CE: Structural and Analytical Design Engineering


The engineers of the CE Structural Analysis and Design Group together have more than 75 years of mechanical, structural, optical, thermal, and systems engineering experience. With this multi-disciplinary background, they bring a wide range of unique talent to the successful conduct of high technology research and development; and in particular to the development of scientific instruments and instrumentation, and general studies in astronomy and astrophysics. Their work ranges from the design, build, and test of support equipment; to the more rigorous design and analysis required for space qualified optics and instruments. Because of their unique expertise in the latter area, for the past five years NASA has contracted with SAO for members of the group to provide independent technical evaluation, performance modeling, and simulation of the optical telescope; and oversight to the development of the primary, secondary and aft optical system mirrors; for the James Webb Space Telescope (JWST).

Analytical Tools and Resources

The group's essential analytical and design tools include ANSYS, Nastran, IDEAS, and MATHCAD. Reliance on such computerized analytical and design tools has markedly increased because of the highly complex nature of the opto-mechanical systems under development at the CfA. While the engineers rely on turn-key systems, they also verify their results using available closed form solutions, by test, and by historical comparison. However, definitive sub-micron displacements can really be determined only by using available software and comparing those simulated results with interferometric measurements.

ANSYS, Nastran and IDEAS are general purpose Finite Element packages that support both the traditional h-method and the newer polynomial p-method of analysis: These packages are used for linear , non-linear (material & geometric non-linearities) static and all types of dynamic analysis (time-history, modal, acoustic pressures, etc) . ANSYS is also used for heat transfer. Because Unigraphics IDEAS is also used by all CE mechanical engineers and designers, certain model making tasks based upon their designs can be greatly expedited. FEMAP is utilized to translate the finite element models that we are provided by, or must be provided to, organizations using other software such as NASTRAN.

To support their analytical work, each engineer has a desktop workstation with a high speed single or dual processor, and access to an 8 processor SGI Itanium 2 server for large models.

Our full telescope model of JWST exceeds 50 million degrees of freedom.

Current and Recently Completed Projects

Structural engineers have made essential contributions to many of SAO's programs. In addition to JWST, current projects include the telescopes comprising the Atmospheric Imaging Assembly (AIA) for the Solar Dynamic Observatory and the BINOSPEC instrument for the converted Multiple Mirror Telescope. More recently completed instruments include: the Solar-B (Hinode) X-ray Telescope , Chandra HRC and HXDS, TRACE, the Hectochelle and Hectospec instruments for the converted MMT, and the SMA. For more extensive project information, please visit the Selected Projects page.


Chief Engineer, Structural and Analytical Design: Mr. Lester M. Cohen (617) 495-7368
MMIRS Optical Performance Model (Click here for a larger version of the image.)

Section Photo