OXYGEN

I think oxygen should be FREE in space, and vessels should be obligated to help others. Of course, people aren't obligated to die while saving others.

Oxygen Trading

Oxygen trading would be useful. Europa and Enceladus hold abundand oxygen. Earth's cities could use some oxygen. Why not build ships that could travel to Europa and Enceladus, harvest exotic oxygen, and return to Earth? That would be good work for adventurous sailors! Why not?