1. AAE450 Spring 2009 Finite Element Analysis (FEA) for Orbital Transfer Vehicle (OTV) Tim Rebold STRC [Tim Rebold] [STRC] [1]

2. AAE450 Spring 2009 Boundary Conditions (BC’s)  8 holes on Payload Attach Fitting (PAF) equally spaced around  Spacecraft attached by bolting into launch vehicle interface  Bolt acts as a clamped boundary condition [Tim Rebold] [STRC] [2] All 6 degrees of freedom constrained Clamped BC z y x

3. AAE450 Spring 2009 Applied Loads - Dnepr Payload Requirements [Tim Rebold] [STRC] Payload Acceleration Loads (g's) Acceleration AxialLateral 1 st stage burn: Maximum lateral acceleration 3.0±0.50.5±0.5 2 nd stage burn: Maximum longitudinal acceleration 7.8±0.50.2 Notes: 1.Lateral accelerations may act in any direction, simultaneously with longitudinal ones 2. Dynamic accelerations are preceded by “±” symbol Spacecraft System Stiffness Requirements Thrust (Hz)Lateral (Hz) 2010 Tables based from Dnepr User’s Guide [3]

4. AAE450 Spring 2009 System Representations  Lander  Propulsion System  E-MOD System  Systems represented by placing lumped mass elements at the center of mass of that system  These elements have the same mass & inertia properties [Tim Rebold] [STRC] [4][4]

5. AAE450 Spring 2009 FEA Analysis  Von Mises Stress observed  Material allowables based on Aluminum 6061-T6 yield strength  Margin of Safety (MS) reported and documented for all major systems and components [Tim Rebold] [STRC] [5][5]

6. AAE450 Spring 2009 Lander Clamped boundary conditions representing bolted hole interface [Tim Rebold] [STRC] [6][6] Skirt Analysis – Set Up (100 grams) The skirt joins the larger 1.8 m diameter OTV to the smaller 1.3 m diameter Lander

7. AAE450 Spring 2009 [Tim Rebold] [STRC] [7] Skirt Analysis – Peak Stress Peak Stress σ = 70 N/mm 2 σ Y = 270 N/mm 2 MS = 2.86 69.6 N/mm 2 64.3 N/mm 2

8. AAE450 Spring 2009 [Tim Rebold] [STRC] [8] Skirt Analysis - Peak Displacement = 0.5 mm, Buckling Load Factor = 2.21

9. AAE450 Spring 2009 Skirt Analysis (100 grams) - Observations  Stress is not a concern  Buckling of thin sheet webs will determine sizing of skirt  As a result of reducing mass, the modal frequencies will decrease which is an adverse effect [Tim Rebold] [STRC] [9]

10. AAE450 Spring 2009 OTV Analysis 100 grams [Tim Rebold] [STRC] [10]

11. AAE450 Spring 2009 Accelerations Yield Propulsion Frame - Stress [Tim Rebold] [STRC] [11] Peak Stress σ = 324 N/mm 2 σ Y = 270 N/mm 2 MS = -0.17

12. AAE450 Spring 2009 Buckling [Tim Rebold] [STRC] [12] Buckling load Factor = 0.19 Buckling

13. AAE450 Spring 2009 FEA – Summary Observations  Yielding in propulsion frame member 4 due to lateral acceleration applied in that member’s direction  Displacement in E-MOD floor skin relatively high, but stresses are low and displacement does not interfere with anything in the surroundings  E-MOD floor supports are stronger than necessary  Buckling in C-Channels  Lateral mode too low [Tim Rebold] [STRC] [13] 1 4 3 2 Design Changes  Increase cross section of member 4 of propulsion frame, and connect propulsion components to more structural members  Decrease cross-sectional dimensions of E-MOD floor beams  Increase cross section dimensions of C-Channels until buckling occurs at a higher load

14. AAE450 Spring 2009 OTV Final Analysis 100 grams [Tim Rebold] [STRC] [14]

15. AAE450 Spring 2009 Accelerations Propulsion Frame - Stress [Tim Rebold] [STRC] [15] Peak Stress σ = 80 N/mm 2 σ Y = 270 N/mm 2 MS = 2.38 Peak displacement is 2.19 mm

16. AAE450 Spring 2009 E-MOD - Stress [Tim Rebold] [STRC] [16] Peak Stress σ = 72 N/mm 2 σ Y = 270 N/mm 2 MS =2.75 Peak displacement remains at 40 cm

17. AAE450 Spring 2009 E-MOD floor support - Stress [Tim Rebold] [STRC] [17] Peak Stress σ = 92 N/mm 2 σ Y = 270 N/mm 2 MS = 1.93 Peak displacement is 3.62 mm and occurs at ring interface

18. AAE450 Spring 2009 OTV Frame – Peak Stress in OTV [Tim Rebold] [STRC] [18] Peak Stress σ = 92 N/mm 2 σ Y = 270 N/mm 2 MS = 1.93 Peak stress occurs at a joint where a C-Channel and E-MOD floor support beam meet

19. AAE450 Spring 2009 Buckling Load Factor is 1.42 [Tim Rebold] [STRC] [19]

20. AAE450 Spring 2009 Modes – Lateral mode at 10.6 Hz [Tim Rebold] [STRC] [20] Axial mode is not a concern

21. AAE450 Spring 2009 FEA Analysis - Conclusions  Stiffness and buckling were driving factors in determining size  Members act together effectively to limit peak stresses and displacements  Low stresses ensure welds and other connection methods will meet strength criteria [Tim Rebold] [STRC] [21]

22. AAE450 Spring 2009 FEA Analysis Breakdown – 100 g [Tim Rebold] [STRC] [22] Peak Stress & Displacement Breakdown SystemDisplacement (mm)Stress (N/mm 2 )MS Propulsion Frame2.1479.72.14 E-MOD40.6072.12.75 E-MOD Floor Support3.6292.11.93 C-Channels3.4692.11.93 Lander Integration Ring 0.5369.62.86 PAF0.2728.78.41

23. AAE450 Spring 2009 Structural Budget – 100 g [Tim Rebold] [STRC] [23] MASS (kg) Components PAF (not included in OTV mass)47.04 E-MOD floor beams & overlay5.25 Shear / Skin panels15.00 Propulsion support frame3.01 Stringers / Stiffeners12.48 Integration (Lander Skirt)12.19 Fasteners (welds, rivets, bolts, adhesives)2.01* TOTAL49.94 *Estimates

24. AAE450 Spring 2009 FEA Analysis Breakdown – 10 kg [Tim Rebold] [STRC] [24] Peak Stress & Displacement Breakdown SystemDisplacement (mm)Stress (N/mm 2 )MS Propulsion Frame2.741061.55 E-MOD40.982.72.26 E-MOD Floor Support4.621181.29 C-Channels4.551181.29 Lander Integration Ring 0.4163.23.27 PAF0.30734.26.89

25. AAE450 Spring 2009 Structural Budget – 10 kg [Tim Rebold] [STRC] [25] *Estimates MASS (kg) Components PAF (not included in OTV mass)41.36 E-MOD floor beams & overlay5.25 Shear / Skin panels15 Propulsion support frame3.01 Stringers / Stiffeners12.12 Integration (Lander and propulsion module)14.24 Fasteners (welds, rivets, bolts, adhesives)2.12* TOTAL51.74