HOPE is the Human Outer Planet Expolration design study that is a first step towards defining what is needed to get humans to Jupiter and beyond. A slow ion-propelled freighter will carry the necessary cargo for a base to be set up on Jupiter’s moon Callisto. Then a human-carrying vehicle will do a “fast” 850 day transfer – a minimum energy Hohmann is ~ 1000 days.
Callisto has been chosen for a base because it’s outside Jupiter’s radiation belts, so an orbitting passenger vehicle won’t be fried. However Ganymede is only just within the Belts and the radiation is quite low, especially for a human-rated vehicle able to protect a crew against a cumulative ~ 5 years of cosmic radiation en route.
And that’s the main hassle of travel to Jupiter and beyond – cosmic ray exposure. A solar-storm shelter can stop astronauts from dying of prompt exposure to excess solar protons, but cosmic rays are a steady dose of extremely energetic particles. Their damage is probably cumulative because they’re energetic enough to kill cells directly, notably brain cells. A decade or two of exposure could be like Alzheimer’s disease.
Space doctors are seriously investigating hibernation for HOPE missions. Here’s a couple of news links…
USAToday Space Hibernation
MSNBC HOPE missions
Space: HOPE and hibernation
…but personally I think launching just a few people on multi-year journeys is plain daft. A more effective approach is to use a magnetic sail – a plasma magnet – to catch the solar wind and drift out a large space station (~ 500 people, like a Space Island.) With the right design the plasma magnet is also a cosmic ray shield.
With enough people on board the colony can have a sufficiently dynamic social life to allow people to take a few years to journey and get there sane enough to build a base or whatever. With robot assistance and advanced manufacturing like rapid-prototypers a colony can set up a quite effective industrial base and build a large habitat in-situ. Then anyone who follows them will actually have a reason to go, a destination.
George Zebrowski’s “Macrolife” had a huge in-space infrastructure arising quite early in the 21st Century thanks to large space-colonies – MacroLifes – kick-starting industry on the Moon, Mars, Asteroids and Ganymede. With Space Elevators and plasma magnets to launch Beal Aerospace-style space-stations we could still bring about such a rapid expansion into space. NASA-style stunt-flights with a dozen crew or less are never going to get more of us everyday people out into space.