1. C ONCEPTUAL M ODELING AND A NALYSIS OF D RAG -A UGMENTED S UPERSONIC R ETROPROPULSION FOR A PPLICATION IN M ARS E NTRY, D ESCENT, AND L ANDING V EHICLES Michael Skeen Ryan Starkey University of Colorado at Boulder Department of Aerospace Engineering Sciences 10 th International Planetary Probe Workshop Cross-Cutting Technologies IV Session San Jose, CA June 21, 2013

2. Overview Introduction and Background ◦Problem Statement ◦Drag-Augmented Supersonic Retropropulsion Aerodynamic Modeling ◦Ballistic Coefficient Comparison ◦Drag Coefficient Modeling ◦Validation and Sensitivity Analysis Trajectory Modeling ◦Drag-Augmented SRP Operation ◦Hybrid Decelerator Systems Conclusions and Future Work M. Skeen21 June 2013 IPPW 10 2

3. Mass Limitations Viking Mars Pathfinder Mars Exploration Rovers Phoenix Mars Science Laboratory Entry Mass (kg)9925848306023300 Touchdown Mass (kg)5903605393641665 Payload Mass (kg)24492173167899 Aeroshell diameter (m)3.52.65 4.5 Ballistic Coefficient (kg/m 2 )64639465135 M. Skeen21 June 2013 IPPW 10 3

4. Supersonic Retropropulsion (SRP) Central Nozzle Configuration CFD images: Bakhtian and Aftosmis, 2011 Flowfield sketch: Korzun, 2012 M. Skeen21 June 20134 IPPW 10

5. Supersonic Retropropulsion (SRP) Peripheral Nozzle Configuration CFD images: Bakhtian and Aftosmis, 2011Flowfield sketches: Korzun, 2012 M. Skeen21 June 2013 IPPW 10 5

6. Drag Trends (Bakhtian and Aftosmis, 2011) M. Skeen High- Thrust SRP Drag- Augmented SRP 21 June 2013 IPPW 10 6

7. Ballistic Coefficient Comparison M. Skeen21 June 2013 IPPW 10 7

8. SRP vs. SIADs M. Skeen21 June 2013 IPPW 10 8

9. Bakhtian and Aftosmis, 2011 Shock Cascades P atm P0P0 Isentropic Normal Shock P0P0 Isentropic P atm Oblique - Normal Shock Cascade M. Skeen 4.0x 6.9x P0P0 Isentropic P atm Oblique-Oblique-Normal Shock Cascade Shock angle: 40° 21 June 2013 IPPW 10 9

10. Drag Model Methodology Shock structure (grey) caused by SRP plumes (orange). Coefficient of pressure shown on aeroshell surface. (Bakhtian and Aftosmis, 2011) M. Skeen Korzun, 2012 21 June 2013 IPPW 10 10

11. Pressure Model 1.Normal shock 2.Accelerated flow near capsule periphery 3.Oblique-normal shock cascade 4.Oblique-oblique normal shock cascade 5.Separated flow 6.Nozzle exit flow CFD (Bakhtian and Aftosmis, 2011) Pressure Model M. Skeen21 June 2013 IPPW 10 11

12. Drag Coefficient Model Results + 14% M. Skeen21 June 2013 IPPW 10 12

13. Model Validation M∞M∞ MethodSourceSource C D Predicted C D % Difference 4-Nozzle Configurations 2CFD[17]1.0921.29518.59% 4CFD[17]1.5611.494-4.30% 6CFD[17]1.6301.628-0.12% 12CFD / Tunnel[21]1.450 * †1.327-8.47% 3-Nozzle Configurations 2Wind Tunnel[13]1.2 ⌂ 0.993-17.23% 2Wind Tunnel[13]0.7 ⌂ †0.99341.89% 2CFD[17]1.3451.295-3.71% 4CFD[17]1.6331.494-8.56% 6CFD[17]1.6251.6280.22% 8CFD[17]1.5431.70010.17% * Nozzles placed at a radius of 55% of the aeroshell diameter. ⌂ Nozzles places at a radius of 80% of the aeroshell diameter, cone half angle of 60°. † Thrust coefficient of 1.5. M. Skeen21 June 2013 IPPW 10 13

14. Sensitivity Analysis – ON Flow Region Size M. Skeen21 June 2013 IPPW 10 14

15. Trajectory Model 3 degrees of freedom ◦Planar movement only Mars GRAM atmosphere ◦Time and location averaged MSL initial / parachute deployment conditions ◦Ballistic trajectory reference (1135 kg) M. Skeen Solver Target ◦Parachute deployment (q ∞, M ∞ conditions) ◦Iterate mass so parachute deploys at 10 km altitude ◦Vehicle mass at parachute deploy → usable mass 21 June 2013 IPPW 10 15

16. Drag Coefficient Sensitivity 2.5 % M. Skeen Mass has low sensitivity to drag coefficient changes Does not take into account operation methodology 21 June 201316 IPPW 10

17. Peak Dynamic Pressure Region M. Skeen21 June 2013 IPPW 10 17

18. Drag-Augmented SRP Results Maximum Mass: Constant SRP Operation Entry: 4433 kg (+ 232%, +3098 kg) ‘Dry’: 1786 kg (+34%, +451 kg) M. Skeen Baseline Vehicle Entry: 1335 kg ‘Dry’: 1335 kg 21 June 2013 IPPW 10 18

19. Drag-Augmented SRP Results (2) Maximum Mass: Constant SRP Operation Entry: 4433 kg (+ 232%, +3098 kg) ‘Dry’: 1786 kg (+34%, +451 kg) SRP Operation Below 50 km 98.8 % of mass performance M. Skeen21 June 2013 IPPW 10 19

20. Constant Thrust Trajectory Maximum Mass: Constant SRP Operation Entry: 6690 kg (+ 401%, +5355 kg) ‘Dry’: 1431 kg (+7%, +96 kg) or Dynamic Pressure Targeted Operation Entry: 3289 kg → 65% less propellant ‘Dry’: 1449 kg (+9%, +114 kg) M. Skeen21 June 2013 IPPW 10 20

21. SRP-IAD Hybrid Maximum Mass: Transition to IAD Entry: 12947 kg (+ 870%, +11612 kg) ‘Dry’: 10770 kg (+708%, +9435 kg) ‘Dry’ Mass Fraction: 83% M. Skeen Baseline Vehicle Entry: 1335 kg ‘Dry’: 1335 kg ‘Dry’ Mass Fraction: 100% 21 June 2013 IPPW 10 21

22. Summary Aerodynamic Modeling IAD systems provide lower ballistic coefficient Drag coefficient model for drag-augmented SRP ◦Analytic model + computational results ◦Drag coefficient can increase by 14% ◦Validation and sensitivity analysis Trajectory Modeling Ideal drag-augmented SRP increases ‘dry’ mass by 34% Operation in maximum dynamic pressure regime critical to efficacy ◦65% savings in propellant for constant-thrust case Hybrid decelerator systems take advantage of appropriate flight regimes ◦SRP-IAD hybrid increases ‘dry’ mass by 708% M. Skeen21 June 2013 IPPW 10 22

23. Future Work SRP Modeling Expand SRP aerodynamics database ◦Experiment or CFD Analytic or semi-analytic modeling of SRP shock structure Correlation with thrust coefficient Angle-of-attack model development Asymmetric thrust operation Systems Analysis Sensitivity to additional performance parameters (C T, I sp, angle of attack, entry conditions, aeroshell size, etc.) Maneuvering flight analysis, landing uncertainty Conceptual vehicle design (aeroshell design, thermal environment, hardware system selection, component sizing, etc.) M. Skeen21 June 2013 IPPW 10 23

24. Acknowledgements Dr. Ryan Starkey Busemann Advanced Concepts Lab CU Aerospace Engineering Department ◦Funding support through TA and CA programs Student Organizing Committee Student Scholarship Sponsors M. Skeen21 June 2013 IPPW 10 24

25. Questions? michael.skeen@colorado.edu

26. Pressure Model Assumptions Isentropic compression between shock structure and aeroshell No ‘mixing’ of flow regions Neglecting ablation, chemical reaction, boundary layer effects Symmetric pressure distribution about each quadrant (symmetric in thirds for 3 nozzle configurations) Flow region sizes remain constant with all parameters Pressure distribution corresponds to C T =1.5 Pressures vary radially in same manner as nominal capsule flow structure Flow is accelerated around nozzle exit Oblique shock angle of 40° Constant backshell pressure Neglect flow turning through shock cascades Steady state model M. Skeen21 June 201326 IPPW 10

27. Grid Size Sensitivity M. Skeen21 June 201327 IPPW 10

28. Real Gas Effects M. Skeen21 June 201328 IPPW 10

29. Sensitivity Analysis – Specific Heat Effects M. Skeen21 June 201329 IPPW 10

30. Sensitivity Analysis – Shock Wave Angle M. Skeen21 June 201330 IPPW 10

31. Sensitivity Analysis – Back Face Pressure M. Skeen21 June 201331 IPPW 10

32. Sensitivity Analysis – NS Flow Region Size M. Skeen21 June 201332 IPPW 10

33. Sensitivity Analysis – Accelerated Flow Region Size M. Skeen21 June 201333 IPPW 10

34. Sensitivity Analysis – OON Flow Region Size M. Skeen21 June 201334 IPPW 10

35. Sensitivity Analysis – Separated Flow Region Size M. Skeen21 June 201335 IPPW 10

36. Sensitivity Analysis – Nozzle Exit Area M. Skeen21 June 201336 IPPW 10

37. Drag-Augmented SRP Results (3) M. Skeen21 June 201337 IPPW 10

38. SRP Propellant Mass M. Skeen21 June 201338 IPPW 10

39. SRP Hybrid Drag-Augmented → High-Thrust Maximum mass performance occurs for fully high-thrust SRP Low ‘dry’ mass fraction M. Skeen21 June 201339 IPPW 10

40. SRP Hybrid Maximum mass performance occurs for fully high-thrust SRP Low ‘dry’ mass fraction Drag-Augmented → High-Thrust M. Skeen21 June 201340 IPPW 10