The James Webb Space Telescope: from the earliest galaxies to the origin of life

Tuesday 18th August, 2015

We were pleased to welcome Dr Sarah Kendrew from Oxford University to talk to us about "The James Webb Telescope (and friends)". Her speciality is in designing the instrumentation on spacecraft and she is currently a member of the test and calibration team for a mid-infrared instrument known as "MIRI" which is one of the instruments on the James Webb Space Telescope (JWST). The MIRI instrument package contains both an infrared camera and a spectrometer.

Dr Kendrew said that the idea of a successor to the Hubble Space Telescope began six years after its launch in 1996. The outcome of many meetings involving leading astronomers and engineers was a telescope in space that would analyse light at infrared wavelengths and it was tentatively named the Next Generation Space Telescope. In 2002 it was renamed the James Webb Space Telescope in honour of NASA's second administrator who played a central role in the Apollo program. Actual construction began in 2004 and it has a provisional launch date of sometime in October 2018. NASA is the lead partner on the project, alongside ESA and the Canadian Space Agency but another fourteen countries are involved in building the telescope.

If all goes to plan, in 2018, the JWST will be launched on an Ariane 5 rocket from Kourou in French Guiana. It will travel to a region in space roughly 1.5 million kilometres directly away from the Earth. This second Lagrangian point (L2) is a place where the spacecraft can maintain a stable orbit around the Sun "behind" the Earth. In this position the JWST can make use of its huge sunshield to keep itself cool by blocking light and heat from the Sun, Moon and Earth. This is vital for an infrared telescope which needs to keep its instruments at temperatures below -220 degrees C. The other advantage of this location is that the spacecraft will be in constant contact with NASA's Deep Space Network, a worldwide network of large radio antennae.

It will take about a year to get the telescope up and running and it is hoped that the mission could last another ten years beyond that. Its 6.5-metre main mirror is made up of 18 hexagonal segments made of beryllium that have a collecting area of 25 square metres, which is five times that of the Hubble Space Telescope. To fit in the launch rocket the mirror will be folded up and its sunshield folded 12 times.

One of the main scientific goals of the mission is to investigate some of the most distant objects in the Universe. Light from these objects will have travelled enormous distances through space that is expanding. As a result of the expansion the wavelength of light will have stretched and so will appear as infrared wavelengths. The James Webb Telescope should allow astronomers to see all the way back to the very first galaxies forming just a few hundred million years after the Big Bang.