WASHINGTON — Contamination on a key sensor aboard the newest U.S. polar-orbiting weather satellite will degrade its performance and delay the spacecraft’s start of operations until early March, NASA said Jan. 19.

The NPP satellite, launched in late October, was supposed to begin its weather monitoring mission in mid-December but has been held up by contamination on the Visible Infrared Imager Radiometer Suite (VIIRS). NASA said a mirror on the sensor had traces of tungsten oxide on it.

The contamination likely was introduced during the manufacturing process and resulted in “a larger than expected decrease in sensor sensitivity in four of VIIRS’s near-infrared and visible channels” when the instrument was activated in space for checkout, NASA said.

“The mirror was exposed to an ion source with a tungsten filament after the top layer of coating was applied,” NASA spokesman Stephen Cole said in a Jan. 20 email to Space News. “This process step is not usually done and our investigation team is working with the coating manufacturer to understand the details of this tungsten exposure, as well as whether this problem may exist in other mirrors.

“A report will be released by the investigation team when it completes its work in about three months.”

Although the contamination is likely irreversible, NASA expects that the NPP will still be able to complete its mission objectives during its scheduled five-year on-orbit life.

Built by Raytheon Space and Airborne Systems of El Segundo, Calif., VIIRS encountered serious development problems that were cited as a key culprit in the delays and cost overruns on the now-defunct National Polar-orbiting Operational Environmental Satellite System. NPP was conceived as a test bed for the primary instruments on that civil-military program but was assigned an operational role because of those delays.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.