Artists concept of the LISA configuration, bathed in the gravitational waves emitted from a distant cosmic event.
Three spacecraft, each with a Y-shaped payload, form an equilateral triangle with sides 5 million km in length. The two branches of the Y at one corner, together with one branch each from the spacecraft at the other two corners, form one of up to three Michelson-type interferometers, operated with infrared laser beams. The interferometers are designed to measure relative path changes dl/l due to gravitational waves, so called strains in space, down to 10-23 for observation times of the order of 1 year.
The diameters of the spacecraft are about 2.5 m, the distances between then 5 x 109 m.