Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Initial acquisition requirements for optical cavities in the space gravitational wave antennae DECIGO and B-DECIGO

Yuta Michimura, Koji Nagano, Kentaro Komori, Kiwamu Izumi, Takahiro Ito, Satoshi Ikari, Tomotada Akutsu, Masaki Ando, Isao Kawano, Mitsuru Musha, Shuichi Sato

TL;DR

This work analyzes the initial acquisition challenges for DECIGO and B-DECIGO, space-based Fabry-Pérot cavity GW detectors that operate in the decihertz band. It partitions the process into deployment, laser link acquisition, and cavity lock acquisition, deriving feasibility-driven precision requirements for inter-spacecraft distances, beam pointing, and mirror alignment. A key finding is that the relative mirror velocity must be reduced to the order of $v \,<\; 1$–$\,2~\mu$m/s and the angular errors must reach sub-microradian or even nanoradian levels to enable cavity resonance with feasible actuators and sensing, particularly during link acquisition when cavity signals are not yet available. The authors argue that achieving these constraints will require additional sensors (e.g., AOD-based deflection, laser ranging, or SILVIA demonstrations) and autonomous, ground-independent ranging strategies, marking an essential step toward validating DECIGO and B-DECIGO feasibility before full-scale deployment.

Abstract

DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1-10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1,000 km sides, forming Fabry-Pérot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires ultra-precise formation flying, where inter-mirror distance and alignment must be precisely controlled. Achieving this necessitates a sequential improvement in precision using various sensors and actuators, from the deployment of the spacecraft to laser link acquisition and ultimately to the control of the Fabry-Pérot cavities to maintain resonance. In this paper, we derive the precision requirements at each stage and discuss the feasibility of achieving them. We show that the relative speed between cavity mirrors must be controlled at the sub-micrometer-per-second level and that relative alignment must be maintained at the sub-microradian level to obtain control signals from the Fabry-Pérot cavities of DECIGO and B-DECIGO.

Initial acquisition requirements for optical cavities in the space gravitational wave antennae DECIGO and B-DECIGO

TL;DR

This work analyzes the initial acquisition challenges for DECIGO and B-DECIGO, space-based Fabry-Pérot cavity GW detectors that operate in the decihertz band. It partitions the process into deployment, laser link acquisition, and cavity lock acquisition, deriving feasibility-driven precision requirements for inter-spacecraft distances, beam pointing, and mirror alignment. A key finding is that the relative mirror velocity must be reduced to the order of –m/s and the angular errors must reach sub-microradian or even nanoradian levels to enable cavity resonance with feasible actuators and sensing, particularly during link acquisition when cavity signals are not yet available. The authors argue that achieving these constraints will require additional sensors (e.g., AOD-based deflection, laser ranging, or SILVIA demonstrations) and autonomous, ground-independent ranging strategies, marking an essential step toward validating DECIGO and B-DECIGO feasibility before full-scale deployment.

Abstract

DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1-10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1,000 km sides, forming Fabry-Pérot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires ultra-precise formation flying, where inter-mirror distance and alignment must be precisely controlled. Achieving this necessitates a sequential improvement in precision using various sensors and actuators, from the deployment of the spacecraft to laser link acquisition and ultimately to the control of the Fabry-Pérot cavities to maintain resonance. In this paper, we derive the precision requirements at each stage and discuss the feasibility of achieving them. We show that the relative speed between cavity mirrors must be controlled at the sub-micrometer-per-second level and that relative alignment must be maintained at the sub-microradian level to obtain control signals from the Fabry-Pérot cavities of DECIGO and B-DECIGO.

Paper Structure

This paper contains 11 sections, 14 equations, 4 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Interferometer design
  3. Configuration and control scheme
  4. Interferometer parameters
  5. Actuator requirements
  6. Initial acquisition sequence
  7. Requirements
  8. Deployment
  9. Link acquisition
  10. Lock acquisition
  11. Conclusions

Figures (4)

  • Figure 1: Schematic view of DECIGO and B-DECIGO. For simplicity, components such as electro-optic modulators, steering mirrors, and mode-matching telescopes are not included in the diagram. The dual-pass differential Fabry-Pérot interferometer scheme is shown as an example interferometer control scheme. BS: beam splitter, PD: photodiode.
  • Figure 2: Schematic view of the optical setup in one spacecraft for the back-linked Fabry-Pérot interferometer control scheme.
  • Figure 3: Schemetic of the initial acquisition sequence.
  • Figure 4: SOFT and HARD modes of angular motion of the cavity mirrors in a Fabry-Pérot cavity. The SOFT mode induces a translation of the cavity axis, while the HARD mode induces a rotation of the cavity axis. Cross marks indicate the mirrors' centers of curvature.