Still, I cannot fathom why Elon Musk is sticking to chemical propulsion (ie. classic rockets) for his Mars endeavour.
Whith his knowledge and SpaceX, he CANNOT not know about NERVA and space nuclear propulsion, and the point of readiness of such technology achieved in the 70s.
I can understand avoiding using it for earth lift-off, due to common hysteria about anything labeled nuclear, but for the half year trip to Mars ?
I mean, come on, we're using nuclear to make our electricity, to power our aircraft carriers, to power our submarines, to power our ice-breakers, but we won't use it for where it is sorely needed which is a trip to Mars, where no one has gone before ?
The journey to Mars is a catch-22 situation.
The length of the trip using chemical rockets requires shielding of the crew, which weighs down the craft, which makes it harder to accelerate and decelerate, which makes the trip longer/harder, etc ...
Most problems are simply dealt with if you use a much powerful propulsion technology.
More thrust available means shorter trip, means less shielding, means more cargo or a ship big enough for artificial gravity (self-rotating part).
I'll be really happy and take Mr Musk's Mars ambitions seriously the day he announces nuclear propulsion for his Mars ship.
Until then ... I really have a hard time doing that.