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The flight dynamics standpoint Alejandro Blazquez (CNES) LSWT Venice, 30/03-01/04/2009
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2 LSWT meeting, Venice, 30/03-01/04/2009 Content Context SDL (Strategy, Requirements & Assumptions) ANDROMAC On-going work
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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.
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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
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5 LSWT meeting, Venice, 30/03-01/04/2009 Content Context SDL Strategy Requirements Assumptions ANDROMAC On-going work
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6 LSWT meeting, Venice, 30/03-01/04/2009 Strategy Orbiter / Lander separation manœuvre Vmss => Modification of the Orbiter trajectory (post delivery orbit)
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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)
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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 ; 0.539 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
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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 ….
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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
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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 = 2.2529e+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
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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 0.529 m/s (the updated value is 0.539 LID-B lv) 0.05 m/s Vmss 0.529 m/s (the updated value is 0.539 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
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13 LSWT meeting, Venice, 30/03-01/04/2009 Content Context SDL (Strategy, Requirements & Assumptions) ANDROMAC On-going work
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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
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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
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16 LSWT meeting, Venice, 30/03-01/04/2009 Content Context SDL (Strategy, Requirements & Assumptions) ANDROMAC On-going work
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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
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