Producer: Popular Science China
Production: Celestial Science Popularization
Producer: Computer Network Information Center, Chinese Academy of Sciences
I first heard about the James Webb Telescope in my childhood popular science book The Astronomical Enthusiast.
James Webb Space Telescope (Image: NASA)
After 25 years of preparation, dozens of extensions and billions of dollars in additional investment, according to NASA's official sources, the telescope was finally transported to the Kourou Launch Site in Guyana, France, and is expected to launch on December 25, 2021.
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The leading astronomical telescope, which began in the 1990s and was scheduled to launch in 2007, is tasked with exploring the boundaries of the universe and finding the infrared rays that remained at the edge of the universe at the beginning of the Big Bang.
Stud tens of billions of dollars to the heavens, what is it for?
In 1996, with the support of the Federal Space Exploration Program, NASA, the European Space Agency and the Canadian Space Agency launched an international cooperation project to study and launch the "Next Generation Space Telescope".
In September 2002, the program was renamed after former NASA Administrator James Weber, the famous James Webb Telescope project in astronomy.
James Webb Telescope (Image: NASA)
Weber works in space, 1.5 million kilometers from Earth at 2 o'clock in Lagrange. The reason why he chose such a far place was related to Weber's special mission.
In the study of astronomy, infrared observations are a crucial part of studying changes in the depths of space. The vacuum of the universe is littered with dust clumps formed by changes in the movement of celestial bodies, which absorb most of the visible light and obscure the large number of stars and planets hidden behind them. The infrared light emitted by the star can penetrate this cloud of dust, helping the astronomical community to reveal the mysteries hidden behind the dust.
Capturing infrared light emitted by stars in the universe is not an easy task, especially when the target of observation is relatively distant. Because the light source object moves away from the observer, the observed electromagnetic radiation frequency will be reduced, resulting in a "red shift" phenomenon, that is, the spectrum of the light source object will be reduced from the high-energy ultraviolet and visible light frequency band to the low-energy near-infrared band.
Therefore, observations of these distant targets, such as the universe's original galaxies, require ultra-high-precision infrared telescopes. This required the Webb telescope to be large enough and have an open design without a lens barrel.
Hubble's comparison of the visible light (left) and infrared view of the Lion's Head Nebula (right). Infrared view allows more galaxies to be observed (Credit: NASA)
When observing the first generation of stars of the Origin of the Big Bang, due to the existence of the redshift effect, visible light of 0.5 microns will redshift to the 10 micron band, and any visible light will have an effect on it. Since the peak of infrared light emitted by the Earth is also around 10 microns, this means that the Earth itself is a strong source of infrared light pollution.
At the same time, the telescope must operate around minus 220 degrees to avoid interference with infrared signals from temperature radiation from parts inside the telescope.
Lagrangian point is the point at which the gravitational attraction of planetary bodies in the solar system creates equilibrium, and objects operating at this position maintain their stable operating state and orbit in sync with the Earth. At this point, the Webb telescope's one-way solar shield is able to block light pollution from the sun, earth and moon at the same time, obtaining more accurate spectral observations.
Weber will orbit the Sun at 2 o'clock (L2) in Lagrange, 1.5 million kilometers from Earth, and keep pace with Earth. (Image source: NASA)
The Webb telescope is an optical telescope, and after successful launch, it will become the replacement and successor of hubble telescope. At the same time, Weber was able to explore longer optical wavelengths that would surpass Hubble's existing work.
However, since lagrange points are not within the operating range (400,000 kilometers) of any manned space vehicle, this means that in the event of an accident, the Weber telescope cannot be repaired. All launch, deployment and deployment tasks must be completed on their own and successfully, and once "shipped" for life, they will not be maintained.
The total investment in the Weber telescope has exceeded $8.8 billion, which is undoubtedly a "tens of billions" level gamble. In NASA researchers' expectations, the tens of billions of dollars worth of telescopes is expected to have a lifespan of five years.
Massive hardcore technology: Weber gathers the most extreme process crystals of human beings
In order to explore the origins of the Big Bang, the Weber telescope gathered the ultimate level of craftsmanship that humans can now achieve.
The Weber Telescope consists of an observation mirror, a five-layer solar shield in the size of a tennis court, and four top-of-the-line instruments, including observation equipment.
Its main lens diameter is 6.5 meters, limited by the size of the rocket, and this lens is subdivided into 18 hexagonal storyboards. In order to resist the deformation of the mirror surface at minus 220 degrees, the lenses are made of alkaline earth metal beryllium, a core material with extremely strong bending stiffness, extremely high thermal stability, excellent thermal conductivity and extremely low density.
At the same time, the polishing error of mirror machining is controlled within 10 nanometers, which is about equal to the length of dozens of beryllium atoms. On the surfaces of these lenses, the ultimate process of gold evaporation and re-solidification is used, and a standard 120-nanometer thickness of gold is coated. In order to correct the small deformation within 10 nanometers, the engineers also installed seven miniature motors behind the daughter lens, and ensured the extreme flatness of the lens by adjusting the curvature and orientation of the sub-mirror surface.
The main lens of the Weber telescope consisting of 18 shots (Source: NASA)
In order to maximize the isolation of infrared radiation pollution from the sun and the earth, engineers equipped the Weber telescope with a five-layer solar shield with an area of 300 square meters. This sun shield is composed of a silicon and aluminum film formed by electroplating, and its thickness is between about 25 microns and 50 microns, which is about 1/3 of the thickness of human hair.
These five layers of carefully processed solar shields can attenuate solar radiation nearly a million times and form a temperature difference of 300 degrees Celsius between the front and back, thus maintaining the operating temperature of the telescope at about minus 230 degrees Celsius.
5-story Webb Telescope Solar Shield (Image: NASA)
In addition, the device is equipped with a spectrometer for recording weak signals, a programmable micro-shutter camera capable of observing 100 targets simultaneously, a cooler capable of reducing temperature to near absolute zero, and a highly sensitive infrared sensor operating at low temperatures.
Upon arrival at the work site, the Weber Telescope would spend tens of days unfolding from a compressed package to a tennis court-sized behemoth.
The James Webb telescope, with its top processing technology and high cost, has become one of the top five projects in the history of human aerospace and astronomy. The extreme technical parameters make it proud of all previous space telescopes, and it is expected to further expand the current human observable cosmic radius of 46 billion light-years and push it to the edge of cosmic space-time.
This is close behind: China's future space optical telescope
Space optical telescopes are the absolute main force in the development of modern astronomy because of their pure observation environment and little interference.
Although China's deep space exploration started late, the speed of development should not be underestimated.
After decades of technological accumulation and exploration, the Chinese Academy of Sciences has successfully established a space science strategic pilot science project to launch 4 satellites, of which the first exploration satellite Wukong, which was launched in 2015, cost 100 million US dollars, successfully completing China's major breakthrough in the field of deep space dark matter exploration.
At the same time, the successive lunar exploration projects of the Celestial Eye FAST and Chang'e Projects also mark many new achievements in China's deep space exploration.
It is expected that by around 2024, China plans to launch the "Sky Survey" optical capsule platform and share the orbit with the Chinese space station. The optical telescope has a resolution similar to hubble and is expected to have a field of view 300 times that of hubble.
In addition, the Chinese Academy of Sciences has launched plans to launch the Enhanced X-ray Time-Varying and Polarization Observatory (eXTP) in 2027, planning to build the world's top flagship observatory. This will become a milestone in the research of China's astronomical telescopes and play a late-mover effect.
Obstacles are long, but human exploration of the universe continues.
bibliography:
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[3] Rieke, G. H., Wright, G. S., B ker, T., Bouwman, J., Colina, L., Glasse, A., ... & Waelkens, C. (2015). The mid-infrared instrument for the james webb space telescope, i: Introduction. Publications of the Astronomical Society of the Pacific, 127(953), 584.
[4] Gardner, J. P., Mather, J. C., Clampin, M., Doyon, R., Flanagan, K. A., Franx, M., ... & Wright, G. S. (2009). The James webb space telescope. In Astrophysics in the Next Decade (pp. 1-29). Springer, Dordrecht.