Among the many challenges with a Mars voyage, one of the most pressing is: How can you get enough fuel for the spacecraft to fly back to Earth?
Houlin Xin, UCI assistant professor in physics & astronomy, may have found a solution.
He and his team have discovered a more efficient way of creating methane-based rocket fuel theoretically on the surface of Mars, which can make the return trip all the more feasible.
The novel discovery comes in the form of a single-atom zinc catalyst that will synthesize the current two-step process into a single-step reaction using a more compact and portable device.
“The zinc is fundamentally a great catalyst,” Xin says. “It has time, selectivity and portability – a big plus for space travel.”
The process of creating methane-based fuel has been theorized before, initially demonstrated by a team led by aerospace engineer Robert Zubrin in 1993. Using solar electricity from infrastructure on Mars it electrolyzes Martian water, generating hydrogen and oxygen then, reacting with carbon dioxide from the Martian atmosphere, produces methane and water.
This so-called Sabatier process is used on the International Space Station to generate breathable oxygen from the electrolysis of hydrogen and oxygen. One of the main issues with this method is that it is a two-stage procedure requiring large faculties to operate efficiently.
The approach developed by Xin and his team will use anatomically dispersed zinc to act as a “synthetic enzyme,” catalyzing carbon dioxide and initializing the process. This will require much less space and can efficiently produce methane using materials and under conditions similar to those found on the surface of Mars.
“The process we developed bypasses the water-to-hydrogen process, and instead efficiently converts CO2 into methane with high selectivity,” Xin says.
Currently, rockets created by Lockheed and Boeing use RP-1 kerosene and liquid hydrogen as fuel. While it is cheap and effective, this fuel source has its drawbacks. Engines burning RP-1 kerosene eventually get fouled through the deposition of significant quantities of carbon residue and require cleaning after each launch, a step that might be challenging on Mars.
SpaceX and Elon Musk have developed and are currently testing a methane fuel-based engine, known as the SpaceX Raptor. Raptor will power SpaceX’s next generation of spacecraft named Starship and Super Heavy. At this time, neither have made it into orbit, and only one has consistently taken flight.
Despite the breakthrough, the process developed by Xin is far from implementation. Currently they only have a “proof of concept,” meaning that while it has been tested and proven in a lab, it has yet to tested in real world – or planet – conditions.
“Lots of engineering and research is needed before this can be fully implemented,” he says. “But the results are very promising.”