May 23, 2019

Lisa

Following on from the LISA Pathfinder in-orbit technology demonstrator mission and the detection of gravitational waves by ground-based observatories, the European LISA mission (Laser Interferometer Space Antenna) is set—around the middle of the 2030s—to detect and conduct long-term observations of these ripples in the fabric of space-time, opening up a new window onto our universe.

Gravitational waves are distant echoes of the most violent events in the cosmos. Predicted by Albert Einstein’s theory of general relativity in 1916, they were observed for the first time—from Earth—in 2015. Travelling through space at the speed of light, gravitational waves are very hard to observe because the ripples they generate are infinitely small, and even the best Earth-bound instruments are limited by ambient noise in particular. In 2017, 20 years after the first concepts, ESA selected LISA as the third large-class mission (L3) of its Cosmic Vision programme, with launch scheduled for 2034.

LISA will consist of three satellites following the Earth around the Sun, trailing about 50 million kilometres behind the planet. Each satellite will be located at the point of an equilateral triangle 2.5 million kilometres on a side, forming a giant optical interferometer inclined at an angle of 60° to the plane of Earth’s orbit.

The satellites will be linked in pairs by identical and synchronized laser beams to measure any relative movements between free-fall test masses inside each instrument. These test masses are in an environment isolated from external disturbances—solar wind, parasitic forces etc.—and will reveal any infinitesimal distortions in space-time. The expected level of sensitivity is 10 picometres over a million kilometres, in a low-frequency range that the ground-based LIGO (Laser Interferometer Gravitational-wave Observatory) and Virgo facilities are unable to measure.

To accomplish this technological feat, CNES is working within the LISA consortium to federate a community of French research laboratories that will be making a major contribution to the mission. LISA-France is expected to be tasked with integrating and testing the instruments, as well as with designing and developing the science ground segment. This work will involve a big contribution to performance simulations and modelling, and to prepare for scientific exploitation of data from the mission.

Between 2015 and 2017, ESA launched and operated a first technology demonstration mission called LISA-Pathfinder. The excellent results validate the key building blocks of the future LISA mission, notably the ability to maintain a test mass in purely gravitational free fall and obtain highly precise interferometric measurements inside the instrument.