Submarine Spaceship

    I got started down this road by thinking about radiation shielding for a long duration space voyage. Concrete makes a good shield, but so does steel, and steel is a lot thinner, and stronger. Which got me to thinking of a spaceship as a submarine, or a submarine as a spaceship. A modern nuclear submarine has several things in common with what we would need a ship for traveling to other planets. They:

• are self contained, 
• are air tight, 
• have a large electrical power supply, and
• they have thick walls.

    Thick walls make good radiation shields. Once you get outside of Earth's magnetic field, radiation becomes a real problem. Thick steel walls would alleviate those concerns. You could generate your own magnetic field to counter radiation, but that would take power, and as we know, power supplies depend on the machinery continuing to function. Thick steel walls pretty much keep working no matter what.

    Putting a submarine in orbit would be a darn near impossible task. A Delta 4 Heavy rocket can put a 25 ton payload into orbit. You would need 300 such rockets to launch a submarine into space. That's as many Delta rockets as have been launched since 1960. 

    A better way would be to build it on the moon. That would mean shipping all the machinery you need to build it up there, but with some clever planning and the discovery of adequate ore deposits on the moon, it should not take any more launches than that, and once we were established on the moon you could build another ship without incurring another 300 launch expense.

    The large electrical power supply (25MW) could be used to drive a linear accelerator for propulsion, which could get us pretty much anywhere we want to go.