IN SPACE, no one can hear you scream – especially if you’re a state-of-the-art space telescope stationed well beyond the reach of a shuttle repair crew. If anything goes wrong with the delicate folding optics of Hubble’s successor, the James Webb Space Telescope, NASA could be facing an $800 million loss.
After years of planning, NASA last week finally gave Californian aerospace firm TRW the contract to build the new telescope, which is due for launch in 2010. Webb’s design marks sweeping changes from Hubble. While Hubble was designed to be launched and serviced by the shuttle, Webb – named after an Apollo-era NASA chief – needs a far more distant orbit to minimise electromagnetic interference. It will sit 1.5 million kilometres from Earth – four times farther from us than the Moon.
Webb will look far back into the Universe to see the first galaxies forming, for which it needs a giant 6.5-metre mirror, dwarfing Hubble’s 2.4-metre optics. But launching and unfurling the giant yet lightweight mirror won’t be easy. It must fold in three for launch, then unfold like a flower when it reaches orbit. It must also be exceptionally thin to minimise its weight. Unfurling just about anything in space – from tethers to solar panels – has often caused problems, even on crewed missions where help is close at hand.
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Webb will look at longer infrared wavelengths than Hubble, so the whole telescope must be kept cold to reduce IR interference. NASA decided that the best approach would be to put Webb in a Lagrange 2 orbit, at a point where the Earth’s and Sun’s gravity cancel each other out.
John Mather of the NASA Goddard Space Flight Center says a plastic shield the size of a tennis court will unfold to shade the telescope from both the Earth and Sun, keeping its temperature near 40 kelvin.
That thermal stability will have the edge on advantage over Hubble, which heats up and cools as its orbit takes it between light and shadow. But the cold may pose freezing problems for the actuators that will focus Webb’s deformable mirror.