Original Date: 04/20/1998
Revision Date: 01/18/2007

Weather satellites use imagers (Figure 3-1) to provide geostationary imaging data such as cloud tracking, sea surface temperature, and atmospheric changes. The satellite directs the imager’s line of sight by rotating its scanning mirror; however, the mirror must stay optically flat within 50 millionths of an inch to keep the imager in focus. For all precision mirror designs, the goal is to create a mirror with minimal optical distortion by selecting the proper thermal, structural, and optical models. Previously, ITT Aerospace/Communications Division (A/CD) would generate (independent of one another) thermal models to predict orbital temperatures, and structural models to predict strength and structural frequencies. The optical model was then determined by using optical codes and manually-calculated, worst-case distortion estimates. As a result, verification testing was expensive and could only be performed on flight-like hardware. ITT A/CD needed an analytical method that could allow the engineers to evaluate numerous design alternatives.

ITT A/CD developed End-to-End Modeling to perform design analyses on complex product development projects such as minimizing the distortion of geostationary scanning mirrors. These efforts were directed at the Geostationary Operational Environmental Satellite (GOES) and the Satellite-Based Infrared System (SBIRS) programs. In mirror design analyses, the engineer first simulates a thermal model and uses its results (analytical predictions) as input for simulating a structural model. These results (distorted mirror shapes) are, in turn, used as input for simulating an optical model. The final results (system performance) help the engineer determine an optimum mirror design. End- to-End Modeling automatically inputs the results of each model’s simulation into the next simulation, allowing the engineer to evaluate numerous design alternatives. This approach also helps the engineer assess conflicting design tradeoffs (e.g., cost, schedules, technology risks, mass, volume, material properties).

End-to-End Modeling promotes a design-of-experiments approach using Taguchi methods to identify key structural aspects that minimize mirror distortion. In addition, the assessments from this modeling enable ITT Aerospace/ Communications Division to verify that the optical system is performing according to the customer’s requirements. In the latest upgrade for the GOES program, the scanning mirror’s distortion was reduced by a factor of three, which translates optically to a factor of nine. In the SBIRS program, the scanning mirror’s distortion was reduced by a factor of two, and the structural stiffness was increased by a factor of two.

For more information see the Point of Contact for this survey.