James Webb Space Telescope:

The space telescope of tomorrow

Outer space is a maze of mysteries. Over many years, the untiring efforts of scientists, engineers, physicists and many other people have contributed to reveal the truth behind these mysteries and present us a vast knowledge about the previously unknown. But still, the quest is not over.

There are greater mysteries left to be solved, and unless the observation models are improved, even the greatest set of theorists together with the greatest supercomputer would not be able to resolve these mysteries.

At the moment giant space tellscopes such as Hubble, Spitzer and Chandra are giving us magnificent views of outer space. The newest member into this family of space telescopes is going to be the 'James Webb Space Telescope', which is expected to overcome many challenges which the other telescopes couldn't.

The James Webb Space tellescope (JWST) is a planned space infrared observatory, which is expected to be a significant improvement on the Hubble Space Telescope which is getting quite old now.

JWST is a group effort between NASA, the European Space Agency and the Canadian Space Agency. This was initially called the Next Generation Space Telescope or NGST.

However in 2002, it was renamed after NASA's second administrator, James E. Webb.

The telescope's launch is planned to take place around June 2013. It will be launched on an 'Ariane 5' rocket from Guiana Space Centre Kourou, French Guiana, with a launch mass of approximately 6.2 tonnes.

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Who is James E Webb?

James Edwin Webb was the second administrator of the National Aeronautics and Space Administration (NASA), formally established on October 1, 1958. Many believe that James E. Webb, who ran the space agency from February 1961 to October 1968, did more for science than perhaps any other government official and that it is correct that the Next Generation Space Telescope would be named after him.
 

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About the telescope

The weight of the JWST is expected to be about half the weight of the Hubble telescope.

However, its primary mirror is almost six times larger. This is known as a 6.5 metre diameter beryllium reflector. As this diameter is much larger than any current launch vehicle, the mirror is made out of 18 hexagonal pieces, which will open up after the telescope is launched.

Since this is an infrared telescope, it must be ensured that the observations are not affected by infrared emission from the telescope and instruments themselves.

Therefore, they have designed the entire observatory to be cold and well-shielded from the Sun so that it can be kept at a low temperature around 40 Kelvin (233 Celsius).

To achieve this, JWST will include a large metalised fanfold sunshield, which will open up to block infrared radiation from the Sun, as well as from the Earth and Moon.

The location of the telescope plays a key role in making this possible. The telescope will be kept in a point in space called the 'L2 Lagrange Point'.

A Lagrange Point, in simpler terms, is a point where a small object affected only by gravity can theoretically be stationary relative to two larger objects. In this case the telescope will be the small object, and the Sun and Earth will be the two large objects.

Therefore, the shield can be effectively used to avoid solar radiation. We will look at Lagrange Points in detail, in a later edition of 'Space Station'.

Several new technologies have been developed for JWST, which include the folding, segmented primary mirror, ultra-lightweight beryllium optics, detectors able to record extremely weak signals, microshutters that enable programmable object selection for the spectrograph, and a cryocooler for cooling the mid-IR detectors to 7 Kelvin (-266 Celsius).
 

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Mission

The JWST's scientific mission has four main objectives. The main objective is to search for light from the first stars and galaxies which formed in the Universe after the Big Bang.

Secondly, it is expected to study the formation and evolution of galaxies. Next, it is to be used to understand the formation of stars and planetary systems and finally it is expected to study planetary systems and the origins of life.

The observatory will begin the science mission, after a commissioning period of about six months, which will be required to go on with the explorations up to a minimum of five years.

The JWST programme is currently in its preliminary design phase which is known as Phase B. In January 2007 nine of the ten technology development items in the programme successfully passed a review and they were considered to have no risk on the programme.

The remaining technology development item, the MIRI cryocooler completed its technology maturation milestone in April 2007.

This technology review represented the first step in the process that will ultimately move the programme into Phase C, which is its detailed design phase. In May 2007 the cost of the project was estimated at about US$ 4.5 billion.

Aravinda Dassanayake