Nimbus 3 (or Nimbus-B2) was a meteorological satellite launched by NASA into a Sun-synchronous near-polar orbit on April 14, 1969. It was the third in a series of second-generation meteorological satellites in the Nimbus program. 

Nimbus 3 was designed to serve as a stabilized, Earth-oriented platform for the testing of advanced meteorological sensor systems and the collection of meteorological data. The spacecraft carried the following experiments:

• High-Resolution Infrared Radiometer (HRIR)
• Image Dissector Camera System (IDCS)
• Infrared Interferometer Spectrometer (IRIS)
• Interrogation, Recording, and Location System (IRLS)
• Medium-Resolution Infrared Radiometer (MRIR)
• Monitor of Ultraviolet Solar Energy (MUSE)
• Radioisotope Thermoelectric Generator (RTG)
• Satellite Infrared Spectrometer (SIRS)

The spacecraft and experiments performed normally until July 22, 1969, when the IRIS experiment failed. The HIRS and SIRS experiments were terminated on January 25, 1970, and June 21, 1970, respectively. The remaining experiments continued operating until September 25, 1970, when the rear horizon scanner failed.