Within the grasp in theory, but not any time soon.
Unless the Apollo overall failure rate probability of 2 out of 17 missions (the
first 9 were either surface or orbital ones) is achieved there is little sense of
proceeding further than the moon orbit. That means (unfortunately) we may
not see a man-on-Mars any time soon since the technology required is
either in the conceptual stage or not mature yet.
Technical malfunctions are not the prime issue - if enough redundancy is
built in the spacecraft and spare parts are carried, the crew can repair the
vast majority of otherwise potentially fatal failures. The problem is the health
hazard - there is yet no sensible medical solution, and there may never be,
to microgravity induced pathological problems (that can be permanent after
a certain level), and to the radiation exposure, in the present mission
time-span calculations of about two years. Those levels (as well as the
microgravity problem) can be reduced by reducing mission time - that is,
making a faster ship - but not entirely eliminated. Added material for
radiation shielding (if just in form of chambers to be used in case of solar
flares), preferably with active energy shields (EM fields to deflect or wrap
around the craft the charged particles part of radiation, will not work against
photons or neutrons) would have to be used, and given the necessity for
technical failsafe approach mentioned above, the ship would be heavier per
volume of space than the ones used today. Also, artificial gravity would have
to be created in form of rotating arms with crew quarters, maybe foldable
during high intensity burns (orbit entry and exit, major corrections). No today
present engine type will move a ship of that weight faster - that will require
nuclear powered propulsion (a revamped NERVA system from the ?60 and
the ?70?), maybe aided with solar powered, over the entire mission time
continuous low-key ion-thrust.
We can see here the problems: ion-propulsion exists but it should be made
more powerful, nuclear engine design would have to be started all over
again but that we know is feasible, artificial gravity is theoretically simple but
was never implemented, while active shielding is still in the conceptual
faze. And we did not start to talk about money.
How do you define success?
