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A Space-Based Gravitational Wave Observatory Is a Step Closer to Reality

The planned LISA mission would involve three spacecraft flying in formation over a million miles apart.

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An illustration of the LISA Pathfinder.
An illustration of the LISA Pathfinder in space.
Illustration: ESA–C.Carreau

A proposal for the first-ever space-based observatory for studying gravitational waves just passed a vital feasibility review with flying colors. The mission is called LISA—the Laser Interferometer Space Antenna—and it cleared Phase A of its mission lifetime cycle, the process by which missions are dreamt up and then created.

Led by the European Space Agency in collaboration with NASA, LISA is made up of three spacecraft that will orbit the Sun in a triangular formation. Each ‘side’ in that triangle will be 1.5 million miles long. As an interferometer (like the ground-based LIGO), LISA will very precisely keep track of the distance between the three spacecraft. When a passing gravitational wave causes a distortion in spacetime, LISA will detect it as the distance between its spacecraft briefly changes. LISA will also be able to detect where in the sky the gravitational wave came from.


Gravitational waves, predicted to exist by Einstein, are produced by some of the most extreme astrophysical phenomena in the universe. When black holes and neutron stars—some of the densest, most massive objects out there—orbit one another or merge, they cause ripples in the fabric of spacetime.

Since LIGO made history by detecting gravitational waves in 2015, astrophysicists have become determined to see more of these ripples, but some are harder to observe than others. Mergers of different masses produce waves of different frequencies; small black hole mergers and explosive events like supernovae are detectable by observatories like LIGO, but supermassive black hole mergers emit frequencies that LIGO’s 2.5-mile-long arms are simply too short to detect. LISA’s 1.5-million-mile arms will be able to detect lower frequency events, like those clashes of giant black holes.

A graphic showing how gravitational waves are detected.
A graphic showcasing how different gravitational wave events can be detected.
Graphic: ESA

LISA’s hardware has already been tested by the LISA Pathfinder mission, which launched in 2015 and demonstrated how masses could be kept in place in free-fall (space) and measured with extraordinary precision. Now, LISA will enter Phase B1 of the ESA’s review, in which the technology for the mission will be developed and its final design will be selected. Technologies for LISA will include the spacecrafts’ laser systems, telescopes, and sensors.

“Transitioning into Phase B1 lifts the mission out of concept studies and marks a major milestone for the involved scientists and engineers,” said Martin Gehler, the ESA’s study manager for LISA, in an agency release. “After a long journey, starting with the first sketches in the 1980s, we now know that we are on track, and that we have a feasible plan forward to adoption.”

The mission is expected to launch in 2037, 20 years after the ESA selected it as a priority. Construction on the spacecraft won’t begin until 2024 at the earliest, according to an ESA website, after which some of the enigmatic physics of our cosmos could be demystified.


More: Astronomers Detected Gravitational Waves. Now They Want to See the Cosmic Ocean