How a powerful new
telescope will reveal distant secrets
The James Webb Space Telescope will
soon soar into the heavens
Nov 23rd 2021
IT
IS A majestic beast. Its primary mirror, a tessellation of golden hexagons,
resembles a honeycomb sitting on a pile of silver-paper wrappers. But the
mirror is six and a half metres across and the wrappers, each as big as a
tennis court, are actually a sunshield. This shield divides the craft into a
cold side and a hot side. On the cold side sit the primary, a tripod-mounted
secondary that reflects light gathered by the primary back through a hole in
its centre, and a pack of instruments behind that hole to parse and analyse the
incoming light. The hot side carries a solar panel and the craft’s control
systems. And all these things must fit into a rocket fairing a mere five metres
across and then unfold in space into the shape above with nanometre precision.
The
beast in question is the James Webb Space Telescope, named after NASA’s boss in
the glory days of the 1960s, when the destination was the Moon and money was no
object. The mirrors’ surfaces, made from gold-plated beryllium, are so smooth
that, scaled up to the size of America, their irregularities would be mere
centimetres high. Were the sunshield bottled and sold in Boots, it would have a
protection factor of a million. One of the instruments behind the primary is so
complicated that it has 250,000 tiny shutters, individually controlled to
ensure that it is illuminated only by the correct narrow slice of the sky. No
uncrewed science mission so sophisticated has previously been sent into orbit.
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