Earth and Mars are in opposition every two years. It’s only practical from a shipping perspective to fly supplies at that same frequency. That includes food. Let’s examine what it would take to feed a crew of astronauts for two years.
NASA cites a daily caloric need of 2500 to 3500 calories, depending on activity level and body size. Assume 3000 calories per day per astronaut. Assuming a long-term staff of ten, and a duration of two years, that’s a total of 21,900,000 calories between shipments for our intrepid explorers.
As far as preservation and storage goes, the space agency can and does use freeze-drying, vacuum sealing, gamma irradiation (to sterilize meat and dairy), refrigeration and freezing.
Diets must contain all the usual vitamins, minerals, protein, carbohydrates and fats. ISS astronauts take a daily multivitamin, too. In zero-g space, humans experience muscle and bone loss. NASA compensates with diets rich in protein and calcium. The same will be true on Mars, where gravity is 1/3rd that of Earth.
Given these nutritional requirements and storage methods, crewmembers aboard the ISS enjoy an astounding variety of foods. But that food comes at a cost: namely about 3.8 pounds per astronaut per day. Our supply ship must provide almost fourteen tons of food for our ten explorers.
The agency is experimenting with a yeast-based nutritional paste to use on long-term missions. An advantage is that it could be dried and shipped as a powder, eliminating the water weight. But living on such a diet would likely increase the psychological strain already experienced by the double whammy of tedium and close quarters. In my opinion, this might work as an emergency backup, but won’t be practical for the long-term. Missions will only be deemed successful if the astronauts return sane.
A lot can happen in two years. An engineer may underestimate the caloric needs of the community. The supply ship could encounter a technical failure. Heck, an unidentified asteroid could strike the vessel.
But there are other options for a long-term Mars mission to obtain nutrition. Red Planet explorers can grow their own crops.
Furthermore, as we’ll see below, agriculture on the Red Planet can, and should, sit at the crux of three critical environmental systems: the carbon, oxygen and water cycles. Plants can be just as critical to existence on Mars as they are on Earth.
How should astronauts farm their own food? I advocate using the Three Sisters method. This ancient practice of planting corn, beans and squash together was first utilized by pre-Columbian Native Americans. It yields an astounding 1774 calories per square foot. Assuming five harvests per year (the grow lights will be on 24/7), that’s 5,870 calories per square foot per year.
At 3,000 calories per day a human requires 1,095,000 calories per year. Doing the math, it will take 187 square feet of garden area per astronaut to provide enough nutrition. If they harvest four times per year, the required “acreage” is 233 square feet. Our crew of ten will need an indoor grow area of between 1,870 and 2,330 square feet. That could be accomplished with one 54-foot diameter dome (not advisable to put all one’s eggs in one basket),or three or four 30-foot diameter domes.
Similar to what I described for the habitat in the
April ’24 edition of JOTH, a closed loop water recycling system will need to be set up for each agri-dome. Otherwise, irrigation will become contaminated with nitrate salts.
While water from transpiration and evaporation will likely condense on the dome wall and be collected at the base, a system similar to the Urine Processor Assembly on the ISS will capture and purify water that percolates through the soil and is collected by a grid of perforated pipes.
The first stage will employ vacuum distillation to extract water vapor. The concentrated brine is then osmotically filtered. The purified liquid that collects on the membrane surface is heated, vaporized and returned to the storage tanks, leaving the salts behind.
This same system will be used to remove perchlorates from the regolith prior to planting. Otherwise, the greenhouse environment would be dangerous to both plants and astronauts alike.
As for the carbon cycle, human waste and food scraps will all go into a composting toilet. A shuttle must be set up to deliver the produce to the kitchen and return the waste back to the garden dome. Composting gives off CO2, which will be absorbed by the crops. The compost will amend the regolith into soil.
Functions within the garden such as pest management, soil chemistry, moisture content monitoring, harvesting and composting will need to be automated. See my earlier discussion on autonomous farming in the
December ’23 issue of JOTH. This will free up astronauts for other scientific and commercial tasks.
But indoor farming in Martian regolith isn’t the only option. Hydroponics has proven to be a reliable growing method for certain crops. Next month I’ll discuss this third option for food production. And I’ll share my preferred solution to the astronaut calorie conundrum.
In the meantime, imagine how difficult it is just to keep our refrigerators and shelves stocked here on Earth. My wife and I end up shopping for groceries twice a week (keeps fresh fruits and veggies in the household).Consider the care and planning needed knowing the consumables will only be delivered every other year! Or if you had to grow everything you ate yourself! Until then,
Happy Reading,
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Want a deeper dive? Check out these sources.
https://www.nasa.gov/wp-content/uploads/2018/05/stemonstrations_nutrition.pdf?emrc=5d7a54https://science.howstuffworks.com/space-food3.htm#:~:text=The%20space%20shuttle%20carries%20about,meals%20a%20day%2C%20plus%20snacks
