A Triangular Underground Gravitational-Wave Observatory with Ten-Kilometre Arms: Noise Budget and Binary-Neutron-Star Horizon Computed from First Principles

A third-generation ground-based gravitational-wave observatory is designed as a triangle of three interferometers with 10 km arms, sited underground, and its performance is computed from an explicit noise model. Quantum shot noise with 3 MW of circulating light and 10 dB of squeezing contributes 1.72e-25 per root hertz; the total strain noise is 1.25e-24 per root hertz at 10 Hz, 5.29e-25 at 100 Hz and 5.29e-25 at 1 kHz. Integrating the inspiral signal of a 1.4 plus 1.4 solar-mass binary against this noise curve gives an optimal-orientation horizon of 7.0 Gpc for one interferometer of the triangle. The vacuum system dominates the mass at 8,939 tonnes, and the site draws 2.1 MW. The figures are computed from the stated noise model; the design is simulated, not measured.