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