Photosynthesis, a process that enables plants and other organisms to convert sunlight, water, and carbon dioxide into oxygen and energy in the form of sugar, is an integral part of Earth’s functioning. It is a process that is 2.3 billion years old and is responsible for the existence of life on our planet. However, as we look beyond our own planet for places to explore and settle on, it becomes apparent how rare and valuable the process is.
The Need for Artificial Photosynthesis in Space Travel
The human need for oxygen makes space travel tricky. Fuel constraints limit the amount of oxygen that can be carried, particularly on long-haul journeys to the Moon and Mars. A one-way trip to Mars usually takes on the order of two years, meaning that supplies of resources cannot be easily sent from Earth. While there are already ways to produce oxygen by recycling carbon dioxide on the International Space Station, these technologies are unreliable, inefficient, heavy, and difficult to maintain. The search for alternative systems that can be employed on the Moon and on trips to Mars is ongoing.
The Potential of Artificial Photosynthesis Devices
One possibility for sustainable space travel is to harvest solar energy and directly use it for oxygen production and carbon dioxide recycling in one device. This is similar to the photosynthesis process that occurs in nature, where the only other input is water. This would circumvent complex set-ups where the two processes of light harvesting and chemical production are separated, such as on the ISS, and would be more efficient.
Theoretical frameworks have been produced to analyze and predict the performance of such integrated “artificial photosynthesis” devices for applications on the Moon and Mars. Instead of chlorophyll, which is responsible for light absorption in plants and algae, these devices use semiconductor materials that can be coated directly with simple metallic catalysts supporting the desired chemical reaction.
The analysis shows that these devices would indeed be viable to complement existing life support technologies, such as the oxygen generator assembly employed on the ISS. This is particularly the case when combined with devices which concentrate solar energy in order to power the reactions.
The Benefits of Artificial Photosynthesis Devices
Artificial photosynthesis devices could operate at room temperature and at the pressures found on Mars and the Moon. That means they could be used directly in habitats and using water as the main resource. This is particularly interesting given the stipulated presence of ice water in the lunar Shackleton crater, which is an anticipated landing site in future lunar missions.
The efficient and reliable production of oxygen and other chemicals, as well as the recycling of carbon dioxide onboard spacecraft and in habitats, is a tremendous challenge that we need to master for long-term space missions. Existing electrolysis systems, operating at high temperatures, require a significant amount of energy input. And devices for converting carbon dioxide to oxygen on Mars are still in their infancy, whether they are based on photosynthesis or not.
The returns from using artificial photosynthesis devices in space would be huge. For example, we could create artificial atmospheres in space and produce chemicals required on long-term missions, such as fertilizers, polymers, or pharmaceuticals. Additionally, the insights gained from designing and fabricating these devices could help us meet the green energy challenge on Earth.
Copying the essential bits from nature’s photosynthesis could give us some advantages, helping us realize sustainable space travel in the not-too-distant future. The exploration of space and our future energy economy have a very similar long-term goal: sustainability. Artificial photosynthesis devices may well become a key part of realizing it.