James Webb Space Telescope

JWST is an international collaboration between NASA and ESA (European Space Agency).

Few things to know about jwst;

• A 21-foot (6.5-meter) primary mirror, built from 18 adjustable segments, to provide the deepest and sharpest images of the cosmos to date
• A 5-layer, tennis-court-sized sun shield to cool the telescope to 40 degrees above absolute zero
• Four pioneering science instruments with superb performance in the infrared part of the spectrum
• A deployable design and an observing environment far from any heat sources, 1 million miles from Earth

The JWST will be the largest infrared telescope ever built with 6.5-meter wide primary mirror for looking more deep into space and produce more descriptive details of the cosmos.
It is planned to be launched on an Ariane 5 rocket from French Guiana in October of 2018.
It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang to the formation of solar systems capable of supporting life on other planets to the evolution of our own Solar System.

Some major components of JWST;

• 18 primary mirror segments
• The Mirrors (Gold-plated beryllium)
• Secondary mirror
• Tertiary mirror
• Fine Steering Mirror
• Sun shield
• Instruments
• NIRCam
• NIRSpec
• MIRI (Mid-Infrared Instrument)
• FGS/NIRISS
• Spacecraft Bus
• Electrical Power Subsystem (Solar panels, etc. to power whole spacecraft)
• Attitude Control Subsystem
• Communication Subsystem (radio communication with Earth)
• Command and Data Handling Subsystem (the “brains” of the spacecraft)
• Propulsion Subsystem (fuel tanks, rockets, etc controlled by Attitude control subsystem)
• Thermal Control Subsystem (maintains temperature of the bus (the bus is on the “hot side” not to be confused with mirror sun-shield the bus is in front of this and not shielded by it)
• Ariane 5 launch system (gets it into space)
Three major sections of the JWST include:
• Optical Telescope Element (OTE), mirror and its structure, etc.
• Spacecraft Element (SE), which includes the Spacecraft Bus and Sunshield
• Integrated Science Instrument Module (ISIM), which holds the instruments and other systems

Scientific Instruments;

 

• Near InfraRed Camera (NIRCam) is an infrared imager which will have a spectral coverage ranging from the edge of the visible (0.6 micrometres) through the near infrared (5 micrometres). NIRCam will also serve as the observatory’s wavefront sensor, which is required for wavefront sensing and control activities. NIRCam was built by a team led by the University of Arizona, with Principal Investigator Marcia Rieke. The industrial partner is Lockheed-Martin’s Advanced Technology Center located in Palo Alto, California.
• Near InfraRed Spectrograph (NIRSpec) will also perform spectroscopy over the same wavelength range. It was built by the European Space Agency at ESTEC in Noordwijk, Netherlands. The leading development team is composed of people from Airbus Defence and Space, Ottobrunn and Friedrichshafen, Germany, and the Goddard Space Flight Center; with Pierre Ferruit (École normale supérieure de Lyon) as NIRSpec project scientist. The NIRSpec design provides 3 observing modes: a low-resolution mode using a prism, a R~1000 multi-object mode and a R~2700 integral field unit or long-slit spectroscopy mode. Switching of the modes is done by operating a wavelength preselection mechanism called the Filter Wheel Assembly, and selecting a corresponding dispersive element (prism or grating) using the Grating Wheel Assembly mechanism. Both mechanisms are based on the successful ISOPHOT wheel mechanisms of the Infrared Space Observatory. The multi-object mode relies on a complex micro-shutter mechanism to allow for simultaneous observations of hundreds of individual objects anywhere in NIRSpec’s field of view. The mechanisms and their optical elements were designed, integrated and tested by Carl Zeiss Optronics GmbH of Oberkochen, Germany, under contract from Astrium.
• Mid-Infrared Instrument (MIRI) will measure the mid-infrared wavelength range from 5 to 27 micrometres. It contains both a mid-IR camera and an imaging spectrometer. MIRI was developed as a collaboration between NASA and a consortium of European countries and is led by George Rieke (University of Arizona) and Gillian Wright (UK Astronomy Technology Centre, Edinburgh, part of the Science and Technology Facilities Council (STFC)). MIRI features similar wheel mechanisms as NIRSpec which are also developed and built by Carl Zeiss Optronics GmbH under contract from the Max Planck Institute for Astronomy, Heidelberg. The completed Optical Bench Assembly of MIRI was delivered to Goddard in mid-2012 for eventual integration into the ISIM. The temperature of the MIRI must not exceed 6 Kelvin: a helium gas mechanical cooler sited on the warm side of the environmental shield provides this cooling.
• Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS), led by the Canadian Space Agency under project scientist John Hutchings (Herzberg Institute of Astrophysics, National Research Council of Canada), is used to stabilise the line-of-sight of the observatory during science observations. Measurements by the FGS are used both to control the overall orientation of the spacecraft and to drive the fine steering mirror for image stabilisation. The Canadian Space Agency is also providing a Near-Infrared Imager and Slitless Spectrograph (NIRISS) module for astronomical imaging and spectroscopy in the 0.8 to 5-micrometer wavelength range, led by principal investigator René Doyon at the University of Montreal. Because the NIRISS is physically mounted together with the FGS, they are often referred to as a single unit, but they serve entirely different purposes, with one being a scientific instrument and the other being a part of the observatory’s support infrastructure.
NIRCam and MIRI feature starlight-blocking coronagraphs for observation of faint targets such as extrasolar planets and circumstellar disks very close to bright stars.
The infrared detectors for the NIRCam, NIRSpec, FGS, and NIRISS modules are being provided by Teledyne Imaging Sensors (formerly Rockwell Scientific Company). The James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) and Command and Data Handling (ICDH) engineering team uses SpaceWire to send data between the science instruments and the data-handling equipment.

Wavelength

Webb will observe primarily in the infrared and will have four science instruments to capture images and spectra of astronomical objects. These instruments will provide wavelength coverage from 0.6 to 28 micrometres (or “microns”; 1 micron is 1.0 x 10-6 meters). The infrared part of the electromagnetic spectrum goes from about 0.75 microns to a few hundred microns. This means that Webb’s instruments will work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range (in particular in the red and up to the yellow part of the visible spectrum).
The instruments on Hubble can observe a small portion of the infrared spectrum from 0.8 to 2.5 microns, but its primary capabilities are in the ultraviolet and visible parts of the spectrum from 0.1 to 0.8 microns.

Orbit

The Earth is 150 million km from the Sun and the moon orbits the earth at a distance of approximately 384,500 km.
The Hubble Space Telescope orbits around the Earth at an altitude of ~570 km above it.
Webb will not actually orbit the Earth – instead, it will sit at the Earth-Sun L2 Lagrange point, 1.5 million km away! Because Hubble is in Earth orbit, it was able to be launched into space by the space shuttle. Webb will be launched on an Ariane 5 rocket and because it won’t be in Earth orbit, it is not designed to be serviced by the space shuttle.

How Far Will Webb see?

Because of the time, it takes light to travel, the further away an object is, the further back in time we are looking.
This illustration compares various telescopes and how far back they are able to see. Essentially, Hubble can see the equivalent of “toddler galaxies” and Webb Telescope will be able to see “baby galaxies”. One reason Webb will be able to see the first galaxies is because it is an infrared telescope. The Big Bang caused the universe (and thus the galaxies in it) to expand, so most galaxies are moving away from each other. The most distant (and thus youngest) galaxies are moving away so quickly that the light they emit gets shifted towards the red end of the spectrum. This is very similar to listening to a train whistle shifting from higher to a lower frequency as it passes by. Because of visible light from far away, quickly moving, “high redshift” galaxies is shifted to the infrared, infrared telescopes, like Webb, are ideal for observing these early galaxies.

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