
Starship Centurion
This is a buildable starship by 2100 AD in my opinion, it is propelled by atomic bomb pulse units in the multi-kiloton yield range, manufactured on the Moon, I would allow 74 years to construct this from lunar materials. I envision a fleet of four of these ships departing from Lunar Orbit by 2100 AD for an arrival at 2550 AD. This is a generation ship of course with a launch population of around 5 million people. One ship is populated, the other three include 2 agricultural ships and one park, the cylinders deploy in orbit around Alpha Centauri A at the optimal habitable distance, the mirrors them open up and collect natural sunlight from the star Alpha Centauri A to illuminate the interior, during cruise a light tube serves this function.