ESA, NASA and the Canadian Space Agency (CSA) have collaborated since 1996 on the definition of a successor to the Hubble Space Telescope (HST).
The James Webb Space Telescope (JWST) is 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 outstanding issues in astronomy.
JWST's investigations will cover questions such as: What did the early Universe look like? When did the first stars and galaxies emerge? How did the first galaxies evolve over time? What can we learn about dark matter and dark energy? How and where do stars form? What determines how many of them form and their individual masses? How do stars die and how does their death impact the surrounding medium? Where and how do planetary systems form and evolve?
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 21.2 m × 14.2 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 28.5 μm (visible to the mid-infrared light), compared to HST's 0.1 μm - 2.5 μm (ultraviolet to the near infrared);
- The total observatory mass will be 6200 kilograms
JWST will operate in an orbit around the L2 point, approximately 1.5 million kilometres away from Earth. This makes its operation, pointing and stability requirements much simpler in comparison with HST.
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 spectrograph 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 - 28 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 launch on an Ariane 5 rocket from Europe's Spaceport in French Guiana in 2021. It will travel for a month to reach its final operating location, approximately 1.5 million kilometres from the Earth (about four times the Earth-Moon distance), in an orbit around the second Lagrange point of the Sun-Earth system, L2.
With the aid of a tennis-court-sized deployable sunshield JWST will be kept in perpetual shadow. This allows the telescope and the instruments to operate at the extremely low temperature of -233°C, which prevents 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 (SOC) for JWST. The team at the SOC, 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.