until we get fusion reactors,

We do have quick acting reactors , both fusion and fission, that could
have been used for almost fifty years of space travel by now; as
documented in Stan Ulam's patent.

http://spacebombardment.blogspot.com...-inventor.html

"The first recorded discussion of nuclear explosive propulsion
was in a Los Alamos Memorandum
by F. Reines and S. Ulam dated 1947."
http://www.fas.org/sgp/othergov/doe/...1/00189777.pdf