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{{DISPLAYTITLE:Challenges In Identifying The Structural Dynamic Characteristics Of Large Deployable Spaceflight Structures And The Impact Of The Space Environmental Effect Upon Them by Dr. James "Jim" Akers, May 2026}}
==Challenges In Identifying The Structural Dynamic Characteristics Of Large Deployable Spaceflight Structures And The Impact Of The Space Environmental Effect Upon Them==

Dr. James "Jim" Akers

NASA Glenn Research Center

May 20, 2026

===Abstract:===

Modern spacecraft have ever increasing power, communication, and sensing requirements.  This necessitates larger deployable solar arrays for converting sunlight into electricity, larger deployable antennae for sensing and communication, and larger deployable reflectors for infrared and optical space telescopes.  All of these deployable spaceflight structures are comprised of numerous types of joints and deployment mechanisms. 

Current research into joints has made significant progress in modeling their linear and nonlinear characteristics.  Joints can beneficially add damping that helps attenuate the responses in otherwise highly resonant structures.  However, joints may also introduce significant nonlinearities due to phenomena such as stick/slip, which can lead to computationally intensive models that makes analysis problematic.  Therefore, ground based testing of large deployable spaceflight structures is required for model validation.

As the size of large deployable spaceflight structures increases, which makes them less capable of supporting their own weight in a 1g environment, the challenges in performing ground based testing increases.  Sophisticated gravity offloading fixtures are required to provide support for deployment testing.  However, these fixtures can severely impact the effectiveness of ground vibration testing (i.e., modal survey) needed to identify the structural dynamic characteristics (i.e., modal frequencies and mode shapes).  Material coupons and individual joints can be tested on the ground in harsh environments approaching their in-space operational environment.  However, exposing a large deployable spaceflight structure on the ground to this same harsh in-space environment becomes impractical.  Operating at reduced/cryogenic temperatures can cause shrinkage that removes free-play in joints, which can end up simultaneously increasing stiffness and reduce damping.  Similarly, chemical reaction/contamination from docking/berthing visiting vehicles jet plumes can change the coefficient of friction of joints.  The challenge therefore is how best to incorporate ground base testing of material coupons, individual joints, large deployable spaceflight structures, and lessons learned from past spaceflight projects to develop accurate models of how large deployable spaceflight structures will perform in their operational in-space environment.  This understanding is crucial in guaranteeing mission success and, in the case of crewed spacecraft, crew safety.

This presentation will outline the major challenges in ground testing large deployable spaceflight structures, the characteristics of the space environment and its potential impacts, lessons learned from past and current NASA spaceflight missions, and provide recommendations for methods to improve large deployable spaceflight structure models.

 
===Biography:===

James (“Jim”) Akers, PhD is an aerospace engineer in the Structural Dynamics Branch at the NASA Glenn Research Center, Cleveland, OH, since 2010. Prior to this,  Jim was a support service contractor to GRC for five years, worked for ATA Engineering in San Diego, CA, for three years, and was an aerospace engineer in the Structural Dynamics Branch at the NASA Johnson Space Center, Houston, Tx, from 1985 – 1990. He received his PhD in Aerospace Engineering from the University of Michigan in 1997 in the area of controls. While working for NASA he has worked on numerous spaceflight projects that include the Space Shuttle, ISS, Artemis (both the Multi-purpose Crew Vehicle (MPCV) Orion and Space Launch System (SLS)), and several GRC developed spaceflight experiments. He was the deputy technical lead for the design and construction of the Mechanical Vibration Facility (MVF) located at the Armstrong Test Facility in Sandusky, OH.  MVF is the world’s largest and most powerful shaker table. Jim has supported the NASA Engineering Safety Center (NESC) since 2011 supporting independent assessments that included the modal test of the Mobile Launcher, Integrated Modal Test, and Operational Modal Analysis of the Artemis I Dynamic Rollout Test and Wet Dress Rehearsal. His interests include modal analysis and testing, coupled loads analysis, digital signal processing, probability & statistics, and control structure interaction.

==Video Presentation ==
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==Slides==
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[[Category:Seminar_Series]]