Why not build a space telescope right on the moon?


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If you want to get the most virgin, cleanest pictures of our Universe, it would be best to leave the Earth. Here, on our planet, you can find a whole bunch of all sorts of effects that interfere with our visualization capabilities. Light pollution limit our range of vision; the atmosphere hurts our resolution and our ability to see clearly; clouds and weather prevent us from collecting light; The sun and the Earth themselves block a huge part of our field of view from any point on Earth.

Yet observatories such as Hubble, Chandra, Fermi, Spitzer, and others have demonstrated how effective space telescopes can be. The types and data that they brought back to Earth taught us much more things than they could have learned from similar observations made on Earth. Why not place a telescope on the moon then? Believe it or not, this is a terrible idea. She has only one positive point. And that’s why.

Telescope on the moon: is it bad?

The moon, at first glance, may seem like an ideal place to house a telescope. There is practically no atmosphere on it, which eliminates any fear of light contamination. It is far from the Earth, which should significantly reduce interference from any signals produced by humans. Super long nights also mean that you can observe the same target continuously for 14 days without interruptions. And since you have solid ground, you don’t need gyros or wheels for guidance. It would seem that everything is cool.

But when you start thinking about how the moon revolves around the earth, about the whole moon-earth system that revolves around the sun, you begin to understand some of the problems that this whole idea inevitably faces.

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First, if you place your telescope on the moon, which side will you choose: the near or far? Each of them has its drawbacks.

If you place your telescope on the near (facing the Earth) side of the Moon, you will always see the Earth. This means that you can send and receive signals, control your telescope and load data with virtually no delays, and the only limit will be the speed of light. But it also follows from this that interference from the Earth, such as broadcast signals, will always be a problem that you will have to reckon with.

On the other hand, if you are on the far side of the moon, you effectively protect yourself from everything that comes from the Earth, but you also have no direct way to transfer data or maintain a communication signal. It will be necessary to install an additional mechanism, an orbiter, or to conduct communications to the near side in order to control the telescope.

In any case, you will have a lot of problems with which you have to fight and which usually is not present in the abyss of interplanetary space. The two largest are:

Moonquakes. Do you think this is the moon directing the tides on Earth? The tidal forces that the Earth exerts on the Moon are 20 times stronger than the tidal forces that the Moon exerts on the Earth. They are enough to provoke non-sickly moonquakes on the satellite.

Temperature difference. Due to the tidal blockage of the Moon by the Earth and its extremely slow rotation, it basks in the sunlight almost constantly for 14 days and then plunges into total darkness for 14 days. Daytime temperatures can reach more than 100 degrees Celsius, and at night the moon cools down to -173 degrees.

While the space telescope can control its temperature through active or passive cooling (or a combination of both), the telescope must cool below the temperature of those wavelengths it is trying to observe, or the noise will cover the intended signal. This would be a huge disadvantage for ultraviolet, optical or infrared astronomy, if at least one of them would try to develop on the moon.

moo-650x358 Science  Why not build a space telescope right on the moon?


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Designing a telescope that can withstand these extreme temperatures and still work is a very difficult task. Not surprisingly, the only telescope on the moon we have is the ultraviolet telescope on the near side of the traveler, which works at wavelengths on which The earth’s atmosphere absorbs almost all of the light.

For most applications, sending into space would be a better option than the Moon. The lunar surface, judging by the extreme temperatures and difficulties of communication with the Earth, offers more disadvantages than the presence of a surface on which to build or do something else.

But there is one very specific application that the Moon offers: radio telescopes. The earth is an incredibly “radio-loud” source, for natural and human reasons. Even in space, signals that come from the Earth permeate the entire Solar system. But the Moon provides tremendous immunity to the Earth’s radio signals: the far side of the satellite literally uses the entire lunar body as a shield.

Earlier this year, cosmologist Joe silk wrote the following:

“The far side of the moon is the best place in the internal Solar system to monitor low — frequency radio waves-the only waves that can detect weak traces left by the Big Bang in space. Terrestrial radio telescopes encounter too much interference from electromagnetic pollution caused by human activity, such as Maritime communication and short-wave broadcasting, to receive a clear signal, and The earth’s ionosphere blocks the longest waves.”

We could detect signals of inflation, the first stages of the Big Bang, and the formation of the first stars in the Universe with a lunar radio telescope. While there is hope to do so on Earth or in space, the moon’s far surface offers more sensitivity because it is protected from the Earth by a screen than any other option.

Nowadays, when any spacecraft goes beyond the moon, when viewed from the Earth, it falls into a radio blackout. The fact that radio waves cannot pass through the moon means that no signals can be sent there or received during this period of time. Orbital satellites, any long-range stations or Rovers, and even Apollo astronauts lose the ability to communicate with the Earth.

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But it also means that they are protected from all kinds of polluting radio signals that are born on Earth. GPS communications, microwave ovens, radar, cellular and Wi-Fi signals, and even digital cameras are among the many ground-based sources polluting radio stations. But on the far side of the moon, all sources of interference are 100% blocked. It is the purest environment for radio astronomy, which you can imagine.

Dr. Jillion Scudder also notes that this idea has its drawbacks. Data transmission requires something like an orbital device that can communicate with both the Earth and the telescope. A telescope or array of radio telescopes should be built and deployed on the moon and linked together if talking about an array (and this option is preferable). Alternatively, cables could be routed to the near side to transmit data to the Ground.

And the biggest problem will be the cost. Transporting material to the moon, landing on the lunar surface, deploying, and more is a tremendous job. Even the most modest proposal, the Lunar array for radiocosmology (LARC), consists of more than a hundred antennas with a simple design, distributed over a two-kilometer range. The project will cost $ 1 billion and will be the most expensive radio array in the history of the Earth, if built.

Almost any sensible proposal in astronomy implies that space is much better than the lunar surface to accommodate the telescope. Temperature changes occur at all points of the moon. Only radio astronomers could gain an advantage by placing a telescope on the far side of the moon, but this opportunity would cost a great deal.

Until we find a way to cut costs or come up with something better, it’s highly unlikely that we’ll ever see a lunar telescope surpassing other options. The universe isn’t going anywhere, it’s waiting for us to reveal its secrets.

 


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