But the weight of the needed solar equipment would go up to more than 20 tons for a Mars outpost closer to the poles. Mars is tilted on its axis by about 25 degrees, slightly more than Earth is, and its orbit is less circular, so less sunlight would reach those PV cells during parts of the year. That means nuclear power becomes more viable at the poles. The power generation equipment needed to produce that much nuclear energy would add up to about 9.5 tons of carry-along mass to produce the same 40 kilowatts of energy. That lift is doable for massive next-generation rockets like NASA’s Space Launch System and SpaceX’s Starship and Super Heavy, which can each carry payloads of at least tens of tons into deep space. (The poles also harbor ice that could provide a water source for the astronauts.)
These same kinds of trade-offs have already arisen with energy technologies used by Mars rovers. Engineers need to find the right balance between transportation weight, storage needs, and an energy system that can handle variations in the availability of sunlight. Significant sunlight reaches the surface only during the Martian day and only when dust and cloud particles don’t get in the way, says Guillem Anglada-Escudé, an astronomer at the Institute of Space Sciences in Barcelona who was not involved in the study. He’s also a member of the Sustainable Offworld Network, a collaboration of researchers, engineers, and architects studying how future colonies on Mars and other worlds might work.
Anglada-Escudé agrees with Abel and Berliner’s findings. He also believes that, if possible, one shouldn’t look at solar and nuclear energy as either/or. “Our conclusion is, you want to have both solar and nuclear,” he says. “It’s a matter of resilience. Things can fail in many different ways. The best option is to have redundancy.”
It’s also important to study solar radiance and how dust and ice affect how much light reaches the planet’s surface, and where that light can best be collected, says Daniel Vázquez Pombo, an energy engineer at the Technical University of Denmark who wrote a paper last year about a possible hybrid power system for a permanent Mars colony that includes PV arrays and storage. Maintenance for energy systems can be risky for those conducting repairs, another argument for having options.
“Do you really want to rely on a single technology? What happens if you have a systematic error or a design flaw,” Pombo says. “Diversifying is a smart idea. You don’t put all your eggs in one basket.”
The calculus may also change when it’s not just a handful of astronauts visiting for a couple months or a year but rather a permanent colony with long-term visitors, Anglada-Escudé argues. “Solar panels are a relatively simple technology, and solar gets more attractive for the very long term,” he says. “You may need more mirrors, but it will work. On Mars, finding plutonium to the quality you need for a reactor is not trivial. Solar is there, it’s safe, and we know how to do it.”
In the end, life in Mars’s rugged conditions will be tougher than anywhere on Earth. And the science and technology issues are only half the story. Settlers will have to navigate complex financial and societal issues as well, Abel says. At least when they get there, though, they’ll know how to keep the lights on.