Researchers at the Georgia Institute of Technology have developed a concept
that would make Martian rocket fuel, on Mars, that could be used to launch
future astronauts back to Earth.
The bioproduction process would use three resources native to the red
planet: carbon dioxide, sunlight, and frozen water. It would also include
transporting two microbes to Mars. The first would be cyanobacteria (algae),
which would take CO2 from the Martian atmosphere and use sunlight to create
sugars. An engineered E. coli, which would be shipped from Earth, would
convert those sugars into a Mars-specific propellant for rockets and other
propulsion devices. The Martian propellant, which is called 2,3-butanediol,
is currently in existence, can be created by E. coli, and, on Earth, is used
to make polymers for production of rubber.
The process is outlined in a paper, “Designing the bioproduction of Martian
rocket propellant via a biotechnology-enabled in situ resource utilization
strategy,” published in the journal Nature Communications.
Rocket engines departing Mars are currently planned to be fueled by methane
and liquid oxygen (LOX). Neither exist on the red planet, which means they
would need to be transported from Earth to power a return spacecraft into
Martian orbit. That transportation is expensive: ferrying the needed 30 tons
of methane and LOX is estimated to cost around $8 billion. To reduce this
cost, NASA has proposed using chemical catalysis to convert Martian carbon
dioxide into LOX, though this still requires methane to be transported from
Earth.
As an alternative, Georgia Tech researchers propose a biotechnology based in
situ resource utilization (bio-ISRU) strategy that can produce both the
propellant and LOX from CO2. The researchers say making the propellant on
Mars using Martian resources could help reduce mission cost. Additionally,
the bio-ISRU process generates 44 tons of excess clean oxygen that could be
set aside to use for other purposes, such as supporting human colonization.
“Carbon dioxide is one of the only resources available on Mars. Knowing that
biology is especially good at converting CO2 into useful products makes it a
good fit for creating rocket fuel,” said Nick Kruyer, first author of the
study and a recent Ph.D. recipient from Georgia Tech’s School of Chemical
and Biomolecular Engineering (ChBE).
The paper outlines the process, which begins by ferrying plastic materials
to Mars that would be assembled into photobioreactors occupying the size of
four football fields. Cyanobacteria would grow in the reactors via
photosynthesis (which requires carbon dioxide). Enzymes in a separate
reactor would break down the cyanobacteria into sugars, which could be fed
to the E. coli to produce the rocket propellant. The propellant would be
separated from the E. coli fermentation broth using advanced separation
methods.
The team’s research finds that the bio-ISRU strategy uses 32% less power
(but weighs three times more) than the proposed chemically enabled strategy
of shipping methane from Earth and producing oxygen via chemical catalysis.
Because the gravity on Mars is only a one-third of what is felt on Earth,
the researchers were able to be creative as they thought of potential fuels.
“You need a lot less energy for lift-off on Mars, which gave us the
flexibility to consider different chemicals that aren’t designed for rocket
launch on Earth,” said Pamela Peralta-Yahya, a corresponding author of the
study and an associate professor in the School of Chemistry &
Biochemistry and ChBE who engineers microbes for the production of
chemicals. “We started to consider ways to take advantage of the planet’s
lower gravity and lack of oxygen to create solutions that aren’t relevant
for Earth launches.”
“2,3-butanediol has been around for a long time, but we never thought about
using it as a propellant. After analysis and preliminary experimental study,
we realized that it is actually a good candidate,” said Wenting Sun,
associate professor in the Daniel Guggenheim School of Aerospace
Engineering, who works on fuels.
The Georgia Tech team spans campus. Chemists, chemical, mechanical, and
aerospace engineers came together to develop the idea and process to create
a viable Martian fuel. In addition to Kruyer, Peralta-Yahya, and Sun, the
group included Caroline Genzale, a combustion expert and associate professor
in the George W. Woodruff School of Mechanical Engineering, and Matthew
Realff, professor and David Wang Sr. Fellow in ChBE, who is an expert in
process synthesis and design.
The team is now looking to perform the biological and materials optimization
identified to reduce the weight of the bio-ISRU process and make it lighter
than the proposed chemical process. For example, improving the speed at
which cyanobacteria grows on Mars will reduce the size of the
photobioreactor, significantly lowering the payload required to transport
the equipment from Earth.
“We also need to perform experiments to demonstrate that cyanobacteria can
be grown in Martian conditions,” said Realff, who works on algae-based
process analysis. “We need to consider the difference in the solar spectrum
on Mars both due to the distance from the Sun and lack of atmospheric
filtering of the sunlight. High ultraviolet levels could damage the
cyanobacteria.”
The Georgia Tech team emphasizes that acknowledging the differences between
the two planets is pivotal to developing efficient technologies for the ISRU
production of fuel, food, and chemicals on Mars. It’s why they’re addressing
the biological and materials challenges in the study in an effort to
contribute to goal of future human presence beyond Earth.
“The Peralta-Yahya lab excels at finding new and exciting applications for
synthetic biology and biotechnology, tackling exciting problems in
sustainability,” added Kruyer. “Application of biotechnology on Mars is a
perfect way to make use of limited available resources with minimal starting
materials."
The research was supported by a NASA Innovative Advanced Concepts (NIAC)
Award.
Reference:
Kruyer, et al. “Designing the bioproduction of Martian rocket propellant via
a biotechnology-enabled in situ resource utilization strategy” Nature
Communications.
DOI: 10.1038/s41467-021-26393-7.
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Space & Astrophysics