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Entry, Descent, and Landing Systems Short Course Subject:Trim Tabs Author:Karl Edquist NASA Langley Research Center sponsored by International Planetary.

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Presentation on theme: "Entry, Descent, and Landing Systems Short Course Subject:Trim Tabs Author:Karl Edquist NASA Langley Research Center sponsored by International Planetary."— Presentation transcript:

1 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

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 (Z CG ) off axis –Mars EDL: Viking I/II (L/D = 0.18, Z CG /D = = 1.83”) MSL (L/D = 0.24, Z CG /D = = 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, 20132International Planetary Probe Workshop 10, EDL Short Course

3 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 3June 15-16, 2013 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 Entry Ballast (~160 kg) Cruise Ballast (~140 kg) 3.92” MSL Entry Ballast System Lift V∞V∞ Drag NASA/TM International Planetary Probe Workshop 10, EDL Short Course

4 Mars Robotic EDL Exo-Atmospheric Hypersonic Guided, L/D > 0 Supersonic Guided, L/D > 0 L/D = 0 at Parachute Deploy Trim TabBallast Deploy Tab (  > 0) Eject Ballast (  > 0) Retract Tab (  = 0) Eject Ballast (  = 0) Powered Descent & Touchdown RCS Bank Control 4June 15-16, 2013International Planetary Probe Workshop 10, EDL Short Course

5 Mars Surface Elevation The mass savings of trim tabs can contribute to making the Mars southern hemisphere accessible to future robotic EDL missions 5 -1 km MOLA+2.5 km MOLA Ref. “Statistics of Mars’ Topography from the Mars Orbiter Laser Altimeter: Slopes, Correlations, and Physical Models” International Planetary Probe Workshop 10, EDL Short CourseJune 15-16, 2013

6 AIAA NASA TM Past Studies June 15-16, 2013 NASA TM X-660, 1962 NASA TM X-770, 1963 NASA TM X-816, 1963NASA TM X-579, 1961 AIAA AIAA International Planetary Probe Workshop 10, EDL Short Course AIAA

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

8 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 (  C m ) increases with tab area & cant angle –Tab aspect ratio (W/H) has a negligible effect June 15-16, 2013 *Ref. Korzun, “Supersonic Aerodynamic Characteristics of Blunt Body Trim Tab Configurations” 8International Planetary Probe Workshop 10, EDL Short Course 60-deg Forebody 3% Tab, 30° Cant, M=4.5

9 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 (x CG /D = 0.291, z CG /D = 0) June 15-16, 2013International Planetary Probe Workshop 10, EDL Short Course Tab Cant Angle, deg Ratio of Ballast to Entry Mass MSL MSL, L/D ≈ notional curve fit Extrapolated Tab Cant Angle, deg (L/D) trim

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

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 11June 15-16, 2013International Planetary Probe Workshop 10, EDL Short Course


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