Comment Go nuclear (Score 3, Interesting) 322
http://www.nuclearspace.com/a_liberty_ship.htm
It is simple, no nuclear materials comes out of the exausts. All you do is super heat some material to rediculous levels and your done. Any activity has a negative impact, but then the biggest human contibutor to radioactivity in the atmosphear is burning coal.
As for accidents, you need about 1000 accidents to release as much nuclear materails as those above ground attomic tests.
Oh, and make them BIG ...