re: Mars in 39 days with Vasimr?
I took a closer look at the page:
http://advancednano.blogspot.com/2007/11/vasimr-engines-plus-200-mw-of-nuclear.htm
and found the total "critical mass" is given as 600-1200 kg. Compare this to the amount of plutonium carried on the Cassini mission of 32.8 kg and the reaction that caused.
Bob Clark