International Planetary Probe Workshop 10 Entry, Descent, and Landing Systems Short Course Subject: Trim Tabs Author: Karl Edquist NASA Langley Research Center sponsored by International Planetary Probe Workshop 10 June 15-16, 2013 San Jose, California

International Planetary Probe Workshop 10, EDL Short Course 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 June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

MSL Entry Ballast System Ballast vs. Trim Tab 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 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 June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

International Planetary Probe Workshop 10, EDL Short Course Mars Robotic EDL Trim Tab Ballast Exo-Atmospheric Deploy Tab (a > 0) Eject Ballast (a > 0) Hypersonic Guided, L/D > 0 RCS Bank Control Eject Ballast (a = 0) Supersonic Guided, L/D > 0 L/D = 0 at Parachute Deploy Retract Tab (a = 0) Powered Descent & Touchdown June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

Mars Surface Elevation The mass savings of trim tabs can contribute to making the Mars southern hemisphere accessible to future robotic EDL missions -1 km MOLA +2.5 km MOLA Ref. “Statistics of Mars’ Topography from the Mars Orbiter Laser Altimeter: Slopes, Correlations, and Physical Models” June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

International Planetary Probe Workshop 10, EDL Short Course 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 June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

International Planetary Probe Workshop 10, EDL Short Course MSL-I Example 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) “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 June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

Recent Supersonic Wind Tunnel Testing* 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 60-deg Forebody 3% Tab, 30° Cant, M=4.5 *Ref. Korzun, “Supersonic Aerodynamic Characteristics of Blunt Body Trim Tab Configurations” June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

Sample Result: Trim Tab vs. Ballast 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) MSL, L/D ≈ -0.29 notional curve fit Extrapolated Tab Cant Angle, deg 20 40 60 80 90 10 30 50 70 (L/D)trim -0.40 -0.30 -0.35 -0.15 -0.10 -0.20 -0.25 -0.45 Tab Cant Angle, deg 20 40 60 80 90 10 30 50 70 Ratio of Ballast to Entry Mass 0.05 0.06 0.09 0.10 0.08 0.07 0.04 0.03 0.02 MSL June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

Potential Trim Tab Applications 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 One-Direction Pitch Control Pitch and Yaw Control 4.3% Area Tabs Shown (NASA TM-2011-216988) Two-Direction Pitch Control June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course

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 June 15-16, 2013 International Planetary Probe Workshop 10, EDL Short Course