Then the 60-year-old The Arecibo Observatory collapsed In 2020, the crash not only brought down one of the world's leading radio telescopes, but also dealt a huge blow to the future of radio astronomy. Arecibo may have been old, but it also had unique capabilities that made it ideal for studying things like gravitational waves, like mapping the surfaces of asteroids as they slide along the earth.
Now radio astronomers around the world are debating what comes next. Does Arecibo need to be rebuilt? If so, where would the money come from?
Those questions are not easy to answer, but discussions are ongoing. Preliminary plans for a new revolutionary radio telescope continue every day. And interestingly, these talks have prompted NASA to rethink a bold idea first conceived half a century ago: building a colossal radio telescope on the far side of the moon.
Arecibo's design benefited from construction in a natural sinkhole in Puerto Rico. Likewise, astronomers could use existing lunar craters to build a radio telescope on the moon for (relatively) cheaply; colliding space rocks have already dug for it. And unlike the Earth, the Moon has no wind or weather to accelerate erosion. Even the pull of gravity itself is weaker on the lunar surface.
Arecibo on the moon
A decades-old idea by lunar scientist Richard Vondrak, who worked at the Apollo Science Operations Center during the lunar landing program, proposed using lunar craters to build radio telescopes, such as the Arecibo Observatory in Puerto Rico. Here, an artist's concept shows how three telescopes can be used individually or combined to create a giant instrument. (Credit: Courtesy of NASA)
As early as the 1960s, astronomers wanted to build a radio telescope on it the far side of the moon. That's because the moon's distance is always pointed away from Earth, which means that the entire moon acts like a shield of some kind, blocking out the cacophony of outgoing radio noise on Earth. This creates an environment in which scientists can theoretically observe the universe in wavelengths that cannot be easily analyzed from our planet – or even in orbit.
However, an Arecibo on the moon would be more than a replacement. The premise is similar to the way astronomers decided to replace the Hubble Space Telescope. Rather than replicating the original, the community embraced the idea of building something completely different. The James Webb Space Telescope (JWST) used insights gleaned from Hubble's tenure. But JWST is purpose-built to study the universe primarily through infrared light, while Hubble focuses on visible and ultraviolet light. That spectral shift means that JWST will be able to examine previously unexplored aspects of the universe in impeccable detail.
The same goes for building a large radio telescope on the moon. While Arecibo devoted half a dozen decades to studying radio waves on centimeter and millimeter scales, a lunar radio telescope could measure wavelengths greater than a meter, something astronomers cannot do from Earth.
If a Arecibo-like observatory were built on the Moon, it could potentially observe many exotic cosmic phenomena, such as auroras around distant Earth-like exoplanets. Most temptingly, it could even pick up radio signals from the earliest days of the cosmos the first stars and galaxies were born.
A 1986 proposal suggested that a system of cables suspended in a lunar crater would allow astronomers to build an Arecibo-like telescope on the moon. (Credit: NASA)
Frank Drake, a world-renowned astronomy, once even pitched the idea for a "Very Large Arecibo-Type Telescopes" on the moon at a 1986 NASA conference. Drake reasoned that using a lunar crater would reduce the need to build large structural elements. minimalize . Some panels, platforms and a ton of cables could suffice, he suggested.
The moon also contains so many craters that it should be relatively easy to find one with a rim sturdy enough to serve as an anchor point for the telescope's support cables. This would avoid the expense of the expensive towers that anchor cables in Arecibo. (In fact, the telescope collapsed in 2020 after the cables attached to the towers failed.)
"Reasonable cross-sections of valley and crater meet this need very well," wrote Drake. “In this case, significant savings on costs and materials are achieved. This approach could be used to build Arecibo-like telescopes on the moon or on the Earth with significant savings over the cost of the actual Arecibo design. "
Lunar Crater Radio Telescope
An artist's concept of how robots would build the Lunar Crater Radio Telescope. (Credit: Saptarshi Bandyopadhya)
In recent years, NASA has shown support for these ideas at unprecedented levels. The space agency has even funded studies on several early proposals to finally build an Arecibo-like observatory on the moon. Of these proposals, the Lunar Crater Radio Telescope (LCRT) reflects some of the same ideas that Drake put forward a generation ago.
But contrary to previous mission designers thought, the latest iterations of moon-based telescopes wouldn't rely on astronauts to build them. Saptarshi Bandyopadhyay, a robot technologist at the Jet Propulsion Laboratory and leader of the LCRT project team – says they plan to build LCRT using simple lunar rovers like NASA has already designed.
LCRT would land a spacecraft full of rovers outside the crater. These would then retrieve the support wires, take them to the crater rim and assemble a mesh system that spans about 1 kilometer. However, the entire system should fit into a single lunar landing spacecraft, such as Blue Origin & # 39; s Blue Moon.
By relying on robots instead of astronauts, the project can save a significant amount of money. Any mission involving astronauts requires extensive – and expensive – safety precautions. Any potential problem requires extra attention and technical safety measures. Sharp edges can cut through space suits, for example, so they are avoided on manned flights. But with rounded edges, you can't maximize cargo space, which is what you'd want to do for a robotic trip to the moon.
NASA has also begun testing a versatile model of a rover called DuAxel, which could be used for a number of different lunar missions. DuAxel can climb crater walls, among other things. And as a bonus, it is relatively inexpensive.
“If we send ten of these robots and two of them die; it's fine, '' says Bandyopadhyay. “Two of them are dead, but eight robots are still working. It's not like that with astronauts. "
A rover operates in a lunar crater in this artist's concept. (Credit: NASA)
But even with all the potential benefits of robot builders, the current cost of the technology likely puts the mission out of reach. SAPART estimates that building a radio telescope on the moon would cost billions of dollars. That is why his team is trying to develop new types of cables and mesh that are significantly cheaper to run than what is currently available. LCRT's initial study was based on $ 120,000 in NASA Innovative Advanced Concepts (NIAC) project funding to investigate the concept. And in the next phase of their mission plan, engineers could get to work developing the mesh. According to Bandyopadhyay, his team hopes to publish their first results in the spring.
“We now have a good initial design that makes sense and potentially allows us to fly,” he says. "If you gave us four or five billion dollars, we can launch it tomorrow."
But despite the enthusiasm, Bandyopadhyay is not optimistic, we will see an Arecibo-like telescope on the moon in the near future. After all, science is slow.
“I would be very surprised to see LCRT being deployed before I retire, and I am a very young scientist,” says Bandyopadhyay. & # 39; These things are difficult. These questions we are trying to solve are difficult. And the scientific windows that these questions will open are tough. Everything is difficult. If it had been easy, we would have already done it. "