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Proceedings Paper

Directed energy deflection laboratory measurements of common space based targets
Author(s): Travis Brashears; Philip Lubin; Gary B. Hughes; Peter Meinhold; Payton Batliner; Caio Motta; Jonathan Madajian; Whitaker Mercer; Patrick Knowles
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Paper Abstract

We report on laboratory studies of the effectiveness of directed energy planetary defense as a part of the DE-STAR (Directed Energy System for Targeting of Asteroids and exploRation) program. DE-STAR and DE-STARLITE are directed energy “stand-off” and “stand-on” programs, respectively. These systems consist of a modular array of kilowatt-class lasers powered by photovoltaics, and are capable of heating a spot on the surface of an asteroid to the point of vaporization. Mass ejection, as a plume of evaporated material, creates a reactionary thrust capable of diverting the asteroid’s orbit. In a series of papers, we have developed a theoretical basis and described numerical simulations for determining the thrust produced by material evaporating from the surface of an asteroid. In the DESTAR concept, the asteroid itself is used as the deflection “propellant”. This study presents results of experiments designed to measure the thrust created by evaporation from a laser directed energy spot. We constructed a vacuum chamber to simulate space conditions, and installed a torsion balance that holds a common space target sample. The sample is illuminated with a fiber array laser with flux levels up to 60 MW/m2 , which allows us to simulate a mission level flux but on a small scale. We use a separate laser as well as a position sensitive centroid detector to readout the angular motion of the torsion balance and can thus determine the thrust. We compare the measured thrust to the models. Our theoretical models indicate a coupling coefficient well in excess of 100 μN/Woptical, though we assume a more conservative value of 80 μN/Woptical and then degrade this with an optical “encircled energy” efficiency of 0.75 to 60 μN/Woptical in our deflection modeling. Our measurements discussed here yield about 45 μN/Wabsorbed as a reasonable lower limit to the thrust per optical watt absorbed. Results vary depending on the material tested and are limited to measurements of 1 axis, so further tests must be performed.

Paper Details

Date Published: 19 September 2016
PDF: 8 pages
Proc. SPIE 9981, Planetary Defense and Space Environment Applications, 998103 (19 September 2016); doi: 10.1117/12.2238462
Show Author Affiliations
Travis Brashears, Univ. of California, Santa Barbara (United States)
Philip Lubin, Univ. of California, Santa Barbara (United States)
Gary B. Hughes, California Polytechnic State Univ., San Luis Obispo (United States)
Peter Meinhold, Univ. of California, Santa Barbara (United States)
Payton Batliner, Univ. of California, Santa Barbara (United States)
Caio Motta, Univ. of California, Santa Barbara (United States)
Jonathan Madajian, Univ. of California, Santa Barbara (United States)
Whitaker Mercer, Univ. of California, Santa Barbara (United States)
Patrick Knowles, Univ. of California, Santa Barbara (United States)


Published in SPIE Proceedings Vol. 9981:
Planetary Defense and Space Environment Applications
Gary B. Hughes, Editor(s)

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