I see. The messed up ozone layers assumption. Works for me!
There are a couple of technicalities that caught my eye in the meanwhile.
If the ship was moving with the velocity of 2 light speeds then the time inside the ship was slowing down significantly and the fact that Tom was around 25 years old could mean that the time elapsed on Earth was close to 50 years or more. So their supply of oxygen should have been quite sufficient.
A child of American and Australian parents could easily be of the same race for example of Aryan, Semitic, Mongoloid, etc. So actual ancestry of his parents should have been extended on if it mattered at all. From my point of view, it was a strange consideration. More appropriate would have been to select people on the base of talent. But that's just me.
Not sure what nine races you are referring to but suppose it was so. How could they be preserved? The budding technique works only on plants. People need to have male and female pare.
Overall though I enjoyed reading your story. There is some air of adventure in it.
RE: Tell A Story To Me || Towards Uncertainty