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4.04.2016
Sunshield Membrane Coatings
The James Webb Space Telescope's primary science comes from infrared light, which is essentially heat energy. To detect the extremely faint heat signals of astronomical objects that are incredibly far away, the telescope itself has to be very cold and stable. This means we not only have to protect JWST from external sources of light and heat (like the sun and the earth), but we also have to make all the telescope elements themselves very cold so they don't emit their own heat energy that could swamp the sensitive instruments. The temperature also must be kept constant so that materials aren't shrinking and expanding, which would throw off the precise alignment of the optics.
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To accomplish all of this, JWST deploys a tennis-court sized Sunshield made of five thin layers of Kapton E with aluminum and doped-silicon coatings to reflect the sun's heat back into space. The Kapton is a commercially available polyimide film from Dupont, while the coatings are applied to a specialized JWST specification.
The Layer 1 membrane (facing the sun) is 0.002" thick, the other four layers are each 0.001". The higher emissivity doped-silicon coating is ~50 nanometers thick, and is applied to the sun-facing side of the two hottest layers (Layer 1 & 2) to maximize stoppage of the sun's heat. Doping is a process whereby a small amount of conductive material is mixed in during the silicon coating process, so that the coating is electrically conductive. The highly-reflective aluminum coating is ~100 nm thick and is applied to all the other surfaces, helping to "bounce" the remaining energy out the gaps between the layers.
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Flight Layer 2 membrane of the James Webb Space Telescope sunshield during shape testing, in Jan 2016. All 5 flight membranes will be complete by late 2016. Image credit: Northrop Grumman.
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Early shape testing of sunshield membranes. Credit: Northrop Grumman
The size, position, spacing and shape of the Sunshield layers are also very important - more information on these aspects can be found on our sunshield page.
Quelle: NASA
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Update: 21.04.2016
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The James Webb Space Telescope Core-2 model in a cleanroom at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Credits: NASA/Goddard/Desiree Stover
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Crouching low beneath the underbelly of the behemoth James Webb Space Telescope “observatory core” test model, surrounded by critical test hardware, a technician toiled for hours wrapping the replica’s surfaces in delicate thermal blankets and strips of Mylar.
The observatory core model will stand in for the real thing in an upcoming test at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Dubbed Core-2, the test will verify that Webb can regulate its core body temperature to the correct specifications, which would be impossible without the blankets created and applied by Goddard technician Andrew Peterson and his team.
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Technician Andrew Peterson installs thermal blankets to the underside of the James Webb Space Telescope test model.
Credits: NASA/Goddard/Desiree Stover
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Webb is an infrared telescope, which means errant heat from the sun, or even a tiny bit from the observatory’s own electronics, could blind it as it peers into the darkness, looking for the most distant galaxies in the universe.
The team must test the observatory in its fully deployed configuration. After launch, Webb will unfold and expand over the course of two weeks. Cooling down to stable operating temperature will take much longer, and most of the heat flow through the observatory happens in its core region—a sort of Grand Central Station for heat flow on Webb.
There’s just one big problem.
Webb is so enormous that it won’t all fit in NASA’s testing chambers. Webb will have to fold up even to fit in the rocket that will take it to space. Fully deployed, Webb will be as wide and as long as a tennis court and about 4 stories tall. The telescope would be almost 20 feet too wide to fit in Goddard’s thermal vacuum chamber, the Space Environment Simulator. Even the famous Chamber A at NASA’s Johnson Space Center in Houston is too small. Moreover, even with a chamber big enough to hold Webb fully-deployed, it is infeasible to recreate the entire temperature environment it will see when operating with a difference of about 500 degrees Fahrenheit between its ‘hot’ and ‘cold’ sides.
The solution? An identical twin of just Webb’s core, which contains the juncture between all four of Webb’s modules – the spacecraft bus, sunshield, mirrors and instrument module.
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This graphic shows how the modules of the James Webb Space Telescope connect in the fully deployed observatory.
Credits: NASA/Goddard/Paul Geithner
As many as 15 technicians at a time labored on the model, working to make it as identical to the actual telescope as possible.
“I’ve been here 10 years, and I think this is the biggest thermal test we’ve ever had,” said Chris Matthews, Goddard mechanical integration technician. His team put the model together and transported it to the test chamber.
Building the core in its deployed form made what would already have been a complicated process even more challenging. It was important that they follow the same procedures as they would for the actual observatory – this was their dress rehearsal, and they had to make sure the core test model accurately reflects how the real thing will behave in space.
The extra effort to build a full-scale, flight-like model is worth it because it’s the only way to test Webb’s core region and measure heat flow through it, and managing heat flow and controlling temperature is one of Webb’s biggest requirements. In flight, nearby heat sources – like instrument module control electronics emitting around 200 watts only a few feet away – could blind Webb’s sensitive infrared sensors, which are designed to observe distant objects in the universe by detecting their heat output. A stargazing astronomer in New York City will not see many stars – the bright surrounding lights will drown out their faint glow. The concept is much the same with Webb and heat. Proper management of heat flow is key: Every bit of unwanted heat passing the wrong way through Webb’s core and ending up where it shouldn’t would make the telescope’s job that much harder, if not impossible.
More than 500 tiny sensors affixed to the replica will monitor each piece’s temperature during the test.
There isn’t much room for error. Goddard thermal engineer Paul Cleveland said the mirrors can’t operate as intended if more than 15 milliwatts of extra heat energy reach them. By comparison, a 100-watt light bulb uses 100,000 milliwatts when it is turned on.
During the test, Cleveland and his team will expose the test model to 48 days’ worth of temperature extremes, dipping as low as minus 423 F. How the twin core reacts will tell the Webb team what they can expect from the real thing.
“This is the only time we’re really testing the thermal center of Webb,” Cleveland said. “This is our chance to make sure we got it right.”
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The Core-2 model being lowered into the Space Environment Simulator chamber at Goddard.
Credits: NASA/Goddard/Desiree Stover
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Cleveland and the team will find out soon: the Core-2 test started mid-April.
With Webb’s twin finished, the same team will turn their sights to constructing the actual flight hardware in the next several months.
Quelle: NASA
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Update: 26.04.2016
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Watch us build the Webb Telescope at NASA Goddard Space Flight Center!
Quelle: NASA
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Update: 27.04.2016
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James Webb's mirror is revealed
Revealed for the first time in all its glory - the main mirror of the James Webb Space Telescope, which will be launched in 2018.
JWST is regarded as the successor to Hubble, and will carry technologies capable of detecting the light from the first stars to shine in the Universe.
Paramount in that quest will be a large primary reflecting surface.
And with a width of 6.5m, JWST's will have roughly seven times the light-collecting area of Hubble's mirror.
It is so big in fact that it must be capable of folding. Only by turning the edges inwards will the beryllium segments fit inside the telescope's launch rocket.
The observatory is currently under construction at the US space agency's Goddard Space Flight Center in Maryland.
When in recent months engineers stuck down the segments to their support structure, each hexagon had a cover on it.
Only now, as the engineers prepare to move to the next stage of assembly, have those covers been removed to reveal the full mirror.
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Shortly, the secondary mirror, which is at the top of the black extension poles will be collapsed into a flat configuration.
Then, the whole edifice will be flipped 180 degrees. This will permit the engineering team to attach JWST's instruments behind the main mirror.
These can be seen in a raised cage off to the left.
Leaving such a sensitive surface exposed even for a short time may appear risky. The fear would be that it might get scratched. But the European Space Agency's JWST project scientist, Pierre Ferruit, said that was unlikely.
"The main danger is to get some accumulation of dust. But it's a cleanroom so that accumulation is very slow," he told BBC News.
"They need to rotate the telescope to get access to the back, and the protective covers were only resting on the mirror segments, so they had to be removed before the rotation.
"When the mirror is upside down, the exposure to dust will be much less, and I doubt anyone will be allowed to walk underneath."
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Once the integration of mirror and instruments is complete, the telescope will be sent for environmental testing. It will be shaken and blasted with sound to mimic the rough rocket ride to orbit.
Assuming that goes well, the whole train - mirror and instruments - will ship to Nasa's Johnson Space Center in Texas for some final deep-chill testing.
This will be conducted in the giant cryo-vacuum chamber built to accommodate the 1960s Apollo hardware.
Once that work is done, engineers must attach the spacecraft bus, which incorporates elements such as the flight computers and communications system. Finally, James Webb will be given an immense deployable visor - the structure that will shield its delicate observations from the Sun's light and heat.
JWST is a joint venture between the US, European and Canadian space agencies.
Each of the partners has supplied instruments for the observatory. A key additional role for Europe is to launch the telescope. An Ariane rocket will be used. It will be the launcher's most valuable ever payload.
The full life-cycle cost of the JWST project is expected to approach $10bn once all the partners' contributions are taken into account.
Quelle: BBC
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Update: 30.04.2016
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Inside the clean room at NASA's Goddard Space Flight Center, the golden James Webb Space Telescope is viewed from overhead with its secondary mirror booms stowed. This is the position the secondary mirror will be in during launch. In the next few months, engineers will install other key elements, and take additional measurements to ensure the telescope is ready for space.
The telescope's mirrors are covered in a microscopically thin layer of gold, which optimizes them for reflecting infrared light, which is the primary wavelength of light this telescope will observe. To ensure the mirror is both strong and light, the team made the mirrors out of beryllium. Each mirror segment is about the size of a coffee table and weighs approximately 20 kilograms (46 pounds). A very fine film of vaporized gold coats each segment to improve the mirror's reflection of infrared light. The fully assembled mirror is larger than any rocket, so the two sides of it fold up. Behind each mirror are several motors so that the team can focus the telescope out in space.
The James Webb Space Telescope is the scientific successor to NASA's Hubble Space Telescope. It will be the most powerful space telescope ever built. Webb will study many phases in the history of our universe, including the formation of solar systems capable of supporting life on planets similar to Earth, as well as the evolution of our own solar system. It’s targeted to launch from French Guiana aboard an Ariane 5 rocket in 2018. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Quelle: NASA
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Update: 8.05.2016
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UNVEILED WEBB TELESCOPE MIRRORS MESMERIZE IN ‘GOLDEN’ GLORY
All 18 gold coated primary mirrors of NASA’s James Webb Space Telescope are seen fully unveiled after removal of protective covers installed onto the backplane structure, as technicians work inside the massive clean room at NASA’s Goddard Space Flight Center in Greenbelt, Maryland on May 3, 2016. The secondary mirror mount booms are folded down into stowed for launch configuration. Credit: Ken Kremer/kenkremer.com
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NASA GODDARD SPACE FLIGHT CENTER, MD – It’s Mesmerizing ! That’s the overwhelming feeling expressed among the fortunate few setting their own eyeballs on the newly exposed golden primary mirror at the heart of NASA’s mammoth James Webb Space Telescope (JWST) – a sentiment shared by the team building the one-of-its-kind observatory and myself during a visit this week by Universe Today.
“The telescope is cup up now [concave]. So you see it in all its glory!” said John Durning, Webb Telescope Deputy Project Manager, in an exclusive interview with Universe Today at NASA’s Goddard Space Flight Center on Tuesday, May 3, after the covers were carefully removed just days ago from all 18 primary mirror segments and the structure was temporarily pointed face up.
“The entire mirror system is checked out, integrated and the alignment has been checked.”
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Up close side-view of newly exposed gold coated primary mirrors installed onto mirror backplane holding structure of NASA’s James Webb Space Telescope inside the massive clean room at NASA’s Goddard Space Flight Center in Greenbelt, Maryland on May 3, 2016. Aft optics subsystem stands upright at center of 18 mirror segments between stowed secondary mirror mount booms. Credit: Ken Kremer/kenkremer.com
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It’s a banner year for JWST at Goddard where the engineers and technicians are well into the final assembly and integration phase of the optical and science instrument portion of the colossal observatory that will revolutionize our understanding of the cosmos and our place it in. And they are moving along at a rapid pace.
JWST is the scientific successor to NASA’s 25 year old Hubble Space Telescope. It will become the biggest and most powerful space telescope ever built by humankind after it launches 30 months from now.
The flight structure for the backplane assembly truss that holds the mirrors and science instruments arrived at Goddard last August from Webb prime contractor Northrop Grumman Aerospace Systems in Redondo Beach, California.
The painstaking assembly work to piece together the 6.5 meter diameter primary mirror began just before the Thanksgiving 2015 holiday, when the first unit was successfully installed onto the central segment of the mirror holding backplane assembly.
Technicians from Goddard and Harris Corporation of Rochester, New York then methodically populated the backplane assembly one-by-one, sequentially installing the last primary mirror segment in February followed by the single secondary mirror at the top of the massive trio of mirror mount booms and the tertiary and steering mirrors inside the Aft Optics System (AOS).
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Up close view shows cone shaped Aft Optics Subsystem (AOS) standing at center of Webb telescopes 18 segment primary mirror at NASA’s Goddard Space Flight Center in Greenbelt, Maryland on May 3, 2016. ISIM science instrument module will be installed inside truss structure below. Credit: Ken Kremer/kenkremer.com
Everything proceeded according to the meticulously choreographed schedule.
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“The mirror installation went exceeding well,” Durning told Universe Today.
“We have maintained our schedule the entire time for installing all 18 primary mirror segments. Then the center section, which is the cone in the center, comprising the Aft Optics System (AOS). We installed that two months ago. It went exceedingly well.”
The flight structure and backplane assembly serve as the $8.6 Billion Webb telescopes backbone.
The next step is to install the observatory’s quartet of state-of-the-art research instruments, a package known as the ISIM (Integrated Science Instrument Module), in the truss structure over the next few weeks.
“The telescope is fully integrated and we are now doing the final touches to get prepared to accept the instrument pack which will start happening later this week,” Durning explained.
The integrated optical mirror system and ISIM form Webb’s optical train.
“So we are just now creating the new integration entity called OTIS – which is a combination of the OTE (Optical Telescope Assembly) and the ISIM (Integrated Science Instrument Module) together.”
“That’s essentially the entire optical train of the observatory!” Durning stated.
“It’s the critical photon path for the system. So we will have that integrated over the next few weeks.”
The combined OTIS entity of mirrors, science module and backplane truss weighs 8786 lbs (3940 kg) and measures 28’3” (8.6m) x 8”5” (2.6 m) x 7”10“ (2.4 m).
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Gold coated primary mirrors newly exposed on spacecraft structure of NASA’s James Webb Space Telescope inside the massive clean room at NASA’s Goddard Space Flight Center in Greenbelt, Maryland on May 3, 2016. Aft optics subsystem stands upright at center of 18 mirror segments between stowed secondary mirror mount booms. Credit: Ken Kremer/kenkremer.com
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After OTIS is fully integrated, engineers and technicians will spend the rest of the year exposing it to environmental testing, adding the thermal blanketry and testing the optical train – before shipping the huge structure to NASA’s Johnson Space Center.
“Then we will send it to NASA’s Johnson Space Center (JSC) early next year to do some cryovac testing, and the post environmental test verification of the optical system,” During elaborated.
“In the meantime Northrup Grumman is finishing the fabrication of the sunshield and finishing the integration of the spacecraft components into their pieces.”
“Then late in 2017 is when the two pieces – the OTIS configuration and the sunshield configuration – come together for the first time as a full observatory. That happens at Northrup Grumman in Redondo Beach.”
Webb’s optical train is comprised of four different mirrors. We discussed the details of the mirrors, their installation, and testing.
“There are four mirror surfaces,” Durning said.
“We have the large primary mirror of 18 segments, the secondary mirror sitting on the tripod above it, and the center section looking like a pyramid structure [AOS] contains the tertiary mirror and the fine steering mirror.”
“The AOS comes as a complete package. That got inserted down the middle [of the primary mirror].”
Each of the 18 hexagonal-shaped primary mirror segments measures just over 4.2 feet (1.3 meters) across and weighs approximately 88 pounds (40 kilograms). They are made of beryllium, gold coated and about the size of a coffee table.
In space, the folded mirror structure will unfold into side by side sections and work together as one large 21.3-foot (6.5-meter) mirror, unprecedented in size and light gathering capability.
The lone rounded secondary mirror sits at the top of the tripod boom over the primary.
Quelle: UT
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Update: 24.05.2016
With surgical precision, two dozen engineers and technicians successfully installed the package of science instruments of the James Webb Space Telescope into the telescope structure. The package is the collection of cameras and spectrographs that will record the light collected by Webb’s giant golden mirror.
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In this rare view, the James Webb Space Telescope team crane lifted the science instrument package for installation into the telescope structure.
Credits: NASA/Chris Gunn
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This side shot shows a glimpse inside a massive clean room at NASA's Goddard Space Flight Center in Greenbelt, Maryland where the James Webb Space Telescope team worked meticulously to complete the science instrument package installation.
Credits: NASA/Desiree Stover
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Inside the world’s largest clean room at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, the team crane-lifted the heavy science instrument package, lowered it into an enclosure on the back of the telescope, and secured it to the telescope.
“Our personnel were navigating a very tight space with very valuable hardware,” said Jamie Dunn, ISIM Manager (ISIM stands for ‘Integrated Science Instrument Module’). “We needed the room to be quiet so if someone said something we would be able to hear them. You listen not only for what other people say, but to hear if something doesn’t sound right.”
Before the procedure, the engineers and technicians had trained with test runs, computer modeling and a mock-up of the instrument package. This is a critical mission operation.
“This is a tremendous accomplishment for our worldwide team,” said John Mather, James Webb Space Telescope Project Scientist and Nobel Laureate. “There are vital instruments in this package from Europe and Canada as well as the US and we are so proud that everything is working so beautifully, 20 years after we started designing our observatory.”
Now that the instruments, mirrors, and telescope structure have been assembled, the combination will go through vibration and acoustic tests in order to ensure the whole science payload will withstand the conditions of launch.
“Designing and building something of this magnitude and complexity, with this amount of new technology, is far from routine,” said Dunn. “While every project has their share of ups and downs, the JWST team has had to work through a lot over the life of this project. The character and dedication of this team is extraordinary, they’ve always recovered brilliantly, and they’ve made many personal sacrifices to get us to this point.”
The James Webb Space Telescope is the scientific successor to NASA's Hubble Space Telescope. It will be the most powerful space telescope ever built. Webb will study many phases in the history of our universe, including the formation of solar systems capable of supporting life on planets similar to Earth, as well as the evolution of our own solar system. It’s targeted to launch from French Guiana aboard an Ariane 5 rocket in 2018. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Quelle: NASA
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Update: 25.05.2016
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NASA's James Webb Space Telescope Reaches Major Milestone in Path to Launch with the Completion and Delivery of Optical Telescope Element
REDONDO BEACH, Calif., May 24, 2016 (GLOBE NEWSWIRE) -- Northrop Grumman Corporation's (NYSE: NOC) delivery of the fully integrated Optical Telescope Element (OTE) for NASA's James Webb Space Telescope marks another major milestone toward the October 2018 launch of the largest telescope ever built for space.
Northrop Grumman delivered the OTE in March to NASA's Goddard Space Flight Center in Greenbelt, Md. Northrop Grumman is under contract to Goddard and leads the industry team that designs and develops the Webb Telescope, its sunshield and spacecraft. Northrop Grumman has completed the integration, testing and delivery of the telescope.
The Webb telescope's 18 hexagonal gold coated beryllium mirrors are supported by the telescope structure. The OTE hardware is made of the most precise graphite composite material system ever created, and contributes to the Webb Telescope's ability to provide an unprecedented exploratory view into the formation of the first stars and galaxies formed over 13.5 billion years ago.
A photo accompanying this release is available at
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The precision manufacturing and integration of the 21.5 foot telescope structure allow it to withstand the pressure and weight of the launch loads when stowed inside the 15-foot-diameter fairing of the Ariane 5 rocket. The cutting-edge design and transformer like capabilities of the telescope structure allow it to fold-up and fit inside the launch vehicle, and then deploy once the Webb telescope reaches its ultimate destination, one million miles away from earth. Furthermore, throughout travel and deployment, the telescope simultaneously maintains its dimensional stability while also operating at cryogenic or extremely cold temperatures, approximately 400 degrees below zero Fahrenheit. The telescope is the world's first deployable structure of this size and dimensional stability ever designed and built.
"The significant milestone of completing and delivering the OTE to NASA's Goddard Space Flight Center, marks the completion of the telescope, and attests to the commitment of our hardworking team," said Scott Texter, telescope manager, Northrop Grumman Aerospace Systems. "The telescope structure is one of the four main elements of this revolutionary observatory. The other elements include: the spacecraft, sunshield and the Integrated Science Instrument Module (ISIM), the latter of which is also complete. All of the elements require a collaborative team effort. We are all committed to the cause and excited about the upcoming phases of development as we prepare for launch in October 2018."
The next step in the progress of the telescope structure includes its integration with the ISIM to combine the OTE and ISIM, referred to as the OTIS. The OTIS will undergo vibration and acoustic testing by the end of this year, and then travel to NASA's Johnson Space Center in Houston, to undergo optical testing at vacuum and operational cryogenic temperatures, around 40 kelvin. The OTIS will be delivered to Northrop Grumman's Space Park facility in Redondo Beach, towards the end of 2017, where it will be integrated with the sunshield and spacecraft.
The James Webb Space Telescope is the world's next-generation space observatory and successor to the Hubble Space Telescope. The most powerful space telescope ever built, the Webb Telescope will observe the most distant objects in the universe, provide images of the first galaxies formed and see unexplored planets around distant stars. The Webb Telescope is a joint project of NASA, the European Space Agency and the Canadian Space Agency.
Quelle: NORTHROP GRUMMAN CORPORATION
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Update: 19.07.2016
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NASA Seeks Picometer Accuracy
Team Develops New Tool to Assure Ultra-Stable Space Telescopes
Finding and characterizing dozens of Earth-like planets will require a super-stable space telescope whose optical components move or distort no more than a few picometers — a measurement smaller than the size of an atom. It also will require next-generation tools with which to assure that level of stability.
With NASA funding, a team of scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, has begun working with an Arizona-based company to develop a highly sophisticated laboratory tool — a high-speed interferometer — capable of assuring picometer-level stability, a feat not yet accomplished.
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At a Goddard cleanroom, technicians unveil the James Webb Observatory’s segmented mirror in preparation for an alignment test this summer. The tool used to determine the segments’ alignment has inspired Goddard technologists to create another that offers picometer accuracy for next-generation observatories. (Photo Credit: Chris Gunn)
Credits: NASA/Chris Gunn
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To date, NASA has yet to launch an observatory with such demanding stability requirements. However, the scientific community is studying the possibility. Last year, the Association of Universities for Research in Astronomy endorsed the High-Definition Space Telescope. It found that with proper stability and instrumentation, a 33-39 foot (10-12 meter) telescope could find and characterize Earth-like planets. Another study group evaluating a similar concept known as the Large Aperture Ultraviolet-Optical-Infrared Space Telescope, or LUVOIR, has reached similar conclusions.
“If the agency wants to search for and analyze Earth-like planets in other solar systems, the telescope it designs and builds will have to be orders of magnitude more stable than anything launched to date, including the James Webb Space Telescope,” said Babak Saif, a Goddard optics specialist.
New Tool to Assure Picometer-Level Stability
To help NASA reach this next level of precision, Saif and his Goddard colleague, Lee Feinberg, have begun working with 4-D Technology, of Tucson, Arizona, to develop the instrument.
Like all interferometers, the instrument would split light and then recombine it to measure tiny changes, including motion. With this tool, technicians would measure distortions in mirror segments, mounts, and other supporting telescope structure primarily during thermal, vibration, and other types of environmental testing.
Displacements and movement occur when materials used to build the optics shrink or expand due to wildly fluctuating temperatures, such as those experienced when traveling from Earth to the frigidity of space or when exposed to fierce launch forces more than six-and-a-half times the force of gravity.
If optics must conform to a specific prescription to carry out a challenging mission, even nearly imperceptible, atomic-size movements caused by thermal and dynamic changes could affect their ability to gather and focus enough light to distinguish a planet’s light from that of its parent star — to say nothing of scrutinizing that light to discern different atmospheric chemical signatures, Saif said.
Leveraging Instrument Developed for Webb Testing
The effort leverages a similar instrument that 4-D Technology created to test the optics of the Webb Observatory, which will be the most powerful observatory ever built once it launches in October 2018. From its orbit 930,000 miles from Earth, it will study every phase in the history of our universe, from the first luminous glows after the Big Bang to the evolution of our own solar system. Among many other firsts, Webb will carry a 21-foot primary mirror made of 18 separate ultra-lightweight beryllium segments that unfold and adjust to shape after launch.
To carry out its job, the Webb Observatory also must be highly stable. However, the movement of its materials is measured in nanometers — the unit of measure that scientists use to determine the size of atoms and molecules.
“What we did was measure the surface of each mirror after each environmental test to see if we could see changes,” Saif said. “I started questioning, what if something behind the mirror moves. Just measuring the surface isn’t enough.”
To assure nanometer-level stability — 4-D Technology worked with the Webb Observatory team at Goddard to develop a dynamic laser interferometer that instantaneously measured displacements in the mirror segments as well as those in their mounts and other structural components, despite vibration, noise, or air turbulence.
“The high-speed interferometer actually enables you to do nanometer dynamics for large structures,” Saif said. “This is absolutely new. The instrument is four orders of magnitude more sensitive than other measurement tools and it measures the full surface of the mirrors.” That instrument now is used in laboratories, manufacturing areas, clean rooms, and environmental-testing chambers operated by the project’s major contractors.
LUVOIR-Type Mission Ups the Ante
However, a next-generation LUVOIR-type mission will demand even greater stability, and consequently an instrument capable of quickly measuring picometer displacements, which are two orders of a magnitude smaller than an atom. Although it is possible to calculate picometer movements with existing tools, the physics are non-linear and the resulting calculations might not accurately reflect what actually is going on, Saif said.
“Every subsystem needs to be designed on a picometer level and then tested at picometers,” Saif explained. “You need to measure what you’re interested in and the instrument needs to calculate these motions quickly so that you can understand the dynamics.”
The team is developing the tool with $1.65 million in funding from NASA’s Cosmic Origins Strategic Astrophysics Technology program. It expects to complete the work in four years.
Quelle: NASA
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Update: 24.09.2016
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NASA's Webb telescope sunshield, opened for inspection. In this photo, engineers and scientists examine the sunshield layers on this full-sized test unit.
Credits: Northrop Grumman Corporation/Alex Evers
NASA's James Webb Space Telescope has a giant custom-built, kite-shaped sunshield driven by mechanics that will fold and unfold with a harmonious synchronicity 1 million miles from Earth.
Like a car, many mechanical pieces in the Webb telescope's sunshield will work together to open it from its stored folded position in the rocket that will carry it into space.
According to car manufacturers, a single car can have about 30,000 parts, counting every part down to the smallest screws. Like getting all of the parts in a car to operate together, the mechanical parts of the sunshield have to work in the same way.
The sunshield support structure contains well over 7,000 flight parts, including springs, bearings, pulleys, magnets, etc. In addition, the sunshield has hundreds of custom fabricated pieces. Most mechanical pieces were developed exclusively for the sunshield, with a few from existing designs.
There are about 150 mechanism assemblies that have to function properly to fully deploy the sunshield. Within those mechanism assemblies, there are numerous small parts that work in harmony. The smaller parts include about 140 release actuators, approximately 70 hinge assemblies, eight deployment motors, scores of bearings, springs and gears, about 400 pulleys and 90 cables. These mechanisms release the sunshield membranes from their folded and stowed launch configuration, deploy the supporting structures, and unfold and tension the membrane layers. In addition there are hundreds of magnets and clips to manage the membrane shape and volume during deployment, and many sensors to tell engineers that each deployment step has been completed.
"The process of opening or deploying the sunshield in space is a multi-step process," said James Cooper, Webb telescope sunshield manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Each step of the deployment will be manually initiated from engineers on Earth. That sequence runs automatically to its completion (with automated stoppage in case of a fault), then the system waits for the next command.
It will be like conducting an orchestra from a million miles away. "Thousands of components work together to deploy the sunshield," Cooper said.
The mechanisms that separate each of the sunshield's five layers do so with precision. Near the center of the sunshield each layer is separated by only a couple inches, but the layer-to-layer gap increases as you move away from the center, to about a foot between layers around the edges. It will take nearly two days to fully deploy the sunshield system when in orbit.
The Webb telescope state-of-the-art composite structure that supports the sunshield “operates with Swiss watch-like precision," said Paul Geithner, Webb telescope technical manager at Goddard. "The engineering of the sunshield is an intricate system with a simple but not easy-to-do purpose."
The stowed sunshield fits inside of a 5-meter (16.4-foot) rocket fairing, folded up against the sides of the telescope. When deployed in space it’s about the size of a tennis court (about 21 meters by 14.5 meters, or 68.9 feet by 47.5 feet).
"There has never been a composite structure this large and complex (for a NASA mission)," Cooper said.
Quelle: NASA
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