  The Subarcsecond Telescope And BaLloon Experiment, STABLE, is the fine stage
of a guidance system for a high-altitude ballooning platform designed to
demonstrate subarcsecond pointing stability, over one minute using relatively
dim guide stars in the visible spectrum. The STABLE system uses an attitude
rate sensor and the motion of the guide star on a detector to control a Fast
Steering Mirror in order to stabilize the image. The characteristics of the
thermal-optical-mechanical elements in the system directly affect the quality
of the point spread function of the guide star on the detector, and so, a
series of thermal, structural, and optical models were built to simulate system
performance and ultimately inform the final pointing stability predictions.
This paper describes the modeling techniques employed in each of these
subsystems. The results from those models are discussed in detail, highlighting
the development of the worst-case cold and hot cases, the optical metrics
generated from the finite element model, and the expected STABLE residual
wavefront error and decenter. Finally, the paper concludes with the predicted
sensitivities in the STABLE system, which show that thermal deadbanding,
structural preloading and self-deflection under different loading conditions,
and the speed of individual optical elements were particularly important to the
resulting STABLE optical performance.
