LISA

LISA (or Laser Interferometer Space Antenna) is a proposed European Space Agency (ESA) space mission to detect gravitational waves by measuring the distance between three spacecraft using laser interferometry. Three probes, placed in a triangle, in an Earth-trailing orbit, spaced 2.5 million kilometers from each other, would continually measure the distances between them, sensing changes to these distances resulting from gravitational waves. A 2037 launch is envisioned. The three would host of three Michelson interferometers with the arms much longer than those of LIGO, which would be sensitive to a considerably lower GW frequency (0.0001 to 0.1 Hz), corresponding to a larger orbital period (roughly 10 to 10,000 seconds). In addition to extragalactic sources, a number of scenarios common to the Milky Way (e.g., co-orbiting binary compact objects) will produce such waves from many simultaneous targets, producing a need for considerable analysis to sort out the data. With analysis, the masses and rotations of the black holes should be determinable from LISA-provided data.

LISA Pathfinder was a 2015-2017 mission to test some of the necessary technology in space, in particular, the technology to provide extremely stable end-points to the interferometers.

LISA was earlier conceived (with 5 million kilometer arms) aiming for deployment in the 2015-2025 time frame, but NASA (an original participant) withdrew in 2011, at which time a scaled-down version called New Gravitational Wave Observatory (NGO) was proposed in its place, which was also not accepted. The current LISA plan is scaled between these earlier efforts, aiming for a much later launch. Some other later proposals also use variants of the name "LISA".