- 3391 - JAMES WEBB - space telescope? The James Webb Space Telescope will change our view of the universe. The new telescope will peer deeper into the most ancient universe 13.4 billion lightyears away.
--------------------- 3391 - JAMES WEBB - space telescope?
- When scientists planned and designed the Hubble Space Telescope, the most groundbreaking astronomical observatory of its era, there were many things about the universe they didn't know. One of these unknowns was that stars and galaxies existed already a few hundred million years after the Big Bang.
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- Galaxies formed much earlier than expected. It became obvious that another space observatory will be needed to get to see those early stars and galaxies. Those that had lit up the universe after hundreds of millions of years of darkness that followed the Big Bang when the expanding space was only filled with hydrogen atoms.
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- The power of infrared eyes was needed. Infrared detectors that would be able to collect the faint light coming from those early stars and galaxies more than 13 billion light-years away.
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- Hubble was built to detect visible and ultraviolet light. These early galaxies do emit visible light, but because of their distance, the wavelength of this light gets stretched into the infrared part of the electromagnetic spectrum by the redshift.
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- The “Near Infrared Camera and Multi-Object Spectrometer” (NICMOS) was the first infrared detector fitted on the Hubble Space Telescope during its second servicing mission in 1997. NICMOS, consisting of three infrared detectors, each of which had 256 by 256 pixels, opened the first door for Hubble into the infrared universe.
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- The “James Webb Space Telescope” (JWST), will orbit the sun 1 million miles from Earth. The detectors have 2,000 by 2,000 pixels. There are many more infrared pixels than Hubble had optical pixels when it was launched.
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- The James Webb's giant mirror will feed the light of stars and galaxies into four cutting edge instruments designed not only to take images, but also to analyze the chemical composition of the near and distant universe.
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- This is done with a technique known as “spectroscopy“, which looks at how matter in the universe absorbs light. As different chemical elements absorb light at different wavelengths, astronomers will be able to reconstruct what stars, nebulas, galaxies and planets within James Webb's sight are made of. The instruments are a factor 10 to 100 times better than anything previously available.
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- Where the Hubble Space Telescope, or the recently retired infrared telescope “Spitzer“, could provide only a rough estimate of an ancient galaxy's age and chemical composition, Webb will deliver with precision, including the Wide Field Camera 3.
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- If we are seeing that material some 500 million years after the Big Bang, it must have been made even earlier by stars we haven't yet seen. Big stars form and die quickly, in only a few million years, so after 500 million years, you may have had lots of generations of massive stars.
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- Astronomers know that the early universe had a very different chemical composition from what we see today. It consisted only of hydrogen, helium and a little bit of lithium. All the other chemical elements that we see now, including those that make life possible, were cooked up throughout eons inside those stars.
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- A lot of the chemical synthesis in the universe is around massive stars when they explode, or low mass stars in their final stages of evolution.
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- The spectroscopes aboard the James Webb will be able to probe the chemicals in those early galaxies, seeing what was cooking inside individual stars and what they fertilized the wider cosmos with when they exploded in powerful supernovas.
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- While the James Webb Space Telescope and the Hubble Space Telescope are frequently compared, their images will be quite different, revealing different aspects of the universe. While Hubble's strength is imaging the visible universe, Webb's infrared superpowers will enable the telescope to see through dust right into the heart of nebulas, galaxies and star-forming regions that are hidden from Hubble's view.
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- The Kuiper Belt is a repository of comets, asteroids and other debris that encircles the outer solar system beyond the orbit of Neptune. It's a dark and cold region that is very difficult to explore because these objects reflect very little light.
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- JWST can do fantastic spectroscopy on the Kuiper Belt objects. These objects are really cold, they don't reflect much light, so you need a big infrared telescope. We know they have ices and various molecules on their surfaces, and we hope to be able to see that.
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- The planets have atmospheres that have various molecules in them. Things like carbon dioxide, oxygen and nitrogen. One of JWST's instruments, the “Near Infrared Camera” (NIRCAM) is fitted with extra implements called “coronographs“, which block out the light of a star to see more clearly what is happening around it.
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- The Near Infrared Camera (NIRCAM) will be crucial for detecting the light from the earliest stars and galaxies. It's not just a simple infrared camera, but is fitted with some extra implements called coronographs. The coronographs will enable astronomers to block out the light of a star and look at what's happening around it, which makes it great for discovering orbiting exoplanets.
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- The “Near InfraRed Spectrograph” (NIRSpec) is the main tool for cracking the chemistry of the universe. It will split the light coming from the distant universe into spectra, revealing the properties of the observed objects, including their temperature, mass and chemical composition.
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- Because some of these objects are extremely distant and the light coming from them will be extremely faint, the Telescope will have to stare at them for hundreds of hours. To make those observations more efficient, NIRSPec will be able to observe 100 such distant galaxies at the same time.
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- The spectroraph basically lets you open little doors and let the light through from one galaxy, but then block off all the light from everything else. But, you can open 100 doors at once
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- The “Mid-Infrared Instrument” (MIRI) is a combination of a camera and a spectrograph, but unlike the previous two, it observes in the longer wavelengths of the mid-infrared part of the electromagnetic spectrum, which will make it good for studying everything from comets and asteroids at the outskirts of the solar system to newly born stars and distant galaxies.
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- Sporting the biggest mirror of any space-bound telescope ever launched, JWST is tasked with collecting infrared light from some of the most distant stars and galaxies in the Universe. With this capability, the telescope will be able to peer far back in time, imaging some of the earliest objects to have formed just after the Big Bang.
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- JWST will be traveling to an extra cold spot located 1 million miles from Earth, where the spacecraft will live out its life, collecting as much infrared light as it can.
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- The telescope has a light-collecting mirror that’s more than 21 feet wide. For comparison, Hubble’s mirror is just under 8 feet and it’s been responsible for imaging some of the most iconic objects we’ve ever seen in the Universe.
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- To assemble this massive mirror engineers had to build it in pieces. It’s made out of 18 hexagonal segments of the lightweight element beryllium, each one roughly the size of a coffee table. Together, the segments must align almost perfectly, moving so precisely they are aligned within a fraction of a wavelength of light, which is about 1/10,000th the diameter of a human hair.
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- One key feature of the mirror is that it is coated in a layer of gold about 200 times thinner than the average human hair. The gold is what allows JWST to see in the infrared. Because the Universe is expanding, the farthest objects away from Earth are speeding away much more rapidly than objects that are nearer to us.
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- The faster they sprint away, the more their light gets stretched, shifting away from the visible part of the spectrum and toward the infrared. With its gold mirrors, JWST should be able to see the infrared light from galaxies that has crossed 13.6 billion light-years to get to Earth, and taken that much time.
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- Light from objects 13.6 billion light-years away will have taken that many years to reach the telescope’s mirror. Since we think the Universe is roughly 13.8 billion years old, that means these objects were around just 100 to 250 million years after the Big Bang.
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- Observing in the infrared is incredibly tough. Infrared light is associated with heat, which is emitted by everything with a temperature above absolute zero. JWST can’t live in our planet’s orbit or anywhere on the ground; the heat from Earth and its atmosphere would disrupt the observations.
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- Even the telescope itself needs to be extra cold so that it doesn’t produce too much heat and throw off its own observations. That’s why JWST is being sent to a place 1 million miles from our world, known as a Lagrange point between the Earth and the Sun, where the pull of gravity and centrifugal forces are just right for the telescope to remain in a stable orbit. At this Lagrange point, JWST will stay at more or less the same distance and position from Earth at all times.
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- Even at this faraway distance, heat from the Sun is still an issue. To stay extra cool, JWST is equipped with a sunshield. It’s made up of five ultra-thin layers of a material called “Kapton“, each the size of a tennis court stacked on top of each other. The outermost layer will always face the Sun and reflect most of its heat, operating at a scorching 230 degrees Fahrenheit. But each successive layer will be cooler and cooler so that JWST’s instruments stay cryogenic, operating at about minus 370 degrees Fahrenheit.
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- JWST launched on December 25th . Its ride to space, the Ariane 5 rocket, has been Europe’s premier rocket for roughly the last two decades. In addition to being a highly capable rocket with a strong launch record, the selection of Ariane 5 also brings NASA’s European partners into what is considered a truly global mission.
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- The launch itself should last roughly 26 minutes before JWST separates from the Ariane 5 rocket.
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- The telescope’s complicated unfurling process is next. Once freed from the rocket and en route to its destination 1 million miles from Earth, the spacecraft will slowly unfurl like a mechanical flower.
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- The first thing JWST must do right after launch is deploy its solar panel to start gathering energy from the Sun needed to power the entire spacecraft. During its next day in space, it’ll deploy its high-gain antenna needed to communicate with Earth.
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- After that, the reverse origami begins. JWST will change its shape and start to deploy its delicate sunshield, a process that is set to last for days. If that goes well, then the telescope will fully deploy its primary mirror.
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- A little less than a month out from launch, the telescope will fire its onboard thrusters to put itself into its final position at its intended Lagrange point. The telescope will have to spend some time cooling down when it reaches its final orbit, and then engineers will need some months to test out all the instruments to see if they work properly. But JWST could be taking its very first breathtaking images as soon as this summer, 2022.
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- The enormous, golden mirror is made up of 18 smaller mirrors that together will allow mission teams to use the scope to measure light from extremely distant galaxies, billions of light-years away. Webb's primary mirror spans 21 feet, 4 inches across and is made up of 18 hexagonal mirror segments measuring 4.3 feet in diameter. Webb also has a small secondary mirror that measures just 2.4 feet across.
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- The James Webb Space Telescope will rest in space at Lagrange Point 2, a spot directly behind Earth from the sun's perspective. There, the instrument will make powerful observations of far-off celestial bodies; the telescope's infrared view will be able to penetrate interstellar dust.
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- The space telescope's signature honeycomb mirror segments are shaped as such because the pieces can fit together in a way that makes it possible for the primary mirror, made up of all of the pieces, to be a roughly circular shape.
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- If the segments were circular, there would be gaps between them. A roughly circular overall mirror shape is desired because that focuses the light into the most compact region on the detectors.
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- In addition to its shape that helps it to pick up light from very far away, Webb's mirror operates with the help of what are called actuators. Actuators are tiny mechanical motors that help the mirror to focus on far-off objects.
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- There are six actuators on the back of each mirror piece that can move each piece of the mirror in minuscule amounts very slowly, allowing the mission team to fine-tune Webb's view. They can move extremely precise, fractional wavelengths of light.
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- Aside from its hexagonal shape and enormous size, Webb's most distinctive feature is the shiny, bright gold color of its mirror. Gold is extremely reflective which is readily apparent in its brilliant appearance.
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- Webb's mirrors are said to be 98% reflective. While Webb's mirror segments are coated in gold, they are not made of solid gold. They are actually constructed from beryllium, a strong but lightweight metal. Each mirror piece weighs about 46 pounds on Earth. In addition to being extremely durable while comparably lightweight, beryllium can also hold its shape at the extreme cold temperatures that Webb will need to operate at.
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- Since infrared light is essentially heat, if Webb were too warm it wouldn't be able to detect infrared light past the glow of its own mirror. Webb's mirrors need to be at about minus 364 degrees Fahrenheit to work as intended.
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- Some 30 years in the making and with an eventual price tag of $10 billion, the James Webb Space Telescope is simply not allowed to go wrong.
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- With the James Webb Space Telescope, rescue missions are impossible and therefore no failures are allowed. That's why JWST is so expensive. Because we've spent two decades building and testing every single piece a million ways to do everything to make sure it doesn't have problems.
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- Infrared radiation is essentially heat, and can be detected with special sensors that are different from those detecting visible light. Since the stars and galaxies that JWST was designed to study are so far away, the incoming signals are also extremely faint.
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- The Telescope will be far away from Earth , about 1 million miles away. That's more than four times farther than the moon. The telescope will orbit the sun, while simultaneously making small circles around the so-called Lagrange point 2 (L2),
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- L2 is a point on the sun-Earth axis constantly hidden from the sun by the planet. At L2, the gravitational pulls of the sun and of Earth keep the spacecraft aligned with the two big bodies.
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- The largest piece of the spacecraft is its tennis court-sized deployable sunshield made of five layers of an aluminum-coated space blanket material, kapton. The sunshield is by far the most mission-critical thing. If it doesn't fully deploy, the telescope doesn't work.
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- The sunshield is not a simple parasol; a lot of clever engineering went into its design. The five layers of the ultralight kapton material are precisely spaced so that the heat absorbed by each layer is perfectly radiated away from the spacecraft through the gaps. While superthin and ultralight, the material is also incredibly sturdy, enough to survive bombardment by meteorites.
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- The Hubble Space Telescope, with its mirror 7.8 feet (2.4 meters) in diameter, couldn't detect those distant early galaxies even if it were as cold as Webb. Webb's mirror collects six to seven times more photons in a given amount of time than Hubble. Some of the deep field work that Hubble has done, they would look in a particular field for a couple of weeks. "Webb can reach that kind of sensitivity limit in seven or eight hours.
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- The Hubble Space Telescope, which measures 44 feet long and at most 14 feet across, fitted into the 60-foot long and 15-foot wide payload bay of the space shuttle Discovery was deployed in 1990.
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- For Europe's Ariane 5 rocket, the telescope's mirror is more than 3 feet too wide to fit. So for Webb, getting to space requires folding and unfolding. The mirror and the sunshield, as well as the usual solar arrays and antennas, must all be neatly stowed for the telescope's launch.
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- The mirror, made of 18 hexagonal segments, each 4.3 feet across, collapses like an origami for the launch. Once in space, these elements unfold, locking together. The jigsaw puzzle is so finely tuned that once the mirror is fully aligned, the seams between the individual segments will be perfectly smooth.
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- At the backs of the 18 hexagonal mirror segments are small motors that delicately press onto the plates, shifting and bending them with extreme precision until they create one giant, perfectly smooth mirror. That means movement at the level of nanometers.
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- There are 25.4 million nanometers in one inch. "It's incredibly complicated. And that's why it takes so long for us to actually commission the telescope. The first images won't come until the summer of 2022 because it takes that long to line everything up.
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- Webb's mirror is about an order of magnitude lighter per unit area compared to Hubble's mirror. Each of the 18 hexagonal segments, made of ultralight metal beryllium, weigh only 46 pounds .
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- The entire spacecraft, despite its enormous size, weighs only 6.5 tons compared to the 11.1 tons of the smaller Hubble.
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- The surface of the mirror is plated with gold, giving it the signature yellow tint. The golden color was chosen because it's the best for reflecting infrared radiation, much better than white or silver.
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- The light reflected by the giant mirror is then concentrated onto the 30-inch secondary mirror that sits opposite the large mirror attached to a foldable tripod that must also deploy in space. From there, the light enters through an opening at the center of the large mirror into the telescope, where a tertiary mirror sends it to the detectors.
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- There are over 300 ways that the new James Webb Space Telescope could fail.
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- It's going to be very, very intense.
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December 29, 2021 JAMES WEBB - space telescope? 3386
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