Peering far: Unlike the Hubble Space Telescope, the JWST can detect faint infrared radiation coming from very distant sources in the universe. The James Webb Telescope, the next step after the Hubble Space Telescope, is a large, infrared-optimized space telescope, scheduled for launch in 2013. It will find the first galaxies that formed in the early universe and peer through dusty clouds to see stars forming planetary systems. The telescope's instruments will be designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. Why is the Webb telescope called the next step after the Hubble telescope? Mr. J.D. Harrington, Public Affairs Officer, NASA, in an email communication to this correspondent, said that one of the important findings from Hubble is that galaxies already existed in forms very familiar to us today very far back in the history of the universe. It was soon realised they would need to peer even further distances to see galaxies as they began to form. Since the universe expands, and in turn stretches the waves of light from distant objects, following the galaxies meant moving into the infrared part of the spectrum. And an infrared optimized telescope with a bigger mirror (21.3 feet in diameter) is needed to collect the weaker signals. The telescope will reside in an orbit about 1 million miles from Earth. According to him, one of the most important components of the telescope is the large primary mirror that collects the faint infrared light and focuses it into the instruments which record the images and spectra. The challenges The biggest challenge remains the production of the high quality mirror segments and then assembling them into a computer controlled system that makes them function as a single collecting surface. And all this must be done at temperatures only around 40 degrees above absolute zero. Finally, securing high quality detectors is always a challenge for space missions. The JWST detectors are those devices that actually record the images (or spectra) once the mirror collects the photons and passes them through the system optics. These devices are analogous to the CCDs (charge coupled devices) found in modern digital cameras. Positioning Why does the telescope have to be positioned one million miles from Earth? Mr. Harrington said: "Because JWST is optimized to look for infrared radiation (heat) it will work best when it is far from sources of such radiation, including the earth [so that the faint infrared light coming from distant astronomical objects are not missed],' he noted. "By putting JWST at the second Lagrange point (L2) which is one million miles from Earth, we can put both the Sun and Earth always on the same side of the observatory and far enough away that all the infrared light from these objects can be blocked by a simple screen called the sunshield. Another advantage of positioning at the L2 point is that little propulsion is needed to maintain the spacecraft's orbit with respect to the Sun and Earth. "Conventional telescopes block extraneous light from outside their fields of view by using a tube because the scattered light comes from any direction. "Because one side of the JWST always faces the sun, this stray light must be blocked on just one side.'