Polar Beacon and Research satellite. Polar Bear, also known as STP P87-1, was a military mission 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 that was retrieved from the Smithsonian's National Air & Space Museum where it had been on display for 8 years. Spacecraft: Gravity gradient stabilized by deployable boom with tip mass.4 small deployable solar arrays. Payload: Auroral Imaging Remote Sensor imaged the aurora borealis; Beacon Experiment monitored ionospheric propagation over the poles.

Design Life: Transit design life = 3 years. Typical orbit: 962 x 1019 km, incl. = 89.5 deg. Length: 1.30 m (4.20 ft). Maximum Diameter: 0.40 m (1.31 ft). Mass: 125 kg (275 lb).