Life support
[[[Live support]]] systems are an essential and necessary part of a Martian settlement, since the natural Martian environment does not allow human beings to survive.
ISS-like systems
The life support system on the ISS is optimized to low weight. It must be fuelled with large amounts of energy and it requires a constant replenishment with consumables.
Near-natural systems
On Mars we will not be able to maintain a life support system that needs consumables. The alternative is a near-natural carbon cycle with the growing of food and producing oxygen at the same time.
