The concept of a city-sized telescope on the moon has piqued NASA's interest.
The space agency recently awarded researchers a grant to further develop the plan for a sprawling array of antennae on the moon's cryptic far side — using minerals mined from the moon. At this stage of the game, a proposal for a 177-square-kilometre telescope snaking over the lunar surface is an idea, not nearly a funded mission. But such a radio telescope, called the FarView Observatory, would allow astronomers to see what no other instrument today can: A period of time before the stars, called the universe's "Dark Ages."
"I've personally been advocating for a radio telescope on the moon for 40 years now," Jack Burns, a professor in the Department of Astrophysical and Planetary Sciences at CU Boulder who's a member of the FarView project, said. "It's going to probe a part of the universe we haven't been able to see before."
Radio telescopes have a lot in common with the radio antenna on your car. But they're not tuning into The Rolling Stones and Metallica. Radio telescopes — often built as giant dishes — capture radio waves emanating through the cosmos from exploding stars, forming stars, black holes, and beyond.
Radio telescopes have to be big because radio waves from the deep universe are extremely weak sources of energy. ("These are very faint signals. The amount of energy collected in radio astronomy's history is less than the energy needed to melt a snowflake," Yvette Cendes, an astronomer and postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics, said earlier this year.)
But the radio telescope arrays on Earth, as vast as they are, receive too much interference to pick up the faintest signals in the universe. A lofty part of our atmosphere called the ionosphere, reflects extremely distant and stretched-out radio waves. And then, there's us. "Random radio emissions from our noisy civilization can interfere with radio astronomy as well, drowning out the faintest signals," NASA explains.
"It's going to probe a part of the universe we haven't been able to see before."
A telescope on the moon's dark far side, however, is free of this noise. There's little to no lunar atmosphere. And the moon itself blocks pesky radio waves from our boisterous planet.
On the moon's far side, there's a (relatively) clear view into the deepest of the cosmos. All we need is an extremely large telescope.
How do we create a 177km square telescope?
The idea is indeed hugely ambitious. But perhaps not as far-fetched as it sounds.
NASA is funding the further conceptual development of FarView, proposed by the aerospace company Lunar Resources, through its "NASA Innovative Advanced Concepts" program. At this Phase II round, researchers receive up to $US 600,000 to advance their ideas. Also included in this year's recipients is a planetary defence mission that would "pulverize" an incoming asteroid or comet, an "astropharmacy" to make needed drugs (for radiation exposure and other ailments) in deep space, and a fast-moving spacecraft powered by a "radioisotope electric propulsion system," among other concepts.
A major selling point for the sprawling lunar observatory, emphasizes Burns, is that nearly all the metallic materials are available on the moon. Giant, expensive rockets won't need to haul bounties of conducting metal for the antennae.
"We don't have to bring all that material from Earth," Burns said. "We can in fact build an array with 100,000 antennas with only a few flights to the moon."
Similar to a giant spiderweb laid on the ground, robotic rovers would lay strips of aluminium extracted from the lunar soil on relatively flat expanses of the moon (as shown in the graphic above). These thin metal strips act like the metal rods or wires commonly seen in antennas, which catch radio signals travelling by (just like your car's antenna).
"In some ways, this is 1950s technology," Burns marvelled.
Yet the radio waves Burns and other astronomers hope to catch on the moon are quite long, at some 20, 30, or more meters. (FM radio waves are some 3 metres long.) The universe is constantly expanding, and the different types of light (visible light, infrared light, X-rays, radio waves, and beyond) are stretched out as space expands. That's a critical reason why an observatory that seeks some of the oldest signals in the cosmos must be so big: The radio waves have been stretched like taffy.
Of course, the greater telescope project will require more than mining aluminium from the moon's soil. A swarm of robotic rovers will need to lay the wiring. Solar panels must be constructed to power the machines. And some level of human oversight will be required, perhaps from astronauts who will inhabit the Lunar Gateway, an outpost that will orbit the moon.
A colossal looming question, of course, is cost.
NASA is considering other large-scale lunar telescope ideas. But cutting the transportation of metals to the moon is a great boon for such an expansive project. And with the rise and success of commercial rockets, any necessary launch costs are falling. Overall, it's too early to know the bill for such a sprawling telescope. But it will almost certainly be billions.
NASA and Congress, however, have been historically committed to spending billions into how the universe formed, and where we and the Milky Way galaxy came from. The James Webb Space Telescope cost taxpayers nearly $US 11 billion – with much of it built and assembled in the U.S. Other scientific undertakings, like the Mars Perseverance rover, cost some $US 2.7 billion. And the first launches of NASA's new mega-rocket, the Space Launch System, will cost over $US 4 billion per launch, as it supports exploration and future missions on the moon.
A project like FarView might be especially enticing to NASA, noted Burns, because it would advance robotic exploration and industrial creation on another world. The space agency wants to establish a permanent presence on and around the moon. And it wants to go to Mars. For such deeper space applications, it will need proven building and industrial technology. "NASA is interested in the technology and engineering along with the science," said Burns, speaking of FarView.
A price tag for constructing a sprawling array of metallic rods on the moon won't be cheap. But it could be reasonable, considering the scope of the project. And the returns could be scientifically, and technologically, invaluable.
"It would be the biggest telescope ever built — and we're going to do it using robots," Burns said.
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