The NGO orbits
The New Gravitational wave Observatory constellation shown trailing Earth by about 20° (or 5 × 107 km), inclined by 60° to the ecliptic.
The mission consists of three spacecraft orbiting the Sun in a configuration that forms a near-equilateral triangle. In course of the mission, the trailing angle will vary from 10° to 25°. The separation between the spacecraft is 1 × 106 km.
To measure the strain, or deformation, on the fabric of spacetime caused by gravitational waves, the mission uses precision laser interferometry. The large distance between the spacecraft makes it necessary to extend the classical concept of an interferometer, so that the measurement technique somewhat resembles doppler spacecraft tracking.
The two sides of the equilateral triangle, from the apex to the two vertices with a spacecraft at each end, form two measurement arms. Each spacecraft carries the interferometry equipment needed to measure changes in arm length arising from the passage of gravitational waves. The spacecraft at the apex - the 'mother' spacecraft - houses two free-falling test masses, forming one set of endpoints of the two measurement arms. The other two spacecraft at the vertices of the triangle - the 'daughter' spacecraft - house one free-floating test mass each and form the two other endpoints of the measurement arms. The mother and daughter spacecraft are identical but for the number of payloads they carry.