Cancellation
Due to a shift in priorities at NASA that favored manned space missions, the project lost funding in 2005, effectively cancelling the JIMO mission. Among other issues, the proposed nuclear technology was deemed too ambitious, as was the multiple-launch and in-orbit assembly mission architecture. Engineers at the Jet Propulsion Laboratory with JIMO were laid off or reassigned during the spring and summer of 2005.
As a result of the budget changes, NASA is instead considering a demonstration mission to a target closer to Earth to test out the reactor and heat rejection systems. The spacecraft would possibly be scaled down from its original size as well.
When it was cancelled, the JIMO mission was in an early planning stage and launch wasn't expected before 2017. It was to be the first proposed mission of NASA's Project Prometheus, a program for developing nuclear fission into a means of spacecraft propulsion.
After JIMO, NASA and ESA planned a joint mission to Jupiter's moons, the Europa Jupiter System Mission. This joined mission was also cancelled in 2011.
ESA has since then continued separately on the design and on 2 May, 2012 selected the Jupiter Icy Moon Explorer mission over two other ESA missions. The JUICE mission will study the Jupiter moons Europa, Callisto and Ganymede and be launched as an ESA L-class mission in 2022 on an Ariane 5 carrier rocket.
Read more about this topic: Jupiter Icy Moons Orbiter