Chapter 5 Robust Performance Tailoring with Tuning - SSL - MIT

Abstract
Next-generation space telescopes in NASA’s Origins missions require use of advanced
imaging techniques to achieve high optical performance with limited launch mass.
Structurally-connected Michelson interferometers meet these demands, but pose specific
challenges in the areas of system dynamics and controls, uncertainty management
and testing. The telescope optics must meet stringent positional tolerances in the
presence of environmental and on-board disturbances, resulting in heavy demands
on structural dynamics and control. In addition, fully integrated system tests are
cost-prohibitive due to the size and flexibility of the system coupled with the severe
differences between the on-orbit and ground testing environments. As a result, the
success of these missions relies heavily on the accuracy of the structural and control
models used to predict system performance.
In this thesis, dynamic tailoring and tuning are applied to the design of precision
optical space structures to meet aggressive performance requirements in the presence
of parametric model uncertainty. Tailoring refers to changes made to the system during
the design, and tuning refers to adjustments on the physical hardware. Design
optimizations aimed at improving both performance and robustness are considered
for application to this problem. It is shown that when uncertainty is high and performance
requirements are aggressive, existing robust design techniques do not always
guarantee mission success. Therefore, dynamic tuning is considered to take advantage
of the accuracy of hardware performance data to guide system adjustments to
meet requirements. A range of hardware tuning techniques for practical implementation
are presented, and a hybrid model updating and tuning methodology using
isoperformance analysis is developed.
It is shown that dynamic tuning can enhance the performance of a system designed
under high levels of uncertainty. Therefore, robust design is extended to include
tuning elements that allow for uncertainty compensation after the structure is built.
The new methodology, Robust Performance Tailoring for Tuning creates a design
that is both robust to uncertainty and has significant tuning authority to allow for
hardware adjustments. The design methodology is particularly well-suited for highperformance,
high-risk missions and improves existing levels of mission confidence in
the absence of a fully integrated system test prior to launch. In the early stages of the
mission the design is tailored for performance, robustness and tuning authority. The
incorporation of carefully chosen tuning elements guarantees that, given an accurate
uncertainty model, the physical structure is tunable so that system performance can
be brought within requirements. It is shown that tailoring for tuning further extends
the level of parametric uncertainty that can be tolerated at a given performance
requirement beyond that of sequential tailoring and tuning, and is the only design
methodology considered that is consistently successful for all simulated hardware
realizations.
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