Polar BEAR (Polar Beacon Experiment and Auroral Research) was an American military satellite designed to study communications interference caused by solar flares and increased auroral activity. The data from the mission complements data taken by its predecessor, HILAT. The core vehicle was a Transit navigational satellite retrieved from the Smithsonian's National Air & Space Museum where it had been on display for 8 years. Polar BEAR's Auroral Imaging Remote Sensor imaged the aurora borealis and its Beacon Experiment monitored ionospheric propagation over the poles.