How NASA’s Nuclear Rockets Will Take Us Way Beyond Mars

"After a multi-decade hiatus, both NASA and the Russian
Federal Space Agency (which developed many of its own
NTRs during the Cold War but never physically tested their
designs) announced in April 2012 that they would be revival
of nuclear-engine powered rocket technology and
coordinating a new $600 million joint engine project along
with potential involvement from France, Britain, Germany,
China, and Japan.

Marshall Space Flight Center is also forging ahead on its
own Nuclear Cryogenic Propulsion Stage as part of the
upcoming Space Launch System. This upper stage would
be super-chilled by its supply of liquid-hydrogen fuel and
be unable to initiate a fission reaction until safely out of
the atmosphere. However, since above-ground nuclear
testing has been universally banned since the last time
NASA tinkered with NTRs, researchers are instead using
Marshall's Nuclear Thermal Rocket Element Environmental
Simulator (NTREES). This model can accurately simulate
the interactions between various components of an NTR
engine, allowing rocket scientists to tweak design and
engineering aspects without the risk of spreading nuclear
fallout."

See:

http://gizmodo.com/5992441/how-nasas...g=giz-explains

NASA-backed fusion engine could cut Mars trip down to 30 days:

"The proposed Fusion Driven Rocket (FDR) is a 150-ton
system that uses magnetism to compress lithium or
aluminum metal bands around a deuterium-tritium fuel
pellet to initiate fusion. The resultant microsecond
reaction forces the propellant mass out at 30 kilometers
per second, and would be able to pulse every minute or
so and not cause g-force damage to the spacecraft's
occupants."

See:

http://www.theregister.co.uk/2013/04...ast_mars_trip/