July in Bend. The summer weather, i.e., “heat,” has kicked in. My wife’s garden box has yielded its last lettuce and spinach for the season. But our half-barrel of raspberries is bearing. I enjoyed a handful on my Cheerios this morning. Our squash plants are blooming, but probably won’t set much fruit until August. (Don’t get me started about the definition of “fruit” vs“ vegetable.”)
     It’s said that an army marches on its stomach. The same is true for a colony on Mars. Read my second and final installment on this topic below.
     Procrastinators take note. Bargain Booksy’s Science Fiction Giveaway featuring my book Crimson Lucre ends July 31st. Not only are 15 titles up for grabs, the winner also receives a free Kindle eReader. Don’t miss out. Scroll down for the link.
     My cover designer for Scarlet Odyssey is hard at work. I hope to preview it to you, my loyal subscribers, before I reveal it on my Facebook page. Stay tuned.  My manuscript revisions are on track to send it to my developmental editor at the end of this month.
Happy Reading,
Brian
          

     Last month we examined the requirements to provide sustenance for ten colonists on a two-year mission to Mars. Recall that at 3,000 calories per day a human requires 1,095,000 calories per year.
     We reviewed NASA’s packaging methods, which are extraordinary. But to my thinking, fresh food is as necessary for mental health as it is for meeting astronauts’ nutritional needs. Its availability will be critical for success and a long-term presence on the Red Planet.
     To accomplish this, we determined it will take 233 square feet of garden area per astronaut to provide enough nutrition if they harvest four times per year. Our crew will need a total indoor grow space of up to 2,330 square feet.
     As I noted in last month’s edition, indoor farming in Martian regolith isn’t the only option for agriculture on Mars. Here on Earth, and to a limited extent on the ISS, hydroponics has proven to be a reliable growing method for certain crops. In many cases, increased crop yields have been documented using this technique.
     Hydroponics is the growing of plants in the absence of soil. Roots are immersed (or sprayed, as in the case of aeroponics) in an aqueous solution of nutrients and minerals essential for plant life. It’s a closed system. Water is pumped from a reservoir into pipes or troughs where the roots draw the water and minerals. Energy is provided by grow lights suspended above the crops. Returning the leftover effluent to the reservoir closes the system.
     Hydroponic systems can be modularized. Trays or racks of plumbing, plants and grow lights can be stacked one on top of another, reducing the overall footprint and increasing the yield per unit area.
     A number of supporting systems and requirements are shared in common between hydroponics and soil-based ag for our Mars colony. Water must be collected and distributed for irrigation. If it’s sourced locally, it must be purified using a Urine Processor Assembly to remove perchlorates. Ongoing water quality must be monitored for the buildup of deleterious compounds such as nitrate salts or organics and rerouted through the UPA.
     Crop production will supplement the base’s oxygen supply and CO2 scrubbers. Both systems will be automated. AI will monitor and manage pests, humidity, water purity, fertilizer, harvesting and composting surplus biomass.
     But hydroponics offers distinct advantages in a closed colony. First, as noted above, it requires a smaller footprint. Depending on the plants selected, and using LED lighting, a given growing rack could be no more than 18 inches high.
     In a 30-foot-diameter dome, as many as nine layers could be stacked close to the center. Assuming two-foot-wide aisles for human and robotic passage, three-foot-wide stacked racks could be arranged in three concentric circles. That provides 2800 square feet of hydroponic growing area within the 707-square-foot structure. A similar planting arrangement for crops planted in soil yields a net production area of 443 square feet. Our hydroponic system yields six times the net growing area!
     The setup would be less laborious. A one-foot soil depth in our dome means a hydroponic system would save astronauts from having to collect and haul over 26 cubic yards of regolith into our sealed dome. That volume of dry soil on Earth would weigh 26 tons! In Mars’s 1/3G gravity, that’s still nearly nine tons. And as noted last month, four domes will be required to provide enough food for our crew of ten colonists. Hydraulic equipment will need to be sent with the mission to facilitate this kind of earthmoving. Plus, as I noted, perchlorate must still be filtered from the regolith before it can be used for crops.
     Native water would also have to be purified to remove perchlorate. But the volume required for hydroponics could be as little as 1/10th of that required for soil-grown crops.
     A final advantage to hydroponics is that it can provide fresh produce for the nine-month flight to Mars. Arriving with growing produce would give the mission a head-start until the full system is up and running.
     To fully realize the above advantages of hydroponics, plants should be selected that only grow a foot tall. Leafy greens, herbs, strawberries, tomatoes (with some pruning) and peppers (more pruning) have all been successfully grown hydroponically. Kale and chard are rich in calcium and folate, vital nutrients for astronauts in the reduced Martian gravity. Herbs will allow for most ethnic cuisines, re-creating a little bit of home for our explorers. Tomatoes and peppers will add variety to the otherwise monotonous three sisters crop regimen I recommended in last month’s issue. And strawberries offer sweet in an otherwise savory diet.
     But there are disadvantages. One drawback to the exclusive use of hydroponics on Mars is that it can’t close the carbon cycle. As I noted last month, with soil-based agriculture, human waste and food scraps will all go into a composting toilet. Composting gives off CO2, which will be absorbed by the crops. But without soil to amend with the remaining compost, that biomass will be lost to the system, likely dumped outside the base.
      Another disadvantage is that most low-growing plants suitable for our system are not calorie-dense. But they are more nutrient-dense than their taller cousins. The larger root mass of these bigger plants make them best suited instead for soil-based cultivation.
     Given what we’ve learned about food on Mars, let’s examine a mission ag plan. Ideally, our astronauts should grow most of their own food. Once our base is established, only specialty commodities too difficult to cultivate on Mars like coffee, wheat flour, sugar and meat should be shipped from Earth. This conserves shipping space for other mission-critical equipment. The more variety in our explorer’s menus, the better will be their mental health and mission success.
     I estimate constructing and outfitting greenhouse domes will take six months apiece. I expect decontamination of soil and water could prove to be a slow process. It will take the full two-year mission duration to build out the agriculture infrastructure.
     The inaugural human mission will rely on its 14-ton allotment of packaged food. If the ag facilities are successful, that produce should be consumed. Any unused packaged food could be set aside as part of a one-year emergency stash for subsequent missions.
     The risk of crop failure due to habitat or equipment failure, or loss due to disease outbreak or environmental toxins is high. Any rescue would be at least a year away, making it prudent to provide adequate packaged food for that amount of time.
     What facilities should be constructed? Recall that our crew will need an indoor grow area of up to 2,330 square feet, requiring four 30-foot diameter domes.
     I propose the construction of one dome at a time. The first dome provides enough hydroponic capacity to address each astronaut’s personal preferences and needs with respect to leafy greens, herbs, strawberries, tomatoes and peppers. 100 square feet apiece would suffice. A ring of hydroponic platforms stacked five-high placed against the outer wall would yield 1000 square feet of production space. The remainder of the floor could be allocated to the three sisters, supplementing the processed fare. The final buildout of three more 30-foot diameter domes dedicated to the three sisters should achieve food self-sufficiency.
     Growing crops on Mars will be a substantial component of any permanent human presence. Installing the necessary infrastructure will divert personnel and computing capacity away from exploration, research and resource extraction. But once established, agriculture will be the foundation on which those endeavors will stand.
Until then,
Happy Reading,

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     Want a deeper dive? Check out these sources.
https://en.wikipedia.org/wiki/Hydroponics
https://getgrowee.com/best-plants-for-hydroponic-farming/#:~:text=What%20are%20the%20best%20crops%20for%20hydroponic,similar%20nutrient%20requirements%2C%20and%20offer%20high%20yields.
https://ourlittlesuburbanfarmhouse.com/18-plants-you-can-grow-year-round-hydroponically/#google_vignette
https://science.nasa.gov/science-research/science-enabling-technology/technology-highlights/a-novel-approach-to-growing-gardens-in-space/
https://www.cnn.com/2023/03/24/world/mars-food-interstellar-lab-climate-scn-spc-intl/index.html