and repair, he suggested that NASA could potentially take the lead in this. Leu also added two new areas to the Manufacturing Process area: multi-scale modeling and simulation (as large increases in computer power make this important), and nanomanufacturing (where NASA should look to leverage existing National Science Foundation investments). Leu provided detailed commentary on several technology areas, including: Laser Assisted Material Processing (which is an advanced type of three-dimensional printing applicable to in-space manufacturing and repair), intelligent integrated manufacturing and cyber physical systems, sustainable manufacturing (including consideration of environment, economy, and energy—E3—aspects), Nondestructive Evaluation (NDE), and loads and environments. On NDE in particular, Leu noted that the roadmap appears to focus primarily on ultrasound techniques; he suggested that other methods (e.g., eddy current, microwave, millimeter wave) should also be looked at, and that sensor fusion is another aspect deserving attention. Relative to the top technical challenges in the NASA roadmap, Leu commented that making accurate predictions based on multi-scale modeling will take a long time, and that trying to make complex three-dimensional parts with high precision is difficult. He also commented that there appeared to be some gaps in the roadmap, including: multi-scale modeling and simulation, nanomanufacturing, and lifecycle product and process design (or E3 technologies). Leu indicated several areas that he views as high-priority for NASA, including autonomous fabrication, repair, and assembly at point of use, advanced robotics, functionally gradients composites capable of surviving very-high-temperature environments. In terms of technologies close to a tipping point, Leu noted that composites manufacturing (and polymer matrix composites in particular) could benefit substantially from additional investment. Finally, Leu commented after his presentation that in his view, it is important for NASA to get involved in these areas as the industry is typically not willing to invest.
Glenn Light (Southwest Research Institute) followed Leu with a presentation on his perspectives on the NASA roadmap. Light noted that the roadmap stated its goals well in terms of how NDE technologies can feed into the safety/reliability of long-duration space missions and the assessment/maintenance of vehicle integrity with minimal human intervention. He also commented that the roadmap provided a good discussion on prognostics (i.e., the ability to detect defects, assess the situation, and provide a prognosis of remaining life or usage), and that this is an area deserving of attention. On the other hand, Light also highlighted some areas that he felt the NASA roadmap did not cover as well, including: types of defects and damage that might be anticipated, practical aspects and effective integration of sensors and sensor life, sensing and monitoring the fields/environment around the structure, technology to route repairing materials through the structure, and wireless power transfer to sensors. In terms of top technical challenges in NDE and sensor systems, Light indicated that these include sensor integration with minimal detrimental effects, sensitivity to early damage, increasing sensor life, sensors and micro-circuitry embedded in the structure, environmental protection for structures (e.g., coatings), and the ability to monitor how coatings are wearing. Light also discussed several areas he felt are high-priority for NASA, including: development of sensors in practical form factors, wireless power transfer to embedded sensors (e.g., local energy harvesting), on-call repair technologies and self-healing metals and composites, and integration of embedded sensors as part of the structural design. As for alignment with NASA, he indicated that many of these areas align well with NASA’s expertise, capabilities, and facilities. Light did suggest that there is a need to set clearly defined national goals for the space program, and minimize the requirement for cost sharing and need to have dual-use technologies (which many federal contracts do). Light also highlighted several technologies that he considers game-changing, including capillary repair materials, practically embedded sensor arrays that positivity impact structural strength, and sending power to all sensors wirelessly. He additionally noted that remote sensing of the environment around the structure is near a tipping point and may benefit from further investment. Regarding embedded sensors, Light indicated that this requires a new concept for teaching structural design. Finally, in responding to a question from a workshop participant on the use of fiber optics embedded for sensing purposes, Light noted that this is good for some things (e.g., stress analysis), but the main issue to date has been the detrimental impact to the structure.
Public Comment and Discussion Session
The following are views expressed during the public comment and discussion session by either presenters, members of the panel, or others in attendance.