Has Hubble found its successor? Will the James Webb Space Telescope take up to the challenge?

Well, there are nearly all of the keys for this little (big) telescope to take up on what Hubble has left it to work with, because there’s still plenty of things to be discovered. With its 6.5 meter diameter, in comparison to Hubble’s 2.4, we can be sure that the JWST will deliver extremely sharp images of the sky. Another plus it will have compared to Hubble is that it will be located at 1.5 million km from Earth, thus freeing itself of all interferences that could be caused by Human Activity on the surface of the globe.

But it could also be seen as a bad aspect. Putting Hubble close to Earth meant that the telescope could be upgraded, and it was designed for that originally. It even had, if you recall, a huge porblem with its primary mirror, which has since been corrected by an optical instrument installed on the telescope. If that were to happen to JWST, there would be no comming back: the telescope would be lost, as 1.5 million km is out of reach of any human inhabited rocket or shuttle.
Another important point is that JWST will only observe in the Infrared spectrum, whereas Hubble also observed in the Visible Spectrum. Astronomers consider they’ve gotten the most out of the visible spectrum with Hubble, and anyway, due to Redshift.

Why would they choose 1.5 million km anyway? The Answer is that they’re going to put JWST at the Second Lagrangian Point. There are 5 lagrangian points per system of two bodies. A lagrangian point is an area of space in which you can place a small object so that it doesn’t move relative to two bigger objects, all of this being orchestred by Gravity. JWST will be located at Lagrangian Point Two, because it’s considered to be the best spot for space observation, having the Sun and the Earth in the back. Lagrangian Point 2 corresponds to the spot where the gravity of the two big bodies exactly counterbalance the centrifugal force of the smaller body (in our case, the JWST is the small body, and the Earth and the Sun the two bigger bodies). Other space exploration missions, such as WMAP, are already at Lgrangian Point 2, and more are planned to arrive there, such as the much anticipated ESA Darwin Mission. Take a look at the picture and you’ll understand what Lagrangian Points are straight away.

Anyway, you might be asking yourself, just as I did, who the hell James Webb was. Ever heard of him? Well, he was the second administrator of the NASA. I always wondered why they named it after a politician. They should have names it after a famous physicist or astronomer. Maybe they didn’t find anyone good enough.

Anyway, the building of the scope has been given to Northop-Grumman (you know, the company that makes jet fighters :D) Just to show you how long it takes to build such a project, the early conception started in 1989, and launch should be in 2013! Hubble took several to build too, the first plans for it were carried out back in 1968 under President Johnson.

Hubble and the JWST also differ on the type of optical configuration they use. While Hubble was a Ritchey-Chretien telescope, JWST will be a Cassegrain Telescope, even though that shouldn’t bring much of a change in the results. JWST’s primary mirror is actually made up of lots of little hexagonal mirrors, so that they can be folded during take-off of the shuttle. On arriving at Lagrangian Point 2, JWST will open its mirror.

We can only hope for this next-generation telescope to arrive, but its arrival also means the end of the fertile years of Hubble, which all astronomers, professional and amateurs, will deeply regret. See you in 5 years for lift-off, JWST, and good luck.
Clement

More Information:

• JSWT @ STSCI
• JWST @ Nasa