Event

Distinguished Seminar Series: "Avoiding Armageddon: The Use of Nuclear Explosives to Disrupt or Divert Asteroids," - David Dearborn, Lawrence Livermore National Laboratory, CA

Dr. David Dearborn

Distinguished Seminar Series sponsored by the Asteroid Deflection Research Center, Iowa Space Grant Consortium, and the Department of Aerospace Engineering

Thursday, November 5, 2009
2:10 - 3:00 PM
Alliant Energy-Lee Liu Auditorium
1140 Howe Hall

Dr. David Dearborn
Lawrence Livermore National Laboratory
(LLNL), California

Avoiding Armageddon: The Use of Nuclear Explosives to Disrupt or Divert Asteroids

Every couple of years, a celestial body impacts the earth with energy near that of the Hiroshima bomb. Fortunately, that energy is usually deposited high in the atmosphere and causes little or no damage.  On much longer timescales, impacts will occur with the potential to destroy regions, or whole civilizations.  This lecture will present an overview on efforts to define the impact threat, followed by a systematic development of the requirements to divert an object on an earth-impacting course. We then examine nuclear explosives as a mature technology with well-characterized effects. With decades of warning, the required speed change to divert an asteroid is small.  A standoff burst can then ablate surface material and nudge the body to a safer orbit. For shorter lead times, a direct sub-surface burst can fragment the body. With only 1000 days lead-time, shattering an NEO disperses the material reducing the amount impacting the Earth to about 1/100,000th of the original body, a huge mitigation factor. To better understand these possibilities, we have used a multidimensional radiation/hydrodynamics code to simulate sub-surface and above surface bursts on an inhomogeneous, 1 km diameter body with an average density of 2 g/cc. The body, or fragments (up to 750,000) are then tracked along 4 representative orbits to determine the level of mitigation achieved.

Biography
Dr. David S. P. Dearborn is a graduate of UCLA (1970) and the University of Texas at Austin (1975). He has held positions at the Copernicus Institute in Warsaw, the Institute of Astronomy in Cambridge, The California Institute of Technology, and Steward Observatory in Tucson.  For the last 25 years, he has been a research physicist/astrophysicist at the Lawrence Livermore National Laboratory (LLNL).  While most of his LLNL research has supported programmatic efforts, he has maintained an active presence in astrophysics, and recently become involved in planetary physics (asteroid deflection). He has also published significantly in Andean studies (particularly Inca Astronomy).

His early astronomical work included stellar observations, but today it is exclusively theoretical. He has published on stellar physics, nucleosynthesis, and astro-particle physics, and is one of the main developers of Djehuty, an LLNL code for the full three-dimensional modeling of stars.  It has all relevant stellar physics, and is able to operate in a massively parallel environment.  With this code he and his collaborators discovered a new mixing mechanism that resolves a decades old conflict between predicted and observed abundances. He is also involved in research on the diversion of asteroids by nuclear explosives. NASA’s 2006 Near-Earth Object Survey and Deflection Study cite some his earlier results, and he is currently serving on a National Academy panel for asteroid mitigation. With DTRA support, he is continuing this research today with detailed hydrodynamic simulations demonstrating the capability of nuclear explosives to provide the required impulses to divert asteroids without dispersing (breaking) them.

His Andean studies included eight field seasons in Peru and Bolivia, working to understand the astronomy practices of the Inca.  This work was supported by grants and two Pollock awards for work in the History of astronomy.  In this area he has published more than a dozen journal articles, recognized solstice markers at Machu Picchu and Pisac, and discovered a set of Inca pillars marking the June solar position at the Island of the Sun in Bolivia.  This work culminated in a book written with an archaeologist, Brian Bauer, entitled Astronomy and Empire in the Ancient Andes.  He is a full member of the Institute for Andean Studies, a founding member of the International Society for Archaeoastronomy, and Astronomy in Culture (ISAAC), and was until recently one of four principal editors for the journal Archaeoastronomy, published by the University of Texas Press.

His programmatic work has included the design and testing of both nuclear and conventional explosives, with current responsibilities for generating models and output for the DTRA Redbook.  He is an active member of the LLNL ICBM flight-test program, and his conventional lethality studies support Strategic Commands interests in prompt global strike. Over the years he has used large lasers for the study of high energy density phenomena, studied non-seismic methods for treaty verification, and designed a shuttle experiment. In recognition of this work he has received three “Weapons Recognition of Excellence” awards from the Department of Energy.  They commend his contributions to laser hohlraum development, his work advancing the analysis of radar data, and for his efforts on the W87 Life Extension Program (LEP). The W87 LEP was the first refurbishment of a nuclear system preformed under the stockpile stewardship program, and established the basis for continued system certification.  More recently he has received Defense and Nuclear Technologies acknowledgements for “outstanding contributions of the cross discipline improvement of ICBM accuracy”, and for “warhead contributions in support of Prompt Global Strike.”