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It was January 4th, 2022. The telescope had successfully unfolded its heat shield, despite having over 300 single points of failure; 300 chances for a 10 billion dollar, 25-year project to end.

Basic Principle

In the early days of the universe, no light could escape the dense, opaque primordial gas. Soon after the formation of the first stars, light began to escape into the expanding universe. Some of these early photons have traveled unhindered through the vast expanse of space for almost 13.5 billion years and will reach their final destination, the infrared sensor of the James Webb Space Telescope (JWST), the most advanced space telescope yet which is going to give us our first detailed glimpse of this early universe from which we and everything we know were born.

Position in Space

Launched on December 25, 2021, from French Guiana, this telescope was not designed to orbit the earth like most satellites. Instead, hover 1.5 million kilometers from the earth in Lagrange Point 2 where the gravity of the sun, earth and centrifugal force balance each other and significantly less fuel is required to maintain a stable position.

The Sensor and Heat Shield

Unlike Hubble, the JWST will not observe the universe in the visible range but instead use an infrared sensor to observe the cold distant past. For the sensor to be operational it has to be cooled down to -233C (7 K). This is achieved by a giant multi-layered heat shield made up of Kapton coated with Aluminium and Silicon. This heat shield had to be folded to fit inside an Ariane 5 rocket carrying the telescope to space and complex deployment mechanisms were used to unfold it in space. The temperature is further reduced to 6.3 K by an innovative cryogenic cooler costing 150 million dollars alone.

The Mirror

The other interesting and innovative part of this telescope is the primary reflecting mirror used for focusing photons onto the secondary mirror which conveys them to the infrared sensor. Measuring 6.5 meters in diameter, this mirror is made up of 18 hexagonal segments. These hexagonal segments are composed of Beryllium coated with 0.1 micron layer of Gold. Gold is an excellent reflector in the infrared region and additionally, gold is very non-reactive and does not tarnish over time. Unlike Hubble, the JWST cannot be repaired in space so everything had to be extremely precise. For this purpose, the mirror segments were made adjustable, which can adjust not only their direction but also their curvature. This telescope needed such a large and complex mirror because it only receives 1 photon per second. For instance, our eye staring at a bright star at night receives approximately 1 million photons per second.

Propulsion in Space

For maintaining its position in space the JWST uses a total of 20 Hydrazine thrusters with Dinitrogen-Tetraoxide as an oxidizer. The telescope has 191L of Hydrazine and 95.5L of oxidizer in total shortening its lifespan to approximately 10 years.

In conclusion, we are on the frontier of a new space age. This state-of-the-art telescope will provide us with some stunning images of the universe and more importantly, a lot of information about the formation of the universe.

For further information on The Insane Engineering of James Webb Space Telescope, check out this video.

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