This is right up my alley.
There are several problems: - A powerful enough inter-stellar propulsion system.
The most powerful reactor we can build is a Deuterium-Tritium fuel based fusion based reactor. But this reactor is MASSIVE, still not controlled(reaction wise), and weighs too much to be put into orbit on an STS.
Thats what I'm going to work on eventually when i graduate.
A fusion based prpulsion system would deliver ten times the energy(and propulsion) as a fission based reactor, and you could in essence replenish your fuel in space...as hydrogen is everywhere in space, whereas uranium is not.
In other words you could get to mars in 18 days instead of 180 days, using the fusion based reactor.
Fonz