Thayer Team Wins NASA Challenge

In late April, a team of Dartmouth engineering students won the 2019 NASA BIG Idea Challenge for their design of a greenhouse intended to support a long-term mission to Mars.   The team was composed of six students: David Dick, Grace Genszler, Thomas Hodsden, Peter Mahoney, Morgan McGonagle, and Christopher Yu. 

The BIG Idea Challenge is a fairly new competition that has only existed for the past several years.  This year, the NASA BIG (Breakthrough, Innovative, and Game-Changing) Idea Challenge asked students to come up with ideas for the design, installation, and operation of a Mars greenhouse.  This greenhouse would have to provide food for four astronauts for six hundred days.  The challenge was open to teams of undergraduate and graduate students from across the country, but only four teams succeeded in making it to the final round.  These finalists presented their designs to NASA at the Langley Research Center in Virginia. 

Students from Thayer initially got involved in the BIG Idea Challenge through the Engineering Department’s capstone courses ENGS 89 and ENGS 90.  “89/90,” as it is typically called by Dartmouth engineering students, is a set of two courses that function as a final project and a way for students to apply their knowledge from previous engineering courses.   In this course, engineering students usually develop projects that are requested by a client, such as private companies or other organizations.  Projects vary widely, and include an explosive ordnance disposal device.   However, the BIG Idea Challenge marked the first time an engineering competition, rather than a client-motivated design, has been used as an 89/90 project.   

Through the 89/90 course, students were able to simultaneously compete in the challenge and complete their coursework in Thayer, as well as get advice from faculty advisors and the Thayer machine shop.  Even though 89/90 is required for Bachelor of Engineering candidates, projects are assigned based on student interest, so all of the students involved in the competition were already excited about the topic.  In fact, the Dartmouth team continued beyond the requirements of the 89/90 course to compete in the competition out of personal interest. 

The greenhouse design itself was based around several main objectives.  The BIG Idea competition required that the design be based around a previously-developed inflatable habitat called the Mars Ice Home.  Various types of cosmic radiation which can severely harm humans can easily reach the surface of Mars, and the Ice Home uses a layer of water in its inflatable roof to protect astronauts against this radiation.  In addition, the greenhouse had to be transported millions of miles from Earth in a compact form, deployed with few tools or human interaction, and then function for almost two years on the hostile surface of Mars.  Finally, as mentioned earlier, the greenhouse needed to supply four astronauts with their needed nutrition for six hundred days. 

To meet these objectives, the Thayer team designed a greenhouse featuring a hydroponic, nutrient-film system.  In a hydroponic system, the roots of the plants are covered in water rather than in soil.  A nutrient-film system is a type of hydroponics in which the roots are kept wet by a thin layer of nutrients.  The alternative is to completely submerge the roots, but this uses a substantial amount of valuable extra water.  To preserve water and save weight, the team elected to utilize a nutrient-film system. 

The team also opted to use an aeroponic system in replacement of the hydroponic system. This decision was also made in the interest of conserving water and promoting efficiency. An aeroponic system suspends the plants and their roots in the air. They receive nutrients from the aforementioned nutrient-film system and are sprayed with water daily (although frequency does depend on the type of plant). Aeroponic systems are known for their ability to maximize use in a compact area- a characteristic conducive for a system. The biggest benefits are that aeroponic systems grow plants quicker than other methods, promote more efficient gas absorption and the plants require far less manual labor.  

The students next planned to use a crop rotation scheme, utilizing a circular structure with many miniature platforms that have spots available for plants.  The platforms can fold up for transport, taking up less of the limited volume available on a spacecraft.  And by using a crop rotation system, the greenhouse can rotate which plants are growing and which plants are ready to eat.  With a rotation system, all of the crops are not harvested at the same time, so there is never any danger of temporarily running out of food.  An analogy on Earth would be a year-round tomato greenhouse, where tomatoes are always available to be harvested no matter the season. 

The next important question was what plants they would use. The team tested about 80 plants. Judging based on growth rates, nutritional value, conditions necessary for growth and if they would have no adverse interactions, the team selected eight plants that would maintain a complete, nutritious diet. The plants selected were: broccoli, chufa, kale, potato, soy, strawberry, sweet potato, and wheat. These plants covered the primary macronutrients, while also containing trace vitamins which would promote good health in space. 

In addition to providing nutrition that can sustain the 600-day mission, the plants play a crucial role in oxygen production. Future plans from NASA for a Martian base will have their own methods of producing oxygen and scrubbing carbon dioxide. In the DEMETER project proposal, the volume of plants produces excessive oxygen to the point where, unregulated, the system would lack sufficient carbon dioxide and the plants would die. 

To combat this and the fire risk of highly concentrated oxygen, the system will have to actively push out oxygen to where the astronauts are to ensure that it is consumed. In addition, atmospheric carbon dioxide would have to be pumped occasionally into the greenhouse. With these countermeasures, excess oxygen is a welcomed “problem” to have; future deployments to space can avoid the weight of large O2 tanks and the human calculations (breathing patterns, exercise levels, etc.) when depending on a finite amount of oxygen. 

Competing against four other skilled teams in the final competition, Dartmouth set itself apart from the competition by focusing on a systems-based approach. The other groups focused on flushing out a single aspect and perfecting it. The Dartmouth team accounted for as many factors as they could in their system and meticulously calculated elements to make it as complete as possible.