This image shows a cutting-edge solar-electric propulsion thruster in development at NASA's Jet Propulsion Laboratory, Pasadena, Calif., that uses xenon ions for propulsion. An earlier version of this solar-electric propulsion engine has been flying on NASA's Dawn mission to the asteroid belt.

This engine is being considered as part of the Asteroid Initiative, a proposal to robotically capture a small near-Earth asteroid and redirect it safely to a stable orbit in the Earth-moon system where astronauts can visit and explore it. This image was taken through a porthole in a vacuum chamber at JPL where the ion engine is being tested.

Image credit: NASA/JPL-Caltech