SONC Flight Dynamics TeamT.Martin , E.Jurado, A.Blazquez, E.Canalias (CNES), R.Garmier,T. Ceolin (CS-SI)

Use of Scilab for the Philae landing on comet Churyumov-Gerasimenko

Credits ESA/ROSETTA/NAVCAM

Outline

I. Comets and Rosetta / Philae mission II. Landing site selection and Landing

operations III.The SONC-FD operational tools and scilab

useIV.Conclusion

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(I)Comets

and Rosetta / Philae mission

Comets and Rosetta mission - Comets■Most primitive objects in the Solar System.

� Record of the physical & chemical processes of the Solar System formation.

■Formed at large distances from the Sun and have been preserved at low temperatures.

■The comets begins to sublimate when the orbit swings in towards the Sun (perihelion).

■Composition: water, CO & CO2, rocks, dust with organics material based on C, N.

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Flyby of comet Halley by Giotto in 1986 (first comet close observation ESA)

All comets visited by spaceprobes before Rosetta

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Science objectives:� Better understanding of the formation of the

solar system� Search for complex organic molecules that could

have been brought to Earth by comets� Did the main ingredients for life come from outer

space?

Mission objectives:� Undertake a lengthy exploration of a

comet at close quarters to watch how it is transformed by the warmth of the Sun along its elliptical orbit

� Land a probe on a comet’s nucleus for in-situ analysis

Main objectives of the Rosetta mission

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■Rosetta� Main structure : 2.8 x 2.1 x 2.0 m� Length of the solar arrays : 32 m x

2� Total mass : 3,000 kg� Propellant mass : 1,670 kg � Number of science instruments :11

■Philae� Size : 0,8 x 0,8 x 0,8m� Mass : 96 kg� Number of scientific instruments :10� 2 batteries + 6 solar arrays� Autonomy with the batteries only

~50 h� Specific equipment

• Active Descent System (a small thruster)

• Harpoons

Comets and Rosetta mission – Satellite and lander

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2 world firsts realized by Europe :

First time that a satelitte (Rosetta) orbits a comet

First time that a probe (Philae) lands « softly » on a comet

Credits ESA/ROSETTA/CIVA

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: 2004 - 2014

■Period around the sun: 6.44 y■Aphelion : 6,2 AU■Perihelion : 1,2 AU (1AU = 149

millions km■Size : 4,1 km x 2,5 km x 2 km■Volume: ~33 km3

■Density : 400-500 kg/m3 (like a poplar)

■Rotation Period 12,4 h■Stable rotation axis

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67P Churyumov-Gerasimenko (1)

4.1

km

2 km

Scilabtec2015

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67P Churyumov-Gerasimenko (2)

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Complex shape• Very irregular surface with a

wide variety of geological features (pit, pick, ridge, dust deposit, rocks, outcrop, cliff…)

Weak and irregular gravity field• Due to the composition (high

porosity)• Due to possible heterogeneity• Due to the complex shape

Outgassing• Sublimation of ice through solar

illumination• Pushing away Rosetta & Philae

Credits ESA/ROSETTA/NAVCAM

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(II)Landing site selection and Landing operations

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The ground segment

Lander Control Center (LCC) • Control of Philae

Rosetta Science Ground Segment (RSGS)• Planification of Rosetta science instruments

SONC: Science Operation and Navigation Center • Provide data for the Landing

Site Selection Process (LSSP)• Planification of the scientifique

instruments .

RMOC: Rosetta Mission OperationCenter (RMOC)• Rosetta flight dynamics• Interface Earth/Rosetta

Landing Site Selection Process: A convergent approach

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■Comet environment: almost unknown before Rosetta arrival in august 2014

■Balance between risks and knowledge : � comet is going closer to the sun => the outgassing is

increasing =>the landing risk is increasing

� As Rosetta is coming closer to the comet => the knowledge on the comet is increasing…

■Landing Site Selection Process:� 4 months to find a landing site (between 08/2014 –

10/2014 )� A complex mechanism! 4 centers across Europe

working together more or less simultaneously. � Necessity to synchronize the activities. (i.e. if data or

a product is not available on time, the whole process may be endangered! )

Credits ESA/ROSETTA/NAVCAM

Landing Site Selection Process milestones

5/28/201528/05/2015

Days to Landing

Date/min distance to

cometMilestones

L-79 24/08/2014 50 km

5 candidate landing sites

L-58 14/09/2014 30 km

nominal and backup landing sites

L-30 12/10/2014 10 km

confirmation of the choice of the nominal

landing site.

beginning of operational preparation

Nominal site

Credits ESA/ROSETTA/NAVCAM

Landing site (OSIRIS)

The landing operations: schedule

Nominal site

Image RolisAltitude ~ 40 m

■Science During Landing phase (SDL)� Philae/Rosetta release� 10 h long descent

• Landing gear and payload deployment (20 min after release)

• Scientific activities (instrument calibration, measurement, photo…)

■First Science Sequence (FSS)� Using only batteries, circa 50h� All instruments supposed to be used

■Long Term Science (up to the death of Philae) (LTS)

� Recharging battery through solar arrays� Up to the death of Philae

Image RolisAltitude ~ 3 km

The landing operations: reality

Nominal site

■Descent and landing� Landing 1 min later and 70 m

away from targeted!!!!! (dispersion ellipse 1 km long!)

� Anchoring system failed => 3 rebounds, 2 extra hours of flight

■The first science sequence � 57 hours of measurement including

the extra flight. � 80% of the nominal plan was

realized

■The Long term science (???)� Very bad illumination of the lander

due to the comet shadowing: impossible to refuel the batteries

� Waiting for more sunny days if Philae is surviving to the cold… Credits ESA/ROSETTA/NAVCAM

First TD 15h34:

Collision with crater rim 16h20m

Second TD 17h24

Final TD17h31

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(III)The SONC-FD operational

Tool & scilab use

SONC – FD

■Hardware� 2 computers (quadri-core processor)� 2 laptops (back office work , LSSP meeting )

■Flight Dynamics team: � 3 x 2 persons� Working 20h/24h during the LSSP � Working 24h/24h during the SDL/FSS

■Flight Dynamics System = tools ■ Operating system : linux■ First development of prototypes in 1995!!!

1) a set of tools for critical computations 2) visualization tools (2D, 3D, 3D + time)

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FDS tools

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Context� Critical tools => highly validated� Fortran 90 + GUI� Fortran tools industrialized and maintained by a

contractor=> If a problem occurred during the operation, obligation to wait at least 24h to receive a patch…

■Type of computation for the landing:� input preparation (format, frame transformation…)� model preparation � Illumination of the comet� Trajectories & landing conditions� Communication slots between Rosetta/Philae� Event prediction (when the comet enter/leaves the

field of view of a Philae Camera…)

■Type of computation for the First Science Sequence

� Lander position and attitude determination� Lander illumination computations� Communication slots between Rosetta/Philae

The scilab ecosystem

■SCILAB� Version V5.4.1, 64 bits

■CELESTLAB (CNES)� library of space mechanics functions for Scilab (not specific to Philae)� developed & maintained by CNES� Goals: attitude computation, elementary maneuver computation, change of

reference frame, change of coordinate systems, ... � Metrics: 440 functions/52 000 lines of codes� http://atoms.scilab.org/toolboxes/celestlab

■TRACELAB (CNES-SONC FD)� Dedicated to SONC-FD needs � Developed and maintained by SONC FD …� Data processing and vizualisation� GUI� Metrics: ~320 functions/ 37 000 lines of codes/17 GUI� Not available to public

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Tracelab : Computations

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■Reading/writing almost all inputs/output s data of FDS

■Mission frames transformation� More than 10 frames (comet inertial and fixed frame, Philae

frame, instrument frames, landing site frame…

■Comets environments� Rotation� Gravity field� Outgassing

■Comets topography and DTM� Global properties (volume, center of mass)� Roughness analysis� Mesh generation

■Statistic and probability analysis� Monte Carlo post post-processing (min, max, mean, std, pdf,

cdf, dispersion ellipse,…)� Boulder statistics: evaluation of the risk to land in a boulder

■Geometry computations� Communication link between Rosetta/Philae� …

Tracelab : Visualisation

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■« low level plot» : almost direct plot of a file (no complex processing of the input data)

■« high level plot »: processing of one or several input files/data

� Example: dynamics slop (angle between plumb-line direction and local normal to the surface) : shape model, rotation model, gravity model

Use of Scilab/Celestlab/Tracelab (1)

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■Preparatory studies (2010 to now)� Comet environment analysis� Mission design� …

■Support to scientific community of Philae� Example: Support to realize the « Rosetta selfie »

■FDS development (2011–November 2014)� Realization of prototypes with scilab� Specification of needs� Validation of the FDS � Investigation on strange behavior, bugs…

Selfie (CIVA camera)

Use of Scilab/Celestlab/Tracelab (2)

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■ Landing Site Selection Process (July 2014 – November 2014)

■ Landing & First Science Sequence (12 November – 15 November)

■ Long Term science sequence preparation & post flight activities (15 November 2014 – now)

� Reconstruction of the events (landing, rebounds, final landing)� Determination of Philae attitude and position� Long term Prediction of Philae shadowing

Landing site with the 1km landing ellipse (OSIRIS)

Philae during its landing (OSIRIS)

First touchdown (OSIRIS)

Why to use scilab!

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Operation is very rigid process!!!!� Procedure to follow� FDS tools = protected system � High level of validation� Commitment to result (timing &

accuracy)

IMPROVISATION IS NOT WELCOME!

Rosetta mission� Comet = almost Terra Incognita� Unforeseen requests/problems� Money/Time constraints (expensive

to integrate new functionalities in FDS)

NEED OF FLEXIBILITY

Scilab/Celestlab/Tracelab was helpful to overcome al l rigidities problems:� Toolboxes brings you tools/functionalities => correct level of validation� To develop code in fortran is more time consuming than scilab� Tracelab = SONC-FD business (possibility to realize new programs, patch…)

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(III)CONCLUSION

Comet Dust (COSIMA)

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SCILAB: thank you for the help!!!!!

Scientific results� On going work!!! (publication about Philae results in

Science end of summer) � probably a decade of work for scientists. � Main result: comet CG-67P is a complex body (more

than what was expected)� Rosetta: Water for Comet CG-67P different from Water

on Earth� Philae: CG-67P is not magnetized at scale of 1 m.

Model of solar system formation based on magnetized comets

� Philae sniffed a complex molecule with 3 Carbons…

Future of the mission� Rosetta continue its work => after perihelion if possible� Philae: hope for a wake-up. After august 2015, Solar

geometry is degrading.

CONCLUSION (I)

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