Members of the Structural Analysis and Design Group bring a broad range of multi-disciplinary experience in mechanical, structural, optical, thermal, and systems engineering to the development of scientific instruments, instrumentation, and general studies in astronomy and astrophysics. Their work ranges from the design, fabrication, and test of support equipment to the highly rigorous design and analysis required for the development of space-qualified optics and instruments. Because of their unique expertise in the latter area, for the past fifteen years the NASA James Webb Space Telescope (JWST) Program Office 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 as well as the large composite structure that holds all of these optical assemblies. For two decades prior to JWST our group supported the Chandra Observatory in a similar manner. Members of SAO are also working directly on state of the art instruments for the Giant Magellan Telescope (GMT) as well as the Solar Wind Electrons Alphas and Protons (SWEAP) instrument for Solar Probe Plus.

Analytical Tools and Resources

The group's essential analytical and design tools include ANSYS, NX Nastran, SOLIDWORKS, SIGFIT, FEMAP and MATLAB. Reliance on such computerized analytical and design tools have 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 (and now we are working in the picometer regime) motions can really be determined only by using available software and comparing those simulated results with interferometric or other optical measurements.

ANSYS and NX Nastran are general purpose Finite Element packages. 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.). 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 dual or quad processor, and access to other multi-processor servers with over 500 GB of memory and many Tb of data storage. On JWST, our full telescope model of JWST exceeds 60 million degrees of freedom.

Contributions

Structural engineers have made essential contributions to many of SAO's programs. In addition to JWST, current projects include:

• The GMT-CfA Large Earth Finder (G-CLEF)


• The GMT-Consortium Large Earth Finder (C-GLEF) is a fiber fed optical echelle spectrograph that is being designed and built for first light at the Giant Magellan Telescope (GMT).
• It is being proposed by a collaboration consisting of the Smithsonian Astrophysical Observatory(SAO), the Pontificia Universidad Católica de Chile (PUC), the University of Chicago, Harvard University, the Korean Astronomy and Space Science Institute (KASI) and the Observatories of the Carnegie Institution of Washington (OCIW).
• G-CLEF has been designed to simultaneously satisfy the need for a general purpose high dispersion spectrograph meeting the requirements for a high resolution visible spectrograph and a precision radial velocity spectrograph.
• While G-CLEF is designed to be a powerful instrument for a broad range of astrophysical investigations, we have defined the performance envelope of G-CLEF to address several of the highest science priorities in the most recent Decadal Survey of Astronomy by the National Research Council - New Worlds, New Horizons in Astronomy and Astrophysics (2010).
• Delivery to the GMT is scheduled for late 2020 and science operations will commence 9 months later.

• Solar Wind Electrons Alphas and Protons (SWEAP) instrument for Solar Probe Plus.


• Solar Probe Plus is a NASA mission designed to plunge directly into the atmosphere of the Sun for the first time in history, reaching 4 million miles from the Sun's surface. At these distances the Sun will be over 500 times brighter than it appears at Earth and particle radiation from solar activity will be harsh.
• The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation is the set of instruments on the spacecraft that will directly measure the properties of the plasma in the solar atmosphere during these encounters. A special component of SWEAP is a small instrument that will look around the protective heat shield of the spacecraft directly at the Sun. This will allow SWEAP to take a sample of the atmosphere of the Sun for the first time.

• More recently completed instruments include:


• Interface Region Imaging Spectrograph


• IRIS is NASA's Interface Region Imaging Spectrograph. Its primary goal is to understand how heat and energy move through the lower levels of the solar atmosphere.
• IRIS is a class of spacecraft called a Small Explorer, which NASA defines as costing less than $120 million. IRIS weighs 440 pounds and is approximately 7 feet (2.1meters) long and, with its solar panels extended, is a little over 12 feet (3.7 meters) across.
• BINOSPEC instrument for the converted Multiple Mirror Telescope.


• Binospec is an imaging spectrograph with dual 8'x15' fields of view, and a very compact layout for excellent stability. It has dual slit-masks which can hold up to 150 slit-lets for multi-object spectroscopy. Superior sky subtraction with these slit-lets will allow Binospec to reach 3-4 magnitudes deeper than Hectospec.
• Binospec uses the fiber spectroscopy configuration of the corrector, which has built-in atmospheric dispersion compensation.

Chief Engineer Mr. Lester M. Cohen (617) 495-7368