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A LUNAR LASER RANGING RETRO-REFLECTOR ARRAY for the 21 st CENTURY Professor Douglas Currie University of Maryland, College Park, MD, USA NASA Lunar Science Institute, Moffett Field, CA INFN – LNF, Laboratori Nazionali di Frascati, Italy
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A LUNAR LASER RANGING RETRO-REFLECTOR ARRAYfor the 21st CENTURY Professor Douglas Currie University of Maryland, College Park, MD, USA NASA Lunar Science Institute, Moffett Field, CA INFN – LNF, Laboratori Nazionali di Frascati, Italy & The LLRRA-21 Teams with the Lunar University Network for Astrophysics Research Jack Burns, Director
OUTLINE • Introduction of Structure • Outline of Talk • Consideration of Apollo Results • Science Areas • Lunar Physics • Lunar Core • Other • Relativity Physics • Inertial Properties of Gravitational Energy • Temporal Change of G • Spatial Change of G • General Review • Problem Due to Librations • Solution – Single CCR • LLRRA-21 • Why a Solution • Design • Signal Performance • Emplacement Issues • Decadal Remarks • Planetary - Astronomy Panel • Astronomical - • Different Accuracies • Expected Science • Lunar • Relativity • Mission – Flights • Google Lunar X Prize • Lunette • LGN • Acknowledgements NLSI Commerce Virtual Lecture 23 February 2011
OVERVIEW • Science Heritage – The Apollo Arrays • Current Status and Science Objectives of LLR • Objectives and Method for the Next Generation Retroreflector • Challenges and Solutions • Robotic Emplacement on Lunar Surface • Will it Work – Heritage • Will it Work – Computer Simulation of Optical/Thermal Performance • Will It Work – Thermal Vacuum Testing of Package • Will it Work – Science Objectives • Critical Vendors • Flight Opportunities NLSI Commerce Virtual Lecture 23 February 2011
Why Laser Ranging • Exquisitely Precise Range • Range is Sensitive to Many Parameters • Relativity • Geo-Physics (Earth Satellites) • Seleno-Physics (Lunar Observations) • Satellite Ranging • Esp. LAGEOS, but also Other Satellites • Gravity Field, Crustal Properties, etc, etc. NLSI Commerce Virtual Lecture 23 February 2011
What do I Mean by Precise • The APOLLO Station is Currently Ranging • At a Level of 2.4 parts in 1,000,000,000,000 • If My Eyes were This Good, I Could • Read a License Plate on the Moon • Inspect Someone’s DNA Amino Acid • In San Francisco from Washington • Detect Tiny General Reletivity Effects • Detect the Sloshing of the Liquid Lunar Core NLSI Commerce Virtual Lecture 23 February 2011
But Why the Moon ?? • Second Brightest Object in the Sky • Basis of Time Keeping – Lunar Calendar • Jewish and Muslim Religious Holidays • First light of moon to Start Ramadan • Results Holidays Moving About Solar Seasons • Solar calendar • Better for Planting of Crops NLSI Commerce Virtual Lecture 23 February 2011
Why Laser Ranging to the Moon • Ideally Want to Track an Object • Which Travels on a Geodesic • Problems • Solar Photons Push Satellite to New Orbit • Heated Surface of Satellite Emits IR Photons • Moon has Much Better Mass/Surface Ratio • Besides, We Learn of the Lunar Interior NLSI Commerce Virtual Lecture 23 February 2011
Background • Retroreflector Array to moon on Apollo 11 1969 • How do we do laser ranging? • Send a very short laser pulse toward the moon • Time the interval between transmission & reflection • But reflection from the Lunar Surface is too weak • Need to send the light back to the Transmitter • Enter the Cube Corner Reflector • Sends the Light Back to the Source • “Strong” i.e. Usable Signal Level NLSI Commerce Virtual Lecture 23 February 2011
What have the Apollo Arrays Done • The Earth-Moon System Provides an Ideal System • To Evaluate Relativity and Einstein’s Theory • To Understand the Interior of the Moon • Moon is Massive enough to Resist Drag/Pressure • Moon is Far Enough to be in a Solar Orbit (Weakly Bound) • LLR Currently Provides our Tests of: • The Weak Equivalence Principle (WEP)*: a / a < 1.310-13 • The Strong Equivalence Principle (SEP): < 4104 • Time-Rate-of-Change of G to < 710 13 per year • Inverse Square Law to 3 10 11 at 10 8 m scales • Geodetic Precession to 0.6 % • Gravitomagnetism to 0.1 % • Initial Definition of Liquid Lunar Core • Love Numbers of the Crust • Free Librations and Q of the Moon NLSI Commerce Virtual Lecture 23 February 2011
ASTRO2010 DECADAL SURVEYGravitational and Particle Physics Panel Much is unknown about fundamental theory: Modifications of general relativity on accessible scales are not ruled out by today’s fundamental theories and observations. It makes sense to look for them by testing general relativity as accurately as possible. Cost-effective experiments that increase the precision of measurement of PPN parameters, and test the strong and weak equivalence principles, should be carried out. For example, improvements in Lunar Laser Ranging promise to advance this area. NLSI Commerce Virtual Lecture 23 February 2011
ASTRO2010 DECADAL SURVEYGravitational and Particle Physics Panel • The direct detection of gravitomagnetic effects (the Lense-Thirring precession) from Lageos/Grace, Gravity Probe B, and lunar laser ranging. • The lunar laser ranging verification of the strong equivalence principle to 10-4, meaning that the triple graviton vertex is now known to a better accuracy than the triple gluon vertex. • Limits on the fractional rate of change of the gravitational constant • G (< 10-12) Limits on the fractional rate of change of the gravitational constant G (< 10-12/yr) from lunar laser ranging. Atomic experiments limiting time variation of the fine structure constant to 10-16/yr over periods of several years. • Experiments that are in progress include the Microscope equivalence principle experiment, the APOLLO lunar laser ranging observations, and tests of general relativity using torsion balances and atom interferometry. • Improved strong and weak equivalence principle limits. Better determination of PPN parameters and and Ġ/G from next generationLunar laser ranging NLSI Commerce Virtual Lecture 23 February 2011
ASTRO2010 DECADAL SURVEYGravitational and Particle Physics Panel • A new Lunar Laser Ranging (LLR) program, if conducted as a low cost robotic mission or an add-on to a manned mission to the Moon, offers a promising and cost-effective way to test general relativity and other theories of gravity (Figure 8.12). So far, LLR has provided the most accurate tests of the weak equivalence principle, the strong equivalence principle and the constancy in time of Newton’s gravitational constant. These are tests of the core foundational principles of general relativity. Any detected violation would require a major revision of current theoretical understanding. As of yet, there are no reliable predictions of violations. However, because of their importance, the panel favors pushing the limits on these principles when it can be done at a reasonable cost. The installation of new LLR retroreflectors to replace the 40 year old ones might provide such an opportunity. The panel emphasizes again that its opinion that experiments improving the measurements of basic parameters of gravitation theory are justified only if they are of moderate cost. Therefore, it recommends that NASA’s existing program of small- and medium-scale astrophysics missions address this science area by considering, through peer review, experiments to test general relativity and other theories of gravity. The panel notes that a robotic placement of improved reflectors for LLR is likely to be consistent with the constraints of such a program. It returns to this recommendation below in the context of a recommendation to augment the Explorer program. NLSI Commerce Virtual Lecture 23 February 2011
ASTRO2010 DECADAL SURVEY Cosmology and Fundamental Physics Panel These complex spin-induced orbital effects are the consequences of “frame dragging,” a fundamental prediction of Einstein’s theory that has been probed in the Solar System using Gravity Probe B, LAGEOS satellites, andLunar laser ranging, and has been hinted at in observations of accretion onto neutron stars and black holes. NLSI Commerce Virtual Lecture 23 February 2011
LLR LUNAR SCIENCEOVERVIEW • Elastic Tides of the Moon • Tidal Dissipation • Size and Oblateness of Liquid Core • Dissipation at Liquid-Core/Solid-Mantle Interface • Lunar Moment of Inertia • Fluid Core Moment of Inertia • Evolution and Heating • Existence of a Smaller Solid Inner Core • Selenodetic Site Positions NLSI Commerce Virtual Lecture 23 February 2011
LLR RELATIVITY SCIENCEOVERVIEW • Strong Equivalence Principle • Weak Equivalence Principle • Time Variation of Gravitational Constant • GravitoMagnetic Effects • Deviation of 1/r2 – • MOND Theories of Gravitation • Fundamental Inconsistency of • General Relativity and Quantum Mechanics NLSI Commerce Virtual Lecture 23 February 2011
LLRRA-21 Science Motivations • Astrophysical Science Motivations • Fundamental Incompatibility Between • Quantum Mechanics and General Relativity • Dark Energy may be Aspect of Large-Scale Gravity • Dvali Idea Replaces Normal GR with “Leaky” Gravity • Can be Seen in Precession of Lunar Orbit • Dark Matter inspires Alternative Gravity Models (MOND) • Further Tests of Inverse Square Law could Confirm or Deny • Lunar Science Motivations • Liquid Core – Dimensions, Shape, Rotation • Inner Solid Core – Existence, Size, Rotation • Rotational Dynamics – Q, External Impacts NLSI Commerce Virtual Lecture 23 February 2011
SHORT HISTORY • Apollo Lunar Laser Ranging Arrays 1969 • Thermal and Optical Analysis and Testing • McDonald LLR Station • 2006 • Return to the Moon • Could Address Accuracy Limit • 2007 • LSSO for 100 mm CCR • Lunar Science Sortie Opportunities • 2009 • NLSI > LUNAR at University of Colorado NLSI Commerce Virtual Lecture 23 February 2011
LIBRATION PROBLEMS • Why is there a Problem with the Apollo Arrays • Libration in Both Axis of 8 degrees • Apollo Arrays are Tilted by the Lunar Librations • CCR in Corner is Further Away by Several Centimeters • Even Short Laser Pulse is Spread • Results in a Range Uncertainty by ~2 cm • APOLLO Station of Tom Murphy UCSD • Thousands of Returns per Normal Point • Root N to Get Range to 1 – 2 millimeters • Needs Large Telescope • Hard to get Daily Coverage NLSI Commerce Virtual Lecture 23 February 2011
APOLLO Data from Tom Murphy NLSI Commerce Virtual Lecture 23 February 2011
LLRRA-21 PROGRAM • Solid 100 mm Cube Corner Reflector • 42 Year Heritage on the Moon • Hundreds on Satellites • Technology Readiness Level (TRL) = 6.5 • Lunar Deployment Program • Phase I • Surface Emplacement • Supports Sub Millimeter Single PhotoElectron Ranging • 2013 - 2014 • Phase II • Anchored Emplacement • Supports SPE Ranging at less than 100 microns • 2016 or Later NLSI Commerce Virtual Lecture 23 February 2011
LLRRA-21 Teams • LSSO Team – NASA • Douglas Currie Principal Investigator • University of Maryland, College Park, College Park m MD, USA • NLSI, Moffett Field, CA, USA & • INFN-LNF Frascati, Italy • Bradford Behr • University of Maryland, College Park, MD, USA • Tom Murphy • University of California at San Diego, San Diego, CA , USA • Simone Dell’Agnello • INFN/LNF Frascati, Italy • Giovanni Delle Monache • INFN/LNF Frascati, Italy • W. David Carrier • Lunar Geotechnical Institute, Lakeland, FL, USA • Roberto Vittori • Italian Air Force, ESA Astronaut Corps • Ken Nordtveldt • Northwest Analysis, Bozeman, MT, USA • Gia Dvali • New York University, New York, NY and CERN, Geneva, CH • David Rubincam • GSFC/NASA, Greenbelt, MD, USA • Arsen Hajian • University of Waterloo, ON, Canada • INFN-LNF Frascati Team • Simone Dell’Agnello PI INFN-LNF, Frascati, Italy • Giovanni Delle Monache INFN-LNF, Frascati, Italy • Douglas Currie U. of Maryland, College Park, MD, USA • NLSI, Moffett Field, CA, USA & • INFN-LNF, Frascati, Italy • Roberto Vittori Italian Air Force & ESA Astronaut Corps • Claudio Cantone INFN-LNF, Frascati, Italy • Marco Garattini INFN-LNF, Frascati, Italy • Alessandro Boni INFN-LNF, Frascati, Italy • Manuele Martini INFN-LNF, Frascati, Italy • Nicola Intaglietta INFN-LNF, Frascati, Italy • Caterina Lops INFN-LNF, Frascati, Italy • Riccardo March CNR-IAC & INFN-LNF, Rome, Italy • Roberto Tauraso U. of Rome Tor Vergata & INFN-LNF • Giovanni Bellettini U. of Rome Tor Vergata& INFN-LNF • Mauro Maiello INFN-LNF, Frascati, Italy • Simone Berardi INFN-LNF, Frascati, Italy • Luca Porcelli INFN-LNF, Frascati, Italy • Giuseppe Bianco ASI Centro di Geodesia Spaziale • “G. Colombo”, Matera, NLSI Commerce Virtual Lecture 23 February 2011
CHALLENGES for SOLID CCR • Fabrication of the CCR to Required Tolerances • Sufficient Return for Reasonable Operation • Ideal Case for Link Equation • Thermal Distortion of Optical Performance • Absorption of Solar Radiation within the CCR • Mount Conductance - Between Housing and CCR Tab • Pocket Radiation - IR Heat Exchange with Housing • Solar Breakthrough - Due to Failure of TIR • Stability of Lunar Surface Emplacement • Problem of Regolith Heating and Expansion • Drilling to Stable Layer for CCR Support • Thermal Blanket to Isolate Support • Housing Design to Minimize Thermal Expansion NLSI Commerce Virtual Lecture 23 February 2011
CCR FABRICATION CHALLENGE • CCR Fabrication Using SupraSil 1 Completed • Specifications / Actual • Clear Aperture Diameter - 100 mm / 100 mm • Mechanical Configuration - Expansion of Our APOLLO • Wave Front Error - 0.25 / 0.15 [ l/6.7 ] • Offset Angles • Specification • 0.00”, 0.00”, 0.00” +/-0.20” • Fabricated • 0.18”, 0.15”, 0.07” • Flight Qualified • with Certification NLSI Commerce Virtual Lecture 23 February 2011
THERMAL ANALYSIS – THEORETICALSolar Absorption within CCR • Solar Heat Deposition in Fused Silica • Solar Spectrum – AMO-2 • Absorption Data for SupraSil 1/311 • Compute Decay Distance for Each Wavelength • Compute Heat Deposition at Each Point • Beer’s Law • Thermal Modeling Addresses: • Internal Heat Transport and Fluxes • Radiation from CCR to Space • Radiation Exchange with Internal Pocket Surroundings • Mount Conduction into the Support Tabs NLSI Commerce Virtual Lecture 23 February 2011
MOUNT CONDUCTANCE • Challenge: • Heat flow from Housing to CCR at Tabs • Optical Distortion due to Heat Flux • Support of CCR with KEL-F “Rings” • Intrinsic Low Conductivity • Use of Wire Inserts - Only Line Contacts • Line Contact of Support Reduces Heat Flow • For Support in Launch Environment • KEL-F Wire Compresses and • Launch Support Comes from Flush on Tab • Estimated (to be Validated in SCF) 1 Milli-W/oK NLSI Commerce Virtual Lecture 23 February 2011
POCKET RADIATION EXCHANGE • Challenge: • IR Radiation Between CCR & Housing • SiO2 Has High IR Absorptivity/Emissivity • Heat Flux Causes Optical Distortion • Isolation Between CCR and Housing • Low Emissivity Coatings – 2% Emissivity • Successive Cans or Multiple Layers • Simulations Show Isolation is Effective • Thermal Vacuum Chamber Validation • In April 2009 at SCF at INFN/LNF at Frascati NLSI Commerce Virtual Lecture 23 February 2011
INNER & OUTER THERMAL SHIELDS NLSI Commerce Virtual Lecture 23 February 2011
THERMAL & SUNSHADE • Role of Sun Shade • Thermal Control and Sun Blocking • Dust Protection • UltraViolet Light Protection • External Surface • Highly Reflective in Visible • High Emissivity in the Infrared • Internal Surface • Black in the Visible • Low Emissivity in the Infrared NLSI Commerce Virtual Lecture 23 February 2011
LLRRA-21 PACKAGE NLSI Commerce Virtual Lecture 23 February 2011
ORBITAL THERMAL EVOLUTION • Simulation Performed with • Thermal Desktop • C&R Technologies • IDL • Code V • Initial Analysis • “Steady State” Behavior • Fixed Elevation of Sun • But During Lunar Month • Changing Illumination • Both Intensity and Angle • For CCR/Housing/Thermal Blanket/Regolith • Some Time Constants are Longer than a Month • Analysis of Behavior of Face to Tip Temperature Difference NLSI Commerce Virtual Lecture 23 February 2011
Simulation Procedure • AutoCad Drawing of Total Package • CCR, Housing, Internal and External Support and Regolith • 4-D Heat Deposition in CCR – UMd IDL Program • Through a Lunation, 1 Nanometer Wavelength Bands, • Many Thousands of Nodes, Reflection Effects of SunShade • Thermal Desktop • Computes Temperature at Each Node • PhaseMap – UMd IDL Program • Converts 3D Temperatures to 2D PhaseMap at Each of 400 Sun Angles • Code V Optical Analysis Program • Adds Optical Errors (Reflection Phases, Offset Angles to Thermal Errors • Analysis Program – UMd IDL Program • Evaluates Laser Return Intensity - Addressing • Velocity Aberrations and Station Latitude • Polarization Effects NLSI Commerce Virtual Lecture 23 February 2011
Thermal Simulation ComparisonEffect of Multi-Layer Insulation Internal Sun Shade: X Dark Mirror Inner Conformal Can: Silver - 0.6% Emissivity External Surface: MLI & SSM Sun Shade Length: 100 mm Internal Sun Shade: X Dark Mirror Inner Conformal Can: Silver - 0.6% Emissivity External Surface: No MLI & SSM Sun Shade Length: 100 mm NLSI Commerce Virtual Lecture 23 February 2011
FULL Thermal SimulationAnchored Emplacement Regolith from Apollo HFE, Thermal Blanket Current Design Housing Temperature Distribution in CCR and Tip to Face Temperature Difference NLSI Commerce Virtual Lecture 23 February 2011
CURRENT STATUS • Preliminary Definition of Overall Package • Completed Preliminary Simulations • LSSO – Lunar Science Surface Opportunities • Thermal (CCR, Regolith, Housing), Optical • Completed Phase I Thermal Vacuum Tests • Solar Absorption Effects on CCR • CCR Time Constants – • IR Camera – Front Face • Thermocouples – Volume • Preliminary Optical FFDP NLSI Commerce Virtual Lecture 23 February 2011
SCF Thermal Vacuum TestInfrared Imager Full Dynamic Range Heat Flow Due to Tab Supports NLSI Commerce Virtual Lecture 23 February 2011
Dust AcceleratorUniversity of Colorado Fused Silica Witness Plates NLSI Commerce Virtual Lecture 23 February 2011
LLRRA-21 SIGNAL STRENGTH • 88% of the Current Apollo 15 Signal Level • At End of First Decade still about the same as Apollo 15 and • 2.64 Stronger than Apollo 11 • Simulated Pattern with Offset Angles to Correct for Velocity Aberration • Relative to Current A11 • On Axis Return is 49% of Apollo 11 • At Velocity Aberrated Latitude , the Return is ~55% of Apollo 11 • But No Dust so Stronger by a Factor of 9.6 • Overall – Stronger Than Apollo 11 by a factor of 2.64 • Overall – 90% of the return of Apollo 15 • If Dust on the Apollo Array is due LEM Launch – LLRRA-21 has a Cover for Landing Dust • If Dust on the Apollo Arrays is due to Steady Deposit of Dust or High Velocity Impacts • There would be at Least a Decade of Good Returns • But LLRRA-21 Should Expect Better Performance • Sun Shade • Dust Mitigator • APOLLO Station gets Many Thousands of Returns in 5 Minutes on Apollo 15 Almost Every Night • 3.6 meter Therefore Smaller Telescopes can Work • At 1,000 Returns on 3.6 Meter, • One Should get 80 Returns on 1 Meter and 25 Returns on 0.6 meter Telescope NLSI Commerce Virtual Lecture 23 February 2011 NLSI Commerce Virtual Lecture 23 February 2011
ROBOTIC DEPLOYMENT • Deployment Methods • Lander Mounting • Few Millimeters • Thermal Expansion of Lander during Lunation • Surface Deployment • Sub-Millimeter • Regolith Expansion during Lunation • Anchored Deployment • Tens of Microns NLSI Commerce Virtual Lecture 23 February 2011
ROBOTIC DEPLOYMENT • Candidate Flight Opportunities • Google X Prize • Astrobotics – David Gump • Moon Express – Bob Richards • Lunette – Discovery Mission Proposal • LLRRA-21 is Backup Retroreflector Package • ILN • Future NASA Possibility NLSI Commerce Virtual Lecture 23 February 2011
ROBOTIC DEPLOYMENTRequirements • Orientation • Three Angles • Toward the Earth • Azimuth and Elevation • About One Degree • :Clocking” • Accommodation for Velocity Aberration • About One Degree NLSI Commerce Virtual Lecture 23 February 2011
LUNAR SURFACE EMPLACEMENT • CCR Optical Performance at Sub-Micron • Want to Assure as Much of This as Possible • We Have Sufficiently Strong Return • Emplacement Issues - Diurnal Heating of Regolith • ~ 400 Microns of Lunar Day/Night Vertical Motion • Solutions – Dual Approach for Risk Reduction • Drill to Stable Layer and Anchor CCR to This Level • ~ one meter – Apollo Mission Performed Deeper Drilling • ~ 0.03 microns of motion at this depth • Stabilize the Temperature Surrounding the CCR • Multi Layer Insulation Thermal Blanket – 4 meters diameter • Support Rod Sees a Constant Temperature Environment NLSI Commerce Virtual Lecture 23 February 2011
SURFACE DEPLOYMENT • Issues • CCR Should Point Toward Earth “Center” • Maintain Clocking Angle • to Handle Sun Break-through • Handle Longitudinal (toward earth) Tilt of Surface • Handle Azimuthal Tilt of Surface • Requirements • Self Orienting Procedure to Keep Clocking Angle • Longitudinal (Elevation) Self Orientation • Azimuth Angle Adjusted by Deployment Arm • Calibrated by Goniometer (Sun Dial) NLSI Commerce Virtual Lecture 23 February 2011
ROBOTIC DEPLOYMENTSurface Deployment NLSI Commerce Virtual Lecture 23 February 2011
DEPLOYMENT APPROACHSSurface Deployment • Candidates • Reference w.r.t. Regolith Surface • Uneven Surface a Problem • Reference to Local Gravity Vector • Wire Support • Clocking and Elevation Self Orienting • Azimuth Correction by: • Lander Arm • Dedicated Motor • Demonstration • Frame Design and Pick-up Procedure • Needs Info on the Capabilities of the Lander Arm NLSI Commerce Virtual Lecture 23 February 2011
ROBOTIC DEPLOYMENTAnchored Deployment • Problem with Regolith Expansion • During a Lunation • 300K at Surface • ~ 400 microns • Solution • Anchor CCR below Thermally Active Region • Drill to a Meter or Less • Small Fraction of a Degree Variation • Anchor at Base NLSI Commerce Virtual Lecture 23 February 2011
ANCHORED DEPLOYMENT NLSI Commerce Virtual Lecture 23 February 2011
PNEUMATIC PROBOSCIS SYSTEMKris Zacny – Honeybee, Inc. NLSI Commerce Virtual Lecture 23 February 2011
CRITICAL VENDORS • Cube Corner Retroreflectors • ITE, Inc. Laurel, Maryland, USA • Ed Aaron, President • Fabricated CCR #1 of LLRRA-21 Program • Successfully met Specifications • Fabricated Flight CCR Arrays of Apollo Design for: • ETS-8, QZSS Japan • Naval Research Laboratory • NASA • U.S. Air Force NLSI Commerce Virtual Lecture 23 February 2011
CRITICAL VENDORS • Thermal Shields, Inner & Outer • Epner Technologies, Inc. • David Epner, President • Fabricated Shields for LLRRA-21 SCF Tests • Successful Operation in Thermal Vacuum Test • Epner has Fabricated LaserGold Shields for • NOAA – GOES Satellites for 25 years • NASA – Hubble WFPC, MOLA Laser Altimiter • Advanced Chemical Experiment NLSI Commerce Virtual Lecture 23 February 2011
CRITICAL VENDORS • Housing and Deployment Frame • L-3. SSG, Inc. In • Joseph Robichaud, Chief Technology Officer • Silicon Carbide – Low Thermal Expansion • Fabricated SiC for Space Applications for • Jet Propulsion Laboratory • NASA • Naval Research Laboratory NLSI Commerce Virtual Lecture 23 February 2011