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The Hubble Space Telescope that has been orbiting Earth since 1990, has and continues to reveal secrets of planets, stars, and galaxies that lie trillions of miles away. In 2018, it will finally be retired and replaced by the larger, and more powerful, James Webb Space Telescope (JWST). The announcement, made by NASA on November 2, culminates a 20-year quest to build a state of the art telescope that cost $8.7 billion and required the construction of new assembly and testing facilities.
The diameter of JWST’s primary honeycomb-shaped mirror measures 21-feet, or about thrice the size of its predecessor. Made of 18 smaller gold-plated mirrors, it boasts a surface area that is seven times that of the Hubble, making it the largest telescope mirror to fly into space. Additionally, the JWST mirror is designed to collect infrared light. This is important because stars and planets that are still forming are often hidden behind dense layers of dust that absorb visible light, making them virtually impossible to observe. However, infrared light can penetrate the cosmic dust and allow us to peek at what lays behind.
The largest structure of the telescope is the sunshade. Measuring 69.5 feet x 46.5 feet, or about the size of a tennis court, it comprises five layers, each separated by a vacuum. This allows heat to radiate out from between the layers, keeping the lower portion of the shade cool at all times. This is important given that the sunshade’s primary purpose is to protect the telescope from the light and heat of the earth, sun, and the moon and keep its external temperature close to below 50 Kelvin (-223° C or -370° F) that is necessary to obtain precise infrared readings. According to NASA scientists, the massive sun shield will give the telescope the equivalent of SPF one million sunscreen!
The JWST will not be orbiting the Earth like the Hubble. Instead, it will be going around the sun from what astronauts call the second Lagrange point, or L2. What makes the orbit unique is that it enables the telescope to stay in line with the Earth as it moves around the sun. There are a number of important reasons for doing this.
The combined gravitational forces of the Sun and Earth help hold the spacecraft almost still, which means that it needs relatively less fuel.
Additionally, the region’s consistently cold temperatures will help the sunshade ensure the telescope's exterior stays at its optimal temperature. The permanent position will also make it possible for scientists to communicate with it at all times of the day and night.
The telescope that is scheduled to be launched on an Arian 5 rocket in October 2018 for a five to ten-year long mission, is currently undergoing extensive testing at NASA’s Goddard Space Flight Center. Among the many things the scientists are checking for is JWST’s ability to withstand the turbulence during launch and the absolute zero temperatures it will encounter in space.
Of course, no amount of testing can guarantee the success of the massive telescope once it is in space. One potential issue could be the mirror assembly, which is too large to be launched fully extended and will take over two weeks to unfurl. Even worse, the researchers will have to wait a full six months to see if the telescope functions as expected. But given that sending a manned spacecraft to conduct repairs is not an option, the scientists, who have spent 20 years constructing JWST, will just have to hope that it works as well, if not better, than the Hubble.
JWST’s first mission will be to capture images of Alpha Centauri, the star closest to the sun, to try and detect water vapor on its orbiting planets, an indication that it could sustain life! Future assignments will include peering through the cosmic dust and sending back data on newly forming planetary systems as well as the oldest galaxies in the universe. JWST will also be able to compare the earliest galaxies to our current ones, answering questions about black hole formations.
This is not the first time scientists have sent a space telescope to L2. The European Space Agency’s Herschel Space Observatory has been peering into the universe from the same location since 2009. However, it is designed to observe longer wavelengths to help find actively forming galaxies. JWST, on the other hand, aims to look at the much shorter infrared wavelengths emanated by the existing galaxies in the early universe. Together, the two will help reveal all of the universe’s secrets. Hopefully, the findings will include a few aliens as well!
Resources: extremetech.com, space.com,popularmechanics.com