NGO measurement concept
The New Gravitational wave Observatory (NGO) mission consists of three spacecraft, separated by 106 km, orbiting the Sun in a configuration that forms a near-equilateral triangle.
To measure the strain, or deformation, on the fabric of spacetime caused by gravitational waves, the mission uses precision laser interferometry.
The constellation of the three NGO spacecraft itself forms the science instrument.
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 send/receive laser ranging terminals and 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 – each house one laser ranging terminal and one free-floating test mass, 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. The laser in the daughter spacecraft is phase locked to the incoming laser light.
In this sketch, the blue dots indicate where interferometric measurements are taken, the yellow blocks indicate test masses and the light green blocks indicate the laser. The sketch leaves out the test mass interferometers for clarity.