It’s widely known by now that the “dark side” of the moon, made famous by Pink Floyd, isn’t actually dark. It gets as much sunlight as the side that is tidally locked facing Earth. However, it is dark in one very important way – it isn’t affected by radio signals emanating from Earth itself. What’s more, it’s even able to see radio waves that don’t make it down to Earth’s surface, such as those associated with the cosmic “Dark Ages” when the universe was only a few hundred million years old. Those two facts are the main reasons the far side of the moon has continually been touted as a potential location for a very large radio telescope. Now, a project sponsored by NASA’s Institute for Advanced Concepts (NIAC) has received more funding to further explore this intriguing concept.
The project, known as the Lunar Crater Radio Telescope (LCRT), is part of NIAC’s Phase II program, and recently received $500k in additional funding to push the project further towards becoming a fully fledged NASA mission. This isn’t the first time a radio telescope on the moon has been proposed. But the LCRT team, led by Saptarshi Bandyopadhyay at JPL, have suggested two new and interesting features that make their approach much more attractive than previous alternatives.
The first feature has to do with limiting the sheer amount of material that is needed to construct a radio telescope. LCRT’s proposed instrument would be a one kilometer wide circle in a three kilometer wide crater. Traditional radio telescopes, such as the Five-hundred-meter Aperture Spherical Telescope (FAST) and the recently destroyed Arecibo Observatory use hundreds of radio-reflective panels to any signals to an observing platform suspended by cable above the receiving dish.
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In order to complete a 1km wide telescope, thousands of reflecting panels would have to be created on Earth, launched into space, and then placed precisely where they need to go. That’s a lot of launches and a lot of weight, and it made the entire concept of a lunar radio telescope untenable.
Dr. Bandyopadhyay’s solution to this problem is to use a wire mesh instead of solid panels to reflect the radio waves to the antenna. This mesh would be much lighter, and less bulky, but will still need to be set precisely in order to work properly. For that, the team turned to their other novel solution – dual robots.
Roboticists at JPL, of which Dr. Bandyopadhyay is one, have been working on a concept called DuAxel. These robots have two separate configurations. In one, they look like a standard four wheeled rover. In the other, the two halves separate. One anchors itself to a specific point while the other uses a tether to ease itself into otherwise unreachable terrain.
Crater walls would likely be such unreachable terrain, so having a robot that is able to access both the bottom of the crater and up above the rim where any landed supplies would be located is invaluable to any such telescope mission. It would also allow the robots to mount the antenna, the critical sensing piece of the telescope, above the crater’s center by applying tension in the mounting wires and lifting it into position.
Some major hurdles still remain, two of which will be the focus of this Phase II NIAC grant. The first is the design of the wire mesh network. It’s physical structure has to be exactly right in order for the telescope to work properly. In addition, it must be able to withstand the extreme temperature differences on the moon, which swing between -173 C and +127 C. If the mesh warps even slightly, the whole project could fail.
DuAxels themselves pose another quandary – should they be automated or have some sort of human intervention. Are they the only tools needed for the massive undertaking of constructing the largest ever radio telescope?
While Dr. Bandyopadhyay and his team work out these questions other factors put a time limit on the possibility of constructing a telescope in this most unique of locations. Part of the appeal of the far side of the moon is its lack of interference from artificial radio sources. However, that silence is not guaranteed. Already there is a satellite orbiting there, and other missions could be planned in the near future that would add confounding signals to the data mix.
That being said, the LCRT is still a long way from reality, and in its press release NASA is quick to point out that it hasn’t been accepted as a full NASA mission. But the intent of the NIAC program is to develop concepts to the point where they could become one. With that in mind, the extra half a million dollars will keep pushing the concept forward and hopefully result in a Phase III grant, which would then transition into a fully fledged NASA program after an additional two years of study. Though it might take awhile, the benefits of having such a massive telescope in one of the most radio quiet place in the solar system cannot be understated.
NASA – Lunar Crater Radio Telescope: Illuminating the Cosmic Dark Ages
NASA – NASA Selects Innovative, Early-Stage Tech Concepts for Continued Study
UT – The Moon is an Ideal Spot for a Gravitational Wave Observatory
Astronomy.com – Arecibo is dead. Should we build its replacement on the Moon?
Artist’s concept of what a completed LCRT would look like from space.
Credit: Vladimir Vustyansky