Thirty days from earth, and James Webb Space Telescope It will glide into a standing orbit nearly a million miles away on Monday, the ideal place to scan the sky for the faint infrared light from The first generation of stars and galaxies.
But Go there – And Posted successfully Giant umbrellas, mirrors and other accessories along the way – that’s only half the fun.
Scientists and engineers must now turn the $10 billion Webb into an efficient telescope, precisely aligning the 18 main mirror segments so that they work together as a single 21.3-foot-wide mirror, the largest ever launched.
NASA
Earlier this week, remote engineers completed a multi-day process of raising each part, the telescope’s 2.4-foot-wide secondary mirror, half an inch from the launch lock that held it in place for the duration of the observatory. Christmas Day Go To Space On board the European Ariane 5 missile.
Now fully deployed, the 18 clips are currently aligned by about a millimeter or so. In order for the telescope to achieve extremely sharp focus, this alignment must be precisely adjusted to 1/10000th the width of a human hair using several actuators to tilt and even change the shape of the part if necessary.
“Our main mirror is segmented, and this segment only needs to align a fraction of the wavelength of light,” said Lee Feinberg, director of the Optical Telescope Elements at NASA’s Goddard Space Flight Center. “We’re not talking in microns, we’re talking about a fraction of a wavelength. That’s what’s really hard to deal with about Webb.”
Strong enough to detect the heat of a bee as far as the moon
Once the tool is adjusted and calibrated, the Webb will be 100 times more powerful than HubbleIt’s so sensitive to infrared, NASA says, that it can detect the faint heat of bees far from the moon.
Each mirror piece has been placed on a prescription that takes into account the distorting effects of gravity on Earth and the expected contraction at the extremely low temperatures in space. They were well aware that if one were blown up to the size of the United States, the 14,000-foot Rocky Mountains would be less than 2 inches high.
But if Webb were to target today’s bright star, the result would be 18 separate images “and they would look terrible, they would be very blurry,” Feinberg said in an interview, “because the main mirror segments weren’t aligned yet.”
This was the next big hurdle for Webb’s team, mapping and then skewing each piece bit by bit, combining the 18 images to form a single point of perfectly focused light. This is an iterative multi-step process that is expected to take several months to complete.
But first, the telescope must enter orbit around Lagrange Point 2,930,000 miles from Earth where the Sun’s and Earth’s gravity combine to form a pocket of stability that allows the spacecraft to stay in place with minimal fuel consumption.
This is also the point at which Webb’s umbrella, the size of a tennis court, can operate to its maximum benefit, blocking heat from the sun, Earth, moon, and even warm interplanetary dust that would otherwise wet the telescope’s sensitive infrared detector.
By Saturday, parts of the mirror had cooled to about minus 340 degrees Fahrenheit, heading for an operating temperature of around minus 390, or less than 40 degrees above absolute zero.
NASA
While the cooldown continues, a 4-minute 58-second trajectory correction detonator is scheduled to launch Monday at 2 p.m. EDT to change the spacecraft’s speed by 3.4 mph, enough to put it into deep orbit around Lagrange Point 2.
If all goes well, the telescope will remain in this six-month orbit for the remainder of its operating life, releasing its periodic urges to remain at the station.
Getting ready to take a “good picture”
With orbital inserts lit up behind them, engineers will move forward with mirror alignment, one of Webb’s most complex aspects. complex publications.
Each 4.3-foot-wide hexagonal main mirror clip features six mechanical actuators in a “hexagonal” arrangement on the back, allowing for movement in six directions. The seventh actuator can push or pull the center of the clip to slightly distort the curvature if necessary.
After Webb’s near infrared camera, or NIRCam, cools to operating temperature, and Webb will target the bright star so that the instrument can plot reflections from 18 sectors, creating a mosaic showing their relative size and position.
that mirror slice Then modified one at a time, using one trigger and then another, to steer each one properly. Additional mosaics will be created as the process continues and depending on the result, the alignment process may have to be repeated.
“The important thing is to make the eighteen main mirror segments point in the same way so that the images are roughly the same size,” Feinberg said. “Some of them might be so out of focus that you might get a big dot (blurred star image) in section 5 and a small dot in section 3.”
The goal is to tilt the portion as needed to reduce the size of the out-of-focus image and then move multiple reflections to the same point in the center of the telescope’s optical axis, all stacked on top of each other to produce a single beam of highly focused light.
“At the highest level, think of it as 18 separate telescopes lined up at roughly the same level,” Feinberg said. “And then we’re going to overlap 18 dots on top of each other. We call this image stacking. This is the process of tilting the main mirror segments so that the images lie on top of each other.”
The key, he says, is “you really have to have really good control of those bikes, very precise tilt, because we need these 18 points to overlap very well.”
Aerospace Ball
Any part can lose any of the six tilt triggers without any effect. Even the loss of the central drive can be compensated to some extent by moving the clip up or down a bit.
But extensive field tests have shown that the high-tech machines are extremely reliable. The procedure was tested before launch using a telescope scale model, and Feinberg said he was confident that the alignment process would go according to plan.
“When will we gradually have a star image? I think it was around March, maybe the end of March,” he said.
“But the next question is, when will we have telescopes in full alignment, including secondary mirrors, optimized for all four instruments? Our original plan had been to achieve that four full months into the mission. So it’s going to be like the end of April.”
This is still not enough to start scientific observations.
Once the optical system is aligned, the team will focus on testing and calibrating the NIRCam, its composite camera and spectrometer, and the other three telescope spectrographs. Equipment, One of these includes the precision guidance sensors needed to keep the Webb locked on the target.
This process will take two months or more to complete. Only then will the focused “first light” image be released to the public.
“We want to make sure that the first image the world sees, that humanity sees, does justice to this $10 billion telescope and not an image of, you know, hi, stars,” said Jane Rigby, Webb Operations Project Scientist. in the Goddess.
“So we’re planning a series of ‘cool’ images to be released at the end of commissioning when we begin normal science operations designed to show what this telescope can do… and to release everyone.”
