The ESA’s MELiSSA zero-g farm could make life sustainable in space

There are basically one two possible solutions: put astronauts into some sort of stasis so they don’t need to eat, or give their spacecraft some way of sustainably creating food as it goes.

The Micro-Ecological Life Support System Alternative (MELiSSA) is to do the latter. It’s an ambitious pitch, with separated ship compartments dedicated to performing different jobs within the cycle. It starts with ship waste — yes, the euphemistic “waste” that magically appears inside all crewed spaceships — which gets put into a “liquefying compartment” that breaks it down to basic minerals, ammonium, fatty acids, and CO₂. The photoheterotrophic compartment comes next, where a bacterium called Rhodospirillum rubrum further breaks down the fats and minerals from the first chamber, purifying out even more basic minerals and nitrogen-based ammonium.

The next section is the “nitrifying compartment,” where a mixture of the Nitrosomonas and Nitrobacter bacteria react oxygen gas with urine from the crew and ammonium from the second chamber. This creates nitrates, fertilizing compounds that enrich soil and allow plants to grow larger, faster — or in some cases, allow allow plants to grow at all.

The need for nitrogen compounds in agriculture is nothing new — legumes like peanuts have been grown for thousands of years because they form a symbiotic relationship with “nitrifying bacteria” that grab and “fix” gaseous nitrogen in the atmosphere into certain compounds. This makes them perfect for enriching soil through crop rotation — or orbital waste-rotation, as the case may be.

The fourth chamber is the “photoautotrophic chamber” that does most of what we generally think of when we imagine space farming: growing things. The nitrogen-enriched growth media are used to grow plants for eating; as of now the team has selected wheat, tomato, potato, soybean, rice, spinach, onion, and lettuce, but with enough physical space they could expand that list in the future.

This fourth chamber is also used to grow also large quantities of algae, particularly two species of cyanobacteria colloquially known as Spirula, for their shape. These are not only widely used already as a dietary health supplement, but they’re naturally very active photosynthesizers. They take up CO₂ produced by the crew, providing oxygen for them to breathe in return, as well as funnel into the nitrifying compartment to keep the whole process moving.

The fifth “chamber” of the system is the crew capsule itself. That might seem like an odd way of looking at the interior of the ship, but it’s where the last crucial step in the process occurs: eating and drinking. By eating the foods grown in the nitrogen-enriched soil, they produce solid and liquid wastes that are used to create more of that very soil, and keep the air breathable at the same time.

One thing the MELiSSA scientists can say about space agriculture is that it’s going to need some serious room. The ISS, the largest space facility ever built, isn’t nearly large enough, they say; NASA’s VEGGIE is a venerable attempt to grow lettuce in space, but so far it has produced only a single crop of lettuce, and that took over a month of grow-time. If we’re going to be producing a livable amount of food in real-time, even just for a few people, then the ISS just is not big enough to do the job.

Worse, once we have something like wheat there’s no quick or easy way to actually get that in your belly. You can just pick up a tomato and eat it, but to make dough you need flour and a zero-g mixer, and to make flour you need to go through several steps to mill and separate the newly grown crop. Even something simple like a non-rising bread has a huge variety of difficult challenges nested within it. The algae, and potentially soy beans, could provide good sources of protein to keep astronauts going, but their vegan diet will still be lacking in certain helpful molecules and likely require supplement with at least a couple of vitamin and mineral pills.

In a very real way, the challenges of weightless cooking could be so extreme that it makes more sense to give up, and simply eat raw food until artificial gravity sections come around. If future spacecraft do end up with a rotating gravity-kitchen, we’d better hope they end up being separated from the sweat-filled atmosphere of the gravity gym.

In the end, we’ve got time to address this issue. The researchers claim that while there are significant psychological benefits to growing your own food, from a weight perspective we can probably get away with canned, prepared foods for up to a couple of years. Anything beyond that, and it will become necessary to grow food on the way. That makes missions more resilient, but also fragile in all new ways — boy would it suck to find out our first interstellar crew died halfway to Alpha Centauri because somebody over-watered a crucial crop and killed it, or because a tiny plant mite stowed away before launch.

But these are problems that must be solved, if we are to make our homes in space. Though we’ll have plenty of room if we ever make it to another planet, these are still the sorts of processes explorers will need to stay alive until more robust terraforming or biodome development can really get going.

ESA scientists have done some preliminary tests on spiringula bacteria in space, creating snack bars laced with the microorganisms that ISS astronauts ate — and not one of them died, which is really the outcome you’re looking for. And the nitrifying technology developed for MELiSSA has been licensed for use in waste treatment.

Eating is one of our most Earth-bound needs, to continually consume different parts of the biome that, so far as we can prove, makes our planet unique in the universe. Going far afield means bringing some part of that biome with us, and making damn sure they stay intact and accessible to our metabolism as we consume them again, and again, and again. Let the cycle lapse, and it may be impossible to get it going again.