NASA Aims to Deploy Terahertz Laser to Help Resolve Lunar Water Mystery

Locating water and other resources on Earth’s moon and beyond in our solar system is a NASA priority crucial to exploring our solar system and beyond. Previous experiments inferred and then confirmed the existence of small amounts of water across the moon; earlier this summer, the Chinese Academy of Sciences reported that China’s lunar lander delivered the first real-time, on-site definitive confirmation of water signal in the basalt’s rocks and soil via onboard spectral analysis in 2020.

However, most space-capable technologies cannot distinguish between water and water-like compounds.

NASA Goddard Space Flight Center engineer Berhanu Bulcha is developing a type of instrument called a heterodyne spectrometer that offers the power and resolution to offer a more definitive solution to this endeavor. Heterodyne spectrometers enable astronomers to examine the behavior and characteristics of specific gas molecules in planetary atmospheres. With the right type of laser, these instruments can dial in to very specific frequencies in the terahertz band, where hydrogen-containing compounds like water emit photonic frequencies ranging between 2 trillion to 10 trillion cycles per second.

A quantum cascade laser (QCL) smaller than a quarter, and with low power consumpion, fits in a 1U CubeSat, about the size of a teapot, along with the spectrometer hardware, processor, and power supply. The technology is poised to aid in the detection of water on the moon and also to distinguish between water and water-like compounds. Courtesy of NASA/Michael Giunto.

Such a laser was prototyped in collaboration with Calif.-based Longwave Photonics through NASA’s Small Business Innovation Research (SBIR) program.

“This laser allows us to open a new window to study this frequency spectrum,” he said. “Other missions found hydration on the moon, but that could indicate hydroxyl or water. If it’s water, where did it come from? Is it indigenous to the formation of the moon, or did it arrive later by comet impacts? How much water is there? We need to answer these questions because water is critical for survival and can be used to make fuel for further exploration.”

Because QCL sources generally emit wide-angle beams that dissipating quickly over short distances, the team leveraged technology supported by Goddard’s Internal Research and Development funding to integrate the laser on a waveguide with a thin optical antenna to tighten the beam. The integrated laser and waveguide unit reduces this dissipation by 50% in a package smaller than a quarter.

The laser’s small size and low power consumption allow it to fit in a 1U CubeSat, about the size of a teapot, along with the spectrometer hardware, processor, and power supply.

Bulcha hopes to continue the work to make a flight-ready laser for NASA’s Artemis program.