For “quietness” NASA wants to install a telescope on the back of the moon
Imagine a telescope with a receiving area three times larger than a 500-meter spherical radio telescope (FAST) on the moon. What will it look like?
Recently, Saputash Bandipahei of the National Aeronautics and Space Administration (hermes 2021 bags) Jet Propulsion Laboratory submitted a new proposal to the NASA Innovative Advanced Concepts Program (NIAC)-the Lunar Crater Radio Telescope Project, which is on the back of the moon A radio telescope with a diameter of 1 km is built in the crater. This intriguing plan immediately sparked heated discussion. Why build a telescope on the back of the moon? Why choose a radio telescope? What mysteries of the universe can this huge telescope help humans explore?
Earth signals cause interference to observations
According to different observation bands, astronomical telescopes can be divided into different types such as radio, optical, infrared, ultraviolet, X-ray, and gamma rays. It stands to reason that these different types of telescopes can be placed on the moon. Why is the radio telescope first considered in Bandipahei’s plan?
Liu Qinghui, a researcher at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences and chief engineer of the Tianma Telescope, told the reporter of Science and Technology Daily: “The radio telescope receives radio waves through its own antenna, and then observes the celestial bodies. If the radio telescope is moved to the moon, its observation ability will be better than that of the earth. Improved a lot.”
This is because there are many interference factors in the observation of radio telescopes on the earth.
First, there is an ionosphere over the surface. Ionization occurs when the sun illuminates the atmosphere. When the wavelength of the signal is relatively long, the ionosphere will block the signal. “Take FAST as an example. It is located in the earth’s atmosphere and the ionosphere. For signals with a wavelength and frequency below 70 megahertz (MHz), the observation effect will be greatly reduced.” Liu Qinghui said.
Secondly, too many artificial signals on the earth will cause interference to radio telescopes. “Man-made signals from mobile phone communications, radars, and satellites are millions of times stronger than signals from the universe, and have a great impact on the observation environment of ground-based radio telescopes.” Liu Qinghui said.
In contrast, telescopes of other bands can still “get quiet and good.” For example, optical telescopes are more afraid of bright light, but if they are “settled” in sparsely populated areas with dark sky backgrounds, the interference from man-made light sources can be reduced.
In addition, the size of the telescope is also a factor that has to be considered. Telescopes in other bands observe shorter wavelengths and are not as large as radio telescopes, so they are more compact and exquisite. Therefore, if these telescopes want better observation results, they can be sent directly to space. For example, the Hubble Space Telescope in space can obtain a clearer observation picture than the surface optical telescope. “If the Hubble Space Telescope is placed on the moon, although better observation results can be obtained, it is unnecessary, and the problem of soft landing on the moon is difficult to solve.” Liu Qinghui said.
In addition, the observation band of radio telescopes can range from meter to sub-millimeter, not as precise as optical and infrared telescopes. Relatively speaking, it is easier to build a radio telescope on the moon than an optical telescope.
The moon is a natural physical barrier
Then why choose the back of the moon instead of other areas?
Because the moon is a natural physical barrier, radio interference from the earth and satellites orbiting the earth can be shielded. “In this way, what the telescope captures is the signal from the observation target, which is more conducive to astronomers in capturing those weak signals and deepening their understanding of the universe.” Liu Qinghui explained.
In fact, on the earth, in the face of radio interference, scientists have also taken some remedial measures, the most important of which is “hide”. The first is to install the telescope as far away as possible to reduce radio interference. Second, try to keep the wavelength observed by the telescope away from the wavelength of radio signals such as mobile phones, radars, and satellites. “In layman’s terms, if the signal from the mobile phone occupies a certain band, the telescope observation will correspondingly avoid the celestial signal of this band. Through the measure of’cannot afford to hide’, it minimizes the influence of artificial radio on radio. The effect of telescope observation.” Liu Qinghui said.
But gaining also means losing. The signal received by the telescope is different, the information about the universe obtained is also different. Taking the observation of sunspots as an example, when scientists use optical telescopes to observe them, they will find that the sunspots are very dark, but when they use radio telescopes to see the sunspots, they will find that the electromagnetic field radiation of the sunspots is stronger than other areas of the sun.
Therefore, astronomers hope to achieve full-wavelength observation of the same observation target. It is naturally best to use radio, optics, ultraviolet, X-ray, gamma-ray and other telescopes of different wavelengths to scan the same target. Because different telescopes will see different scenes, only in this way can we have a deeper and more comprehensive understanding of the observed objects. Is the carambola shape an ellipse or a five-pointed star? Depends on different viewing angles.
The signal observed by a radio telescope overlaps with the signals of mobile phones, satellites, etc., and the observation effect will be very poor; if the band used by these interference sources is avoided, the purpose of reducing interference can be achieved, but it also means the observation of the radio telescope. There are blind spots that cannot cover certain bands of signals, so certain signals from the universe cannot be captured.
This is a pity for astronomers, and it also left a little blank in the field of astronomical observation.
Capture the ancient signals of the universe
Let the radio telescope land on the moon is a kind of idea to fill the gap.
According to the plan submitted by Bandipahei, a radio telescope with a diameter of 1 km is to be built on the moon. Compared with the FAST with a diameter of 500 meters, the diameter of this ultra-long wave radio telescope is doubled and the antenna receiving area is increased. 3 times larger, so you can observe cosmic radiation with a wavelength greater than 10 meters and a frequency lower than 30 MHz.
“This wavelength corresponds to the early dark ages of the universe. It is just the beginning of the universe. At that time, the cosmic signal was very far away from us. When it was transmitted to the earth, it was already quite weak. With the addition of radio interference on the earth, explore the universe during this period. The physical properties of this wavelength have become a problem.” Liu Qinghui said, because this ultra-long wave is reflected by the earth’s ionosphere, it cannot be observed on the earth, and humans know very little about the cosmic signal of this wavelength.
Experts said that due to the larger diameter of this telescope and its ability to get rid of all kinds of interference from the earth, its sensitivity may be greatly improved compared with FAST. The higher the sensitivity, the better the ability to capture weak signals from far away places.
However, ideals are full and reality is very skinny. In principle, astronomical telescopes need to see deep and far and see clearly, the larger the diameter, the better, and the less interference the better. However, in the actual process, due to the difficulty of the project and the high cost, the ideal configuration of the telescope is often not as expected.
Liu Qinghui said frankly that to build a radio telescope with a diameter of 1 km on the back of the moon, “I dare not think about the difficulties we face.”
This proposal describes how to build this telescope system. Find a suitable lunar crater with a diameter of 3 to 5 kilometers on the back of the moon, and use a spacecraft to transport the telescope and installation equipment to the moon by a biaxial vehicle. After the telescope and the biaxial vehicle land at the designated positions respectively, the telescope installation is completed after a series of steps such as deployment, connection, and fixing.
Since the back of the moon cannot be seen on the earth, it can only be controlled remotely through a relay star. “What kind of crater to choose? How to build the telescope softly? How to deploy the telescope after landing? How to ensure the continuous power supply required to build and maintain the telescope? These are all problems.” Liu Qinghui said, according to the existing conditions, only Build a rough, low-precision telescope with a long observation wavelength on the back of the moon.
“But, as former US President John F. Kennedy said: We chose to go to the moon, not because it is easy, but because it is difficult.” Liu Qing will say that the wonderful ideas satisfy the curiosity of human beings and finally push humans one step further. Step forward.
