Building Earth's largest telescope on the far side of the moon

NASA engineers are studying the feasibility of building a massive, kilometre-wide radio telescope on the moon that would dwarf anything we could build on Earth.

The telescope, which would be constructed by robots, would take the form of a huge, wire-mesh antenna in a dish shape that would hang suspended in a three-kilometre-wide crater on the far side of the moon. 

The Lunar Crater Radio Telescope would provide a unique perspective on the early universe, though it likely won't be built for decades, according to NASA robotics engineer Saptarshi Bandyopadhyay, who is leading the project.

"We all want to know what happened. How did the universe evolve? What happened after the Big Bang?" Bandyopadhyay told Quirks & Quarks host Bob McDonald.

In the 14 billion years since that event, the light waves from that era have been stretched out from tiny fractions of a millimetre to more than 10 metres as the universe expanded. They're now extremely long radio waves, and those can't be seen on Earth "because the ionosphere absorbs it," said Bandyopadhyay.

"So we want to go somewhere away from [Earth] so that we can get a picture of the Big Bang and evolution of the universe."  

Telescope size presents challenges

The problem, however, is that in order to capture those wavelengths, not only does this telescope need to be on the moon, it needs to be very large, which makes it hard to build.

There are giant radio telescopes on Earth, which observe shorter radio wavelengths that do penetrate the atmosphere. The 300-metre-wide Arecibo telescope in Puerto Rico — recently demolished in a catastrophic accident — or the 500-metre-wide FAST telescope in China represent significant engineering challenges.

Standalone, self-supporting, dish-shaped radio telescopes can only get to a certain size, based on the strength of the materials they're made from and the need to resist wind loads. To avoid these issues, the largest radio telescopes are built into natural features in the terrain. Arecibo and FAST, for example, were built in natural, dish-shaped sinkholes. 

Building such a telescope on the moon is, in one sense, easier. The lower gravity on the moon means a larger structure can be built with lighter materials. No atmosphere means no windstorms or other earthly environmental risks, though there are challenges from the moon's harsh temperatures.  

According to Bandyopadhyay, the moon also has no shortage of appropriately shaped terrain structures in the form of ubiquitous impact craters. 

"These craters seem like natural places to put this dish-shaped telescope because the crater also looks like a bowl."  

To find a crater candidate, Bandyopadhyay and his team combed over detailed pictures taken by NASA's Lunar Reconnaissance Orbiter and discovered more than 80,000 suitable craters on the far side of the moon.

Origami-inspired transport and construction 

While the location would provide advantages, there are unique and significant challenges to building on the moon, in particular the harsh working conditions and the difficulty of transporting materials.  

The team studied a range of scenarios for how a telescope might be constructed and transported to the moon. The one they have arrived at is inspired by Japanese paper folding, said Bandyopadhyay.

"Origami is the art of folding paper into smaller and more interesting designs. But in space, origami is extensively used to take these large structures, like a large dish of one kilometre, and we can literally fold it multiple times and make it into a pretty small structure."

The antenna would be built on Earth in the form of a large, but extremely lightweight net-like structure made of conductive aluminum wire. It would be carefully folded into a package that would fit inside the nose cone of a large rocket, possibly the Space Launch System that NASA is currently developing.

Once launched, the antenna would be carried to the moon and land on the floor of the crater into which it would be installed. Then it would need to be deployed.  

"We will have these robots that will go down ... to the lander and then pull lift wires that will connect to the lander sitting at the crater floor," Bandyopadhyay said.

These lift wires would be anchored on the crater rim and as they are winched up, the antenna would unfold and deploy. Ultimately the net-like antenna would be suspended over the crater floor, looking a little like a dish-shaped spider web.  

The tension in the wires would be adjusted to result in the appropriate dish shape to receive radio signals from space and reflect them to a receiver.

All of this technology (the launch rocket possibly excepted) is available today, said Bandyopadhyay.  

The robots, for example, are currently being tested at NASA's Jet Propulsion Laboratory.  

"These robots are called DuAxel, and they are actively being built at JPL for over a decade now. And these robots have the speciality that they can go down almost steep terrain like just cliff faces."

For now, this is an early stage engineering feasibility study, rather than a fully developed mission proposal, but Bandyopadhyay suggests it would certainly be expensive and would be a very high-profile endeavour for NASA.  

"Cost is a big uncertainty right now. Right now, all I can say is we think this will be a flagship-class mission."

Given that, it's likely decades away, at least. 

"Space is hard," said Bandyopadhyay. "I would be surprised if I could see this launched and deployed before I retired, and I'm a young scientist."

Written and produced by Jim Lebans