Three Agency Team Scrutinizes VIIRS as It Approaches Testing

WASHINGTON
— A team of senior officials from the U.S. Air Force, NASA and the National Oceanic and Atmospheric Administration is assessing the future of a troubled sensor that has been blamed for cost overruns and delays that have plagued the next generation of
U.S.
polar-orbiting weather satellites.

The team is examining a wide range of options for the Visible Infrared Imaging Radiometer Suite (VIIRS), including scrapping plans to fly it for the first time on a demonstration satellite NASA is building as a precursor to the National Polar-orbiting Operational Satellite System (NPOESS).

NPOESS is being developed under a partnership between NASA, the U.S. Air Force and the National Oceanic and Atmospheric Administration (NOAA) with its first launch scheduled for 2013.

Launch of the NPOESS Preparatory Project (NPP), which was intended to provide early flight opportunities for VIIRS and other major NPOESS sensors, has been pushed to at least
2010, a
date that is under review because of uncertainties surrounding VIIRS’s ability to stay on schedule, government officials said.

“There are some – I’m not sure I’m one of them – but there are some pretty senior people at NASA who wonder if they’ll ever get there,” said Robert Strain, director of NASA’s Goddard Space Flight Center, the Greenbelt, Md., facility overseeing NPP.

As a result of persistent concerns about VIIRS, consideration is being given to flying NPP without the tardy sensor.

“There’s a group of people – Air Force, NOAA, [NASA] – thinking about VIIRS alternative strategies, which could be taking on a lesser VIIRS, no VIIRS [or] finding something else,” Strain said in a Dec. 5 interview. “They’re looking at other alternatives. It’s too early to guess. … But I think they have to allow for the possibility of that because if it doesn’t get there, or doesn’t get there in a timeframe you can stomach, what do you do?” The VIIRS assessment comes as VIIRS, designed to monitor cloud formations and other atmospheric and ocean-surface phenomena, enters a critical testing phase that includes vibration tests in January and about three months of thermal vacuum testing scheduled to begin in February. The instrument completed electromagnetic interference testing in November.

Raytheon Space and Airborne Systems of El Segundo, Calif., and NPP prime contractor Northrop Grumman Space Technology of Redondo Beach, Calif., are planning for VIIRS to be delivered this summer.

“The VIIRS program is proceeding through its final check-out prior to delivery. [Electromagnetic interference] testing was completed last month,” said Raytheon spokesman John Barksdale. “Vibration testing will be completed in January and the thermal-vacuum facility stands ready to accept the sensor for the last stage of its evaluation.”

Among those waiting for VIIRS, an instrument now 44 months behind schedule, Raytheon’s assurance of a summer delivery are met with skepticism.

An industry official familiar with the program said the chances of a July or August delivery are “slim to none.”

NASA spokesman Steve Cole said in a statement that “the possibility of further delivery delays” were among the reasons a team of senior officials from NASA, NOAA and the Air Force was chartered in October to conduct a wide ranging review of VIIRS delivery and capability issues and their possible impact on NPP and NPOESS.

Cole said the team is reviewing “several alternatives that span a broad range of possibilities,” adding that no decisions have been made to change NPP. Findings of the review are expected in January.

Clark Snodgrass, director of system engineering, integration tests and operations for the NPOESS program at Northrop Grumman, said an engineering model of VIIRS already has been through the tough environmental testing phase the NPP flight instrument is about to begin. The engineering model also was integrated onto the Ball Aerospace-built NPP platform and underwent command and telemetry testing to make sure it was compatible with the spacecraft, he said.

“That gives us a lot of confidence that when we deliver the flight unit to the spacecraft it will have the same compatibility, because we’ve already done it with the engineering model,” Snodgrass said. “I think we’ve been making steady progress with the test program.”

VIIRS is expected to be able to deliver all but one of its 22 environmental data products, according to Snodgrass. Engineers have been working for the past year to correct unwanted scattering of light by the sensor’s filters that can hamper collection of ocean color data. Scientists use the ocean color data to monitor chlorophyll levels, a key measure of ocean health and biological vitality.

“The ocean color mission is the most challenging of the VIIRS missions because the ocean signal we’re seeking to see from space is low compared to the rest of the environment we’re looking through,” Snodgrass said.

Northrop and Raytheon are hopeful software and algorithm tweaks will improve VIIRS’s ocean color data. “In this particular case, we’re doing some additional techniques to deal with the ocean color issue,” Snodgrass said. “I think we are optimistic that we will be able to make improvements from what people believed [they’d get] a year ago when the filter problem first arose.”

Scientists, however, have said VIIRS is not likely to deliver the ocean color data they need to continue the collection of data begun a decade ago with the launch of Dulles, Va.-based GeoEye‘sSeaWIFS and continued with NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite. They are concerned about a gap in collection of ocean color data if VIIRS does not work. Decades of such data can show whether changes in the ocean’s biology are cyclical or from climate change.

“Simply stated, existing satellites are aging while the U.S. operational missions that are aimed to extend these climate data records … will not likely fill the need for climate or operational requirements,” scientists David Siegel of University of California at Santa Barbara, James Yoder of Woods Hole Oceanographic Institute and Charles McClain of NASA wrote in a recent letter to oceanographers.

Other capabilities scientists are counting on VIIRS for include the collection of data such as land and sea surface temperatures and cloud properties, Snodgrass said. “We expect [VIIRS] to be able to support the missions in all the other areas,” he said. “If we can get the improvements we are looking for out of the algorithms, we believe it should be able to carry forward the basic ocean mission that MODIS would have been performing,” he said. “We will know that after [thermal vacuum] testing.”