The Apollo Constellation Engine (ACE) is a Hall effect thruster propulsion system which leverages the past 50 years of Hall thruster research in a clean sheet design with major innovations, including: multi-propellant capability with Krypton, Xenon, and proprietary propellants, heaterless, center-mounted, instant-start cathode, novel magnetic lensing and magnetic circuit, advanced high temperature materials, and a 95% efficient single board PPU.