For the past 31 years, the Hubble Space Telescope has been an invaluable all-round observation platform for astronomers, but it has recently begun to show its age. Last serviced in 2009, the telescope had to go into partial shutdown. “safe way“Several times in the last few years – recently, this October. And while optimistic estimates suggest Hubble could remain in operation for the rest of the decade, NASA and its ESA and CSA partners have already spent more than a decade developing a successor, the James Webb Space Telescope (JWST). When Webb is launched – which is currently scheduled to take off on Christmas – it will take over as the main eye of humanity in the sky in the coming decades.
The 7.2-tonne JWST will be the largest telescope NASA has ever put into orbit. Its primary array of 6.5-meter mirrors – consisting of 18 gilded hexagonal segments – is more than twice the size of Hubble’s and nearly 60 times larger than Spitzer telescope, who retired in 2020. The sun visor he uses to protect his sensitive infrared sensors is almost as long as a tennis court, and the telescopic apparatus as a whole is three stories high. The 458 gigabits of data collected daily will first be redirected through NASA’s Deep Space Network and then forwarded to the Space Telescope Science Institute in Baltimore, Maryland, which will collect and distribute this information to the wider astronomical community.
When it reaches its orbital home at L2 Lagrange point 930,000 miles from Earth, JWST will begin its mission at four points: seeking light from the earliest stars after the Big Bang; studying the formation and development of galaxies, examining the evolution of stars and planetary systems; and the search for the origin of life.
To do so, Webb will take a different approach than Hubble before him. While Hubble observed the universe in the visible and ultraviolet spectrum, JWST will see in the infrared, just as Spitzer knew, but with far greater resolution and clarity. Using this infrared radiation is crucial to Webb’s mission because that wavelength can peek through clouds of interstellar gases and dust to see otherwise obscured objects outside of it.
Webb’s package of cameras consists of four individual components: a medium infrared instrument (MIRI), a near-infrared camera (NIRCam), a near-infrared spectrograph (NIRSpec), and a near-infrared imaging device and a slot-free spectrograph / fine guidance sensor (NIRISS / FGS). These instruments are actually so sensitive that they can detect their own thermal radiation while working. To keep these infrared emissions to a minimum, the three sensors were cooled to negative 388 degrees Fahrenheit (-233 degrees C). Particularly sensitive MIRI cools even more to -448 degrees F (-266 degrees C) – that’s just 7 degrees Kelvin above absolute zero.
Getting MIRI so cold is not an easy feat. Once JWST enters orbit, the telescope will spend weeks slowly cooling the sensor to its optimum operating temperature using a helium-based cooling system.
“It’s relatively easy to cool something to that temperature on Earth, typical of scientific or industrial applications,” said JPL cryocooling expert Konstantin Penanen in a recent NASA blog post. “But these terrestrial systems are very cumbersome and energy inefficient. For the space observatory, we need a cooler that is physically compact, highly energy efficient, and must be very reliable because we can’t get out and fix it. So, these are the challenges we have faced, and in that respect, I would say that MIRI cryocooler is definitely at its peak. ”
The extra effort required by MIRI will be worth it because terrestrial infrared telescopes – especially those operating within the mid-infrared spectrum such as MIRI, are greatly hampered by the emission of heat from the devices themselves and the surrounding atmosphere.
“With the other three instruments, Webb observes wavelengths up to 5 microns. Adding wavelengths to 28.5 microns with MIRI really increases his range of science, ”said George Rieke, a professor of astronomy at the University of Arizona. he said earlier this month in a NASA blog. “This includes everything from studying protostars and their surrounding protoplanetary disks, the energy balance of exoplanets, the loss of mass of evolved stars, the circumnuclear manure around central black holes in active galactic nuclei, and much more.”
Given the very specific needs for low JWST temperatures, keeping the telescope sensor assembly away from direct sunlight (and blocked from other light sources such as the Moon and Earth) is crucial. To ensure these cameras were permanently shaded, NASA engineers built five-layer sun visor made of kapton foil coated with aluminum to keep them cool and cool in the dark.
“Shape and design also direct heat from the sides, around the perimeter, between layers,” said James Cooper, JWST’s Sunshield Manager at Goddard Space Flight Center. “The heat generated by the spacecraft’s bus in the ‘core’, or in the center, is expelled between the layers of the membrane so it can’t heat the optics.”
Measuring 69.5 x 46.5 feet x 0.001 inches, the dragon-shaped sun visor is stacked five layers high so the energy absorbed by the top layer radiates into the space between them, making each subsequent layer slightly cooler than the one above it. In fact, the temperature difference at the outermost (383K or 230 degrees F) and innermost layers (36K, about -394 degrees F) is about an order of magnitude.
To gather enough light to see the faintest, most distant possible stars – some as far back as 13 billion light-years away – JWST will rely on its massive array of 6.5-meter primary mirrors. Unlike Hubble, which used a single 2.4 m wide mirror, Webb’s mirror is divided into 18 individual segments, each weighing just 46 pounds thanks to its beryllium construction. They are coated with gold to enhance their reflection of infrared light and are hexagonal in shape so that, when fully assembled in orbit, they will fit together firmly enough to act as a single, symmetrical reflective plane with no gaps. Their small size also allows them to be easily separated and folded to fit into the narrow frames of the Ariane 5 rocket to be launched into orbit.
The role of coordinating these single-point focusing segments in a distant galaxy belongs to the mirror actuator assembly. Seven small engines are located at the rear of each segment of the mirror (one in each corner and the seventh in the middle), which allows precise control of their orientation and curvature. “Alignment of the primary segments of the mirror as if they were one large mirror means that each mirror is aligned to 1 / 10,000th the thickness of a human hair,” He said Webb’s Optical Telescope Element Manager, Lee Feinberg.
After more than 20 years of development and delays, which cost $ 10 billion and involve the efforts of more than 10,000 people, the Webb Telescope is finally ready to launch – and hopefully this time it will actually take time. The program had a delay, after a delay, after a delay in the startup schedule. NASA has given up on the launch date March 2021, following the initial epidemic of COVID-19 and related closures – although, to be fair, GAO in January 2020. gave JWST only a 12 percent chance run by the end of this year – and set a vague schedule “sometime in 2021.” for its launch.
OUR later revised that estimate to the company “sometime in October 2021.”, eventually settling into a Halloween launch, only to postpone again by the end of November / beginning of December. Of course, the beginning of December quickly became late December, to be exact 22, which was then reverted to the current date December 24th. Actually, let it be 25.
These delays are caused by a myriad of factors involved in preparing an instrument of this size and sensitivity for launch. After completing its construction, JWST had to pass an exhaustive battery of tests, then lightly load it into a shipping container and transport it to the launch site in Kourou, French Guiana. Once there, the actual task of preparation, refueling and refueling of the JWST on the Ariane 5 rocket it lasted another 55 days.
That time frame was further extended by the Nov. 9 “incident” in which “the sudden, unplanned release of a clamp – which attaches Webb to a rocket launcher adapter – caused vibration throughout the observatory,” according to NASA. The Webb’s anomaly review committee launched an additional round of testing to ensure that these vibrations do not damage other components or break something important out of alignment.
Now that it’s a telescope is considered A-OK, final preparations are underway. Excluding more downtime, JWST will launch at 7:20 ET on Christmas (watch live here!) begin his 30-day, 1.5 million-mile journey from Lagrange 2 where he will spend two weeks slowly developing his mirrors and sun shield, and then begin exploring the depths of early space.
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