DEIMOS Engenharia - ICATTtrajectory.estec.esa.int/Astro/2nd-astro-workshop-presentations/021... ·...

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2nd European Workshop on Astrodynamic Tools and Techniques

ESTEC, Noordwijk, 13-15 September 2004

© 2004 DEIMOS Engenharia S.A. – www.deimos.com.ptDEI

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PLANAVImage-based Navigation for

Planetary Landers

Nuno Avila MartinsDr Miguel Belló MoraDeimos Engenharia S.A.

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The PLANAV ToolThe PLANAV Tool

• The Image-based Navigation for Planetary Lander (PLANAV) is a software tool with the following options:– Calculation and Visualisation of the Lander Optical System

image opportunity (characterisation of lander cameras)– Covariance Analysis and Monte Carlo simulation of the

expected landing location accuracy– Estimation of the Lander Location by using two methods:

• Navigation Filter (SRIF)• Two-cone intersection single point solution

– Estimation of Lander Attitude– Visualisation of Lander position dispersion error ellipse on

planetary maps• PLANAV has been developed by Deimos Engenharia

under contract with ESA/ESTEC

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• Overview of PLANAV architecture

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• Physical World Modelling

– Constants of Solar System (Sun, planets and most important natural moons)

– Planetary (Mars, Phobos and Deimos for Beagle 2) Rotational and Shape models

– Planets and Moons Ephemeris

– Planetary Topography model

– Planetary Gravitational model

– Planetary Atmospheric models

– Star Catalogue

– Reference Coordinate Systems

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• Phobos and Deimos Physical Models– An ellipsoidal model is selected for the shape of Phobos

and Demos:

• Phobos: 13.3 x 11.1 x 9.3 km

• Deimos: 7.5 x 6.2 x 5.4 km

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• Mars Topography– European MCD Mars atmosphere based on MOLA (Mars

Orbiter Laser Altimetry)

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• Image Opportunity Calculation

– The user selects a planet or moon as central body and a nominal landing position on the surface

– The tool scans over several user-defined time periods for navigation images where a set of selected targets bodies are in the FOV of the left and/or right camera

– A full camera optical model has been implemented to completely simulate the signal (digital number, SNR) of each pixel within the cameras

– Two different sets of filters (left/right) are implemented

– Sun elevation and eclipse conditions are checked

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• Optical System Model

– A number of factors jointly contribute to degrade the signal from objects and targets reaching the sensor

• Atmospheric condition (spectral optical depth)

• Optical system properties (f, f#, exposure time, …)

• CCD performance (pixel size, noises, CCD quantum efficiency)

– A full optical system model has been implemented to completely simulate the images actually seen by the camera. It includes:

• Radiometric Model

• Optical System Model (including atmospheric absorption)

• Sensor Model

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• Localisation Operational Strategies

– Two different Lander Location Operational Strategies have been implemented:

• Landing Site estimation using a navigation filter by starting with an a-priori knowledge and processing measurements (Covariance Analysis and Monte Carlo)

• Landing site estimation by single point solution computing the intersection of the two cones for each pair of stars and a root finder for the exact intersection of the ray with the accurate Mars topography model

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• Identification of Error SourcesError Source Comment Estimated value (1-σ) Formulation

Initial landing dispersion

Initial knowledge, input from flight dynamics

17 x 8 km (19º) to90 x 11 km (54º)

depends on nominal/safe mode, entry angle

To be estimated

Moon ephemeris Depends on JPL moon ephemeris file accuracy,dominant error

Phobos: 3 x 5 x 3 km or3 x 15 x 7 km

Deimos: 3x30x16 km

To be estimated, independent for each image or correlated as epocherror

Clock error Timestamp error, bias or white noise?

1 sec To be estimated as a bias, constant or independent for each image

Centerfinding Difference between center of image andc.o.g.

33 % rad. no correction< 10% rad. corrected

To be estimated for each moon and picture as a 2-component

Mars topography Altitude error 100 m level To be estimated

Star photocentricdetermination

Stars extending overmore than 1 pixel

< 1 pixel (1/4 pixel?) To be combined as 1-sigmarandom noise in the angularmeasurement, by the root square of the sum of squares of each contribution, in total between ½and 1 pixel

Atmospheric effects

Low for high elevation;the error in magnitude is only important for star identification

< 1 pixel (TBC)

Angle measurement

Camera distortion < 1 pixel (TBC)

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• Opportunities Visualisation Tool (OVT)

– Dual independent windows for easy comparison of image

opportunities in any combination of

• Epoch, Camera, Filter, FOV, SNR threshold, etc

Dual FOV for easy image comparison

Independent controls

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• OVT. Control and Display Panel

Image browser

Star data display on mouse clickFOV Zoom &

Camera selection

Object labels on/off

Filter selection

SNR threshold

LOS (Local coordinates)

Nominal Landing Site display

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LOS (Earth Coordinates.)

Image browser


Camera selection


Filter selection

SNR threshold selection



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*.TIFF picture saveQuit application

Image browser


Camera selection


Filter selection

SNR threshold



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Image browser


Camera selection


Filter selection

SNR threshold selection



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*.TIFF picture saveQuit application

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• OVT. Sky Plotting Window

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• Graphical User Interface

1. EditingInput Files

3. Viewing Output Files

2. Running Programs

1. EditingInput Files1. EditingInput FilesScrolling

Files

ResizingFrames

Choosing Applications

CurrentApplication

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• Lander Dispersion Map Display

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ConclusionConclusion

• Summary

– A user friendly, general and flexible software tool for optical navigation of planetary and natural moon landers has been developed

– A sophisticated optical system model is implemented, providing arealistic simulation of the navigation images

– Covariance Analysis, Monte Carlo and Estimation of lander location and attitude angles can be performed using different algorithms (navigation filter and 2-cone single point solution)

– Realistic simulation for Beagle-2 shows an expected accuracy in Mars of about 1 km in position and 0.03º in attitude estimation

– The tool flexibility has been demonstrated with examples for Mars, Europa and Mercury landers

DEIMOS Engenharia - ICATTtrajectory.estec.esa.int/Astro/2nd-astro-workshop-presentations/021... ·...

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Transcript of DEIMOS Engenharia - ICATTtrajectory.estec.esa.int/Astro/2nd-astro-workshop-presentations/021... ·...