What is the Polaris disease?

Polaris disease or Polar-orbiting Operational Meteorological Satellite System (POMSS) anomaly is a problem that affected TIROS-N and subsequent generations of National Oceanic and Atmospheric Administration (NOAA) weather satellites when orbiting the Earth's poles.

The issue was first revealed in 1978 with NOAA 6 during the postlaunch test phase. As the spacecraft orbited over northern Canada, the scanning radiometer stopped spinning and became stuck. The radiometer remained in this locked state for the rest of the mission, making meteorological data from this instrument unavailable.

The source of the problem was eventually traced to the radiometer mounting ring. During orbital operations, the heat generated by the radiometer caused the mounting ring to expand, binding the bearings and stopping the rotation. Once the problem was identified, the design was modified to allow the radiometer to rotate freely regardless of temperature changes.

Polaris disease was not observed again on any subsequent NOAA satellites.