Delivery of a key instrument for the U.S. government’s next generation of polar-orbiting weather satellites

likely will be delayed while contractors work to resolve the latest in a string of problems with the troubled sensor, according to a source familiar with the issue.

The repeated difficulty with the Visible Infrared Imaging Radiometer Suite (VIIRS), which is intended to monitor cloud formations and other atmospheric and ocean-surface phenomena for the National Polar-orbiting Operational Environmental Satellite System (NPOESS), led government officials overseeing the effort to express disappointment with the performance of the contractors involved during a meeting

Jan. 16, the source said.

Northrop Grumman Space Technology of Redondo Beach, Calif., is the prime contractor for the NPOESS effort, which

jointly is funded by the U.S. Air Force and National Oceanic and Atmospheric Administration, with NASA contributing personnel to the government program office. The VIIRS instrument is built by Raytheon Space and Airborne Systems of El Segundo, Calif.

The latest difficulty is due to issues with circuit boards and problems securing a cooling instrument known as a cryoradiator, for

the sensor, the source said.

U. S. Air Force Secretary Mike Wynne, NASA Administrator Mike Griffin

and Conrad Lautenbacher, administrator of the National Oceanic and Atmospheric Administration, each

expressed frustration with Northrop Grumman and Raytheon’s work during the Jan. 16 meeting, the source said.

Sally Koris, a Northrop Grumman spokeswoman, said in a written response to questions from Space News that VIIRS had been slated for delivery

July 31, and the company is “working side by side with the government to revise the VIIRS delivery schedule.”

All of the other NPOESS sensors are proceeding on schedule for delivery for the NPOESS Preparatory Project launch, Koris said. She declined to comment on the concerns raised about the company’s performance by Wynne, Lautenbacher

and Griffin.

David Desilets, a Raytheon spokesman, also said

the company is working with the government to revise the VIIRS delivery schedule.

said Raytheon has modified the cryoradiator, which is needed to cool the infrared detectors on the instrument, in order to better enable it to withstand the stress of launch into space, and the instrument has

passed a vibration test successfully.

While VIIRS could be delayed by about eight months, the impact on the launch of the NPOESS Preparatory Project, a demonstration spacecraft that is slated to launch in 2010, is not clear, the source said.

Program officials indicated that they do not expect a delay at this point on the first NPOESS spacecraft, which

currently is expected to launch around 2013, due to the latest issues with VIIRS, the source said. The cost impact

is also not clear at this time, the source said.

VIIRS was blamed for much of the technical difficulty and cost growth that forced the government to restructure the NPOESS effort in June 2006. Following the restructure, program officials found interference that could impair the sensor’s ability to monitor ocean color, an issue that may not be resolved before the NPOESS Preparatory Project but is expected to be addressed by the time of the first NPOESS launch.