First we have to develop photonic laser thrusters (amplifying laser propulsion by bouncing between mirrors to recycle photons). Photonic laser thrusters are described in a previous nextbigfuture article. There has been experimental work that indicates that it is feasible.
The systems described here are an improvements by several orders of magnitude over regular power beaming. Recycling photons between mirrors reduces the energy requirements as does lightening the spacecraft and shortening the wavelength of the laser. There are other technological solutions to interstellar travel but this looks like one potential feasible technological solution.
Then we can develop a Photonic Railway, a permanent transport structure based on photon propulsion, has a potential to enable routine interstellar commutes via Spacetrains.
The Photonic Railway, as the transcontinental railway systems did, is projected to inspire sustainable economic interest and return investment, and to potentially achieve the goal: rountrip manned interstellar flight potentially within a century.
In this section, a four-phased developmental pathway of the Photonic Railway toward interstellar manned roundtrip is proposed:
1) Development of PLTs for satellite and NEO maneuvering,
2) Interlunar Photonic Railway,
3) Interplanetary Photonic Railway, and
4) Interstellar Photonic Railway.
It is projected that these developmental phases will result in systematic evolutionary applications, such as satellite formation flying, NEO mitigation, lunar mining, and Space Solar Power, which is projected to generate sufficient sustainable economic interest and return investment to the development pathway.