The James Webb Space Telescope – The opportunities to scream

Much has already been said about the size, cost, and mission of the James Webb Space Telescope, currently hurtling through space to its destination point, far, far away. But to really appreciate its wondrousness, you need to consider all the things that could possibly go wrong with it.


The 1979 sci-fi horror film Alien was released with the tagline ‘In space, no one can hear you scream’. When the James Webb Space Telescope (‘Webb’) took to the skies at 13:20 CET on 25 December, sitting atop an Arianespace Ariane 5 rocket, there must have been buried screams in the bated breaths of those watching – so much could go wrong.


Much of the reporting on the telescope has focused on the numbers: its size (as big as a tennis court), its cost ($10bn), how long it took to design and build (almost 30 years), how far from Earth it will orbit about the Sun (1.5 million kilometres), and how far ‘back in time’ it will search space (13.8 billion years). But what should really boggle the mind is the number of ‘scream points’ – opportunities for the hundreds of astronomers, cosmologists, astrophysicists, and engineers following the telescope’s journey to bury their heads in their hands and go, ‘Aaaargh!’


Adam Evans, CC BY 2.0, via Wikimedia Commons

The first, of course, was the moment of ignition of the Ariane 5. But it’s a trusted workhorse, so no real worries there. The first real test came about three minutes into the rocket’s arc into space, with the jettisoning of the fairing around the folded telescope. A problem at that point could have damaged the telescope; but, no, that went perfectly. The next was the moment of separation from the rocket: no separation, and Webb would tumble down to Earth in an ignominious burn. But that went like a dream. In fact, the precision of the launch was such that it exceeded the requirements to put Webb on the right path. When the telescope separated from the rocket, it required only minimal correction to put it exactly where it needed to be.


The next ‘scream point’ was the deployment of the ‘solar array’ – no array, no power, no system, and Webb becomes a $10bn, 6-tonne ball of origami-folded space litter. Pat on the back, everyone involved – the ‘solar array’ opened on cue, on time, like a welcoming hand holding out an invitation to the Sun. With power to the system, Webb could now deploy the two pallets over which the sun shield could stretch itself and snap into place. Like giant arms, the pallets each reach 10m out into space. They needed to be firm but flexible and perfectly aligned. So, how did that go? Like a dream.


The sun shield is mission-critical. Webb searches space for faint infrared signs of long-lost stars, so the last thing it needs is our own star breathing down its neck. The shield keeps Webb’s mirrors hidden from the Sun at a less-than-balmy -238oC. It is not a single shield. It comprises five fragile membranes that must unfold, separate, and be drawn into position through the perfect coordination of hundreds of movements of hinges, pullies, motors, gears, and springs if it’s to work correctly. The opportunities for failure are imaginable. And yet, the shield unfolded like a glorious galactic rose to the cheers of the Earth-bound Webb team.


Webb’s successful operation to date is testimony to science and the skill, foresight, and planning of all involved. But worries are not over yet. As Webb makes its way to its operational point in space, it still has other critical moments to endure before returning a single signal to Earth. And if something goes wrong, we may not find out until it’s too late, because, in space, no one can hear you scream.


Daryl Ilbury is a farm-based science journalist, writer, and author.

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