Structural design and performance analysis of laser transmitting telescope for space gravitational wave detection

Objective The spaceborne laser emission telescope serves as a core component of space-based gravitational wave detection systems. Compared with ground-based telescopes, the on-orbit environment imposes more stringent requirements on both optical performance and structural robustness. To address these challenges, this paper presents a laser emission telescope based on an off-axis four-mirror configuration, designed specifically for space gravitational wave detection. The telescope achieves a capture field of view of ±300 μrad, an optical transmission efficiency of 86.3%, and an optical path length stability of TTL ≤ 0.025 nm/μrad. During the design phase, the primary mirror thickness was optimized through lightweight structural design, and a flexure-based support scheme was implemented, yielding a surface figure accuracy of RMS ≤ 9.42 nm. The total mass of the opto-mechanical structure, excluding mirrors, is merely 3.845 kg. Comprehensive finite element analyses were conducted under representative mission profiles: support structure strength was verified under self-weight and 10 g acceleration loads; After removing rigid-body displacements via Zernike polynomial fitting, the residual surface deformation of the primary mirror was maintained within 1/30 wavelength. Thermal deformation simulations under a uniform 60 °C temperature variation demonstrate that all inter-mirror decenters and tilts comply with optical design tolerances. Modal analyses indicate that the first natural frequency exceeds 200 Hz under both gravity and zero-gravity conditions, confirming excellent dynamic characteristics. The results collectively demonstrate that the proposed telescope meets the optical performance and structural reliability requirements for space-based gravitational wave detection.

Methods The telescope system was designed following a systematic opto-mechanical co-design approach. First, the optical configuration was established using an off-axis four-mirror architecture, with even-order aspheric surfaces introduced to suppress aberrations. Following the optical design, support structures for each optical element were developed. The primary mirror, fabricated from Zerodur, was lightweighted and supported by a flexure hinge system to minimize stress-induced figure errors. The secondary, tertiary, and quaternary mirrors are each equipped with five-degree-of-freedom adjustment mechanisms to facilitate alignment relative to the primary mirror, and flexure features were incorporated to accommodate thermal deformations. The inter-mirror support frame, constructed from carbon fiber reinforced polymer (CFRP), adopts a hexagonal body with a rectangular outer frame. Finally, structural simulations were performed under multiple environmental conditions, including self-weight and 10 g static loads, thermal deformations under a 60 °C temperature excursion, and both natural and prestressed modal analyses, to verify that the structure meets the optical requirements across all design cases.

Results and discussions The telescope achieves a capture field of view of ±300 μrad, an optical transmission efficiency of 86.3%, and an optical path length stability (TTL) of ≤0.025 nm/μrad. The RMS wavefront error is below λ/300 across the entire field of view. Following lightweighting and support optimization, the primary mirror surface figure remains below 10 nm RMS in all gravity orientations, and the total structural mass (excluding mirrors) is 3.845 kg, satisfying the lightweight requirement. Under self-weight and 10 g acceleration, the maximum von Mises stress in the structure is 494 MPa, substantially below the yield strength of CFRP. Under a 60 °C thermal load, the maximum inter-mirror axial displacement is 1.5759 μm and the maximum relative decentering is 0.8563 μm, with all parameters falling within the allocated tolerances, demonstrating sound thermal dimensional stability. Modal analysis yields a first natural frequency of 287.31 Hz and a first prestressed frequency of 221.21 Hz, both well above the 80 Hz design requirement. These dynamic characteristics are sufficient to avoid resonance risks under typical on-orbit disturbance environments.

Conclusions This study presents the collaborative opto-mechanical design of a laser emission telescope for space-based gravitational wave detection, establishing the off-axis four-mirror optical configuration and the corresponding structural implementation. The primary mirror incorporates both lightweighting and flexure support to mitigate environmental disturbances, while the secondary, tertiary, and quaternary mirrors are equipped with five-degree-of-freedom adjustment mechanisms for alignment compensation. Multi-condition finite element simulations confirm that the telescope meets all optical performance and structural integrity requirements under self-weight, 10 g acceleration, and 60 °C thermal excursion, demonstrating its suitability for space gravitational wave detection missions. Furthermore, the design methodology and performance verification framework presented herein offer practical reference values for the development of similar on-orbit high-precision optical systems.