A huge radio telescope in a crater on the far side of the Moon: this is the goal of the colossal project Lunar Crater Radio Telescope (LCRT) of NASA for the realization of what it would actually be the largest telescope ever builtwith a diameter of 1.3 km. For comparison, the largest radio telescope in the world (FAST, in China) has a diameter of “only” 500 meters. The main objective of this project is to study with unprecedented precision the so-called It was Dark of the cosmos, the period between 400 million years and 1 billion years after the Big Bang in which the first stars and galaxies formed. The project currently exceeds our technological and engineering capabilities, therefore it does not have a set date, but we will proceed in subsequent steps: already in 2025 or 2026 the American space agency could launch the pilot mission LuSEE-Nightwhich will install the first – albeit small – radio telescope to operate on the Moon.
According to the NASA project, the telescope would consist of thousands of panels arranged by exploiting the concavity of a large crater to build a gigantic antenna capable of observing the universe in the radio band as had never been done before. A radio telescope on the far side of the Moon would not have the problem of the atmosphere (which absorbs the shorter wavelengths) and the “radio noise” produced by human activities, which would be shielded by the Moon itself. The enormous dimensions would also allow it to reach a resolution impossible today in the radio band unless with very particular techniques.
How the huge radio telescope on the Moon will be made
Simplifying, to build a radio telescope two main elements are needed: theantenna and the receiver. The antenna has the task of reflecting the radio waves and making them converge towards a very specific point, at a certain height above the center of the antenna: the receiver must be installed here, inside which is the sensor that collects the waves conveyed by the antenna. In the case of the Lunar Crater Radio Telescope, the idea consists in partially “carpeting” a crater with a diameter between 3 and 5 km with panels capable of reflecting radio waves, arranged to form a sort of parable: the curvature of this antenna (which will have a diameter of 1.3 km) will reflect the radio waves in the position where the receiver is located (350 m in diameter). This will be suspended via a system of cables fixed to the edge of the crater.
Installing the telescope will constitute a technological and engineering challenge of enormous proportions: much of the necessary know-how still needs to be developed. The project involves landing on the Moon two modulesone at the bottom of the crater that will place the panels to build the antenna and the other around its edge that will install the cables for the receiver.
To this we will need to add a satellite in orbit around the Moon to act as radio link, collecting the data produced by the telescope and sending it to Earth. In fact, since there is the entire Moon between us and the telescope, the latter cannot communicate with our planet except by using an “intermediary”.
The pilot mission: LuSEE-Night
Given the considerable complexity of the operation, which for now does not have a set date, NASA has planned the mission LuSEE-Night (Lunar Surface Electromagnetic Explorer) already for 2025 or 2026. This pilot mission involves the launch of a small radio telescope that will be operational on the far side of the Moon. The telescope will be carried by the lunar module Blue Ghost in the southern region of the far side of the Moon, from which it will be able to communicate with the Earth only through the satellite Lunar Pathfinder, which will “forward” the signal and data to astronomers working on our planet. LuSEE-Night will be an exceptional opportunity to study the cosmos at very low radio frequencies: thanks to the absence of the atmosphere on the Moon and the absence of terrestrial radio disturbances, LuSEE-Night will provide the best observations in this electromagnetic band in the history of ‘astronomy.
