KEYWORDS: Systems modeling, Integrated modeling, Mirrors, Telescopes, Optical instrument design, Space telescopes, Motion models, Observatories, Control systems, Thirty Meter Telescope
In the conceptual design phase for a large ground-based observatory, it is often necessary to make major design decisions affecting output figures of merit before sufficiently detailed models are available for predicting results. While a single "point design" may be selected based on expert opinion, for new and complex structures the optimal design that meets both cost and science requirements may not be obvious without analysis of many models. One solution to evaluating different designs early in the design process is to create a parametric model of the telescope structure and predict the dynamic behavior using an integrated model. An integrated model is an environment where the major disciplines of disturbance, optics, controls and structures are modeled. In this way a large tradespace across different design configurations and parametric values can be rapidly evaluated using metrics such as image motion and estimated system cost. This paper describes the steps taken by the MIT Space System Laboratory (MIT SSL) for large ground-based observatory preliminary design using a parametric integrated model. The parametric finite element structural model is described and representative results are shown. In particular, this paper will describe lessons learned about the advantages and challenges
encountered during development and implementation of the parametric integrated model such as the usefulness of a visualization tool and the importance of subsystem model modularity.
KEYWORDS: Mirrors, Space telescopes, Optical instrument design, Systems modeling, Lightweight mirrors, Actuators, Performance modeling, Finite element methods, Space mirrors, Space operations
Development of low-cost, lightweight space imaging systems requires a combination of technologies including
lightweight optics to reduce the areal density of the mirrors and application of controls-structures technologies to
compensate for the increased flexibility of these systems. These new design technologies have led to many new
possibilities for architectures of large space telescopes, creating a necessity for new design tools during the conceptual
design phase. The MIT Space Systems Laboratory (MIT-SSL) is examining alternative architectures for a Modular
Optical Space Telescope (MOST) by developing a tool to automatically generate unique realizations of a spacecraft
based upon parametric inputs to the model. This tool allows system metrics to be evaluated across combinations of
design variables so that promising architecture families utilizing different technologies can be identified on the basis of
system performance. This paper will describe advances to the structural components of the MOST model, particularly
the primary mirror and secondary support tower. Lightweight, rib-stiffened mirrors and a variety of geometries for a
lightweight secondary support tower have been modeled. Both of these parameterized sub-components can be analyzed
to determine the effects of changing geometries on the structural stiffness. These advanced components can then be
used in the system in order to more fully understand the effects of lightweight structures on the system performance
metrics.
KEYWORDS: Systems modeling, Data modeling, Detection and tracking algorithms, Integrated modeling, Performance modeling, Mathematical modeling, Motion models, Monte Carlo methods, Space operations, Sensors
Future spaceborne astronomy missions will require telescopes with increasingly greater resolving power, driving the dimensions of the optics to a significant size. Fully integrated observatory verification becomes problematic as the systems approach or exceed the size of the test facilities required to control environmental factors (temperature, vibration, etc). Such tests also require extremely precise test optics. Under such conditions, system verification will start to rely on analytical propagation of ground test data to in-situ performance. Reliable analytical predictions must be grounded in a thorough characterization of system uncertainty. A methodology is proposed to experimentally characterize uncertainty using component test data and integrated system models. The approach relies on uncertainty propagation techniques to identify critical uncertainties and bound the resulting performance predictions, and test data (on the component, subsystem, and if possible system levels) to confirm probabilistic models. The methodology is demonstrated on the Mid-Deck Active Control Experiment (MACE), an articulated flexible test article.
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