Fiber-optic cables could be used to detect moonquakes, offering a simpler way to gather seismic data to support future missions.
A scientist at Los Alamos National Laboratory in New Mexico has cowritten two studies examining how fiber-optic cables on the lunar surface could be used to detect seismic activity.
Seismometers are good at collecting data but are typically deployed in a fixed location, according to the scientist, Carly Donahue. To monitor a wider area, she and others were interested in the possibility of using a rover to deliver fiber-optic cables over many kilometres on the surface of the moon without burying them. This technique is called distributed acoustic sensing (DAS).
“Fiber-optic cables are lightweight, robust, and inexpensive, so we wondered: Could they be used on the surface of the moon to detect seismic activity there?” Donahue stated.
With this in mind, the first paper “Earthquake detection in a simulated lunar regolith using distributed acoustic sensing,” looked at whether burying the cables would affect signal sensitivity.
Regolith is a layer of loose material that covers much of the lunar surface.
Unlike on Earth, where fiber-optics for sensing must be buried because even a gentle breeze can agitate the cables and create background noise, the lab tests demonstrated that burial depth did not significantly affect the clarity of the signal in the simulated regolith.
The second paper, “Controlled Source DAS Coupling Tests: Implications for Unburied Deployment on the Moon and Earth,” examined which physical attributes might make fiber-optic cables deployed on the moon’s surface work reliably. The researchers report that stiffer, thicker cables and continuous ground contact improved signal strength.
Seismic data could help scientists to form a clearer picture of our largest natural satellite, such as the composition of its core. It could also contribute to a better understanding of hazards such as particles blasted from the lunar surface when a rocket takes off or lands.
These could move at speeds of about 2 kilometers per second and cause damage to equipment or man-made structures on the moon, but Donahue says there is little current knowledge of how far those particles travel. Fiber-optic cables deployed far from a landing site could provide some data on how widely debris spreads, she claimed.
This isn’t the first such proposal to put fiber on the moon. A couple of years ago, scientists at the Woods Hole Oceanographic Institute published a paper saying that a fiber-optic network on the lunar surface could probe the moon’s interior by detecting seismic waves. They said that this would likely require “tens of kilometers” of cable at a minimum.
Meanwhile, the distributed acoustic sensing (DAS) technique could also prove useful on Earth as well. Last week, UK telecoms firm Openreach claimed that its fiber network infrastructure can be used to detect leaks in underground water supply pipes, using machine learning to detect the vibrations caused by a leak in the light beams carried by the cable. ®
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