vbnat: a european platform for descent & landing...

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ASTRIUM

Astrium Satellites

VBNAT: a European Platform for Descent & Landing Simulation and GNC Prototyping

3rd International Workshop on Astrodynamics Tools and TechniquesOctober 2nd-5th, 2006 ESTEC, Noordwijk,The Netherlands

Guillaume Bodineau, Xavier Sembely, ASTRIUM Satellites

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Astrium SatellitesThis document is the property of ASTRIUM. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed.

VBNAT Overview

• VBNAT : Vision-Based Navigation Analysis Tool.

• It corresponds to an overall simulation environment, including all the modules needed for the Visual Based Navigation.

• It has been developed in the frame of NPAL study for ESA, following an incremental approach, by a progressive upgrade of the simulation environment

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VBNAT Overview

NPAL: A technology Breakthrough for Vision Based Landing• ESA-Science Critical Technology Program (2001-2005)• Design of a navigation camera for autonomous Landers• Development of a generic validation test bench, virtual scenes• Real Time validation of the navigation functional chain

TDA in support of the BepiColombo missiondefinition

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Summary

1. Modelling the Physics

2. Simulating Reference Missions

3. Tool Functionalities

4. Simulated environment and integrated sensors

5. Integrated GNC Loop : from dynamic simulator to functional validation test bench

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• Simulating full descent phases and landing missions requires the use various complex models

• The objective is to be representative of the physics of the environment, of the spacecraft and of the various dynamical couplings to evaluate the performance of the descent and landing strategies, under realistic simulations.

• This implies the development of modular models, which can be adapted to each mission scenario :

- Spacecraft dynamics : full coupled 6 DoFs behaviour, parachute, sloshing perturbation

- Environment modelling : gravity model, atmosphere, wind representation

- Sensors and actuators : thruster configuration (main engine, reaction control and transverse control thrusters), IMU, Camera, LiDAR

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• Modular modules embedded within simulation framework

Vision-Based Navigation Analysis Tool V3.5

Actuators Sensors

GNC

Environment

z

1

ThrusterDemands

Thrust Power

RCS Power

Forces _vec_RSF

Torques_vec_RSF

Inertia_mat_RSF

Mass

Fuel Consumption

PROPULSION

OUTPUTS TO WORKSPACE

Forces_vec_RSF

Torques_vec_RSF

Inertia_mat_RSF

Mass

Fuel Consumption

Aspec_IPQ_RSF

W_ipq2rsf_RSF

dot_W_ipq2rsf_RSF

ActualState

ORBIT & DYNAMICS

LS position in Camera Screen

Visual Measurements

Velocity Increments

Attitude Increments

derivative Homography Matrix

Estimated State

Estimated LS Position in IPQ

NAVIGATION

Actual State LS Position in Camera Frame

Landing Site Projection : IPQ to Camera Screen

Aspec_IPQ_RSF

W_ipq2rsf _RSF

Attitude_Increments

Velocity_Increments

IMU

Estimated State

LS Position IPQ

Propulsion Power

Thruster Commands

Attitude Control Power1

GUIDANCE AND CONTROL

[ActualState][Mass]

[w_ipq2rsf][F_rsf]

0

In1

In2

In3

In4Covariance Analysis

Trajectory

vbn_Output.outputCovTraj

Constant

In1

In2

In3

Out1

Out2

ClosedLoopSwitch

Clock

Actual State

Aidings

XCam_ls

Visual Measurements

CAMERA

Actuators :Main engine, AOCS thrusters

Sensors :IMU, Camera, IP

Environment :S/C dynamics, Atmosphere,

parachute, sloshing, gravity

Navigation :Navigation Filter,

LS position estimation

G&C :Guidance laws,

position andAttitude control

Post-processing Covariance analysis

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Atmosphere model• Description of Mars atmosphere model is an input to the module providing

aerodynamics forces and torques applied to spacecraft

• Planet atmosphere model· Simple interpolated look-up table· Based on European Martian Climate Database

altitude (m) rho (kg.m -̂3)

Planet Atmosphere Model

1rho (kg.m^-3)

Atmosphere Look-UpTable

1altitude (m)

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Wind Gust Perturbation• Either deterministic wind gust perturbation (User-defined wind scenario)• Or stochastic wind gust perturbation (the user define the statistics)

Wind Prof ile

Wind Profi le Scenario

1Wind Profile

Wind VelocityZ axis

Wind VelocityY axis

Wind VelocityX axis

-C-

Start Time

Clock

Wind Prof iles Random

Wind Profile Random

integration of time during Wind gust duration

1Wind Profiles Random

start wind gust

windGustMagnitude

Wind Gust Magnitude

windGustDuration

Wind Gust Duration

windGustDirection

Wind Gust Direction

>=

<=

-C-

Probabil ity of wind gust occurence

NOT

1s

Integrator

1|u|

Abs

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Aerodynamics Perturbation• Aerodynamics Forces and Torques model• Impact of incidence angle on forces and torques: simplified calculation of the

aerodynamic coefficient versus incidence

Velocity RBF

rho(h)

Aerody namics_F_RBF

Aerody namics_T_RBF

AERODYNAMICSFORCES AND TORQUES MODEL

2

X Aerodynamics _ RBF X X RBF

2

Y Aerodynamics _ RBF Y Y RBF

2

Z Aerodynamics _ RBF Z Z RBF

1F S C V21F S C V21F S C V2

= ⋅ρ ⋅ ⋅ ⋅

= ⋅ρ ⋅ ⋅ ⋅

= ⋅ρ ⋅ ⋅ ⋅

uuuur

uuuur

uuuur

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Thrusters configuration• Various Thrusters configuration can be implemented • Implementation of thrusters selection algorithms

PressurantTank

Propulsion Tank

Reaction Control System

MSR Thrusters configuration as defined for the LiGNC

study

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Example of Propulsion system characteristics used for NPAL study

Thrusters configuration

Parameter 12 RCS thrusters

1 Main Engine

4 TCT thrusters

Isp 290 s 315 s 290 s

Nominal thrust 10 N or 22 N 2000 N to 4000 N 110 N Nominal direction +XRSF +XRSF

Thrust amplitude dispersion 1% of the nominal thrust 1% of the nominal thrust 1% of the nominal thrust Thrust direction dispersion 1° half-cone 1° half-cone 1° half-cone

Thrust modulation capacity Yes No Yes Actuation Period 50 ms Not Applicable 200 ms

Minimum Impulse Bit 30mNs Not applicable 300 mNs

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Spacecraft dynamics• Coupled 6 DoFs dynamics• Parachute model• Aerodynamics forces• Sloshing perturbation

ZTANK

M

Fuel Tank

XTANK

YTANK AP

an

FTANK

Up

L

CLiquid Fuel

V

M0,X0

M1,X1

M1 g

M0 g

-F1

F1

P

D(dX1/dt)

G

u

t

T


Modelling Sloshing perturbation

Parachute Model developed for Mars Scenario

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Various reference missions have been integrated within simulator environmentLibrary of reference missions and reference vehicles

• Lunar landing / Euro Moon

• BEPI Colombo / MSE

• Mars Missions :

- Exomars Lander

- Mars Sample Return Lander

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• Mission & landing site: The BepiColombo Mission • The reference mission for NPAL is BEPI-Columbo lander• The selected site : 80° of elevation, 36° from terminator line

Area of candidate landing sites as definedduring BC PM3, in Nov 2001

MPO Orbit1500 x 400 km

Descent Orbit465.5 x 10 km

∆V(1) = 250 m/s

∆V(2) = 3592 m/sPeriherm

MPO Orbit1500 x 400 kmMPO Orbit

1500 x 400 km

Descent Orbit465.5 x 10 kmDescent Orbit465.5 x 10 km

∆V(1) = 250 m/s

∆V(2) = 3592 m/s

∆V(1) = 250 m/s

∆V(2) = 3592 m/sPerihermPeriherm


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Trajectory point

Time from DOB (s)

Position Velocity (m/s) Trajectory phase

Phase duration (s)

Prior to DOB 0.0

Range : 5019.9 km

Ground range : 9208.2 kmAltitude : 400.0 km

2802

DOB 18.0

After DOB 18.0 Range : 5034.0 km


2696

Coast phase 3140.7

PDI 3158.7 Range : 589.9 km


3108

IGP 278.7

High gate 3437.4 Range : 21.9 km

Ground range : 20.1 km Altitude : 8.46 km

745.9

VGP 53.8

Low Gate 3491.2 Range : 147.5 m

Ground range : 40.0 m Altitude : 142 m

36.0

Final descent 2.4

MECO 3493.6 Range : 126 m

Ground range : 0.0 m Altitude : 126 m

0 Free fall

-22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 00

1

2

3

4

5

6

7

8

9

10

Range to go (km)

Alti

tude

(km

)

Reference trajectory - final approach

Low gate

High gate

Maximum dispersions at high gate1.5 km position, 25 m/s velocity

• Reference trajectory for a non atmospheric Lander

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High Level specification are based on landing scenario hypothesis20 m/s max. at touch-down50 m of horizontal accuracy30 m of altitude to avoid landing site contamination

MECO

Residual V

50 m: Horizontal accuracy 20 m/s:

Maximum Vertical Velocity

30 m: Minimum height at MECO


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Non Atmospheric scenarios Description• NPAL Reference Scenario : simulation starts with the S/C located at an altitude

of 8350 m

0 10 20 30 40 50 600

5000

10000

X (m

)

S/C Position in inertial frame : Mercury descent scenario

0 10 20 30 40 50 600

1

2x 10

4

Y (m

)

0 10 20 30 40 50 600

2000

4000

6000

Z (m

)

time (s)

0 10 20 30 40 50 6062

62.2

62.4

62.6

62.8

63

φ (d

eg)

S/C Attitude Euler angles (Euler convention (3,1,3) : Mercury descent scenario

0 10 20 30 40 50 60

-0.2

-0.1

0

0.1

0.2

θ (d

eg)

0 10 20 30 40 50 60150

155

160

165

170

ψ (d

eg)

time (s)

S/C Position S/C Attitude

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Scenarios Definition for Atmospheric lander• Navigation outline• Timeline of the descent from Entry Point to touchdown as evaluated in the LiGNC study

Atmosphere Entry Point (h = 120 km)

Drogue chute Deployment (h = 7 km)

Shield jettisoning

Main chute Deployment

High Gate

Main chute jettisoning

Propulsion Ignition Point

Landing Site Freezing

Final Descent Entry Point

Low Gate

Touchdown

~3.5 km~150 m

Atmosphere Entry Point (h = 120 km)

Drogue chute Deployment (h = 7 km)

Shield jettisoning

Main chute Deployment

High Gate

Main chute jettisoning

Propulsion Ignition Point

Landing Site Freezing

Final Descent Entry Point

Low Gate

Touchdown

~3.5 km~150 m

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Atmospheric scenarios Description• LIGNC Reference scenario

· retargeting manoeuvres had been tested and validated. It corresponds to a closed loop trajectory, obtained with realistic disturbances and manoeuvring capability.

· The trajectory starts at 3500 m, with 3 retargetings (first retargeting at 2000 m). Red crosses represent retargetingspositions.

-1000 -800 -600 -400 -200 0-500

0

500

1000

1500

2000

2500

3000

3500

4000

XLDS (m)

Z LDS (m

)

trajectory in the X-Z plane

referenceestimate

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Atmospheric scenarios Description• LIGNC Reference scenario

0 10 20 30 40 50 60 70 80 90-2

0

2

4

X A

ccel

erat

ion

(m/s

2 )

S/C Acceleration in IPQ

0 10 20 30 40 50 60 70 80 90-2

-1

0

1

2

Y A

ccel

erat

ion

(m/s

2 )

0 10 20 30 40 50 60 70 80 90-4

-2

0

2

Z A

ccel

erat

ion

(m/s

2 )

Time (s)

0 10 20 30 40 50 60 70 80 90-100

0

100

Γ p (d

eg/s

2 )

S/C Attitude angular acceleration

0 10 20 30 40 50 60 70 80 90-50

0

50

Γ q (d

eg/s

2 )

0 10 20 30 40 50 60 70 80 90-50

0

50

Γ r (d

eg/s

2 )

0 10 20 30 40 50 60 70 80 900

50

100

norm

(deg

/s2 )

Time (s)

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Atmospheric scenarios Description• Kinematics Parameters Variations• Variation range of the S/C representative variables (velocity, attitude), that can

be reached during the whole Martian descent.

Angular acceleration [- 50 ; 50] deg/s^2

S/C parameters Variation range Description

Velocity [2 ; 6300] m/s After Aeroshell braking phase, velocity is 450 m/s

Acceleration (m/s2) [1 ; 20] m/s2

High acceleration levels are due to Aeroshell braking, drogue chute deployment and retargeting manoeuvres. During final phase of the descent, vertical non-gravitational deceleration can reach around max value of 5 m/s2, and non gravitational acceleration can reach 3 m/s2 cross track during retargeting manoeuvres

Attitude (deg) [-30 ; +30] deg For cross track axis during retargeting phases Angular rates (deg/s) [-20 ; 20] deg/s For all axes during retargeting phases

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VBNAT : lander GNC design• Vision-Based Navigation Analysis Tool (VBNAT)

• Overall simulation environment• Incremental Development approach,

by a progressive upgrade of the simulation environment• Modular tool that can be easily adapted to integrate new functionalities• Intensive validation campaigns through reference scenarios, to guarantee

representativity of the models

PanguInputs for VBNAT 1.0

Navigation Algos

Image Processing Algos

FEIC board

VBNAT 1.0

VBNAT 2.0

VBNAT 3.0

VBNAT 4.0

Set-up of simulation environmentPangu Integration

Navigation performance

Nav & IP Algos performance

VBNAT update & improvement

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VBNAT Characteristics :• Modularity / Simulator Families

• Multi User

• Dedicated Post Treatments

• Campaign Facility· Monte Carlo / Parametric runs· Specific MultiRun Post Treatments· Also compatible with EADS Astrium’s internal Monte-Carlo tool « Astrostat »

• Genericity

• Support to prototyping of embedded solution

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• Post processing : • Navigation performances• Back-projection• tracking performances : Guidance

Realisation Errors, Navigation estimation Errors and Covariance, Homography Matrix, Landing Site Position

• Cumulative histograms, Impact diagram, Enveloppes

• Covariance Analysis Facility : • Inertial Navigation dispersions errors• Dynamic dispersions

• Multi Run Tool


3 4 4 0 3 4 5 0 3 4 6 0 3 4 7 0 3 4 8 0 3 4 9 0 3 5 0 0-8

-6

-4

-2

0

2

4

6

8

V e lo c i t y e s t im a t io n e r ro r , IP Q

Erro

r, m

/s

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

20

40

60

80

100Velocity error histogram, Along Track/Cross Track

0 0.01 0.02 0.03 0.04 0.05 0.060

20

40

60

80

100

Per

cent

age

of ru

ns

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

20

40

60

80

100

Value, m/s

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• Image generation/ Image Processing : • direct interface with PANGU• simulation of FEIC• management of feature points lists,

various selection methods

• Spacelab compatibility• Pangu Interface, read/write pgm image

files, Camera model, IMU


error

New pointTracked pointProjected point

error

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PANGU: virtual scene generator embedded, developped by University of Dundee• VBNAT PC : VBNAT under Matlab/Simulink environment with TCP/IP interface with PANGU

PC. Run the S/C dynamics, environment, GNC, and provides usefull information for image generation

• PANGU PC : PANGU uses Digital Elevation Model (DEM) of the terrain and Camera position and attitude to generate images at the Camera frequency. • Provides the image to the VBNAT environment• Hierachical level definition (up to 12), large terrain surfaces (100 km). • Future of PANGU : Towards integration of Real scenes : boulders, clouds…

Images

Vehicle true position and attitude

VBNAT PC PANGU PC

TCP/IP

-20000

20004000

60008000

1000012000

1400016000

-2000

0

2000

4000

0

1000

2000

3000

4000

5000

6000

7000

8000

Y (m)

Mercury descent scenario

Y

X

Z

Z (m)

X (m

)

S/C trajectory

S/C attitude

DEM

Image

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PANGU: virtual scene generator embedded

• Generation of Image sequences (using Pangu, and Camera Model)

• NPAL Simulation from Images stored « off-line »

• Full Loop NPAL Simulation (Nav+GC+CameraModel+IP)

ActualState

SceneRendering(PANGU)

TrackedPoints

ImageProcessing

ImagesCameraPhysicalModel

RawImages

DEM

LOS to tracked points

Actual position of trackedpoints

Navigation

Images stored off line

50 100 150 200 250 300 350 400 450 500

50

100

150

200

250

300

350

400

450

500


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Mars Descent – A visual Impression…

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PANGU LIDAR Model• The LIDAR model is composed of 2 elements:

• PANGU, which generates perfect Range images of a synthetic Martian terrain. Adaptations of PANGU:· Compatible with LIDAR scanning· Martian terrain feature (e.g. sand dune)

• A LIDAR physical model • Very similar to NPAL’s camera model

PANGU and True Martian terrain image: Which is which?


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Sensor models connected to Navigation and environment • Camera model

• Distorted image after geometrical distortions. • Blurred Image is the distorted image after blurring effects (optical, detector and

motion) and under sampling (aliasing effects).• Numerical Image is a digitised image including all the detector defects and noises

• IMU model• Gyrometer scale factor, angular noise, bias, and random drift

• Accelerometer scale factor, bias and noise


Distortion

MTF

Radiometry

vbn_PANGU_Image DistortedImage

BlurImage

NumericalImage

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VBNAT v4 : hardware in the loop• Progressive validation of Hardware components :

•Transition to real time test bench : Test of FEIC hardware within Simulink environment, withoutNavigation filter. Simple images sent to FEIC

• Non real time test bench :

Y axis

X axis

-1.5 pixel-0.5 pixel

Navigation Filter

USB SpaceWireinterface

Synchronisation withImage sequences

FEIC transtech board

Spacewire Minirouter

Tracking andcorrelation function

image

Aidings

T-list

USB Spacewire


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Development and validation activity towards real-time test bench


Actuators Sensors

GNC

Environment

z

1

ThrusterDemands

Thrust Power

R CS Power

Forces _v ec_RSF

Torques_v ec_RSF

Inertia_mat_RSF

Mass

Fuel Consumption

PROPULSION


Forces_v ec_RSF

Torques_v ec_RSF

Inertia_mat_RSF

Mass

Fuel Consumption

Aspec_IPQ_RSF

W_ipq2rsf _RSF

dot_W_ipq2rsf_RSF

ActualState

ORBIT & DYNAMICS


Visual Measurements

Veloc ity Increments

Attitude Increments

deriv ative Homography Matrix

Estimated State


NAVIGATION



Aspec_IPQ_R SF

W_ipq2rsf _RSF

Attitude_Increments

Veloc ity _Increments

IMU

Estimated State

LS Position IPQ

Propuls ion Power

Thruster Commands



[ActualState][Mass]

[w_ipq2rsf][F_rsf]

0

In1

In2

In3


Trajectory


Constant

In1

In2

In3

Out1

Out2

ClosedLoopSwitch

Clock

Actual State

Aidings

XC am_ls

Visual Measurements

CAMERA

FEIC development UoD VBNAT development Astrium VBNC Development

Galileo Avionica

VBNAT V4

USBspacewireinterface

SRAM board

FEIC SRAMUSB SpaceWire

spacewire

spacewire

Host station is VBNAT V4 and contains:Navigation algorithmsCamera interface functionsFEIC interface functionsOperating system is Windows XP

PCI NI 6534

Host station is ESG test bench and contains:Picture transfer function though NI 6534 boardOperating system is Windows XP

Camera developmentVbnat software simulink validation

FEIC simulation on ModelSim

Functional validation

FEIC validation on Transtech board


Actuators Sensors

GNC

Environment

z

1

ThrusterDemands

Thrust Power

R CS Power

Forces _v ec_RSF

Torques_v ec_RSF

Inertia_mat_RSF

Mass

Fuel Consumption

PROPULSION


Forces_v ec_RSF

Torques_v ec_RSF

Inertia_mat_RSF

Mass

Fuel Consumption

Aspec_IPQ_RSF

W_ipq2rsf _RSF

dot_W_ipq2rsf_RSF

ActualState

ORBIT & DYNAMICS


Visual Measurements

Veloc ity Increments

Attitude Increments

deriv ative Homography Matrix

Estimated State


NAVIGATION



Aspec_IPQ_R SF

W_ipq2rsf _RSF

Attitude_Increments

Veloc ity _Increments

IMU

Estimated State

LS Position IPQ

Propuls ion Power

Thruster Commands



[ActualState][Mass]

[w_ipq2rsf][F_rsf]

0

In1

In2

In3


Trajectory


Constant

In1

In2

In3

Out1

Out2

ClosedLoopSwitch

Clock

Actual State

Aidings

XC am_ls

Visual Measurements

CAMERA

FEIC development UoD VBNAT development Astrium VBNC Development

Galileo Avionica

VBNAT V4

USBspacewireinterface

SRAM board

FEIC SRAMUSB SpaceWire

spacewire

spacewire


PCI NI 6534


Camera developmentVbnat software simulink validation

FEIC simulation on ModelSim

Functional validation

FEIC validation on Transtech board

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End to end validation • Real Time test bench

spacewire


PCI NI 6534



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End to end validation • Example of results with Mercury descent validation test

Distance to mean plane

Cross-track velocity Along-track velocity


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End to end validation • Example of results with Mercury descent performance test

Distance to mean plane

Track Ids Correlations


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End to end validation

• Mercury Scenario

• Mars Scenario

Play video

Play video

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Synthesis

• Lot of modules and functionalities have been developed for the VBNAT framework :• DKE module with library of reference scenarios and reference landers• Interface between Dynamics and environment simulation : embedded image

generation module• Interface between image generation and navigation sensor : simulated camera

and Lidar, real navigation camera allowing hardware in the loop simulations, back projection of the tracked points in the simulated environment

• Design and validation of full hybrid navigation solution, based on inertial measurements and image sensor (Camera, Lidar)

• Performance assessment of the navigation in the simulation environment and in real-time

• Test of Guidance and Piloting algorithms : MBTL Guidance law, Hazard avoidance algorithms, retargeting

• Towards a full closed-loop simulator :• Hazard avoidance / Hazard Mapping coupled with Guidance and Control

module• Landing Site Designation, retargeting capabilities with Closed loop Guidance

and Navigation

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Mars Landing: Mars Sample Return as ReferenceMission

• The Challenge of a Soft Landing

Mars Sample Return

vbnat: a european platform for descent & landing...

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