Making Martian rocket biofuel on Mars

Four football-field-sized photobioreactors, covered in cyanobacteria and able to produce rocket fuel on Mars could be used. Credit: BOKO mobile study
Georgia Institute of Technology researchers have created a concept to make Martian rocket fuel on Mars that could be used for future astronauts.

Three resources are required for bioproduction: sunlight, carbon dioxide, and frozen water. It would also involve transporting two microbes from Mars. The first would be cyanobacteria, or algae. It would use CO 2 from Mars' atmosphere to make sugars. E. coli engineered from Earth would transform these sugars into a Mars-specific propellant to rockets and other propulsion devices. E. coli can create the Martian propellant 2,3-butanediol. It is already in existence and is used on Earth to make polymers for rubber production.

This process is described in Nature Communications' paper.

Rocket engines that leave Mars will be powered by liquid oxygen (LOX) and methane. They are not found on Mars, so they must be transported from Earth in order to power a return craft to Martian orbit. Transporting the required 30 tons of methane or LOX from Earth to Mars is costly. It is estimated that it will cost $8 billion. NASA proposes using chemical catalysis to convert Martian CO2 into LOX. However, this still requires methane being transported from Earth.

Georgia Tech researchers have proposed a biotechnology that is in situ resource utilized (bio-ISRU), which can make both propellant and LOX out of CO 2. According to the researchers, Mars could be used to produce the propellant using Martian resources. This could reduce mission costs. The bio-ISRU process produces 44 tons of clean oxygen, which could be used for other purposes such as human colonization.

"Carbon dioxide is the only resource on Mars. "Carbon dioxide is one of the few resources on Mars. Knowing biology is particularly good at converting CO2 into useful products makes it a good match for creating rocket fuel," Nick Kruyer, first author of this study and recent Ph.D. winner from Georgia Tech's School of Chemical and Biomolecular Engineering.

The paper describes the process. It begins with transporting plastic materials to Mars. These would then be assembled into photobioreactors that are four times the size of football fields. Photosynthesis, which requires carbon dioxide, would allow cyanobacteria to grow in these reactors. Separate reactors would use enzymes to break down the cyanobacteria to sugars. These sugars could then be fed to E. coli to make rocket propellant. Advanced separation techniques would allow the propellant to be separated from E. coli fermentation broth.

Research by the team found that bio-ISRU uses 32% less power, but weighs three times as much, than the chemically enabled strategy for shipping methane from Earth to make oxygen via chemical catalysis.

The gravity on Mars is only one-third that of Earth's, so the researchers were able be imaginative in their search for potential fuels.

Pamela Peralta Yahya, a corresponding writer of the study, is an associate professor at the School of Chemistry & Biochemistry. She engineers microbes that produce chemicals. "We began to look at ways to use the planet's lower gravity, and its lack of oxygen to make solutions that aren’t relevant for Earth launches.

Artist's concept of Mars astronauts and their human habitats. Credit: Courtesy: NASA

Although 2,3-butanediol is a well-known propellant, we had never considered using it. Wenting Sun, an associate professor at the Daniel Guggenheim School of Aerospace Engineering who works on fuels, said that after analysis and preliminary experimental studies, it was a good candidate.

Georgia Tech has a team that spans campus. To develop the process and idea for creating a viable Martian fuel, chemists, chemical, mechanical and aerospace engineers worked together. Kruyer, PeraltaYahya and Sun were also part of the group. Caroline Genzale was a combustion expert, associate professor at the George W. Woodruff School of Mechanical Engineering and Matthew Realff was professor and David Wang Sr. Fellow in ChBE. Expert in process synthesis, design.

Now, the team is focusing on the biological and material optimization to make the bio-ISRU process lighter and lighter than the chemical process. The photobioreactor's size will be significantly reduced if cyanobacteria can grow faster on Mars. This will also reduce the amount of equipment that must be transported from Earth.

Realff, an expert in algal-based process analysis, said that experiments are needed to prove that cyanobacteria can grow on Mars. "We must consider the differences in the solar spectrum of Mars due to its distance from the Sun as well as the lack of atmospheric filtering. Cyanobacteria could be damaged by high ultraviolet levels.

Georgia Tech emphasizes the importance of acknowledging differences between Mars and Earth in developing efficient technologies to produce ISRU fuel, food, or chemicals on Mars. In an effort to help achieve the goal of human presence beyond Earth's borders, they are addressing biological and material challenges in their study.

Kruyer said, "The Peralta Yahya lab excels in finding new and exciting uses for synthetic biology and/or biotechnology, and tackling exciting issues in sustainability." "Biotechnology can be applied to Mars in a way that makes the most of scarce resources and requires minimal starting materials.

Learn more Martian carbon dioxide fuel reactor

More information: Nicholas S. Kruyer et al, Designing the bioproduction of Martian rocket propellant via a biotechnology-enabled in situ resource utilization strategy, Nature Communications (2021). Journal information: Nature Communications Nicholas S. Kruyer et al, Designing the bioproduction of Martian rocket propellant via a biotechnology-enabled in situ resource utilization strategy,(2021). DOI: 10.1038/s41467-021-26393-7