A simulation-based systems engineering framework is defined to design, optimize and simulate complex, large scale systems under uncertainty through integrated models encompassing multiple disciplines such as, for example, structural-thermal-optical. A model's input parameter uncertainties are rigorously quantified upstream of the model through literature reviews, experiments or elicitation from subject matter experts and then propagated through the model to determine their influence on specific quantities of interest requested in output. A variance-based global sensitivity analysis is used to identify and rank the critical system parameters, based on their contribution to the variance of the quantities of interest. These parameters can then be targeted by additional research through optimal parameter inference experiments in order to reduce their variability. By so doing, one incorporates uncertainty in the model and updates the model iteratively as new parameter information becomes available. This process increases one's knowledge about the system, its subcomponents and all of their mutual interactions, and represents a crucial commodity when important design decisions are to be made. When applied early in a project's life-cycle, it can potentially reduce mission costs related to resources (e.g., mass or power) and processes (e.g., design, verification and validation). As a case study, this paper presents results from the application of this framework to the integrated model of the James Webb Space Telescope, used to ultimately revise the model uncertainty factors applied to nominal temperature predictions for the benchmark hot-to-cold slew thermal analysis case.
KEYWORDS: Systems modeling, Thermal modeling, James Webb Space Telescope, Data modeling, Model-based design, Optimization (mathematics), Mathematical modeling, Thermal engineering, Optical instrument design, Space telescopes
Spacecraft thermal model validation is normally performed by comparing model predictions with thermal test data and reducing their discrepancies to meet the mission requirements. Based on thermal engineering expertise, the model input parameters are adjusted to tune the model output response to the test data. The end result is not guaranteed to be the best solution in terms of reduced discrepancy and the process requires months to complete. A model-based methodology was developed to perform the validation process in a fully automated fashion and provide mathematical bases to the search for the optimal parameter set that minimizes the discrepancies between model and data. The methodology was successfully applied to several thermal subsystems of the James Webb Space Telescope (JWST). Global or quasiglobal optimal solutions were found and the total execution time of the model validation process was reduced to about two weeks. The model sensitivities to the parameters, which are required to solve the optimization problem, can be calculated automatically before the test begins and provide a library for sensitivity studies. This methodology represents a crucial commodity when testing complex, large-scale systems under time and budget constraints. Here, results for the JWST Core thermal system will be presented in detail.
μ-Spec is a compact submillimeter (~ 100 GHz - 1:1 THz) spectrometer which uses low loss superconducting microstrip transmission lines and a single-crystal silicon dielectric to integrate all of the components of a diffraction grating spectrometer onto a single chip. We have already successfully evaluated the performance of a prototype μ-Spec, with spectral resolving power, R=64. Here we present our progress towards developing a higher resolution μ-Spec, which would enable the first science returns in a balloon flight version of this instrument. We describe modifications to the design in scaling from a R=64 to a R=256 instrument, as well as the ultimate performance limits and design concerns when scaling this instrument to higher resolutions.
The complex dielectric function enables the study of a material's refractive and absorptive properties and provides information on a material's potential for practical application. Commonly employed line shape profile functions from the literature are briefly surveyed and their suitability for representation of dielectric material properties are discussed. An analysis approach to derive a material's complex dielectric function from observed transmittance spectra in the far-infrared and submillimeter regimes is presented. The underlying model employed satisfies the requirements set by the Kramers-Kronig relations. The dielectric function parameters derived from this approachtypically reproduce the observed transmittance spectra with an accuracy of < 4%.
The far-infrared and submillimeter portions of the electromagnetic spectrum provide a unique view of the astrophysical processes present in the early universe. Our ability to fully explore this rich spectral region has been limited, however, by the size and cost of the cryogenic spectrometers required to carry out such measurements. Micro-Spec (μ-Spec) is a high-sensitivity, direct-detection spectrometer concept working in the 450-1000 μm wavelength range which will enable a wide range of flight missions that would otherwise be challenging due to the large size of current instruments with the required spectral resolution and sensitivity. The spectrometer design utilizes two internal antenna arrays, one for transmitting and one for receiving, superconducting microstrip transmission lines for power division and phase delay, and an array of microwave kinetic inductance detectors (MKIDs) to achieve these goals. The instrument will be integrated on a ~10 cm2 silicon chip and can therefore become an important capability under the low background conditions accessible via space and high-altitude borne platforms. In this paper, an optical design methodology for μ-Spec is presented, with particular attention given to its two-dimensional diffractive region, where the light of different wavelengths is focused on the different detectors. The method is based on the maximization of the instrument resolving power and minimization of the RMS phase error on the instrument focal plane. This two-step optimization can generate geometrical configurations given specific requirements on spectrometer size, operating spectral range and performance. Two point designs with resolving power of 260 and 520 and an RMS phase error less than ~0:004 radians were developed for initial demonstration and will be the basis of future instruments with resolving power up to about 1200.