Starship Generations Update

The latest incarnation of Starship Generations incorporates Aerogel
as a nutrient growth medium for agriculture, replacing sandy loam
topsoil. Aerogel has a density of just 75 kg/cu.m and results in an 8-
fold decrease in starship mass. The result is a faster ship, faster
on-orbit assembly time, reduced antimatter requirements, and
generally a more feasible starship design.

The only drawback of a less massive ship is reduced heat capacity,
resulting in faster internal temperature changes during power
failure. However temperature fluctuations still take months to become
critical, so there is plenty of time to conduct repairs.

I've also included a section on renewable energy transportation:

http://geocities.com/womplex_oo1/StarshipGenerations.html