Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna (LISA) is a planned space probe to detect and accurately measure gravitational waves—tiny ripples in the fabric of spacetime—from astronomical sources. LISA will be the first dedicated space-based gravitational-wave observatory. It aims to measure gravitational waves directly by using laser interferometry. The LISA concept has a constellation of three spacecraft arranged in an equilateral triangle with sides 2.5 million kilometres long, flying along an Earth-like heliocentric orbit. The distance between the satellites is precisely monitored to detect a passing gravitational wave.

The LISA project started out as a joint effort between NASA and the European Space Agency (ESA). However, in 2011, NASA announced that it would be unable to continue its LISA partnership with the European Space Agency due to funding limitations. The project is a recognized CERN experiment (RE8). A scaled-down design initially known as the New Gravitational-wave Observatory (NGO) was proposed as one of three large projects in ESA's long-term plans. In 2013, ESA selected 'The Gravitational Universe' as the theme for one of its three large projects in the 2030s whereby it committed to launch a space-based gravitational-wave observatory.

In January 2017, LISA was proposed as a candidate mission. On June 20, 2017, the suggested mission received its clearance goal for the 2030s, and was approved as one of the main research missions of ESA.

On 25 January 2024, the LISA Mission was formally adopted by ESA. This adoption recognises that the mission concept and technology are advanced enough that building the spacecraft and its instruments can commence.

The LISA mission is designed for direct observation of gravitational waves, which are distortions of spacetime travelling at the speed of light. Passing gravitational waves alternately squeeze and stretch space itself by a tiny amount. Gravitational waves are caused by energetic events in the universe and, unlike any other radiation, can pass unhindered by intervening mass. Launching LISA will add a new sense to scientists' perception of the universe and enable them to study phenomena that are invisible in normal light.

Potential sources for signals are merging massive black holes at the centre of galaxies, massive black holes orbited by small compact objects, known as extreme mass ratio inspirals, binaries of compact stars, and possibly other sources of cosmological origin, such as a cosmological phase transition shortly after the Big Bang, and speculative astrophysical objects like cosmic strings and domain boundaries.