On December 25, 2021, the National Aeronautics and Space Administration (NASA) launched the James Webb Space Telescope (JWST) from Europe’s Spaceport in French Guiana jointly with the European Space Agency (ESA) and the Canadian Space Agency. The observatory was lifted from the launchpad to the space by launch vehicle, an Ariane-5 rocket for a destination nearly 15,00,000 km away from the earth, and will reach the second Lagrange point in the next 30 days. (Lagrange points are positions in space where the gravitational pull of two objects precisely equals the centripetal force, needed for a small object to move with the large one.) It was named after James E Webb, a NASA astrophysicist, who had played a key role in the Apollo Moon landings.
Mission Goals of the JWST
The JWST would observe the formation of stars and evolution of galaxies. It would gaze into that era when the very first galaxies came into being over 13.5 billion years ago and could help analyse atmospheres of the exoplanets. It would measure the physical and chemical properties of planetary systems and investigate their potential for life. With the help of its infrared range capabilities, it would pierce through the dust and watch stars taking shape at the centre of dense and dusty clouds. The project would perform mission assurance testing of the flight system to guarantee five years of scientific operations. Its mission would start at the end of the commissioning period of six months after the launch.
About James Webb Space Telescope
The JWST is a large space-based observatory which is optimised for infrared wavelengths. This observatory would complement and extend the discoveries of the 32-year-old space observatory, Hubble Space Telescope (HST). The JWST has a longer wavelength coverage and greatly improved sensitivity, which would enable the JWST to look further back in the earliest Universe. It is designed to have a mission lifetime of not less than five-and-half years after the launch. Its lifetime is expected to be more than 10 years as it is loaded with fuel for a 10-year lifetime.
As the JWST would be operated at the second Sun-Earth Lagrange point which is approximately 1 million miles away from Earth, it would be beyond the reach of any crewed vehicle. Therefore, the servicing of this observatory would not be possible.
It took more than 25 years in the making of the JWST, as there were major delays due to various reasons including the cost overrun. It is the largest and the most powerful telescope ever built and sent to space. Scientists, engineers, and technicians from 14 countries were involved in building the JWST.
Components of the Telescope
The JWST comprises various scientific instruments such as four infrared cameras, spectrographs, and coronagraphs. The spectrographs would break the light into constituent colours which would help in analysis. Coronagraphs would block starlight to allow observation of planets orbiting around those stars. It also has a stabilisation flap, antenna, and spacecraft bus. The primary mirror of the observatory has 18 hexagonal sections which would unfold into a giant 6.5m mirror made of beryllium, which is a grey brittle metal and has high strength per unit weight. Beryllium has been added to some alloys to get high heat resistance, improved corrosion resistance, greater hardness, greater insulating properties, and better casting qualities. The specific advantages of using beryllium are its light weight, stiffness, and stability at very cold temperatures. The beryllium mirrors are plated with gold to optimise them for infrared light. The primary mirror of the JWST must be cooled to less than -223 °C to enable it to pick up faint infrared light from the early Universe. The shield at the other side facing the sun would be hot at 93 °C. It also has a 0.74m secondary mirror.
It has five thin sunshades each approximately of the size of a tennis court. These sunshades would shield the mirrors from sunlight. There are 107 pins or membrane-release devices, which would further release to unfold the sunshield. Thereafter, there are the main near infrared cameras and a clutch of machines to detect and capture galactic bodies and the exoplanets.
JWST’s Communication with Scientists on Earth
The JWST would send science and engineering data to Earth using a high-frequency radio transmitter. Its handler astrophysicists would move the segments for getting mirror to stare at the silver of the sky for days and record infrared light. Despite this exposure, light would register only as little red spots. The aligned mirrors would give a magnified image of each tiny red spot to give a clearest view of a single pioneering star. The telescope would rotate its high-gain antenna towards Earth to further facilitate communications with the astrophysicists. The large radio antennas, a part of the NASA Deep Science Network, would receive the signals and forward them to the Webb Science and Operation Center, the Space Telescope Science Institute, Baltimore, USA.
The calibration and commissioning is expected to complete in a period of six months from its launch. Initially, the JWST would tack nearby objects like asteroids, comets, moons, etc. Thereafter, it would start to conduct its routine science operations.
The JWST versus the HST
The HST was launched into the space by NASA’s Space Shuttle Discovery in 1990. Scientists have used the HST to observe some of the most distant stars and galaxies yet seen, as well as the planets in our solar system. The JWST would primarily study the Universe in the infrared light, while the HST looks at the Universe mainly at optical and ultraviolet wavelengths. While the HST has a mass of 12,200 kg and lifetime of 31 years, the JWST has a mass of 6,200 kg and a lifetime of 10 years.
The primary mirror of the JWST is of about 6.5m diameter, but the HST has a 2.4m primary mirror, which means that JWST is nearly 100 times more sensitive. The HST operates in the visible spectrum while JWST works on infrared and could pierce through stellar dust to reveal structures.
The JWST operates on four instruments to capture images and spectra of astronomical objects with a wavelength coverage from 0.6 to 28 microns as compared to the HST which can observe mainly the ultraviolet and visible parts of the spectrum ranging from 0.1 to 0.8 microns.
The HST orbits Earth at an altitude of about 570km whereas the JWST would sit at the Earth-Sun L2 Lagrange point at about 1.5 million kilometres away.
© Spectrum Books Pvt Ltd.