James Webb: How the Most Advanced Space Telescope Works

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James Webb: How the Most Advanced Space Telescope Works
James Webb: How the Most Advanced Space Telescope Works
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The moment is approaching that all the astronomers of the world have been looking forward to for many years. We are talking about the launch of the new space telescope "James Webb", which is considered to be a kind of successor to the famous "Hubble".

Space telescope

Why are space telescopes needed?

Before proceeding to consider the technical features, let's figure out why space telescopes are needed at all and what advantages they have over complexes located on Earth. The fact is that the earth's atmosphere, and especially the water vapor contained in it, absorbs the lion's share of the radiation coming from space. This, of course, makes it very difficult to study distant worlds.

But, the atmosphere of our planet with its distortions and cloudiness, as well as noise and vibrations on the Earth's surface, is not a hindrance for a space telescope. In the case of the automatic Hubble observatory, due to the absence of atmospheric influence, its resolution is approximately 7–10 times higher than that of telescopes located on Earth. Many photographs of distant nebulae and galaxies that cannot be discerned in the night sky with the naked eye were obtained precisely thanks to the Hubble. For 15 years of work in orbit, the telescope has received more than one million images of 22 thousand celestial objects, including numerous stars, nebulae, galaxies and planets. With the help of "Hubble", scientists, in particular, proved that near the majority of the stars of our Galaxy there is a process of formation of planets.

But the Hubble, launched in 1990, does not last forever, and its technical capabilities are limited. Indeed, over the past decades, science has made great strides forward, and now it is possible to create much more advanced devices that can reveal many of the secrets of the universe. The James Webb will be just such a device.

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Features of "James Webb"

As we have already seen, full-fledged space exploration without such devices as the Hubble is impossible. Now let's try to understand the concept of "James Webb". This unit is an orbiting infrared observatory. In other words, its task will be to study the thermal radiation of space objects. Recall that all bodies, solid and liquid, heated to a certain temperature, emit energy in the infrared spectrum. In this case, the wavelengths emitted by the body depend on the heating temperature: the higher the temperature, the shorter the wavelength and the higher the radiation intensity.

Among the main tasks of the future telescope is to reveal the light of the first stars and galaxies that appeared after the Big Bang. This is extremely difficult, since light moving over millions and billions of years undergoes significant changes. So, the visible radiation of a star can be completely absorbed by a dust cloud. In the case of exoplanets, it is even more difficult, since these objects are extremely small (by astronomical standards, of course) and "dim". In most planets, the average temperature rarely exceeds 0 ° C, and in some cases it can drop below –100 ° C. It is very difficult to detect such objects. But the equipment installed on the James Webb telescope will allow detecting exoplanets, the surface temperature of which reaches 300 K (which is comparable to the terrestrial index), located more than 12 astronomical units from their stars and distant from us at a distance of up to 15 light years.

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The new telescope was named after the second head of NASA. James Webb was at the helm of the US Space Agency from 1961 to 1968. It was on his shoulders that control over the implementation of the first manned space launches in the United States lay.He made a great contribution to the implementation of the Apollo program, the purpose of which was to land a man on the moon.

In total, it will be possible to observe the planets located near several dozen stars "adjacent" to our Sun. Moreover, "James Webb" will be able to see not only the planets themselves, but also their satellites. In other words, we can expect a revolution in the study of exoplanets. And, perhaps, not even one. If we talk about the solar system, then there may be new important discoveries. The fact is that the sensitive equipment of the telescope will be able to detect and study objects of the system with a temperature of –170 ° C.

The capabilities of the new telescope will make it possible to understand many of the processes taking place at the dawn of the existence of the Universe - to look into its very origins. Let us consider this issue in more detail: as you know, we see stars that are 10 light years away from us exactly as they were 10 years ago. Therefore, we observe objects located at a distance of more than 13 billion light years in the form that they were almost immediately after the Big Bang, which is believed to have occurred 13.7 billion years ago. The instruments on the new telescope will see 800 million farther than Hubble, which set a record in its day. So it will be possible to see the Universe as it was only 100 million years after the Big Bang. Perhaps this will turn the ideas of scientists about the structure of the Universe. It remains only to wait for the telescope to start working, which is scheduled for 2019. It is assumed that the device will be in operation for 5-10 years, so there will be plenty of time for new discoveries.

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General device

To launch "James Webb" they want to use the "Ariane-5" launch vehicle, created by the Europeans. In general, despite the dominant role of the US space agency, the project can be called international. The telescope itself was developed by the American companies Northrop Grumman and Ball Aerospace, and in total experts from 17 countries of the world took part in the program. In addition to specialists from the US and the EU, Canadians have also made significant contributions.

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After launch, the spacecraft will be in a halo orbit at the L2 Lagrange point of the Sun - Earth system. This means that, unlike the Hubble, the new telescope will not revolve around the Earth: the constant “flickering” of our planet could interfere with observations. Instead, James Webb will orbit the sun. At the same time, to ensure effective communication with the Earth, it will move around the star synchronously with our planet. Removal of "James Webb" from the Earth will reach 1.5 million km: because of such a long distance, it will not be possible to upgrade or repair it like "Hubble". Therefore, reliability is at the forefront of the entire James Webb concept.

But what exactly is the new telescope? Before us is a spacecraft weighing 6, 2 tons. To be clear, the weight of the Hubble is 11 tons - almost twice as much. At the same time, the Hubble was much smaller in size - it can be compared to a bus (the new telescope is comparable in length to a tennis court, and in height to a three-story building). The largest part of the telescope is the sun shield, which is 20 meters long and 7 meters wide. It looks like a huge layer cake. For the manufacture of the shield, a special special polymer film was used, covered with a thin layer of aluminum on one side and metallic silicon on the other. Vacuum fills the voids between the layers of the heat shield: this complicates the transfer of heat to the "heart" of the telescope. The purpose of these steps is to protect from the sun's rays and to cool the telescope's ultrasensitive matrices down to –220 ° C. Without this, the telescope will be "blinded" by the infrared glow of its parts, and you will have to forget about observing distant objects.

Most striking is the mirror of the new telescope.It is necessary for focusing beams of light - the mirror straightens them and creates a clear picture, while color distortions are removed. James Webb will receive the main mirror, the diameter of which is 6.5 m. For comparison, the analogous figure for the Hubble is 2.4 m. The diameter of the main mirror for the new telescope was chosen for a reason - this is how much is needed to measure the light of the most distant galaxies. It must be said that the sensitivity of the telescope, as well as its resolution, depends on the size of the area of ​​the mirror (in our case it is 25 m²) that collects light from distant space objects.

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A special type of beryllium is used for the Webb mirror, which is a fine powder. It is placed in a stainless steel container and then pressed into a flat mold. After removing the steel container, a piece of beryllium is cut into two pieces, making mirror blanks, each of which is used to create one segment. Each is ground and polished and then cooled to –240 ° C. Then the segment size is refined, its final polishing, and gold is applied to the front part. Finally, the segment is retested at cryogenic temperatures.

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Scientists have considered several options for what a mirror can be made of, but in the end, experts opted for beryllium - a light and relatively hard metal, the cost of which is very high. One of the reasons for this step was that beryllium retains its shape under cryogenic temperatures. The mirror itself resembles a circle in shape - this allows you to focus the light on the detectors as compactly as possible. Had "James Webb", for example, an oval mirror, the image would be elongated.

The main mirror consists of 18 segments, which will open after the spacecraft is put into orbit. If it were solid, then it would be physically impossible to place the telescope on the Ariane-5 rocket. Each of the segments is hexagonal to make the best use of the space. The mirror elements are colored gold. Due to gilding, the best reflection of light in the infrared range is ensured: gold will effectively reflect infrared radiation with a wavelength of 0.6 to 28.5 micrometers. The thickness of the gold layer is 100 nanometers, and the total weight of the coating is 48, 25 grams.

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In front of the 18 segments, a secondary mirror is installed on a special mount: it will receive the light of the main mirror and direct it to scientific instruments located in the back of the apparatus. The secondary mirror is much smaller than the main one and has a convex shape. As is the case with many ambitious projects, the cost of the James Webb telescope turned out to be higher than anticipated. Initially, experts planned that the space observatory would cost $ 1.6 billion, but new estimates say that the cost could rise to $ 6.8 billion. Because of this, they even wanted to abandon the project in 2011, but then it was decided to return to it. implementation. And now "James Webb" is not in danger.

Scientific Instruments

The following scientific instruments are installed on the telescope to study space objects:

- NIRCam (near infrared camera)

- NIRSpec (near infrared spectrograph)

- MIRI (mid-infrared device)

- FGS / NIRISS (precision targeting sensor and near infrared imaging device and slitless spectrograph)

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NIRCam

The NIRCam is the main imaging unit. These are the "main eyes" of the telescope. The working range of the camera is from 0, 6 to 5 micrometers. The pictures taken by her will subsequently be studied by other instruments. It is with the help of NIRCam that scientists want to see light from the earliest objects in the Universe at the dawn of their formation.In addition, the instrument will study the young stars of our Galaxy, create a map of dark matter, and much more. An important feature of NIRCam is the presence of a coronagraph that allows you to see planets around distant stars. This will be made possible by suppressing the light of the latter.

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NIRSpec

With the help of a spectrograph of the near infrared range, it will be possible to collect information concerning both the physical properties of objects and their chemical composition. Spectrography is very time-consuming, but with the help of micro-gate technology, it will be possible to observe hundreds of objects in an area of ​​the sky of 3 × 3 arc minutes. Each NIRSpec micro-gate cell has a lid that opens and closes under the influence of a magnetic field. The cell has individual control: depending on whether it is closed or open, information about the investigated part of the sky is provided or, on the contrary, is blocked.

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MIRI

The mid-infrared instrument operates in the 5-28 micrometer range. This device includes a camera with a sensor, which has a resolution of 1024 × 1024 pixels, and a spectrograph. Three arrays of arsenic-silicon detectors make MIRI the most sensitive instrument in the James Webb telescope's arsenal. It is assumed that with the help of a device in the mid-infrared range, it will be possible to distinguish between nascent stars, many previously unknown objects of the Kuiper belt, the redshift of very distant galaxies, as well as the mysterious hypothetical planet X (aka the ninth planet of the solar system). The nominal operating temperature for MIRI is 7 K. The passive cooling system alone is not able to provide it: for this, two levels are used. First, the telescope is cooled down to 18 K using a pulsating tube, and then the temperature is lowered to 7 K using a heat exchanger with adiabatic throttling.

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FGS / NIRISS

FGS / NIRISS consists of two instruments - a precision pointing sensor and a near-infrared imaging device and a slitless spectrograph. In fact, NIRISS duplicates the functions of NIRCam and NIRSpec. Operating in the range of 0.8-5.0 micrometers, the device will detect the "first light" from distant objects, directing equipment at them. NIRISS also comes in handy for detecting and studying exoplanets. As for the FGS precision pointing sensor, this equipment will aim the telescope itself in order to be able to obtain better images. The FGS camera allows you to form an image from two adjacent areas of the sky, the size of which is 2, 4 × 2, 4 arc minutes each. It also reads information 16 times per second from small groups of 8 × 8 pixels, enough to identify the corresponding reference star with a 95% probability at any point in the sky, including high latitudes.

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The equipment installed on the telescope will make it possible to have a high-quality connection with the Earth and transmit scientific data at a speed of 28 Mbit / s. As we know, not all research vehicles can boast of this capability. The American probe "Galileo", for example, transmitted information at a speed of only 160 bps. This, however, did not prevent scientists from obtaining a huge amount of information about Jupiter and its moons.

The new spacecraft promises to become a worthy successor to the Hubble and will help answer questions that remain a mystery to this day. Among the possible discoveries of "James Webb" - the discovery of worlds similar to Earth and suitable for habitation. The data obtained by the telescope can be useful for projects considering the possibility of the existence of alien civilizations.

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