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) in honour of NASA's administrator who led the agency at the time of the Apollo programme.

JWST will be a general-purpose observatory with a large aperture telescope optimised for infrared observations and a suite of astronomical instruments capable of addressing many of the outstanding issues in astronomy.

Mission Objectives

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, the birth of stars and planets and the search for protoplanetary systems.

Mission Name

The James Webb Space Telescope honours NASA's second administrator, James E. Webb, who headed the agency from February 1961 to October 1968. The James Webb Space Telescope (JWST) was formerly known as the Next Generation Space Telescope (NGST).

Observatory

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 mirror will be 6.5 metres in diameter, made of beryllium with a thin gold coating
• It will have a giant shield (about 22m × 12m) protecting it from the light of the Sun
• JWST's wavelength range covered by the scientific instruments will be from about 0.6 to 28 μm (visible to the mid-infrared light), compared to Hubble's 0.1-2.5 μm (ultraviolet to the near infrared)
• The total payload 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.

Instruments

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 - 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 The Fine Guidance System will include a near-IR tunable filter imaging capability (2.3' × 2.3'; R~100) covering wavelengths 1.5 - 5 µm.
   

Orbit

JWST will be launched in 2014 on an Ariane 5 ECA rocket. After 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 payload to cool to the extremely low temperatures required to keep the instrument's own infrared emission from overwhelming the signals from the astronomical targets.

Operations Centre

The Space Telescope Science Institute (STScI) in Baltimore, US, is responsible for the Science and Operations Center (S&OC) for JWST. The team at the S&OC, which will include ESA astronomers, will be responsible for the scientific operation of the observatory, including:

• Selecting, planning and executing 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, and
• Archiving and distributing raw and calibrated data from the observatory