James Webb Space Telescope infrared technologies allow a deeper, more thorough look into space than Hubble

"JWST People" by NASA. Public domain.

“JWST People” by NASA. Public domain.

In 1996, the National Aeronautics and Space Administration (NASA) began construction of a space telescope which would be the planned successor to the Hubble Space Telescope, a massive scientific instrument sent into orbit just a few years earlier in 1990. The James Webb Space Telescope (JWST), currently scheduled to launch in October 2018, is a large infrared telescope which will dramatically improve upon the vision of the universe which we get through Hubble. This November, NASA moved into an important phase of tests that will aid in assessing whether the JWST can get through launch conditions, including intense sound and vibrations, without affecting the operation of JWST’s optical system afterward.

JWST is named after James Webb, NASA’s second administrator who served from February 1961 to October 1968, a very important period for the agency. Webb is credited with ensuring that NASA wasn’t solely focused on the mission to the Moon and was an early supporter having a telescope like Hubble in orbit. A government official and not a scientist, Webb set a very successful path for the agency in terms of its engagement with universities and private industry. JWST was renamed in 2002 in honor of Webb, the project having previously been referred to as the Next Generation Space Telescope (NGST).

The design and construction of JWST is a collaboration between international space agencies including NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA). The project has tapped unmanned systems developer Northrop Grumman (NYSE:NOC) of Falls Church, VA, as an industrial partner. Development of JWST is being managed by the Goddard Space Flight Center in Greenbelt, MD and once in orbit it will be operated by the Space Telescope Science Institute, a Baltimore, MD-based science operations center which is also responsible for Hubble’s operation.

Like any NASA project, the James Webb Space Telescope is being built to serve lofty and useful scientific goals for a better understanding of the universe in which we live. The telescope’s infrared technologies will be capable of adjusting for very high redshift which prevents us from seeing details of the galaxies which are furthest from us. Infrared light covers a very wide spectrum of electromagnetic radiation wavelengths, but infrared wavelengths are longer than the human eye can see alone; the longer the wavelength, the more the light shifts towards red. JWST will be capable of obtaining detailed images of galaxies which are 13.6 billion light years away, giving scientists a clear view of the “era of recombination” of the first particles pairing up about 300,000 years after the Big Bang. It will also shine a light on the “epoch of reionization,” or the formation of the universe’s first stars. JWST also gives scientists a look at how entire planetary systems and galaxies have developed from their earliest days onward. Spectroscopy equipment on JWST will yield information on the chemical and physical properties of planetary systems and can help search for life on nearby exoplanets.

Ball engineers dismantle array of JWST mirrors, from NASA. Public domain.

Ball engineers dismantle array of JWST mirrors, from NASA. Public domain.

The primary mirror of the James Webb Space Telescope has a diameter of 6.5 meters, or a little more than 21 feet. By contrast, Hubble uses a primary mirror which has a diameter of 2.4 meters, or 7.9 feet. JWST’s primary mirror has a large aperture of 25 square meters, allowing JWST to collect a great deal of light in a single image exposure and better isolate images collected from deep space. JWST’s primary mirrors includes 18 hexagonal segments which are arranged in a honeycomb configuration for high optical performance at a much lighter weight than a single-segment mirror of the same size. The 2016 class of inductees into the National Inventors Hall of Fame includes British-American astronomer Roger Angel, who developed the honeycomb mirror structure which enables the construction of large telescopes like JWST.

There are four scientific instruments included within the part of JWST’s payload which is known as the Integrated Science Instrument Module (ISIM), the skeletal structure housing the scientific instruments. The primary imaging instrument on JWST is the Near Infrared Camera (NIRCam) which can record images picked up in the near-infrared light range from 0.6 microns to 5 microns including early-formation stars and galaxies, star populations in nearby galaxies and young Milky Way stars. NIRCam is also outfitted with coronagraphs, instruments which can block the light of brighter objects in order to see more dimly lit objects which are closer, similar to how a person can use a hand to block the sun from their vision and better see objects when the sun is shining in his or her face. JWST’s other imaging instrument is the Mid-Infrared Instrument (MIRI), which can cover the mid-infrared range from 5 microns to 28 microns to see more distant galaxies. MIRI’s wide-field imaging capacity allows the capture of detailed images from deep space. MIRI also includes spectroscopy equipment which can determine some physical characteristics of faraway celestial bodies.

Spectroscopy can reveal physical properties of distant objects by analyzing electromagnetic radiation, but a fuller understanding of the temperature, mass and chemical composition of those bodies is made possible by JWST’s Near Infrared Spectrograph (NIRSpec). NIRSpec will be the first spectrograph launched into space which can focus on multiple objects at once, up to 100 different celestial bodies at a time. This capability is made possible by an innovative microshutter array, a collection of microshutter cells, each about the width of a human hair, which can be individually controlled to focus upon or block out a portion of the sky. The microshutter array is specifically engineered to work in cryogenic environments so that 62,000 individual microshutters can be magnetically opened and closed. Coupled with the wide spectrum of light collected by JWST’s imaging components, NIRSpec can help unlock a gold rush of knowledge on the physical makeup of the universe.

Ball Aerospace technicians remove final six JWST mirrors after testing, from NASA. Public domain.

Ball Aerospace technicians remove final six JWST mirrors after testing, from NASA. Public domain.

Of course, it’s not enough to send a telescope with a camera up into space and hope that they’ll get the right images at the right time. That job becomes the responsibility of the Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS) instrument array. The FGS helps to guide JWST’s camera in such a way that it can find a specific star with 95 percent probability, even at high galactic altitudes. Although packaged with FGS, NIRISS is functionally independent as a spectrograph offering multiple modes of observation. It offers the highest angular resolution of any JWST instrument, capturing images at the highest possible resolution and enabling the detection of planets which are very close to their parent stars. NIRISS also affords scientists a better idea of the temperature and gravity of exoplanets, including planets which aren’t in our solar system but are in the Milky Way.

The near-infrared and mid-infrared sensors in JWST’s instruments reflects innovations in building sensors to detect infrared wavelengths. Near-infrared sensors developed by California research and development firm Teledyne Scientific & Imaging are made with a mercury-cadmium-telluride material made with varying compositions of those chemicals to provide peak performance for NIRCam on each wavelength of the near-infrared range and detecting four million pixels. The mid-infrared sensors, developed by a vision systems subsidiary of Massachusetts-based Raytheon Company (NYSE:RTN), are made of arsenic-doped silicon and can detect about one million pixels each. 10 near-infrared sensors can be found on NIRCam, three sensors on FGS/NIRISS and two on NIRSpec. MIRI has been outfitted with three mid-infrared sensors.

Holding all of JWST together is a backplane engineered to support JWST’s large primary mirror. The backplane is perhaps the most durable mirror frame created on Earth, composed of a graphite material which offers stability at temperatures of less than -400°F. The high performance stability of this material is designed to hold the mirror steady down to 32 nanometers, or 1/10,000 of the width of a human hair. The backplane also enables deployment of the primary mirror after JWST has reached space; the mirror is too large itself to be launched from an unfolded position.

Other innovations abound on JWST. A wavefront sensing and control system developed by the aerospace division of Colorado-based Ball Corporation (NYSE:BLL) corrects optical errors to help the honeycomb mirror structure operate more like a single monolithic mirror. Sunshield membrane coatings of aluminum and doped silicon covering an area about the size of a tennis court regulate the telescope’s temperature from interference with heat energy from the sun, enabling more accurate readings of very distant sources of light; the membrane coating material is made commercially available by DuPont (NYSE:DD), based in Delaware. More temperature control for the scientific instruments comes courtesy of a cryocooler designed to keep MIRI’s specially formulated infrared sensors at a constant temperature of less than 7°K (-447°F).

The James Webb Space Telescope’s primary mission will have a lifetime of at least 5 years with a potential lifetime of greater than 10 years for continued scientific observation. JWST’s time of service is limited by its fuel supply necessary to maintain its orbit and operate the scientific instruments. Unfortunately, JWST cannot simply be refueled and maintained like Hubble, which had to essentially be given a pair of glasses to correct a manufacturing defect after launch. Hubble is in low-Earth orbit 375 miles from the Earth. By contrast, JWST will orbit the Earth at the second Sun-Earth Lagrange point about one million miles from the Earth. Although NASA looked at scenarios where JWST could be in low-Earth orbit for servicing, it was concluded that keeping JWST that close to the Earth would make the other engineering for scientific instruments too complex to complete.

Share

Warning & Disclaimer: The pages, articles and comments on IPWatchdog.com do not constitute legal advice, nor do they create any attorney-client relationship. The articles published express the personal opinion and views of the author as of the time of publication and should not be attributed to the author’s employer, clients or the sponsors of IPWatchdog.com.

Join the Discussion

No comments yet.