The Airborne Phased Array Radar (APAR): Implementation, Lessons Learned, and Path Forward

The Airborne Phased Array Radar (APAR) Mid-Scale Research Infrastructure-2 (MSRI-2) award was made by the National Science Foundation (NSF) to NSF National Center for Atmospheric Research (NCAR) for construction, installation, and flight testing of the four C-band Active Electronically Scanned Array (AESA) panels on the NSF NCAR C-130 ready for deployment by 2028. APAR’s dual-Doppler and dual-polarization capabilities would provide unprecedented observations of the dynamics and microphysics characteristics of hurricanes, atmospheric rivers, explosive cyclones, and other weather phenomena with impacts from mesoscale to global scale. The APAR MSRI-2 project included partnerships among NSF NCAR, NOAA, multiple universities, and private industry. The APAR design can be adapted for operation in the future. While work proceeded on schedule and within budget during 2023 and early 2024, cost and schedule delays began to materialize in the second half of 2024 due to unexpected technical challenges from contractors. Before NSF made the decision to cancel the APAR MSRI-2 project in April 2025, significant progress had been made including software for radar backend and scientific analysis, thermal control of the AESA panel, and aircraft mounting structure design. Additionally, lessons learned by NSF NCAR and the efforts to address the technical challenges encountered have lowered the research and development risks for future APAR-like development efforts. The demand for APAR capability from the research and weather forecasting communities remains high and NSF NCAR is committed to taking the knowledge gained from the APAR MSRI-2 project and finding a new path for developing and delivering an airborne phased array radar capability.