The New Horizons deep space probe is powered by radioisotopethermoelectric generators (RTG) based on the radioactive decay ofplutonium. During mission planning, the safety of the plutonium was asignificant concern, especially if command destruction of the launch vehiclebecame necessary shortly after launch. The third-stage self-destruct systemconsists of two shaped charges aimed at the top of the motor to burst themotor casing, reduce the internal pressure, and render the motoroperationally inert. Our studies, both experimental and computational,showed that the primary RTG threat was fragments from shaped chargeinducedbreakup of the payload attach fitting. We quantified the size ofpotential fragments from the fitting and showed that fragments from theshaped charge casings themselves were not a concern. We developedfragment shields, comprised of ceramic and Kevlar, to protect the RTG.The availability of effective shields was critical to passing the critical designreview and launch safety evaluation. However, as the program progressedadditional testing showed that fragment impacts to the RTG were unlikely,rendering the shields unnecessary for flight. The space probe wassuccessfully launched in January 2006 and is currently on its way to Plutofor a July 2015 flyby.
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