In the last year, the James Webb Space Telescope embarked on a groundbreaking mission, capturing stunning and unprecedented images of the universe.
Positioned to shield itself from the sun’s blinding light, it turned its colossal golden mirrors toward the cosmos, allowing cryogenically cooled sensors to capture the ancient red-shifted light emitted 13.5 billion years ago during the universe’s infancy.
This remarkable achievement was a testament to human ingenuity, but it left us with a tantalizing question: could we delve even further into the past and detect signals from the primordial universe, something the James Webb Telescope couldn’t achieve?
The Challenges with Radio Telescopes
The answer lies in the realm of massive radio telescopes, instruments that could potentially unlock the secrets of the universe’s earliest moments.
However, constructing such colossal structures presents a monumental challenge, even here on Earth.
The collapse of the Arecibo telescope in 2020, after 57 years of service due to two snapped supporting cables, serves as a stark reminder of the difficulties associated with these colossal instruments.
Arecibo, nestled in a natural sinkhole, utilized Earth’s geography to shape and support its spherical dish.
Yet, our atmosphere blocks radar waves from the distant past, making it necessary to consider building a similar instrument in space.
Enter NASA scientists with an audacious plan: a radio telescope situated on the far side of the moon, leveraging naturally formed craters as the foundation.
This ambitious undertaking would result in the largest space telescope ever constructed, promising not only to reveal the mysteries of the universe but also potentially costing significantly less than its optical counterpart, the James Webb Telescope.
This is the incredible story of NASA’s lunar radio telescope project.
The notion of a massive radio telescope is not entirely new, with the Arecibo Observatory in Puerto Rico boasting a substantial 300-meter diameter dish.
However, the proposed moon-based telescope would dwarf its terrestrial predecessor, featuring a colossal 1.3-kilometer-wide crater that would allow engineers to suspend a dish 50 meters larger in diameter than the Arecibo Observatory.
Is the Moon Telescope Possible?
But is such a venture feasible? Constructing structures on the moon is no easy feat.
The fundamental idea behind this telescope is to use a lunar crater as a natural bowl, eliminating the need for heavy support structures, and construct the dish from wire meshes that sag naturally under the moon’s gravity, forming a reflective surface.
The use of mesh wire significantly reduces the system’s weight while enabling radio waves to bounce off it.
As long as the gaps in the mesh are shorter than the incoming signal’s wavelength, the waves will bounce off, akin to how a microwave oven’s mesh allows visible light to pass through while reflecting microwaves.
The Proposition of the Moon Telescope
For this concept to work, the ideal crater must be found, and scientists have meticulously analyzed data from the Lunar Reconnaissance Orbiter since 2009 to identify the perfect location.
First and foremost, the crater must be on the moon’s far side, perpetually shielded from Earth’s radio noise due to the moon’s tidal lock. Additionally, the crater should be located as far away as possible from the moon’s near side.
To accommodate the 350-meter-wide dish, the crater should have a circumference of 5 kilometers and a depth of 175 meters. It must also have a smooth terrain free of large boulders or mounds, with a level rim for secure wire anchoring.
Lastly, it should be oriented away from the Milky Way galaxy’s center to observe radio waves emitted from the early universe in the universe’s quieter regions.
These stringent criteria narrowed down the options from a vast pool of 82,000 craters on the moon’s far side to just 300.
Among these, 50 were selected for further evaluation, with one crater, situated almost 10 degrees north, emerging as the chosen candidate.
Challenges of the Moon Telescope
The greatest challenge facing this project is the construction of the moon itself.
The telescope aims to capture information within the electromagnetic spectrum ranging from 4.7 MHz to 47 MHz, corresponding to wavelengths between 6.4 to 64 meters.
This presents one of the initial engineering constraints: the dish must reflect and focus these waves.
While mass isn’t a significant constraint for stationary structures on Earth, the need to transport materials from Earth at a substantial cost per kilogram necessitates a focus on minimizing weight.
Lightweight carbon fiber cables serve as the support structure, addressing the lunar temperature swings that range from -170 degrees Celsius to 120 degrees Celsius during the moon’s day and night cycles.
These carbon fiber wires are anchored on the crater sides, with the wire’s natural sag forming the support structure.
However, the hanging wires naturally form a catenary shape, unsuitable for a concave mirror. The solution lies in creating a shape closer to a half-circle, which is more conducive to focusing reflected electromagnetic waves within the crater.
Achieving this with just two anchor points is a fascinating challenge. Wires can only hang in pure tension and will naturally sag between two points. However, adding weight will result in a deeper parabolic arch, allowing it to remain in tension.
Weight distribution along the wire’s length can be used strategically to alter its shape, achieved by tailoring the wire’s shape or coating it with materials of varying densities along its length.
Anchoring the tethers to the crater rim is easier said than done, especially when constructing without the aid of astronauts. Fortunately, the moon’s weaker gravity simplifies this task.
Lunar gravity, which is about 16% of Earth’s, makes supporting a 2000 kg telescope equivalent to holding up just 320 kg on Earth.
The use of Duaxel robots developed by JPL to manually tow the wires into place, forming the anchoring wire shape above the crater before landing, or deploying a single lunar lander to the crater’s center to fire anchors above the crater rim.
These anchors, similar to boat anchors, will dig into the lunar regolith upon tensioning.
However, the lunar regolith’s sharpness requires precautions to minimize friction between the tethers and the ground.
Relying on projectiles for anchoring offers cost savings, with an estimated total cost of $2.4 billion compared to $4.5 billion for rover-based deployment.
Once deployed, these anchors serve as the framework upon which the rest of the structure is built.
The antenna receiver is elevated to the focal point, and the reflective mesh, composed of ultra-light reflective materials like gold-plated molybdenum, is unfurled using guide wires.
This ingenious origami-inspired concept, employed in various space missions, allows for packing a 350-meter-wide radar dish into a confined lunar lander.
The Moon Telescope’s Primary Mission
The radio telescope’s primary mission is scheduled for one year, during which it aims to gather sufficient data to piece together the early universe’s evolution.
By listening for radio waves at the specific frequency of the 21 cm line, scientists can quantify hydrogen formations across the cosmos and track these formations over time through redshifting as the universe expands.
This data will refine our understanding of the universe’s evolution following the Big Bang.
While the telescope’s primary mission is set for one year, it holds immense potential beyond its initial purpose.
The telescope can detect and quantify magnetic fields around exoplanets, potentially identifying planets hospitable for life.
With the increasing number of lunar missions and advancements in communication technology, relaying data from the moon to Earth has become more efficient, further enhancing the telescope’s capabilities.
In conclusion, NASA’s lunar radio telescope project is a bold endeavor that promises to revolutionize our understanding of the universe’s origins and evolution.
Despite the challenges of construction on the moon, the potential scientific rewards are boundless.
This monumental project is a testament to humanity’s insatiable curiosity and unyielding spirit of exploration.
Hello, fellow aerospace enthusiasts! I’m Matthew, a high school student at Portola High School and the creator of The Aero Blog. My journey with aerospace started as a childhood fascination and has grown into a full-blown passion that I am thrilled to share with you through this blog.