The flight dynamics standpoint

Alejandro Blazquez (CNES)LSWT Venice, 30/03-01/04/2009

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Content

Context SDL (Strategy, Requirements & Assumptions) ANDROMAC On-going work

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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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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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Content

Context SDL

StrategyRequirementsAssumptions

ANDROMAC On-going work

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Strategy

Orbiter / Lander separation manœuvre Vmss

=> Modification of the Orbiter trajectory

(post delivery orbit)

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Strategy

ADS : active descent system

Two feasible strategies :Two feasible strategies :• passive (without ADS manouvre)• active (with ADS manouver)

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Requirements (1/2) Landing after 2 months of global mapping/close observation (2014)Landing after 2 months of global mapping/close observation (2014)

Distance to the Sun:Distance to the Sun:~ 3 UA (outgassing and electrical power)

Séparation Manœuvre Séparation Manœuvre Vmss :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 ADS Manœuvre Vads :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 Lander shall be in a rotational motion around its Z axis during the descent phasephase

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Requirements (2/2)

Safe pre-delivery orbitSafe pre-delivery orbit : : no Sun eclipses visibility between Earth stations and Orbiter

Separation altitudeSeparation altitude :: maximum between 1 km and 1 comet radius

Distance betweenDistance between Vmss and Vmss and Vads :Vads : 100 m minimum

Maximal descent duration :Maximal descent duration : 3 hours

Maximum impact velocity :Maximum impact velocity : 1.2 m/s

post-delivery orbitpost-delivery orbit : : no impact trajectory for the orbiter … …..

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Assumptions (1/3) Nucleus shape Hubble Space Telescope Observations in March 2003:Hubble Space Telescope Observations in March 2003:

Construction of an overall 3D-model of the comet nucleus [Lamy 2007]

Main characteristics:Main characteristics: Nucleus volume equivalent to that of a 1.72 km1.72 km

radius sphere Presence of humpshumps (high radius) and hollowshollows (low

radius) Density ~ 370 Kg/m3 Albedo =0.04 Spin period of 12.6 hours and

no rotational state

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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 H2O 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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Assumptions (3/3) constraints

Optimization criterion:Optimization criterion:modulus of impact velocity or descent duration

Main mission constraints:Main mission constraints: V impact 1.2 m/s1.2 m/s 30 mn descent duration 3 hours 1 km1 km release altitude 0.05 m/s Vmss 0.529 m/s 0.529 m/s (the updated value is 0.539 LID-B lv)(the updated value is 0.539 LID-B lv) 0.05 m/s Vads 1.0 m/s 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:Control parameters: execution dates and magnitudes of MSS and ADS maneuvers orbital parameters of delivery orbit

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Content

Context SDL (Strategy, Requirements & Assumptions)

ANDROMAC On-going work

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ANDROMAC (1/2)

Shape

Outgassing

Gravity field

Ephemerides

Landing siteOrbiter’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 scenariosBackup trajectories

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ANDROMAC(2/2)

Conclusions :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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Content

Context SDL (Strategy, Requirements & Assumptions)

ANDROMAC On-going work

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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