程 =T 星 -T 器 -CT 空间链路 .

Images