We don't have enough study on the effect on humans or the levels in deeper space yet to create radiation shielding safe enough to venture far in space, nor the technology to power engines & life support to travel fast enough to make proper space travel feasible (plus the constraints of storing enough fuel, food and other supplies to travel that far). For example, Voyager 2 took 50 years to exit our solar system. Our communications systems are also not yet advanced enough for a mission of such, taking 16 hours to reach or return from Voyager (utterly useless in a true emergency)