JWST TO BE LAUNCHED IN 2019

 

… in case there is no any other unexpected delay.

The JWST (James Webb Space Telescope) is a space telescope, that is, an artificial satellite destined to observe the cosmos and the celestial objects in a similar way as a ground telescope does it.

Since “Cosmos 215” was launched on April 18, 1968, an important number of space telescopes have been sent to the outer space, but among all of them we have to highlight the so-called «Great Observatories», which are the four larger and more advanced space telescopes launched ever, each one of them focusing on a particular region of the electromagnetic spectrum:

  • HST (Hubble Space Telescope): Sent to space on April 24, 1990, it rotates around the Earth at 593 km above sea level and mainly observes visible, near ultraviolet light, and since 1997 can also detect near infrared radiation.
  • CGRO (Compton Gamma Ray Observatory): It was launched on April 5, 1991 and burned in the atmosphere on June 4, 2000. It orbited 450 km from Earth, avoiding the Van Allen radiation belt, which extends from 500 km in height. CGRO observed mainly in the spectrum of the gamma rays, and secondarily also in the hard X-rays.
  • CXO (Chandra X-ray Observatory): Launched on July 23, 1999. It describes a highly elliptical geocentric orbit with a perigee of 14,307.9 km and an apogee of 134,527.6 km, being the semi-major axis of the orbit of 80,795.9 km. It observes mainly soft X-rays.
  • SST (Spitzer Space Telescope): Launched on August 25, 2003, it follows a heliocentric orbit with an apohelion of 1,026 AU and a perihelion of 1.003 AU. It observes the infrared spectrum.

JWST will replace Hubble, and partly also Spitzer, since it will observe in infrared as well as in visible.

Plans for developing a successor to Hubble began in 1993 or perhaps even earlier, but it was not until 1996 that the JWST project was created under the name NGST (Next Generation Space Telescope). It was in 2002 when the former denomination was changed to the current JWST.

After that year of 2002, there were a number of changes in the original planning of the project and also successive increases in the total budget initially estimated.

In 2011 JSWT reached its latest design and manufacturing phase, and for that year it was expected to be launched in 2018. Finally, in 2017, the forecast was delayed by one year, until 2019.

The assembly of the 18 hexagonal pieces of the main mirror, one of the final construction steps, was completed in 2015, and the manufacture of the JSWT was finally over in November 2016. Since then, the test phase started and it is still on process.

Foto 1

Structure of JWST with its main components.

 

JWST is a project of NASA, but ESA and CSA are also collaborating in it.

JSWT has the following four key goals:

1) The search for light coming from the galaxies and stars that formed in the universe just after the Big Bang.

2) The study of the formation and evolution of galaxies.

3) Achieve a deeper understanding of the formation processes of stars and planetary systems.

4) Study planetary systems and the origins of life.

In order to achieve these objectives, JWST will have a great capacity of observation in the infrared region of the electromagnetic spectrum.

JWST can be very useful in trying to clarify the origin of Tabby’s Star (KIC 8462852) light-curve strange fluctuations.

The main mirror of the telescope is a beryllium reflector laminated with gold. It is 6.5 meters in diameter, and is composed of 18 hexagonal pieces.

The telescope will carry the following instruments, assembled together in the so-called Integrated Science Instrument Module (ISIM):

  • Near-Infrared Camera (NIRCam): It is a camera that will capture radiation with wavelengths between 600 and 5000 nm. At the same time, it functions as a wavefront sensor designed to keep the 18 segments of the main mirror aligned. As a camera, it will have 10 mercury-cadmium-telluride (HgCdTe) detector arrays and each one of these detector arrays will integrate an array of 2048×2048 pixels.
  • Near-Infrared Spectrograph (NIR Spec): It is a multi-object spectrograph that will perform spectrophotometry tasks in the same range of wavelengths as the NIRCam. This instrument is an ESA contribution to JWST.
  • Mid-Infrared Instrument (MIRI): It contains both a mid-infrared camera and an imaging spectrometer, and will detect wavelengths ranging from 5000 to 27000 nm.
  • Fine Guidance Sensor/Near-InfraRed Imager and Slitless Spectrograph (FGS/NIRISS): This instrument is a contribution of CSA. FGS will take measures that will serve to control the overall orientation of the telescope and to drive the fine steering mirror image for stabilization. NIRISS will perform imaging and spectroscopy tasks in the range of 800 to 5000 nm wavelength. In general, FGS and NIRISS are referred to as a unit. This is because they are physically assembled together, but they have totally different purposes, NIRISS being a scientific instrument and the FGS an auxiliary element of the telescope’s infrastructure.

Foto 2

Drawing of the ISIM (Integrated Science Instrument Module).

 

Launching of JWST is currently planned for the spring of 2019 using an Ariane 5 rocket. A 5-year mission has been planned, although it is estimated that the telescope could remain in space for another more 5 years, finally reaching a total of 10 years in active.

It will be located in a halo orbit around the second Lagrange point (L2) of the Sun-Earth system. Such orbit will have a period of 6 months, a periapsis of 374,000 km and an apoapsis of 1,500,000 km.

The second Lagrange point (L2) is located on the Sun-Earth line, at a distance of about 1,500,000 km from the Earth in the direction opposite to the Sun. According to Kepler’s laws, an object located on L2 should orbit around the Sun, as Earth does, but at a slower speed than Earth, so that it would take more than a year for such object to complete its orbit. However, when located exactly on L2, the effect of Earth’s gravity on the object makes the period of the object’s orbit to be equal to that of Earth.

Nevertheless, JWST will not be static at point L2 but will orbit around it. That is precisely a halo orbit: an orbit around a Lagrange point. JWST, then, will orbit around a point (the L2), and such point L2 itself orbits around the Sun with an orbital velocity and period equal to those of Earth.

Foto 3

Position of Earth-Sun system’s five Lagrange points (L1, L2, L3, L4 and L5).

 

Once in orbit, JWST will communicate with Earth using several large antennas that will be located in Australia, Spain and California (USA).