The humble radish will never occupy pride of place on a gourmet menu. But it made global headlines recently when it was grown at the International Space Station
(ISS). The space radishes will not be eaten; they will be frozen and sent back for study.
The radish is the latest addition to several plant species grown at the ISS’s veggie chamber, a carefully constructed “greenhouse”. This is a small plant growth chamber designed and built by Orbital Technologies Corporation. It has been operational since 2014. The chamber uses LED lights and fans to circulate air. Any debris is directed to the bottom by air flow. Plants growing here are exposed to any bacteria or chemicals in the ISS. The first such plant to be grown was the red romaine lettuce.
Last year, in January, China’s Chang’e 4 mission —the world’s first to land on and explore the Moon’s side facing away from Earth — successfully germinated cotton seeds on its moon
lander. It has also sent silkworms to the Moon
in a special habitat capsule. NASA
has a long-running experiment on Earth called the APH (Advanced Plant Habitat), where soils are treated to simulate typical soils from Mars and the Moon.
Plants are grown here to see if they can thrive in these conditions.
“Astroculture”, as it’s called, has also led to Arabidopsis thaliana (a cousin of the mustard plant) being grown in space, while soybean seed has been sent into space and returned and planted to see if it was damaged. (It wasn’t.)
This interest in growing vegetables goes beyond curiosity and giving ISS inhabitants a choice of salads. If man is to ever set up sustainable colonies on Mars (or the Moon), those must grow their own food.
This subject has been explored extensively in science fiction on different scales. Kim Stanley Robinson wrote a trilogy (The Martian, Andy Weir imagined how an individual may be able to survive on Mars by growing potatoes.
SpaceX CEO Elon Musk has a grandiose scheme to send 1 million people to Mars by 2050 in his SpaceX Mars Program. This may be science fiction, but he’s sharing details of how challenges of transportation, habitation and sustainability may be met. Musk has focussed on transportation technology and logistics, and on technologies for a Martian mining and fuels industry.
But food would obviously have to be grown as well.
So what are the challenges of growing food in space? While a vast range of physical conditions are available in different places on Earth, those conditions are not replicated elsewhere in the Solar System.
Earth has a gravity with an acceleration of 9.8 metres per second squared. It has a thick atmosphere with a mix of roughly 78 per cent nitrogen and 21 per cent oxygen. It receives radiant energy from the sun in specific doses. Temperatures vary between minus 50 degrees Celsius and plus 55 degrees Celsius.
Importantly, a strong magnetic field and thick atmosphere block a very large proportion of certain wavelengths of solar radiation, which can be harmful. Earth also has abundant liquid water. The soils contain many mixes of useful chemicals.
Plants have evolved to use those conditions. Their root systems depend on gravity, and pull nutrients from soil. Most use photosynthesis to convert solar energy via chlorophyll in the leaves. Most plants also have a complex cycle of energy exchange, taking carbon dioxide from air and releasing oxygen, and vice-versa, during daylight and darkness.
The Moon has no air to speak of and huge temperature ranges of between minus 173 degrees Celsius and 260 degrees Celsius. The gravity is one-sixth that of Earth with no radiation shield. Mars has temperature ranges of minus 150 degrees Celsius to 20 degrees Celsius and gravity at one-third of the Earth’s. It has a very thin atmosphere, with little oxygen. It has no radiation shield due to a very weak magnetic field. And it receives far less sunlight since it is much further from the sun. At that, it’s still the most habitable of planets in our system.
The ISS experiments show plants can handle micro-gravity. The APH experiments suggest they can use Martian soils and lunar soils. They can also manage on lower sunlight. We don’t know about radiation effects really, since that is hard to replicate. But so far, the experiments have been promising. If Musk can get his colonists there, they may be able to survive, even if their cuisine doesn’t qualify for Michelin stars.