There is a critical need to sustain and inspect aging radar sites around the world, many of which are over 50 years old, but still provide essential support to warfighters. A non-destructive sustainment and inspection (NDI) tool that uses a method more sensitive than visual inspection will be particularly useful. IAI will develop and test a wireless, multi-channel and low power consumption Acoustic Emission (AE) sensor network system to monitor steel and composite radar tower structures for fatigue and stress corrosion cracking. This system leverages the team's extensive experience with structural monitoring of steel highway bridges. The AE sensor system will use a sparse sensor network to detect and discern damage sound from the environmental noise and localize the damage site within a few inches. First, the team will develop the AE sensor network and test its feasibility for representative structures with cyclic fatigue tests in the lab, and with field trials of the prototype device on a target radar tower. In the next phase, the team will develop the system further, and deploy it on a radar tower for long-term data collection in an operational environment. The system will also be made ready to transition to real radar system applications for other civil infrastructures. This technology will provide accurate and reliable assessment of damage status and fatigue life of radar towers, allowing condition-based maintenance, and reducing cost and labor. The AE NDI systems have significant potential in both military and civil structure integrity monitoring and maintenance applications.