High power density electric propulsion devices hold the promise of changing the paradigm of human and robotic spaceflight. Results from recent Variable Specific Impulse Magnetoplasma Rocket (VASIMR) VX-200 engine experiments will be discussed in the context of subsystem performance and magnetic nozzle plasma physics. New experimental data on Ar and Kr ionization cost, ion fraction, exhaust plume expansion angle, thruster efficiency, and total force are presented that characterize the VX-200 engine performance at 200 kW. A semi-empirical model of the thruster efficiency as a function of specific impulse was developed and gives component-level efficiency estimates. Work done on developing a new material surface erosion measurement technique using ion beam Rutherford Backscattering Spectrometry (RBS) will be presented and promises to provide nm-scale erosion resolution, improving the predictive capability for thruster lifetimes, fusion first-wall/limiter lifetimes, hypersonic vehicle materials lifetimes, internal combustion engine wear, etc. Recent experiments with a 30 kW helicon plasma source and a 5m expanding magnetic nozzle give new insights into laboratory double layer physics. A new ion acceleration mechanism is identified as an ambipolar electric field produced by an electron pressure gradient, resulting in supersonic ion velocities downstream of the magnetic nozzle. New insights into ambipolar ion acceleration physics are applied to near-term CubeSat propulsion concepts. Recent work on CubeSat plasma instrumentation development and qualification on high altitude balloons will also be presented.