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PULLING BACK THE CURTAIN ON THE UNIVERSE When it is launched in 2018, the James Webb Space Telescope will be able to look further back in time than we have ever seen. DAN FALK reports. WITH 18 HEXAGONAL mirrors designed to unfold in space, the Webb will be the grand successor to the Hubble Space Telescope. 01 COSMOS Issue 62 FEATURE — 75 74 — FEATURE
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Pulling back the curtain on the universe- Dan Falk

Aug 16, 2015

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Pulling back the curtain on the universe- Dan Falk
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PULLING BACK THE CURTAIN ON THE UNIVERSEWhen it is launched in 2018, the James Webb Space Telescope will be able to look further back in time than we have ever seen. DAN FALK reports.WITH 18 HEXAGONAL mirrors designed to unfoldin space, the Webb will be the grand successor to theHubble Space Telescope.01COSMOS Issue 62FEATURE 75 74 FEATUREON THE FLOOR BELOW, a couple dozen scientists and engineers are buzzing about, weaving around cranes, ladders, miles of cables and one very large robotic arm. With their all-white protective suits and face masks, the workers look like little snowmen. The suits arent for their protection, but for the protection of the delicate equipment theyre handling because the machine theyre assembling is one of the mostambitious and expensive telescopes ever conceived.If all goes well, it will be launched into space on top ofan Ariane 5 rocket a little more than four years fromnow. Eventually, fromits desolate home 1.5 million kilometres fromEarth, it will send back images and data that will revolutionise our picture of the cosmos.Its been nearly 25 years since the launch of the Hubble Space Telescope, and the hardy instrumentis still going strong. But Hubble wont last forever.Astronomers have been planning a larger, more ambitious telescope since the mid-1990s. Thattelescope is fnally beginning to take shape in Building 29. Originally dubbed the Next Generation Space Telescope, it was later renamed in honour of James E. Webb, the man who served as NASAadministrator back in the days of the Apollo Moon missions. Not that this is a solely American project:the Webb telescope is too big, too complex and toocostly for any one country to go it alone, and the European Space Agency and the Canadian Space Agency are both playing a signifcant role. In all, more than 1,000 scientists and engineers, fromat least 17 countries, are working on the project.The biggest diference between the Webb and Hubble is sheer size: Hubble has a single mirror a bitless than 2.5 metres across, while Webb will use an array of 18 hexagonal mirrors. Arranged honeycomb-style, theyll function as a single mirror 6.5 metres across (thats a bit wider than the cabin of a jumbojet). True, the largest ground-based telescopes in use today are bigger, with mirrors about 10 metres across but 6.5 metres is still enough to make Webb by far the largest telescope ever planned for space.The other crucial diference between Webb and Hubble is that, while Hubble works primarily in visible light, Webb is designed to work in the infrared. This long wavelength light passes rightthrough the dust and gas clouds that can obscure Hubbles view one of the reasons infrared is the best way to study phenomena fromancient galaxies at the edge of the visible universe to stellar nurseries where newsolar systems are taking shape. Hubble is wonderful, but not quite wonderful enough, John Mather, senior project scientist for Webb, put itrecently. Theres stuf just beyond what Hubble can see, that we really want to be able to pursue.Webb is often described as a successor to Hubble but since its designed to probe the infrared, it might more accurately be thought of as a successor to the Spitzer Space Telescope, an infrared space observatory launched in 2003. But again, size is ofthe essence. Spitzers main mirror, at 85 centimetres across, will be dwarfed by Webbs 6.5-metre refector. On the day of my visit, engineers were using the clean rooms robotic armto manipulate Webbs secondary mirror or rather, the fight-sparesecondary, an exact duplicate of the telescopes secondary mirror designed to collect light fromthe massive primary and direct it back toward the telescopes detectors. My guide for the day was MarkClampin, observatory project scientist for Webb, and a veteran of several previous projects including Hubble. We watched as the robotic armslowly lifted the fight-spare secondary mirror for a series of tests.IM STANDING IN THE SECOND-FLOOR viewing gallery in Building 29 at NASAs Goddard Space Flight Centre, just outside Washington DC.On the other side of the enormous plate-glasswindow is the facilitys giant clean room,one of the largest in the world.02A birds eye view of NASAs Goddard clean room.Issue 6276 FEATURECOSMOSFEATURE 77Just to give you some idea of the scale, the secondary mirror up there is about 10 centimetres smaller than the Spitzer Space Telescopes primary mirror, Clampin says. So that gives you an idea of howbig this telescope is. Belowthe secondary mirror, and partially hidden by the clean rooms massive steel scafolding, I can see the fight-spare backplane the carbon-composite structure that will hold the mirrors in place. The robotic arm, Clampin explains, will be used to put each of the mirrors into place on the backplane, one at a time.The fight-spares exact copies of the components that will travel into space are essential as back-ups, in case anything happens to the actual fighthardware; plus, theres always a risk of parts being damaged during testing. The actual primary mirror segments are kept under wraps. They were manufactured at Ball Aerospace in Colorado and were shipped to Goddard more than a year ago theyre kept in sealed, nitrogen-flled steel chambers (which look rather like giant pots for cooking spaghetti). Still, one only needs to click on the Webb telescopes website to see what the fully assembled mirror will look like. Cast fromlightweight berylliumand coated with a microscopically thin layer of gold, the hexagonal mirror segments will look spectacular when theyre eventually deployed in space ifanyone were around to see them.While Hubble circles the Earth some 500 kilometres up, the James Webb Space Telescope is heading for the L2 Lagrange point, located 1.5 million kilometres out in space. Back in the 18thcentury long before anyone had imagined sending a telescope into space the French mathematician Joseph-Louis Lagrange was working on whatphysicists call the three-body problem: If you have a pair of massive bodies like the Earth and the Sun, with each bodys motion dictated solely by the force of gravity, would there be any stable locations where you could place a third body and have it stay there, without drifting away? Lagrange found that, yes, there are fve such points, and L2 is one of them.If you think of the Sun, and drawa line fromthe Sun to the Earth, and keep going for a million miles thats basically where its located, Clampin explains.We picked that because its a point that has a quasi-stable gravitational feld. Its a great place to be, for doing astronomy. Great, but lonely: L2 is aboutfour times more distant than the Moon. Hubble was serviced by astronauts four times once in orbit, but Webb will not feel human hands after launch.Everything has to work perfectly the frst time.But working so far fromhome has its advantages:L2 is so far fromEarth that our planet never blocks the Suns light. That means the telescope will efectively be in daytime 24/7, with notroublesome day-night fuctuations in temperature.Even so, Webbs infrared detectors need to be protected fromthe Suns heat a dazzling streamof infrared radiation that would swamp the faintsignals the telescope is designed to detect. Even the telescopes own heat needs to be carefully managed. The telescope will have, in efect, a hotside that faces the Sun, and a cold side that faces deep space. The hot side will house the telescopes communications equipment and electronics, while the mirrors and delicate infrared detectors will be on the cold side.Separating the two halves of the telescope will be another unique feature a giant, diamond-shaped sunshield. Dwarfng even the giant primary mirror, the sunshield is the telescopes largest component, spanning an area about the size of a tennis court.Its composed of fve parallel layers of ultra-thin plastic flmwith a refective metallic coating (whichgoes by the trade name of Kapton). Once deployed, it will block the Suns heat while also radiating the telescopes own heat out into space. This way the cold side of the telescope will be kept down to 40 Kelvin about 230 degrees belowzero on the Celsius scale.Acold telescope makes for great infrared observing but also for staggering engineering hurdles. This is one of the challenges that the telescope has to work at 40K, but we polish the mirrors at roomtemperature, Clampin says.The fne-polishing of the mirrors has to be carried out in stages: at Goddard, engineers will work on the mirror surfaces until a precision of 100 nanometres is reached thats about one-thousandth of the thickness of a human hair. Then the mirrors will be sent to the Marshall Space Flight Centre in Alabama, where theyll be cooled in a cryogenic chamber thatmimics the conditions the telescope will experience in space with engineers noting exactly howthe mirrors shape changes as the temperature drops.Then the mirrors return to Goddard for a fnal tweak.That way, the next time we cool it down to 40K, well have the right prescription, Clampin says.When the mirror is fnally sent into space, the largestirregularities on its surface will be no more than 20 nanometres in size. If the mirror were scaled up tobe the width of the continental United States, those defects would be less than two centimetres high.And cryogenic testing is only a part of the challenge. At Goddard, I gawked at the machines that have been pushing and pulling on the telescopes various components, to ensure that each piece ofequipment can survive the launch. After all, being launched into space inside an Ariane 5 rocket is a bitlike being strapped to a giant frecracker. Theres a lot of shaking and rattling. Goddard also has a massive centrifuge that can whirl objects around DRAWALINE FROMTHE SUNTOTHE EARTHAND KEEPGOING FORAMILLION MILESTHAT S . . . WHEREIT S LOCATED.Artists impression of the Webb as it will look in space. Light gathered by the honeycomb-shaped primary mirror is reflectedon to the small secondary mirror (top right) which directs it back to the detector at the centry of the primary mirror. 04The five Lagrange points, where objectsin space can be held in place by gravity. 03L5MOONSUNL4L1L3L2EARTHJAMES WEBBCOSMOS Issue 6278 FEATURE FEATURE 7905The Hubbles best known image, the Pillars of Creation,and right as the star nursery would look with the Webbs infrared vision.Issue 6280 FEATURECOSMOSFEATURE 81Distant galaxies make appealing targets, butthere are equally enticing objects to focus on closer to home. Webb will also be looking at the birth ofplanetary systems around stars in our own galacticneighbourhood. These days, of course exoplanetsare a booming business; the Kepler observatory, a space telescope launched in 2009, has already found more than 1,000 planets orbiting stars beyond our solar system. Webb wont compete with Kepler; rather, the two will function as a team. While Webb may well discover some newplanets, its bigger strength is as a planet characterisation machine, says Ray Jayawardhana, an astronomer at York University in Toronto, and the author of a popular book on the search for exoplanets, Strange New Worlds. Webb willbe able to tell us more about some of the exoplanets Kepler has discovered.Thanks to its exquisite resolution, Webb will be able to discern some exoplanets as distinct objects, separated fromtheir parent stars what astronomers aptly call direct imaging. (Most exoplanets found todate were discovered using indirect methods. Kepler, for example, infers the existence of exoplanets by watching as the light of the parent star is periodically dimmed, as a planet passes in front.)Giant planets, roughly the size of Jupiter or Saturn, will be easier for Webb to pick out, because of their girth. Such planets emit a fair bit of heat, meaning they radiate strongly in the infrared whichis what the telescope is designed to detect. Ahandfuluntil they feel a pull equivalent to 15 times that ofgravity more than enough to simulate the g-forces experienced at launch. But the launch also produces a lot of sound which is why theres also an acoustics chamber, to blast the telescopes parts with high-intensity sound waves. Ray Lundquist, one of the lead engineers for Webb, explained the chamber can produce sounds up to about 150 decibels, though100 to 115 decibels are typical. What if I were unlucky enough to be in the chamber when it was cranked up to that level? Youd pass out, Lundquistassures me.The real excitement will begin in 2018, when the James Webb Space Telescope unfolds, origami-like, fromits launch vehicle, and makes its way to the L2 Lagrange point. And then when it starts recording data and sending it back to planet Earth. Some of the data will be coming fromthe most distant matter in the visible Universe structures that formed perhaps a fewmillion years after the Big Bang. In this quest, Webbs use of infrared wavelengths is key: because the Universe is expanding, the light fromthese distant objects has been stretched in astronomicaljargon, the light has been redshifted. (Think of an ambulance driving past you as it speeds away, its siren seems to emit a lower pitch sound.) Because of this redshift, light that would have been emitted at visible wavelengths is nowshifted well into the infrared and is ripe for detection by Webb.For astronomers such as Marcia Rieke, thatancient light holds the promise of newinsight intothe Universes turbulent early years. Rieke, based atthe University of Arizona, grewup reading science fction and pondering the possibility of visiting distant stars and planets. I was good at science, so Isort of gravitated toward physics and astronomy, she says. Shes nowthe principal investigator for Webbs Near Infrared Camera, known as NIRCam. Its one of Webbs four main detectors, and has been carefully designed to snare the light fromthose ancientstructures. Exactly howfar we can push back the clock, so to speak, is hard to say; it depends on howrapidly matter in the early Universe condensed intothe frst stars and galaxies. We may get as close as a fewmillion years after the Big Bang, Rieke says.Our models of the early Universe specifcally, those frst fewmillion years are a bit sketchy. We knowthat gravity was the great choreographer; under its pull, and in spite of the Big Bangs initialoutward push, matter attracted matter; clouds of gas and dust spawned the frst stars; those stars came together to formprimordial galaxies. Imhoping that when it comes to things like looking at howgalaxies assemble, that we really will be able to see the full sweep of cosmic history, Rieke says. Wed like to see the very frst galaxies.WEMAY GETAS CLOSEASA FEWMILLION YEARSAFTER THEBIG BANG.of exoplanets have already been directly imaged using ground-based instrumentsbut Webb, with its greater resolution, will be much better at spotting an exoplanet in spite of the overwhelming glare ofthe parent star. But thats not all: by monitoring a planet carefully for many hours, the telescope should reveal any regular changes in brightness the sortof pattern one might expect if some irregularity in a planets atmosphere were periodically coming intoview. (We knowthat the giant planets in our own Solar Systemhave such features think of the GreatRed Spot on Jupiter.) You might actually learn something about the storms in the atmospheres ofthese directly-imaged Jovian planets that would be very cool, says Jayawardhana.Any information about the atmospheres ofthese distant worlds would be a goldmine for astronomers especially for those pondering the question of life beyond our own blue-white orb.Webbs spectrograph will split an exoplanets lightinto its component colours, allowing scientists tolook for the chemical signatures of water vapour or carbon compounds in its atmosphere, explains Jayawardhana. Again, these planets are most likely to be larger than Earth; the smaller the planet, the closer it has to be for Webb to detect it, and sothe smaller the area of space in which to hunt for them. But slightly larger planets may well turn upin abundance, their atmospheres prime targets for study. And thats a very exciting prospect, because some of these super Earths may well be rocky planets, with atmospheres that at least in principle allowfor habitability, says Jayawardhana. Thats probably the most exciting thing that were planning for. He emphasised the element of surprise. In the exoplanet business, weve learnt time and again toexpect the unexpected.Webb is, frst and foremost, a scientifcinstrument but like Hubble it holds the promise of producing images that resonate far beyond the scientifc community. They wont have the same favour as Hubbles images, though; in infrared light, everything looks diferent. In fact, by collecting these longer wavelengths of light, the telescope will be able to look through the clouds of dust and gas that, in visible light, would obscure whatever might lie behind them. The telescope will, in efect, be pulling back the curtain to reveal newcelestial vistas.Consider Hubbles best-known image the Eagle Nebula, known as the Pillars of Creation. Deep in the interior of the nebula, newstars and perhaps newplanets are being born. Webb will allowyouto peer into these objects in much more detail, says Mark Clampin, my guide at Goddard. So if you thinkof the Eagle Nebula, Webb will be able to ... lookinside the nursery, if you like.The James Webb Space Telescope is big science, and it inevitably comes with a big price tag whichhas gotten even bigger over the years. Initially estimated to cost between $US1-2 billion, the latestestimates put the fgure at around $9 billion. There are, of course, some equally expensive science projects out there the Large Hadron Collider comes to mind but its still a lot of cash. And its been a bumpy ride: in the spring of 2011, Congress moved topull funding fromthe project, but NASAfought back, and by autumn of that year, the funding was restored.The project has also taken longer than planners had originally thought. The launch had frst been planned for 2011; the newdate is 2018.Will the Webb be the last of the big-budget space observatories? Perhaps. The project is so large and complex, that its right at the limit of what people can do, says Rieke. And obviously froma costperspective, it really is right at the limit. And yet, as Jayawardhana points out, its all relative. Should we choose to one day send astronauts to Mars, the expense would almost certainly be tallied in hundreds of billions of dollars. One often hears howmuch good could come fromthat sort of money if it were spenthere on Earth. There are various responses to suchobjections, but an internet video-blogger named Hank Green has as pithy a reply as any: There are two ways to make the world a better place, he says.You can decrease the suck, and you can increase the awesome. The Webb is a perfect example ofincreasing the awesome, he argues and many astronomers (although not all) would agree.Back at the Goddard Space Flight Centre, there is still plenty of nuts-and-bolts work to be done. The assembly and testing of the components will continue for another four years. Eventually, the mirror and the main instrument package will be shipped to NorthropGrummans Space Park complex in Los Angeles, where the giant sunshield will be integrated with the rest of the telescope. Eventually the whole shebang will be folded up and packed on to a barge bound for French Guiana and the European Spaceport on its coast. Then its million-mile odyssey will begin.INTHE EXOPLANET BUSINESS WE VE LEARNTTO EXPECTTHE UNEXPECTED.DAN FALK is a science journalist based in Toronto.IMAGES01 NASA/ MSFC/ David Higginbotham02 NASA/ Chris Gunn 03 Cosmos Magazine 04 Northrop Grumman 05 NASA/ ESA/ Hubble Heritage Team(STScI/AURA) 06 NASA/Ames / JPL-Caltech06The Webb will be able to tell us more about exoplanets such as Kepler 69c, above.COSMOS Issue 6282 FEATURE FEATURE 83