Air purification on the International Space Station presents unique engineering challenges due to budgetary, gravitational, and atmospheric constraints. The current ISS air filtration system involves electrolyzing water to produce oxygen and hydrogen and conducting the Sabatier Reaction to eliminate CO2. Though currently adequate, the system has various flaws: it requires a lot of energy and produces gases and heat that simply become waste products. We believe air purification on the ISS can be innovated upon by targeting sustainability and efficiency – two guiding principles essential for designing the technology of the future.
We aimed to create an air purification system that reused all waste products, thus minimizing energy cost. By using cyanobacteria to consume carbon dioxide and produce oxygen, we bypass both water electrolysis and the Sabatier Reaction. Skipping water electrolysis and the Sabatier Reaction saves at least 3.508 * 10^7 J per day (similar to the energy contained in 35 sticks of dynamite). (This estimate comes from an analysis of the resources required to complete each reaction, the resources required to ship materials to the ISS necessary for these reactions, and the resources required to eliminate the byproducts of these reactions). As an added benefit, the cyanobacteria used in our system can be studied to discover the influence of microgravity on organisms.
Our solution further exemplifies sustainability in its source of energy: heat produced as waste by ISS machinery. Currently, the International Space Station dispels heat via an Active Thermal Control System (ATCS), whose various subsystems collect, transport, and reject the heat. While the IATCS is a closed system that aids in cooling the various machinery in the station, the External Active Thermal Control System (EATCS) redirects energy to space through the circulation of anhydrous ammonia and the use of radiators. We propose that this system can be improved upon by diverting heated ammonia to power an air purification system through paramagnon drag.
Paramagnons are similar to magnons in that they act as spin waves that propel free electrons across a temperature gradient. Paramagnons, however, operate in short, approximately 30 femtosecond bursts and their power—represented by the equation md = 2Cm3ne11+ em/m (where mdis the magnon drag thermopower, Cm is specific magnon heat, n is the number of free electrons, τem is the magnon momentum relaxation time-limited by magnon-electron interactions, and τm is total momentum relaxation time for magnons)—exceeds that of electrons alone. Paramagnon drag thermopower thus offers new opportunities for efficient design because it unlocks magnetic potential in semiconductors, which are typically paramagnetic at or above room temperature. Plus, it allows for the benefits of thermoelectric generators—reliability, functionality in microgravity, and sustainability—with better efficiencies than those of the conventional variety.
Improvements in efficiency are futile if the system lacks efficacy, but our system offers great promise. An antiferromagnetic substance becomes paramagnetic when it exceeds its Néel temperature. The excess heat of the ISS, which well exceeds the Néel temperature of the semiconductor MnTe, makes it ideally suited for paramagnon drag thermopower. In our system, we propose that a channel of high-temperature anhydrous ammonia circulates from the Interface Heat Exchangers and heats a thermoelectric generator with a 3% Li-doped MnTe (the concentration optimizes ZT, the thermoelectric figure of merit, among tested values) as the p-type. In order to create a sufficient difference in temperature, the unit would be placed between the flue of ammonia and a copper heat sink. The voltage derived from the temperature gradient between the two would then push electrons through a circuit that powers two UV lights — one to strike the titanium tubes, and one to power the cyanobacteria.
Infinity Synthesis chose “Purify the Air” due to our passion for terrestrial and atmospheric environments and our desire to solve tangible problems. By designing a complex mechanical system, the challenge allowed us to synthesize our unique strengths and interests for data science, engineering, coding, biology, and physics. Orienting the design for use on the ISS was particularly motivating because of our fascination with space travel, as well as the notion that equipment and inventions designed for space have often inspired life-improving technology suited for Earth.
Our first meeting was the brainstorming session in which we discussed various inspirations, deciding that we wanted to focus on reusing the components of CO2. As we researched carbon scrubbing techniques, we stumbled upon a method known as “ethylene scrubbing,” which had been used in enclosed plant ecosystems but not in entire spacecraft. While this process eliminates bacteria, viruses, fungi, mold, and ethylene, it produces additional CO2. We therefore resumed our search for a way to reuse CO2. Knowing that spacecraft would not have the space needed for enough plants to absorb all the CO2 produced by humans, we searched for photosynthetic bacteria and learned about cyanobacteria. We knew that any chemical reactions done to reuse waste products would require energy. This is when we thought to use the heat produced by ISS machinery to power our chemical reactions. We investigated methods of harnessing room heat into usable energy and discovered research done with paramagnons.
During our second meeting, we settled on our final plan: combining ethylene scrubbing, cyanobacterial photosynthesis, and paramagnons. We each then selected topics to specialize in, dividing the work between those interested in conducting research and those with backgrounds in coding and circuitry. After a brief check-in, we recentered our values and honed in on the specific components that needed work, whilst beginning preparations for the video. Sunday morning we each shared our progress, from the codes to the animation. We continued to work individually for the remainder of the day and brought all our elements together in the evening.
Working in a team of two members from the United States, two members from Egypt, a member from the UAE, and a member from England was a rewarding experience thanks to the variety of perspectives and backgrounds. However, it was not without its challenges. Scheduling meetings was difficult due to the breadth of time zones covered. Furthermore, English was not the first language of all members. However, overcoming these minor challenges allowed for a greater solution than what would be achieved by a homogenous group, and all members are extremely grateful for the opportunity to connect with others abroad and share their love of science with passionate individuals.
Here's is a link to our movie: https://drive.google.com/file/d/1_CGnU-V2btJXhdBTwO8PhvsamD0tK0K7/view?usp=sharing. We hope you enjoy it! Thank you.
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