Space

ESA to launch mission to study elusive gravitational waves

ESA to launch mission to study...
Artist's concept of eLISA passing through gravitational waves (Image: AEI/MM/exozet)
Artist's concept of eLISA passing through gravitational waves (Image: AEI/MM/exozet)
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LTP's flight optical bench (Image: Albert Einstein Institute)
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LTP's flight optical bench (Image: Albert Einstein Institute)
Preparing the LISA Pathfinder optical bench for vacuum tests at the AEI (Photo: AEI/N. Michalke)
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Preparing the LISA Pathfinder optical bench for vacuum tests at the AEI (Photo: AEI/N. Michalke)
The LPF laser modulator unit. The input light from the laser is fiber coupled into the unit and two modulated beams are output (Image: Albert Einstein Institute)
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The LPF laser modulator unit. The input light from the laser is fiber coupled into the unit and two modulated beams are output (Image: Albert Einstein Institute)
eLISA can study black holes at the heart of galaxies (Image: ASA, ESA, M. Livio (STScI) and the Hubble Heritage Team (STScI/AURA))
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eLISA can study black holes at the heart of galaxies (Image: ASA, ESA, M. Livio (STScI) and the Hubble Heritage Team (STScI/AURA))
History of the Universe (Image: Albert Einstein Institute)
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History of the Universe (Image: Albert Einstein Institute)
Black Hole Cygnus X-1 (Image: NASA/CXC/M.Weiss)
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Black Hole Cygnus X-1 (Image: NASA/CXC/M.Weiss)
Diagram of the electrodes of the capacitive sensors (Image: Albert Einstein Institute)
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Diagram of the electrodes of the capacitive sensors (Image: Albert Einstein Institute)
Artist's concept of eLISA passing through gravitational waves (Image: AEI/MM/exozet)
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Artist's concept of eLISA passing through gravitational waves (Image: AEI/MM/exozet)
Artist's impression of eLISA formation (Image: AEI/MM/exozet)
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Artist's impression of eLISA formation (Image: AEI/MM/exozet)
Artist's impression of an eLISA instrument (Image: AEI/MM/exozet)
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Artist's impression of an eLISA instrument (Image: AEI/MM/exozet)
Cosmic strings (Image: Albert Einstein Institute)
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Cosmic strings (Image: Albert Einstein Institute)
eLISA will give insights into the development of galaxies, such as NGC 1232 (Image: ESO)
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eLISA will give insights into the development of galaxies, such as NGC 1232 (Image: ESO)
The flight model GPRM for one test mass (Image: Albert Einstein Institute)
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The flight model GPRM for one test mass (Image: Albert Einstein Institute)
Components of LPF's GRS (Image: Albert Einstein Institute)
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Components of LPF's GRS (Image: Albert Einstein Institute)
LTP's Nd:YAG laser (Image: Albert Einstein Institute)
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LTP's Nd:YAG laser (Image: Albert Einstein Institute)
Artist's impression of an eLISA satellite (Image: AEI/MM/exoze)
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Artist's impression of an eLISA satellite (Image: AEI/MM/exoze)
Artist's impression of the laser interferometers on the eLISA optical bench (Image: AEI/MM/exozet)
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Artist's impression of the laser interferometers on the eLISA optical bench (Image: AEI/MM/exozet)
eLISA's spacecraft in a near-equilateral triangular formation and the "cartwheel" orbits (Image: NASA)
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eLISA's spacecraft in a near-equilateral triangular formation and the "cartwheel" orbits (Image: NASA)
LPF Flight Optical bench (Image: Astrium)
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LPF Flight Optical bench (Image: Astrium)
LISA Pathfinder in space chamber with test crew (Photo: ESA/Astrium/IABG)
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LISA Pathfinder in space chamber with test crew (Photo: ESA/Astrium/IABG)
LISA Pathfinder in space chamber (Photo: ESA/Astrium/IABG)
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LISA Pathfinder in space chamber (Photo: ESA/Astrium/IABG)
Lisa Pathfinder and the propulsion module (Image: ESA)
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Lisa Pathfinder and the propulsion module (Image: ESA)
Computer graphics of the LTP (Image: eLISA consortium)
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Computer graphics of the LTP (Image: eLISA consortium)
Capacitive sensors (Image: Albert Einstein Institute)
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Capacitive sensors (Image: Albert Einstein Institute)
Artist's impression of micro-newton thrusters on an eLISA satellite (Image: AEI/MM/exozet)
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Artist's impression of micro-newton thrusters on an eLISA satellite (Image: AEI/MM/exozet)
Gravitational waves from Extreme Mass Ratio Inspirals in non-pure Kerr space-times (Image: AEI/ZIB)
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Gravitational waves from Extreme Mass Ratio Inspirals in non-pure Kerr space-times (Image: AEI/ZIB)
Numerical simulation of amerger of two neutron stars (Image: L. Rezzolla (AEI), M. Koppitz)
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Numerical simulation of amerger of two neutron stars (Image: L. Rezzolla (AEI), M. Koppitz)
LPF optical bench interferometer built in Glasgow (Image: U. Glasgow, U. Birmingham)
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LPF optical bench interferometer built in Glasgow (Image: U. Glasgow, U. Birmingham)
Components of the LTP's Optical Metrology System (Image: ESA/Astrium Ltd)
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Components of the LTP's Optical Metrology System (Image: ESA/Astrium Ltd)
One of the delicate test mass release mechanisms (Image: Albert Einstein Institute)
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One of the delicate test mass release mechanisms (Image: Albert Einstein Institute)
Optical bench under development (Image: Astrium)
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Optical bench under development (Image: Astrium)
A CAD drawing of the LTP with the optical bench and beam paths highlighted (Image: Albert Einstein Institute)
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A CAD drawing of the LTP with the optical bench and beam paths highlighted (Image: Albert Einstein Institute)
Artist's impression of early black hole (Image: NASA/JPL-Caltech)
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Artist's impression of early black hole (Image: NASA/JPL-Caltech)
The LPF Phasemeter mounted on the spacecraft (Image: Albert Einstein Institute)
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The LPF Phasemeter mounted on the spacecraft (Image: Albert Einstein Institute)
LTP's multi-channel phasemeter mounted on the spacecraft (Image: Albert Einstein Institute)
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LTP's multi-channel phasemeter mounted on the spacecraft (Image: Albert Einstein Institute)
PSR J0348+0432 is a record-breaking binary system (Image: ESO/L, Calçada)
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PSR J0348+0432 is a record-breaking binary system (Image: ESO/L, Calçada)
Artist's impression of a pulsar evaporates an orbiting star remnant (Image: Albert Einstein Institute)
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Artist's impression of a pulsar evaporates an orbiting star remnant (Image: Albert Einstein Institute)
Numerical simulation of merging black holes (Image: NASA/C. Henze)
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Numerical simulation of merging black holes (Image: NASA/C. Henze)
eLISA will provide an unprecedented new view of the universe (Image: NASA / JPL-Caltech)
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eLISA will provide an unprecedented new view of the universe (Image: NASA / JPL-Caltech)
Diagram of the test mass chamber (Image: Albert Einstein Institute)
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Diagram of the test mass chamber (Image: Albert Einstein Institute)
LISA Pathfinder preparing to enter the space simulator at IABG, Munich (Image: Albert Einstein Institute)
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LISA Pathfinder preparing to enter the space simulator at IABG, Munich (Image: Albert Einstein Institute)
Vacuum chamber for developing test mass chamber (Image: Albert Einstein Institute)
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Vacuum chamber for developing test mass chamber (Image: Albert Einstein Institute)

Mark your calendars for 2034, because that is when science is set to get a whole new spectrum to play with when the European Space Agency (ESA) launches its eLISA mission. Consisting of a constellation of three spacecraft flying in precise formation, eLISA will study gravitational waves in a manner that may one day revolutionize our understanding of the Universe.

Gravitational waves were first predicted in Einstein’s General Theory of Relativity almost a century ago. They’re basically similar to sound, but instead of waves pushing through air, they are ripples in the very fabric of space and time. Though predicted and sought for decades, none have been witnessed directly yet. They’re believed to be produced by all manner of phenomena, such as merging black holes, massive stars and planets pulling at one another, and even the Big Bang itself.

Artist's impression of early black hole (Image: NASA/JPL-Caltech)
Artist's impression of early black hole (Image: NASA/JPL-Caltech)

What makes gravitational waves so interesting to scientists is that, unlike light, electromagnetism, and other forces, gravitational waves move without interference. Dust, gas, and glare mean nothing to them, meaning that astronomers could use them to look farther out into space and farther back in time than was previously possible.

The eLISA team says that being able to detect and study gravitational waves would also open up new insights into dark energy, the relics of the early universe called cosmic strings, compact stellar-mass binaries, quasars, the structure of the Milky Way, and help produce detailed history of black holes. This is particularly important because astronomers believe that all bright galaxies have supermassive black holes at their centers, so understanding black holes is necessary for understanding the evolution of galaxies themselves. Gravitational waves could even shed light on the Hubble constant, which describes the expansion of the Universe, and allow for new tests of general relativity.

Artist's impression of an eLISA instrument (Image: AEI/MM/exozet)
Artist's impression of an eLISA instrument (Image: AEI/MM/exozet)

The problem with gravitational waves is that detecting ripples in space-time requires extremely sensitive equipment, which would make the touch of the finest needle look like being hit by an asteroid. The preferred method is a laser interferometer, which involves making a laser beam interact with itself over long distances. The pattern resulting from the interaction provides scientists with a tool for measuring extremely small displacements. However, it’s also a technique that requires very long distances and near-absolute stability.

Earth-based attempts to detect gravitational waves haven’t amounted to much because the baseline for the interferometer can’t be very large, there are all sorts of tremors and vibrations getting in the way, and having the detector sitting in the middle of Earth’s gravitational field is a bit like trying to observe stars by setting up an observatory on the Sun.

In contrast, the eLISA mission is composed of a constellation of three spacecraft that form a high precision Michelson interferometer floating in outer space with a baseline of one million kilometers (620,000 mi). The interferometer, or gravitometer, works by detecting how the length of the baselines change in infinitesimal increments as the ripples of gravity stretch and compress space-time.

Artist's impression of the laser interferometers on the eLISA optical bench (Image: AEI/MM/exozet)
Artist's impression of the laser interferometers on the eLISA optical bench (Image: AEI/MM/exozet)

The international consortium of scientists and engineers behind eLISA call it a “sciencecraft” because the payload and the spacecraft had to be specially designed so that one would not interfere with the operation of the other. Though it won’t launch for twenty years, the design of the interferometric measurement system, the telescope, and the gravitational reference sensor have been settled for a decade.

eLISA will orbit the Sun at a Sun-Earth Lagrange Point trailing 20 degrees behind the Earth, where the gravitational forces of Sun and Earth balance out, allowing objects to remain on station. The spacecraft maintain their positions in a near-equilateral triangle between one and five million km (three million mi) apart by performing a “cartwheel” orbit about a common center. The spacecraft can be kept at a constant distance from Earth or allowed to drift as far away as 70 million km (44 million mi), which is the eLISA’s communications limit.

Inside each thermally stable spacecraft are “test masses.” These are 46-mm (1.8 in) cubes made from a dense non-magnetic gold-platinum alloy that are floating free in their sealed vacuum chambers. This may seem odd in outer space, but the spacecraft emits gases from time to time and the test masses need protection from these. In addition, UV lights shine inside the chamber periodically to free electrons and keep the chamber electrostatically neutral in the event of a cosmic ray bombardment.

Diagram of the test mass chamber (Image: Albert Einstein Institute)
Diagram of the test mass chamber (Image: Albert Einstein Institute)

The clever bit about eLISA is that the whole system is “drag-free.” What this means is that the spacecraft moves itself to keep the test masses centered at all times. Each chamber has capacitive sensors that monitor how the test masses shift relative to the spacecraft and the laser interferometer measures how they shift relative to each other. If the masses leave their null positions, micro-propulsion thrusters make the spacecraft follow them until they recenter.

The measurements are done using a 20-cm (8-in) telescope that beams a Nd:YAG laser along the baseline arm. On an optical bench, the received light interferes with that of a reference laser. This interference allows the systems to calculate the minute movements of the test masses with tremendous sensitivity. There’s even a system to virtually eliminate laser “noise” that might upset the measurements.

Using the laser interferometer, the spacecraft can use the test masses to measure distance between the satellites to within less than a picometer – that’s less than 1/31 the size of a helium atom. This allows eLISA to detect gravitational waves between 0.1 mHz to 100 mHz and it can determine frequency, phase, and polarization. In addition, eLISA can see the entire sky and can resolve and distinguish overlapping signals.

Artist's impression of micro-newton thrusters on an eLISA satellite (Image: AEI/MM/exozet)
Artist's impression of micro-newton thrusters on an eLISA satellite (Image: AEI/MM/exozet)

The first target for eLISA will be binary compact stars, which will act as a sort of calibration benchmark because of their known positions and periods. This will allow for extrapolation and more confident future measurements.

"This mission will enable us to study the universe in a completely new way – we’ll be 'listening' to it as well as looking at it," says Physicist Professor Tim Sumner, who leads the work on eLISA at Imperial College London. "Over the centuries astronomy has grown to cover more and more of the electromagnetic spectrum, seeing more colors if you like, whether visible light, infrared, X-rays or submillimeter. With gravitational waves, we’ll have a totally different way of collecting information. It’s as though we've been watching a television with the sound off, and now we’re going to be able to turn the sound up and have a much clearer sense of what’s happening. The possibilities are mind-blowing. We’ll be able to get to grips with black holes; see how gravity works more precisely than ever before; and potentially even see what happened in the seconds after the Big Bang."

LISA Pathfinder in space chamber (Photo: ESA/Astrium/IABG)
LISA Pathfinder in space chamber (Photo: ESA/Astrium/IABG)

In order to test the eLISA technology, ESA is sending up the LISA Pathfinder (LPF) in 2015 on a six-month mission to test the systems that will be used in eLISA, and to study the effectiveness of optical measurements, any stray forces in the spacecraft, and the limits of the technology.

eLISA is classed by ESA as its “L3 mission” (L for Large) and will follow the 2028 launch of ESA’s L2 mission, which will be an advanced X-ray observatory.

The video below outlines the eLISA and the related Athena mission.

Sources: Imperial College, eLISA

Athena and eLISA: Together We Will Unveil the Hidden Secrets of the Universe

5 comments
Mark Gilbreath
So its going to be twenty years before they launch this thing? I wonder how many of the current project people will still be working on it by then?
JAT
Where do cosmic rays come from and how are they generated?
b@man
Waste of time and money. Gravity waves are up to 50 trillion light years in length. Search Infinite Wave Theory.
Gregg Eshelman
So the designs have been done for a decade, yet it won't launch for 20 years... Sounds like a government project! 30 year meal ticket for a bunch of people. Spend three decades on R&D then launch 30 year out of date technology. Would be quite the egg on their faces if someone invents FTL before this tech turkey gets launched.
MarkmBha
This project looks dead in the water.