NASA's James Webb Space Telescope, the largest space observatory in history, will launch on an Ariane 5 rocket from the Guiana Space Center in Kourou, French Guiana on December 24, after 14 years of delays.
The telescope has two primary missions. Its first mission is to explore the early phases of the universe by collecting infrared light from the cosmos to shed light on the origins of the universe. Its second mission is to discover planets that are out of our solar system and investigate their atmospheres for signs of life.
The cost of the Webb telescope is around $10 billion (€9 billion), covering the 20-year build period, the launch, and five years of operations in space.
The telescope, equipped with a 21 ft-wide (6.5 m) mirror and four super-sensitive instruments, will stare at a very narrow spot in the sky for days to detect light. "They will be just little red specks," says John Mather, a JWST senior project scientist, and Nobel Prize winner. "We think there should be stars, or galaxies, or black holes may be beginning at 100 million years after the Big Bang. There won't be many of them to find at that time but the Webb telescope can see them if they're there, and we're lucky," he told the BBC World Service.
But the telescope will also emit infrared light itself from its electronic devices, so its instruments need to be really cold, about 40 kelvins (388°Fahrenheit below zero or 233°Celsius below zero), while the detectors inside the mid-infrared instrument (MIRI) needs to be at even colder temperatures, less than 7 kelvins (448° Fahrenheit below zero or 266°Celsius below zero).
After its launch, Webb will unfold a sun shield the size of a tennis court, to block the MIRI and other instruments from the Sun's heat. MIRI's cryocooler will spend 19 days lowering the temperature of the instrument's detectors to less than 7 kelvins, after approximately 77 days after launch.
"It's relatively easy to cool something down to that temperature on Earth, typically for scientific or industrial applications," said Konstantin Penanen, a cryocooler specialist at NASA's Jet Propulsion Laboratory in Southern California, which manages the MIRI instrument for NASA. "But those Earth-based systems are very bulky and energy inefficient. For a space observatory, we need a cooler that is physically compact, highly energy-efficient, and it has to be highly reliable because we can't go out and repair it. So those are the challenges we faced, and in that respect, I would say the MIRI cryocooler is certainly at the cutting edge,” he added.
One of Webb's goals will be to study the properties of the first generation of stars that were formed in the universe. Webb's Near-Infrared Camera, or NIRCam instrument, will be able to detect these extremely distant objects, while MIRI will help confirm that these faint sources of light are clusters of first-generation stars. It will also detect molecules that are common on Earth, such as water, carbon dioxide, and methane, and those of rocky minerals like silicates, in suitable environments around nearby stars, where planets may form.
"By combining expertise from both the United States and Europe, we have developed MIRI as a powerful capability for Webb that will enable astronomers from all over the world to answer big questions about how stars, planets, and galaxies form and evolve," said Gillian Wright, co-lead of the MIRI science team and the instrument's European principal investigator at the U.K. Astronomy Technology Centre (UK ATC).