To The Moon, to Learn About Disruption from the Sun

By Patrick L. Kennedy

In 2023, a device developed at ENG will ride a rocket into space and land on the moon, where it will snap the first-ever X-ray images of solar wind slamming into the Earth’s magnetosphere. The experiment just might help prevent a civilization-crippling communications blackout someday.

The Lunar Environment heliospheric X-ray Imager (LEXI) will be one of 10 science investigations and technology demonstrations attached to a NASA-sponsored mission to Mare Crisium, the “Sea of Crises,” on the lunar surface.

Associate Professor Brian Walsh (ME, ECE) is the principal investigator for LEXI, coordinating the project and collaborating with NASA’s Goddard Space Flight Center as well as Johns Hopkins University, and the University of Alaska, Fairbanks. Walsh’s students designed and assembled the X-ray telescope, with parts machined in the BU Scientific Instrument Facility.

“It’s almost like a weather buoy,” says Walsh of Lexi. “It will help us understand the weather for our space traffic.”

That traffic includes the 3,000-plus operational satellites orbiting the Earth. They’re the engines of our modern society, enabling the technologies relied upon by truckers, banks, farmers, airlines, militaries and utilities as well as television and the internet.

And the sun could fry them.

The star at the center of our solar system gives us the energy we need to sustain life, but it also throws some plasma particles at our planet that would be harmful if we didn’t have a magnetic field, which acts as a shield. Once in a while, a particularly large solar flare can give off millions of atomic bombs’ worth of energy, which can break through that shield (also known as the magnetosphere). In the pre-industrial past, such events were startling curiosities—causing the Northern Lights to flash as far south as Cuba, for example. Today, a flare of that size would be significantly more disruptive.

Fortunately, humans can take measures to minimize the damage. For example, we can shut off satellite systems temporarily, to avoid permanent shutdowns. But we need to learn a lot more about how the sun’s flares interact with the magnetosphere. That’s where space scientists and engineers such as Walsh come in.

“It’s not really clear how the energy breaks through the shield,” says Walsh. “Is it lots of small holes, or one big hole that gets torn in the shield? Does it happen in bursts, or does it slowly erode inward? These are the types of questions we’re going to answer with LEXI. It will provide great insights to allow us to better model and predict the response of the space environment to a solar storm.”

Students Jeff McShane and Rousseau Nutter testing the LEXI unit.

The BU-built telescope is novel in a couple of ways. It’s a wide-field-of-view X-ray detector, using a curved plate that picks up X-ray light from multiple angles. Moreover, the state-of-the-art sensor is specially coated to be super-sensitive with the ability to count individual photon strikes. Even in low light, it will pick up the soft X-rays emitted when the sun’s heavy ions hit our upper atmosphere.

As for the journey to the moon, LEXI and the nine other scientific projects will be bolted to a lunar lander built by Firefly Aerospace. A rocket will carry the Firefly lander into the sky. The lander will then detach from the rocket, perform a number of maneuvers, and land on Mare Crisium at sunrise.

“Literally, once the dust settles, we open the door,” says Walsh of the scope’s protective dust door, another innovation of his team. “Then we’ll point at the Earth’s magnetic field, steering it [remotely] from our operations center. It’ll be a big room with a lot of stressed-out people working in eight-hour shifts to keep it manned for 24 hours a day for eight days.”

By the time the sun sets on the Sea of Crises, LEXI will have collected indispensable data that will be posted to a public NASA website for the use of physicists and astronomers around the globe. “Ultimately,” Walsh says, “it will give us the measurements we need to make better models of space weather, the same way we can predict the path of hurricanes, with modeling.”

To see Walsh’s team in action, check out this video on The Brink.