It is known that Alpha Centauri A & B both have habitable zones that could be as comfortable as the one around Sol. To reach Alpha Centauri would take at least 860 years at 1500 km/sec (0.5% lightspeed). This calls for at least a 30-generation starship, where each couple, perhaps representing 1/3rd of the crew, aboard waits at least until age 28 before having children, for a total of perhaps 3 children per couple.

Besides getting Starship "Generations" up to cruise speed, what are the problems associated with this approach to interstellar travel?

1. Heat
2. Recycling
3. Zero growth

The first problem exists because the heat loss by radiation is substantial in interstellar space, where the outside temperature is only 4 degrees Kelvin above Absolute Zero. The best shape for retaining heat would be a spherical ship which is then coated with a polished metal with an ultralow emissivity around 0.01. The surface must be polished regularly to prevent an ice film from accumulating which would then radiate heat much faster. Then a Uranium nugget is placed at the geometric centre of the spherical ship where it will naturally radiate heat to compensate for radiative heat losses. The ship must be isolated from redundant structures such as the Whipple Shield, Engines, and other external structures. These could be rigged to fly in formation with the habitat structure without touching it. For a rotating spherical ship with a diameter of 500 meters, a radiative heat loss of 3.282 megawatts would occur, and would require 5.744 million tonnes of 4%-enriched Uranium Dioxide to compensate. This amount of Uranium would take up only 0.46 percent of the total volume of the habitat, if configured into a spherical nugget with a diameter of 83.194 meters. At current market prices this much Uranium would cost at least $517 billion US.

The second problem is recycling. The ship must recycle 100 percent of all materials. I think that this is simply a matter of energy. I think that with enough energy even the most difficult materials can be recycled. However the ship should be designed so that difficult materials are produced in minute amounts. After all, Starship Generations is not supposed to be a "growth" environment. Zero growth is essential. Of course I have no idea how much more energy would be required above & beyond that needed to keep the habitat warm.

I should also point out that it might be very difficult to get a generation starship up to even a modest speed because of the enormous mass required, i.e. structure + uranium core + biomass + machine equipment. This is obviously something we would need substantial experience in understanding what we would need, how much redundancy, etc.