From: adam.w.krajewski@gmail.com   
      
   In my own sf universe, I have dealt with too high mass ratio problem by   
   setting the action in a dense star cluster, where distances between stars   
   rarely go higher than 2 lightyears. Kind off like Firefly show, huh?    
   If you use seedship, the payload can be quite small I think, because you   
   eliminate the need for habitat module, consumables and people. On the other   
   hand, the ship must provide human embryos someplace to grow, consumables   
   needed to survive, teach them    
   etc. And build a cover on targeted planet, you don't wanna just throw embryos   
   out there on Venus/Mars like planet and say goodbye huh? As for me the seed   
   ship is not optimal solution for space colonization, it's basically "planting"   
   a completely new    
   civilization somewhere in space, and IMO best for "survival of the human race"   
   scenario.    
   For propulsion, you can certainly go with fusion drive, because it seems   
   achievable in not so distant future, and gives quite good performance. Think   
   of Deadalus interstellar probe, but with a capability to brake near   
   destination. The laser sail is good    
   idea too, but it depends on what's going on in mothersystem, so not best for   
   survival of species. Surprisingly, the Orion nuclear pulse drive could work as   
   well, although it would need high mass ratio. But, it's almost "combat ready"!   
   Next system you    
   could use, is the Bussard Ramjet, although it needs speeding up on the   
   beginning IIRC, and uses proton fusion, which is very hard to achieve. You   
   could even go with antimatter, but with lower mass ratio, and instead of   
   getting to 0.7 c get to 0.1 or 0.2    
   c, which is still pretty good   
   These are just some example drives, check out the "engine list" on Atomic   
   Rockets, there is quite a lot to choose from here!   
   Also, what's your setting? Is it out world, Earth, or something else?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)