Low Frequency Thermal Performance of the LISA Sciencecraft

Thermal fluctuations are a major contributor to the low-frequency performance of LISA. The LISA orbits and sciencecraft are designed to provide as quiet a thermal environment as possible. Since producing such a quiet thermal environment on-ground is very challenging, detailed modeling is necessary to verify that the sciencecraft will meet its on-orbit performance requirements. We developed a thermal Finite Element Model (FEM) of the current LISA design based on the solid model. This thermal model is being used to understand the thermal behavior of the LISA sciencecraft design, in particular for the thermal isolation aspects. We present the latest LISA temperature fluctuation estimates and discuss some techniques developed to reduce the computation time. The FEM was imported into a radiation analysis code, which was used to generate radiation interchange factors and the corresponding FE thermal network. The complete model was then solved for temperature predictions. Various sinusoidal input heat loads were applied and a curve fitting technique was used to extract the fluctuating component of the response signal before the solution had reached quasi-steady state, greatly reducing the necessary solution time. The transfer functions were then derived from the input signal and response fluctuations and are presented herein.