Since 1996, ESA, NASA and the Canadian Space Agency (CSA) have collaborated on the definition of a successor to the Hubble Space Telescope (HST). Known initially as the Next Generation Space Telescope (NGST), the project was later renamed to the James Webb Space Telescope (JWST).
JWST will be a general-purpose observatory with a large aperture telescope optimised for infrared observations and a suite of state-of-the-art astronomical instruments capable of addressing many of the outstanding issues in astronomy.
The primary aim is to examine the first light in the Universe - those objects which formed shortly after the Big Bang. Further aims include: looking at how galaxies form and evolve, studying the birth of stars and planets, looking at our own Solar System, and studying the properties of exoplanets.
The James Webb Space Telescope honours NASA's second administrator, James E. Webb, who headed the agency from February 1961 to October 1968, at the time of the Apollo programme. The James Webb Space Telescope (JWST) was formerly known as the Next Generation Space Telescope (NGST).
The JWST observatory includes three main elements, the Integrated Science Instrument Module (ISIM), the Optical Telescope Element (OTE) and the Spacecraft Element which comprises the spacecraft bus and the sunshield. Some of the key characteristics of JWST are:
- The primary mirror will be 6.5 metres in diameter and is made of 18 mirror segments of gold-coated beryllium;
- It will have a giant shield protecting the telescope and the instruments from the light of the Sun. At 22 m × 12 m this is about the size of a tennis court;
- JWST's wavelength range covered by the scientific instruments will be from about 0.6 μm to 28 μm (visible to the mid-infrared light), compared to Hubble's 0.1 μm - 2.5 μm (ultraviolet to the near infrared)
- The total observatory mass will be 6500 kilograms
JWST will operate in the L2 orbit, approximately 1.5 million kilometres away from Earth. This makes its operation and pointing/stability requirements much simpler in comparison with Hubble.
JWST will carry four science instruments:
- NIRCam: A wide field (2.2' × 4.4') near-IR camera covering wavelengths 0.6 - 5 µm;
- NIRSpec: A wide field (3.5' × 3.5') multi-object near-IR spectrometer covering wavelengths 0.6 μm - 5 µm at spectral resolutions of R~100, R~1000 and R~2700;
- MIRI: A combined mid-IR camera (1.4' × 1.9') and spectrograph (R~3000) covering wavelengths 5 - 27 µm;
- FGS/NIRISS: A combined observatory Fine Guidance System and near-infrared imager and slitless spectrograph covering wavelengths 0.6 μm - 5 μm with a 2.2' × 2.2' field of view.
JWST will be launched in Spring 2021 on an Ariane 5 ECA rocket. After travelling on a transfer trajectory, the observatory will operate approximately 1.5 million kilometres from the Earth, in an orbit around the second Lagrange point of the Sun-Earth system, L2.
With the aid of a tennis-court-sized deployable sunshield the 6.5-m JWST telescope will be kept in perpetual shadow. This allows the telescope and the instruments to cool to the extremely low temperature of -233 °C required to keep the instrument's own infrared emission from overwhelming the signals from the astronomical targets.
The Space Telescope Science Institute (STScI) in Baltimore, USA, is the Science and Operations Center (S&OC) for JWST. The team at the S&OC, which will include 15 ESA astronomers, will be responsible for the scientific operation of the observatory, including:
- Selecting, planning and carrying out all approved science observations;
- Flight operations, which entails performing observations, uplinking and downlinking data, and monitoring the behaviour of the observatory, all in near real-time;
- Generating calibrated data, and
- Archiving and distributing raw and calibrated data from the observatory.