Deep Space Propulsion: A Roadmap to Interstellar Flight - K. F. Long - Google Books

https://books.google.de/books?id=EAD2-GrarkEC&pg=PA229&dq=deep+space+propulsion+Long+a+roadmap+Aimstar#v=onepage

The technology of the next few decades could possibly allow us to explore with robotic probes the closest stars outside our Solar System, and maybe even observe some of the recently discovered planets circling these stars. This book looks at the reasons…