by S. Prasad Ganti
It was the most awaited event – launch of the James Webb telescope into space on Christmas day 2021. In development for close to two decades and a hefty price tag of $10 billion. It is considered as a successor to the Hubble space telescope which still continues to be used and provides great pictures of our universe. Why did it cost more and take much longer with so many overruns ? And what is it expected to do after it settles down in its new home far from Earth over the next six months ?
It is a very complex scientific instrument ever built by humanity. Its primary mirror is about 2-3 times bigger than Hubble, although much lighter. Building and deploying a mirror of that size is a gigantic exercise. Unlike Hubble, this mirror is not a single piece of glass. It is made of eighteen hexagonal segments. Each made of lighter Beryllium and coated with a thin layer of gold. This was done to fold the mirror at the time of launch and unfold it once in space. Else, there is no rocket capable of taking it up unfolded. So are the solar panels which will provide power to the telescope. The panels are folded for launch and were unfolded in space.
Next are the most sophisticated instruments onboard. With each new generation of technology, the detectors become more sensitive. The basic instrumentation is a camera and a spectrograph. A camera captures the image while the spectrograph splits the incoming radiation into different frequencies (colors for visible radiation). Unlike Hubble which looked at the Universe in the visible region, Webb will operate in the infrared region, of lower frequencies than the visible light. Since Webb is going to look at further and hence older objects in the Universe, something like viewing the Universe when it was a baby in its diapers, infrared is more suitable. All the ancient light is now stretched so that its remnants are in the infrared region. The gold coating of the mirror will reflect the infrared waves much better. Maybe the next generation telescope may attempt to look at when the Universe was in its mother’s womb !
Next is an enormous heat shield which will protect its instrumentation from the heat of the Sun and the Earth. The instruments need to be cooled down to the lowest temperatures in the Universe so as to be able to view the infrared waves. Else, any heat, even from the telescope and its instruments will distort the picture. To get away from Earth’s heat, the telescope will be positioned about a million miles away at a point in space called Lagrangian point L2. Postulated by French mathematician Joseph Lagrange, there are five points in space where the Sun’s and Earth’s gravity almost cancel each other. Given below is the picture courtesy NASA. L2 is a point away from both the Earth and the Sun. The heat shield will protect from Earth and Sun on the left so that the telescope is free to look into deep space into the right. At L2, the fuel consumption is minimum so that the telescope can function for about ten years or hopefully longer. with the given fuel budget.
Once the telescope was constructed in California, its long terrestrial journey started. Too big to fit into any aircraft, it was placed in a specialized container and loaded onto a ship. The ship made the perilous journey through the Panama canal before reaching French Guiana in South America where the European Space Agency (ESA) has its Ariane launch facilities. While ESA is a partner in the telescope mission, its Ariane is the largest and the most reliable rocket. The rocket did its job on Christmas day. After unfurling its solar panels, the telescope is travelling towards the L2 Lagrange point. It is expected to take about a month to reach.
After reaching its destination, the heat shield and the mirror will unfurl. Then the mirror needs to be tuned. Each segment of the mirror is actuated by a motor. There are too many points of failure in this whole process. Any failure can doom the mission. The telescope will be beyond any human mission for servicing. If everything goes well, we will start getting pictures by about mid 2022. Else, bad luck and we go back to the drawing board again.
Other than viewing the original glare from the infancy of the Universe, the telescope will also help in detecting exoplanets, the planets outside of our solar system. Although Kepler and now TESS space telescopes are on the job, Webb will be much more sensitive because of its abilities in the infrared region. Planets like Earth emit radiation in this region. Webb also has a coronagraph, an instrument which blocks out the brilliant glare of the central star and helps the infrared detectors gather information from the orbiting planets.
Hoping that Webb will work flawlessly and give us glimpses of our early universe and the hidden universe of exoplanets for many years to come.