[dtparr]

Regarding the interpretation of

> It's chemical rockets, nukes or a space elevator. At least given known physics.

He's giving a series of 3 things that he's asserting are viable given known physics, so the second two are alternatives to the first. Would it make more sense to you with an Oxford comma? E.g.

> It's chemical rockets, nukes, or a space elevator. At least given known physics.

Are you interpreting the nukes/elevator as sub types of chemical rockets? That might be written (counterfactually) as

> It's chemical rockets: nukes or a space elevator. At least given known physics.

[thaumasiotes]

> He's giving a series of 3 things that he's asserting are viable given known physics, so the second two are alternatives to the first.

To be clear, the meaning of the construction used is that, given known physics, the only alternatives are the list elements (chemical rockets, nukes, or a space elevator). This is completely conventional American English.