MORE SPECULATION ABOUT BEAMRIDERS
This is all highly speculative, but most of it makes common sense and does not violate any known laws of physics. Comets for mass beam mass could be captured by robotic ships, nudged towards their star and decelerated into circular stellar orbits with magnetic sails of large dimension. Gravity of large planets might be used to guide the comets as they race towards star.  Robots could mine out the comet and grind its ices up into dust with centrifugal impact grinders then feed the dust into mass beam projectors. The hollowed out shell of the comet could then be used as cosmic ray shield for space colony made of asteroidal metal assembled within the shell of ice, although it would have to be located at distance from star or surrounded with another layer of reflective metal. 
to Interstellar Shuttles index
more food for thought
Silicon solar cells are not highly efficient.  More efficient solar cells require rare elements.  Perhaps it will be possible to use parabolic reflectors of highly polished aluminum or chromium to focus stellar energy on carbon spheres with thermionic power elements in them to tap power more efficiently and without moving parts.  Giant helium gas filled turbogenerator units seem like a megascale engineering night mare.  Large numbers of reflectors and thermionic units could be clustered together. These will use more common elements.  Mass beam projectors will use expansion of magnetic fields to propell particles and this will make shorter accelerators possible.
Reader's comments welcomed.