EXPLAINED: James Webb's largest gold-plated telescopic mirrors ever designed

The James Webb Space Telescope, which has been brought into existence by joint efforts, is nearing its launch which is scheduled for December 18. The project is a collaboration of the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA). Deploying the next-generation science equipment, that carries a gamut of delicate instruments, will be a challenge that scientists have never faced before. Among these instruments are the mirrors of the telescope, the proper functioning of which will pave the way for unraveling new mysteries of the universe. 

James Webb Telescope and its mirrors

The telescope actually contains 18 gold-plated hexagonal mirrors, measuring 6.5 metres in diameter, that combine to form the massive hexagonal main mirror. Scientists have chosen the element Beryllium for its composition as it is extremely lightweight when speaking in relative terms. In an interview with NASASpaceflight, Lee Feinberg, James Webb’s Optical Telescope Element Manager justified their choice saying-

It is true that beryllium is very light and has what we call a very high stiffness-to-mass ratio, meaning not only is it light, but it’s very stiff for the amount of mass that it weighs. You would think that’s the number one reason why we chose beryllium, but that actually wasn’t the primary driver, although it is a side benefit. 

Reflecting on another advantage of Beryllium, Feinberg said that the element’s thermal expansion at cold temperatures prompted them to choose it while designing the telescope. “The reason why you want a mirror that’s stable at your operating temperature is if there are small deviations of temperature, your mirror won’t change its shape,” he added. In order to ensure an unhindered scientific exploration of the universal elements, the scientists must apply sheer precision in Webb’s deployment as its orbit will offer no scope for maintenance if anything goes wrong.

NASA has learned from the mistakes that it committed with the Hubble Space Telescope in the 1990s. Unfortunately, the telescope’s mirror had been polished the wrong way, resulting in severe spherical aberration. However, the telescope was repaired during the Space Shuttle missions as it is nearly 550 kilometres above the Earth. The Webb telescope on the other hand will be deployed at the second Lagrange point or L2 which is 1.5 million kilometres from our planet.

Another harrowing challenge before scientists

The telescope is currently undergoing the final stages of testing before it gets launched from Europe’s Spaceport in Kourou, French Guiana. NASA has chosen the Ariane 5 rocket to ferry it to the final destination but before that happens, the telescope and mainly the scientists have a major challenge facing them. One major challenge will emerge during the takeoff, where the Webb telescope will have to endure rigorous vibrations and shaking for eight minutes before it enters space. 

This is a matter of concern as the tennis-court-sized telescope will be crammed in the rocket that has a diameter of just 5.4 metres. This will be possible owing to the telescope’s design as it could be folded like origami. Surprisingly, it has 300 points of failure and even the slightest miscalculation can jeopardise the entire mission.

Image: NASASpaceflight