http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1312.6554
http://www.electric-sailing.fi/
Abstract: "The solar wind electric sail is a novel propellantless space propulsion concept. According to numerical estimates, the electric sail can produce a large total impulse per propulsion system mass. Here we consider using a 0.5 N electric sail for boosting a 550 kg spacecraft to Uranus in less than 6 years. The spacecraft is a stack consisting of the electric sail module which is jettisoned at Saturn distance, a carrier module and a probe for Uranus atmospheric entry. The carrier module has a chemical propulsion ability for orbital corrections and it uses its antenna for picking up the probe's data transmission and later relaying it to Earth. The scientific output of the mission is similar to what the Galileo Probe did at Jupiter. Measurement of the chemical and isotope composition of the Uranian atmosphere can give key constraints for different formation theories of the solar system. A similar method could also be applied to other giant planets and Titan by using a fleet of more or less identical electric sail equipped probes."
