The LISA concept features three spacecraft arranged in an equilateral triangle with each side 2.5 million kilometers long, flying in an Earth-like heliocentric orbit.

However, in 2011, NASA announced that it would be unable to continue its LISA partnership with the European Space Agency[4] due to funding limitations.

[8] In 2013, ESA selected 'The Gravitational Universe' as the theme for one of its three large projects in the 2030s[9][10] whereby it committed to launch a space-based gravitational-wave observatory.

[14] The LISA mission is designed for direct observation of gravitational waves, which are distortions of spacetime travelling at the speed of light.

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.

[22] The LISA mission's primary objective is to detect and measure gravitational waves produced by compact binary systems and mergers of supermassive black holes.

LISA will observe gravitational waves by measuring differential changes in the length of its arms, as sensed by laser interferometry.

[25] To eliminate non-gravitational forces such as light pressure and solar wind on the test masses, each spacecraft is constructed as a zero-drag satellite.

As the satellites are free-flying, the spacing is easily adjusted before launch, with upper bounds being imposed by the sizes of the telescopes required at each end of the interferometer (which are constrained by the size of the launch vehicle's payload fairing) and the stability of the constellation orbit (larger constellations are more sensitive to the gravitational effects of other planets, limiting the mission lifetime).

This difference means that LISA cannot use high-finesse Fabry–Pérot resonant arm cavities and signal recycling systems like terrestrial detectors, limiting its length-measurement accuracy.

[34] Gravitational-wave astronomy seeks to use direct measurements of gravitational waves to study astrophysical systems and to test Einstein's theory of gravity.

[36] In February 2016, the Advanced LIGO project announced that it had directly detected gravitational waves from a black hole merger.

A LISA-like instrument should be able to measure relative displacements with a resolution of 20 picometres—less than the diameter of a helium atom—over a distance of a million kilometres, yielding a strain sensitivity of better than 1 part in 1020 in the low-frequency band about a millihertz.

[46] LISA will be able to detect the nearly monochromatic gravitational waves emanating of close binaries consisting of two compact stellar objects (white dwarfs, neutron stars, and black holes) in the Milky Way.

At low frequencies these are actually expected to be so numerous that they form a source of (foreground) noise for LISA data analysis.

[52] LISA will be able to independently measure the redshift and distance of events occurring relatively close by (z < 0.1) through the detection of massive black hole mergers and EMRIs.

At larger ranges LISA events can (stochastically) be linked to electromagnetic counterparts, to further constrain the expansion curve of the universe.

[11] LISA will be sensitive to the stochastic gravitational wave background generated in the early universe through various channels, including inflation, first-order cosmological phase transitions related to spontaneous symmetry breaking, and cosmic strings.

[53][54] Previous searches for gravitational waves in space were conducted for short periods by planetary missions that had other primary science objectives (such as Cassini–Huygens), using microwave Doppler tracking to monitor fluctuations in the Earth–spacecraft distance.

[citation needed] Other gravitational wave antennas, such as LIGO, Virgo, and GEO600, are already in operation on Earth, but their sensitivity at low frequencies is limited by the largest practical arm lengths, by seismic noise, and by interference from nearby moving masses.

Despite NGO being ranked highest in terms of scientific potential, ESA decided to fly Jupiter Icy Moons Explorer (JUICE) as its L1 mission.

One of the main concerns was that the LISA Pathfinder mission had been experiencing technical delays, making it uncertain if the technology would be ready for the projected L1 launch date.

[59] Following the successful detection of gravitational waves by the LIGO, ground-based detectors in September 2015, NASA expressed interest in rejoining the mission as a junior partner.