A novel seldom used, thermal analysis approach for system-level thermal design is developed that leverages frequency-based techniques and metrics common in structural dynamics modeling. The ULTRA study, which is assessing technological capabilities for a 15-meter telescope requiring sub nanometer optical stability was the foundation for the initial thermal math model and requirements design space discussed in this paper. For such a large, space-based system under tight tolerances, a typical thermal analysis approach will not generate a meaningful understanding of which effects drive the thermal management design. To address this issue, a perturbance-based thermal modeling approach, which is more suited to generating an understanding of the bulk system-level sensitivities, was used instead. The model developed begins by running discrete sensitivities over a range of input perturbance frequencies. The output quantifies the system response to the various sources of thermal energy input. Results are gathered and combined to from Bode plots to quantify the effect of the system perturbances. These plots can quickly characterize the impact of certain thermal designs in relation to a frequency-based wave front error budget. Resulting sensitivities at the system / sub-system scale and the process for producing such results for the LUVOIR thermal math model utilized in the Ultra study are presented. Thermal stability is key to achieving coronographic missions with 10 E-10 contrast.
