Read this article to learn:

1. The diversity of crops grown in space
2. First food crop grown in space (onion)
3. What ‘lightsicles’ are
4. NASA and air purification
5. Space Seeds™
6. The primary problem facing astroculture (irrigation) and why (microgravity)
7. First space-grown vegetable eaten in space (lettuce)
8. Expansion of production area in astrocultural trials (1000x increase)

Why astroculture?

Astroculture: growing food in space! ‘Sure, cool concept,’ you might be thinking, ‘but what does this have to do with garden ecology?’ Well, the tight confines onboard spacecraft are more constraining than most any compact, dense city on Earth could claim. Perhaps only those in capsule-style housing can begin to appreciate the cramped living quarters of astronauts.

The effort to grow food in space is about more than creating a system which can reduce the need for supply shuttles from Earth. Astroculture is the proving ground for compact, synthetic production environments. Any experiments are as isolated as possible. This has resulted in NASA (or the National Aeronautics Space Administration) and other space agencies playing a central role in the development of new technologies to support the growth of plants in artificial conditions.

From 1970 to the present there have been:

• 21 plant growth chamber design systems
• 50 different cultivation experiments
  • across ~40 species

The first food crop grown in space were onions in July, 1975, by cosmonauts Klimuk and Sevastianov during the Salyut space program of the Soviet Union. They aimed a few bulbs from the crew’s on-board lighting system at the seeded trays, but nothing more. Some plants did germinate, and for the first plants humans have put in space, that’s a significant enough accomplishment on its own. One of the limitations to this and all the other experiments at this time were the short flight durations. Only two years previous, the record time in space was set at just eight weeks—by the United States.

NASA pioneered research into intra-canopy lighting with a technique they called ‘lightsicles’—poles of lights which lit ever-higher as the plants grew taller. This idea itself isn’t new. Experiments ‘on the ground’ had shown that shading out lower leaves will lead to senescence or the decay and loss of those leaves.

See, the problem wasn’t in supplying the right spectrum of light—controlled conditions in space quickly produced plants with lush growth in their upper canopy. The problem they quickly realized was a shading out and subsequent decay and loss of leaves below the plant canopy. Lights like high-pressure sodium or metal halide were simply too hot to be placed within the plant canopy itself. This heat also meant there was significant distance between light source and plant. This empty space between light and plant was the most the aeronautic agencies were willing to sacrifice to carry out these agricultural experiments. They definitely were not going to now account for empty space between lights on multiple sides of a plant’s growing area!

The scientists at NASA were ready and waiting for something better. They quickly embraced emerging technologies like LEDs for all the same reasons Earth-bound producers have: they’re energetically efficient with little waste heat all in a compact design. This lighting design and strict need for density meant NASA also found itself on the frontier of vertical farming innovations.

Experiments in astroculture, of growing plants in space, mostly boil down to understanding plant function in microgravity. Be this on a shuttle, station, Luna, or Mars, all locations exert less gravitational force than the Earth.

In 1982 Arabidopsis was successfully grown seed-to-seed in space then germinated back on Earth. This was proof of concept, plant life off-planet was possible. But the success rate was only about half, and all with a simple, model plant. This is like sending mice into space before chimps or humans. Subsequent experiments of greater scope found microgravity seriously impedes and sometimes even alters plant physiology.

Now, let’s talk about carbon dioxide for a second. Plants breathe the air, just like us, but they’ve got a use for CO₂: it plays a key role in photosynthesis. Atmospheric enrichment of CO₂ within closed production environments has been practiced since the 1970s. A limited set of experiments in 1989 found CO₂ supplementation also improved a great number of factors in microgravity. But this might not be so groundbreaking or critical to astroculture. This is still well before the current field of controlled environment agriculture had developed. We now see carbon dioxide as key to increasing plant growth but also recognize a number of other inherently limiting factors within artificial environments. Put shortly: most plants, on terra firma or in outer space, do better with CO₂ supplementation.

What has emerged as uniquely problematic in microgravity is irrigation. Maintaining a reliable range of moisture in the root zone has become the critical adaptation of astrocultural production. I’m sure we’re all familiar with water adhesion and its surface tension. On the planet’s surface, adhesion and tension are frequently dwarfed by the force of gravity itself. This pulls water into the soil, pulls water through the soil, and actually plays a large part in the water cycle itself. In microgravity, adhesion and tension begin to exert their dominance. It’s difficult to direct and instead will cling to most surfaces it touches. So when water is applied to the root zone, it clings to the roots. Many plants end up anoxic: they’ve drowned in their flooded conditions.

The latest developments are using porous tubes and/or plates to slow the delivery of water and nutrients. It seems like, if we can’t stop water from coating everything it touches, the plan is to greatly restrict its flow and access to non-target areas. A slow osmosis via a clay pipe works as a bottleneck to prevent drowning.

In the early 2000s on board the International Space Station, astronauts successfully completed two generations–that’s seed-to-seed,-to-seed—of soy: Space Seeds™. Ok, they’re not really trademarked, but it’s fun to call them ‘space seeds.’

On August 10, 2015, NASA astronauts were officially allowed to eat space-grown produce for the first time: some leaves of lettuce.

In addition to innovative irrigation control techniques, the latest astrocultural experiments have just recently begun to increase in scale. The first growing area, in 1971, was a mere 10cm². Little gains were made until 2014 when they achieved 1700cm² of production area by using an ‘inflatable’ model which astronauts assembled once in outer space. The latest plans utilize a vertical racking system and aim for a full square meter (10,000 cm²).

Well, that’s a lengthy enough primer on growing plants in space. There’s plenty more to be told and a wealth of discoveries yet to be made. If you’re interested in some further reading, perhaps try some of these options.

A grand summary of astroculture is nicely reported in Zabel et al. (2016) http://dx.doi.org/10.1016/j.lssr.2016.06.004

Read a report from NASA (2010):  https://www.nasa.gov/mission_pages/station/research/10-074.html

Space Gardening with NASA: https://science.nasa.gov/science-news/news-articles/space-gardening

There are some visually pleasing, incredibly informative graphics here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160013269.pdf

ISS: from NASA to Napa  https://www.nasa.gov/mission_pages/station/research/news/ADVASC