Kinetic Impactors and Gravity Tractors for Asteroid Deflection

Bong Wie Asteroid Deflection Research Center Department of Aerospace Engineering Iowa State University

ADRS 2008 October 23-24, 2008 1 Presentation Outline

• Introduction

• Kinetic Impactors

• Gravity Tractors

• Concluding Remarks

2 ADRC’s Mission Statement Develop the science, engineering, and technology needed to reliably deflect or disrupt those large asteroids or comets that could collide with Earth and cause a global climate change or the end of civilization

65 Million Years Ago 13,000 Years Ago Sooner or later 3 Major Impact Craters in North America

Courtesy of Planetary and Space Science Centre University of New Brunswick, Canada 4 Asteroid-Earth Collision Problem = Astrodynamical “Traffic Accident” Problem

Wie, B., “Solar Sailing Kinetic Energy Interceptor (KEI) Mission for Impacting/Deflecting Near-Earth Asteroids,” AIAA Guidance, Navigation, and Control Conference, August 15-18, 2005. 5 “The asteroid we should worry about is the asteroid that we don't know about, and there are many NEOs yet to be discovered and characterized.” ------Detection/Characterization problem

6 “The asteroid we should worry about is the asteroid that we don't know about, and there are many NEOs yet to be discovered and characterized.” ------Detection/Characterization problem “An Earth impact by a large NEO and its resulting global climate change will cause the end of civilization, and the high-energy deflections or disruptions may be the only practically viable option for the prevention of human extinction.”

------Deflection problem 7 Full Deflection Alternatives Trade Tree From “Near Earth Object Program” by Lindley Johnson, Presented to Aerospace Technology Working Group, 27 May 2008

DeflectionDeflection

NuclearNuclearNuclear NonNonNon- -Nuclear-NuclearNuclear

FastFastFast Reaction Reaction Reaction SlowSlowSlow Reaction Reaction Reaction FastFastFast Reaction Reaction Reaction SlowSlowSlow Reaction Reaction Reaction

NuclearNuclearNuclear Electric Electric Electric ExplosivesExplosivesExplosives ExplosivesExplosivesExplosives MassMassMass Driver Driver Driver PropulsionPropulsionPropulsion

FocusedFocused Solar Solar NuclearNuclearNuclear Standoff Standoff Standoff GravityGravityGravity Tractor Tractor ConventionalConventionalConventional Standoff Standoff Standoff Focused Solar

YarkovskyYarkovsky Effect Effect NuclearNuclearNuclear Surface Surface Surface SpaceSpaceSpace Tug Tug ConventionalConventionalConventional Surface Surface Surface Yarkovsky Effect

GravityMass TractorDriver NuclearNuclearNuclear Subsurface Subsurface Subsurface ConventionalConventionalConventional Subsurface Subsurface Subsurface Mass Driver

KineticKineticKinetic Energy Energy Energy FocusedFocusedSpace Tug Laser Laser

8 KineticKineticKinetic Impactor Impactor Impactor Researchers at Iowa State Alric Rothmayer: Asymptotic analysis (matched asymptotics, multiple scales, homogenization, etc.); Large scale computational simulations for simple geometries (including parallel); Fluid/solid phase transitions (i.e. melting).

Z.J. Wang: Parallel computing on large scale parallel architectures; Geometry modeling and grid generation for complex geometry; Computational fluid dynamics including moving interface problems. Director of the CFD Center at Iowa State

9 Tom Shih: Thermal-fluid sciences and computational methods.

John Basart: Electromagnetic theory and radiation mechanisms; Astrophysical plasmas and waves in plasmas; Radio astronomy and remote sensing.

Alfred Kracher (Scientist at Ames DOE Laboratory): Cosmochemistry, asteroid composition and structure. Previously at the Arkansas Center for Space and Planetary Sciences (Kracher and Sears, Icarus 174, 36/2005)

10 Ping Lu: Spacecraft guidance and trajectory optimization for asteroid intercept, rendezvous and proximity operations.

Bong Wie: Space vehicle dynamics and control; dynamics and control of kinetic impactors, gravity tractors, and solar sails; space mission design for asteroid deflection utilizing high-energy as well as low-energy options

11 ADRC’s 5-Year Research Plan for High-Energy Nuclear Approach • Multi-phase physical modeling of asteroid surface ablation/vaporization due to X-rays, gamma-rays, and neutrons from nuclear standoff explosions • Surface material characterization, ejecta modeling, and DV computation • Validation of an optimal standoff distance of 20 m • Fragmentation modeling, analysis, and simulation • Orbital trajectory analysis/simulation and Earth-impact damage assessment for fragmented bodies • Development of a high-performance (e.g., peta-scale) computer code for efficient modeling, analysis, and simulation of asteroid deflection using nuclear blasts 12 B. Kaplinger, B. Wie, and J. Basart, “Analysis of Nuclear Standoff Explosions for Deflecting Near-Earth Objects,” AIAA Paper, 2008.

1-km Target Asteroid

)

s

V (cm/ V D

Standoff Distance (m) 13 Behavior of Volatiles in High Energy Deflection Strategies (Prof. Alric Rothmayer, Iowa State University)

• Comet out-gassing simulations use rarefied gas models to create thrust • Current nuclear and thermal heating deflection strategies focus on coupling to solids • Examine the role of volatiles in creating thrust or uncertainty in thrust and spalling Initial state Rarefied vapor/particle flow

Interior Vacuum/coma

Ice-free “crust” Preliminary computed surface force Embedded volatiles (water ice, carbon dioxide ice, etc.)

Overall geometry

Energy deposition (gamma rays, neutrons, light and heavy particles, residual debris)

Comet Source 1D near-surface thin-layer laminar/compressible simulation

(comets are estimated to have produced about 36% of known craters over 30 km diam and 70% of craters over 60 km diameter in last 100M years. Source: Rampino & Haggerty, “Extraterrestrial 14 impacts and mass extinctions of life,” in Hazards due to Comets & Asteroids, 1994) Behavior of Volatiles in High Energy Deflection Strategies (Prof. Alric Rothmayer, Iowa State University)

• Current focus – High density/pressure dissociated water vapor in local chemical equilibrium – 1D models for dissociated-vapor expansion into vacuum from solid/porous ice – Neutron deposition models for hydrogenated media with rapid heating – Assess flow regimes for small-scale pore expansion and larger-scale blow-off (i.e. laminar/turbulent, subsonic/supersonic, etc.)

15 Behavior of Volatiles in High Energy Deflection Strategies (Prof. Alric Rothmayer, Iowa State University) • Near future work – Assess thermal ionization levels within computations – Assess time-scale coupling between the vapor expansion, blow-off, melting, vaporization and chemical non-equilibrium flows – Add radiation transport models – Develop models for larger scale gravitational coupling to the blow-off • Longer term work – Add fluid-solid coupling to solid-aggregate and incorporate 3D effects – Improve energy deposition models and create residual debris impact models 16 ADRC’s Research Plan for Non-Nuclear Approaches

• Prograde (rear-end) vs. retrograde (head-on) kinetic impactor mission design (Wie, 2005) • Trajectory optimization for kinetic-impactor missions (Dachwald and Wie, 2007) • Impact dynamics, ejecta modeling, and fragmentation • Precision orbital guidance, navigation and control • A single hovering gravity tractor (Lu and Love, 2005) vs. multiple gravity tractors in halo orbits (Wie, 2008) • Gravitational potential modeling of spinning irregular shaped asteroids and its effect on spacecraft controls

17 ADRC’s Research Plan for Non-Nuclear Approaches

Other non-nuclear options:

• Solar-reflector GT (Jeff Fisher, Lockheed Martin)

• Antimatter-based planetary defense system (AFRL)

18 Kinetic Impactors

• Deep Impact Mission (July 4, 2005)

• ESA's Don Quijote Mission

• Solar-Sailing Kinetic Impactors (Wie, 2005)

19 20 21 22 23 24 “Solar-Sail Kinetic Impactor Concept,” B. Wie, AIAA GNC, 2005

NASA Workshop on NEO Detection and Mitigation, June 2006

“Solar-Sail Kinetic Impactor Trajectory Optimization,” Dachwald and Wie, Journal of Spacecraft and Rockets, 2007

Solar Polar Imager 25 26 27 Gravity Tractors • Asteroid Tugboat (Schweickart et al, 2003)

• Gravity Tractor (Lu and Love, 2005)

• Solar-Sail Gravity Tractor (Wie, 2007)

• Solar-Reflector Gravity Tractor (Fisher, 2008)

• Multiple GTs in Halo Orbits (Wie, 2008)

• OSC's 1250-kg Dawn Spacecraft Propelled by Ion Engines with 8-year Mission Lifetime

28 29 30 31 32 33 34 35 “Solar-Sail Gravity Tractor Spacecraft Concept,” B. Wie 2007 Planetary Defense Conference, March 2007

Pros: a “propellantless” propulsion system Cons: a large 100-m solar sail required, not available

36 37 “Gravitational Tractor for “Multiple Gravity Tractors Using Towing Asteroids,” Lu and Ion Engines in Halo Orbits,” B. Wie, Love, November, Nature, 2005, pp. 177-178 August 2008

A single-point failure No redundancy

38 “Dynamics and Control of Gravity-Tractor Spacecraft for Asteroid Deflection,” B. Wie presented at AIAA Astrodynamics Conference, Aug. 2008 published in Journal of Guidance, Control, and Dynamics, Sept. 2008

39 40 41 42 43 44 GT Spacecraft Employing Dawn Mission Heritage (Quang Lam, Orbital Sciences)

• Dawn’s 30 cm IPS Thruster at 92 mN (2.2 kW) versus 25 cm IPS thruster at 168 mN at higher power (4.2kW)

• Dawn’s GN&C sensor suites and algorithms designed for sciences mode (asteroid nadir or asteroid surface-based target tracking and pointing) are directly “adopted” to best fit GT mission

45 Ion Engine Selection for GT (The Best Out of L-3 Com IPS To Maximize GT Performance)

46 L-3 Com/ETI COTS Electric Propulsion Better Engine & Higher TRL

47 Best Ion Engine Selection Via Thrust Magnitude & Isp

48 Concluding Remarks Kinetic impactors, solar-reflector gravity tractors, and multiple GTs in halo orbits are practically viable low-energy options for asteroid deflection, although they need detailed system-engineering studies and flight demonstrations.

65 Million Years Ago 13,000 Years Ago Sooner or later 49