CN105203114A - Planet safe landing point online selecting method - Google Patents

Abstract

The invention discloses a planet safe landing point online selecting method, and belongs to the technical field of deep space exploration. The planet safe landing point online selecting method comprises the following steps of step 1: after obtaining a mobile ability periphery, taking the intersection of an area covered by mobile ability and the view of a sensor, and taking the intersection range as a safe landing point range; step 2: obtaining the information about terrain safety, landing speed and burn-up amount online in real time, and utilizing a safe landing point selecting index overall considering the terrain safety, the landing speed and the burn-up amount to select a safe landing point. According to the planet safe landing point online selecting method, the view of the sensor and the mobile ability are overall considered, and the safe landing point is selected in real time by combining the terrain safety, the landing speed and burn-up, so that a detector can avoid obstacles, and meanwhile, lands on the surface of a planet with a lower speed and burn-up, thereby improving the safety and the reliability of a detecting task, and providing a technical support and reference for a planet landing task.

Description

The online choosing method of a kind of planet safe landing point

Technical field

The present invention relates to the online choosing method of a kind of planet safe landing point, belong to field of deep space exploration.

Background technology

The planetary surface precision of information that can obtain due to ground is limited, the obstacle of reduced size often could accurately obtain when distance planetary surface is nearer, and due to the factor such as navigation error, model uncertainty in landing mission, may there is larger departing from nominal state in the virtual condition of detector, thus cause detector cannot accurately arrive expected point of impact or occur that expected point of impact surrounding terrain complexity is unfavorable for the situations such as landing.Traditional obstacle detection and bypassing method focus on the analysis to terrain obstruction, have ignored the impact of landing mission on landing tasks secure.And in the method choosing landing point, then lack the analysis and thinking to selection range and index for selection method for expressing.In order to address these problems, need a kind of real-time online to choose the method for landing point, both having considered the security in detector landing mission, current terrain obstruction can be evaded again, thus improve the security of landing task.

Summary of the invention

The online choosing method of a kind of planet safe landing point disclosed by the invention, the technical matters solved is by providing a kind of online choosing method of planet safe landing point considering many factors, detector is effectively averted danger region, land in the area of safety with very little landing speed and less burnup, and the safety and reliability of planetary landing task can be improved, for following planetary landing task provides technical support and reference.Wherein, choose at planet safe landing point the factor considered in process and comprise viewing field of camera, detector self maneuverability, and affect the factor of safe landing, as landform, landing speed, burnup etc.

The object of the invention is to be achieved through the following technical solutions:

The online choosing method of a kind of planet safe landing point disclosed by the invention, refer in decline process, consider sensor visual field and detector maneuverability determination landing point selection range, and landform and landing data are assessed, thus select safe landing point in real time.

The online choosing method of a kind of planet safe landing point disclosed by the invention, comprises the steps:

Step 1: determine safe landing point selection range.After obtaining maneuverability border, common factor is got in the region cover maneuverability and the sensor visual field, and using this intersection range as safe landing point selection range, the landing point for step 2 is selected.

The selection range of safe landing point is determined jointly by sensor field range and detector maneuverability.Herein, sensor is mainly camera, and the maneuverability of detector is weighed by burnup ellipse.

For obtaining high pixel resolution image and making image overlapping region more, for planetary detection optical camera field angle generally between 20 to 50 degree between.When camera perspective is 45 degree, image resolution ratio and image Overlap syndromes effect best.The field range of camera is by the impact of detector attitude with height, consider that detector is less in descending branch attitudes vibration amplitude, only using taking pictures highly as the factor affecting field range, highly higher, field range is broader, and the area carrying out observing is also more.

Maneuverability refer to detector exhaust all carry fuel time the maximum distance that can fly to.Detector is mainly derived from high-power trust engine in the burnup of descending branch.Before the section of falling starts under power, the maneuverability within the scope of detector 360 degree can be calculated by status predication, fuel mass etc.Specifically, the maneuvering range of detector is in following burnup ellipse

$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1---\left(1\right)$

Its semi-major axis a and semi-minor axis b is

$\left\{\begin{array}{c}a=\frac{({\mathrm{\ΔV}}^2-2E/m)\mathrm{\Δ}t}{2\mathrm{\Δ}V(1-{(v_H/\mathrm{\Δ}V)}^2)}\\ b=a\sqrt{1-{(v_H/\mathrm{\Δ}V)}^2}\end{array}\right.---\left(2\right)$

In above formula, Δ V refers to the maximal rate increment that can change in burnup allowed band, and E refers to the energy of detector, and m is the quality of detector, and Δ t is residue landing times, v _hfor horizontal velocity.

By initial position r ₀, initial velocity v ₀and the impact of various constraint, described various constraints refer to the constraint determining camera fields of view and maneuverability scope, comprise viewing field of camera angle θ, maximal rate increment Delta V, detector energy E, detector quality m and landing times Δ t, camera fields of view may be contained in maneuvering range completely, also may be crossing with maneuvering range, namely some camera fields of view region is outside maneuverability scope, the extraneous region of maneuverability, beyond the maneuverability of detector, is therefore not suitable for as final touch-down zone and should be rejected.After calculating maneuverability border, also need the region of maneuverability covering and camera fields of view to get common factor, using this intersection range as safe landing point selection range, the landing point for step 2 is selected.

Step 2: online Real-time Obtaining landform security, landing speed and burnup size information, utilize consider landform security, the formula (3) of landing speed and burnup size selects safe landing point.

$LSSI={\mathrm{\τ}}_1\frac{1}{1+e^{c(R/|\left|r_f\right||-1)}}+{\mathrm{\τ}}_2\frac{v_{fz}-v_{fz\min }}{v_{fz\max }-v_{fz\min }}+{\mathrm{\τ}}_3\frac{PMF-{\mathrm{PMF}}_{\min }}{{\mathrm{PMF}}_{\max }-{\mathrm{PMF}}_{\min }}---\left(3\right)$

Wherein, τ _i(i=1,2,3) are every weight, and determine that every part in formula (3) affects size to result, through normalized, the value of every part is all in [0,1].

Described safe landing point index for selection LSSI choosing method is:

In order to ensure the security of landing, first it is envisaged that the security of landform.The security of landform comprises two aspects: the barrier size in touch-down zone must within detector tolerable scope; Touch-down zone is sufficiently large with the maximum landing deviation meeting detector.Given this, after obtaining terrain information, first to the obstacle in visible range be identified, the pixel at the place, region constituted a threat to detector is labeled as dangerous pixel, all the other are labeled as safe pixel, determine the radius of safety R of each safe pixel, then estimate landing deviation r by navigation error, execution error and external interference _f, adopt formula (4) to obtain landform safety evaluation index

$I_t=\frac{1}{1+e^{c(R/|\left|r_f\right||-1)}},c>0---\left(4\right)$

Given landing deviation r _f, by choosing suitable parameter c, landform safety evaluation index I _tcan ensure that nearly all radius of safety R is less than landing deviation r _fregion get 1, be greater than landing deviation r _fregion get 0.The region of getting 1 means have obstacle to exist in landing ellipse, and the region of getting 0 then means in whole landing ellipse it is all safe, thus is distinguished in the region and hazardous location that can be used for safe landing.When c is larger, the value more than 90% of whole index is all 0 or 1.As radius of safety R and landing deviation r _fwhen size is close, landform safety evaluation index I _tthere will be violent change, show now have obstacle to exist at the oval boundary that lands.

After ensure that landform safety, also need the landing speed v considering detector _f.Landing speed is crossed conference at the component of vertical direction and is caused fatal harm to detector, and its two components in the horizontal direction then likely cause detector turn on one's side or topple over, and considers emphatically vertical direction component v herein _fz.For landing speed v _fzestimation need to add navigation error equally, perform error and external interference.The patient maximum impact speed of Mars probes is generally 3m/s, actual landing speed v _fzonce exceed maximum impact speed, then may cause the damage of detector self structure and interior instrument, therefore need to choose landing speed v in evaluation process _fzregion little as far as possible.

In addition, the burnup situation in landing mission should also be considered.The fuel that can carry due to detector is limited, in order to ensure that the safety of landing task completes, should choose the less place of burnup as far as possible and landing.The burnup fuel mass of whole power dropping section characterizes than PMF

$PMF=\frac{{\∫}_{t_0}^{t_f}\stackrel{\·}{m}dt}{m_0}=1-e^{-\frac{\underset{i=1}{\overset{N}{\Σ}}\left|\right|a_i\left|\right|\mathrm{\Δ}t}{I_{sp}{g}_e}}---\left(5\right)$

Consider landform security, landing speed and burnup, obtain safe landing point index for selection LSSI:

$LSSI={\mathrm{\τ}}_1\frac{1}{1+e^{c(R/|\left|r_f\right||-1)}}+{\mathrm{\τ}}_2\frac{v_{fz}-v_{fz\min }}{v_{fzmax}-v_{fz\min }}+{\mathrm{\τ}}_3\frac{PMF-{\mathrm{PMF}}_{\min }}{{\mathrm{PMF}}_{max}-{\mathrm{PMF}}_{\min }}---\left(6\right)$

Wherein, τ _i(i=1,2,3) are every weight, and determine that every part in formula (6) affects size to result, through normalized, the value of every part is all in [0,1].

The Weight Value Distributed Methods determination safe landing point index for selection LSSI of preferred formula (7).

$\left\{\begin{array}{c}{\mathrm{\τ}}_1=1\\ {\mathrm{\τ}}_2=\frac{{\mathrm{sum}}_2}{{\mathrm{sum}}_2+{\mathrm{sum}}_3}\\ {\mathrm{\τ}}_3=\frac{{\mathrm{sum}}_3}{{\mathrm{sum}}_2+{\mathrm{sum}}_3}\end{array}\right.---\left(7\right)$

Due to landform safety evaluation index I _tvalue is 0 or 1 time most, and therefore, the value of the point of the safe landing corresponding to the region index for selection LSSI of safety is all less than 1, and dangerous region is then greater than 1, and the coordinate at global minimum place is new safe landing point.

Beneficial effect:

The online choosing method of a kind of planet safe landing point disclosed by the invention, consider camera fields of view and maneuverability, Combining with terrain security, landing speed and burnup, choose safe landing point in real time, make detector while avoiding obstacle, land at planetary surface with less speed and burnup, thus the safety and reliability of detection mission can be improved.

Accompanying drawing explanation

Fig. 1 is the online choosing method process flow diagram of a kind of planet safe landing point disclosed by the invention;

Fig. 2 is emulation topomap used;

Fig. 3 is landing point selection range figure;

Fig. 4 is that safe landing point chooses process and result figure.

Embodiment

In order to better objects and advantages of the present invention are described, below in conjunction with accompanying drawing and example, summary of the invention is described further.

In this example, the specific impulse I of trust engine _spfor 225s, detector quality m is 1905kg, and maximal rate increment Delta V is 190m/s, and landing times Δ t is 35s, the initial position r of detector power dropping section ₀for [-300 ,-200,1700] m, initial velocity v ₀for [18,20 ,-80] m/s, negative sign represents that direction straight down.The landform adopted in emulation is shown in Fig. 2.

Disclosed in the present embodiment, the online choosing method of a kind of planet safe landing point, comprises the steps:

Step 1: determine safe landing point selection range.After obtaining maneuverability border, common factor is got in the region cover maneuverability and the sensor visual field, and using this intersection range as safe landing point selection range, the landing point for step 2 is selected.

Given descending branch dynamics, after weighing pixel resolution and image overlapping cases, select the camera of 45 degree of field angle, when not considering detector attitude, suppose camera and plane-parallel, take ground, power dropping section elemental height is 1700m, using this height as shooting and computed altitude.By detector initial position r ₀, initial velocity v ₀, maximal rate increment Delta V, detector energy E, detector quality m, landing times Δ t substitute into formula (2), obtain the semi-major axis a=1537.4m of burnup ellipse, semi-minor axis b=1521.9m, and then the maneuverability scope that can draw detector in XY plane.As shown in Figure 3, wherein, grey filled lines is the former landing path of detector to MATLAB simulation result, and in XY plane, solid-line rectangle is camera fields of view, and dotted ellipse is detector maneuverability scope.Under given starting condition, detector maneuverability contains camera fields of view completely, therefore only need in field range application safety landing point choosing method, final landing point can be obtained.

Step 2: online Real-time Obtaining landform security, landing speed and burnup size information, utilize consider landform security, the formula (3) of landing speed and burnup size selects safe landing point.

When considering landform security, landing deviation r _fbe decided to be 50m, landform safety evaluation index parameter c=50, carries out obstacle analysis to the landform that Fig. 2 provides, calculates the radius of safety R of each point in selection range, result is substituted into formula (4), obtains the landform safety evaluation index I of each point _t.When analyzing detector landing speed, add the model of the execution error of 5% and the wind of Follow Weibull Distribution, carry out by sliding mode guidance the final landing speed v calculating each point _fz.Similarly, calculate with sliding mode guidance and formula (5) fuel mass arriving every bit in selection range and compare PMF.The result of calculation of landform security, landing speed and burnup index is through min-max normalized, and result is as shown in Fig. 4 a, 4b, 4c.Calculate weight according to the weighting scheme provided in formula (7) and obtain τ=[1,0.5789,0.4211], result is substituted into formula (6), draw the value condition of the whole point of safe landing within sweep of the eye index for selection LSSI as shown in figure 4d, the position coordinates calculating safe landing point is [1166,-1389,0], value and the global minimum of this some place index for selection LSSI are 0.3558, and this point is selects safe landing point.

Scope is not only confined to embodiment, embodiment for explaining the present invention, all changes with the present invention under same principle and design condition or revise all within protection domain disclosed by the invention.

Claims (6)

1. the online choosing method of planet safe landing point, is characterized in that: comprise the steps:

Step 1: determine safe landing point selection range; After obtaining maneuverability border, common factor is got in the region cover maneuverability and the sensor visual field, and using this intersection range as safe landing point selection range, the landing point for step 2 is selected;

Step 2: online Real-time Obtaining landform security, landing speed and burnup size information, utilize consider landform security, the formula (3) of landing speed and burnup size selects safe landing point;

$LSSI={\mathrm{\τ}}_1\frac{1}{1+e^{c(R/|\left|r_f\right||-1)}}+{\mathrm{\τ}}_2\frac{v_{fz}-v_{fz\min }}{v_{fzmax}-v_{fz\min }}+{\mathrm{\τ}}_3\frac{PMF-{\mathrm{PMF}}_{\min }}{{\mathrm{PMF}}_{max}-{\mathrm{PMF}}_{\min }}---\left(3\right)$

Wherein, τ _i(i=1,2,3) are every weight, and determine that every part in formula (3) affects size to result, through normalized, the value of every part is all in [0,1].

2. the online choosing method of a kind of planet safe landing point as claimed in claim 1, is characterized in that: the concrete methods of realizing of described step 1 is:

The selection range of safe landing point is determined jointly by sensor field range and detector maneuverability; Herein, sensor is mainly camera, and the maneuverability of detector is weighed by burnup ellipse;

For obtaining high pixel resolution image and making image overlapping region more, for planetary detection optical camera field angle generally between 20 to 50 degree between; The field range of camera is by the impact of detector attitude with height;

Maneuverability refer to detector run out all carry fuel time the maximum distance that can fly to; Detector is mainly derived from high-power trust engine in the burnup of descending branch, before the section of falling starts under power, calculates the maneuverability within the scope of detector 360 degree by status predication, fuel mass etc.; The maneuvering range of detector is in following burnup ellipse

$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1---\left(1\right)$

Its semi-major axis a and semi-minor axis b is

$\left\{\begin{array}{c}a=\frac{({\mathrm{\ΔV}}^2-2E/m)\mathrm{\Δ}t}{2\mathrm{\Δ}V(1-{\left(v_H/\mathrm{\Δ}V\right)}^2)}\\ b=a\sqrt{1-{(v_H/\mathrm{\Δ}V)}^2}\end{array}\right.---\left(2\right)$

In formula (2), Δ V refers to the maximal rate increment that can change in burnup allowed band, and E refers to the energy of detector, and m is the quality of detector, and Δ t is residue landing times, v _hfor horizontal velocity;

By initial position r ₀, initial velocity v ₀and the impact of various constraint, described various constraints refer to the constraint determining camera fields of view and maneuverability scope, comprise viewing field of camera angle θ, maximal rate increment Delta V, detector energy E, detector quality m and landing times Δ t, camera fields of view may be contained in maneuvering range completely, also may be crossing with maneuvering range, namely some camera fields of view region is outside maneuverability scope, the extraneous region of maneuverability, beyond the maneuverability of detector, is therefore not suitable for as final touch-down zone and should be rejected; After obtaining maneuverability border, also need the region of maneuverability covering and camera fields of view to get common factor, using this intersection range as safe landing point selection range, the landing point for step 2 is selected.

3. the online choosing method of a kind of planet safe landing point as claimed in claim 1 or 2, is characterized in that: described safe landing point index for selection LSSI choosing method is:

In order to ensure the security of landing, first it is envisaged that the security of landform; The security of landform comprises two aspects: the barrier size in touch-down zone must within detector tolerable scope; Touch-down zone is sufficiently large with the maximum landing deviation meeting detector; After obtaining terrain information, first to the obstacle in visible range be identified, the pixel at the place, region constituted a threat to detector is labeled as dangerous pixel, all the other are labeled as safe pixel, determine the radius of safety R of each safe pixel, then estimate landing deviation r by navigation error, execution error and external interference _f, adopt formula (4) to obtain landform safety evaluation index

$I_t=\frac{1}{1+e^{c(R/|\left|r_f\right||-1)}},c>0---\left(4\right)$

Given landing deviation r _f, by choosing suitable parameter c, landform safety evaluation index I _tcan ensure that nearly all radius of safety R is less than landing deviation r _fregion get 1, be greater than landing deviation r _fregion get 0; The region of getting 1 means have obstacle to exist in landing ellipse, and the region of getting 0 then means in whole landing ellipse it is all safe, thus is distinguished in the region and hazardous location that can be used for safe landing; When c is larger, the value more than 90% of whole index is all 0 or 1; As radius of safety R and landing deviation r _fwhen size is similar, landform safety evaluation index I _tthere will be violent change, show now have obstacle to exist at the oval boundary that lands;

After guaranteeing landform safety, also need the landing speed v considering detector _f; Landing speed v _fcross conference at the component of vertical direction and cause fatal harm to detector, its two components in the horizontal direction then likely cause detector turn on one's side or topple over, and consider emphatically vertical direction component v herein _fz; For landing speed v _fzestimation need to add navigation error equally, perform error and external interference; Actual landing speed v _fzonce exceed maximum impact speed, then may cause the damage of detector self structure and interior instrument, therefore need to choose landing speed v in evaluation process _fzregion little as far as possible;

In addition, the burnup situation in landing mission should also be considered; The fuel that can carry due to detector is limited, in order to ensure that the safety of landing task completes, should choose the less place of burnup as far as possible and landing; The burnup fuel mass of whole power dropping section characterizes than PMF

$PMF=\frac{{\∫}_{t_0}^{t_f}\stackrel{\·}{m}dt}{m_0}=1-e^{-\frac{\underset{i=1}{\overset{N}{\Σ}}\left|\right|a_i\left|\right|\mathrm{\Δ}t}{I_{sp}{g}_e}}---\left(5\right)$

Consider landform security, landing speed and burnup, obtain safe landing point index for selection LSSI:

$LSSI={\mathrm{\τ}}_1\frac{1}{1+e^{c(R/|\left|r_f\right||-1)}}+{\mathrm{\τ}}_2\frac{v_{fz}-v_{fz\min }}{v_{fzmax}-v_{fz\min }}+{\mathrm{\τ}}_3\frac{PMF-{\mathrm{PMF}}_{\min }}{{\mathrm{PMF}}_{max}-{\mathrm{PMF}}_{\min }}---\left(6\right)$

Wherein, τ _i(i=1,2,3) are every weight, and determining in formula (6) every part affects size to result, and through normalized, the value of every part is all in [0,1].

4. the online choosing method of a kind of planet safe landing point as claimed in claim 3, is characterized in that: the Weight Value Distributed Methods determination safe landing point index for selection LSSI of preferred formula (7),

$\left\{\begin{array}{c}{\mathrm{\τ}}_1=1\\ {\mathrm{\τ}}_2=\frac{{\mathrm{sum}}_2}{{\mathrm{sum}}_2+{\mathrm{sum}}_3}\\ {\mathrm{\τ}}_3=\frac{{\mathrm{sum}}_3}{{\mathrm{sum}}_2+{\mathrm{sum}}_3}\end{array}\right.---\left(7\right)$

Due to landform safety evaluation index I _tvalue is 0 or 1 time most, and therefore, the value of the point of the safe landing corresponding to the region index for selection LSSI of safety is all less than 1, and dangerous region is then greater than 1, and the coordinate at global minimum place is new safe landing point.

5. the online choosing method of a kind of planet safe landing point as claimed in claim 4, is characterized in that: when camera perspective is 45 degree, image resolution ratio and image Overlap syndromes effect best.

6. the planet safe landing method of guidance chosen online of a kind of landing point as claimed in claim 4, is characterized in that: the described patient maximum impact speed of Mars probes is 3m/s.