Downloaded from on February 18, 2016
FEATURES
Published by AAAS
THE NEXT
BIG EYE
The pressure is on the builders of the James Webb Space Telescope to ensure that NASA’s $8 billion gamble pays off By Daniel Clery, in Greenbelt, Maryland
One of Webb’s gold-coated beryllium mirror segments is inspected before assembly.
PHOTOS: (LEFT TO RIGHT) NASA/CHRIS GUNN; K. W. DON, UNIVERSITY OF ARIZONA
F
or months, inside the towering in Washington, D.C., and former JWST teleBuilding 29 here at Goddard Space scope scientist. Like that of Hubble, however, Flight Center, the four scientific inWebb’s construction has been plagued by struments at the heart of the James redesigns, schedule slips, and cost overruns Webb Space Telescope (JWST, or that have strained relationships with conWebb) have been sealed in what looks tractors, partners in Canada and Europe, like a house-sized pressure cooker. A and—most crucially—supporters in the U.S. rhythmic chirp-chirp-chirp sounds Congress. Other missions had to be slowed as vacuum pumps keep the interior or put on ice as Webb consumed available reat a spacelike ten-billionth of an atmosphere sources. A crisis in 2010 and 2011 almost saw while helium cools it to –250°C. Inside, the it canceled, although lately the project has instruments, bolted to the largely kept within its schedframework that will hold ule and budget, now about them in space, are bathed in $8 billion (Science, 24 April infrared light—focused and 2015, p. 388). diffuse, in laserlike needles But plenty could go and uniform beams—to test wrong between now and their response. the moment in late 2018 The pressure cooker is when the telescope begins an apt metaphor for the sending back data from its whole project. Webb is the vantage point 1.5 million biggest, most complex, and Sensors proved too fragile in kilometers from Earth. It most expensive science mistesting, forcing a redesign. faces the stresses of launch, sion that NASA has ever the intricate unfurling of its attempted, and expectations among asmirror and sunshield after it emerges from tronomers and the public are huge. Webb its chrysalis-like launch fairing, and the poswill have 100 times the sensitivity of the sibility of failure in its many cutting-edge Hubble Space Telescope. It will be able to technologies. Unlike Hubble, saved by a look into the universe’s infancy, when the space shuttle mission that repaired its faulty very first galaxies were forming; study the optics, it is too far from Earth to fix. And not birth of stars and their planetary systems; just the future of space-based astronomy, and analyze the atmospheres of exoplanets, but also NASA’s ability to build complex sciperhaps even detecting signs of life. “If you ence missions, depends on its success. put something this powerful into space, who That’s why those instruments sat in Godknows what we can find? It’s going to be dard’s pressure cooker for what is known revolutionary because it’s so powerful,” says as cryo-vacuum test 3 (CV3). And it is why Matt Mountain, director of the Association Webb’s other components—including the of Universities for Research in Astronomy mirror and telescope structure, the “bus” 19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
805
NEWS | F E AT U R E S
BUILDING THE BIGGEST EYE IN SPACE
Constructing a successor to the Hubble Space Telescope has been an epic undertaking involving more than 1000 people in 17 countries over 2 decades. As that efort reaches its climax, the telescope components face a complex series of tests to ensure that the telescope deploys—and works—perfectly. July
December
April
May
July–Sept.
February
August–Nov.
December
Structure to hold Webb’s instrument module arrives at Goddard Space Flight Center.
Main mirror segments fnish testing at Marshall Space Flight Center.
Center section of main mirror's backplane support structure fnished.
First instrument arrives at Goddard from Europe.
Remaining three instruments delivered to Goddard.
Main mirror backplane wing structures complete.
First cryo-vacuum test of instrument module.
Main mirror segments delivered to Goddard.
2011
2012
2013
2014
Testing and technology Instrument module test
Telescope test
Webb’s instruments were tested three times inside a pressure vessel at Goddard to simulate the cold and vacuum of space. While inside, various forms of light were shone through the instruments to test their operating modes.
The combined telescope and instruments will be tested in 2017 inside the giant Chamber A at Johnson Space Center. Suspended from the ceiling to reduce vibration, the telescope will look up at an artifcial universe.
Space environment simulator Instrument module
Telescope simulator
Vibration isolation system
Telescope primary mirror
Vibration isolation supports
Deployment in space Like a butterfy emerging from its cocoon, Webb will unfurl its components step by step on its way to its fnal orbit. Sunshield
Sunshield pallet
1 30 min 10,000 km Webb separates from launch vehicle.
3 2 34 min 11,000 km Solar array deploys.
6 days 680,000 km Sunshield extended and tensioned.
Moon 384,800 km
Earth
806
4
3 days 480,000 km Sunshield pallets deploy.
sciencemag.org SCIENCE
19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
Webb’s range of vision Webb is designed to study the infrared sky, for the frst time at such high resolution.
May–Sept. April Second cryovacuum test of instrument module.
Telescope deployment tower completed.
10-12
Visible light 10-6
10-9
Gamma rays
X-rays
Ultraviolet
10-3
Infrared
Webb
Hubble Kepler
Wavelength 1 m
Microwaves
Radio
Spitzer Herschel
June–July
October–January
April
Feb.–May
May
Oct.–May
August
October
Vibration and acoustic testing of instrument module.
Third cryo-vacuum test of instrument module and mirror segments ftted to backplane.
Telescope and instrument module joined.
Telescope/ instruments in cryo-vacuum test in Johnson’s Chamber A.
Telescope/ instruments shipped to California.
Telescope/ instruments combined with bus/sunshield and tested.
Webb transferred by ship to French Guiana.
Launch on Ariane 5 from ESA spaceport.
2016
2017
2018
Primary mirror
Light
6.5 meters wide and composed of 18 hexagonal segments made of beryllium and coated with gold to refect infrared light. Behind each mirror segment are actuators to accurately control its position and curvature.
Secondary mirror
Deployment of secondary mirror
Actuators
Mirror backside
Antenna
Spacecraft bus
Solar radiation
5 1.8-m person to scale
11–14 days 1,000,000 km After the secondary mirror swings into place on its supports, the wings of the main mirror rotate into position and mirror phasing begins.
Hot side
Curvature
Cold side
Thermal protection
–233°C
The heat of the sun would swamp faint infrared signals from deep space so Webb’s sunshield reduces solar heat to less than one-millionth its normal value.
85°C Day 29 Final orbit of telescope. 1,500,000 km
SCIENCE sciencemag.org
19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
CREDITS: (DATA) NASA; (ILLUSTRATIONS) SOHAIL AL JAMEA; .MEA; A. CUADRA/SCIENCE
Position
807
NEWS | F E AT U R E S
cated computer modeling with a laborious, iterative process of grinding, cooling, measuring, warming, regrinding, cooling again, and so on. After testing both glass and the metal beryllium, Webb planners chose beryllium because it is strong and light, and it behaves more predictably during repeated cooling and warming cycles. The final design for Webb fell short of NASA’s original ambitions. Beginning in 2001, concerns about the swelling cost of the telescope forced NASA to shrink the IN THE MID-1990S, after Hubble had had mirror from 8 meters to 6.5 meters, reducing its optics corrected and was busy revolutionthe number of mirror segments from 36 to izing astronomy, researchers began plan18 and its light-collecting area from ning its successor. The catch phrase 50 square meters to 25. But rein NASA at the time, championed view panels decided that Webb by agency chief Daniel Goldin, was could still achieve its scientific “faster, better, cheaper.” Goldin chalgoals. To cut costs further, NASA lenged NASA engineers and the asdecided to use less precise mirtronomical community to come up rors that could be manufactured with a follow-on that was cheaper with many fewer cooling-warmingthan Hubble but bigger, with a mirgrinding steps. The change would ror 8 meters across. He received a make Webb less sharp at nearstanding ovation when he described infrared wavelengths between 1 and the plans to the American Astro2 micrometers—no great loss, as nomical Society in 1996. Whereas ground-based telescopes already Hubble covered the whole range of cover that part of the spectrum. visible light, plus a smidgen of ulBy 2006, all of Webb’s key techtraviolet and infrared, the Next Gennologies had been tested and proven eration Space Telescope (as it was viable. The final design was drawn then known) would be a dedicated up, and construction of components infrared observatory. got underway. Meanwhile, NASA enFor astronomers, the infrared gineers began dreaming up the byzspectrum was a beckoning frontier. antine series of tests each separate Visible light from the most distant component would have to pass—and objects in the universe, the very first the additional tests to be done as stars and galaxies that formed after components were combined to form the big bang, gets stretched so much larger elements of the spacecraft. “As by the expansion of the universe that soon as we put two or three parts it ends up in the infrared range by together, we test them,” says Scott the time it reaches us. Many chemical Willoughby, who is in charge of the signatures in exoplanet atmospheres Webb effort at Northrop Grumman in also show themselves in the infraRedondo Beach, California. red region. Yet Earth’s atmosphere To put Webb’s enormous mirror blocks most infrared. Webb will give Webb’s mirror backplane is made from a graphite composite that is through its paces, engineers at the us “the first high-definition view lightweight and rigid, retaining its shape down to cryogenic temperatures. Johnson Space Center in Houston, of the midinfrared universe,” says Texas, completely refitted Chamber A, Matt Greenhouse, JWST project scientist for ments would have to be minutely controlled a huge cryo-vacuum chamber built to test the instrument payload at Goddard. to meld them into a single optical surface, the crew-carrying spacecraft of the Apollo To capture that light, however, NASA enwith their reflected light completely in step— program. For the instruments, they devised gineers had to overcome huge challenges. a process known as phasing. In Webb, each the peculiar tortures at Goddard. The first was heat: To keep the infrared hexagonal segment will sit on six actuators glow of the telescope itself from swampthat control its orientation, plus one in the THE FLIGHT MODELS of the instruments ing faint astronomical signals, Webb would center to adjust its curvature. began arriving in 2012: four infrared imagneed to operate at about –233°C, 40° above Choosing the mirror material itself was ers and spectrographs built by collaboraabsolute zero (40 K). That would require a challenge, because it would have to stand tors including the European Space Agency, entirely new instrument designs. Size and up to a grueling ordeal. Because any matea NASA/European consortium, the Univerweight constraints posed additional hurdles: rial will change shape as it cools, each segsity of Arizona, and the Canadian Space An 8-meter mirror would never fit inside a ment would have to be ground to a shape Agency. Once the instruments were secured rocket fairing, so it would have to fold up for that is optically wrong at room temperaon their rigid framework, they were vigorlaunch. The sunshield, too, would have to be ture but warps into one that is correct—to ously shaken to simulate the stresses of collapsible and made of a superthin, lightwithin nanometers—at 40 K. To do that, the launch, as well as blasted with 150 decibels weight membrane. And the telescope strucmirrormakers planned to combine sophistiby loudspeaker horns as tall as a person. 808
ture would have to be absolutely rigid but lightweight enough to limit the weight of the whole orbiting observatory to no more than 6 tonnes, just a few percent of the weight of a similar-size ground-based telescope. “We knew we would have to invent 10 new technologies” to make the telescope work, says NASA’s JWST Program Director Eric Smith, in Washington, D.C. Take the mirror. Hubble’s was made from a single slab of glass, but Webb’s folding mirror would need to be segmented, made up of separate hexagonal pieces—a design used in many top ground-based instruments, including the Keck telescopes in Hawaii. The seg-
sciencemag.org SCIENCE
19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
PHOTO: NASA/CHRIS GUNN
that will supply power and control the telescope, and the tennis court–sized, multilayer parasol that will help keep it cool—must undergo a gauntlet of testing, alone and in combinations, until the whole spacecraft is ready. For those on the inside, the strain will only increase as assembly continues, the tests get bigger and more comprehensive, and the spacecraft is launched into space. Only when Webb opens its eye and successfully focuses on its first star will the strain be released.
PHOTO: NORTHROP GRUMMAN/ALEX EVERS
The multilayered sunshield protects the telescope and instruments from the sun’s heat.
Next came the first cryo-vacuum test to simulate space conditions. Problems emerged almost immediately. The heating and cooling caused the delicate multilayer semiconductor sandwiches that make up the infrared detectors to swell and crack. Another critical technology, the microshutter array in the near-infrared spectrograph, also succumbed. This is a device the size of four postage stamps with a grid of 250,000 tiny flaps that can be opened selectively so that the instrument can take separate spectra from, say, 100 galaxies in a single field of view—the first such multiobject spectrograph to fly in space. But the deafening noise of the acoustic chamber caused many of the flaps to jam. Instrument teams and manufacturers scrambled to identify the problems and produce new parts. Meanwhile, testing went on. All the replacements came together in time for the recent CV3 test, and as the test ended in late January the signs were encouraging that the fixes had worked. “We’re quite pleased with the performance,” says astronomer Marcia Rieke of the University of Arizona’s Steward Observatory in Tucson, principal investigator for the near-infrared camera. “We’re very close to ready for launch.” While the instruments underwent their ordeal, white-clad engineers in a nearby clean room were painstakingly fitting the mirror segments onto their support, known as the backplane. Hollowed out on the back to reduce weight, each 1.3-meterwide segment can be carried by a single person, and each has a particular destination on the backplane, depending on its precise optical qualities.
Now that the instruments have been tested and the mirror assembled, these two elements will be mated in March. Then the combined telescope and instrument package, collectively known as OTIS, will endure the shaker tables and acoustic chamber before being inserted into a specially built shipping container. In the dead of night, a truck will carry the container at just 8 kilometers per hour from Goddard to Joint Base Andrews, where it will be placed into a huge C-5 Galaxy transport plane, with just centimeters of clearance, for its flight to Houston. The few months OTIS spends in Chamber A early next year will be the most critical it will face. Light sources on the ceiling will create an artificial universe, allowing NASA engineers to run light all the way through the system from main mirror to detectors for the first and only time in spacelike conditions. They will practice phasing up the mirror and will check out all observing modes of the four instruments. “Hubble didn’t do an end-to-end optical test. We’re not skipping that on this program,” Greenhouse says. Then it’s back into the shipping container and another C-5 flight to Redondo Beach, where Northrop Grumman has been building the bus and sunshield. There the full observatory will take shape as the telescope and instruments are mated to these last two elements. Now too large to fit inside a plane, Webb will make its final prelaunch journey by ship, down the California coast and through the Panama Canal to French Guiana—home of Europe’s spaceport, and a waiting Ariane 5 launcher, part of Europe’s contribution to
SCIENCE sciencemag.org
the project. In October 2018, the Ariane will fling Webb toward L2, a gravitational balance point 1.5 million kilometers from Earth, directly away from the sun. The journey will take 29 days. Webb will begin unfolding and deploying components almost as soon as it hits space. Deployment will be “3 weeks of terror,” Mountain says. “No one has done this before, ever.” First to deploy will be solar arrays and antennas to provide power and communications with Earth; then the sunshield will unfurl to begin cooling the telescope and instruments; finally, the secondary mirror will swing into position and the main mirror wings will snap into place. Once the mechanical gymnastics routine is finished, there will come the heartstopping moment when the mirror first looks at the sky. Then the mirror has to be phased up, and the instruments cooled and all their modes tested. Commissioning is expected to take a full 6 months after launch. “A whole chain of things have to be done to get that really good-looking star,” says Lee Feinberg, JWST telescope manager at Goddard. “But then we can really rest.” Until then, the pressure will be unrelenting. But the builders of Webb say they do find time to reflect on what they are doing. Pierre Ferruit, JWST project scientist at the European Space Agency in Noordwijk, the Netherlands, recalls watching from the control room at Goddard during CV3 as technicians carried mirror segments into the clean room and fitted them to the backplane. “Even for someone working on the mission, it’s quite incredible,” he says. Rieke had the same sensation: “It’s just enchanting to be witnessing history.” ■ 19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
809
FEATURES
Published by AAAS
THE NEXT
BIG EYE
The pressure is on the builders of the James Webb Space Telescope to ensure that NASA’s $8 billion gamble pays off By Daniel Clery, in Greenbelt, Maryland
One of Webb’s gold-coated beryllium mirror segments is inspected before assembly.
PHOTOS: (LEFT TO RIGHT) NASA/CHRIS GUNN; K. W. DON, UNIVERSITY OF ARIZONA
F
or months, inside the towering in Washington, D.C., and former JWST teleBuilding 29 here at Goddard Space scope scientist. Like that of Hubble, however, Flight Center, the four scientific inWebb’s construction has been plagued by struments at the heart of the James redesigns, schedule slips, and cost overruns Webb Space Telescope (JWST, or that have strained relationships with conWebb) have been sealed in what looks tractors, partners in Canada and Europe, like a house-sized pressure cooker. A and—most crucially—supporters in the U.S. rhythmic chirp-chirp-chirp sounds Congress. Other missions had to be slowed as vacuum pumps keep the interior or put on ice as Webb consumed available reat a spacelike ten-billionth of an atmosphere sources. A crisis in 2010 and 2011 almost saw while helium cools it to –250°C. Inside, the it canceled, although lately the project has instruments, bolted to the largely kept within its schedframework that will hold ule and budget, now about them in space, are bathed in $8 billion (Science, 24 April infrared light—focused and 2015, p. 388). diffuse, in laserlike needles But plenty could go and uniform beams—to test wrong between now and their response. the moment in late 2018 The pressure cooker is when the telescope begins an apt metaphor for the sending back data from its whole project. Webb is the vantage point 1.5 million biggest, most complex, and Sensors proved too fragile in kilometers from Earth. It most expensive science mistesting, forcing a redesign. faces the stresses of launch, sion that NASA has ever the intricate unfurling of its attempted, and expectations among asmirror and sunshield after it emerges from tronomers and the public are huge. Webb its chrysalis-like launch fairing, and the poswill have 100 times the sensitivity of the sibility of failure in its many cutting-edge Hubble Space Telescope. It will be able to technologies. Unlike Hubble, saved by a look into the universe’s infancy, when the space shuttle mission that repaired its faulty very first galaxies were forming; study the optics, it is too far from Earth to fix. And not birth of stars and their planetary systems; just the future of space-based astronomy, and analyze the atmospheres of exoplanets, but also NASA’s ability to build complex sciperhaps even detecting signs of life. “If you ence missions, depends on its success. put something this powerful into space, who That’s why those instruments sat in Godknows what we can find? It’s going to be dard’s pressure cooker for what is known revolutionary because it’s so powerful,” says as cryo-vacuum test 3 (CV3). And it is why Matt Mountain, director of the Association Webb’s other components—including the of Universities for Research in Astronomy mirror and telescope structure, the “bus” 19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
805
NEWS | F E AT U R E S
BUILDING THE BIGGEST EYE IN SPACE
Constructing a successor to the Hubble Space Telescope has been an epic undertaking involving more than 1000 people in 17 countries over 2 decades. As that efort reaches its climax, the telescope components face a complex series of tests to ensure that the telescope deploys—and works—perfectly. July
December
April
May
July–Sept.
February
August–Nov.
December
Structure to hold Webb’s instrument module arrives at Goddard Space Flight Center.
Main mirror segments fnish testing at Marshall Space Flight Center.
Center section of main mirror's backplane support structure fnished.
First instrument arrives at Goddard from Europe.
Remaining three instruments delivered to Goddard.
Main mirror backplane wing structures complete.
First cryo-vacuum test of instrument module.
Main mirror segments delivered to Goddard.
2011
2012
2013
2014
Testing and technology Instrument module test
Telescope test
Webb’s instruments were tested three times inside a pressure vessel at Goddard to simulate the cold and vacuum of space. While inside, various forms of light were shone through the instruments to test their operating modes.
The combined telescope and instruments will be tested in 2017 inside the giant Chamber A at Johnson Space Center. Suspended from the ceiling to reduce vibration, the telescope will look up at an artifcial universe.
Space environment simulator Instrument module
Telescope simulator
Vibration isolation system
Telescope primary mirror
Vibration isolation supports
Deployment in space Like a butterfy emerging from its cocoon, Webb will unfurl its components step by step on its way to its fnal orbit. Sunshield
Sunshield pallet
1 30 min 10,000 km Webb separates from launch vehicle.
3 2 34 min 11,000 km Solar array deploys.
6 days 680,000 km Sunshield extended and tensioned.
Moon 384,800 km
Earth
806
4
3 days 480,000 km Sunshield pallets deploy.
sciencemag.org SCIENCE
19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
Webb’s range of vision Webb is designed to study the infrared sky, for the frst time at such high resolution.
May–Sept. April Second cryovacuum test of instrument module.
Telescope deployment tower completed.
10-12
Visible light 10-6
10-9
Gamma rays
X-rays
Ultraviolet
10-3
Infrared
Webb
Hubble Kepler
Wavelength 1 m
Microwaves
Radio
Spitzer Herschel
June–July
October–January
April
Feb.–May
May
Oct.–May
August
October
Vibration and acoustic testing of instrument module.
Third cryo-vacuum test of instrument module and mirror segments ftted to backplane.
Telescope and instrument module joined.
Telescope/ instruments in cryo-vacuum test in Johnson’s Chamber A.
Telescope/ instruments shipped to California.
Telescope/ instruments combined with bus/sunshield and tested.
Webb transferred by ship to French Guiana.
Launch on Ariane 5 from ESA spaceport.
2016
2017
2018
Primary mirror
Light
6.5 meters wide and composed of 18 hexagonal segments made of beryllium and coated with gold to refect infrared light. Behind each mirror segment are actuators to accurately control its position and curvature.
Secondary mirror
Deployment of secondary mirror
Actuators
Mirror backside
Antenna
Spacecraft bus
Solar radiation
5 1.8-m person to scale
11–14 days 1,000,000 km After the secondary mirror swings into place on its supports, the wings of the main mirror rotate into position and mirror phasing begins.
Hot side
Curvature
Cold side
Thermal protection
–233°C
The heat of the sun would swamp faint infrared signals from deep space so Webb’s sunshield reduces solar heat to less than one-millionth its normal value.
85°C Day 29 Final orbit of telescope. 1,500,000 km
SCIENCE sciencemag.org
19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
CREDITS: (DATA) NASA; (ILLUSTRATIONS) SOHAIL AL JAMEA; .MEA; A. CUADRA/SCIENCE
Position
807
NEWS | F E AT U R E S
cated computer modeling with a laborious, iterative process of grinding, cooling, measuring, warming, regrinding, cooling again, and so on. After testing both glass and the metal beryllium, Webb planners chose beryllium because it is strong and light, and it behaves more predictably during repeated cooling and warming cycles. The final design for Webb fell short of NASA’s original ambitions. Beginning in 2001, concerns about the swelling cost of the telescope forced NASA to shrink the IN THE MID-1990S, after Hubble had had mirror from 8 meters to 6.5 meters, reducing its optics corrected and was busy revolutionthe number of mirror segments from 36 to izing astronomy, researchers began plan18 and its light-collecting area from ning its successor. The catch phrase 50 square meters to 25. But rein NASA at the time, championed view panels decided that Webb by agency chief Daniel Goldin, was could still achieve its scientific “faster, better, cheaper.” Goldin chalgoals. To cut costs further, NASA lenged NASA engineers and the asdecided to use less precise mirtronomical community to come up rors that could be manufactured with a follow-on that was cheaper with many fewer cooling-warmingthan Hubble but bigger, with a mirgrinding steps. The change would ror 8 meters across. He received a make Webb less sharp at nearstanding ovation when he described infrared wavelengths between 1 and the plans to the American Astro2 micrometers—no great loss, as nomical Society in 1996. Whereas ground-based telescopes already Hubble covered the whole range of cover that part of the spectrum. visible light, plus a smidgen of ulBy 2006, all of Webb’s key techtraviolet and infrared, the Next Gennologies had been tested and proven eration Space Telescope (as it was viable. The final design was drawn then known) would be a dedicated up, and construction of components infrared observatory. got underway. Meanwhile, NASA enFor astronomers, the infrared gineers began dreaming up the byzspectrum was a beckoning frontier. antine series of tests each separate Visible light from the most distant component would have to pass—and objects in the universe, the very first the additional tests to be done as stars and galaxies that formed after components were combined to form the big bang, gets stretched so much larger elements of the spacecraft. “As by the expansion of the universe that soon as we put two or three parts it ends up in the infrared range by together, we test them,” says Scott the time it reaches us. Many chemical Willoughby, who is in charge of the signatures in exoplanet atmospheres Webb effort at Northrop Grumman in also show themselves in the infraRedondo Beach, California. red region. Yet Earth’s atmosphere To put Webb’s enormous mirror blocks most infrared. Webb will give Webb’s mirror backplane is made from a graphite composite that is through its paces, engineers at the us “the first high-definition view lightweight and rigid, retaining its shape down to cryogenic temperatures. Johnson Space Center in Houston, of the midinfrared universe,” says Texas, completely refitted Chamber A, Matt Greenhouse, JWST project scientist for ments would have to be minutely controlled a huge cryo-vacuum chamber built to test the instrument payload at Goddard. to meld them into a single optical surface, the crew-carrying spacecraft of the Apollo To capture that light, however, NASA enwith their reflected light completely in step— program. For the instruments, they devised gineers had to overcome huge challenges. a process known as phasing. In Webb, each the peculiar tortures at Goddard. The first was heat: To keep the infrared hexagonal segment will sit on six actuators glow of the telescope itself from swampthat control its orientation, plus one in the THE FLIGHT MODELS of the instruments ing faint astronomical signals, Webb would center to adjust its curvature. began arriving in 2012: four infrared imagneed to operate at about –233°C, 40° above Choosing the mirror material itself was ers and spectrographs built by collaboraabsolute zero (40 K). That would require a challenge, because it would have to stand tors including the European Space Agency, entirely new instrument designs. Size and up to a grueling ordeal. Because any matea NASA/European consortium, the Univerweight constraints posed additional hurdles: rial will change shape as it cools, each segsity of Arizona, and the Canadian Space An 8-meter mirror would never fit inside a ment would have to be ground to a shape Agency. Once the instruments were secured rocket fairing, so it would have to fold up for that is optically wrong at room temperaon their rigid framework, they were vigorlaunch. The sunshield, too, would have to be ture but warps into one that is correct—to ously shaken to simulate the stresses of collapsible and made of a superthin, lightwithin nanometers—at 40 K. To do that, the launch, as well as blasted with 150 decibels weight membrane. And the telescope strucmirrormakers planned to combine sophistiby loudspeaker horns as tall as a person. 808
ture would have to be absolutely rigid but lightweight enough to limit the weight of the whole orbiting observatory to no more than 6 tonnes, just a few percent of the weight of a similar-size ground-based telescope. “We knew we would have to invent 10 new technologies” to make the telescope work, says NASA’s JWST Program Director Eric Smith, in Washington, D.C. Take the mirror. Hubble’s was made from a single slab of glass, but Webb’s folding mirror would need to be segmented, made up of separate hexagonal pieces—a design used in many top ground-based instruments, including the Keck telescopes in Hawaii. The seg-
sciencemag.org SCIENCE
19 FEBRUARY 2016 • VOL 351 ISSUE 6275
Published by AAAS
PHOTO: NASA/CHRIS GUNN
that will supply power and control the telescope, and the tennis court–sized, multilayer parasol that will help keep it cool—must undergo a gauntlet of testing, alone and in combinations, until the whole spacecraft is ready. For those on the inside, the strain will only increase as assembly continues, the tests get bigger and more comprehensive, and the spacecraft is launched into space. Only when Webb opens its eye and successfully focuses on its first star will the strain be released.
PHOTO: NORTHROP GRUMMAN/ALEX EVERS
The multilayered sunshield protects the telescope and instruments from the sun’s heat.
Next came the first cryo-vacuum test to simulate space conditions. Problems emerged almost immediately. The heating and cooling caused the delicate multilayer semiconductor sandwiches that make up the infrared detectors to swell and crack. Another critical technology, the microshutter array in the near-infrared spectrograph, also succumbed. This is a device the size of four postage stamps with a grid of 250,000 tiny flaps that can be opened selectively so that the instrument can take separate spectra from, say, 100 galaxies in a single field of view—the first such multiobject spectrograph to fly in space. But the deafening noise of the acoustic chamber caused many of the flaps to jam. Instrument teams and manufacturers scrambled to identify the problems and produce new parts. Meanwhile, testing went on. All the replacements came together in time for the recent CV3 test, and as the test ended in late January the signs were encouraging that the fixes had worked. “We’re quite pleased with the performance,” says astronomer Marcia Rieke of the University of Arizona’s Steward Observatory in Tucson, principal investigator for the near-infrared camera. “We’re very close to ready for launch.” While the instruments underwent their ordeal, white-clad engineers in a nearby clean room were painstakingly fitting the mirror segments onto their support, known as the backplane. Hollowed out on the back to reduce weight, each 1.3-meterwide segment can be carried by a single person, and each has a particular destination on the backplane, depending on its precise optical qualities.
Now that the instruments have been tested and the mirror assembled, these two elements will be mated in March. Then the combined telescope and instrument package, collectively known as OTIS, will endure the shaker tables and acoustic chamber before being inserted into a specially built shipping container. In the dead of night, a truck will carry the container at just 8 kilometers per hour from Goddard to Joint Base Andrews, where it will be placed into a huge C-5 Galaxy transport plane, with just centimeters of clearance, for its flight to Houston. The few months OTIS spends in Chamber A early next year will be the most critical it will face. Light sources on the ceiling will create an artificial universe, allowing NASA engineers to run light all the way through the system from main mirror to detectors for the first and only time in spacelike conditions. They will practice phasing up the mirror and will check out all observing modes of the four instruments. “Hubble didn’t do an end-to-end optical test. We’re not skipping that on this program,” Greenhouse says. Then it’s back into the shipping container and another C-5 flight to Redondo Beach, where Northrop Grumman has been building the bus and sunshield. There the full observatory will take shape as the telescope and instruments are mated to these last two elements. Now too large to fit inside a plane, Webb will make its final prelaunch journey by ship, down the California coast and through the Panama Canal to French Guiana—home of Europe’s spaceport, and a waiting Ariane 5 launcher, part of Europe’s contribution to
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the project. In October 2018, the Ariane will fling Webb toward L2, a gravitational balance point 1.5 million kilometers from Earth, directly away from the sun. The journey will take 29 days. Webb will begin unfolding and deploying components almost as soon as it hits space. Deployment will be “3 weeks of terror,” Mountain says. “No one has done this before, ever.” First to deploy will be solar arrays and antennas to provide power and communications with Earth; then the sunshield will unfurl to begin cooling the telescope and instruments; finally, the secondary mirror will swing into position and the main mirror wings will snap into place. Once the mechanical gymnastics routine is finished, there will come the heartstopping moment when the mirror first looks at the sky. Then the mirror has to be phased up, and the instruments cooled and all their modes tested. Commissioning is expected to take a full 6 months after launch. “A whole chain of things have to be done to get that really good-looking star,” says Lee Feinberg, JWST telescope manager at Goddard. “But then we can really rest.” Until then, the pressure will be unrelenting. But the builders of Webb say they do find time to reflect on what they are doing. Pierre Ferruit, JWST project scientist at the European Space Agency in Noordwijk, the Netherlands, recalls watching from the control room at Goddard during CV3 as technicians carried mirror segments into the clean room and fitted them to the backplane. “Even for someone working on the mission, it’s quite incredible,” he says. Rieke had the same sensation: “It’s just enchanting to be witnessing history.” ■ 19 FEBRUARY 2016 • VOL 351 ISSUE 6275
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