The challenges of surviving in space (with or without hostile enemies intent on dominating the universe) has made and will continue for a long time to make for a good sci-fi story. The resourcefulness required to survive in the vast emptiness between (and on) planets also forces us think deeply about better ways of propelling, feeding, housing and medicating ourselves. The cost of launching extra weight into space plus the limited lifespan of necessities such as food and medicine leaves us with complex questions about how to sustain ourselves as we look to explore more of our solar system and, hopefully one day, beyond it.
A 2015 review in the Journal of the Royal Society Interface considered a number of space missions and analysed how synthetic biology may assist those missions in the four resource areas mentioned above; propellant, food, habitat and medication. Of most interest, given the significance of the challenges presented, is a six-person, 916 day return voyage to Mars which would include 420 days of traveling there and back plus a 496 day stay on the red planet.
What are we going to have to do to be real-life Martians?
Although one of the shorter sections of the paper, how we will advance food production being the focus of this blog means that we will put the section of food production in space up-front and centre.
Based on astronauts living on the International Space Station, living in space requires 1.83kg of food per crew member per day. As a result, the six person Mars mission requires around 10 tonnes of food that needs to be shipped in order to sustain a mission if all of it was shipped from Earth although more accurate assessments of food amounts required to be produced whilst on mission have a lower estimate of 4.5 to 5 tonnes.
So the ability to produce food using available elements and compounds whilst away from the Earth is a significant problem. And the most accessible food production option is to use photosynthesizing bacteria and plants. Producing food using bacteria has the most significant weight savings, with Spirulina (a nutritional biomass made from either Arthrospira platensis or Arthrospira maximum) being promoted in earlier papers as a suitable option to producing food in space compared to attempting to grow and harvest plants. According to those previous papers, it is possible to produce 5.271kg of Spirulina per day using three 2,000 litre bioreactors. This rate of production would sustain the crew for the entirety of their stay on Mars and for the return to Earth and save a significant amount of launch mass.
So how can synthetic biology help if Spirulina is already producible in adequate amounts to sustain the majority of a Mars trip? If you can imagine eating the same substance every meal for 706 days straight, one problem is easy to identify. It is suggested in the paper that synbio efforts could be directed to diversifying the textures and the tastes produced by the bacteria so that a variety of ‘foods’ can be consumed by those on the Mars mission.
Increasing the rate that the bacteria is able to reproduce will also aid the weight reductions at lift off and increase the redundancy built into the rations of food for the trip. There are some reported increases in production rates reported in the paper, but, for example, whether increased photosynthetic efficiency can be engineered into the bacteria to increase production is a question common to current research efforts in earth-bound food production.
Finally, being able to increase the nutrient content in the food produced to aid general health and space-specific health problems will increase the chances of a successful mission.
The shelf-life of pharmaceuticals are shortened in space travel and at present the issues caused by this are solved by sending more supply missions. Given the time and distance involved in a trip to Mars, such a solution has little practical use.
Synthetic biology has the ability to play a role in readily producing pharmaceutical substances during a mission to Mars. For example, acetaminophen (paracetamol) can be produced using a modified chromisate pathway in E. coli. Unfortunately, space travel doesn’t suit E.coli as the compounds it requires to survive are not readily available. But if an autotroph can be manipulated to contain the same pathway and produce the same substance, we may have a new way to produce the pharmaceutical with the restricted inputs. The cyanobacterium Synechocystis sp. PCC 6803 has been identified as a possible candidate that will survive on the inputs available in space and could host the appropriate pathway to produce acetaminophen.
Figure 8 from article demonstrating the proposed pathway to create acetaminophen from Synechocystis sp. PCC 6803.
It can be imagined that with enough research we should be able to produce a range of pharmaceuticals or at least their components from the limited inputs available in space.
The further we go and the more weight we carry, the greater the fuel required. Complicating the matter further, the more fuel we carry into space, the more fuel we require to lift the extra fuel off the ground. The problem of needing more fuel to lift even more fuel to be able to propel more weight into space is one that permeates through the problems of supplying enough food and equipment to astronauts traveling for long periods of time.
The possibility of producing fuel in space is limited, according to this paper, to using methanogens to create methane. The type of methanogen used in bioreactors effects the quality of methane gas created and the rate of production. Further, a number of methanogens are able to use the compounds, particularly CO2, created by the crew of a space mission.
Synthetic biology uses to address the problem of fuel production in space will likely focus on the production of methane by methanogens. Particularly, the ability to produce methane using the least amount of inputs and with the greatest nutrient recycling efficiencies will be key. Similarly, modification of cyanobacterial production of ethylene, an alternative propellant, for greater production efficiency is another possible use of synthetic biology to aid space flight.
Lastly, the ability of erect a habitat on Mars will require either the supply of material from Earth and/or the use of material available on Mars with equipment supplied from Earth. The proposed use of 3D printing to construct habitat allows the use of finer materials in an additive manufacturing process. But the possibility of biologically produced materials (biopolymers) provides a method of producing the base materials using inputs available away from the Earth and significantly reducing the launch mass of materials dedicated to habitat construction.
Figure 7 from article demonstrating the shipping mass saved for habitat construction in missions to Mars (left) and the Moon (right).
Synthetic biology efforts focused on increasing the synthesis of biopolymer material per unit of bacteria will result in less equipment in the form of bioreactors being required to travel with the crew with the time for construction of the habitat being reduced as well.
Synbio in Space
At its most basic level, the quest to man a mission to Mars creates problems that must solved using the most efficient means possible. As a result, the use of synthetic biology to solve problems in the four areas listed above looks little further than what inputs are available in space and how they can be used to solve the problems spaceflight presents.
However, advances in modifying organisms to meet these challenges will likely lead to flow-on effects in the same areas here on a better-resourced planet. For example, should it be possible to create different textures and tastes in Spirulina in the confines of space then one would expect that it will be possible to use different inputs and different genetic circuits to create a variety of foods. Further, food produced should be more efficient, sustainable and economical than traditionally generated food.