What’s a Radio Telescope and how does it work?
Humanity has been using the radio telescope for almost a century, precisely since 1932 when Karl Guthe Jansky, an American engineer, was assigned the task of identifying sources of “static” (basically a radio noise unwanted always present in a radio receiver in addition to the desired radio signal) that might interfere with radiotelephone service of that time.
From that “little” experiment we’ve moved forward enormously, radio astronomy has become a new science, and the complex technology known as radio telescopes have enhanced human knowledge of the universe and the phenomena that happen within it.
All astronomy is about observing waves of light. Galaxies, stars, and other celestial bodies in space emit visible light together with light from other parts of the electromagnetic spectrum in the form of gamma rays, radio waves, infrared radiation, and X-rays. Optical telescopes (like Hubble Space Telescope) show us what’s visible in space together with infrared and ultraviolet light but this doesn’t give us the whole picture of what’s happening in space. Telescopes tuned to different parts of the electromagnetic spectrum can reveal hidden objects in space; the resulting images can then be combined to give a more complete picture.
Just like you tune the radio to a particular station, radio astronomers tune their telescopes to pick up radio waves millions of light years from Earth. Using sophisticated computer programming, they can unravel signals to study the birth and death of stars, the formation of galaxies, and the various kinds of matter in the Universe.
What’s the downside of doing radio astronomy on Earth?
Huge discoveries have been done since the dawn of radio astronomy however in these last times, we’re facing more and more problems that could threaten its future, and is called radio frequency interference (RFI)!
Since the invention of radio transmission by Nikola Tesla, humans have evolved using it, transmitting every possible signal they could transmit with it till arriving at the current day where we’re living in an ambient with radio spectrum pollution!
To alleviate this huge problem, scientists, organizations, together with nations have agreed to establish the so-called “Radio Quiet Zones” around radio observatories to keep the RFI levels to a minimum.
Unfortunately, most of the time this trick doesn’t completely remove the RFI as almost every electronic device we’re surrounded by (like for example cellphones and computers) gives off some form of RFI!
In addition to that, the Earth-based and Earth-orbiting radio telescopes have a huge limitation connected with the reflection done by the Earth’s ionosphere which blocks radio frequencies below 30MHz that, to this day, is still largely unknown by humans.
Can Lunar Crater Radio Telescopes be the solution to these problems?
So, why not move radio astronomy out of Earth’s atmosphere and create a radio version of the James Webb Space Telescope? Well, it’s not that simple.
In principle radio telescopes have to be large, really large! That’s because the wavelengths of radio light are so large (on the order of centimeters), a radio telescope must be physically much larger than an optical telescope to obtain the same resolution.
Just to make a comparison: the largest radio telescope on Earth called the “Square Kilometre Array” (currently under construction) will count when finished, 3000 antennas of 15 meters in diameter. So, comparing that to the 8 meters of the JWST, tell us immediately where the space-based radio telescope problem stands: dimensions, which means waiting and sending all that material into space is not feasible at all!
Well, what if instead, we replicate the Arecibo telescope style on the Moon? This idea is around since the ’50s, but just in these last few years, scientists have started looking into it with more effort, considering launch costs are decreasing rapidly and space science budgets are going up exponentially.
The proposal is quite simple: find a crater, on the far side of the Moon big enough for a probe that can land on it and can automatically deploy the telescope.
The advantages of this project are enormous: because on the Moon, the telescope can see the universe at wavelengths greater than 10 meters, which equates to frequencies of 30MHz and lower. Putting an observatory on the Moon not only lifts the antenna above the ionosphere, but by locating it on the far side, the Moon acts as a physical shield that isolates the telescope from radio interference from Earth-based sources, Earth-orbiting satellites, and Sun’s radio noise during the lunar night.
Lunar Crater Radio Telescope (LCRT) on the Far-Side of the Moon
The Lunar Crater Radio Telescope (LCRT) will be a kilometer in diameter, in comparison to 300 meters for the collapsed Arecibo radio telescope and 500 meters for the FAST facility in Guizhou, China.
NASA’s plan is for a lander to drop the necessary components into a suitable three-to-five-kilometer crater (there’re already 82000 sites available) on the far side of the moon, where dual-axle robots called DuAxels would assemble the antenna in situ.
For the launch mission, the plan is a single launch with a vehicle carrying two landers.
“One half carrying the reflector mesh and the receiver antenna lands in the crater flow, the other half carrying some dual-axle rovers, and power and communications equipment, land on the crater rim.”—Saptarshi Bandyopadhyay, Robotics Technologits at NASA’s JPL
“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.”—Joseph Lazio, Project Scientist at NASA’s JPL
LuSEE-Night and the future of Lunar Crater Radio Telescope (LCRT)
Before any decision on whether or not to proceed with a real project regarding radio telescopes on the far-side of the Moon, NASA wants to test some key technologies together with facing some challenging problems (like surface temperature that change between – 173°C to + 120°C).
The plan is to do all that with another project called LuSEE-Night, which primary goal is not to collect scientific data but merely to survive the harsh environment on the lunar far side, to test the feasibility of installing future telescopes there. Whatever radio observations it collects will be a welcome bonus!
LuSEE-Night may launch as soon as 2025 on a Commercial Lunar Payload Services mission, meanwhile, the Lunar Crater Radio Telescope research has received $500000 in funding from NASA.
The Lunar Crater Radio Telescope project could create a radio telescope on the far side of the Moon to carry out unprecedented studies of the early universe. LCRT received additional support as it progresses in @NASA’s Innovative Advanced Concepts program. https://t.co/0yB4PXIj9f pic.twitter.com/MC04VSfugF— NASA JPL (@NASAJPL) May 5, 2021
We can’t wait to see more progress about this amazing project that, may one day give us more glimpses about the formation of the Universe and allow us to understand better that Dark Age!