If Hubble got you all excited, JWST you wait...
- Andy Rice
- 14 Sep 2010 10:00 (South Africa)
The Hubble Space Telescope let us peer deeper into space and further back in time than ever before, tantalizing scientists and ordinary Earthlings alike with its breathtaking images. But there are things out there even Hubble can’t see. And that’s where the James Webb Space Telescope - spectacular in itself – comes in.
More than 20 years in the making, the JWST promises to show us more than Hubble ever could, and, in so doing, take us back almost to the beginning of it all. It will be inaugurated four years from now, and will take up station a staggering 1.5 million kilometres away from the Earth at a spot in space with the aptly scifi-sounding name of the Lagrangian point L2.
It is expected we will be able to see almost to the very first luminous objects formed in the universe that date back to around a few hundred-million years after the Big Bang itself almost 14 billion years ago. There is even the possibility of seeing matter that has not gone through the process of becoming stars yet.
Photo: JWST's primary mirror segment is coated in gold. (Nasa)
Apart from its new scope of vision, the JWST will be an infrared telescope, whereas Hubble works in ultraviolet and visible wavelengths; this will also explain why JWST must be much colder than Hubble.
It’s also one of the reasons it cannot be near Earth. The optimal location for it is the stationary point 1.5 million kilometres away from the Earth, (the Moon's distance is 380,400km on average) in the side opposite to the sun. A unilateral sun shield, which casts a shadow on the telescope and keeps out solar radiation, will ensure that the temperature remains at an icy 50 Kelvin (-223 degrees Celsius).
Photo: The cryogenic testing of the mirrors by Ball Aerospace at Marshall Space Flight Center. (Nasa)
However, JWST has to be as big as possible. It’s four metre-wide mirror is currently being designed to be folded to fit into the launch rocket and will be unfurled once in space. But to meet weight limitations, it has to be built of ultra-light beryllium and has a complicated, honeycomb structure to increase strength and rigidity. It will also be very thin, at just about 2mm thick.
Scientists and engineers working on JWST have learnt crucial lessons from the Hubble experience and have been using a lot of mathematical models that proved themselves on Hubble - except this time with much greater precision. Hubble was never tested on the ground, so this time, scientists plan to have at least one test run. They will use the vacuum tank at the Johnson Space Flight Centre to drop the temperature to 40 Kelvin (-233 degrees Celsius) to test the completed machine.
Photo: This illustration shows that the Chandra X-ray Observatory and the Hubble Space Telescope's Advanced Camera for Surveys looked back billions of years to see the first galaxies. Their combined effort was part of the Great Observatories Origins Deep Survey (GOODS). Hubble's successor, the James Webb Space Telescope (JWST), will gaze even farther back in time to the birth of the first stars. REUTERS/NASA and Ann Field
Dark matter, supermassive stars, the origin of galaxies, the formation of the first luminous objects, black holes in the galaxies far, far away: all of these from the annals of science fiction will come alive when JWST is launched; and it is expected that the JWST will yield far richer results than Hubble. Until then – “watch this space” takes on a whole new dimension of meaning. DM
Main illustration: NASA