IN THE 1970S, US government researchers imagined digging through rock with a nuclear-powered tunneling machine. They thought this machinery could change the world by traveling through the Earth’s upper mantle like a submarine moves through water, influencing national security and potentially allowing people to control earthquakes and volcanoes. More than a decade earlier, experiments by scientists at Los Alamos National Laboratory had led to the creation of a rock-melting drill. That attracted attention from some businesses and, according to the scientists’ paper, “serious consideration was given to use the device as a lunar drill for the Apollo flight series,” but the idea never made it past a prototype.
Now Petra, a three-year-old startup inspired by that vision, says it’s developing tech to cut through rock without grinding into it. The company first tested cutting through rock with a plasma torch in an industrial park in Oakland, California in 2018. A larger plasma torch later cut through slabs of stone at temperatures above 10,000 degrees Fahrenheit.
Petra later abandoned plasma for a mix of gas and heat above 1,800 degrees Fahrenheit that breaks rock into small pieces. Sensors attached to small rods touch the rock, but the excavation is carried out by the heat and gas. Using this tech, which was created in part by one of Tesla’s cofounders, Petra wants to make tunneling through bedrock cheap enough to encourage utilities to bury electricity and other lines underground.