The giant successor to the Hubble Space Telescope was seen for the first time in its full glory this week, with its 18-segment, gold-coated mirror unfolded as it will be in space. Due to be launched in 2018, the tennis-court-sized instrument must get it right the first time.
The James Webb Space Telescope is a $10-billion international project involving NASA, the European Space Agency and the Canadian Space Agency. Canada is providing a fine guidance system and two instruments.
Although it will operate in space like the famous Hubble, it is vastly different in every way.
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First of all, it's much bigger. The new primary mirror spans 6.5 metres, compared to Hubble's 2.5, giving it seven times more light-gathering power.
That's still small by Earthly standards, where telescopes on the ground are approaching 30 metres across. But as Hubble has shown so dramatically, a smaller telescope in space does not have to peer through the Earth's atmosphere, so it gets a perfectly clear view of the universe.
The second big difference is how the JWST will see. Rather than capturing visible light like Hubble or our own eyes, the new telescope will look in the infrared part of the spectrum.
These longer wavelengths of light are better at penetrating clouds of gas and dust, where stars are being born — which Hubble cannot see through — and they should give us a view farther back to the beginning of the universe.
From a scientific point of view, the potential of this new telescope is enormous.
While astronomers are anxious to use this new eye in the sky, its sheer size poses a huge challenge for the engineers.
They are faced with the daunting task of folding up the giant structure, origami style, into a package that will fit into the nose cone of a French Ariane-5 rocket.
It must survive the vibrations and stresses of launch, then unfold itself in space in a complicated sequence involving more than a dozen individual steps, which must all be carried out automatically within tolerances less than a human hair.
If anything goes wrong, the entire mission could be lost because the telescope will be well out of reach of astronauts with repair tools.
As we saw immediately after Hubble was launched in 1990, a flaw in the shape of the primary mirror gave the telescope blurry vision.
But Hubble was designed to be repaired by space shuttle astronauts, and thanks to brilliant design efforts on the ground, a set of corrective optics was developed and then installed in a dramatic rescue mission that restored Hubble's sight.
Since then, the telescope has been visited five times to be updated with new instruments and solar panels, making it an even better instrument than when it was new.
That can't happen with the JWST.
Since it will be looking in the infrared, which is basically heat, the telescope must be kept away from any heat source, including the Earth and even the moon.
Beyond the moon
So rather than orbiting the Earth at relatively low altitude, where astronauts could get to it, James Webb will be sent to a point more than a million kilometres out in space, beyond the moon, called L2.
This is where the gravity of the Earth and the sun balance out, so a spacecraft parked there will remain there.
At that distance, the telescope will be entirely on its own.
In other words, all the eggs are in this one, very expensive, basket.
Ultra-sensitive instruments are being mounted on the back of the telescope. Then the entire assembly will be shaken and cold-tested inside a gigantic vacuum chamber before it is readied for launch out of French Guiana.
It is vitally important that every component works absolutely perfectly because there is only one chance for success.
Of course, NASA has had remarkable success with big expensive missions in the past, such as the Mars Curiosity Rover — a one-ton vehicle the size of a small car that made the most complicated landing ever on another planet in 2012 and is still running today.
Let's hope the James Webb Space Telescope follows in the little Martian's footsteps.