Scientists are making strides in growing food in space, and their efforts could be critical to eventually supporting a permanent human colony on Mars.
"We can grow plants on Mars just by compressing the atmosphere," SpaceX founder and CEO Elon Musk said Tuesday in a long-awaited speech detailing his vision for sending humans to Mars by 2025. The billionaire engineer said the Red Planet is "resource rich" with water ice and compounds necessary to support plants, such as nitrogen.
Experts say astronauts could pack enough packaged or freeze-dried food to get to Mars and back, although living on the planet for extended periods would get increasingly difficult without regular food-supply missions. Mars would require a six-month journey to the planet, an 18-month stay and a six-month trip back.
NASA has a stated goal for a manned Mars mission in the 2030s. The agency is studying the effects of long-duration space exploration on astronauts as well as learning how to best grow vegetables or other plants aboard a spacecraft or on Mars. The tests on plants, part of NASA's "Veggie" program, have been conducted in a pressurized space garden aboard the International Space Station as well as in terrestrial laboratories.
At present, red romaine lettuce is the only food grown in space that NASA has approved for astronaut consumption. The lettuce's antioxidant properties could reduce the consequences of humans getting radiation exposure in space. Researchers also are testing cabbage and peppers.
"For the astronauts to grow a portion of their food to augment their diet with fresh, nutritious food, I think would be a tremendous benefit and savings overall," said Trent Smith, Veggie project manager at NASA's Kennedy Space Center in Florida. He said the cost and weight to deliver food to Mars "is pretty significant" and indicated that plants could also grow aboard the spacecraft on the long journey to Mars.
In recent years, NASA has relied on private companies such as SpaceX, Orbital Sciences and others to resupply the Space Station with a cargo load of supplies, including freeze-dried food that has a long shelf life. These cargo deliveries have taken place roughly around every three months, but when astronauts go outside of low Earth orbit in long duration missions on Mars, it will not be practical to resupply missions every few months.
Musk this week estimated that a one-way trip to Mars for one person would cost about $10 billion and indicated there were ways to reduce that cost drastically by refilling the spaceship tanks in orbit. He also talked about the need to build a methane-based propellant production plant on Mars for the spaceships.
The methane could be created through the extraction of ice water on Mars and combining it with the planet's abundant carbon dioxide. Having the local propellant source and fresh food production could go a long way to creating a self-sustaining colony on the Red Planet located 33.9 million miles from Earth.
Moreover, chemical plants could use some of the compounds found on Mars to create plastics that might be used to build shelters, greenhouses, vehicles and high-tech potting systems for growing food.
"On Mars it will be easier to grow plants, and we can use a lot of advanced hydroponics and aeroponics systems that we currently have on Earth and grow plants in lava tubes or any other place where we can keep an atmosphere," said Robert Ferl, a professor of Horticultural Sciences at the University of Florida in Gainesville. Both hydroponic and aeroponic gardening can be done without any soil.
The surface gravity on Mars is about one-third of that on Earth, but that is not a major concern when it comes to growing plants. The same cannot be said for growing plants aboard the Space Station in microgravity, where it's a challenge getting the air and water mixture just right for the plant's roots.
Plants under zero gravity conditions can suffer from either flood or droughts since there's no natural convection and the water can stick around the roots or edges of the pot.
One way around the microgravity is to use a pillow-like technology developed by NASA. Seed and soil-like particles are put into the pillow chamber where they can be more efficiently controlled in zero gravity conditions to support plant growth.
"Turns out that managing water and managing fluids, especially around the roots of plants, is fairly tricky stuff in the absence of gravity," said Ferl, who has conducted NASA-funded experiments on plants.
Space agriculture, whether aboard the space station or in an extraterrestrial habitat, can provide food and recycling benefits for crews. The plants recycle the astronaut's exhaled carbon dioxide and also can use the excreted water. LED lights are used for sunlight to increase the photosynthetic activity by the plants.
The public's awareness of the possibilities of space farming may be limited to what they saw in the 2015 Hollywood blockbuster movie "The Martian," starring Matt Damon. His character is a botanist who gets stranded on the planet and grows food to survive using Martian soil mixed with a fertilizer made of human manure.
Experts say there's some truth in the movie but suggest using untreated human excrement as a fertilizer on Mars would be dangerous. They also suggest that the Martian soil contains toxic elements that also would need to be removed.
"Matt Damon would have had to clean the soil a little bit and remove all these toxic things before using it to grow plants," said Lucie Poulet, who has conducted research simulating Martian soil. She recently published a space agriculture research paper in Botany Letters with colleagues from France's University Blaise Pascal.
Astronaut Mark Watney, Damon's character in the movie, harvested Martian potatoes. Turns out potatoes and sweet potatoes are on the list of vegetables that could be grown in space, according to NASA. Tomatoes, wheat and soybeans also have been mentioned by plant researchers as a crop that offers the potential for space gardens in the future.
Tomato seeds were tested aboard space shuttle missions but didn't produce fruit as it would have required pollination. Some have raised the possibility of sending bees or other insects into space to pollinate plants in space gardens, although there are other solutions.
"The astronauts are going to have to become the bees for the testing," said NASA's plant expert Smith. "My hope is we'll be able to do some of this robotically. There's no reason why you can't have a robotic system with sensors to cross-pollinate the plants."
For deep space travelers, growing plants isn't just a source of food but could have less obvious benefits, too. Caring for plants could offer a psychological boost as astronauts go to Mars and see the Earth getting smaller and smaller.
"Having that little piece of Earth while they're on the journey to Mars to remind them of the smells and the sights of home will be very important," said Smith.