ISRU is how humans will eventually live on Mars

I for one want to quit hearing about producing breathing oxygen on the Moon.

You can breathe 100% oxygen but if you do it long enough you will wind up like

https://www.youtube.com/watch?v=M0YB5r4vzVo

You are going to have to mix in a larger quantity something inert like He, Ar, N2 or SF6 to make a good breathing gas.

I've been sketching out chemical factories that you could send to a place like

https://en.wikipedia.org/wiki/24_Themis

and I would say it is the availability of Nitrogen that has be worrying. Also the idea that you have to go to some special asteroid to get iron is wrong I think.

https://www.space.com/moon-metal-mystery-clue-in-craters.htm...

is a recent result but astronauts brought back top-quality hematite from the moon in the Apollo era. Not only is iron a great structural material but iron and related elements have great catalytic activity for turning materials common on asteroids like

https://en.wikipedia.org/wiki/Asphaltite

into something useful.