A novel seldom used, thermal analysis approach for system-level thermal design is developed that leverages frequencybased 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.
Direct imaging of exoearths with high-contrast internal coronagraphs depends on ultra-stable opto-mechanical systems. Ultra-stable mirror assemblies enable decadal survey missions like LUVOIR and HabEx. To precisely define the necessary level of stability, the essential first step is to budget the maximum allowable disturbances for each optic in the system. Ideally, allocations are budgeted with respect to spatial- and time-domain frequencies. If allocations do not span these domains, the optic assembly designer cannot take advantage of frequency bands where requirements are looser because of assumptions about telescope control systems and internal coronagraph filtering. This paper explores how mirror assembly technologies and designs are predicted to impact stability, especially within the frequency bands that drive coronagraph contrast performance.
NASA is exploring telescope and mirror technology options to meet the demanding science goals of the proposed HabEx space telescope. A key priority for the HabEx mission concept would be to leverage affordable telescope solutions that can meet challenging telescope performance requirements with a demanding program timeline. The baseline approach for HabEx is to use an unobscured, monolithic primary mirror with a coronagraph to optimize system performance. NASA is performing an initial study to investigate the feasibility of a HabEx Lite concept which would not leverage a coronagraph and would therefore, have lower exoEarth yield as a consequence, but could provide system mass, cost, and schedule advantages. The HabEx Lite concept leverages replicated, ULE® mirror segments to provide an attractive, alternative telescope architecture to meet the HabEx threshold mission needs. We present the initial mirror design and performance assessment for the HabEx Lite concept.
KEYWORDS: Mirrors, Adhesives, Wavefronts, 3D modeling, Control systems, Systems modeling, Thermal modeling, Temperature metrology, Coronagraphy, Metrology
For internal coronagraph options on the LUVOIR or HabEx mission concepts, the stated challenge of 10 picometers RMS wavefront stability over 10 minutes will govern the performance of every structure that connects the focal plane assembly to each optical surface. This paper interrogates wavefront stability of a mounted mirror assembly for a primary mirror segment assembly, and stability of the optical surface. Analysis describes stability of each element in a primary mirror segment assembly (PMSA) to understand the impact of each component of the PMSA on surface figure error (SFE) over short time periods.
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