Final Technical Report of a NIAC Phase 2 Study December 9, 2014 NASA Grant and Cooperative Agreement Number: NNX12AQ60G NIAC Phase 2 Study Period: 09/10/2012 – 09/09/2014 An Innovative Solution to NASA’s NEO Impact Threat Mitigation Grand Challenge and Flight Validation Mission Architecture Development PI: Dr. Bong Wie, Vance Coffman Endowed Chair Professor Asteroid Deflection Research Center Department of Aerospace Engineering Iowa State University, Ames, IA 50011 email: [email protected] (515) 294-3124 Co-I: Brent Barbee, Flight Dynamics Engineer Navigation and Mission Design Branch (Code 595) NASA Goddard Space Flight Center Greenbelt, MD 20771 email: [email protected] (301) 286-1837 Graduate Research Assistants: Alan Pitz (M.S. 2012), Brian Kaplinger (Ph.D. 2013), Matt Hawkins (Ph.D. 2013), Tim Winkler (M.S. 2013), Pavithra Premaratne (M.S. 2014), Sam Wagner (Ph.D. 2014), George Vardaxis, Joshua Lyzhoft, and Ben Zimmerman NIAC Program Executive: Dr. John (Jay) Falker NIAC Program Manager: Jason Derleth NIAC Senior Science Advisor: Dr. Ronald Turner NIAC Strategic Partnerships Manager: Katherine Reilly Contents 1 Hypervelocity Asteroid Intercept Vehicle (HAIV) Mission Concept 2 1.1 Introduction ...................................... 2 1.2 Overview of the HAIV Mission Concept ....................... 6 1.3 Enabling Space Technologies for the HAIV Mission . 12 1.3.1 Two-Body HAIV Configuration Design Tradeoffs . 12 1.3.2 Terminal Guidance Sensors/Algorithms . 13 1.3.3 Thermal Protection and Shield Issues . 14 1.3.4 Nuclear Fuzing Mechanisms ......................... 15 2 Planetary Defense Flight Validation (PDFV) Mission Design 17 2.1 The Need for a PDFV Mission ............................ 17 2.2 Preliminary PDFV Mission Design by the MDL of NASA GSFC . 20 2.2.1 Overview ................................... 20 2.2.2 HAIV System and Mission Design ...................... 20 2.2.3 Terminal Guidance, Navigation, and Control Subsystem . 26 2.2.4 Future Work for HAIV Mission Design . 29 2.2.5 Summary ................................... 31 2.3 Target Selection for the PDFV Mission ........................ 31 2.3.1 Reference Targets of the Don Quijote Mission Study . 32 2.3.2 Target Selection Problem Formulation . 32 2.3.3 Direct Intercept PDFV Mission ....................... 35 2.4 Recommendations for Planetary Defense . 38 3 Terminal Intercept Guidance with Optical and Infrared Seekers 43 3.1 Introduction ...................................... 43 3.2 Optical Image Rendering . .............................. 49 3.2.1 3D Polyhedron Optical Model for an Irregularly Shaped Asteroid . 49 i 3.2.2 Camera Focal Plane ............................. 50 3.2.3 Lighting Conditions ............................. 52 3.2.4 Pixel Value Assignment ........................... 52 3.2.5 Line-of-Sight Vector ............................. 54 3.3 Terminal Intercept Guidance with Optical Cameras . 54 3.4 IR Telescope/Seeker Characterization ........................ 55 3.4.1 IR Telescope/Seeker ............................. 55 3.4.2 Classical Cassegrain Telescope Optics . 55 3.4.3 Signal-to-Noise Ratio ............................ 61 3.4.4 NEOWISE IR Telescope ........................... 65 3.4.5 HAIV IR Telescope .............................. 65 3.5 Terminal Intercept Guidance with an IR Seeker . 67 4 Hypervelocity Kinetic Impact and Nuclear Subsurface Explosion: Modeling and Sim­ ulation 70 4.1 Introduction ...................................... 70 4.2 GPU-based ASPH Hydrocode Development ..................... 71 4.2.1 Adaptive Smoothed Particle Hydrodynamics (ASPH) Method . 72 4.2.2 Tensor Damage Model ............................ 74 4.2.3 Neighbor Finding Implementation ...................... 75 4.2.4 Grid Generation ............................... 75 4.3 Energy-Coupling Models ............................... 77 4.3.1 Introduction .................................. 77 4.3.2 Energy Deposition Modeling ......................... 78 4.3.3 Tillotson Equation of State .......................... 80 4.3.4 Shock Equation of State ........................... 82 4.3.5 Jones-Wilkins-Lee (JWL) Equation of State . 82 4.4 GPU-based ASPH Hydrocode Simulations . 82 4.4.1 Disruption of an Asymmetric Asteroid Model . 84 4.4.2 Subsurface Explosion Sensitivity Analysis . 86 4.4.3 GPU-Accelerated Computations ....................... 89 4.5 Thermal Shield Analysis and Design ........................ 91 4.5.1 Thermal Analysis Procedure ......................... 91 4.5.2 Improved Thermal Analysis Procedure . 97 4.6 Whipple Shield Analysis and Design ......................... 98 ii 5 Suborbital Intercept and Disruption of NEOs 108 5.1 Introduction ......................................108 5.2 An Optimum Suborbital Intercept Problem and Its Solutions . 111 5.2.1 Problem Formulation .............................111 5.2.2 Intercept Trajectory Optimization ......................115 5.2.3 Suborbital Intercept Examples ........................115 5.2.4 Late Intercept Solutions ...........................118 5.3 Higher ΔV Interceptors . 119 5.4 Practical Issues and Future Research Work ......................121 5.4.1 Fragmentation and Airbursts .........................121 5.4.2 EMP (Electromagnetic Pulse) Effects . 121 5.4.3 Launch Vehicle Mission Planning Issues . 122 5.4.4 Future Research Work ............................122 5.5 ATLAS (Asteroid Terrestrial-impact Last Alert System) . 123 6 Close Proximity Dynamics and Control Around Asteroids 125 6.1 Introduction ......................................125 6.2 Gravitational Models of an Irregular-Shaped Asteroid . 128 6.2.1 Spacecraft’s Equation of Motion .......................128 6.2.2 Polyhedron Gravitational Model .......................128 6.2.3 Spherical Harmonics Expansion Model . 131 6.2.4 Inertia Dyadic Gravitational Model . 133 6.2.5 Comparison of Gravitational Models . 137 6.3 Close Proximity Dynamics and Fuel-Efficient Orbit Control . 138 6.3.1 Close Proximity Orbital Dynamics ......................138 6.3.2 Fuel-Efficient Close Proximity Orbit Control . 140 6.4 Summary .......................................148 iii List of Figures 1.1 A summary of the ideal deflection ΔV performance characteristics of nuclear standoff explosions [9]. ............................... 4 1.2 Initial conceptual illustration of a two-body hypervelocity asteroid intercept vehi­ cle (HAIV) system, which was proposed for a NIAC Phase 1 Study in 2011 [12]. 6 1.3 A notional depiction of the HAIV mission concept further investigated for a NIAC Phase 2 Study in 2012–2014. ............................ 7 1.4 HAIV configuration options [13]. .......................... 7 1.5 A reference HAIV flight system and its terminal guidance operational concept [13]. 8 1.6 A 70-m asymmetric asteroid model disrupted by a 10-km/s kinetic impact and a subsequent 70-kt nuclear subsurface explosion of the HAIV system [17–19]. 10 1.7 Illustration of the disruption modeling and simulation problem [23]. 10 1.8 A summary of orbital dispersion simulation study results for nuclear subsurface explosions [23, 24]. .................................. 11 2.1 The Deep Impact mission trajectory [25–27]. 18 2.2 An experimental HAIV flight system designed by the MDL of NASA GSFC [15]. 21 2.3 A reference HAIV launch configuration with Atlas V 401 [15]. 22 2.4 A reference PDFV mission trajectory for a target asteroid (2006 CL9) [15]. 24 2.5 HAIV flight validation mission timeline by the MDL of NASA GSFC [15]. 25 2.6 Block diagram of the Autonomous Navigation System (ANS) of an experimental HAIV [15]. ...................................... 27 2.7 Block diagram of the Attitude Control System (ACS) of an experimental HAIV [15]. 28 2.8 Monte Carlo simulation results for intercepting an ideal 100-m target asteroid using the B-plane targeting method [15]. .......................... 29 2.9 Typical orbits of Amor, Apollo, Aten, and Atira asteroids. 33 2.10 Illustration of the Earth-Sun-Asteroid line-of-sight communication angle excluded for the PDFV mission [28]. .............................. 35 iv 2.11 International efforts in preparing for a planetary defense mission. Image courtesy of Lindley Johnson at NASA/NEOO. ........................ 38 2.12 A summary of various mitigation options for planetary defense. 39 2.13 Applicability of the HAIV mission concept to various mission scenarios. 40 3.1 Two-dimensional geometry illustration of the terminal intercept guidance problem [35, 36]. ........................................ 44 3.2 Trajectories, line-of-sight angle, commanded acceleration, and applied accelera­ tion of the pulsed PN guidance law applied to an ideal asteroid intercept prob­ lem [35, 36]. ..................................... 46 3.3 Closing velocity, line-of-sight rate, ΔV usage, and position error of the pulsed PN guidance law applied to an ideal asteroid intercept problem [35, 36]. 46 3.4 A 3D model of asteroid 433 Eros generated using NEAR’s laser rangefinder mea­ surements (left) and the surface gravitational acceleration of Eros computed using its polyhedron shape model (right) [37]. ....................... 47 3.5 Comparison of an optical image (left) and an ideal fictive IR image (right) of a scaled Eros polyhedron shape model [38, 39]. 48 3.6 An illustration for comparing optical and infrared images of asteroids with differ­ ent sizes and albedos (Image courtesy of NASA/JPL). 48 3.7 A triangulated shape model of asteroid 433 Eros. 49 3.8 Geometry illustration for optical image rendering and triangulation of surface points. 50 3.9 Illustration of a parallel trim reduction