A reader points me to a very successful Kickstarter campaign that raised $96,799, far beyond the goal of $50,000,  to fund  development of a low cost propulsion system capable of sending nanosats on deep space missions: CAT: Launch a Water-Propelled Satellite into Deep Space by Benjamin Longmier, Ph.D. — Kickstarter

Our vision is to enable extremely low-cost access to deep space. We are developing the CubeSat Ambipolar Thruster (CAT), a new rocket propulsion system powered by the Sun and propelled by water, which will push small spacecraft like CubeSats around and far beyond the Earth. New propulsion technologies can cost billions of dollars and take a decade to build and launch. CAT will be one of least expensive and most rapidly developed deep-space-capable systems ever built.