The Viper Pulsed Fusion Rocket (PFR) is an ultra-high specific impulse, variable thrust, space probe concept recently proposed for unmanned interstellar exploration. The design is based on an aneutronic Inertial Electrostatic Confinement (IEC) fusion power unit producing an Isp in the range of 104 Â 106 seconds with advanced proton - Boron-11 (p-11B) fuel and a neutral propellant. The IEC is fed highly ionized p-11B by an RF permanent magnet helicon array. Anisotropic alpha particle products produced in the fusion reaction are magnetically collimated and are quasi-equilibrated with a neutral gas and exhausted through a magnetic nozzle. Through the coupling of a pulsed helicon array, Viper accomplishes a power gain of greater than seven by achieving very high plasma densities in the Helicon. The probe has a launch mass of approximately 30 metric tons and a total power production of 360 MW.