All Eyes on the Moon

The Moon race (part deux) is officially in full swing now with Japan, India, China, and even a private corporation making their marks on the surface. The calendar is packed with a whole slew of planned missions in the coming months and years to set the stage for a more sustained presence on the lunar surface. But some astronomers want to use the Moon for something perhaps less expendable than water ice — sorry, fans of For All Mankind — or a cosmic home base: a vantage point to peer into Cosmic Dark Ages.

Getting a look at the Cosmic Dark Ages — the period when the early universe was covered in pure darkness — has long been a holy grail for astronomers. It could tell us about the most fundamental aspects of our Universe and potentially help solve mysteries that puzzle us today.

“This is a wonderful place to look for any new physics,” says Jack Burn, a University of Colorado physicist, including understanding “the nature of dark matter, and maybe early dark energy, and really probe and test our fundamental models of cosmology and physics.”

But to see back into the Cosmic Dark Ages you need a very dark place indeed, free from a radiation-blocking ionosphere and away from the constant chatter we create here on Earth. This is why astronomers like Burns and the Jet Propulsion Laboratory’s Joseph Lazio have plans to build radio telescopes on the far side of the Moon.

If engineers and astronomers at private companies, universities, NASA’s Jet Propulsion Laboratory, and Brookhaven National Laboratory have their way, the far side of the moon could soon be the spot from which astronomers stare 13 billion years back in time, to an era before the first stars were born. Teams of scientists worldwide are developing concepts to build huge radio telescopes on the far side of the Moon, and the first prototype could launch as early as 2025, with more rudimentary telescopes set to go even sooner. Here’s a look at the race so far.

“If We Didn’t Have a Moon, We’d Have to Build It”

In the beginning, as hydrogen gas drifted through the darkness of the early Universe, atoms occasionally bumped into each other, releasing energy in the form of radio waves. The radio waves from those dark clouds of gas were 21 centimeters long (that’s just the natural wavelength that hydrogen atoms emit, and they’re very consistent about it). But those radio waves have spent billions of years crossing a rapidly expanding universe, and that journey has stretched them out until they’re several meters long.

Charged particles in an upper layer of Earth’s atmosphere, called the ionosphere, block radio waves longer than about 10 meters, so it’s impossible to study the Cosmic Dark Ages with a telescope here on Earth. And radio telescopes, especially ones meant to map the sources of such long radio waves, have to be much too large to build in space. You need something like a planet, but without an ionosphere – or all the radio noise that surrounds our busy, high-tech world.

Burns has argued for decades that the far side of the Moon is the best of both worlds. There’s solid ground to build on, but there’s no ionosphere to block incoming radiation, and the whole bulk of the Moon (2,000 miles of solid rock) would shield the telescope from Earth’s constant radio noise and – for two weeks out of every month, during the lunar night – the Sun’s radio emissions, too.

“It's the ideal place,” says Burns. “If we didn't have a moon, we'd have to build it.”

Fortunately, we don’t have to build the Moon — just the observatory. Burns is working with Texas-based Lunar Resources, Inc. on a project called the Farview Observatory, which will — if everything goes according to plan — be a 5-square-mile array of radio antennas sprawling across a lunar plain. Picture an antenna something like an old-fashioned television antenna; now picture roughly 100,000 of them, lined up end-to-end in a series of zig-zags. Combined, those antennas will act as one giant radio receiver, listening for faint signals from the Cosmic Dark Ages.

Meanwhile, at JPL, a team led by JPL robotics technologist Saptarshi Bandyopadhyay is working on the Lunar Crater Radio Telescope, which has the same scientific goal as Farview but will look very different. LCRT would be a semicircle of wire mesh about a third of a mile wide, lining the bottom of a 1.9-mile-wide crater on the Moon. The result will be a radio dish similar to Arecibo (the large, now-shuttered observatory in Puerto Rico), but with bare wires instead of the aluminum panels that lined Arecibo’s crater.

Comparing these two possible Moon telescopes is similar to comparing Earth-based telescopes like the Very Large Array (VLA) and China’s Five-hundred-meter Aperture Spherical Telescope (FAST). The VLA is an array of dish-shaped radio antennas lined up across a swath of New Mexico desert. It turns out that if you line up several radio receivers (or mirrors, if you’re studying shorter wavelengths like infrared or visible light), and connect them with the right software, those individual antennas can add up one giant telescope. Astronomers call this an interferometer.

FAST and the LCRT, like the now-defunct Arecibo, are something called single-aperture, or filled-aperture, telescopes. FAST is one enormous radio dish, set into a crater that provides structural support for the dish (and the delightful irony of using a crater formed by a meteor impact to study other objects in space).

Each design has its advantages. An interferometer like the VLA or Farview can see the universe in much higher resolution than a filled-aperture telescope like FAST or LCRT, because the interferometer is wider. But the tradeoff is that a filled-aperture telescope like FAST or LCRT can "see" fainter signals than an interferometer, because it's got an entire surface to catch them with. Neither is a “better” option than the other; radio astronomers here on Earth rely on both types of telescope to scan the skies.

A Truly High-Tech Construction Crew

There’s one thing both telescope designs require: robotic construction teams. The LCRT team plans to use pairs of rappelling construction robots, developed at JPL, to lay the mesh grid in the base and along the sides of their chosen crater. Each pair of robots — together called a DuAxel — will be linked by a tether. One robot will anchor itself on the rim of the crater, while its partner rappels down the crater’s side to actually lay out the mesh for the telescope.

Farview, meanwhile, has even more ambitious plans for its robotic builders, starting with making the array’s 100,000 antennas from scratch, using aluminum extracted from lunar regolith (the dusty, ground-up rock that covers the lunar surface). The goal, says Burns, is to reduce the amount of material that has to be launched to the Moon from Earth.

And both telescopes will depend on a satellite in lunar orbit to send data home to Earth, since the far side of the Moon is constantly pointed out into the vastness of space, which is the whole point.

At the moment, both are in their second phase of development under a program called NASA Advanced Innovative Concepts, which funds projects that work out the engineering and science details of possible future missions like Farview and LCRT. Farview’s team will spend the next two years devising the best antenna layouts, narrowing down mission requirements, and tackling other engineering issues. They’ll also ask more specific science questions and plan how to use Farview to answer them. At JPL, the LCRT team is busy working on similar problems.

One Small Step For A Lunar Lookout

One or the other of the more ambitious observatory concepts could be ready to launch to the Moon by the late 2030s, but there are no guarantees.

Meanwhile, the first telescope to land on the Moon was a much smaller, much simpler version of a radio telescope: a crossed pair of antennas, spanning about 20 feet, called Radio wave Observation at the Lunar Surface of the photoElectron Sheath (ROLSES). ROLSES landed near the south pole of the Moon aboard Intuitive Machines’ Odysseus Lander earlier this year. Its goal was to study the background radiation that already exists on the Moon. (Most of that radiation comes from our Sun, but that’s likely to change soon, since nearly everyone with a space program seems to be aiming to set up shop near the lunar south pole.) Its other goal is to simply prove that a radio telescope could work on the Moon

“These are all kinds of multi-billion dollar projects that I think are, in some sense, ahead of their time,” Brookhaven National Laboratory physicist Anže Slosar tells Inverse. “You're not going to get a $2 billion project unless you can at least prove the principle at some point.”

Near the end of 2025, a similar telescope called the Lunar Surface Electromagnetic Experiment – Night (LuSEE-Night) is scheduled for launch aboard a Firefly Aerospace rocket. If all goes well, it will touch down on the far side of the Moon in January 2026.

Like ROLSS, LuSEE-Night will be a fairly simple telescope: a pair of 20-foot-wide radio antennae, spring-loaded and mounted on a turntable. But LuSEE-Night will try to last through a two-week-long lunar night. To do that, it will carry a 110-pound battery, heavily insulated against the deep cold of lunar darkness.

“The main role of LuSEE-Night is really to test this theoretical promise – whether the Moon really is such a great place to do observation,” says Slosar. “Maybe the Moon has more ionosphere than we thought; maybe there are plasma tracks; maybe there are micrometeorites; maybe there's something we haven't thought about. Really, there is this kind of notion that the Moon is the best place, but nobody has tested it.”

LUSEE-Night will do some real science, too. It’s too small to capture the long, slow radio waves rippling in from the Cosmic Dark Ages, but it will also be astronomers’ first chance to test their models of what the galaxy should look like at low radio frequencies they can’t see from Earth.

Once we have eyes on the moon, there’s no telling what we’ll be able to see.