Webb Telescope gets hard shaking before space launch
January 18 2017 09:02 PM
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Marco Sirianni, ESA chief development officer, outside the clean-room at the Goddard Space Flight Center in Greenbelt, Maryland where the James Webb Space Telescope is being assembled.

By Andrea Barthelemy

The clean-room at Nasa’s Goddard Space Flight Center is the largest in the world.
The 10-storey-high dust-free space has numerous engineers running around in full protective suits including hoods and facial masks, and it is freer of bacteria than an operating room.
The assembly platforms are wrapped with foil. The only loose bit of anything is the obligatory US flag hanging high up on the wall of the facility in Greenbelt, Maryland, just outside of Washington, DC.
All of this rigour is to protect a valuable baby – the golden James Webb Space Telescope.
Webb – as it is called for short, or JWST – will serve as the successor to the Hubble Space Telescope, aiming its golden mirror at the deep sky. It will be launched in October 2018 and fly 1.5 million kilometres into space to record new images of the far side of the universe.
The scientists and engineers have less than two years until Webb will be launched aboard a European Ariane 5 rocket. And you can sense the excitement and anxiety in the Goddard Center.
“It took a long time for us to get this far. And we almost didn’t get this far,” Nasa administrator Charles Bolden said.
Bolden’s comments came at the presentation of Webb’s composite mirror, which consists of 18 hexagonal golden mirrors. To make it, Nasa called upon the services of its counterparts from Europe and Canada – the ESA and CSA, respectively – as well as dozens of highly specialised suppliers.
The development of Webb, which is named after the second administrator of Nasa, James E Webb, has been under way for more than two decades. One of the leaders on the development team from the very beginning was astrophysicist John Mather, who won the Nobel Prize in Physics in 2006 and is the Webb project manager in Goddard.
When asked about the difference between Webb and Hubble, Mather laughed briefly and said: “It is gigantic. It could track a bee on the moon. From earth.”
Unlike Hubble, which recorded images in the optical and ultraviolet spectrums, Webb works in infrared and can therefore look back even further into the past of the universe.
The core of Webb is the modules forming its 25-square-metre mirror.
“It takes five years to manufacture one of these modules,” said Allison Barto of Ball Aerospace.
The 18 mirrors were produced at Ball all at the same time. The beryllium modules are extremely light and polished with a coating of gold atoms. And they must withstand cold just above the absolute zero mark of minus 273 degrees Celsius.
That is how heat-free it will be where Webb is heading, and the engineers want it kept that way. In order to ensure a consistently low temperature, they are equipping Webb with immense solar shades.
Five razor-thin foils will fold out in space to the size of a tennis court. This XXL-size solar protection shield will be used to keep the sun’s rays off the mirror and other instruments.
The engineers still must test the complicated unfolding procedure as well as the adjusting of the mirror and control of the scientific instruments before the launch.
The especially critical point for the hardware is the eight minutes of searing ascent before leaving the Earth’s atmosphere.
“(The) Ariane (rocket) must be constructed so that the folded up telescope can be safely transported,” said Marco Sirianni, ESA development manager.
Sirianni is on site in the United States with 14 ESA colleagues to co-ordinate the European agency’s contributions to Webb, including a spectograph and the infrared instrument Miri. And of course the Ariane 5 rocket.
Engineers and scientists are putting the mirror under stress tests now in Goddard to simulate the launch forces.
Webb has been folded up in its transport position and placed in a protection tent of air cushions before being pushed out of the clean room to a vibration chamber.
“This is where it will be shaken, back and forth, up and down, in increasing intensity,” said engineer Jason Hylan, pointing to various shaking platforms.
The mirror will then be moved to an adjoining noise chamber, where two huge turbines will shiver it with a barrage of sound as loud as a jet plane taking off.
The moment of truth will follow: will the optical characteristics of the telescope after that ordeal remain exactly the same as before the test, or will the surfaces be out of plumb?
Just 50 metres away, more tests are being done in the cold chamber – a steel, egg-shaped chamber the size of a house. Scale-model mirrors and telescope instruments are being exposed there to extremely cold temperatures to test their capability to keep functioning.
“For these tests we [worked]from Thanksgiving to Christmas, every day in three shifts,” the executives said.
But they were oozing excitement.
“We have been working on this for so long. It’s a really big deal for us.”
All of the individual parts will not be put together for good until the Webb telescope arrives at the NASA facility in Houston, Texas.
Then everything will be assembled, including the solar protection sail, and a special freighter will transport a container with clean-room conditions inside it to the ESA Spaceport near Kourou, French Guiana. Then up it goes.
The entire Webb mission will cost an estimated 8.7 billion dollars (7.8 billion euros) and is expected to last five to 10 years. –DPA




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