Interplanetary Preliminary Mission Design: GA and AGA sequences optimisation

Transcription

1 Interplanetary Preliminary Mission Design: GA and AGA sequences optimisation Michelle LAVAGNA Amalia ERCOLI FINZI Angelo POVOLERI 1

2 Tool purpose Space mission design Mission analysis System design (concurrent approach) Aero-assisted manoeuvres Thermal loads Inertial loads Configuration Control Integration of mission analysis into concurrent approach Tool for preliminary mission analysis 2

3 Problem statement (1/2) min g j ( ) C i ( x, p) ( x, p) 0 [ v, t Q] C i ( x, p) =, Criteria vector [ g ] g,..., j ( x, p) 1 g q = Constraints [ y y, z ] x =,..., 1 1,..., n z m Optimisation variables vector Interplanetary trajectory p1 p r [ ] p,..., Planetary flyby = Optimisation parameters vector 3

4 Problem statement (2/2): Interplanetary trajectory optimisation S=[number, planets involved, manoeuvres type (GA/AGA)] Classical approach: pre-defined flyby sequence flyby sequence vector s p Sequence 1 Sequence 2 Sequence n Optimisation Optimisation Optimisation Favourite solution selection Innovative approach: optimisation with non-imposed 4 sequences Optimisation 3n extra degrees of freedom and mixed continuous-discrete optimisation problem Favourite solution selection s x

5 5 Linked conics approach: No detail of planetary flyby Instantaneous change in interplanetary trajectory Need for flyby energetic recovery estimate: immediate for GA complex for AGA Problem modelling (1/3): Interplanetary trajectory = 2 sin 2 δ v v GA + Φ = / 1 V V C C k v v abs v C D L AGA

6 Patched conics approach Planetary flyby in detail Non-instantaneous flyby Flyby parameters can be treated as optimisation variables Problem modelling (2/3): Interplanetary trajectory v i v o v v o v i v p v~+ o δ ~ vi 6

7 Problem modelling (3/3): Atmospheric paths analysis P v = = ( r, λ, L) ( v, γ, β ) 7 2 free dynamics: Bank angle Angle of attack Configuration: ballistic coefficient β = m x C S x x p

8 LINKED MODULE Optimisation variables: Flyby number, sequence, type Launch date Intermediate transfer times Optimisation architecture Transfer optimisation Pareto front v t Favourite solutions choice: Designer 8 Pareto front v Q Manoeuvres optimisation PATCHED MODULE Optimisation variables: Pericentre radii and flyby planes Bank angle modulation Aerodynamic surfaces Transfer times small correction Capture parameters (optional)

9 Environment: MATLAB Computational scheme (1/2): linked conics module User s specifications: departure and target planets launch date range min/max number of flybys 9

10 Computational scheme (2/2): patched conics module Environment: MATLAB + SIMULINK User s specifications: 10 interplanetary transfer (from linked module) capture manoeuvre type target orbit parameters

11 Optimisation algorithm (1/2) -Global optimisation -Wide range of solutions -Continuous-discrete problem EVOLUTIVE ALGORITHM -Highly multimodal problem GENETIC EVOLUTIVE ALGORITHM Crossover 11 Algorithm convergence towards a portion of the Pareto front (genetic drift) Convergence criterion selection Constraints handling

12 Optimisation algorithm (2/2) Algorithm convergence towards a single flyby sequence ELITISM TABU SEARCH INTERFERENCE SEVERITY Fitness=f(criteria, interference severity, constraint violation penalty) 12

13 Pluto mission (1/2): linked module Flyby: max 4 gravitational only -Launch Date: MJD (19/6/2005-3/10/2054) -320 individuals iterations Computational time: 6h (AMD Athlon 2.4GHz, RAM 256Mb) 13

14 Pluto mission (2/2): linked module Flyby: max 4 GA+AGA -Launch Date: MJD (19/6/2005-3/10/2054) -320 individuals iterations Computational time: 6h (AMD Athlon 2.4GHz, RAM 256Mb) 14

15 Titan mission (1/4): Saturn transfer (linked module) Flyby: max 4 gravitational only -Launch Date: MJD (19/6/2005-3/10/2054) -320 individuals iterations Cassini Computational time: 6h (AMD Athlon 2.4GHz, RAM 256Mb) 15

16 Titan Mission (2/4): Saturn transfer (linked module) Flyby: max 2; GA +AGA -Launch Date: MJD (19/6/2005-3/10/2054) -160 individuals iterations solution GA only GA+AGA min dv dv=9.77km/s dv=7.25km/s dv=15km/s dt=5.15 years dt=3.91 years dt=5 years dv=15.23km/s dv=12.55km/s Computational time: 3h (AMD Athlon 2.4GHz, RAM 256Mb) 16

17 Titan mission (3/4): Complete mission (patched module) Mission optimisation using knee solution for interplanetary transfer Trajectory [E Ma(aga) S], Launch 21/8/2005 v =19.21km / s t = 1099 days v calculated from LEO (300km) to parking on Titan orbit m=1000kg CL=1 CD=0.1 Q Manoeuvre with max Q 6km/s 6Km/s saving 17

18 Titan mission (4/4): Mars AGA 29km 17.7MW/m 2 65g 18 γ < 1 / s Max acceleration 27g Energetic recovery preserved

19 Mars aerocapture (1/3): Interplanetary transfer (linked module) Direct transfer: knee solution dv=7.232km/s, dt=147days min dv solution dv=5.617km/s, dt=318days 19

20 Mars aerocapture (2/3): complete mission (patched module) m=5000 kg CD=0.2 CL= km/s 1.2km/s -High thermal load -Energetic saving 20

21 Mars aerocapture (3/3) 38km 2.3MW/m 2 1.8g 21

22 Conclusions Tool for a wide range of preliminary solutions Multidisciplinar optimisation No imposed flyby sequences No imposed control law 22