James Webb Space Telescope "The Miracle of Science" Fitting in Ariane 5 Rocket

James Webb Space Telescope "The Miracle of Science" | Part 4

That’s one of the bigger challenges, along with just designing a deployment system that does this complicated and necessary unfolding- reliably and correctly.

    In order to fit into the fairing of the Ariane 5 rocket, the sunshield has to be folded and stowed before launch, leading to some incredibly complicated mechanics to ensure it unfolds correctly when the time arrives.

Deploying things in space is always difficult. But when you’re deploying a rigid structure - that’s generally what engineers call deterministic…that’s relatively easy….Membranes and cables are almost inherently non-deterministic and if you want to have or illustrate what that means - try pushing on a string.

The string will move. If i ask you to determine the shape that it will assume you will have a very very hard time doing it. So to control these almost non-deterministic things takes a great deal of effort, takes a great deal of trial and error.

And even after we’re done getting the design right, the one thing about the sun-shield is it’s almost like a parachute or similar to a parachute.

You know the parachute will work, but it’s also only as good as the very very last time you fold it. And you’re going to find out whether you folded it correctly or not when you use it.

The unfolding process will begin a few days after launch, not too far from Earth. Starting with relatively simple mechanisms with the solar panels and communications antenna deploying. The truly nerve wrecking process begins on Day 7, as the satellite is coasting towards L2.

There are over 300 single points of failure in this unfolding sequence. 300 chances for a 10 billion dollar, 25 year project to end. 107 pins, holding the sunshield together, have to be released on queue, to allow the system of pulleys, motors, cables, bearings and springs to begin unfurling the sunshield into its precise complete shape. This process will take 3 days, and once complete the optical components will unfold and lock into place.

Completing the transformation process, but we are most certainly not in the clear.

The likelihood of the tennis court sized sun-shield being struck by micrometeorites is fairly high, and because this a thin layer of plastic stretched out under tension, a small tear caused by an impact could cause a runaway tear ripping through the whole sun-shield.

To prevent this, rip stop seams have been molded into the sunshield, which will arrest tears and keep them confined to a single portion of the shield without compromising structural integrity.

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