"Use of Scilab for the Philae landing on comet Churyumov-Gerasimenko" By Thierry Martin, Cnes & Romain Garmier, CS-SI for ScilabTEC 2015

1. SONC Flight Dynamics Team
T.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

2. Outline
I. Comets and Rosetta / Philae mission
II.Landing site selection and Landing
operations
III.The SONC-FD operational tools and scilab
use
IV.Conclusion
2

3. 3
(I)
Comets
and
Rosetta / Philae mission

4. 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.
4
Flyby of comet Halley by Giotto in 1986 (first
comet close observation ESA)
All comets visited by spaceprobes before Rosetta

5. 5
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

6. 6
■ 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

7. 7
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

8. 8
: 2004 - 2014

9. ■ 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
9
67P Churyumov-Gerasimenko (1)
4.1km
2 km
Scilabtec
2015

10. 10
67P Churyumov-Gerasimenko (2)
10
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

11. 11
(II)
Landing site selection
and Landing operations

12. 12
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 Operation
Center (RMOC)
• Rosetta flight dynamics
• Interface Earth/Rosetta

13. Landing Site Selection Process:
A convergent approach
13
■ 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

14. Landing Site Selection Process milestones
5/28/201528/05/2015
Days to
Landing
Date/min
distance to
comet
Milestones
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)

15. The landing operations: schedule
Nominal site
Image Rolis
Altitude ~ 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 Rolis
Altitude ~ 3 km

16. 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 TD
17h31

17. 17
(III)
The SONC-FD operational
Tool & scilab use

18. 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)
18

19. FDS tools
19
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

20. 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
20

21. Tracelab : Computations
21
■ 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
…

22. Tracelab : Visualisation
22
■ « 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

23. Use of Scilab/Celestlab/Tracelab (1)
23
■ 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)

24. Use of Scilab/Celestlab/Tracelab (2)
24
■ 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)

25. Why to use scilab!
25
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 all 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…)

26. 26
(III)
CONCLUSION
Comet Dust (COSIMA)

27. 27
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)

28. 28
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Gerasimenko and a full scale mockup of PHILAE on the
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Place Clémenceau
75008 Paris
10th – 25th mai 2015
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