The sort of Life Support System required to nourish a generation ship to fly through space for millennia is beyond our current capabilities

Monday, November 21st, 2022

No life support system miracles are required to keep humans alive on Mars in the near future, Casey Handmer’s argues:

A common criticism of ambitious space exploration plans, such as building cities on Mars, is that life support systems (LSS) are inadequate to keep humans alive, ergo the whole idea is pointless. As an example, the space shuttle LSS could operate for about two weeks. The ISS LSS operates indefinitely but requires regular replenishment of stores launched from Earth, and regular and intense maintenance. Finally, all closed loop LSS, both conceptual and built, are incredibly complex pieces of machinery, and complexity tends to be at odds with reliability. The general consensus is that the sort of LSS required to nourish a generation ship to fly through space for millennia is beyond our current capabilities.

No matter how big the rocket, supplies launched to Mars are finite and will eventually be exhausted. These supplies include both bulk materials like oxygen or nitrogen, and replacement parts for machinery. This doesn’t bode well. Indeed, much of the dramatic tension in The Martian is due precisely to the challenges of getting a NASA-quality LSS to keep someone alive for much longer than originally intended.


On Earth, we breath a mixture of nitrogen and oxygen, with bits of argon, water vapor, CO2, and other stuff mixed in. The LSS has to scrub CO2, regenerate oxygen, condense water vapor evaporated by our moist lungs, and filter out contaminants that are toxic, such as ozone and hydrazine.

With breathing gas sorted out, humans also drink water, consume food, and excrete waste. For extended habitation, these needs also need to be addressed by the LSS.

On Earth, these various elemental and chemical cycles are produced, and buffered by, the immensely large natural environment. I don’t think anyone thinks that a compact biological regeneration system is adequate to meet the needs of a growing city on Mars. Biosphere 2 had a really good go at this and failed for a variety of reasons. One major one was complexity. If the LSS depends on the good will of tonnes of microbes, most of which are undescribed by science, it is very easy to have a bad day.

The alternative is a physical/chemical system. Much simpler, it employs a glorified air conditioning system to process the air and recycle/sanitize waste products. Something like this exists on every spacecraft, and submarine, ever built. The difficulty arises when a simple, robust machine that is 90% efficient is asked to perform at 99.999% efficiency.


Once on the surface, there is an entire planet of atoms ready to harvest. Rocky planets such as the Earth or Mars are, to a physicist, a giant pile of iron atoms encapsulated by a giant pile of oxygen atoms, with other stuff in the gaps. Nearly all rocks, plus water, contain more oxygen than any other element. The Moon and Mars have a lot of water if one knows where to look. Nitrogen is another issue but does exist in the Martian atmosphere. The upshot is that the LSS on Mars doesn’t have to be closed loop. It can depend on constant air mining or environmental extraction to make up for losses, leaks, and inefficiencies. The machinery can be relatively simple, robust, and easy to maintain. The ISS LSS is, after all, 1980s technology at best.


  1. Lu An Li says:

    I can remember that it was said decades ago that Mars could be terraformed and ready for human settlement in a process that would take the better of a thousand years. Create an atmosphere suitable for colonization and do so remotely.

  2. Jim says:

    With enough energy, you can do anything.

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