Is thinking of your home as a spaceship a useful maybe even practical metaphor?
As we execute carefully planned Extra Vehicular Activities (EVAs: the weekly grocery shopping in masks and gloves), our account of inputs and outputs and the circular nature of flows of our homes may become clear.
And realizing how that works in our homes, may lead us to a more immediate perception that the same applies to Earth in its entirety.
Martian colonies won’t have the dumb luxury of wasting resources. Only 100% sustainability will let them last. Their valuable export is going to be the technologies and practices to make it happen on Earth as well.