The flight dynamics standpoint Alejandro Blazquez (CNES)‏ LSWT Venice, 30/03-01/04/2009

2 LSWT meeting, Venice, 30/03-01/04/2009 Content  Context  SDL (Strategy, Requirements & Assumptions)‏  ANDROMAC  On-going work

3 LSWT meeting, Venice, 30/03-01/04/2009 Context (1/2) Andromac  ANDROMAC: Powerfull tool to optimise the descent trajectory profile of Philae  Inputs: gravity potential and outgassing environment ephemerides, comet geometry  Outputs: Determination of the descent trajectory: nominal case, Determination of the backup descent trajectories: FDIR cases, Robustness and Monte Carlo analysis of the trajectories.

4 LSWT meeting, Venice, 30/03-01/04/2009 Context (2/2) Laboratories involved  Outgassing and dust production model : Service d’Aéronomie, LESIA  Gravity potential model : Groupe de Recherche en Géodésie Spatiale CNES/CNRS GRGS  Geometry / shape of the comet : Laboratoire d’Astrophysique de Marseille LAM  Mechanical stability of the Lander : Max-Plank-Institut für Aeronomie

5 LSWT meeting, Venice, 30/03-01/04/2009 Content  Context  SDL  Strategy  Requirements  Assumptions  ANDROMAC  On-going work

6 LSWT meeting, Venice, 30/03-01/04/2009 Strategy Orbiter / Lander separation manœuvre  Vmss => Modification of the Orbiter trajectory (post delivery orbit)

7 LSWT meeting, Venice, 30/03-01/04/2009 Strategy ADS : active descent system Two feasible strategies : passive (without ADS manouvre)‏ active (with ADS manouver)‏

8 LSWT meeting, Venice, 30/03-01/04/2009 Requirements (1/2)‏  Landing after 2 months of global mapping/close observation (2014)‏  Distance to the Sun: ~ 3 UA (outgassing and electrical power)  Séparation Manœuvre  Vmss :  module : [ 0.05 m/s ; m/s ] : nominal case  module : 0.17 m/s : backup case  fixed orientation towards the Lander X axis (or -X Orbiter)‏  ADS Manœuvre  Vads :  module : [ 0.05 m/s ; 1 m/s ] (hold-down thrust after touch down not included)‏  fixed orientation towards the Lander -Z axis  Lander shall be in a rotational motion around its Z axis during the descent phase

9 LSWT meeting, Venice, 30/03-01/04/2009 Requirements (2/2)‏  Safe pre-delivery orbit :  no Sun eclipses  visibility between Earth stations and Orbiter  Separation altitude:  Separation altitude :  maximum between 1 km and 1 comet radius  Distance between  Vmss and  Vads :  Distance between  Vmss and  Vads : 100 m minimum  Maximal descent duration :  Maximal descent duration : 3 hours Maximum impact velocity :  Maximum impact velocity : 1.2 m/s  post-delivery orbit :  post-delivery orbit : no impact trajectory for the orbiter  ….

10 LSWT meeting, Venice, 30/03-01/04/2009 Assumptions (1/3) Nucleus shape  Hubble Space Telescope Observations in March 2003: Construction of an overall 3D-model of the comet nucleus [Lamy 2007] Main characteristics: 1.72 km  Nucleus volume equivalent to that of a 1.72 km radius sphere humpshollows  Presence of humps (high radius) and hollows (low radius)‏  Density ~ 370 Kg/m3  Albedo =0.04  Spin period of 12.6 hours and no rotational state

11 LSWT meeting, Venice, 30/03-01/04/2009 Assumptions (2/3) Forces  Gravitational Force  The comet nucleus is homogeneous, i.e. constant density 370 Kg/m3  Gravitational acceleration: maximum value of 5.5e-4 m/s2   = e+03 m3/s2  Outgassing Force  presence of H 2 O and CO  gas production rate 1e+27 molecules/s  regular and steady state  Dust pression Force  neglected for the moment  Studies on going

12 LSWT meeting, Venice, 30/03-01/04/2009 Assumptions (3/3) constraints  Optimization criterion: modulus of impact velocity or descent duration  Main mission constraints: 1.2 m/s  V impact  1.2 m/s  30 mn  descent duration  3 hours 1 km  1 km  release altitude m/s (the updated value is LID-B lv)‏  0.05 m/s   Vmss  m/s (the updated value is LID-B lv)‏ 1.0 m/s  0.05 m/s   Vads  1.0 m/s  constrained direction of MSS maneuver (collinear to orbiter X-axis)‏  constrained direction of ADS maneuver (collinear to Lander Z-axis)‏  Lander Z-axis collinear to the local surface normal (landing site)‏  Control parameters:  execution dates and magnitudes of MSS and ADS maneuvers  orbital parameters of delivery orbit

13 LSWT meeting, Venice, 30/03-01/04/2009 Content  Context  SDL (Strategy, Requirements & Assumptions)‏  ANDROMAC  On-going work

14 LSWT meeting, Venice, 30/03-01/04/2009 ANDROMAC (1/2)‏ Shape Outgassing Gravity field Ephemerides Landing site Orbiter’s post-orbit Final purpose A) Inputs generation B) Trajectories extrapolation Undetermined calculus C) Optimisation method Best trajectory for each landing site D) Robustness analysis Feasibility of the landing site E) Non-nominal scenarios Backup trajectories

15 LSWT meeting, Venice, 30/03-01/04/2009 ANDROMAC(2/2)‏  Conclusions :  Descent trajectories computation: nominal and backup cases  Optimal trajectories : duration, impact velocity...  robustness of the solutions : Monte Carlo analysis  Feasible solutions after the close observation phase

16 LSWT meeting, Venice, 30/03-01/04/2009 Content  Context  SDL (Strategy, Requirements & Assumptions)‏  ANDROMAC  On-going work

17 LSWT meeting, Venice, 30/03-01/04/2009 On-going work  NEXT MISSION ANALYSE  Currently working on inputs consolidation  Presentation foreseen for July’09 at next SWTM  ANDROMAC  Improvements on-going New models (shape, gravity and outgassing)‏ More perturbations in the montecarlo analysis ( rotational period, position and motion of pole axis)‏ New constraints  Operational adaptation