By Peter Rejcek, science writer
A crewed mission to Mars will require transporting equipment for creating electricity to power life support systems. The choice for the type of device used will require a tradeoff between mass and energy efficiency. Researchers here show that a photovoltaic system using compressed hydrogen energy storage can compete with nuclear energy across about 50% of the Red Planet.
No other planet in our solar system has sparked the human imagination more than Mars. While modern science has debunked the Red Planet as a likely source of an alien invasion, today’s technology is bringing us closer to a crewed mission. A research team out of the University of California, Berkeley published a paper in the journal Frontiers in Astronomy and Space Sciences that argues a human expedition on the surface could be powered by harvesting solar energy.
The concept is not new. The main source of power for some NASA Mars rovers comes from a multipanel solar array. But, in the last decade or so, most people had assumed that nuclear power would be a better option than solar energy for human missions, according to co-lead author Aaron Berliner, a bioengineering graduate student in the Arkin Laboratory at UC Berkeley.
What makes the current study unique is how the researchers compared various ways to generate power. The calculations took into account the amount of equipment mass that would need to be transported from Earth to the Martian surface for a six-person mission. Specifically, they quantified the requirements of a nuclear-powered system against different photovoltaic and even photoelectrochemical devices.
Weighing the options
While the energy output of a miniaturized nuclear fission device is location-agnostic, the productivity of solar-powered solutions rely on solar intensity, surface temperature, and other factors that would determine where a non-nuclear outpost would be optimally located. This required modeling and accounting for a number of factors, such as how gasses and particles in the atmosphere might absorb and scatter light, which would affect the amount of solar radiation at the planet’s surface.
The winner: a photovoltaic array that uses compressed hydrogen for energy storage. At the equator, what the team calls the “carry-along mass” of such a system is about 8.3 tons versus about 9.5 tons for nuclear power. The solar-based system becomes less tenable closer to the equator at more than 22 tons, but beats out fission energy across about 50% of the Martian surface.
“I think it’s nice that the result was split pretty close down the middle,” Berliner said. “Nearer the equator, solar wins out; nearer the poles, nuclear wins.”
Such a system can employ electricity to split water molecules to produce hydrogen, which can be stored in pressurized vessels and then re-electrified in fuel cells for power. Other applications for hydrogen include combining it with nitrogen to produce ammonia for fertilizers – a common industrial-scale process.
Other technologies, like water electrolysis to produce hydrogen and hydrogen fuel cells, are less common on Earth, largely due to costs, but potentially game-changing for human occupation of Mars.
“Compressed hydrogen energy storage falls into this category as well,” noted co-lead author Anthony Abel, a chemical and biomolecular engineering PhD student at UC Berkeley. “For grid-scale energy storage, it’s not used commonly, although that is projected to change in the next decade.”
Leaning on nature
Both Abel and Berliner are members of the Center for the Utilization of Biological Engineering in Space (CUBES), a project developing biotechnologies to support space exploration. For example, CUBES is focused on engineering microbes to make plastics from carbon dioxide (CO2) and hydrogen or pharmaceuticals from CO2 and light.
The new paper establishes a baseline for the electricity and hydrogen budget that would enable these sorts of applications.
“Now that we have an idea of how much power is available, we can start connecting that availability to the biotechnologies in CUBES,” Berliner said. “The hope is ultimately to build out a full model of the system, with all of the components included, which we envision as helping to plan a mission to Mars, evaluate tradeoffs, identify risks, and come up with mitigation strategies either beforehand or during the mission.”
Beyond science and technology, Abel said it is important to consider the human element of space exploration as well. “To quote Chanda Prescod-Weinstein, ‘Our problems travel into space with us.’ So, when we think about going to Mars, we also have to think about how to address problems like racism, sexism, and colonialism, to make sure we go to Mars in the ‘right’ way.”
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