CN105844046A - Complex terrain safety degree assessment method based on safety factors - Google Patents

Abstract

The invention relates to a method for evaluating the safety degree of complex terrain, in particular to a method for evaluating the safety degree of complex terrain based on safety factors, and belongs to the technical field of deep space exploration. A safety factor-based safety evaluation method for complex terrain, by proposing the concept of safety factor and applying it to the evaluation of complex terrain safety, it provides a quantitative method for the investigation of the safety of complex terrain landing tasks method, and further classify the evaluation results to obtain the safety degree of complex terrain. By adjusting the specific form of the safety factor, this method can be widely applied to the pre-mission planning and design of various planetary landing missions and the mission execution process to avoid obstacles, improve landing performance, and reduce failure risks.

Description

A safety factor-based safety evaluation method for complex terrain

technical field

The invention relates to a method for evaluating the safety degree of complex terrain, in particular to a method for evaluating the safety degree of complex terrain based on safety factors, and belongs to the technical field of deep space exploration.

Background technique

Future planetary exploration missions require probes to land in areas of scientific value. Such areas often have complex terrain, which poses great challenges to landing accuracy and landing safety. In order to solve this problem, in the design phase of the mission and the execution phase of the mission, it is necessary to conduct technical analysis and evaluation of the candidate landing areas of the target celestial body to obtain the suitable landing areas and provide reference for the subsequent landing work. At present, scholars at home and abroad have proposed a number of methods for comprehensively evaluating landing areas and landing sites. Most of these methods are scattered in content and in different forms. In order to perfect and unify the existing methods, it is necessary to propose an index that comprehensively considers multiple factors to meet the needs of different planetary landing missions, and to reasonably quantify the safety of complex terrain on the planetary surface, so that when the landing object or environment changes, it can still Completed the evaluation of the safety of complex terrain, analyzed the dangers of landing in different places, and improved the safety and success rate of missions.

Contents of the invention

The purpose of this invention is to provide a kind of complex terrain safety evaluation method based on safety factor, this method is by proposing the concept of safety factor, and it is applied in complex terrain safety evaluation problem, is the investigation of complex terrain landing task security A quantitative method is provided to further classify the evaluation results to obtain the safety degree of complex terrain.

The purpose of the present invention is achieved through the following technical solutions.

A safety factor-based safety evaluation method for complex terrain, comprising the following steps:

Step 1. Determine the concrete safety factor expression. The safety factor is obtained by weighting several factor indicators. Combined with the task requirements and the characteristics of the detection target, the factor indicators that need to be evaluated, the functional form and the weighting method are selected to obtain a specific expression of the safety factor.

From the perspective of safety, the concept of Safety Index (SI) is proposed as a universal evaluation standard for quantitative analysis of complex terrain, which is defined as

$\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; I</span>}\stackrel{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}{<span\; class="notranslate">\; =</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; 2...</span>}\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

The smaller the value of the safety factor, the safer the area. The factor indicators (factor1, factor2...factorN) in the safety factor mainly include: terrain conditions, landing accuracy, landing speed and attitude, fuel consumption, error and environmental interference. The specific function form adopted by each factor index can be either a discrete function or a continuous function changing within a limited range. The weighting method is determined according to the importance of each factor index to the success or failure of the task. If the selected factors are considered to have similar impact on the task and are equally weighted, each part of the factor index can be given the same weight; if one or several factors If it has a greater impact on the success or failure of the task, the weight of the factor index can be increased to increase the proportion of the factor in the analysis results.

Considering the above factor indicators, the function form and the weighting method, a specific safety factor is obtained;

Step 2. Evaluate the safety degree of complex terrain. Quantitatively evaluate the complex terrain after gridding according to the specific safety factor obtained in step 1; by setting intervals, the evaluation results are graded to obtain the safety degree of complex terrain.

The function form of the factor index of the safety factor mentioned in step 1 is: Sigmoid function, min-max normalization function, polynomial function or trigonometric function;

The safety degree of complex terrain is the result of a reasonable division of the value of the safety factor, which indicates the possible danger of the probe landing in different places. The higher the safety degree, the smaller the danger. When choosing to divide the interval, it is necessary to combine the overall value range of the safety factor and the value characteristics of each part of the evaluation index, and divide the safe area, dangerous area and the fuzzy area in between as much as possible. The number of levels of safety can vary. Adjust according to the actual situation, and use the safety degree to measure the success rate of the complex terrain landing mission, so as to achieve the purpose of evaluation and play a guiding role in the subsequent landing process.

Beneficial effect

A complex terrain safety evaluation method based on safety factors disclosed in the present invention proposes the concept of safety factors and applies it to the evaluation of complex terrain safety to provide a basis for the investigation of the safety of complex terrain landing tasks. A quantitative method is proposed, and the evaluation results are further graded to obtain the safety degree of complex terrain. The higher the safety level, the more suitable the area is for landing; on the contrary, the lower the safety level, the higher the risk of landing in the area. By adjusting the specific form of the safety factor, this method can be widely applied to the pre-mission planning and design of various planetary landing missions and the mission execution process to avoid obstacles, improve landing performance, and reduce failure risks.

Description of drawings

Fig. 1 is a flow chart of a safety factor-based complex terrain safety evaluation method disclosed by the present invention;

Fig. 2 is the direction of the thrust vector under the inertial system;

Figure 3 is the complex terrain evaluated in the simulation, where (a) is a three-dimensional topographic map, and (b) is a top view of the terrain;

Figure 4 is the S-shaped function change curve, where (a) is the change of the terrain condition index, and (b) is the change of the landing speed index;

Figure 5 shows the evaluation process and the calculation results of the safety factor, where (a) is the evaluation result of the terrain condition index, (b) is the evaluation result of the landing speed index, (c) is the evaluation result of the landing attitude index, and (d) is the calculation of the safety factor result;

Figure 6 is the evaluation result of safety degree of complex terrain, where (a) is the contour map of safety factor, and (b) is the calculation result of safety degree of complex terrain.

detailed description

In order to better illustrate the purpose and advantages of the present invention, the content of the invention will be further described below in conjunction with the accompanying drawings and examples.

Without loss of generality, this example selects the Mars landing process for analysis, and adopts optimal control guidance under the fixed inertial system at the landing site, and the analytical form of the guidance law is

$\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 4</span>}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; v</span>}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 6</span>}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; r</span>}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; o</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, a is the control acceleration, Δv and Δr are the difference between the current speed/position of the detector and the speed/position at the scheduled landing point, t _go represents the remaining landing time, and g is the local gravitational acceleration. The direction of the acceleration vector a is the direction of the main thrust T. As shown in Figure 2, the angle between the direction of the thrust T and the vertical z-axis It can be calculated by formula (3)

In Figure 3, the size of complex terrain used for evaluation is 2000m×2000m. The initial position r ₀ of the detector is [-300,-200,1700]m, and the initial velocity v ₀ is [18,20,-80]m/s. Under ideal conditions, the probe should land vertically on the surface of the planet at zero speed, but in the actual process, due to the existence of errors and disturbances, the landing speed and attitude of the probe deviate from the predetermined state. In order to truly simulate the landing process The environmental uncertainty and system error in the simulation, adding 5% execution error and gust interference in the simulation.

A safety factor-based complex terrain safety evaluation method disclosed in this embodiment includes the following steps:

Step 1. Determine the concrete safety factor expression. The safety factor is obtained by weighting several factor indicators. Combined with the task requirements and the characteristics of the detection target, the factor indicators that need to be evaluated, the functional form and the weighting method are selected to obtain a specific expression of the safety factor.

It should be noted that in the process of specifying the expression of the safety factor, the differences in the detection process of different target celestial bodies also need to be considered, which is specifically reflected in the length of time spent and the content of emphasis. Asteroids and comets are smaller in size and irregular in shape, and the gravitational force generated is small and unevenly distributed. It usually takes longer to land on such celestial bodies, and the landing speed is relatively slower. Therefore, the probe has enough time to detect and analyze the surface of the planet, and complete the evaluation of complex terrain through the on-board computer or receiving command information from the ground station. In terms of evaluation factors, due to the limited constraints of weak gravity on the detector, excessive landing speed and inclined landing attitude may cause the detector to bounce violently or even escape in complex terrain, and the impact of external disturbances on landing performance is also more obvious , these factors should be considered in the evaluation process. In contrast, the major celestial bodies represented by Mars have a large gravitational force and a relatively uniform distribution, which can tolerate a certain range of landing speeds and external disturbances, but their landing process is relatively faster, and with the delay in communication with the earth, only It can rely on the onboard autonomous system to conduct a simple and rapid assessment of the complex terrain within a limited range before landing, so the form of the safety factor is required to be simple and easy to calculate.

In this embodiment, the probe is required to land vertically on the surface of Mars at a speed as small as possible while avoiding obstacles, so terrain conditions, landing speed and landing attitude are selected as evaluation factors. In order to intuitively judge whether the given complex terrain is safe or not and to facilitate the unification of the form and value of the three factor indicators when forming the safety factor, the specific function form of each factor indicator is set as an S-type function, and then the specific safety factor is obtained. factor expression

Among them, c _i (i=1,2,3) is a normal constant, R, v _fz , Respectively, the safety radius (referring to the distance between the landing point of the detector and the nearest obstacle), the vertical velocity component and the angle between the thrust direction and the vertical direction, D, v _fzmax , are their critical values, respectively. Here, it is considered that terrain conditions, landing speed, and landing attitude have an equal impact on the success or failure of the mission, and the weights are all set to 1.

The calculation results of the S-type function can be divided into three categories, that is, greater than the critical value, less than the critical value, and near the critical value. It can be seen that the form of the first part in formula (4) is slightly different from the last two parts, because the critical value D in the terrain condition index is the lower boundary, and the critical value v _fzmax of the landing speed index and the landing attitude index, is the upper boundary. By properly adjusting the specific form, it can be ensured that the three indicators of terrain conditions, landing speed, and landing attitude are all smaller, and the area is safer. Taking the terrain situation as an example, assuming that the safety radius critical value D=50m, the safety radius R of the target landing point varies from 0m to 100m, and the change of this part of the index is shown in Figure 4(a). The indicators of landing speed and landing attitude also have a similar change law, but the direction of change is opposite to that of terrain conditions, as shown in Figure 4(b).

Step 2. Evaluate the safety degree of complex terrain. Quantitatively evaluate the complex terrain after gridding according to the specific safety factor obtained in step 1; by setting intervals, the evaluation results are graded to obtain the safety degree of complex terrain.

Before using specific safety factors to analyze complex terrain, it is necessary to first obtain the calculation results of the three indicators of terrain conditions, landing speed, and landing attitude. The terrain is divided into grids, and each grid is calculated according to the three factor indicators, and the calculation results of all grids are integrated on a map, and Figures 5(a), 5(b) and 5( c). The results of the above three figures are added according to the weighting method in the safety factor, that is, formula (4), to obtain the calculation result of the safety factor, as shown in Figure 5(d). It can be seen that the overall value range of the safety factor is between 0 and 3. The larger the value, the more dangerous the area is, and vice versa.

The evaluation results of safety factors are further divided by setting intervals to obtain the safety degree of complex terrain. Since the index value of each part of the area that satisfies the constraints of terrain conditions, landing speed and landing attitude is close to 0, and the value of any part exceeding the constraints is close to 1, so the overall value of the safety factor of the area that is judged suitable for landing is less than 1. The safety factor contour map shown in Figure 6(a) is obtained by analyzing the calculation results of the safety factor. Since the overall value range of the safety factor is (0,3), the part less than 1 is considered to satisfy the constraint. Here, its value is divided into 6 intervals, corresponding to different terrain safety degrees

The higher the degree of safety, the smaller the value of the safety factor, indicating that the landing is less dangerous. Corresponding the safety degree to the complex terrain, Figure 6(b) is obtained, in which the lighter the color is, the higher the safety degree is, and the safety of landing in this area is more guaranteed; on the contrary, the darker the color is, the greater the danger . In the subsequent landing process, the probe only needs to move towards an area with a high degree of safety to ensure the smooth completion of the landing task to the greatest extent.

The scope of protection of the present invention is not limited to the embodiments, which are used to explain the present invention, and all changes or modifications under the same principle and conceptual conditions as the present invention are within the scope of protection disclosed by the present invention.

Claims (5)

1. a complicated landform degree of safety appraisal procedure based on factor of safety, it is characterised in that: include as follows Step:

Step one, determine the factor of safety expression formula of materialization；Factor of safety is passed through to add by some questions index Power obtains, and in conjunction with mission requirements and detection target characteristic, chooses factor index, the employing needing to be estimated Functional form and weighting scheme, obtain embody factor of safety expression formula；

The definition of factor of safety is

$SI\stackrel{\mathrm{\&Delta;}}{=}F(factor1,factor2...factorN)---\left(1\right)$

Factor1, factor2...factorN are the factor index in factor of safety, and described factor index specifically includes that Topographic features, landing precision, landing speed and attitude, burnup, error and environmental disturbances；

In the case of considering above-mentioned factor index, the functional form of employing and weighting scheme, obtain one specifically The factor of safety changed；

Step 2, the complicated landform degree of safety of assessment；The factor of safety of the materialization obtained according to step one is to grid Complicated landform after change carries out quantitative evaluation；By arranging interval, by assessment result classification, obtain intricately Shape degree of safety.

A kind of complicated landform degree of safety appraisal procedure based on factor of safety, its It is characterised by: the concrete functional form that factor index described in step one is used both can be discrete function, also It can be the continuous function of change in limited range.

A kind of complicated landform degree of safety appraisal procedure based on factor of safety, It is characterized in that: the significance level of task success or failure is come by weighting scheme described in step one according to every kind of factor index Determine, if thinking that selected factor is close on task impact, making no distinction of rank, every some factors index can be given Identical weights；If a certain item or a few factors are bigger on task success or failure impact, then can be by strengthening this factor The weights of index, increase the proportion that this factor is shared in analysis result.

A kind of complicated landform degree of safety appraisal procedure based on factor of safety, its It is characterised by: the functional form that the factor index of factor of safety described in step one uses is: S type function, Min-max normalization function, polynomial function or trigonometric function.

A kind of complicated landform degree of safety appraisal procedure based on factor of safety, its It is characterised by: described in step 2, complicated landform degree of safety is the knot that the value to factor of safety carries out classifying rationally Really, indicating detector and land in the differently issuable danger in side size, degree of safety is the highest, its danger Dangerous the least；When selecting demarcation interval, need to combine the overall span of factor of safety and each The characteristics taking value of component assesses index, as far as possible by safety zone, deathtrap and intervenient fuzzy Region demarcates, and the rank number of degree of safety can be adjusted according to practical situation, comes complexity by degree of safety The success rate of landform landing task is weighed, thus reaches the purpose of assessment, rises for landing mission afterwards To directive function.