While terrestrial telescopes have to deal with several constraints such as electromagnetic pollution and atmospheric dynamics, and space telescopes are certainly powerful but difficult to access, a lunar telescope could be the ideal compromise. While the latter would indeed have some advantages, there are many obstacles to achieving such a facility on the surface of the Moon.
The Moon, at first glance, seems like the ideal location for a telescope. There is virtually no atmosphere, which eliminates all light pollution problems. It's far from Earth, which should significantly reduce interference from signals produced by human activities. The very long nights would allow the same target to be observed continuously, up to 14 days in a row without interruption.
And since the Moon provides a solid surface for setting up a telescope, there is no need to resort to gyroscopes or reaction wheels to properly orient the direction of observation. However, the Moon is not an isolated object; it is part of the Earth-Moon system, itself orbiting around the Sun. This situation gives rise to several obstacles.
If the telescope is placed on the geosynchronous side of the Moon, the Earth will therefore face it permanently. This is an advantage for the transmission and reception of signals, controlling the telescope, as well as downloading data almost in real time, with the only limit being the speed of light. But it is also a disadvantage because terrestrial interference such as radio waves will always be a source of electromagnetic pollution against which the instrument must be protected.
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If the telescope is placed on the far side of the Moon, then this position provides a natural shield against terrestrial radio interference. But this implies that there would be no direct path for data transfer or signal transmission. This would therefore require the installation of an additional module such as a lunar orbiter or an antenna array up to the geosynchronous face.
Even if the Moon seems calm and sleepy to us, the reality is quite different. It is indeed the site of lunar earthquakes. There are four types:shallow, deep, thermal (caused by solar radiation) and meteoritic (caused by meteorite impacts). Some of these earthquakes can reach 5.5 on the Richter scale and last several tens of minutes. Such a phenomenon could greatly destabilize the telescope permanently, or even lead to its destruction.
In terms of its dynamics, the Moon experiences consecutive periods of 14 days and 14 nights, leading to extreme temperature differences. Thus, during the day, the lunar surface can reach 100°C and at night, -173°C. While space telescopes can regulate their temperature through passive or active cooling systems, a telescope must be cooled below the temperature of the wavelength it is observing, otherwise loud noise will pollute the signal.
These extreme temperatures would therefore be a huge obstacle for a lunar telescope observing in the UV, infrared or visible. Apart from the Earth and the Sun, the instrument could not observe anything else with sufficient clarity. Building a resistant telescope that can cope with these temperatures is a real technical challenge. Placed on the Moon in 2013 by Chinese lander Chang'e 3, the Lunar-based Ultraviolet Telescope (LUT) is currently the only existing lunar telescope.
For the vast majority of technological purposes, space is therefore a better choice than the lunar surface. However, the Moon offers a non-negligible advantage for a very specific field:radio astronomy. The Earth is a permanent source of radio waves propagating through the Solar System.
The dark side of the Moon presents a natural shield against this pollution. And according to astrophysicists, it is the best place in the Solar System to observe low-frequency radio waves. And the latter are rich in information because they could bear the cosmic signatures of events such as inflation or the formation of the first stars. On this side of the Moon, all terrestrial signals are blocked and therefore no electromagnetic contamination is possible; the perfect place for a lunar radio telescope.
Routing the data to the visible side, however, would require additional facilities such as a lunar module constantly in orbit, or a network of radio telescopes (or fiber optics) in order to be able to transmit the data correctly to Earth.
The biggest obstacle, however, remains the cost of such an operation. Transporting the equipment to the Moon, landing it and deploying it, already represents an enormous technological challenge. Even the currently smallest project, the Lunar Array for Radio Cosmology (LARC) — a simple array of a hundred antennas deployed over an area of two kilometers, would exceed the budget of the most expensive ground-based radio telescope array by $1 billion.
