Engineers for the James Webb Space Telescope are in the midst of an intricate, three-month-long process of aligning the telescope’s 18 separate mirror segments to work together as one giant, high-precision 6.5-meter (21.3-foot) primary telescope mirror.
This process, called phasing, began in early February and includes seven different steps, which goes from taking the mirrors’ initial placements after they were deployed to doing a “coarse” and then “fine” alignment, and then making sure the mirror works with all four of Webb’s instruments and their various fields of view.
As of this week, engineers are just on step number two, an indication of how precise and detailed this procedure is. And while Webb teams have tested and simulated the process countless times here on Earth, they’ve never been able to perform the entire process under all of the in-space conditions the telescope is now experiencing. Engineers can simulate the cold and vacuum of space here on Earth, but they can’t simulate zero G.
Fully functional, 1/6th scale model of the JWST mirror in optics testbed. Credit: NASA
“We built a testbed telescope, which looks a lot like Webb but is 1/6th the size,” explained Lee Feinberg, the Optical Telescope Element Manager for the mission, in an interview last month, “and we proved we knew how to move the mirrors to align them. Then we tested the full telescope in the vacuum chamber at Johnson Space Center at temperature and pressure. There, we were able to demonstrate aspects of the process, but not the whole thing. So, the first full time we’re doing the entire process is when the telescope is in space.”
On February 12, the telescope team announced the first photons of starlight had traveled through the entire telescope and were detected by the Near Infrared Camera (NIRCam) instrument. NICCam is being used to align the mirrors and calibrate the telescope, and it took 18 out-of-focus images of one star, one picture from each mirror segment. Now, scientists and engineers have taken these unfocused images and are using them to slowly fine-tune the telescope. The team says that so far, the initial results match expectations and simulations.
“I like to think of it as, that we have 18 mirrors that are right now, little prima donnas, all doing their own thing, singing their own tune in whatever key they’re in,” said Jane Rigby, Webb operations project scientist, during a press briefing earlier this month. “We have to make them work like a chorus, and that is a methodical, laborious process.”
The telescope’s 18 primary mirror segments need to match each other to a fraction of a wavelength of light – approximately 50 nanometers. Each segment has six actuators or tiny mechanical motors attached to the back that can align the segments, along with an additional actuator at the center of each segment that adjusts its curvature.
The first stage in this process, called “Segment Image Identification” had the team move each of Webb’s 18 primary mirror segments to bring 18 unfocused copies of a single star into a planned hexagonal formation. The lead image, above, shows that alignment. The first movements of the mirror segments can be as small as a centimeter or less, the final movements will be tens of nanometers, which is only one-ten thousandth the width of a human hair.
The remaining steps:
2. Segment Alignment: A process called Phase Retrieval uses mathematical analysis to determine the precise positioning errors of the segments. Adjustments of the segments then result in 18 well-corrected “telescopes.” However, at his current stage, the segments still don’t work together as a single mirror.
?? In the coming weeks, our team will align & focus each of these 18 dots, then stack the dots on top of each other to form a single point — one unified image from all of Webb’s 18 mirror segments. What’s ahead: https://t
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Not Getting Enough Data From Mars? Set Up A Solar System Pony Express
Getting data in from deep space can be difficult. Almost all of our missions that have flown into deep space use the Deep Space Network, a system of transmitters and receivers that already imposes constraints on the amount of data we can transfer from the far reaches of space. So a team led by Joshua Vander Hook, then at NASA’s Jet Propulsion Laboratory and now at a start-up called Outrider.ai, came up with a way to dramatically enhance the throughput of the DSN. In so doing, they gave it a very catchy name – the Solar System Pony Express.
Dr. Vander Hook was initially supported by a NASA Institute for Advanced Concepts (NIAC) grant in 2021. The basic concept utilizes what is known as a “cycler” orbit, where a spacecraft repeatedly orbits between two bodies in the solar system using their gravity wells to swing around in sync with when their orbits pass each other.
In this case, the spacecraft would consist of a communications relay module that would collect high-throughput data from an observer module parked in orbit around the other body. The observer module would consistently download data from the missions operating in its local area and then, when a relay module gets close, would rapidly send all of that data to the cycling spacecraft. The cycler then returns to Earth, where another rapid download process begins, and the cycle repeats itself.
Fraser discusses some of the problems of communicating with deep space probes – especially those going to other stars.
That sounds like the Pony Express – a system in the 1800s whereby mail carriers would ride physical ponies (or horses) to deliver mail occasionally to remote outposts in the American West. In another homage to that mail carrier heritage, the team named the cycling relay satellites “data mules.”
Those data mules would have a long trip between Earth and their target destination. It might come as no surprise that in much of the literature surrounding the idea that the target destination was Mars. Buzz Aldrin, the most famous proponent of cycler orbits, suggested that cycler “castles” could effectively shuttle people and goods between Mars and Earth. But in this new configuration, instead of physical things, it would be more beneficial to ship data.
Another Depiction of how the observer / data mule interaction would go.
Credit – Marc Sanchez-Net et al.
Calculations described in a paper released last year estimate that with as little as six data mules, the network could provide a bandwidth of 1 petabyte a year from the surface of Mars while only requiring a minor allocation of time on the DSN. That would potentially allow some real-time high-definition video from the red planet, which would undoubtedly be attractive to many of the inhabitants of its nearest neighbor.
However, such high data rates come at a cost. In the case of the Solar System Pony Express, that cost is latency. The high throughput data transfer possible between the observer and a data mule, and then again from the data mule back to a receiving station on Earth, is only possible if they are in physical proximity to each other, as the network would use a type of high-throughput optical communications network. And since cycler orbits can take years, it would be years after the data was collected on the red planet that anyone could use it.
That is not a show stopper – indeed, many people would be okay with waiting for over a year for a high-definition video from Mars if that is the only way for them to see it. But it makes funding such a mission more difficult given the immediate feedback culture prevalent in many of today’s media. Give the authors credit, though – they recognize this limitation and, as all good scientists do, mention that it would be a good topic for further study.
For right now, that further study seems to be on hold. Dr. Vander Hook has moved on to other non-space-related efforts. While there has been some interest from researchers elsewhere, such as a paper from the University of Illinois, there’s currently no clear path forward for the project. But, there will always be a desire for more data transfer from farther out in the solar system. If the Pony Express is the most cost-effective way to get it at the beginning of our explorations, then don’t be surprised if this concept is resurrected sometime in the future.
Pascarella et al – Low-thrust trajectory optimization for the solar system pony
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A Protoplanetary Disc Has Been Found… in Another Galaxy!
Astronomers have imaged dozens of protoplanetary discs around Milky Way stars, seeing them at all stages of formation. Now, one of these discs has been found for the first time — excitingly — in another galaxy. The discovery was made using the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile along with the , which detected the telltale signature of a spinning disc around a massive star in the Large Magellanic Cloud, located 160,000 light-years away.
“When I first saw evidence for a rotating structure in the ALMA data I could not believe that we had detected the first extragalactic accretion disc, it was a special moment,” said Anna McLeod, an associate professor at Durham University in the UK and lead author of the study published in Nature. “We know discs are vital to forming stars and planets in our galaxy, and here, for the first time, we’re seeing direct evidence for this in another galaxy.”
McLeod and her fellow researchers were doing a follow-up study on a system named HH 1177, which was located deep inside a gas cloud in the Large Magellanic Cloud LMC). In 2019, the researchers reported that in using the Very Large Telescope, they observed a jet emitted by a fledgling but massive star with a mass 12 times greater than our Sun. This was the first time such a jet has been observed in visible light outside the Milky Way, as they are usually obscured by their dusty surroundings. However, the relatively dust-free environment of the LMC allowed for HH 1177 to be observed at visible wavelengths. At nearly 33 light-years in length, it is one of the longest such jets ever observed.
This dazzling region of newly-forming stars in the Large Magellanic Cloud (LMC) was captured by the Multi Unit Spectroscopic Explorer instrument on ESO’s Very Large Telescope. The relatively small amount of dust in the LMC and MUSE’s acute vision allowed intricate details of the region to be picked out in visible light. Credit: ESO, A McLeod et al.
“We discovered a jet being launched from this young massive star, and its presence is a signpost for ongoing disc accretion,” McLeod said in an ESO press release. But to confirm that such a disc was indeed present, the team needed to measure the movement of the dense gas around the star.
The gas motion indicated that there is a radial flow of material falling onto a central disk-like structure. In their new observations, the team found that the disk exhibits signs of Keplerian rotation – which is a disk of material that obey’s Kepler’s laws of motion due to the dominance of a massive body at its center. Their observations revealed that “the rotating toroid [was] feeding an accretion disk and thus the growth of the central star,” the McLeod and team wrote in their paper. “The system is in almost all aspects comparable to Milky Way high-mass YSOs (young stellar objects) accreting gas from a Keplerian disk.
As matter is pulled towards a growing star, it cannot fall directly onto it; instead, it flattens into a spinning disc around the star. Closer to the center, the disc rotates faster, and this difference in speed is the clear evidence to show astronomers an accretion disc is present.
“The frequency of light changes depending on how fast the gas emitting the light is moving towards or away from us,” said Jonathan Henshaw, a research fellow at Liverpool John Moores University in the UK, and co-author of the study, in the ESO press release. “This is precisely the same phenomenon that occurs when the pitch of an ambulance siren changes as it passes you and the frequency of the sound goes from higher to lower.”
Massive stars like HH 1177 live fast and die hard. In the Milky Way, stars like this are challenging to observe because they are often clouded from view by the dusty material from which they form — which also obscures the disc that might be shaping around them.
“They form in heavily embedded regions full of gas and dust, such that the accretion phase typically occurs before the star has time to become exposed due to stellar feedback, whether internal or external,” the team wrote in their paper. “The primary reason for the lack of observations of extragalactic accretion disks around forming stars has been the limited spatial resolution of both ground- and space-based observatories.”
But the Large Magellanic Cloud is fundamentally different from because the stars that form there have a lower dust content than in the Milky
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A Gamma-ray Burst Disturbed the Earth’s Ionosphere
You’d think that something happening billions of light-years away wouldn’t affect Earth, right? Well, in 2002, a burst of gamma rays lasting 800 seconds actually impacted our planet. They came from a powerful and very distant supernova explosion. Its gamma-ray bombardment disturbed our planet’s ionosphere and activated lightning detectors in India.
This particular gamma-ray burst (GRB) occurred in a galaxy almost 2 billion light-years away (and took two billion years to reach us). Not only did ground-based detectors record the bombardment, but satellites sensitive to high-energy outbursts “saw” it, too. That included the European Space Agency’s International Gamma-Ray Astrophysics Laboratory (INTEGRAL) mission. It typically records gamma-ray bursts on a daily basis, but this one—named GRB 221009A—outshone all the rest.
GRBs this strong happen (on average) about once every 10,000 years, so this was one that caught everyone’s attention. “It was probably the brightest gamma-ray burst we have ever detected,” says Mirko Piersanti, University of L’Aquila, Italy, and lead author of a paper analyzing the event.
How The Gamma-ray Burst Affected the Ionosphere
Most of the time, radiation from the Sun bombards our planet. That’s often strong enough to affect the ionosphere. That’s an atmospheric layer that bristles with electrically charged gases called plasma. It stretches from around 50 km to 950 km in altitude above the surface. There’s a “top-side ionosphere” (which lies above 350 km) and a “bottom-side ionosphere”) which lies below that. Scientists are pretty familiar with how the Sun treats this region of the atmosphere, particularly during periods of heavy solar activity.
GRB 221009A: looking back through time at a gamma-ray-burst. Courtesy ESA
This GRB blast triggered instruments generally reserved for studying the immense explosions in the Sun’s atmosphere known as solar flares. “Notably, this disturbance impacted the very lowest layers of Earth’s ionosphere, situated just tens of kilometers above our planet’s surface, leaving an imprint comparable to that of a major solar flare,” says Laura Hayes, research fellow and solar physicist at ESA. That imprint basically was an increase in ionization in the bottom-side ionosphere. It left an imprint in low-frequency radio signals that move between Earth’s surface and the lowest levels of the ionosphere. “Essentially, we can say that the ionosphere ‘moved’ down to lower altitudes, and we detected this in how the radio waves bounce along the ionosphere,” explained Laura.
Gamma Ray Bursts in the Data
Past GRBs bothered the bottom-side ionosphere but didn’t always disturb the topside. Scientists just assumed that by the time it reached Earth, the blast from a GRB didn’t have the “oomph” to change that part of the ionosphere. GRB 221009A proved that idea wrong. Thanks to data from the orbiting China Seismo-Electromagnetic Satellite (CSES), scientists saw a strong disturbance in the upper ionosphere. It created a strong electric field variation and was the first time scientists saw this connected to a GRB. The result is the first-ever top-side ionospheric measurement of electric field variations triggered by a gamma-ray outburst at cosmic distances.
INTEGRAL and other spacecraft continually record GRBs from around the Universe. Have they all affected our ionosphere in some way? Is there a way to find out? Now that scientists know what ionospheric effects to look for, they can search the data to find answers. Data from INTEGRAL, and CSES will be particularly useful. They should be able to correlate it with other GRBs seen since 2018. That’s when CSES was launched.
Evidence of ionospheric disturbances from GRBs goes back as far as 1988. That’s when the effects of a 1983 gamma-ray burst were first reported. Scientists now have an array of ground-based and space-based detectors—such as Swift, Fermi, MAXI, AGILE, INTEGRAL, and CSES—gave strong detections of the emissions from GRB221009A.
Implications for Future GRB Effects on Earth
This kind of disturbance
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