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ScilabTEC 2015 - CNES


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

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ScilabTEC 2015 - CNES

  1. 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. 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. 3 (I) Comets and Rosetta / Philae mission
  4. 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. 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. 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. 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. 8 : 2004 - 2014
  9. 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. 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. 11 (II) Landing site selection and Landing operations
  12. 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. 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. 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. 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. 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. 17 (III) The SONC-FD operational Tool & scilab use
  18. 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. 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. 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 ■ 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. 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. 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. 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. 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. 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. 26 (III) CONCLUSION Comet Dust (COSIMA)
  27. 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. 28 ADVERTISING You can see a 3m model of Comet Churyumov- Gerasimenko and a full scale mockup of PHILAE on the Champs Elysées ! Place Clémenceau 75008 Paris 10th – 25th mai 2015 Subway station: Roosevelt or Concorde