2.01.2022

NASA begins unfurling James Webb telescope's critical sunshade

Webb's sunshade has been deployed, but the work will not be complete until its five layers have been pulled tight and separated, providing gaps between each membrane to permit heat to escape to the sides. Motor-driven cables will begin pulling the layers taut on Saturday. NASA

Now a half-million miles and six days outbound from Earth, the James Webb Space Telescope began the most critical phase of its initial activation on Friday, unfolding a fragile five-layer sunshield the size of a tennis court that's essential to its mission.

The two pallets holding the sunshade's hair-thin Kapton layers were unfolded and locked in place Tuesday, one on either side of Webb's 21.3-foot primary mirror. On Thursday, protective covers were commanded to roll off each pallet, exposing the still-folded sunshade membranes to space.

The actual deployment began Friday when the first of two telescoping booms at right angles to the pallets began extending, slowly pulling out one side of the shield, unfolding the membranes as it went. The boom was verified to be fully extended at 4:49 p.m. EST.

"This has been a BIG DAY of @NASAWebb deployments! Closing off the year strong!" NASA science chief Thomas Zurbuchen tweeted.

The deployment of the first boom was held up several hours to give engineers time to make sure the protective covers had, in fact, rolled off to the side of the sunshade pallets as required.

"Switches that should have indicated that the cover rolled up did not trigger when they were supposed to," NASA said in a blog post. "However, secondary and tertiary sources offered confirmation that it had."

"The deployment of the five telescoping segments of the motor-driven mid-boom began around 1:30 p.m., and the arm extended smoothly until it reached full deployment," NASA said. 

Engineers then sent commands to deploy the second sunshade boom, which extended smoothly and locked in place at 10:13 p.m., finally giving Webb its iconic kite-like shape.

"Today is an example of why we continue to say that we don't think our deployment schedule might change, but that we expect it to change," said Keith Parrish, the observatory manager at NASA's Goddard Space Flight Center.

Referring to the cautious approach to deploying the first boom, he said "the team did what we had rehearsed for this kind of situation - stop, assess, and move forward methodically with a plan. We still have a long way to go with this whole deployment process."

Simply extending the sunshade is not enough for Webb to meet its science goals. For the shield to work properly, blocking out heat from the sun, its five layers must be pulled taut and separated.

The temperature on the sun-facing side of the fully-deployed shade will reach 230 degrees Fahrenheit. But thanks to the separated layers of the sunshield, the optics on the side facing deep space will be passively cooled to nearly 400 degrees below zero.

That's what's required for Webb to register the faint infrared light from the first stars and galaxies to form in the wake of the Big Bang, one of the telescope's top priorities. And to do that, all five sunshade layers must be pulled taut and fully separated to reach the required low temperature.

Assuming no overnight problems and the full extension of both booms, motor-driven cables will slowly pull the first four layers taut on New Year's Day, separating them from each other in the process. The fifth layer is expected to be tensioned Sunday.

With the sunshade fully extended and taut, engineers will focus on Webb's optical system erecting the telescope's secondary mirror at the tip of an articulating tripod on Tuesday. 

Webb's primary mirror, the largest ever launched, is made up of 18 segments, six of which were folded back out of the way to fit inside the nosecone of the telescope's Ariane 5 rocket.

If all goes well, those six segments, three on each side, will be rotated into position Thursday.

After that, engineers will begin a months-long process to precisely align each segment to achieve a razor-sharp focus. After instrument checkouts and calibration, the first science images are expected in about six months.

Quelle: CBS News

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Webb telescope unfurls diamond-shaped sunshield

Flying outbound from Earth at a distance of more than 400,000 miles, the James Webb Space Telescope extended two booms Friday and unfurled the mission’s five-layer sunshield to the size of a tennis court, notching a major milestone for the observatory after a nail-biting New Year’s Eve for astronomers and engineers on Earth.

The critical deployments marked some riskiest moments to ready the nearly $10 billion observatory for science operations, following its successful launch Dec. 25 aboard a European Ariane 5 rocket.

NASA confirmed the successful extension of the port-side mid-boom in an update shortly after 7 p.m. EST Friday (0000 GMT Saturday). Nearly four hours later, NASA announced the starboard boom was extended.

Webb’s two sunshield mid-booms are designed to pull out the shade’s five membranes into their distinctive diamond shape.

“The mid-booms are the sunshield’s workhorse and do the heavy lifting to unfold and pull the membranes into that now-iconic shape,” said Keith Parrish, Webb observatory manager at NASA’s Goddard Space Flight Center.

Ground teams started extending the two sunshield booms several hours later than originally scheduled, NASA said in an update Friday evening. The space agency said mission controllers at the Space Telescope Science Institute took extra steps to confirm that a sunshield cover had fully rolled up before proceeding with the first mid-boom deployment.

“Switches that should have indicated that the cover rolled up did not trigger when they were supposed to,” NASA said. “However, secondary and tertiary sources offered confirmation that it had. Temperature data seemed to show that the sunshield cover unrolled to block sunlight from a sensor, and gyroscope sensors indicated motion consistent with the sunshield cover release devices being activated.”

The covers were opened and rolled back to expose the sunshield to space Thursday, but the covers were supposed roll back more in the early phase of mid-boom deployment.

“This final preparation to begin extending the mid-boom was what the team was analyzing before beginning the deployment,” NASA tweeted.

Five telescoping segments of the port, or left-side, mid-boom began extending around 1:30 p.m. EST (1830 GMT) Friday. The motor-driven boom reached full deployment at 4:49 p.m. EST (2149 GMT), NASA said.

The starboard, or right-side boom extension began at 6:31 p.m. EST (2331 GMT) and completed at about 10:13 p.m. EST (0313 GMT).

Both mid-booms are now locked into position o

“The completion of the sunshield cover and mid-boom deployments over the past two days marks a critical milestone for Webb,” NASA said in a written update Friday night.

Webb has 344 devices that must work exactly as intended. Of those, 107 are membrane release devices, non-explosive actuators that pinned the sunshield in place for launch. All 107 successfully released to allow the sunshield to open to its full dimension.

In total, the mission’s deployment sequence relies on 140 release mechanisms, 70 hinge assemblies, eight deployment motors, 400 pulleys, and 90 cables running a quarter-mile in length. There are also an array of bearings, springs, and gears to transform Webb from its launch to operational configuration.

The sunshade stretches 69.5 feet (21.2 meters) long and 46.5 feet (14.2 meters) wide.

Officials have repeatedly said Webb’s deployment schedule could change based on real-time conditions.

“Today is an example of why we continue to say that we don’t think our deployment schedule might change, but that we expect it to change,” Parrish said. “The team did what we had rehearsed for this kind of situation – stop, assess, and move forward methodically with a plan. We still have a long way to go with this whole deployment process.”

Made of five fragile kapton membranes, each as thin as a human hair, the sunshield will keep Webb’s mirrors, instruments, and detectors in constant shadow, allowing their operating temperature to plummet to near minus 400 degrees Fahrenheit. Such cold conditions are required to allow Webb to see the faint infrared light from the first galaxies in the universe more than 13.5 billion light years away.

Before Webb’s launch, most NASA managers and astronomers waiting to use the Webb telescope, the product of nearly three decades of development, gave the same answer about the most stressful moment of the mission: Sunshield deployment.

“The sunshield is one of these things that is almost inherently indeterministic,” said Mike Menzel, Webb’s mission systems engineer at NASA’s Goddard Space Flight Center in Maryland. “NASA is used to deploying rigid beams on hinges, because they’re deterministic, you can determine how they move.”

“Given that there are 40 different major deployments, and hundreds of pulleys and wires, the whole thing makes me nervous and will until its fully deployed,” said John Grunsfeld, an astrophysicist, former astronaut, and head of NASA’s science mission directorate from 2012 until 2016, a key period in Webb’s development.

But it’s the sunshield that got the biggest share of Menzel’s attention during the design and testing of Webb.

Menzel compared predicting the behavior of the sunshield layers to guessing what a string will do when you push it on a table top.

“So it is with the membranes of the sunshield,” he said. “So we can’t really predict their shape, but we can constrain it. “We can try to prevent it from going in places that we don’t want it to go, places where it could snag or tear, or maybe impede the deployment of other members.”

Each layer of the sunshield is slightly different in size and shape, created using thermally bonded sections of kapton with around 10,000 seams, according to Krystal Puga, Webb’s lead spacecraft systems engineer at Northrop Grumman.

There are reinforcement strips, or rip stops, to contain any tears or holes, and metallic ribbons giving the kapton some structural support.

The sunshield membranes are coated with aluminum, and two of the outermost layers are treated with silicon, giving the skin-like material a purple hue.

With the sunshield in its diamond shape, Webb controllers will send commands for the observatory to tension each of the five layers over two days — currently planned on Saturday and Sunday.

“Once we get the sunshield out, that’s great, but then we have to sort of tighten it up,” Parrish said in an interview before launch. “All five layers have different points around them where they’re connected up, and then we’ll pull on cables in each one of those corners to actually tighten up the sunshield.”

“The very last step is super important,” Puga said. “We need to tension all of the membranes using a series of pulleys and cables to create the separation between each of the five layers.”

The tensioning will separate each of the five ultra-thin kapton membranes, spacing them a few inches at the center and a few feet at the outermost edges. The tapered spacing helps allow heat from the sun to reflect between the layers, and eventually radiate back into space.

Tightening the sunshield will begin with the largest and flattest membrane closest to the sun, which will reach the hottest temperatures during the mission. One-by-one, each of the other four layers will be tensioned, ending with the smallest and coldest layer closest to Webb’s mirror.

“Tensioning the layers involves sending commands to activate several motors to reel in a total of 90 cables through numerous pulleys and cable management devices. Sunshield tensioning will take at least two days but may take longer, due to the complexity of the process and the flexibility built into the timeline,” NASA said Friday night.

Webb’s instruments and telescope need to be super-cold to make them sensitive to infrared light. And astronomers want to observe the cosmos in infrared wavelengths because it allows them to see the oldest galaxies, whose light waves have been stretched by the expansion of the universe.

Infrared astronomy also reveals star-forming regions obscured by clouds of gas and dust opaque to telescopes that see in visible wavelengths, the kind of light detectable by the human eye.

McCaughrean, an astronomer working on Webb since the 1990s, tweeted that infrared astronomy with a warm telescope “is like trying to observe in the visible in broad daylight with a telescope made of light bulbs. Possible, but you won’t see faint things very well.”

Once the sunshield is deployed and tensioned, ground teams will turn their attention to unfolding Webb’s huge mirror to its full size and shape. Those events are scheduled for next week.

Webb is cruising toward its operations post in a halo-like orbit around the L2 Lagrange point, a gravitational balance point nearly a million miles (1.5 million kilometers) from Earth.

Quelle: SN

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Update: 5.01.2022

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NASA's new space telescope 'hunky-dory' after problems fixed

NASA's new space telescope is doing well more than a week after liftoff, following a pair of problems overcome by ground controllers

CAPE CANAVERAL, Fla. -- NASA’s new space telescope is on the verge of completing the riskiest part of its mission — unfolding and tightening a huge sunshade — after ground controllers fixed a pair of problems, officials said Monday.

The tennis court-size sunshield on the James Webb Space Telescope is now fully open and in the process of being stretched tight. The operation should be complete by Wednesday.

The $10 billion telescope — the largest and most powerful astronomical observatory ever launched — rocketed away Christmas Day from French Guiana. Its sunshield and primary mirror had to be folded to fit into the European Ariane rocket.

The sunshield is vital for keeping Webb's infrared-sensing instruments at subzero temperatures, as they scan the universe for the first stars and galaxies, and examine the atmospheres of alien worlds for possible signs of life.

Getting the sunshield extended last Friday "was really a huge achievement for us," said project manager Bill Ochs. All 107 release pins opened properly.

But there have been a few obstacles.

Flight controllers in Maryland had to reset Webb’s solar panel to draw more power. The observatory — considered the successor to the aging Hubble Space Telescope — was never in any danger, with a constant power flow, said Amy Lo, a lead engineer for the telescope's prime contractor, Northrop Grumman.

They also repointed the telescope to limit sunlight on six overheating motors. The motors cooled enough to begin securing the sunshield, a three-day process that can be halted if the problem crops up again, officials said.

“Everything is hunky-dory and doing well now,” Lo said.

Ochs expects the tightening of the sunshield to be drama-free.

“The best thing for operations is boring, and that’s what we anticipate over the next three days, is to be boring," he told reporters in a teleconference.

If that holds true, the telescope's gold-plated mirror — more than 21 feet (6.5 meters) across — could unfold as soon as this weekend.

Webb should reach its destination 1 million miles (1.6 million kilometers) away by the end of January. As of Monday, the telescope was more than halfway there. The infrared telescope should begin observing the cosmos by the end of June, ultimately unveiling the first stars and galaxies formed in the universe 13.7 billion years ago. That's a mere 100 million years after the universe-creating Big Bang.

Launched in 1990, Hubble, which sees primarily visible light, has peered as far back as 13.4 billion years ago. Astronomers hope to close the gap with Webb, which is 100 times more powerful.

In another bit of good news Monday, officials said they expect Webb to last well beyond the originally anticipated 10 years based on its fuel efficiency.

Quelle: abcNews

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James Webb Space Telescope: Everything is 'hunky dory'

 

So far, so good. The US space agency says the post-launch set-up of the new James Webb telescope has gone very well.

"As smoothly as we could have hoped for."

Engineering teams are in the middle of unpacking the observatory from its folded launch configuration to the layout needed for operations.

This involves the deployment of several structures, the most critical of which are Webb's mirrors and sun shield.

Monday saw the start of what is probably the most complex set of activities - the separation and tensioning of the five individual layers that make up the shield.

Each membrane in the shield is as thin as a human hair and must be gently pulled tight to form a rigid, kite-like barrier the size of a tennis court.

The task was practised multiple times on the ground with full-scale and sub-scale models, which Nasa's Bill Ochs says gives him confidence that all will go well.

"I don't expect any drama," the project manager told reporters on Monday. "The best thing for operations is 'boring'. And that's what we anticipate over the next three days - to be boring."

Engineers refer to "single point failures" to describe the actions, which, if they don't occur on cue and in the right order, are likely to scupper the whole undertaking. Webb must get past 344 of these hurdles to achieve its operational layout.

If the sun shield opens perfectly - which may even be accomplished as early as Tuesday - then 75% of those failure modes will have been overcome.

Mission controllers at the Space Telescope Science Institute (STScI) in Baltimore, Maryland, would then move on to deploying Webb's mirrors

The telescope has a secondary reflector that must be extended on long booms in front of the primary mirror. Friday is the current target for this.

 

The main mirror has "wings" that were tucked back for launch but which must now be rotated through 90 degrees to make a full, 6.5m-wide surface. Again, assuming things continue to run like clockwork, this should happen over the weekend.

The unfolding schedule has slipped somewhat from the prelaunch plan, but not because of any particular problems, said Bill Ochs. The engineering teams were simply taking a steady, methodical approach to their work, he stressed.

"We are still in the 'getting to know you' phase with the telescope. All satellites will be a little bit different on orbit than they are on the ground," he explained.

"It takes time to get to understand their characteristics, and that's a lot of what we've been doing over the last week, as well as still making excellent progress on the commissioning timeline."

IMAGE SOURCE, NASA

One of these learning moments involved the teams getting a better handle on how to manage the temperatures inside the motors that are used to drive the sun shield's deployment. A second involved the fine-tuning of Webb's solar array so that it can output the necessary power for the separation and tensioning of the membranes - as well as the mirror unpacking.

"Everything is hunky dory and doing well," said Amy Lo from Northrop Grumman, the American aerospace company that assembled Webb.

 

"The rebalancing of the array gives us quite a lot of margin for the expected increase in power that we will be needing as we proceed on commissioning."

James Webb was launched on 25 December on an Ariane rocket from French Guiana.

The telescope is regarded as the successor to the Hubble space observatory which is now 31 years old and nearing the end of its operational life.

Webb will do similar science to Hubble but with the next-generation technologies that allow it to see deeper into cosmos and, therefore, further back in time. Indeed, scientists expect the new facility to detect the very first stars to ignite after the Big Bang more than 13.5 billion years ago.

But, unlike Hubble, Webb cannot be serviced by astronauts and so cannot achieve the same longevity as its predecessor.

That said, officials now think Webb will work for "a lot more" than the 10 years originally envisaged because its Ariane rocket was so accurate.

The European booster put Webb on a near-perfect trajectory with just the right amount of velocity. This performance meant the telescope didn't have to use so much of its own fuel when making later course refinements. The saved fuel will now be available for the everyday manoeuvres required to keep Webb sitting tidily at its observing position 1.5 million km from Earth.

James Webb is a joint venture between the American, European and Canadian space agencies.

 Quelle: BBC

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Update: 6.01.2022

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Sunshield Successfully Deploys on NASA’s Next Flagship Telescope