The head of NASA’s nuclear push says a scientific mission to the inner solar system — perhaps to the moon, Mars or an asteroid — will be used to demonstrate a new propulsion system in place of a mission to Jupiter’s icy moons. But the Jupiter trip is only delayed, not canceled, Ray Taylor said. It could fly in 2017, a few years later than the demonstration mission. In the meantime, “we have a range of options being looked at in the analysis,” he said. “They’re all in the inner solar system . . . and they’re all shorter mission duration.”