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NASA’s $10 billion James Webb Space Telescope will study the origins of the universe


For the past 31 years, the Hubble Space Telescope has been a versatile observation platform for astronomers, but it’s only recently beginning to show its age. The telescope was last serviced in 2009, and it has had to enter “safe mode” for partial shutdowns several times over the past few years – most recently, in October of this year. And while optimistic estimates suggest that Hubble could remain in operation until the end of the decade, NASA, along with its European Space Agency and Canadian Space Agency partners, has already spent more than a dozen years developing the James Webb Space Telescope (JWST). When Webb – currently set to take off on Christmas Day – is launched, it will serve as humanity’s preeminent eye in the sky for decades to come.

The 7.2-ton JWST will be the largest telescope NASA has ever put into orbit. The primary mirror’s 6.5-meter array – made up of 18 gold-plated hexagons – is more than twice the size of the Hubble telescope and about 60 times the size of the Spitzer Telescope, which was discontinued in 2020. The sun shield it uses for protection is roughly the size of its precise infrared sensors. The length of the tennis court, the height of the telescope as a whole is three stories. The 458 gigabytes of data collected daily will first be routed through NASA’s Deep Space Network, and then sent to the Space Telescope Science Institute in Baltimore, Maryland, which will collect and disseminate this information to the larger astronomy community.

When it reaches its orbital home at L2 Lagrange, 930,000 miles from Earth, JWST will begin its four-point mission: searching for light from the oldest post-Big Bang stars; The study of the formation and evolution of galaxies, the study of the evolution of stars and planetary systems; The search for the origins of life.

To do so, Webb will take a different approach than Hubble before him. While Hubble has been looking at the universe in the visible and ultraviolet spectra, JWST will see infrared radiation, just as Spitzer used to but with much greater precision and clarity. Using this infrared is critical to the Webb mission as this wavelength can peer through interstellar clouds of gas and dust to see obscured objects beyond.

NASA / Chris Jenn

The Webb camera family consists of four individual components: the medium infrared instrument (MIRI), the near-infrared camera (NIRCam), the near-infrared spectrometer (NIRSpec), the near-infrared imager and the slit spectrophotometer/precision orientation sensor (NERIS). / FGS). These devices are actually so sensitive that they can detect their own thermal radiation while they are in operation. To reduce infrared emissions, three of the sensors are cooled to minus 388 degrees Fahrenheit (-233 degrees Celsius). The particularly sensitive MIRI is cooled even further to -448 degrees Fahrenheit (-266 degrees Celsius) – that’s just 7 degrees Kelvin above absolute zero.

Getting cold MIRI is not easy. After the telescope makes its way into orbit, the telescope will spend weeks slowly cooling the sensor to its optimum operating temperature using a helium-based cooling system.

“It is relatively easy to cool something to this temperature on Earth, usually for scientific or industrial applications,” Konstantin Benanen, a coolant specialist at the Jet Propulsion Laboratory, said in a recent NASA blog. But those land-based systems are very bulky and inefficient in using energy. For a space observatory, we need a cooler that’s physically compact, very energy efficient, and it has to be very reliable because we can’t go out and fix it. So these are the challenges we faced, and in that regard, I would say the MIRI cryogenic cooler is definitely on the cutting edge. “

The extra effort that MIRI requires is worth it because terrestrial infrared telescopes—particularly those within the mid-infrared spectrum such as MIRI—are largely hampered by heat emissions from the instruments themselves and the surrounding atmosphere.

“With the other three instruments, Webb observes wavelengths of up to 5 microns. Adding wavelengths to 28.5 microns with MIRI really increases the scope of science,” George Rick, professor of astronomy at the University of Arizona, said earlier this month in a NASA blog. “This includes everything from studying protostars and their surrounding protoplanetary disks, the energy balance of exoplanets, mass loss from evolving stars, circumscribing to central black holes in active galactic nuclei, and much more.”

Sunscreen Web

NASA

Given JWST’s own lower temperature needs, keeping the telescope’s sensor array out of direct sunlight (and blocking it from other light sources such as the Moon and Earth) is critical. To make sure these cameras were permanently shaded, NASA engineers built a five-layer sunshade made of aluminum-coated Kapton film to keep them in the cold, cold darkness.

“The shape and design also direct heat outward, around the perimeter, between the layers,” said James Cooper, Director of Sunshield at JWST at the Goddard Space Flight Center. “The heat generated by the spacecraft’s vector in the ‘core,’ or center, is pushed out between the layers of the membrane so that it cannot heat the optics.”

Measuring 69.5 feet by 46.5 feet by 0.001 inches, the kite-shaped sunscreen is five layers high so that the energy absorbed by the top layer radiates into the space between them, making each successive layer slightly cooler than the one above it. In fact, the temperature difference at the outermost (383 K, or 230 degrees Fahrenheit) and innermost layers (36 K, about -394 degrees Fahrenheit) is roughly an order of magnitude.

JWST is much bigger

NASA

In order to gather enough light to display the faintest and most distant stars — some as far as 13 billion light-years away — JWST will rely on the massive 6.5-meter primary mirror array. Unlike Hubble, which used a single 2.4-meter-wide mirror, the Web mirror is divided into 18 individual segments, each weighing just 46 pounds thanks to its beryllium construction. It’s gold-plated to enhance infrared light reflection and its hexagonal shape, when fully assembled into orbit, will fit together snugly enough to function as a single, symmetrical gapless reflector plane. Its small size also allows it to split and fold easily in order to fit within the narrow confines of the Ariane 5 missile it will put into orbit.

JWST aboard Ariane 5

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The role of coordinating these fragments to focus on a single spot in a distant galaxy falls on the set of mirror actuators. Seven small motors are located on the reverse side of each mirror segment (one in each corner and the seventh in the middle), allowing precise control of its direction and curvature. “Aligning the primary mirror segments as if they were one large mirror means that each mirror aligns with the thickness of a human hair by 1/10000,” said Webb Optical Telescope Element Director Lee Feinberg.

After more than 20 years of development and delays, costing $10 billion and involving the efforts of more than 10,000 people, the Webb Telescope is finally ready to launch — hopefully this time around. The program has seen a delay, after a delay, after the delay in its launch date. NASA ditched the initial March 2021 date in the wake of the initial COVID-19 outbreak and associated shutdowns — but to be fair, the Government Accountability Office in January 2020 only gave a 12% chance of getting off the ground. The end of this year — and a vague “sometime in 2021” timeline for its release.

The whole web has been folded

NASA

NASA later revised that estimate to “sometime in October 2021,” eventually settling on the Halloween launch window, only to delay it again to late November/early December. Of course, early December soon became late December, specifically the 22nd, which was pushed back to its current date of 24 December. In fact, make that twenty-fifth.

These delays are caused by the myriad factors that go into getting a tool of this size and sensitivity ready for launch. After its construction was completed, JWST had to undergo a comprehensive set of tests, then gently load it into a shipping container and transport it to the launch site in Kourou, French Guiana. Once there, the actual task of equipping, refueling and loading the JWST onto the Ariane 5 rocket took another 55 days.

That timeline was extended further due to an “accident” on November 9 in which the sudden, unplanned release of the clamp bar — which Webb secures to the launch vehicle’s adapter — caused a vibration throughout the observatory, according to NASA. The Web Anomaly Review Board has begun an additional round of testing to make sure those vibrations don’t damage other components or knock anything important out of alignment.

JWST Posting Schedule

NASA

Now that the telescope is A-OK, final preparations are underway. Barring any other setbacks, JWST will launch at 7:20 ET on Christmas Day (watch live here!) to begin its 30-day, 1.5-million-kilometer journey outside Lagrange 2 where it will spend two weeks slowly emerging its mirrors and solar shield. Then you begin to explore the depths of the early universe.

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