ESA gives gravitational wave space probe LISA the nod for a 2035 launch

Trio of spacecraft to capture ripples in spacetime

The European Space Agency (ESA) has signed off on the Laser Interferometer Space Antenna (LISA) mission to detect gravitational waves from space.

The plan is to send three spacecraft, trailing the Earth as it orbits the Sun, forming a highly accurate equilateral triangle in space. Each side will be 2.5 million kilometers long, and the spacecraft will exchange laser beams over the distance.

A pair of free-floating solid gold-platinum cubes – slightly smaller than Rubik's cubes – will act as test masses within each spacecraft. According to ESA: "Gravitational waves will cause tiny changes in the distances between the masses in the different spacecraft, and the mission will track these variations using laser interferometry."

This is where those laser beams come in. By firing beams from one spacecraft to another, scientists can determine changes in masses' distances down to a few billionths of a millimeter.

The mission will be able to detect ripples in spacetime caused when massive black holes at the center of galaxies collide. Scientists also hope to capture the gravitational 'ringing' from the initial moments of the universe and detect events closer to home.

LISA project scientist Oliver Jennrich said, "For centuries we have been studying our cosmos through capturing light. Coupling this with the detection of gravitational waves is bringing a totally new dimension to our perception of the Universe.

"If we imagine that, so far, with our astrophysics missions, we have been watching the cosmos like a silent movie, capturing the ripples of spacetime with LISA will be a real game-changer, like when sound was added to motion pictures."

With the mission now approved, work on building the spacecraft and its instruments will start a year from now, in January 2025, once a European industrial contractor is chosen. The launch is planned for 2035 atop an Ariane 6 rocket.

Should the launch go on time, it will be 20 years since ESA demonstrated that the project was possible with the LISA Pathfinder mission. This launched on December 3, 2015, onboard a Vega rocket and, among other achievements, showed that a mass could be put in a gravitational free-fall and demonstrated laser interferometry with a free-falling mirror.

The mission ended in 2017.

LISA will follow the same basic principles as the Earth-bound Laser Interferometer Gravitational-Wave Observatory (LIGO), which first proved the existence of gravitational waves and was recently upgraded to increase its sensitivity.

However, the distances used by ground-based instrumentation such as LIGO pale compared to what is possible in space, thanks to the millions of kilometers separating the LISA spacecraft.

LISA lead project scientist Nora Lützgendorf said, "Using laser beams over distances of several kilometers, ground-based instrumentation can detect gravitational waves coming from events involving star-sized objects – such as supernova explosions or merging of hyper-dense stars and stellar-mass black holes. To expand the frontier of gravitational studies we must go to space.

"Thanks to the huge distance travelled by the laser signals on LISA, and the superb stability of its instrumentation, we will probe gravitational waves of lower frequencies than is possible on Earth, uncovering events of a different scale, all the way back to the dawn of time."

Should all go to plan, data from LISA will be combined with other ESA missions, such as the next-generation X-ray observatory NewAthena – currently scheduled for 2037 – to give scientists a deeper insight into the origins of the Universe. ®

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