In exploring the outer planets of the solar system, humankind will want to do more than send unmanned probes that merely fly rapidly by, snapping a few pictures. Eventually, we will want to send spacecraft that go into orbit around the gas giants or land on their moons, perhaps even returning samples to Earth. And one day, we will follow those pioneering probes ourselves, sending astronauts to explore and eventually colonize the far reaches of our stellar neighborhood.

For missions such as these, we will need rockets that are more efficient than the current chemical rockets. A likely alternative to rockets powered chemical combustion are those powered by nuclear fission.