RedNova News - Space - Ion Thrusters Propel NASA into Future
: "In a nuclear electric propulsion system, a nuclear reactor produces heat, a power-conversion system converts the heat to electricity, and an ion thruster uses the electricity to propel the spacecraft.
Deep Space 1, which launched in 1998, was the first spacecraft to use an ion thruster as its primary propulsion system. But that thruster, developed at the Glenn Research Center, drew its electricity from solar panels.
'Solar power is efficient and lasting, but it cannot stop a spacecraft at targets in the outer solar system that are past Mars,' Oleson said. 'The best way to study a planet is to land on it or travel in its orbit, and the only way we can do that in the outer solar system is with nuclear propulsion.'"