The Oort cloud is a cloud of icy planetesimals including comets that surround the Sun at distances ranging from 2,000 to 200,000 au (0.03 to 3.2 light-years). That is more than halfway to the nearest stars, the Centauri triple star system, which is slightly more than four light-years from Earth. If we assume that the Centauri star system is also surrounded by a sphere of comets, then there might be a continuous trail of comets connecting it to Earth. It may be possible to establish a series of refueling stations, outposts, and relay locations on a grand interstellar highway. An alternative to spaceships or faster-than-light travel might be “comet hopping” to the Centauri system, creating mankind's first cosmic route to its nearest star from the Sun. Faster-than-light technology may be delayed indefinitely and this may be a more viable solution for shorter-term and shorter-distance interstellar goals.
The Rosetta spacecraft Philae was able to send a probe to land on a comet. Some comets have a hard rock/ice core, which may be strong enough to support a robotic relay station. One day, robots may land on a distant comet in the Oort Cloud and drill into its surface. Minerals and metals from the core could be used to fashion a space station, and ice could be melted to provide drinking water, rocket fuel, and oxygen for astronauts.
Techniques used in the moon base and asteroid mining could be employed for the bases across the comets.
An idea was pioneered by Carl Sagan in his book, Comet. Robots would build mass drivers on comets, using them to eject materials at very high velocities, which in turn would exert a thrust on the comets, causing them to accelerate. The comets are thus converted into spaceships and using these “spaceship comets” people could move together in tightly compact “comet bundles” and hurtle through interstellar space. The hollowed-out and ejected materials would be used to construct rotating cylindrical habitats for humans to live in, such as an O’Neill cylinder. Therefore the mass driver on the comet would be used as for propulsion systems as well as habitation for the long interstellar journeys.