At long last, a radio telescope on the moon’s far side

A mesh laid into a crater on the moon with receiver and other parts labeled.
The Lunar Crater Radio Telescope has a proposed 1-km diameter (.6 mile), much larger in the moon’s low gravity than any earthly radio telescope. If completed, this telescope will be the largest filled-aperture radio telescope in our solar system. Image via Saptarshi Bandyopadhyay/ NASA.

In late 2020, the beloved Arecibo radio telescope in Puerto Rico collapsed and was decommissioned. It was a dish-type radio telescope, built into a natural depression in the landscape. Now, as the astronomy community mourns Arecibo’s loss, a team of scientists has just cleared another hurdle to building a much-larger radio telescope. In April 2021, NASA’s Innovative Advanced Concepts awarded the Lunar Crater Radio Telescope project $500,000 for further research and development. This telescope, too, is to be built into a natural depression in the landscape, in this case a bowl-shaped crater on the far side of the moon.

Where and how would a telescope be built in such a remote and inaccessible place? After all, so far, only one spacecraft has successfully soft-landed on the moon’s far side, and that is China’s Chang’e 4, which achieved humanity’s first soft landing on the far side on January 3, 2019. To scientists, Chang’e 4’s success only shows it can be done, and the Lunar Crater Radio Telescope team has an innovative plan. Their idea is to deploy space robots to build the half-mile-wide (1-km-wide) radio telescope in one of several proposed craters on the far side of the moon. The telescope itself is to consist of a wire mesh.

DuAxel is a robotic concept under development that would consist of two tethered rovers. One rover would stay on the edge of the crater and act as an anchor, while the second rover would travel down the crater’s wall into the bowl to build the telescope. A separate spacecraft would deliver a wire mesh dish to the center of the crater that the robots would unfold and drag up the walls of the crater to anchor on the rim.

The design of the wire mesh itself will be challenging, because it must be strong, flexible and lightweight. The mesh will have to maintain a precise spacing and parabolic shape while still being able to withstand temperature ranges from -280 degrees Fahrenheit (-173 C) to 260 degrees Fahrenheit (127 C).

Can it be done? Should it be done? The fact is, a radio telescope on the far side of the moon has been a long-held dream of space visionaries.

Closeup oblique view of crater with wires stretching across.
Artist’s concept of DuAxel rovers erecting the wires and dish of the Lunar Crater Radio Telescope. Image via NASA/ Vladimir Vustyansky.

A radio telescope on the moon’s far side would have many advantages over a similar instrument built on Earth. While large radio telescopes do exist on Earth (the biggest one, currently, is FAST in China), our ionosphere blocks Earth-bound radio telescopes from seeing wavelengths longer than 33 feet (10 meters). The moon’s lack of an atmosphere will allow the longer radio wavelengths to reach a telescope built on the moon. And the far side of the moon is an excellent site for a radio telescope. That’s because the moon itself will block the radio chatter emitted from Earth. These advantages will open up a range of wavelengths that astronomers have not been able to explore. As Saptarshi Bandyopadhyay of JPL, leader of the Lunar Crater Radio Telescope research team, said about Earth’s limiting factors:

There’s a whole region of the universe that we simply cannot see.

NASA said on May 5, 2021, that access to the longer radio wavelengths, via the Lunar Crater Radio Telescope, will be particularly effective for probing the universe’s Dark Ages. This period in our universe’s early history happened after the Big Bang and before the first stars. The time period directly after the Big Bang can be studied via the cosmic microwave background. The Hubble Space Telescope (and soon the James Webb Space Telescope) can peer back in time to the first stars and galaxies. But our universe’s Dark Ages are … well … dark. They lasted for a few hundred million years after the Big Bang and might hold the answer to secrets about why our universe looks as it does. Lunar Crater Radio Telescope team member Joseph Lazio of JPL said:

While there were no stars, there was ample hydrogen during the universe’s Dark Ages, hydrogen that would eventually serve as the raw material for the first stars. With a sufficiently large radio telescope off Earth, we could track the processes that would lead to the formation of the first stars, maybe even find clues to the nature of dark matter.

View from inside crater and proposed antenna receiver.
Artist’s concept with a view from inside the crater hosting the Lunar Crater Radio Telescope – where the wire mesh dish would be – looking up at the receiver suspended above. Image via NASA/ Vladimir Vustyansky.
Cratered moon with metal dish in one crater.
Artist’s concept of the proposed Lunar Crater Radio Telescope in a crater on the moon’s far side, as seen from a distance. Image via NASA/ Vladimir Vustyansky.

The team will spend the next two years further developing its ideas, in the hopes that their dreams of a large radio telescope on the far side of the moon will come to life and reveal secrets of the early universe. Bandyopadhyay said:

The development of this concept could produce some significant breakthroughs along the way, particularly for deployment technologies and the use of robots to build gigantic structures off Earth. I’m proud to be working with this diverse team of experts who inspire the world to think of big ideas that can make groundbreaking discoveries about the universe we live in.

Cartoon boxes showing deployment landers and also rovers moving around the crater.
Artist’s concept showing, step by step, how the DuAxel lander and rover would be deployed and build the radio dish in a crater on the moon. Image via University of Illinois.

Bottom line: The team trying to make the Lunar Crater Radio Telescope a reality has been granted $500,000 to further their development ideas. Such a large telescope on the far side of the moon would allow scientists to explore a range of radio wavelengths they can’t see from Earth and would open the door to learning more about the Dark Ages of the universe.


May 19, 2021

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