The second mirror of the James Webb telescope is installed. Thus, both mirror surfaces are provided. The construction of the first mirror was completed on 3 February with the installation of the last segment of eighteen mirror parts.
The James Webb reflecting telescope, which should eventually be located at a fixed point from Earth about 1.5 million kilometers away, will mainly investigate longer wavelengths than the current Hubble space telescope. The latter celebrated its twenty-five anniversary about 570 kilometers from Earth in space less than a year ago.
The Webb telescope is lighter and larger than its illustrious predecessor. For example, the large segmented first mirror is already 6.5 meters in diameter compared to Hubble’s 2.7 meters. The whole thing has to be folded to fit in an Ariane 5 rocket.
Unlike the eighteen segments of the first mirror which has a honeycomb structure, the second mirror is round and convex so that the reflected light is reflected in such a way that it ends in the center of the first mirror, where there is a third mirror system that ensures for image stabilization. The collected light then ends up on the instruments.
The mirrors are made of beryllium, a material that is very stiff, light and stable under extremely low temperatures. The deviation is no more than a few millionths of a millimeter at temperatures in space. Because beryllium does not reflect very well, all mirrors have a gold coating to reflect infrared light well. This allows Webb to look further into the past than Hubble. One of the main goals of Webb’s scientific mission is therefore to search for light from the first stars and galaxies that formed in the universe after the Big Bang. These observations can be made better in near-infrared than in visible light. For example, Hubble looks at visible or ultraviolet light. Webb will be able to observe wavelengths between 0.6 and 28 micrometers, with 0.6 micrometers being the wavelength of orange light.
The James Webb telescope costs more than budgeted. Initially, the whole was supposed to go into space in 2011, and the cost of the project was estimated at 1.6 billion dollars. Now the goal is to have the telescope in space by 2018 and should not cost more than $8 billion.