Deceleration of Interstellar Spacecraft Utilizing Antimatter Author: Gerald Jackson, Ph.D. Physics, Co-Founder and President, Hbar Technologies, LLC Description: This paper summarizes the results from a recently completed NASA Innovative Advanced Concepts (“NIAC”) Phase I grant. The grant explored a mission architecture wherein a 10kg-scale unmanned spacecraft decelerates and inserts itself into orbit around an exoplanet. In this research the antimatter-initiated fission of depleted uranium produces electrical power, thrust, or both to accomplish these maneuvers and enable robust scientific discovery and two-way communications with Earth. A mission to the nearby habitable-zone exoplanet Proxima b is explored as a concrete example, wherein the acceleration stage of the spacecraft is separated after its 10-year burn and deflected to perform a fly-by through the Alpha Centauri AB binary system. Similar to the Voyager 2 mission, wherein a grand tour of the outer planets justified the spacecraft investment that is still yielding scientific results decades later beyond the heliopause, a program of prompt science results regarding interstellar clouds, Oort cloud population distributions, interstellar magnetic fields, and radiation spectra in the interstellar void are envisioned. As one example, an exciting conclusion is that the detection of 10km-scale Oort cloud objects by a small semi-relativistic spacecraft is indeed feasible. During this grant, several potential methods of deceleration were investigated, starting with the emission of electrostatically-focused fission daughters as reaction mass, each having an average exhaust velocity of 4.6% of the speed of light. The other methods involve dissipating the large kinetic energy of the spacecraft into the interstellar medium, using a variety of possible coupling mechanisms. A significant impediment to progress along these lines is the lack of data concerning plasma composition and density of the interstellar medium and the directions and intensities of the interstellar magnetic field. The allure of these other methods is the possibility that their consumption of scarce antimatter, in this case used to generate onboard electrical power, might be smaller than the primary reaction mass method. This paper will also briefly summarize other results in the areas of antimatter production and storage, spacecraft instrumentation, and other mission objectives.