sponsored by International Planetary Probe Workshop 10 June 15-16, 2013 San Jose, California

1. Entry, Descent, and Landing Systems Short CourseSubject: Trim TabsAuthor: Karl Edquist NASA Langley Research Center sponsored by International Planetary Probe Workshop 10 June 15-16, 2013 San Jose, California

2. Introduction • Aerodynamic lift is beneficial to EDL performance: • Improves landing elevation & accuracy • Decreases entry loads • Allows for more payload mass • The standard method for generating lift on a blunt capsule is by shifting the radial center of gravity (ZCG) off axis • Mars EDL: • Viking I/II (L/D = 0.18, ZCG/D = 0.01326 = 1.83”) • MSL (L/D = 0.24, ZCG/D = 0.02212 = 3.92”) • CG offset is achieved by moving payload (if volume is available) or by adding ballast mass • The following slides discuss trim tabs for blunt entry capsules • Body flaps (e. g. Space Shuttle) are another example of aerodynamic control International Planetary Probe Workshop 10, EDL Short Course

3. Ballast vs. Trim Tab • Aerodynamic control of trim angle of attack is more mass-efficient • Tab size ~ heatshield diameter • If payload , tab size stays the same to maintain L/D • A trim tab system that gives = L/D is estimated to be ~10% of ballast • Reduced mass = more payload and/or better EDL performance MSL Entry Ballast System Cruise Ballast (~140 kg) 3.92” V∞ Drag Lift Entry Ballast (~160 kg) NASA/TM-2011-216988 • MSL used > 300 kg of ballast (>35% of rover mass) to achieve L/D = 0.24 • Ballast ~ payload mass • If payload , ballast to maintain L/D International Planetary Probe Workshop 10, EDL Short Course

4. Mars Robotic EDL Trim Tab Ballast Exo-Atmospheric Deploy Tab (a > 0) Eject Ballast (a > 0) Hypersonic Guided, L/D > 0 RCS Bank Control Supersonic Guided, L/D > 0 L/D = 0 at Parachute Deploy Eject Ballast (a = 0) Retract Tab (a = 0) Powered Descent & Touchdown International Planetary Probe Workshop 10, EDL Short Course

5. Mars Surface Elevation -1 km MOLA +2.5 km MOLA Ref. “Statistics of Mars’ Topography from the Mars Orbiter Laser Altimeter: Slopes, Correlations, and Physical Models” The mass savings of trim tabs can contribute to making the Mars southern hemisphere accessible to future robotic EDL missions International Planetary Probe Workshop 10, EDL Short Course

6. Past Studies AIAA 2002-4409 AIAA 2002-4408 AIAA 2002-4506 NASA TM X-660, 1962 NASA TM X-770, 1963 AIAA 2002-4407 NASA TM X-816, 1963 NASA TM X-579, 1961 NASA TM-2011-216988 International Planetary Probe Workshop 10, EDL Short Course

7. MSL-I Example “Technology set 5, utilizing the hypersonic trim tab, provides the most payload mass at the relatively lower site elevations, due to the mass savings over replacement of the entry balance masses.” AIAA 2011-7294 • The MSL-Improved (MSL-I) study showed that the mass savings of a trim tab transfers to more payload mass • At least 150 kg more payload to 0 km MOLA than other advanced robotic EDL systems (4.7 m aeroshell, 30 m ringsail parachute) • The mass savings could also be used to reach higher elevation with a slightly smaller payload (~1460 kg to +1.83 km) International Planetary Probe Workshop 10, EDL Short Course

8. Recent Supersonic Wind Tunnel Testing* 60-deg Forebody 3% Tab, 30° Cant, M=4.5 *Ref. Korzun, “Supersonic Aerodynamic Characteristics of Blunt Body Trim Tab Configurations” • Langley Unitary Tunnel • Mach 2.5, 3.5, 4.5 • 38 different configurations • 50°/60°/70° cones, Apollo • Trim tab effectiveness (DCm) increases with tab area & cant angle • Tab aspect ratio (W/H) has a negligible effect International Planetary Probe Workshop 10, EDL Short Course

9. Sample Result: Trim Tab vs. Ballast 0.10 -0.10 0.09 -0.15 0.08 -0.20 MSL, L/D ≈ -0.29 0.07 -0.25 MSL 0.06 Ratio of Ballast to Entry Mass (L/D)trim -0.30 0.05 -0.35 0.04 notional curve fit -0.40 0.03 Extrapolated -0.45 0.02 0 10 20 30 40 50 60 70 80 90 0 10 20 30 40 50 60 70 80 90 Tab Cant Angle, deg Tab Cant Angle, deg International Planetary Probe Workshop 10, EDL Short Course • A 3% tab area with a 33° cant angle gives MSL L/D=0.29 at Mach 4.5 • No CG offset needed with tab (xCG/D = 0.291, zCG/D = 0)

10. Potential Trim Tab Applications One-Direction Pitch Control Pitch and Yaw Control 4.3% Area Tabs Shown (NASA TM-2011-216988) Two-Direction Pitch Control • Applications for single deployment or actuated tab(s): • 1 tab  One-direction pitch control  L/D magnitude • 2 tabs  Two-direction pitch control +/-L/D magnitude • 2+ tabs  Pitch & yaw control  L/D magnitude & direction International Planetary Probe Workshop 10, EDL Short Course

11. Technology Maturation Needs • No NASA missions are actively pursuing EDL missions with trim tabs, but improvements are needed to prepare the technology • Flight Mechanics: • Quantitative benefits of tabs vs. ballast for a range of EDL missions • EDL control strategies using fixed, single deployment, or actuated trim tab(s) • Aerodynamics & Aerothermodynamics: • Databases are needed for a range of tab parameters (area, cant angle) & Mach numbers • Validated CFD tools • Mechanical & TPS Design: • Mechanisms for tab stowage, deployment, and dynamic actuation • Lightweight TPS materials that minimize shape change (e. g. hot structures) • Mass estimation tools for entire tab system International Planetary Probe Workshop 10, EDL Short Course