Multidisciplinary Analysis Tools for Orbit and Re-entry. G. Koppenwallner, HTG ; B. Fritsche; T. Lips, HTG

Transcription

1 Multidisciplinary Analysis Tools for Orbit and Re-entry G. Koppenwallner, HTG ; B. Fritsche; T. Lips, HTG ESTEC, Oct. 2006

2 Introduction The overview covers RAMSES, (Rarefied Aerodynamic Modelling System for Earth Satellites) ANGARA, (Analysis of Non Gravitational Accelerations due to Radiation and Aerodynamics) SCARAB (Space Craft Atmospheric Re-entry and Aero-thermal Break up) The codes combine geometric modeling for the SC and analysis modules for various disciplines in an integrated system. The codes have been developed with contracts from ESOC, Dr. Klinkrad during the last 14 years. Codes have been applied to many SC projects ESTEC, Oct Page 2

3 The RAMSES System RAMSES covers Geometric and physical modelling of the SC A series of analysis modules for aerodynamic forces Standard free molecular flow Test Particle Monte Carlo method for free molecular flow Bridging methods for hypersonic re-entry flow Post-processing Main application is at present the free molecular flow around SC ESTEC, Oct Page 3

4 RAMSES Free molecular flow problems Flow parameters: Knudsen number Kn = /L >> 1 Mol. Speed ration S = V/c c ' 2( / M ) T Free molecular flow: Kn >> 1 Force- moment coefficients are function of: Geometry, Attitude (, ), Speed ratio S, Gas surface interaction ESTEC, Oct Page 4

5 Ramses Space Craft modelling The geometric SC model Geometry module provides geometric panellized primitives, size, shape, position can be adjusted. Complex shapes can be generated by combination of compounds The physical SC model with surface properties Material or relevant gas surface interaction parameters are appointed to each geometric element The gas surface interaction can be treated with the following models. Maxwell, Schaaf/Chambre, Nocilla with material dependent coefficients. Surface temperature Tw ESTEC, Oct Page 5

6 The RAMSES aerodynamic analysis methods 3 Methodes for satellite aerodynamics 1. Integral method without shadow analysis 2. Integral method with aerodynamic shadow analysis 3. Test Particle Monte Carlo method Confidence and computation time increase from 1 to 3. Integral Method, IM This method determines the overall forces by integration of pressure and shear stress over the whole external surface. It does not consider the shielding or shadowing of individual surface elements by other elements. p 1 2 N N TW cp ( S ) ( ) 2 n S N q S 2 T c q T 1 ( S S ) N sin( ) S S N *cos( ) ESTEC, Oct Page 6

7 The RAMSES aerodynamic analysis methods Integral Method with shadow analysis, IMS Improved integral method, Considers the molecular shadowing of down-stream body components by upstream components. Analysis is based on a flow with infinite speed ratio S; (optical shadow). It neglects multiple wall collision between concave elements. The Test Particle Monte Carlo method, TPMC TPMC is a molecular approach tracing the particle path through the flow field. TPMC thus treats shadowing and multiple wall collisions. Statistical error depends on the number of particles traced. Direct control of statistical error by the number of molecules or surface hits to be simulated. After surface hits (~ particles) the statistical error is below 0,3%. The TPMC represents therefore within this error margin exact solution ESTEC, Oct Page 7

8 Typical RAMSES applications GEC, Geospace Electrodynamic Connections, (Astrium;NASA) GOCE ( ESOC) SWARM, ( ESA, OHB) ESTEC, Oct Page 8

9 Typical GOCE analysis results Drag coeff. c D as function of speed ratio S Diffuse reflection; In flight variation of S = 5-11 Moment coefficients as function of angle of attack (side slip angle beta = 0 ). CMy indicates flight stability and trimm CMz indicates no trimm at beta = 0 C D S peed ratio S Integral no sh adowing Integral with sh adow ing T est P articl e M onte C arlo -0, Moment coefficients CMx, CMy, CMz as function of α; S = 7,5, β = 0; σ =1,0 C D as fun ction of speed ratio S, m ethod com parison 3rd International Workshop α= β on = 0 ; Astrodynamics diffuse reflection Tools and Techniques; ESTEC, Oct Page 9 CMx, CMy, CMz 0,1 0,05 0-0,05 alpha, CMx CMy CMz

10 The ANGARA System (Analysis of Non Gravitational Accelerations due to Radiation and Aerodynamics) There exists similarity between the flow of molecules at S = and photons RAMSES has therefore been extended to cover also radiation forces. ANGARA provides an interactive modelling of the SC with surface properties for momentum exchange of molecules and photons with the SC surface. ANGARA determines aero and radiation forces for orbiting satellites in real atmospheric and radiation environment. ANGARA uses a 2 phase approach. Phase 1 SC is modelled and parameter ranges for aerodynamic free stream conditions and radiation fluxes are established. For this reference matrix, normalised aerodynamic and radiation pressure forces are calculated and stored in files. Phase 2 Results of Phase 1 are de-normalized according to the real atmosphere and radiation environment encountered at a particular orbit point. Phase 2 includes an orbit generator with steering modes for SC orientation. This allows aerodynamic and radiation force analysis along the orbit. ESTEC, Oct Page 10

11 Radiation sources and radiation forces acting on a Spacecraft ESTEC, Oct Page 11

12 Radiation forces treated by ANGARA Direct solar radiation flux as function of season including earth full and semi shadow. Earth Albedo re-radiation Earth infrared radiation as function of geographic position and time of the year based on IR maps and ERBE data. Self radiation due to different wall temperatures Each radiation source is different and requests special analysis effort. Solar radiation with earth semi-shadowing considers the influence of atmospheric adsorption and the refraction of solar photon rays by the density gradient normal to the ray path. Earth albedo re-radiation requires special integration of the reflected momentum flux from the visible and illuminated earth surface area. ESTEC, Oct Page 12

13 ANGARA Prediction of diffuse reflected indirect solar flux with local Albedo space craft visible earth cap reflected flux e r diffuse dark d illuminated Diffuse reflected flux e r = A e S sin(h) A = albedo value Angular distribution. de r /d = (e r /pi) cos( ) incident solar flux e s h = solar elevation latitude equatorial plane ESTEC, Oct Page 13

14 ANGARA results for ERS 1 Influence of land sea coverage on Aero-, IR- Earth, Albedo forces land sea Aero force land sea ERS land, sea ground tracks IR- force Albedo Influence of land sea coverage on Aero-, IR-,<Earth Albedo forces ESTEC, Oct Page 14

15 Introduction to SCARAB (Spacecraft Atmospheric Re-entry and Aerothermal Break-up) SCARAB is an integrated system for destructive re-entry analysis. SCARAB combines Spacecraft modelling Geometric modelling Physical modelling. Re-entry analysis External Loads Aerodynamic and aero-heating analysis Vehicle Response Flight dynamic analysis for trajectory and attitude dynamics Thermal analysis Structural analysis Fragmentation Mechanical fracture Melting of panels Demise: Complete melting of an object Survival: Ground impact ESTEC, Oct Page 15

16 Special demands on the code Re-entry uncontrolled with tumbling motion Shape of spacecraft may be very complex Internal structure must be considered Shape is not based on aerodynamic principles No distinct head or tail as for most flying objects Many technical disciplines involved Different couplings between disciplines ESTEC, Oct Page 16

17 SCARAB Introduction input forces, moments pressure input forces moments Input aerod. free stream Vehicle orient.atio time Input temperatures Input aerod. free stream Vehicle orient.atio input aerothermal heating The coupling and dependence between the different physical disciplines for disintigration prediction ESTEC, Oct Page 17

18 Space-Craft modelling with SCARAB Physical modelling Geometric model similar to RAMSES Thickness, Material appointment to each element Material data base 20 physical properties for each material 12 Temperature independent 8 Temperature dependent Physical model Material with all properties connected to each element Automatic calculation of: Mass, CM, Moments of Inertia for each basic element next higher compound level next higher compound level complete SC Typical SC is modelled with 300 basic elements ; surface panels ESTEC, Oct Page 18

19 Analysis modules of SCARAB Flight dynamics 6 degree freedom flight dynamics for SC and for fragments during melting phase ( Ma > 5) Numerical integration with Runge Kutta order 1-8 Fixed or variable time step d dt ) d dt ( mi ) M ( mv F ext ext External forces and moments gravity (earth, sun, moon) aerodynamic pressure and shear stress Solar radiation SCARAB 1.5 and 2 entry uncontrolled, no thrust SCARAB 3 definite thrust pulses possible In super to subsonic flow: Fragments treated with 3-d flight dynamics ESTEC, Oct Page 19

20 Analysis modules of SCARAB Aerodynamic analysis overview The aerodynamics is based on local panel methods For each elementary surface panel pressure, shear stress and heat transfer rates are calculated. Integration over all surface elements gives then the integral aerodynamic forces and moments. F aero q ( c n c t ) ds The panel aerodynamics is applied in the hypersonic regime (Ma >5) It distinguishes between free molecular flow rarefied transitional flow continuum flow S p M aero q ( r c n r c t ) ds S p ESTEC, Oct Page 20

21 Analysis modules of SCARAB Aerodynamics analysis II Free molecular flow regime c pfm 2 ( S ) 1 2 ( S N N w 2 n n S N T T ) c FM S sin( ) ( S n ) Continuum flow regime Modified Newtonian method for pressure Skin friction is set to zero for high Re c PC k N 2 1(, Ma, )cos ( ) k N 2 (, Ma, ) c C 0 Rarefied transitional flow Local coefficients are determined by bridging functions c p c pc c c C ( c c ) f P ( Kn, 0 ) p FM p C ( c FM c C ) f ( Kn, 0 ) ESTEC, Oct Page 21

22 Analysis modules of SCARAB Aero-heat-transfer Continuum heating Continuum heating is related to the stagnation point Reynolds number and to the local inclination of the surface element 2.1 V r St C ( cos( )) Re N,0 Re ( T ),0 ( 0 0 T T ) / ( T ) ( T / ) with = Rarefied transitional heating Bridging formula derived from experiments ( Legge, DLR) is used St St C 1 ( StC / St FM 2 ) ESTEC, Oct Page 22

23 Analysis modules of SCARAB Thermal analysis and thermal fragmentation Heat flow balance for single panel q ' q' q' q' pan aero rad cond Panel heating rate for T< T melt q' pan cpsdt / dt Panel melting rate for T = T melt sm = melt thickness Growth of melt layer thickness s m q' pan hmelt dsm / dt Panel element with temperature T thickness s aerodynamic heat flux q aero Conductive loss by conduction q cond Heat stored in panel element: q pan = ρ s cp dt/dt Heat loss by radiation q rad. = εσt 4 Heat flow balance for wall surface element Thick panels can be divided into N layers Thermal node analysis will then be conducted Loss of panel elements: Melt thickness = panel thickness Thermal Fragmentation :Loss of connectivity due to a string of molten panels Demise: Melting of all panels of an object ESTEC, Oct Page 23

24 Analysis modules of SCARAB Structural analysis and mechanical fragmentation The analysis method used in the SCARAB 1.5 version is restricted to stress and fracture analysis in predefined cut planes. Elementary elements are joints and sections, which are positioned within a cut plane. SCARAB determines then the differential loads resulting from aerodynamic forces and inertia forces SCARAB conducts a stress analysis for the sections at cut position. Fx A M J y y z M J z z y M x J Fracture condition is given by ( T ) > Mechanical Fragmentation eq ult n.b. Reduction of the ultimate material stress σ ult (T) with temperature at cut plane is considered. ESTEC, Oct Page 24

25 Analysis modules of SCARAB Special interactions between modules During melting of panels the SC looses mass. Internal surfaces are exposed to the flow and the geometry of the SC changes. All these changes are communicated between the different modules. Thus SCARAB considers during the melting process the following effects: Change of mass, shift of CM, change of moment of inertia matrix Change of active aerodynamic surface elements. Exposure of internal surfaces to flow. Some other special SCARAB features: The fragmentation tree is automatically generated, Individual fragments are pursued to next break-up, to their full demise or to their ground impact. Effort for re-entry analysis increases with fragment, sub-fragment generation. ESTEC, Oct Page 25

26 SCARAB Applications Benchmark calculations between NASA ORSAT code and SCARAB Destructive re-entry of the following SC has been analysed: ATV ROSAT ARIANE 5 cryogenic main stage EPC Ariane 5 upper stage VEB/EPC, BeppoSAX, TERRASAR-X [12];[13],[14],[15]. Ariane 5 upper stage ESC-A with payload satelltes In the following we demonstrate the SCARAB application on the example VEB /EPS ESTEC, Oct Page 26

27 EPS/VEB/SDM modelling SCARAB Model of Ariane 5- EPS/VEB ARIANE Upper Stage Main Components VEB Vehicle Equipment Bay EPS Etage a Propergol Stockable SDM, Separation, Distancing Module EPS VE B SDM EPS/VEB/SDM main data Mass, kg Length,m Diam. m VEB 1078,4 1,1235 5,430 EPS 1737,2 3,4515 3,940 SDM,ACY 239,8 1,925 3,940 Total 3055,4 VEB EPS-SDM model consists of 229 basic elements surface panels volume panels 6 cuts have been modelled ESTEC, Oct Page 27

28 EPS / VEB/ SDM modelling SCARAB Model of VEB VEB Level 1 compounds VEB Structure Thruster bracket TB Thruster bracket TB El-Equipment Tank Prop-Lines ESTEC, Oct Page 28

29 EPS/VEB/SDM Re-entry Analysis Altitude and Flight velocity till first fragmentation Some initial conditions : Epoch HO s; V = 7163 m/s; h= 302 km, ωx = 60 /s, ωy = 8 /s After about 6070 s at 84 km altitude EPS is captured by atmosphere First thermal fragmentation at 6103 s at altitude of 71 km ESTEC, Oct Page 29

30 EPS/VEB/SDM Re-entry Analysis Drag and Lift coefficients during re-entry 117 km 71km 117 km 71km Drag coefficient Lift coefficient ESTEC, Oct Page 30

31 EPS/VEB/SDM Re-Entry Analysis Angular velocities during re-entry till first fragmentation Initial motion Spinning around x axis Small coning h= 117 km h= 100 km h= 70 km After aero capture Motion strongly disturbed below 90 km SDM pointing in flight direction SDM protects EPS-VEB angular velocities /s magnitude roll; ωx; /s pitch; ωy; /s yaw; ωz; /s aero influence time, s ESTEC, Oct Page 31

32 EPS/VEB/SDM Re-Entry Analysis First fragmentation by melting Up to first melting no mechanical fracture Maximum wall temperature of specific part increases till melting starts. First melting at 6080 s at 82 km altitude At 6100 s / 73 km first surface panel molten. First hole in structure and mass decrease starts. First fragmentation at 6103s/ 71,1 km Melting start Melt through panel > hole Melt through object > 1th fragmentation ESTEC, Oct Page 32

33 EPS/VEB/SDM Re-Entry Analysis Fragmentation events and mass loss main fragment SDM Loss by melting 60 Loss by fragment altitude h, km VEB EPS 40 thermal fragmentations 35 mechanical fragmentations time, s Fragmentation events Mass versus time of main fragment ESTEC, Oct Page 33

34 EPS/VEB/SDM Re-Entry Analysis Fragmentation of VEB/EPS; Thermal maps Mechanical break off engine Thermal fragmentation on VEB 16 sec later ESTEC, Oct Page 34

35 Conclusions A short description of the 3 major codes developed by HTG has been given. All codes allow to construct the SC geometry with the relevant physical parameters required for the analysis purpose. Truly multidisciplinary software could be realised by a consistent development of the modules covering the different disciplines. This required to abandon aerodynamic codes which need flow field volume grids. SCARAB analysis methods are based on panelised surfaces with artificial volume panels for the solid structure. This allowed to reconstruct the actual SC configuration during the destruction process and to analyse fragments till complete demise or ground impact. ESTEC, Oct Page 35