Next Stop: Interstellar Space

This is an excellent article. Not much to add.

In a paper to be published as a chapter in a book on NASA ‘Vision’ missions this summer, Thomas Zurbuchen (University of Michigan) and a team of researchers discuss the specifics of powering such a probe by nuclear methods and find them wanting. The paper is so rich that I want to discuss several issues from it in coming weeks. For now, though, let’s consider the propulsion dilemma as seen by scientists running the numbers using existing technologies.
A solar sail gets you to the interstellar medium more quickly than the kind of chemical propulsion with gravity assists used by Voyager, but even so the task is daunting, requiring the probe’s escape velocity to be a factor of 3 greater than Voyager 1’s. And existing sail designs deliver speed but at a cost in payload weight.

NASA’s now defunct Prometheus project would have created a spacecraft too heavy and slow for a mission to the nearby interstellar medium — the Zurbuchen paper centers around a nuclear power source in conjunction with electric propulsion fine-tuned for the mission. For a variety of reasons, the best compromise between the various proposals seems to be the radioisotope electric propulsion advocated by Ralph McNutt and the IIE team.