Low atmospheric pressure can make plants think they’re dying of thirst. Experiments conducted at the University of Florida under simulated Martian pressure conditions showed that Arabidopsis thaliana, a member of the broccoli plant family, reacted badly to rarefied conditions. This will need to be addressed as the Martian atmosphere is only 4/1000ths the pressure of Earth’s and Martian greenhouses will have to be kept at low pressure to make leaks less dangerous. In low pressure environments water evaporates more easily, and the plants dry out even in humid conditions. This triggers the plants’ drought defences, which can damage crop yield.
Lunar soil, in reality pulverised rocks known as regolith, lacks any of the nutrients necessary for plants to grow. On Mars the situation is worse, with the Martian top surface containing chemicals that are actually harmful to organic molecules. Importing huge quantities of topsoil or compost is impractical because of the weight involved and so astronauts will have to grow plants hydroponically, using water that they mine from the surface of the Moon or Mars. They will have to introduce the necessary nutrients, brought from Earth, into the water, then compost and recycle everything for the next harvest.
Watch this space
NASA studies have shown that each astronaut will need at least 100m2 of crop space to grow all the food they require. Stored supplies could reduce this by half. Such a space requirement may not sound like much, it’s about the size of a large garden allotment, but multiply that by a six-man crew and the structure to house the garden is indeed considerable. Perhaps trees could be grown to reinforce the greenhouse structures rather than using more precious metals or plastics. The upside is that all those plants will provide plenty of oxygen for the astronauts to breathe.
Let there be light
Providing plants with natural light could be a problem, especially in spacecraft en route to Mars. Plants can be picky about what colour light they grow in – they thrive in red and green light, but not in blue. LED lights could be the perfect solution because they use little power and can be tuned to exactly the right light for each crop. Cary Mitchell, of NASA’s Specialized Center of Research and Training for Advanced Life Support at Perdue University, has developed strings of LEDs that hang down between plants providing all-round illumination. He calls them ‘lightsicles’.
Crumbs in space
Bread is bad when it comes to space stations and other zero-gravity spacecraft. It produces crumbs that float around, which make a mess, but can also make their way into sensitive electrical components, inducing short circuits. Even on Earth this can be a problem; the Large Hadron Collider recently broke down after a breadcrumb got into one of the magnet assemblies. Back in 1965, astronaut John Young smuggled a corned-beef sandwich onto Gemini 3 and, upon his return to Earth, was reprimanded for the danger it presented. So for astronauts, tortilla wraps are the order of the day, and definitely no croissants.