The James Webb Space Telescope (JWST), was developed by the space agencies NASA, ESA and CSA. JWST is designed to operate primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible. It will succeed in 2018 to Hubble Space Telescope which observe the spectrum in the ultraviolet and visible light. JWST, with 6.2 tons of technology is better in resolution and speed of image capture. Its primary mirror is 6.5 meters in diameter, against 2.4 meters for Hubble. The ambitious objective of this project with 5 or 6 billion dollars, is to capture the first light of our universe, to understand how appeared the galaxies, stars, planetary systems, and why not, life.
The infrared observation was chosen is in the range of wave, between 0.6 and 28 microns, because the objects to be studied do not emit visible light.
The telescope will be placed in orbit at the Lagrange point L2, by an Ariane 5 from Kourou.
L2 is located far from electromagnetic interferences, to 1.492 million kilometers of the Earth, on the line defined by the Earth and the Sun (image opposite). Its distance will not allow maintenance as Hubble. Theoretically the telescope should move more slowly than the Earth because the solar gravitational force, at this distance, is weaker, but the gravitational field of the Earth tends to accelerate it.
This allows the satellite to orbit the Sun at the same angular velocity as the Earth. On this point is since June 2001, the WMAP satellite, since 2009, the Planck satellite, since 2011 the satellite GAIA and James Webb will arrive in 2013. JWST is maintained at a very low temperature of about -233.15 degrees Celsius, in order to protect its own infrared emissions. It features a metallic heat shield on the size of a tennis court, which protects, infrared rays from the Sun, Earth and Moon.
A set of girders and cables enable its deployment once in orbit. Lagrange point L2 allows this protection because the heat shield is constantly between its sensors and 3 transmitters (Sun, Earth and Moon).
The most noble is the primary reflector with a diameter of 6.5 meters and a mass of 705 kg. The main mirror fold in orbit, consists of 18 hexagonal elements beryllium, lighter than glass (625 kg against one ton for glass mirror of Hubble). The secondary mirror focuses the light of the primary mirror and returns to the instruments (NIR camera and spectrometer, guidance system,...).
||Km > 1 m
||1 m > 1 mm
||1 mm > 1 µm
||0.38 µm > 0.78 µm
||10 nm > 400 nm
||5 pm > 10 nm
||≈ 1018 Hz
||> 5 pm
||> ≈ 1022 Hz
|Between wavelength (λ) and frequency (ν) is the following relationship: ν = c / λ
ν = wave frequency in hertz
c = speed of light
in vacuum in m/s
λ = wavelength in meter
| || |
Image: Orbit James Webb Space Telescope.
The James Webb Space Telescope is named after the NASA administrator who designed the Apollo program, James Edwin Webb (1906-1992). Credit: NASA / ESA