Per MSNBC http://cosmiclog.msnbc.msn.com/_news/2012/01/07/10035158-skipper-chosen-for-starship-effort So we can start building the thing then? or are we waiting for appropriate tech to be developed?
This is a good site for options: http://www.projectrho.com/public_html/rocket/enginelist.php Smoother than the nuclear pulse orion concept is the Nuclear Salt Water Rocket http://www.projectrho.com/public_html/rocket/enginelist.php#id--Nuclear_Salt-water_Rocket Its fringe-worthy--but look how well it does with a 90% solution on this graph: www.projectrho.com/public_html/rocket/images/enginelist/rocketChart.jpg Best yet: The advantage of NSWR is that this is the only known propulsion system that combines high exhaust velocity with high thrust. Thrust 13,000,000 newtons with 4,700,000 m/s exhaust velocity--a one two punch! NTR DUMBO looks more do-able http://www.projectrho.com/public_ht..._Core_Nuclear_Thermal_Rocket--NTR-SOLID/DUMBO This would provide 3,500,000 newtons thrust Now imagine you use that in place of a Centaur upper stage, and have AIMSTAR as a payload: http://www.engr.psu.edu/antimatter/Papers/AIMStar_99.pdf This would provide 598,000 m/s exhaust velocity. This alone would allow a trip to 10,000 AU in 50 years. Couple this with DUMBO NTR to get most of its useful life extra-solar--NOW you have a souped up New Horizons.