Where we’re going, we’ll need roads. But before long-term settlers arrive on Mars or the moon, one engineer is working under a NASA grant to make sure that the proper infrastructure is already in place.
For almost two years, the University of Southern California’s Dr. Behrok Khoshnevis has been building machines that can extrude lunar and Martian soil into hangars, roads, and landing pads. Last month, NASA released a simulation of what this might actually look like in space. But according to Khoshnevis, his team is only getting started.
"I’m hoping to continue this if there’s more funding," he says. "I like difficult challenges. The more difficult problems are, the more satisfaction I get by solving them."
Khoshnevis didn’t launch his career with interplanetary construction in mind. For nearly 14 years, the engineer has been advancing a method of construction called "contour crafting," a way to quickly 3-D print buildings using robots. But moving contour crafting into space presented Khoshnevis with an entirely new set of constraints. Where would he find concrete on Mars? And what would happen if one of the machines broke down millions of miles away from engineers on Earth?
One of Khoshnevis’s breakthroughs came by way of sulfur concrete. There’s about four times as much sulfur in Martian soil as there is on Earth, and Khoshnevis discovered that it could help bind jagged bits of space rock together. But even once he began using sulfur concrete, extruding the material still proved difficult. Compared to Earth beach sand, Martian and lunar sand is pretty abrasive.
"Go to Home Depot, buy a one-foot section of metallic pipe, go to the beach, fill it with sand, hold it horizontally, and use your thumb and try to push it out. It’ll get caught," Khoshnevis explains. "Beach sand [particles] have been rubbed against each other by the waves for billions of years, so it’s not as sharp as particles of lunar material. For billions of years these dust particles have not moved; there is no wind. So it’s like 10 times harder to move them than sand on Earth."
But building for space on Earth does have its advantages. Because there’s only about one-sixth of the gravitational pull on the moon as there is on Earth, Khoshnevis says that anything built here is almost guaranteed to hold up in the less straining lunar atmosphere. Still, he doesn’t expect that he’ll see his robots launched into space for quite a while.
"I am not necessarily banking on this to happen in my lifetime," he says. "I’m just glad that I’m doing my share. And I’m hoping that some day somebody will use them."