Tunga and his team envisioned a system that would use solar panels and batteries to provide power to reduce the temperature inside the lava tube to the cryogenic temperatures needed to build a lunar ark. This is a crucial difference between Tunga’s design and Hagedorn’s thought experiment: While Tunga’s group aims to actively cool the ark, Hagedorn and the Smithsonian team envision a repository that would use natural features of the moon to keep the samples at cryogenic temperatures.
“The idea behind our proposal is to make it as passive as possible,” Parenti said, noting that the idea of building something to store supplies on the lunar surface has long been explored, but all of those ideas would require crew maintenance.
To passively maintain the frozen state, they propose building a repository on the moon’s south pole, where a coincidence of celestial geometry creates areas of permanent shadow within some craters, where temperatures can drop to minus 196 degrees Celsius. These conditions would allow the samples to be stored without the need for a crew, and could be maintained by the rover and robots alone.
In theory, the permanent polar shadows are ideal for such projects, but “we fundamentally don’t know what those places are like,” Thanga counters. Just last month, NASA canceled a mission that would have been the first spacecraft to explore the poles, citing technical challenges. “That’s ironic,” Thanga says. “It’s close to Earth, but it’s probably one of the most hostile places in the entire solar system.”
But Fitzpatrick believes NASA’s current lunar exploration roadmap, including a mission scheduled for later this year to land on a ridge overlooking the polar shadow, provides ample opportunity to explore and understand the dark polar regions. But as NASA begins to explore these regions, Tanga noted, we may learn more about how difficult it is to live and function in that level of cold.
“Just getting it to work at cryogenic temperatures is no mean feat,” Thanga said. “Machines behave strangely. In an environment like space, they can freeze up, they can lock up, they can do anything. Even at moderately cold temperatures in a vacuum, you get a phenomenon called cold welding, where when two pieces of metal touch, they melt.”
Tanga argues that building the ark inside a lava tube would be a smarter approach, because his planetary science colleagues expect it to be quite similar to ours on Earth, but much colder, so researchers and engineers would know what to expect and how to plan.
But as with Hagedorn’s vision, the price and timeline have yet to be determined, though Thanga expects that once the design is finalized (which could still be years away), it could be built and assembled faster and cheaper than the International Space Station.
