James Webb Space Telescope
By Azka Amjad
JAMES WEBB SPACE TELESCOPE
Abbreviations used in article:
JWST: James webb space telescope
IR: infrared
ISIM: Integrated science instrument module.
HISTORY:
The construction of JWST was started in 1996 by collaboration of NASA, ESA(European Space agency),CSA (Canadian space agency). And it was planned to launch in 2007 and its budget was fixed to be 500 million dollars. But in 2005 many changes were made in its initial design and its launch date was delayed. Its construction was completed in 2016at the expense of about 10 billion dollars. Then some initial tests were conducted, which continued till 2019and it was planned to launch it in March 2021.But due to some technical issue its launch was again delayed till December 2021 and finally it was launched on 25 december at 12:20 UTC by an Ariane 5 rocket from European Space Agency's launch site in Kourou, French Guiana.
MAIN PARTS OF JWST:
•PRIMARY MIRROR
It consists of 18 hexagonal segments made of beryllium metal coated with gold to capture near infrared light . Its diameter is 6.5 meters.
Credit: Axios
•SECONDARY MIRROR
It reflects the light gathered from the primary mirror to science instruments.
Credit: Axios
• ISIM Integrated science instrument module
It contains all of Webb's cameras and science instruments.
Credit: jwst.nasa.gov.pk
• SUNSHIELD
It contains five layers made of silicon to shield jwst from light and heat coming from Sun and Earth.
Credit: Axios
• Solar array
It faces the sun and converts solar energy into electrical energy to power the telescope.
Credit: science blogs
• Earth pointing antenna
It sends data back to Earth and receives commands from NASA's deep space network.
Credit: research gate
• Trim Flap
It helps to stabilize the the telescope by preventing solar winds from affecting its direction.
Credit: Axios
•Star trackers
These are small telescopes that use star patterns to target the observatory.
Spacecraft bus:
It contains most of the telescope steering and machinery control.
•Deployment sequence
°JWST separated from Ariane 5 rocket about 27 minutes after launch at 12:47 UTC
°31 minutes after launch, solar array deployment took place.
° 2 hours after launch, antenna deployment
°2.5 hours after launch, thrusters pushed the telescope.
°2.5 days after launch, Thrusters corrected its position.
° 3 days after launch, Sunshield pallet deployment.
°4 days after launch, deployable tower assembly.
° 5 days after launch, stabilization flap deployment so that solar winds may not affect its direction.
°5 days after launch, sunshield membrane cover release
°6 days after launch, sunshield mid boom deployment
°7 days after launch, sunshield membrane tensioning.
°10 days after launch, secondary mirror deployment
°12 days after launch, primary mirror wing deployment
°13 days after launch, primary mirror wing deployment.
° 28 days after launch, JWST will begin to communicate with Earth.
°29 days after launch, JWST will reach its L2 orbit.
°6 months after launch, JWST will send its first image to Earth.
•Why infrared sensitive
As our universe is expanding, all galaxies are moving away from each other. So they show redshift. But if we want to see 13.5 billion years old history then we'll have to use infrared light as the earliest galaxies have moved so far away that they have entered the infrared spectrum. So by using infrared, we can see approximately 13.5 billion years ago. The Hubble telescope can only view red shifted galaxies. Infrared light has a longer wavelength than red, so IR can see through dust clouds. In this way, JWST will allow us to image the first celestial body.
Why JWST is kept at extremely low temperature:
As JWST is designed in such a way that it is sensitive to infrared photons, so it must be kept at insanely low temperature as low as -230°C because even if it gets little bit hot, it will emit its own Infrared photons which will affect its observation of cosmos.
JWST's Orbit:
JWST will reach its L2 orbit on 29th day of launch. L2 is the second lagrange point in space.
Lagrange points are some specific positions in space where the gravitational pull of two large bodies precisely equals the centripetal force required for a small object to move with them.
Why L2
As the telescope needs extremely low temperatures, so to protect it from the heat of the Sun, Earth and moon, it is made to orbit the L2 point. Because at this point, all the hot bodies (sun, earth and moon) are behind its sunshield and protect the telescope from getting hot.
L2 is located 1.5 million kilometers behind earth as viewed from the sun.
Is JWST really a Time Machine?
James Webb Space telescope is also known as NASA's time machine because it will take us to that time when the big bang took place. JWST will be able to see 13.5 billion years old cosmic history, the time when our universe began to form. JWST will be able to see the formation of the earliest stars and galaxies. Due to expansion of the universe, the earliest galaxies that were formed approximately 13.5 billion years ago have now gone so far away that the light emitted from these have shifted to the infrared spectrum. As JWST is designed to receive IR photons so it will be able to see the formation of the earliest galaxies.
What will JWST be able to see?
With JWST we can see planets , distant galaxies, minor planets like pluto and small bodies in space like comets, asteroids. This telescope can also see through alien's atmospheres. So JWST will have a big impact on our search for extraterrestrial life. It will also reveal signs for aliens (if they exist). So in short, JWST is going to change our perspective of the cosmos. JWST opened a gateway to a new era in astronomy.
Comparison between Hubble telescope and James webb space telescope:
By Azka Amjad
Masha Allah, brilliant work.
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