Octahedron configuration for a displacement noise-cancelling gravitational wave detector in space

TL;DR

This paper introduces a novel octahedral constellation for space-based gravitational wave detection that simplifies the payload by removing the need for drag-free control and explores its sensitivity and scientific potential.

Contribution

It presents the first study of a 3D octahedron configuration for gravitational wave detection, including noise cancellation techniques and sensitivity analysis.

Findings

The octahedral design can cancel laser and acceleration noise without drag-free control.

Short-arm-length version has a sensitivity peak near 100 Hz of about 2×10^{-23} Hz^{-1/2}.

Performance is between initial and advanced ground-based detectors, with potential for improvement with longer arms.

Abstract

We study for the first time a three-dimensional octahedron constellation for a space-based gravitational wave detector, which we call the Octahedral Gravitational Observatory (OGO). With six spacecraft the constellation is able to remove laser frequency noise and acceleration disturbances from the gravitational wave signal without needing LISA-like drag-free control, thereby simplifying the payloads and placing less stringent demands on the thrusters. We generalize LISA's time-delay interferometry to displacement-noise free interferometry (DFI) by deriving a set of generators for those combinations of the data streams that cancel laser and acceleration noise. However, the three-dimensional configuration makes orbit selection complicated. So far, only a halo orbit near the Lagrangian point L1 has been found to be stable enough, and this allows only short arms up to 1400 km. We derive the sensitivity curve of OGO with this arm length, resulting in a peak sensitivity of about $2\times10^{-23}\,\mathrm{Hz}^{-1/2}$ near 100 Hz. We compare this version of OGO to the present generation of ground-based detectors and to some future detectors. We also investigate the scientific potentials of such a detector, which include observing gravitational waves from compact binary coalescences, the stochastic background and pulsars as well as the possibility to test alternative theories of gravity. We find a mediocre performance level for this short-arm-length detector, between those of initial and advanced ground-based detectors. Thus, actually building a space-based detector of this specific configuration does not seem very efficient. However, when alternative orbits that allow for longer detector arms can be found, a detector with much improved science output could be constructed using the octahedron configuration and DFI solutions demonstrated in this paper. (abridged)