LUVOIR - ScienceVOL 362 ISSUE 6420. 1233. A cold stare at the faint glow of gas and dust. The Origins Space Telescope will stare at the cold universe: galactic . gas clouds, planet-forming

NEWS | FEATURES

1232 14 DECEMBER 2018

Sunshield

SLS block 2rocket

Fairing

Mirror rotated

SunshieldTelescope support

Instrumentmodule

LUVOIR

Mirror support

Optics system

Mirrorsegment

15-meterprimarymirror

111 m

Secondary mirror

Edge sensors

Pistons

Control electronics

Rear viewof segment

Visible

UltravioletSpectrum

InfraredX-ray

Orbit location: Sun-Earth L2

Launcher: Space Launch System block 2

Instruments: Four

Primary science targets: Earth-like exoplanets and �rst galaxies

Launch mass: 25 metric tons

A giant eye to see to the beginning of timeThe Large UV Optical Infrared Surveyor (LUVOIR) “is a Swiss army knife,” says LUVOIR study scientist Aki Roberge of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Much like its multipurpose predecessor, the Hubble Space Telescope, LUVOIR would gather light over a broad spectrum. But Hubble has a 2-meter mirror, whereas LU-VOIR’s would be up to 15 meters across in one version, larger than that of any of today’s ground-based telescopes.

Like its chief competitor, the Habitable Exoplanet Observatory, LUVOIR will scrutinize Earth-like exoplanets for signs of life. But the telescope’s extraordinary light-gathering power would allow it to see more of those worlds. Another big question will be within its reach: How do galaxies form and evolve? By capturing ultraviolet wavelengths invisible from the ground, LUVOIR will see gas cycling in and out of galax-ies to fuel star formation. The observatory will even be able to pick out individual stars in distant galaxies, giving a picture of what sort of stars are born where.

LUVOIR comes with risks. Fitting the mirror inside a rocket fairing will require origami even more complex than that for the 6.5-meter James Webb Space Telescope (JWST), which LUVOIR would supersede. And the planned heavy-lift rocket—a future version of NASA’s troubled Space Launch System—may never materialize. At more than twice the JWST’s size, LUVOIR will more than double its $8 bil-lion cost, critics say.

Not so, supporters say: The mirror is only a fraction of the mission’s cost and LUVOIR won’t need the elaborate sunshield or cryocoolers that were essential for the JWST’s infrared instruments. And LUVOIR’s mirror will be made of glass, not the JWST’s trickier be-ryllium. “There’s no magic involved. All the technology is feasible,” says LUVOIR team member John O’Meara, chief scientist of the Keck Observatory in Hawaii.

LUVOIRFolded for liftoffLUVOIR’s mirror will fold to fit inside the 8.4-meter-wide fairing of NASA’s Space Launch System (SLS) block 2. The troubled heavy-lift rocket isn’t expected until the 2030s, however, and it may never fly.

Movable mirrorsTiny pistons will tip and tilt LUVOIR’s 120 mirror segments into a perfect shape with the help of 622 edge sensors.

Built to lastRobotic servicing missions could extend LUVOIR’s life to several decades. Standardized valves, latches, and rails ease the replacement of batteries, solar panels, computers, reaction wheels, and propellant. Rotating the mirror away from the sunshield eases instrument replacement.C

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VOL 362 ISSUE 6420 1233

A cold stare at the faint glow of gas and dustThe Origins Space Telescope will stare at the cold universe: galactic gas clouds, planet-forming disks, exoplanet atmospheres, and other objects that don’t burn bright but glow feebly in the far infrared. That means the telescope itself must be frigid, chilled to 4° above absolute zero to stanch its own infrared light. Earth’s atmosphere largely blocks the far infrared, and few instruments have studied the range of wavelengths targeted by Origins. One pioneer was Europe’s Herschel Space Observatory, which from 2009 to 2013 cooled its instruments by boiling off a lim-ited supply of liquid helium. Origins will be much more sensitive as well as long-lived: Solar-powered me-chanical cryocoolers will chill the entire 9.1-meter telescope and its five instruments while a sunshield fends off the sun’s heat.

The three biggest challenges in developing Origins are “detectors, detectors, and detectors,” says Ori-gins study scientist Dave Leisawitz of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Neither industry nor the military has much interest in far-infrared detectors, so astronomers are do-ing the R&D themselves, weighing three rival technologies. “There is a clear path to choosing one or the other,” Leisawitz says. Such detec-tors have not flown in space before, and Origins co-leader Margaret Meixner of the Space Telescope Science Institute (STScI) in Balti-more, Maryland, says, “We want to make them bigger, more sensitive, and more efficient.”

By tracking infrared emissions from simple molecules, dust, and aromatic hydrocarbons, Origins could follow gas clouds collapsing into stars and dust disks spawn-ing planets. Water also falls into Origins’s spectral sweet spot. By monitoring water’s spectral lines, Origins could track it from interstellar clouds to proto- planetary disks and onto habit-able worlds. “The greatest discov-eries,” says Origins team member Klaus Pontoppidan at STScI, “will be things we haven’t even thought about yet.”

Sunshield

SLS block 2rocket

Fairing

Mirror rotated

SunshieldTelescope support

Instrumentmodule

LUVOIR

Mirror support

Optics system

Mirrorsegment

15-meterprimarymirror

111 m

Secondary mirror

Edge sensors

Pistons

Control electronics

Rear viewof segment

Visible

UltravioletSpectrum

InfraredX-ray

Orbit location: Sun-Earth L2

Launcher: Space Launch System block 2

Instruments: Four

Primary science targets: Earth-like exoplanets and �rst galaxies

Launch mass: 25 metric tons

9.1-meterprimarymirror

Solar panel

Mirror

Mirror (4 K)

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Sun’s rays

Outer sunshield(350 K)

Inner sunshield(35 K)

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Innersunshield

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Front viewof Origins

Orbit location: Sun-Earth L2

Launcher: Space Launch System block 2

Instruments: FiveVisible

UltravioletSpectrum

InfraredX-ray

Primary science targets: Gas clouds and planet-forming disks

Launch mass: 30 metric tons

ORIGINS

Stay coolOrigins must be chilled to reduce its own infrared glow. Sunshields drop temperatures to 35 K. Solar-powered, mechanical cryocoolers take the telescope to 4 K without the need to rely on a limited supply of liquid helium.

Sensing the far infraredFar-infrared photons are feeble. Two rival detector types, never flown in space, each rely on superconducting circuits with zero resistance. Detector arrays must be scaled up from 1000 to as many as 16,000 pixels.

Microwave kinetic inductance detectorIncoming photons break up the pairs of electrons that confer superconductivity in a resonant circuit, resulting in a detectable change in electrical properties.

Transition edge sensorThe detector is kept right at its superconducting transition temperature. The slight heating from a photon creates a detectable rise in resistance.

Approaching absolute zeroDetectors must be cooled even further, to 0.05 K. A magnetic field aligns salt molecules in a “salt pill.” As they drift out of alignment they absorb heat. Realignment pumps heat out of the capsule.

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NEWS | FEATURES

1234 14 DECEMBER 2018

Solar panel

Instrumentmodule

Thruster

Nested mirror

Imager

Microcalorimeter

X-raysenter

Spectrometer

Spectrometergrating

CryocoolerInfrared-blocking �lters

Sensor arrayX-rays enterOpen position

Closed position

X-rayssplit intospectrum

X-rays

Main bus

Glancing x-rayde�ection

Sunshield

3-meternestedmirrors Orbit location: Sun-Earth L2

Launcher: Unspeci�ed heavy launcher

Instruments: Three

Launch mass: 7.9 metric tons

Primary science targets: First supermassive black holes

Visible

UltravioletSpectrum

InfraredX-ray

An x-ray journey to the dawn of black holesX-rays, so useful in penetrat-ing the body, are a pain for astronomers to gather. Earth’s atmosphere blocks them, so astronomers must get to space to see the million-degree gases that shine in x-rays. But even in space the energetic photons are elusive, passing straight through conventional mirrors instead of reflecting. Only a few thou-sand x-ray sources are known, despite the work of pioneer-ing missions such as NASA’s Chandra X-ray Observatory and Europe’s X-ray Multi-Mirror Mission–Newton.

The Lynx X-ray Observatory is designed to find thousands more sources by going deeper and fainter. It would gain its unprecedented sensitivity from hundreds of silicon mirrors, each just a millimeter thick, arranged in nested shells to focus the x-rays in glancing reflections.

One target will be super-massive black holes in the early universe. They are a puzzle because they could not have grown so big, so fast simply by gobbling the star-size black holes they are thought to dine on. Seeing the gas being sucked into them may yield clues to the puzzle. Lynx would also capture stellar winds, supernovae, and the energetic jets that expel hot gases from galaxies, quenching their star formation. “We will unlock the secrets of galaxy evolution,” says project co-chair Alexey Vikhlinin of the Smithso-nian Astrophysical Observatory in Cambridge, Massachusetts.

U.S. x-ray astronomers have been unlucky in recent years. They built novel instruments for three Japanese x-ray satellites that failed. And in 2012, NASA pulled out of the International X-ray Observatory, a joint effort with Europe and Japan that be-came Europe’s Athena mission, planned for launch in 2028. But the Lynx team thinks it has a compelling case. “Black holes are very easy for people to un-derstand, and we have a unique way to see them,” Vikhlinin says.

LYNX

At a glanceX-rays penetrate conventional mirrors and so must be deflected at grazing angles. Lynx will use hundreds of concentric silicon mirrors, just 1 millimeter thick, to focus photons on detectors 10 meters away.

Between the linesGratings that swing into the light path from behind the mirror can tease apart spectral absorption lines from gas clouds in galactic halos and in the cosmic web.

Counting photonsLynx’s microcalorimeter takes both high-definition images and spectra. It logs every photon’s location and energy by recording temperature rises in an array of silicon sensors.

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VOL 362 ISSUE 6420 1235

Solar panel

Instrumentmodule

Thruster

Nested mirror

Imager

Microcalorimeter

X-raysenter

Spectrometer

Spectrometergrating

CryocoolerInfrared-blocking �lters

Sensor arrayX-rays enterOpen position

Closed position

X-rayssplit intospectrum

X-rays

Main bus

Glancing x-rayde�ection

Sunshield

3-meternestedmirrors Orbit location: Sun-Earth L2

Launcher: Unspeci�ed heavy launcher

Instruments: Three

Launch mass: 7.9 metric tons

Primary science targets: First supermassive black holes

Visible

UltravioletSpectrum

InfraredX-ray

Forward scarf

Instrument box

Starshade petal

72-mdiameter

HabEx

Starshade

Lightblocked Star

Exoplanet

124,000-kilometer separation

Ba�e tube

Deformable mirror

Masked image�eld

Exoplanet

Mask

Incoming beam

Lyot stop

Sunshade Main bus/avionics

1 Stowed shade 2 Petals unfurl 3 Petals rotate 90° 4 Truss deploys 5 Deployed starshade

Primary o�-axis mirrorBa�e tube

Secondary mirror Tertiary mirror

4-meterprimarymirror Orbit location: Sun-Earth L2

Launcher: Space Launch System block 1B

Launch mass: 35 metric tons

Primary science targets: Earth-like exoplanets

Visible

UltravioletSpectrum

InfraredX-ray

Instruments: Three Seeking the light of Earth-like worldsThe Habitable Exoplanet Observa-tory (HabEx) would look for signs of life light-years away. Although thousands of exoplanets have been discovered indirectly, only a few large ones have emerged shyly from the glare of their star for a snapshot. No current telescope can capture the faint light of small rocky worlds like our own, let alone tease it apart for signs of oxygen, methane, and other biosignatures. “We want to design [HabEx] from the ground up to image Earth-sized planets,” says team co-leader Scott Gaudi of Ohio State University in Columbus.

HabEx’s monolithic 4-meter mirror is designed to work in concert with a starshade, a flower-shaped mask 72 meters across, which would float 124,000 kilometers away from the tele-scope. With the starshade blocking light from a star, HabEx could see planets around it that are one ten-billionth as bright. “These are potentially the faintest objects ever studied with telescopes,” says team member Chris Stark of the Space Telescope Science Institute in Baltimore, Maryland. HabEx will also have a coronagraph, a com-plex internal device that blocks starlight, but less effectively than the starshade and over a narrower range of wavelengths.

Using just the coronagraph, HabEx would survey about 50 nearby planetary systems, iden-tifying promising Earth-like planets. Then the fuel-hungry starshade would maneuver into place for observations of about 10 systems that host exo-Earths. No starshade has ever flown. But Gaudi says HabEx is still a cheaper, safer choice than its primary competitor, the giant Large UV Optical Infrared Surveyor. “HabEx is the least risky telescope to do this,” he says.

With report after report arguing for the importance of finding life on an Earth-like planet—as well as public and congressional support for the quest—the team believes it has momentum. “It’s a goal for many astronomers: the ultimate answer to the question, are we alone?” Stark says.

HABEXFormation flyingThe starshade must fly far from HabEx to block the glare of a distant star so that orbiting planets— 10 million times dimmer—can be seen.

Unobstructed viewThe off-axis design avoids the need for secondary mirror support struts that could scatter light and swamp precious exoplanet photons.

The petal shape softens the edge of the starshade, reducing the amount of scattered starlight.

The ultimate shadesA coronagraph does the job of a starshade, but internally. Deformable mirrors smooth incoming light. A mask less than a millimeter across removes the star’s glare, while a Lyot stop catches stray light. G

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