CN110542423B - Moon soft landing vertical approach obstacle avoidance guidance method - Google Patents
Moon soft landing vertical approach obstacle avoidance guidance method Download PDFInfo
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Abstract
本发明一种月球软着陆垂直接近避障制导方法,步骤如下:1)设探测器制导指令计算周期为T,每N个制导指令计算周期进行一次制导参数更新;假设外部导航系统建立在惯性坐标系下,当前周期由导航系统提供的目标着陆点位置矢量为
探测器自身在惯性系的位置矢量为ri,速度矢量为vi;设计数器k是一个非负整数,初值为0;所述惯性坐标系用i表示,原点在月球中心,三个坐标轴在惯性空间指向固定方向;N≥1;2)以目标着陆点为中心,在空间中沿固定的方向建立制导坐标系,获得由惯性系向制导坐标系的旋转矩阵;3)解算得到制导参数;4)计算得到制导指令,并交给外部姿态控制系统和发动机执行。The present invention is a method for guiding the vertical approach of lunar soft landing and obstacle avoidance. Under the system, the position vector of the target landing point provided by the navigation system in the current cycle is
The position vector of the probe itself in the inertial system is ri, and the velocity vector is vi; the counter k is a non-negative integer, and the initial value is 0; the inertial coordinate system is represented by i , the origin is at the center of the moon, and the three coordinates are The axis points to a fixed direction in inertial space; N≥1; 2) Take the target landing point as the center, establish a guidance coordinate system along a fixed direction in space, and obtain the rotation matrix from the inertial system to the guidance coordinate system; 3) Solve to get Guidance parameters; 4) The guidance command is obtained by calculation and handed over to the external attitude control system and the engine for execution.Description
Technical Field
The invention relates to a moon soft landing vertical approach obstacle avoidance guidance method, and belongs to the field of spacecraft guidance control.
Background
For soft landing of the moon, the terrain is an important factor endangering the landing safety. Therefore, in the descending and flying process, the distribution situation of the obstacle on the surface of the moon is observed, a safe landing point is searched, and the flight track is changed to implement obstacle avoidance. Existing landing probe barriers generally use an inclined descent trajectory, for example, apollo uses a descent trajectory having an angle of 16 ° to 24 ° with the horizontal plane, and Chang' e # uses a descent trajectory having an angle of 45 ° with the horizontal plane. This approach requires a relatively large flat area, which is advantageous for probes landing in the moon's area. However, this trajectory of descent is very unfavorable for landing missions that extend over the meteorite crater, to the south of the moon, to the back, etc. Firstly, for a detector navigation system depending on distance measurement relative measurement, the bumpy flight path can be aggravated by the fluctuant ground; secondly, there is a risk of accidental impact during descent in terrain with severe changes.
Therefore, for such rough terrain landing tasks, it is preferable to use a vertical approach descent trajectory. The advantages are that: firstly, the vertical projection position of the detector on the lunar surface is basically fixed when the detector vertically descends, so that the influence of terrain change is eliminated, and the method is favorable for the stability of a ranging correction navigation system; and secondly, when the landing platform descends vertically, the detector can observe the same landing area continuously and stably, and obstacle avoidance is facilitated. However, after the descending track is changed to be vertical, the original approach guidance method is not suitable any more, and the main problems include: firstly, a guidance coordinate system based on the direction of a target landing point relative to a detector can have the problem of rapid angle rotation when the guidance coordinate system vertically descends, and secondly, the guidance parameter resolving period is the same as the guidance instruction resolving period, so that guidance and attitude control self-oscillation easily occurs; and thirdly, after the landing points are updated, the guidance parameters cannot be updated in time, and the guidance response is slow.
Disclosure of Invention
The technical problem solved by the invention is as follows: the defects of the prior art are overcome, the lunar soft landing vertical approach obstacle avoidance guidance method is provided, and the safety landing requirement under the rugged terrain environment on the back of the moon or in the south pole area is met.
The technical scheme of the invention is as follows:
a moon soft landing vertical approach obstacle avoidance guidance method comprises the following steps:
1) setting a calculation period of the detector guidance instruction as T, and updating guidance parameters once in every N calculation periods of the guidance instruction; assuming that the external navigation system is established under an inertial coordinate system, the position vector of the target landing point provided by the navigation system in the current period isThe position vector of the detector in the inertial system is riVelocity vector is vi(ii) a Designing a counter k to be a non-negative integer, wherein the initial value of the counter k is 0; the inertial coordinate system is represented by i, the origin is at the center of the moon, and the three coordinate axes point to a fixed direction in the inertial space; n is more than or equal to 1;
2) establishing a guidance coordinate system in a fixed direction in space by taking a target landing point as a center, and obtaining a rotation matrix from an inertial system to the guidance coordinate system;
3) resolving to obtain a guidance parameter;
4) and calculating to obtain a guidance instruction, and handing the guidance instruction to an external attitude control system and an engine for execution.
The process of obtaining the rotation matrix from the inertial system to the guidance coordinate system in the step 2) is as follows:
according to the image processing of the navigation camera, finding a flat landing zone, and taking the central point of the landing zone as a new safe landing point, otherwise, keeping the original value of the safe landing point; if the updated safe landing point is obtained in the period, changing the current period into a guidance parameter resolving period; then, establishing a guidance coordinate system by taking the safe landing point as an origin and taking the local fixed direction as a reference, and further obtaining a rotation matrix of the inertial system to the guidance coordinate system;
the specific process of the step 2) is as follows:
setting the current target landing point position asIf the target landing point is a new safe landing point obtained again by the navigation and obstacle avoidance sensor, making k equal to 0;
establishing a guidance coordinate system by taking the safe landing point as a center, wherein the x-axis direction points to the safe landing point from the moon center and represents the local vertical direction; the two axes of y and z are in the local horizontal plane; with a predetermined reference direction p in spaceiRequiring the establishment of a z-axis and a vector p of the guidance coordinate systemiAnd if the included angle is minimum, the representation of three axes of the guidance coordinate system in the inertial space is as follows:
z=x×y
when the guidance parameters are obtained through resolving in the step 3), if the current period is a parameter resolving period, the position and speed parameters of the detector given by the navigation system are converted into a guidance coordinate system; calculating guidance time by taking the position, the speed and the acceleration of the vertical motion terminal as constraints and taking the change rate of the vertical acceleration of the terminal equal to 0 as a design target; calculating a guidance parameter according to the guidance time;
the specific process of the step 3) is as follows:
setting lead time tgoIndicates that the initial value is a number greater than 10;
(3.1) if t is satisfiedgo>And if k is equal to 0, updating the guidance parameters, specifically as follows:
firstly, converting the position and the speed of a detector into a guidance coordinate system, and acquiring the position r relative to a target landing point in the guidance coordinate systemgAnd velocity vg;
Wherein, ω ismIs the angular velocity of the moon rotating relative to the inertial space,the method is a representation of the velocity direction vector of the self-rotation angle of the moon in an inertial system, and the velocity direction vector of the self-rotation angle of the moon is known quantity;
calculating to obtain the remaining guidance time:
setting the target acceleration vector of the lead terminal asTarget speed isThe target position vector is rt g(ii) a The three quantities mentioned above are the design values,x component of (i.e. 1)The value is larger than 0 and smaller than the difference between the acceleration generated by the maximum thrust of the engine and the gravity acceleration of the moon,both the y and z components of (a) are 0;x component of (i.e. 1)Is a number not greater than 0,both the y and z components of (a) are 0; r ist gX component of (1)Is the terminal height in the vertical approach process, the value is a number greater than 0, rt gBoth the y and z components of (a) are 0;
setting the target of the vertical acceleration change rate of the terminal to be zero, and enabling WhereinIs vgThe x-component of (a) is,is rgX component of (1), then the guidance time tgoThe calculation is as follows:
calculating updated guidance parameters c1,c2,c3:
(3.2) if t is not satisfiedgo>10 and k is 0, then:
tgo←tgo-T
the symbol "←" represents an assignment; guidance parameter c1,c2,c3And not updated.
The specific process of the step 4) is as follows:
Wherein, ggIs the gravity acceleration vector under the guidance system;
converting the command acceleration under the guidance system into the command acceleration under the inertia system to obtainAnd output to an external attitude control system and an engine for execution, so that the longitudinal axis of the detector, namely the thrust direction of the engine and the thrust direction of the engineCoincidence, acceleration due to engine output thrust, andtargetEqual in size;
updating k ← k +1 by a counter k, and judging that k is 0 if k is larger than or equal to N;
judging the ending condition: if tgo<0, finishing the vertical approaching obstacle avoidance guidance, and returning to the step 1 in the next period).
Compared with the prior art, the invention has the beneficial effects that:
firstly, the establishing mode of the guidance coordinate system is modified, the guidance coordinate system is established in a fixed space direction by taking the target landing point as the center, and the large-scale rotation of the coordinate axis direction of the guidance coordinate system caused by the small-scale change of the detector relative to the direction of the target landing point in the vertical descending track is avoided.
Secondly, a guidance parameter updating period and a guidance instruction updating period are separated, so that guidance stability is improved;
thirdly, after the landing points are obtained again, the guidance parameters are immediately recalculated, and the response speed of the guidance law is improved.
Drawings
Fig. 1 is a structural diagram of a moon soft landing vertical approach obstacle avoidance guidance method.
Fig. 2 is a schematic diagram of guidance instruction output under a guidance system in a vertical approach obstacle avoidance process.
Fig. 3 is a schematic diagram of a motion trajectory in a vertical approaching obstacle avoidance process.
Detailed Description
As shown in fig. 1, the detailed process of the present invention is as follows:
1) obtaining external navigation data
Setting a calculation period of the detector guidance instruction as T, and updating guidance parameters once in every N calculation periods of the guidance instruction; assuming that the external navigation system is established under an inertial coordinate system, the position vector of the target landing point provided by the navigation system in the current period isThe position vector of the detector in the inertial system isriVelocity vector is vi(ii) a Designing a counter k to be a non-negative integer, wherein the initial value of the counter k is 0; the inertial coordinate system is represented by i, the origin is at the center of the moon, and the three coordinate axes point to a fixed direction in the inertial space; n is more than or equal to 1.
2) Establishing a guidance coordinate system
Setting the current target landing point position asIf the target landing point is a new safe landing point obtained again by the navigation and obstacle avoidance sensor, making k equal to 0;
establishing a guidance coordinate system by taking the safe landing point as a center, wherein the x-axis direction points to the safe landing point from the center of the moon, and the x-axis direction is the local vertical direction; the y and z axes are in the local horizontal plane, and the specific direction can be set according to the requirement: with a predetermined reference direction p in spaceiRequiring the establishment of a z-axis and a vector p of the guidance coordinate systemiAnd if the included angle is minimum, the representation of the three axes of the guidance coordinate system in the inertial space can be calculated as follows:
z=x×y(3)
3) Guidance parameter solution
T for guidance timegoThe initial value is a number greater than 10.
a) If t isgo>10 and k is 0, then
Firstly, converting the position and the speed of a detector into a guidance coordinate system, and acquiring the position r relative to a target landing point in the guidance coordinate systemgAnd velocity vg;
Wherein, ω ismIs the angular velocity of the moon rotating relative to the inertial space,is the representation of the velocity direction vector of the self-rotation angle of the moon in an inertial system, and the velocity direction vector of the self-rotation angle of the moon and the inertial system are known quantities.
The remaining guidance time is then calculated.
Setting the target acceleration vector of the lead terminal asTarget speed isThe target position vector is rt g(ii) a The three quantities mentioned above are the design values,x component of (i.e. 1)The value is larger than 0 and smaller than the difference between the acceleration generated by the maximum thrust of the engine and the gravity acceleration of the moon,both the y and z components of (a) are 0;x component of (i.e. 1)Is a number not greater than 0,both the y and z components of (a) are 0; r ist gX component of (1)Is the terminal height in the vertical approach process, the value is a number greater than 0, rt gBoth the y and z components of (a) are 0;
setting the target of the vertical acceleration change rate of the terminal to be zero, and enabling WhereinIs vgThe x-component of (a) is,is rgX component of (1), then the guidance time tgoThe calculation is as follows:
calculating updated guidance parameters c1,c2,c3
b) If t is not satisfiedgo>10 and k is 0, then
tgo←tgo-T
The symbol "←" represents an assignment; guidance parameter c1,c2,c3And not updated.
4) Commanded acceleration calculation
Wherein, ggIs the gravity acceleration vector under the guidance system, and is known. Then, it is converted into inertia system to obtain
Then will beThe output is executed by an external attitude control system and an engine so that the longitudinal axis of the detector, namely the thrust direction of the engine and the thrust direction of the engineCoincidence, acceleration due to engine output thrust, andare equal in size.
Followed by an update of the counter k
k ← k +1, and when k is judged to be equal to or greater than N, k ═ 0
And finally, judging the ending condition: if tgo<0, finishing the vertical approaching obstacle avoidance guidance, and returning to the step 1 in the next period).
Simulation analysis
Assuming that a certain detector enters an approaching obstacle avoidance process at 3000m height at a vertical speed of-30 m/s and an upward speed direction as positive and a horizontal speed of 0m, an initial target landing point is right below the detector, and the value of a guidance terminal parameter isrt g=[3,0,0]T. The guidance instruction calculation period T is 0.1s, and the guidance parameter update period is 10 times the guidance instruction calculation period, that is, N is 10. When the probe descends to the height of 1500m, the target safe landing point is determined to be 180m away from the initial target landing point. The target acceleration vector approaching the descending process under the guidance system is shown in fig. 2, and after the safe landing point is updated, the guidance acceleration has sudden change with a certain amplitude, so that the original descending flight trend is changed; the corresponding flight trajectory is shown in fig. 3, the detector first descends in a vertical manner, and after the obstacle avoidance starts, the detector descends and translates to the position above the target safe landing point. Simulation results show that the moon soft landing vertical approach obstacle avoidance guidance method provided by the invention is effective.
Those skilled in the art will appreciate that the invention may be practiced without these specific details.
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