Speaker
Description
The Laser Interferometer Space Antenna (LISA) mission will detect gravitational waves through picometre-level interferometric measurements between three spacecraft separated by 2.5 million kilometres. Achieving the required sensitivity demands accurate prediction of the thermo-optic and thermo-elastic behaviour of the Payload Module. Within the Optical Bench Assembly (OBA), the Quadrant Photoreceiver (QPR) is one of the dominant thermal disturbance sources, and thermal transfer functions describing the propagation of temperature fluctuations through the instrument are directly used in performance analyses. Consequently, confidence in both the magnitude and dynamic behaviour of the thermal model is essential.
To support these activities, a dedicated thermal test campaign was performed on three pre-Structural Model (pSM) QPR units incorporating different thermo-optical surface treatments. In addition to conventional steady-state thermal balance correlation, the campaign investigated methods for dynamic model validation. Several excitation approaches were considered, including discrete single-frequency sinusoidal inputs and broadband thermal excitation techniques. A pseudo-random binary heater input was ultimately selected as it enabled efficient excitation across a wide frequency range within a practical test duration while maintaining representative thermal operating conditions. The resulting temperature measurements were processed in the frequency domain to derive transfer functions and power spectral densities relating thermal inputs and responses.
Measured frequency responses were compared directly with transient thermal model predictions. The correlation exercise identified deficiencies associated with thermal capacitances, contact conductances and radiative coupling paths, leading to an improved model representation and significantly enhanced agreement between prediction and test. The correlated model demonstrated good reproduction of both steady-state temperatures and dynamic thermal behaviour, providing confidence in the transfer functions subsequently used within the LISA thermo-optic performance analyses. Furthermore, the work demonstrates that frequency-domain thermal testing can provide substantially greater insight into model fidelity than traditional thermal balance testing alone and offers a practical methodology for future spacecraft thermal verification programmes.