US researchers have developed a technique that would help astronomers develop Martian rocket fuel using microbes on the Red Planet.
While the bioproduction process would use three resources native to the Red Planet -- carbon dioxide, sunlight, and frozen water -- two microbes will be transported from Earth to Mars.
The first is cyanobacteria (algae), which would take CO2 from the Martian atmosphere and use sunlight to create sugars, and second an engineered E. coli which will convert those sugars into a Mars-specific propellant for rockets and other propulsion devices, said a team led by researchers at the Georgia Institute of Technology.
The Martian propellant, which is called 2,3-butanediol, is currently in existence and can be created by E. coli, they explained in the paper, published in the journal Nature Communications. On Earth, it is used to make polymers for production of rubber.
"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, from Georgia Tech's School of Chemical and Biomolecular Engineering (ChBE).
Rocket engines departing Mars are currently planned to be fuelled by methane and liquid oxygen (LOX). As neither exists on Mars, they need to be transported from Earth to power a return spacecraft into Martian orbit.
That transportation is expensive: ferrying the needed 30 tonnes of methane and LOX is estimated to cost around $8 billion. To reduce this cost, NASA proposed using chemical catalysis to convert Martian CO2 into LOX, but this still requires methane to be transported from Earth.
As an alternative, Georgia Tech researchers proposed a biotechnology based in situ resource utilisation (bio-ISRU) strategy that can produce both the propellant and LOX from CO2.
The process 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 researchers said that making the propellant on Mars using Martian resources could help reduce mission cost. In addition, the bio-ISRU process will generate 44 tonnes of excess clean oxygen that could be set aside to use for other purposes, such as supporting human colonisation.