How a telescope on the far side of the moon could help us see the cosmic dark ages

Millions of years ago, an asteroid crashed into the far side of the moon, the hemisphere always facing away from Earth. In the coming years, a robot might land in the crater it left behind and build a radio telescope fit for the future of astronomy.

That’s the premise behind an ambitious project called the Lunar Crater Radio Telescope, or LCRT, that aims to turn a moon crater into a telescope using self-assembling robots. The moon blocks out noisy radio interference from Earth, and its far side is littered with craters that could serve as a telescope dish. This makes it an ideal spot the to listen for faint radio waves coming from the so-called cosmic dark ages—a mysterious epoch sandwiched between the big bang and the birth of the very first stars.

Being able to hear those ancient radio waves will allow scientists to probe the very nature of reality. “We would know whether our physics is correct, or whether we need to build new physics,” says Saptarshi Bandyopadhyay, a robotics technologist at NASA’s Jet Propulsion Laboratory in California, and the lead researcher on the LCRT project.

This moon crater telescope is just one of several projects competing to do astronomy on the far side of the moon. The LCRT is still in development; it hasn’t been built yet, nor is a launch date set. But a much smaller, prototype telescope is slated launch later this year. And with the recent acceleration of NASA’s Artemis program promising a higher cadence of missions to the moon—both crewed, and robotic—there is new momentum behind the idea of putting a radio telescope on Earth’s companion.

“It opens a new window on the universe—and we don’t have many windows left,” says Michael Garrett, an astronomer and the director of the Jodrell Bank Centre for Astrophysics in England. “This is the big one.”

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The ghosts of the early universe

From exploding stars to planetary auroras, pretty much everything that produces energy in the cosmos emits radio waves—the same type of wave that your car radio converts into sound. Unlike visible light, these waves are invisible and inaudible to humans. Unfortunately, for astronomers wanting to hear all this, Earth acts like a thundering loud megaphone: Not only does its ionosphere—the electrified layer of the planet’s upper atmosphere—make quite the racket, but all our technology can’t stop beaming out artificial radio waves.

“It’s a horrendous amount of noise,” says Anže Slosar, a researcher at Brookhaven National Laboratory in New York. If you’re an astronomer hoping to perceive the far-flung cosmos, “it’s like looking upward from the bottom of a swimming pool.” And there isn’t much scientists can do from Earth. “The only way to escape it is to hide from it,” he says.

Thankfully, there’s a great hiding spot just 240,000 miles away. “For radio astronomy, the moon is one of the best places,” says Garrett. If you’re on the lunar far side, you’re facing away from Earth, and the moon acts as a giant geologic barrier to the planet’s cacophony. And if you take measurements at night, it also filters out the sun’s own radio interference.

Without all that noise, a lunar telescope could pick up a variety of signals that are harder for radio telescopes to pick up on Earth. “It’s also important for the search for extraterrestrial intelligence,” says Garrett. One of the biggest obstacles to identifying a radio signal coming from alien technology is trying to pick it out of Earth’s own radio commotion. This would be far easier to do on the tranquil lunar far side.

Any radio astronomy conducted on the moon would be welcome. But detecting a signal from “the cosmic dark ages is the long-term goal,” says Slosar. Around 380,000 years after the Big Bang, the universe was a soup of neutral hydrogen gas. That hydrogen would eventually clump together and ignite as the first stars, but back then, there was nothing but darkness.

But raw hydrogen emanates radio waves of a very specific wavelength. This distant signal would be extremely weak, but if scientists could tune into it, they could find out how ordinary matter interacted with enigmatic dark matter—an as-yet undetected ‘glue’ that binds the universe together—to shape the cosmos we live in today.

There’s no guarantee that a telescope on the lunar far side will be able to hear anything: Even with Earth and the sun blocked out, the hum of the Milky Way galaxy itself is still far louder than those hydrogen whispers. But if it does detect those murmurs, our understanding of the universe will change forever. “It’s totally uncharted territory,” says Garrett.

(The moon’s far side has a huge mystery blob.)

A radio telescope pathfinder

First, scientists need to demonstrate that radio astronomy is possible on the moon. That’s the purpose of the upcoming Lunar Surface Electromagnetics Experiment-Night, or Lu-SEE Night experiment, a collaboration between NASA, the Department of Energy’s Brookhaven National Laboratory, and the University of California, Berkeley.

Lu-SEE Night’s most important instrument is its sensitive radio—one that, in theory, can hear a plethora of ancient radio signals coming from the early universe. It’s a simple test facing a steep challenge.

“No U.S. mission has landed on the far side of the moon. No private company has landed on the far side of the moon,” says Slosar, who leads the Lu-SEE project. And nobody has listened to cosmic radio signals on the lunar far side.

The biggest menace will be the lunar environment. There is a small risk of a bullet-like micrometeorite fatally wounding the robot. And “the temperature swings are horrendously large,” says Slosar, going from hundreds of degrees above zero to hundreds below zero from lunar day to lunar night. Lu-SEE Night is equipped with radiators and internal heating mechanisms to try to keep it from freezing or sweltering. But nobody knows for certain if they will work.

“If we can survive the first night, we can survive many,” says Slosar. Ideally, the radio telescope-in-miniature operates for around 18 months.

Lu-SEE Night is scheduled to hitch a ride to the moon aboard Firefly Aerospace’s commercial lander later this year. The world’s radio astronomers will be watching closely. If it works, then the prospect of something grander will feel much more tangible.

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A self-building lunar sentry

Scientists have put forward a range of lunar radio telescope ideas. The final form will need to be large enough to “hear” those far-flung radio signals—something the LCRT offers by taking advantage of the moon’s chasm-covered topography.

The task of building the telescope would be left to a family of robots: A lander would deliver a concave mesh material made of wires and adorned with reflecting panels to the center of one of the moon’s many impact craters. These panels would bounce radio waves from the sky into a receiver that’s hanging above the crater floor. Several additional rovers would hoist the wires up to the crater rim and pull them tight, elevating both the mesh and receiver. The crater would shield the telescope from any radio waves not coming from the sky, including any solar radio waves that have managed to skip along the lunar surface.

That, at least, was the original idea for the LCRT. But Bandyopadhyay had some concerns. Relying on several robots to accomplish this task means that, should one malfunction, the telescope would be incomplete. It would also be a somewhat slow process, one that could take the robots through several dangerous night-day cycles that might kill them off.

Bandyopadhyay shared revised designs for the telescope with National Geographic. The LCRT team has reduced its fleet of robots to just one. A solitary droid would land in the middle of a large impact crater—one 4,300 feet across, sufficiently sizable to give the LCRT its expansive form but also not too large to hinder self-assembly—and fire out anchored cables in multiple directions. When their anchors are attached to the crater rim, motors will make them taut, lifting a radio receiver above the lander in the process.

During this deployment, a 1,150-foot-long radio wave reflector designed to concentrate the radio waves coming from the sky onto the receiver will unfurl like a star-shaped flower in bloom. “We took some ideas from origami,” says Bandyopadhyay.

This iteration of the LCRT isn’t just elegant, but pragmatic. The use of just one robot means there are fewer points of failure, and the overall mission cost is lower. Suspending the telescope in midair also avoids interference from electrically charged moon dust that other designs stuck to the lunar surface might encounters. Plus, relying on an existing structure (the crater) helps with a speedy assembly and offers protection from unwanted sources of radio waves (like the sun).

By putting all their eggs in one robotic basket, the LCRT would still be a bit of a spaceflight gamble. But it’s being supported by NASA’s Innovative Advanced Concepts Program, and its Astrophysics Research and Analysis Program, which suggests the powers-that-be think it might be worth a shot.

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The LCRT team is currently testing out different kinds of anchors to see which may work best. Engineers are also using scale models of the telescope to see if its origami pattern can effectively pick up radio waves. Ideally, they want to eventually send some prototype components up to the moon itself to put them through their paces in a way that’s not possible on Earth.

Perhaps the radio telescope that sprouts on the lunar far side won’t end up being the LCRT, but one of the other mission concepts. Bandyopadhyay, for one, won’t be too upset by that outcome: If someone is up there listening—for extra-terrestrial dispatches and those ghostly whispers from the cosmic dark ages—he’ll be thrilled.

“The science is what matters—opening humanity’s understanding to a part of the universe we’ve never seen before,” he says.