A method for acquiring three-dimensional terrain in a high-dynamic landing process of an extraterrestrial object

Abstract

The application discloses a three-dimensional terrain acquisition method in a high-dynamic landing process of an extraterrestrial celestial body, and comprises the following steps: establishing a celestial body fixed coordinate system at T0, compensating system time motion, etc. A three-dimensional measurement sensor adopts a swing mirror scanning scheme, and realizes the function of acquiring the terrain of a landing area in the dynamic landing process. The probe can obtain the terrain data of the landing area without hovering, and fuel consumption of the system is significantly reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of spacecraft control, and particularly relates to a method for acquiring three-dimensional terrain in a high-dynamic landing process of an extraterrestrial celestial body. BACKGROUND

[0002] At present, a hovering mode is usually adopted in a landing process of a probe, so as to provide a stable attitude and position for a laser three-dimensional measurement sensor of a three-dimensional terrain obstacle detection sensor, so that the laser three-dimensional measurement sensor can ignore the motion of the probe during imaging, and consider that the target fluctuation measured during obstacle detection is caused by the terrain of the moon surface. This strategy needs to consume a large amount of propellant to maintain the hovering stability of the probe. For a deep space probe such as the moon, in order to achieve mission success, the weight of the propellant is very precious, and the propellant weight should be saved as much as possible. In some cases, the propellant may be insufficient, and if the hovering mode is still adopted, the probe will be at great risk. SUMMARY

[0003] The technical problem of the application is to overcome the shortcomings of the prior art, and provide a method for acquiring three-dimensional terrain in a high-dynamic landing process of an extraterrestrial celestial body. The method acquires three-dimensional terrain in a high-dynamic landing process of an extraterrestrial celestial body by using a system dynamic data and product measurement coupling solving method, can obtain high-quality three-dimensional terrain obstacle detection capability in the case that the probe does not hover (that is, has a larger angular velocity and translational velocity) during the landing process of the probe, and cancels the hovering mode in the traditional landing process, thereby greatly saving the consumption of propellant.

[0004] In order to solve the above technical problem, the application discloses a method for acquiring three-dimensional terrain in a high-dynamic landing process of an extraterrestrial celestial body, comprising:

[0005] During the three-dimensional terrain acquisition task, when it is ready to start acquiring three-dimensional terrain, a control computer sends a scanning instruction to a three-dimensional measurement sensor, and then sends a synchronization signal to the three-dimensional measurement sensor and a platform sensor;

[0006] When the three-dimensional measurement sensor receives the first synchronization signal, the laser scanning is started, and the scanning of the terrain of the landing area is started, and a celestial body fixed coordinate system at T0 time is established; wherein the T0 time is the time when the three-dimensional measurement sensor receives the first synchronization signal;

[0007] The control computer records the angular velocity measurement information and the acceleration measurement information of the synchronization signal effective time measured by the platform sensor, and calculates the motion information of the probe during scanning;

[0008] The three-dimensional measurement sensor completes the scanning of the landing area terrain according to the preset scanning time; the control computer stops sending the synchronization signal to the three-dimensional measurement sensor after the preset scanning time is exceeded, and sends the motion information of the probe during the scanning to the three-dimensional measurement sensor;

[0009] After receiving the motion information of the probe during the scanning, the three-dimensional measurement sensor performs motion compensation on each scanning measurement point of the three-dimensional measurement sensor according to the motion information of the probe during the scanning, to obtain the position vector of each scanning measurement point of the three-dimensional measurement sensor in the celestial body fixed coordinate system at T0 moment;

[0010] According to the obtained position vector of each scanning measurement point of the three-dimensional measurement sensor in the celestial body fixed coordinate system at T0 moment, the terrain data of the landing area in the celestial body fixed coordinate system at T0 moment is determined, which is used for subsequent identification of the landing safety area.

[0011] In the above three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial celestial body, the origin of the celestial body fixed coordinate system at T0 moment is the substar point of the probe at T0 moment, the X axis points to the sky, the Y and Z axes are in the local horizontal plane, the Y axis points to the east, and the Z axis points to the north.

[0012] In the above three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial celestial body, the motion information of the probe includes: attitude information and translation information of the probe; wherein the attitude information of the probe includes: attitude Euler angles of the probe body relative to the local north-east-up coordinate system; the translation information of the probe includes: a velocity vector of the probe body relative to the local north-east-up coordinate system.

[0013] In the above three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial celestial body, the motion compensation on each scanning measurement point of the three-dimensional measurement sensor includes: rotation compensation and translation compensation.

[0014] In the above three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial celestial body, each scanning measurement point of the three-dimensional measurement sensor includes: a scanning measurement point at a synchronization signal effective moment and a scanning measurement point at a non-synchronization signal effective moment.

[0015] In the above three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial celestial body, for the scanning measurement point at the synchronization signal effective moment, the rotation compensation process is as follows:

[0016] According to the attitude information of the probe obtained at each synchronization signal moment during the scanning, a conversion matrix C Cg(i) is obtained, which is the conversion matrix of the probe body coordinate system relative to the celestial body fixed coordinate system at the measurement moment; wherein the origin of the celestial body fixed coordinate system at the measurement moment is the substar point of the probe at the measurement moment, the X axis points to the sky, the Y and Z axes are in the local horizontal plane, the Y axis points to the east, and the Z axis points to the north; the probe body coordinate system is a three-dimensional rectangular coordinate system fixed to the probe;

[0017] Based on the conversion matrix C Cg(i) The position vector P of the scanning measurement point at the effective time of the synchronization signal in the detector body coordinate system 1(i) Coordinate system conversion is performed to obtain the position vector P of the scanning measurement point at the effective time of the synchronization signal in the celestial body coordinate system at the measurement time 2(i) : P 2(i) =C Cg(i) ·P 1(i) .

[0018] In the three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial object, for the scanning measurement point at the effective time of the synchronization signal, the translation compensation process is as follows:

[0019] According to the translation information of the detector obtained at each synchronization signal time during scanning, the velocity vector V of the i-th detector body relative to the local celestial body northeast coordinate system is determined i ;

[0020] According to V i , the position vector P 2(i) is translation compensated to obtain the position vector P of the scanning measurement point at the effective time of the synchronization signal in the celestial body coordinate system at the time T0 3(i) :

[0021]

[0022] Where, Δt represents the period of the synchronization signal.

[0023] In the three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial object, for the scanning measurement point at the effective time of the synchronization signal, the rotation compensation and translation compensation process is as follows:

[0024] The attitude information and translation information of the detector obtained at each synchronization signal time during scanning are interpolated to obtain the attitude information and translation information of the detector at the non-synchronization signal effective time;

[0025] According to the obtained attitude information and translation information of the detector at the non-synchronization signal effective time, the scanning measurement point at the non-synchronization signal effective time is rotation compensated and translation compensated to obtain the position vector of the scanning measurement point at the non-synchronization signal effective time in the celestial body coordinate system at the time T0.

[0026] In the three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial object, during the non-three-dimensional terrain acquisition task, the control computer does not send the synchronization signal to the three-dimensional measurement sensor.

[0027] The three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial object comprises the following steps: a control computer, a three-dimensional measurement sensor and a platform sensor are arranged on a probe; the platform sensor comprises at least three gyroscopes and at least three accelerometers.

[0028] The present application has the following advantages:

[0029] The present application discloses a three-dimensional terrain acquisition method in a high-dynamic landing process of an extraterrestrial object, which adopts a system dynamic data and product measurement coupling solving method to acquire the three-dimensional terrain in the high-dynamic landing process of the extraterrestrial object, and can obtain high-quality three-dimensional terrain obstacle detection capability in the case that the probe does not hover (that is, has a relatively large angular velocity and translational velocity) during the landing process. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Fig. 1 is a schematic diagram of the composition of a probe and three-dimensional terrain scanning imaging in an embodiment of the present application;

[0031] Figure 2 Fig. 4 is a schematic diagram of the interaction process between a control computer and a three-dimensional measurement sensor in an embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application clearer, the following will further describe the disclosed embodiments of the present application in combination with the drawings.

[0033] One of the core ideas of the present application is that, in view of the problem of large propellant consumption in the hovering obstacle avoidance stage of the existing lander, a three-dimensional terrain acquisition method in a high-dynamic landing process of an extraterrestrial object is proposed, which mainly includes three aspects: 1) establishment of a T0 time object fixed coordinate system: a T0 time object fixed coordinate system is established with the probe nadir point at the initial scanning time of the three-dimensional measurement sensor as the origin, which is used to describe the landing area terrain data; 2) system time system: the hardware time synchronization mode of the control computer, the three-dimensional measurement sensor and the platform sensor is used to obtain the motion information of the probe corresponding to the accurate time during the scanning period of the three-dimensional measurement sensor, which provides necessary conditions for accurate compensation of each scanning measurement point of the three-dimensional measurement sensor; 3) motion compensation: the control computer calculates the motion information of the probe according to the measurement information of the platform sensor, and sends the motion information of the probe to the three-dimensional measurement sensor; the three-dimensional measurement sensor performs kinematic compensation accordingly to obtain the landing area terrain data in the T0 time object fixed coordinate system.

[0034] In the present embodiment, the three-dimensional terrain acquisition method in the high-dynamic landing process of the extraterrestrial object comprises the following steps:

[0035] Step 1, during the three-dimensional terrain acquisition task, when preparing to start acquiring the three-dimensional terrain, the control computer first sends a scanning instruction to the three-dimensional measurement sensor, and then sends a synchronization signal to the three-dimensional measurement sensor and the platform sensor.

[0036] In the embodiment, the control computer, the three-dimensional measurement sensor and the platform sensor are arranged on the probe; the platform sensor comprises at least three gyroscopes and at least three accelerometers. The three-dimensional measurement sensor measures the distance information between the three-dimensional measurement sensor and the ground based on the laser scanning imaging measurement principle, measures the distance information between the three-dimensional measurement sensor and the ground by emitting a laser beam, and sequentially scans to obtain the distance information of multiple measurement points on the ground and the three-dimensional measurement sensor. The control computer sends a synchronization signal to the three-dimensional measurement sensor and the platform sensor to obtain the accurate correspondence between the scanning time of the three-dimensional measurement sensor and the measurement information of the platform sensor, and further obtain the accurate correspondence between the scanning time of the three-dimensional measurement sensor and the motion information of the probe.

[0037] Preferably, the control computer synchronizes the three-dimensional measurement sensor and the platform sensor by the synchronization signal. The synchronization signal adopts the rising edge or the falling edge of a periodic pulse signal, and the synchronization accuracy can reach microseconds; the synchronization signal period is generally tens of ms, and the specific length is determined according to the motion compensation accuracy requirement. Further, the synchronization signal is a homologous hardware synchronization signal, that is, the synchronization signal between the control computer and the platform sensor and the synchronization signal between the control computer and the three-dimensional measurement sensor are hardware synchronization signals and are homologous.

[0038] It should be noted that the control computer always sends a synchronization signal to the platform sensor (that is, during the three-dimensional terrain acquisition task and the non-three-dimensional terrain acquisition task, the control computer always sends a synchronization signal to the platform sensor), and the platform sensor provides the angular velocity measurement information and the acceleration measurement information of the synchronization signal time to the control computer, and then calculates the attitude information and the translation information of the probe. During the non-three-dimensional terrain acquisition task, the control computer does not send a synchronization signal to the three-dimensional measurement sensor.

[0039] Step 2, when the three-dimensional measurement sensor receives the first synchronization signal, the laser scanning is started, and the landing area terrain is scanned, and at the same time, the celestial body fixed coordinate system at T0 time is established.

[0040] In the embodiment, T0 time is the time when the three-dimensional measurement sensor receives the first synchronization signal. The origin of the celestial body fixed coordinate system at T0 time is the substar point of the probe at T0 time, the X axis points to the sky, the Y and Z axes are in the local horizontal plane, the Y axis points to the east, and the Z axis points to the north.

[0041] Step 3: The control computer records the angular velocity measurement information and acceleration measurement information at the effective moment of the synchronization signal obtained by the platform sensor, and calculates the motion information of the detector during the scanning period.

[0042] In this embodiment, the motion information includes: the detector's attitude information and translation information. Further, the detector's attitude information includes: the Euler angles of the detector body relative to the local celestial northeast coordinate system; the detector's translation information includes: the velocity vector of the detector body relative to the local celestial northeast coordinate system.

[0043] Step 4: The 3D measurement sensor completes the terrain scan of the landing area according to the preset scan time (usually several hundred milliseconds); after the preset scan time is exceeded, the control computer stops sending synchronization signals to the 3D measurement sensor and sends the motion information of the detector during the scan to the 3D measurement sensor.

[0044] Step 5: After receiving the motion information of the detector during the scanning period, the three-dimensional measurement sensor performs motion compensation on each scanning measurement point of the three-dimensional measurement sensor according to the motion information of the detector during the scanning period, and obtains the position vector of each scanning measurement point of the three-dimensional measurement sensor in the celestial fixed coordinate system at time T0.

[0045] In this embodiment, motion compensation for each scanning measurement point of the three-dimensional measurement sensor includes rotational compensation and translational compensation. Each scanning measurement point of the three-dimensional measurement sensor includes: the scanning measurement point at the effective time of the synchronization signal and the scanning measurement point at the effective time of the asynchronous signal.

[0046] Preferably, for the scanning measurement point at the valid moment of the synchronization signal:

[0047] The rotation compensation process is as follows: Based on the detector's attitude information obtained at each synchronization signal moment during the scanning period, the transformation matrix C between the detector's body coordinate system and the celestial fixed coordinate system at the measurement moment is obtained. Cg(i) Based on the transformation matrix C Cg(i) The position vector P of the scanning measurement point in the detector body coordinate system at the effective moment of the synchronization signal. 1(i) By performing a coordinate system transformation, the position vector P of the scanning measurement point at the effective moment of the synchronization signal in the celestial fixed coordinate system at the measurement moment is obtained. 2(i) :P 2(i) =C Cg(i) ·P 1(i) Where i represents the sequence number of the synchronization signal; the origin of the celestial fixed coordinate system at the measurement time is the nadir point of the detector at the measurement time, the X-axis points to the sky, and the Y and Z axes are in the local horizontal plane, with the Y-axis pointing east and the Z-axis pointing north; the detector body coordinate system is the three-dimensional rectangular coordinate system fixed to the detector, and the measurement data of the three-dimensional measurement sensor is described in this coordinate system.

[0048] Further, the conversion matrix C Cg(i) is calculated as follows:

[0049]

[0050] where (a i , b i , g i ) are the Euler angles of the attitude of the i-th synchronization signal.

[0051] The translational compensation process is as follows: according to the translational information of the detector obtained at each synchronization signal time during scanning, the velocity vector V i of the i-th detector body relative to the local celestial northeast coordinate system is determined; i According to V 2(i) , the position vector P 3(i) of the scanning measurement point at the effective time of the synchronization signal in the T0 time celestial body coordinate system is obtained by translational compensation: Delta t represents the period of the synchronization signal.

[0052] Preferably, for the scanning measurement point at the non-synchronization signal effective time, the rotation compensation and translational compensation process is as follows: the attitude information and translational information of the detector obtained at each synchronization signal time during scanning is interpolated to obtain the attitude information and translational information of the detector at the non-synchronization signal effective time; according to the obtained attitude information and translational information of the detector at the non-synchronization signal effective time, the scanning measurement point at the non-synchronization signal effective time is rotationally compensated and translationally compensated to obtain the position vector of the scanning measurement point at the non-synchronization signal effective time in the T0 time celestial body coordinate system.

[0053] Step 6, according to the obtained position vector of each scanning measurement point of the three-dimensional measurement sensor in the T0 time celestial body coordinate system, the landing area terrain data in the T0 time celestial body coordinate system is determined, which is used for subsequent identification of the landing safety area.

[0054] On the basis of the above embodiment, a specific example is described below.

[0055] In this embodiment, a method for acquiring three-dimensional terrain in the high-dynamic landing process of an extraterrestrial celestial body is disclosed, which is suitable for acquiring three-dimensional terrain and calculating safety points without hovering of a detector in the high-dynamic landing process of an extraterrestrial celestial body. A control computer, a three-dimensional measurement sensor and a platform sensor are arranged on the detector, the detector scans the terrain as shown in Figure 1 , and the interaction process between the control computer and the three-dimensional measurement sensor is shown in Figure 2 . Among them:

[0056] 1) ΔT represents the interval between the sending of the scanning instruction by the control computer and the first synchronization signal, and ΔT should satisfy the time required for the three-dimensional measurement sensor to correctly receive the scanning instruction and prepare for it.

[0057] 2) The period of the synchronization signal between the control computer and the three-dimensional measurement sensor is 16 ms. The reason for determining 16 ms is as follows: when the angular velocity of the probe is less than 10° / s, the maximum change of the angle within 16 ms is 0.08°, and the three-dimensional position measurement error caused by the scanning imaging at a height of 100 m is 0.014 m. When the probe velocity is less than 5 m / s, the acceleration is less than 1 m / s 2 , and the maximum change of the position within 16 ms is 0.000064 m, and the three-dimensional position measurement error caused thereby is 0.000064 m.

[0058] 3) Scanning instruction: after receiving the scanning instruction sent by the control computer, the three-dimensional measurement sensor waits for the sending of the synchronization signal by the control computer, and takes the first valid synchronization signal as the initial time T0 of imaging, and establishes the celestial body fixed coordinate system at T0 based on the time T0 and the subspace point of the probe at T0, and the scanning time of each scanning is not greater than 500 ms.

[0059] 4) Transmission of the motion information of the probe: the control computer sends the motion information (including the attitude information and the translation information) of the probe during the scanning imaging to the three-dimensional measurement sensor.

[0060] 5) Compensation calculation: the three-dimensional measurement sensor performs motion compensation on each scanning measurement point of the three-dimensional measurement sensor according to the received motion information of the probe during the scanning, to obtain the position vector of each scanning measurement point of the three-dimensional measurement sensor in the celestial body fixed coordinate system at T0, and calculate the safe landing point based thereon.

[0061] Although the present application has been disclosed with the above preferred embodiments, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents without departing from the spirit and scope of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, which does not depart from the content of the technical solutions of the present application, all belong to the protection scope of the technical solutions of the present application.

[0062] The contents not described in detail in the specification of the present application belong to the known technology of the person skilled in the art.

Claims

1. A method for acquiring three-dimensional terrain in a high-dynamic landing process of an extraterrestrial body, characterized in that, The method comprises the following steps: During a three-dimensional terrain acquisition task, when it is ready to start acquiring the three-dimensional terrain, a control computer sends a scanning instruction to a three-dimensional measurement sensor first, and then sends a synchronization signal to the three-dimensional measurement sensor and a platform sensor; When the three-dimensional measurement sensor receives the first synchronization signal, it starts laser scanning and begins to scan the terrain of the landing area, and at the same time, a celestial body fixed coordinate system at T0 is established; wherein T0 is the time when the three-dimensional measurement sensor receives the first synchronization signal; The control computer records the angular velocity measurement information and acceleration measurement information of the synchronization signal effective time measured by the platform sensor, and calculates the motion information of the probe during scanning; The three-dimensional measurement sensor completes the scanning of the terrain of the landing area according to the preset scanning time; the control computer stops sending the synchronization signal to the three-dimensional measurement sensor after the preset scanning time is exceeded, and sends the motion information of the probe during scanning to the three-dimensional measurement sensor; After receiving the motion information of the probe during scanning, the three-dimensional measurement sensor compensates the motion of each scanning measurement point of the three-dimensional measurement sensor according to the motion information of the probe during scanning, and obtains the position vector of each scanning measurement point of the three-dimensional measurement sensor in the celestial body fixed coordinate system at T0; According to the obtained position vector of each scanning measurement point of the three-dimensional measurement sensor in the celestial body fixed coordinate system at T0, the terrain data of the landing area in the celestial body fixed coordinate system at T0 is determined, which is used for subsequent identification of the landing safety area; Each scanning measurement point of the three-dimensional measurement sensor includes a scanning measurement point at the synchronization signal effective time and a scanning measurement point at the non-synchronization signal effective time; the motion compensation of each scanning measurement point of the three-dimensional measurement sensor includes rotation compensation of the scanning measurement point at the synchronization signal effective time, translation compensation of the scanning measurement point at the synchronization signal effective time, rotation compensation and translation compensation of the scanning measurement point at the non-synchronization signal effective time; The translation compensation of the scanning measurement point at the synchronization signal effective time comprises: According to the panning information of the detector obtained at each synchronization signal moment during scanning, the velocity vector V of the i-th detector body relative to the local celestial northeast coordinate system is determined i ; According to V i The position vector P of the scanning measurement point at the effective time of the synchronization signal in the celestial body fixed coordinate system at the measurement time 2(i) The position vector P of the scanning measurement point at the effective time of the synchronization signal in the celestial body fixed coordinate system at the measurement time 3(i) : Wherein, Δt represents the period of the synchronization signal.

2. The method of claim 1, wherein, The origin of the celestial body fixed coordinate system at T0 is the substar point of the probe at T0, the X axis points to the sky, the Y and Z axes are in the local horizontal plane, the Y axis points to the east, and the Z axis points to the north.

3. The method of claim 2, wherein, The motion information of the probe includes the attitude information and the translation information of the probe; wherein the attitude information of the probe includes the attitude Euler angle of the probe body relative to the local sky-north-east coordinate system; the translation information of the probe includes the velocity vector of the probe body relative to the local sky-north-east coordinate system.

4. The method of claim 3, wherein, The rotation compensation of the scanning measurement point at the synchronization signal effective time comprises: According to the attitude information of the detector obtained at each synchronous signal moment during scanning, a conversion matrix C of a detector body coordinate system relative to a celestial body fixed coordinate system at a measurement moment is obtained Cg(i) ; wherein the origin of the celestial body fixed coordinate system at the measurement moment is a subpoint of the detector at the measurement moment, the X axis points to the sky, the Y and Z axes are in a local horizontal plane, the Y axis points to the east, and the Z axis points to the north; the detector body coordinate system is a three-dimensional rectangular coordinate system fixed to the detector; Based on the conversion matrix C Cg(i) The position vector P of the scanning measurement point at the effective time of the synchronization signal in the detector body coordinate system 1(i) Coordinate system conversion is performed to obtain the position vector P of the scanning measurement point at the effective time of the synchronization signal in the celestial body coordinate system fixedly connected at the measurement time 2(i) : P 2(i) =C Cg(i) ·P 1(i) .

5. The method of claim 4, wherein, The rotation compensation and translation compensation of the scanning measurement point at the non-synchronization signal effective time comprise: The attitude information and the translation information of the probe at the non-synchronization signal effective time are obtained by interpolating the attitude information and the translation information of the probe at each synchronization signal time during scanning. According to the obtained attitude information and the translation information of the non-synchronous signal effective time detector, the scanning measurement points of the non-synchronous signal effective time are rotationally compensated and translationally compensated, so as to obtain the position vector of the scanning measurement points of the non-synchronous signal effective time in the celestial body fixed coordinate system at the T0 moment.

6. The method of claim 1, wherein: During the non-three-dimensional terrain acquisition task, the control computer does not send a synchronization signal to the three-dimensional measurement sensor.

7. The method of claim 1, wherein: The detector is provided with a control computer, a three-dimensional measurement sensor and a platform sensor; the platform sensor comprises at least three gyroscopes and at least three accelerometers.

Images