The visible time machine. The telescopes. When we look into space, we are actually looking back in time. Just to give an example, the light takes 2.5 sec to reach us from the moon i.e. we are looking at the moon as it was 2.5 seconds ago. Similarly, if a galaxy or a star is at a distance of some 10 billion light-years, when we look at them, we can see it as it was 10 billion years ago and we donβt have an idea on how it is in the present. It might be gone, but still, itβs visible. We are literally looking at ghosts.
What are we trying to look at in space? Well, everything(almost). We, humans, see under the wavelengths of 380 to 740 nm which comes under the visible spectrum in the broad range of the electromagnetic spectrum. There are plenty of other wavelengths that we need to look through to know the universe. Like Infra, radio, cosmic, gamma waves. Thereβs something called a Doppler shift. When the objects move far away from us, they appear to be in red colour. When the object closes by us they appear blue. So, when the object is much farther away, the objects fade from red to black( on visible spectrum). To view whatβs beyond, we use the infrared spectrum. Even infrared is of broad range, but for scientific purposes, we differ from range to range. Until date, we know the wonders what Hubble space telescope has done. We know how it shone light (literally) upon the scientific community. In fact, without Hubble, we cant prove the existence of dark energy. So, how long with the Hubble last? well, it was actually made to be operable for 15 years since its launch (which was in 1990). Despite the recent repairs, Hubble is expected to serve for 5 more years.
So, what after Hubble? JAMES WEBB SPACE TELESCOPE. Expected to launch on March 20, 2021, JWST could lead through a series of breakthroughs. It is one of its kind. As far as we know, we were able to look back at 13.8 billion years. Itβs just that the Hubble was able to capture the light that far. But what might, exists beyond that? Weβve found a few planets and stars which were 14 billion light-years old. What might be the starting point? How far can we look back into time?
JWST is an extremely complicated telescope and not to mention, itβs an engineering marvel. Nothing of its kind has ever been built on this scale and no mission of this scale has ever been attempted. Hubble orbits at 547 kilometres above the earthβs surface while JWST would be orbiting at a point known as Lagrange 2. Nothing complex, just have a look at this
Out of these 5 L1, L2, L3 are unstable; i.e. we need to maintain the position by some thrusters to keep that satellite in the position.
If theyβre unstable, why go for L2?
- The combined gravitational forces of the Sun and the Earth can hold a spacecraft at this point so that in theory it takes no rocket thrust to keep a spacecraft in orbit around L2.
- The distance between L2 and earth is 1.5 million km. whereas, the distance from L4/L5 to earth is 1AU= 150 million km.
- Since its closer when compared to L4/L5, light takes only 5 seconds to reach JWST from earth. Whereas L4/L5 takes 9 minutes.
- L2 earth- moon is the area where the sun, moon and the earth are scaled into tiny objects for the telescope so that it can have a clear view at the rest of the universe.
- L1, its for the earth-sun orbit.
Since itβs located at 1.5 million km from earth, itβs literally impossible to go back and repair the JWST if there is ANY problem. This is a one-shot mission. One go, everything should be perfect. Every instrument on the board should be working without any delay or without any error. It needs to work under the given speed. The shield takes (ill brief about this below) nearly 3 days to be completely deployed, it is fast, it needs to happen fast because; did I mention? Its -260 C out there at that point. Metal parts can easily be frozen. Timing is very critical. This is a massive project. More than 1000 people from 17 countries are working on this. This project began in 1996 and the JWST design is built to last for 5 years but the goal is for 10 years. Just imagine the scale at which the project is taking place.
Now that weβve seen where it is and what it might do, letβs look at the design and components of the JWST.
JWST carries 4 major science instruments.
NIRSpec
Near-Infrared Spectrograph, provided by ESA with some elements provided by NASA’s Goddard Space Flight Center. A wide field (3.4′ Γ 3.6′) multi-object near- infrared spectrometer covering wavelengths 0.6Β΅m – 5 Β΅m at spectral resolutions of R~100, R~1000 and R~2700.
MIRI
Mid-Infrared Instrument, provided by a partnership composed of ESA, a consortium of nationally funded European institutes, NASA’s Jet Propulsion Laboratory, and NASA’s Goddard Space Flight Center (GSFC) A combined mid-infrared camera (1.3′ Γ 1.7′) and spectrograph (R~100 and R~3000) covering wavelengths from 5 Β΅m to 28.3 Β΅m. It also includes a coronagraph.
NIRCam
Near-Infrared Camera, provided by the University of Arizona. A two-channel wide field (2.2′ Γ 4.4′) near-infrared camera covering wavelengths 0.6 Β΅m – 5 Β΅m with a large selection of filters. NIRCam will also provide key measurements for the in-orbit adjustment of the shape of JWST’s primary mirror segments.
FGS/NIRISS
Fine Guidance System/Near-InfraRed Imager and Slitless Spectrograph, provided by the Canadian Space Agency. NIRISS is a wide-field (2.2′ Γ 2.2′) imager capable of 1.0 Β΅m – 2.5 Β΅m slitless spectroscopy. It also includes a spectroscopic observing mode optimized for exoplanet spectroscopy.
The four instruments are housed within the JWST payload module called the Integrated Science Instrument Module (ISIM)
The JWST is too big that it canβt fit in any rocket. The primary mirror is of 6.5 meters or 21 feet 4β.
There are 18 hexagonal mirrors which make up the primary mirror. Each of those hexagonal mirrors is of 1.32 meters or 4.3 feet. The mirror is bent and is made to fit in the rocket. (the origami mirror).
When deployed in its orbit. The mirrors should unfold themselves equally precise to nanometres. To observe in the IR region, webb mirrors should be cryogenic i.e. the mirrors should be very cold, -220 degrees C cold. Webb is what is known as a three mirror anastigmat telescope. In this configuration, the primary mirror is concave, the secondary is convex, and it works slightly off-axis. The tertiary removes the resulting astigmatism and also flattens the focal plane. This also allows for a wider field of view.
The mirrors are made of beryllium. They chose that metal because its strong and light. We cant use beryllium to make all telescope because they are extremely hard to polish. The gold coating on the mirrors was applied by the processes called vacuum deposition. They just used 3 grams of gold!. Through vacuum deposition, maximum reflection can be achieved. Through spray paint or other techniques, we cant achieve that, as the layer is deposited in such a way that even the Nano metric scales are covered.
The James Webb Space Telescope will observe primarily the infrared light from faint and very distant objects. In order to be able to detect those faint heat signals, the telescope itself must be kept extremely cold. To protect the telescope from external sources of light and heat (like the Sun, Earth, and Moon) as well as from heat emitted by the observatory itself, Webb has a 5-layer, tennis court-sized sunshield that acts like a parasol providing shade. The sunshield will be in a position such a way that itβs always between sun/earth/moon and the telescope. This allows the telescope to be below 50K (-223 C). each successive layer is cooler than the before. The temperature difference between first and the last layer is nearly 600 C. Each of the layers are incredibly thin. Each layer of the sunshield is incredibly thin. Layer 1 will face the sun and is only 0.05 millimetres (0.002 inches) thick, while the other four layers are 0.025 mm (0.001 inches). The thickness of the aluminium and silicon coatings is even smaller. The silicon coating is ~50 nanometres (nm) (1.9 micro inches) thick, while the aluminium coating is ~100 nm (3.93 micro inches) thick. The membrane material is tough, but if it gets a small tear or hole, the hole could become much larger. So, there is a special process called a Thermal Spot Bond (TSB) – areas where each layer are melted together. In addition, reinforcing strips of membrane material are Thermal Spot Bonded to the parent membrane about every 6 feet or so, forming a grid pattern of “rip-stops.” And this is the major reason why the JWWST launch was delayed. During the testing process, there was a tear in one of the layers. Due to that, they had to change the whole of the sheet.
Microshutters: its is a new technology which was developed specifically for JWST. They are basically tiny windows with shutters that each measure 100 by 200 microns, or about the size of a bundle of only a few human hairs. They can observe upto 100 objects at a time. This is a major key for JWST.
The backplane, the spine or the structure of the telescope was incredible. This structure is also designed to provide unprecedented thermal stability performance at temperatures colder than -400Β°F (-240Β°C). At these temperatures, the backplane was engineered to be steady down to 32 nanometres, which is 1/10,000 the diameter of a human hair! And remember the origami style? Yes , its difficult .
Through JWST We can see the heat that was there at about 380,000 years after the expansion of the universe began 13.8 billion years ago (which is what we refer to as the Big Bang). Big bang is something we cant see but the major aim of the project is not that. Its main aim is to observe the first galaxies and the stars.
Besides that, there are plenty of chances that JWST might find exoplanets which are much more similar to earth. This is a true blessing for astrobiology and astronomy.
About the rocket, JWST will be launched on Ariane 5 rocket.
This is one incredible telescope we will be seeing. As said before, due to the location at which this telescope orbits, its impossible to do any repairs. Even the slightest mistake can cost the whole mission unimaginable disaster. The JWST will deploy on its 30th day after covering the 1.5 million km journey. This is one hell of a project.
There are plenty more videos and websites explain about JWST and its status. Links are below. Status right now? JWST is ready and will be launched on date set. Its going through final test procedures.
Launch and Deployment video:
Thanks for the read. Do share if you like .
Links: https://jwst.nasa.gov/index.html , https://sci.esa.int/web/jwst/-/33079-summary , https://en.wikipedia.org/wiki/James_Webb_Space_Telescope , https://www.youtube.com/watch?v=UmvnwzhDhCE
Cosmic Writer 