New Horizons‘ lead scientist Alan Stern describes their “Gold Standard” plan to return to Pluto:
First, after an orbital tour of Pluto, a final pair of close gravity-assist flybys of Charon will free the orbiter from the Pluto system to explore the Kuiper Belt without any need for any propulsion from the orbiter. Next, using only the existing capabilities of the NASA Dawn mission electric propulsion system, the craft will conduct a flyby tour of up to a half-dozen small Kuiper Belt objects and any one of a number of dwarf planets. In fact, in some scenarios, the Dawn propulsion system can even place the Pluto orbiter around a second dwarf planet for another orbital mission.
Lots more on the particulars of the design trades that have to be made for an orbital vs. flyby mission in the article at Astronomy.com. One of the balancing acts that always intrigued me is the need to cover the distance quickly but still arrive with enough propellant to slow it into orbit when it gets there.
An earlier piece at Astronomy lays out just why we ought to be interested in this icy world at the end of the Solar System:
Pluto generates enough heat to comfortably sustain a subsurface ocean over billions of years. The evidence scientists have accumulated so far suggests such an ocean is present — although it most likely remains locked beneath a thick, rigid shell — and would be detectable by a future orbiter. Also keep in mind that Pluto is not unique: Other bodies in the Kuiper Belt have similar sizes and most likely also possess oceans. So, the outermost reaches of our solar system are not universally hostile. Despite the cold and the dark, Pluto and its brethren may represent welcoming oases.
This is fascinating to me, and was part of my premise for Frozen Orbit. When it became apparent it held organic compounds known as “tholins” similar to what we’ve found on Saturn’s moon Titan, I naturally wondered about what else might be hiding out there in the Kuiper Belt. If comets were the source of Earth’s water and organic materials, most of which came from the Kuiper Belt and Oort Cloud, then that kind of makes the whole belt into one big freezer pantry. That made for some intriguing story ideas about how we came here and our place in the universe.