Application Briefs
Femap™ engineering simulation software
Siemens PLM Software
Plano, TX
972-987-3000
www.siemens.com/plm

Scheduled for launch in 2018, the James Webb Space Telescope (JWST) Observatory will operate 1.5 million kilometers above the Earth. Its mission is ambitious: examining every phase of cos mic history. The telescope will look back light years into the past.

Primary mirror segments are prepared for final cryogenic testing at NASA’s Marshall Space Flight Center. (Chris Gunn)
Considered the next generation — not the replacement — of the Hubble Space Telescope, the JWST is an infrared telescope that enables the viewing of more distant, highly red-shifted objects. The Hubble is used to study the universe in optical and ultraviolet wavelengths. The JWST will also be larger than Hubble, which is about the size of a large tractor-trailer truck. At 22 by 12 meters, the JWST will be almost as large as a Boeing 737. Fully deployed, the JWST will feature a reflecting mirror with seven times more collecting area than the Hubble.

The JWST will have a hot side and a cold side, with the hot side consisting of the observatory spacecraft, which manages pointing and communication, and a shield that blocks heat and radiation from the Sun, Earth, and Moon. The cold side of the JWST, operating at temperatures near absolute zero, is where the science will happen.

Four major instruments will be in opera tion, including the near-infrared camera or NIRCam, provided by the University of Arizona. Other major instruments include the near-infrared spectrograph (NIRSpec), provided by the ESA, with additional instrumentation provided by NASA Goddard Space Flight Center (GSFC); the mid-infrared instrument or MIRI, pro vided jointly by the European Space Agency (ESA) and NASA’s Jet Propulsion Laboratory (JPL); and the fine guidance sensor/near infrared imager and slitless spectrograph, provided by the Canadian Space Agency.

There are more than 1,000 people in 17 different countries working on JWST, including academic and indus trial partners ATK, Ball Aerospace, ITT, Lockheed Martin, Northrop Grumman (the prime contractor), and the Space Telescope Science Institute.

Designing, testing, building, and assembling JWST is a team effort, taking place on three continents. The instruments are being tested using a variety of computer-aided engineering (CAE) solvers for modal, thermal, thermal distortion, and structural analysis. Gluing all this analysis and simulation work together is Femap, the JWST team’s standard application for pre- and post-processing.

A Femap model of the ISIM (Integrated Structural Instrument Model) with instruments.
“We use Femap as the pre- and post-processor,” said Emmanuel Cofie, who leads thermal distortion analysis on the ISIM (integrated structural instrument model). “The mechanical design team provides us with CAD files and we use Femap to generate meshes for our mathematical model and, after finite element analysis, to extract results and view the condition and state of the structure under the various load conditions. It is the primary tool we use for visualization of the structure in its operational/launch states before actual environmental testing.”

Because there will be only one opportunity for the JWST to succeed, every part and assembly of every system needs to be thoroughly tested on Earth to ensure that all instruments will function flawlessly under expected conditions. Simulating the JWST’s performance on Earth is the only way to determine that the observatory will function once it is in place.

Using CAE solvers in conjunction with Femap, NASA engineers conduct simulations to ensure each part does not interfere with another, and that parts and assemblies have sufficient strength to withstand extreme heat or cold as well as vibrations experienced during launch and normal operating conditions.

According to Mark McGinnis, thermal distortion working group leader at NASA Goddard, Femap “enables us to carry out our mission of analyzing the structural and thermal performance of parts and systems.” He estimates that the software is used frequently by at least 75 engineers at Goddard.

“For example, we will import a back-plane sub-assembly model from a contractor and populate it with 18 mirrors to visualize how they come together,” said McGinnis. “We need to be sure the interface grids are coincident as they are supposed to be, and then use it to build the more than 8 million required grids, which makes a very large model from a computing standpoint. We assemble the model using Femap.”

Femap also was used during the development of Hubble. “We used it for a lot in those days, and we continue to use it,” McGinnis said. “Femap helps us understand loading conditions so we can take a structure, run the analysis, and see what gets hot and what gets cold. It helps us visualize whether or not a model is feasible.”

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