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Astronomy’s $10 billion Christmas Present

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Although it’s still in the process of unwrapping itself.

A few hours ago, on America’s Christmas Morning, the James Webb Space Telescope was launched by a European Space Agency (ESA) rocket, an Ariane 5, from the ESA site in French Guiana. About half and hour later it detached from the upper stage, as shown in the video below.

Rocket launches are always fairly tense, but at maximum when you’ve got a one-of-a-kind bird like this. The original plan had the telescope being launched by 2007 and costing a billion dollars, but for once I won’t throw shade at NASA about these factors because this telescope simply cannot be allowed to fail as it will be stationed about one million miles from Earth and therefore unfixable if anything goes wrong.

By contrast the Hubble Space Telescope orbits Earth about 300 miles up and was designed to be serviced by the Space Shuttles. A good thing too as when it was first launched in 1990 its images were blurred and NASA was horrified to find that its giant mirror had been improperly polished. A problem that basic in the very heart of the machine seemed like a show-stopper, but they finally fixed it in 1993 by fitting it with the equivalent of reading glasses.

It has since become one of the greatest science machines of all time, but astronomers were already planning its successor, built to see the first stars and galaxies that emerged from dust and gas of the early universe, only a few millions of years after the Big Bang. The Hubble can see back to within a billion years of that event. As a result the Webb telescope is sometimes fondly referred to by astronomers as the ‘First Light machine’.

Knowing that Hubble might not last more than twenty years and guessing that Webb would take a long time (although they never imagined it would be this long, and Hubble is still working – just) work on Webb began even before Hubble was launched – and given how Webb had to work, a repeat of the Hubble problem was not acceptable; the machine “is not allowed to fail”. As a result much of the last decade has been spent simply testing the hell out of it:

[Tests] involved lowering the telescope’s temperature to the minus 390 degrees Fahrenheit (minus 217 degrees Celsius) in which it will operate, and in a vacuum similar to that of space.

“The cryo-vacuum tests for Webb were long and gruelling,” [Project scientist] Kimble said. “It would take weeks just to cool everything down safely and then warm up again safely at the end of the test. And in the middle, when you are cold and stable, that’s when you do your detailed testing.”

And there’s a lot that can still go wrong. It has a lot of moving parts that must work to enable it to unfold in space like a giant origami sculpture:

Perhaps the most nerve-wracking move will be the unfurling of the sunshield, which is scheduled to occur in the first week after launch. The sunshield system has 140 release mechanisms, 70 hinge assemblies, 400 pulleys, 90 cables and eight deployment motors, all of which need to perform correctly to get the five thin membranes extended

The mirror consists of 18 hexagonal segments, each of which is made of beryllium and coated with a thin layer of gold.

That second link covers the engineering challenges and has a video of how it’s all supposed to unfold. The sun shade has five layers, spaced apart for maximum thermal cooling to allow the telescope instruments to be as cold as possible, which they have to be to detect faint infrared light from the oldest objects in the universe. That’s also the reason it has to be stationed so far from Earth. Hubble has IR detectors now, but was never designed for the job and so is too warm itself and too close to our warm planet, to be able to see the faintest (and oldest) objects in the sky:

[Webb] will orbit the sun, while simultaneously making small circles around the so-called Lagrange point 2 (L2)… At L2, the gravitational pulls of the sun and of Earth keep the spacecraft aligned with the two big bodies. 

It will take Webb about a month to fly to that point, unfolding all the way. Since they’re made of metal the mirror’s segments can actually be warped slightly by small electric motors mounted behind each one; all part of the process of turning those 18 mirrors into one mirror 6m wide.

If all goes according to plan, the telescope will detect cosmic objects 10 billion times fainter than the dimmest star you can see in the night sky without a telescope. That’s 10 to 100 times fainter than anything Hubble can pick up, NASA officials said. And Webb’s vision will be so sharp that it can see details the size of a penny from 24 miles (40 km) away, they added.

Fingers crossed but so far it’s all good. Check out those two links, Engineering Webb and Launching Webb for more details and videos about how it works and what it will do.

Written by Tom Hunter

December 26, 2021 at 2:07 pm

Posted in Aerospace, Europe, Science, Space, Technology, USA

Tagged with ,

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