Astronauts: Space-Age Weed Eaters?
While NASA contemplates what plants might be grown in space for the Astronauts based on the moon or on their way to Mars, may I offer a few of my own plant candidates? These candidates probably haven't been researched much so far because, for most people, they're dismissed as common weeds.
Summer Purslane - Portulaca oleracea
Summer Purslane, or common purslane, is a common bane to most gardeners. This flat-growing, succulent-leafed plant grows just about anywhere soil is devoid of other plants, "it tolerates poor, compacted soils and drought" -- See the Wikipedia link, above. It grows during the warmer times of the year and contains more Omega 3 fatty acids than any other leafed vegetable. It also contains a fair bit of vitamin C.
I like summer purslane for four reasons: (1) it's tasty, (2) it likes poor soils, (3) you can eat almost the whole thing, and (4) it grows as a flat mat, which allows a space-cramped astro-farmer to grow closely stacked shelves of it in a corner of his/her biosphere. Here I envision shelves where the bottom side is covered in LEDs to illuminate the plants on the shelves below it.
Miner's Lettuce - Claytonia perfoliata
Miner's lettuce, sometimes called Winter Purslane, is one of the first plants to appear in the California springtime. When it's still chilly outside, it's tender shoots break through the poor soil into the shady areas in which it usually grows. When the heat of summer kicks in, Claytonia begins to fade from the spotlight, but not before producing a bounty of seeds. The name "Miner's Lettuce" comes from the Gold Rush era, when miners would eat it to prevent scurvy, obviously because of it's vitamin C content. I like miner's lettuce for six reasons: (1) it's tasty - much like lettuce or spinach, (2) it likes cool shade, (3) it contains vitamin C, (4) with its round central leaf it looks like it should be a space vegetable, (5) you can almost eat the entire plant, and (6) it doesn't much care what soil you try growing it in. From our astro-farmer's point of view, miner's lettuce is an ideal vegetable when you're running short of light and heat, such as during the lunar nighttime when power consumption would be at a minimum.
Common Chickweed - Stellaria Media
Another fine winter plant, chickweed is tasty stuff that grows almost anywhere there is space. Like miner's lettuce and summer purslane, above, chickweed is almost entirely edible. As a medicinal plant, it has been traditionally used to treat skin-related ailments. I like this plant for 5 out of the 6 reasons I like miner's lettuce -- chickweed, however, doesn't look much like a space vegetable.
Common Dandelion - Taraxacum officinale
Dandelions can be used as salad greens and the taproot can be dried and roasted as a coffee substitute. Naturally this means that nearly the entire plant can be consumed. Dandelions are easy to grow, perhaps much harder not to grow. No space garden should be without a patch of the cheery yellow flowers.
You'll notice by now that the candidates I've offered have a few common attributes. The first, in all cases the plants can be almost entirely consumed. When you look at many of the NASA-tested vegetables, such as tomatoes, potatoes, and wheat, there remains a fair amount of plant waste after harvest that needs to be broken down and returned to the soil/nutrient solution. This requires room and energy to accomplish and effects the O2/CO2 balance if composting or incineration are used.
All the candidates can grow in relatively poor soil. Weeds are robust members of the plant community. They are opportunists which usually grow quickly wherever they end up, and they generate a fair number of seeds as a matter of course, allowing for a multitude of re-plantings. Two of the candidates are winter vegetables, requiring less energy than typical summer vegetables. One of the candidates grows as a flat mat, allowing it to grow on tightly spaced shelves where space is limited.
These candidates demonstrate that by looking a bit "outside of the box", growing space vegetables may be easier than currently anticipated.