Troubled Weather Satellite Program

Delays in critically needed polar instruments could affect all of U.S. environmental monitoring

5 min read

Cost overruns and project delays have led to a cloudy forecast for the United States’ new polar-orbiting weather satellites, which were originally supposed to start circling the North and South Poles in 2008 [see artist's conception, " Pole to Pole”]. The greatly upgraded satellites, to consist of a group of three with three replacements, are meant to beam back weather data that would enable scientists to better predict hurricanes such as Katrina and help the military plan sorties in the war on terror. But development of the satellites is far behind schedule, and their total estimated cost has ballooned from US $6.5 billion to more than $10 billion—an immense amount, considering that the whole annual budget for Earth observation from space is about $3 billion, with at least half of that going for satellite construction, operation, and maintenance.

This means, observes a member of a National Academy committee reviewing space-based earth science research, that the problems with the polar satellites are a major concern for the whole enterprise of monitoring Earth from outer space.

Early this month, the U.S. Defense Department will send a crucial report to Congress on the management of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) program, as mandated by a law that requires a formal review when cost overruns in a federal program exceed 25 percent. (This is the Nunn-McCurdy Amendment, written by a former senator and a congressman.) The Defense Department report, with input from the National Oceanic and Atmospheric Administration (NOAA) and NASA, will recommend ways to restructure NPOESS, which they manage jointly. How those recommendations are formulated and how Congress reacts to them could determine whether the United States will ever receive its full measure of benefits from the new generation of polar weather satellites.

Inaugurated during the Clinton administration in 1994, the NPOESS combines the Defense Department’s Defense Meteorological Satellite Program (DMSP) and NOAA’s Polar-orbiting Operational Environmental Satellite (POES) program. Each program has two polar satellites aloft in low orbit circling the North and South Poles about 800 kilometers high. Sounding data—atmospheric vertical temperature and moisture profiles—from the two pairs of satellites currently make up about 90 percent of all information used in the global numerical weather prediction models run by the U.S. Navy and NOAA. In particular, the polar satellites provide data used to make forecasts beyond three days, working in conjunction with the Geostationary Operational Environmental Satellites (GOES), positioned some 35 000 kilometers above the Earth.

The problems with the polar satellites are a major concern for the whole enterprise of monitoring Earth from outer space NOAA

The NPOESS satellites would improve long-term weather prediction by producing more detailed images of ocean surface temperatures and winds, ocean color, land surface temperatures, terrestrial vegetation, and land cover characteristics. The satellites would also transmit that information to ground stations at much higher speed than is currently possible. Two of the satellite’s 10 sensors are really the keys to the enhanced weather imagery: the Visible Infrared Imager Radiometer Suite (VIIRS) and the Conical Microwave Imager/Sounder (CMIS).

The 22-channel VIIRS will provide complete global coverage of Earth in one day, based on infrared imaging, yielding the first-ever color pictures to be available from a satellite in real time. This improved fidelity will allow a closer look at the intensity of particular weather patterns, because the cameras won’t just look at the top of the clouds but will be able to peer into hurricanes and drag out data on their interior temperature and moisture, information U.S. forecasters now get from less-capable sensors mounted on aircraft. What that means is that the National Weather Service will be able to predict where a hurricane will land with up to twice the accuracy now available, according to David L. Ryan, vice president and NPOESS program director at Northrop Grumman Space Technology.

In a military application, VIIRS could help predict, for example, whether there will be a sandstorm in a desert area—obviously a useful thing to know when launching an attack plane off a carrier, as laser-guided weapons do not work well in such conditions.

The conical microwave imager reads microwaves bouncing off Earth to create readouts of surface wind speeds, rain rates, liquid water in clouds, total precipitable water in a given volume of sky, sea surface temperatures, and wind directions. Because it uses an antenna measuring 2.2 meters across, the CMIS instrument will provide more precise data at a higher resolution than is available from current polar satellites. The Defense Department’s current polar satellites use a sensor whose antenna is 0.6 meter across.

Not only will more detailed weather data be available, but it will also be made available much faster. The NPOESS SafetyNet data relay network and the ground processing system will improve delivery of processed data to users by a factor of between five to seven, compared with the current polar satellite systems. Roughly 80 percent of the processed NPOESS data is to be made available within 15 minutes, and 95 percent will be available within just 24 minutes.

The collection of data from sensors in the satellites will be sped up by a factor of 100, to 100 megabits per second, and it will be downloaded virtually continuously from the satellites to Earth. There are to be 14 Earth stations receiving weather data at all times, whereas today just one ground station in northern Norway takes data from the polar satellites only once every 100 minutes.

Promise is one thing, however, realization of that promise another. Since Northrop Grumman obtained an overall production contract in 2002, developmental problems with both VIIRS and CMIS have put the entire NPOESS program in jeopardy. During initial testing in mid-2004, Raytheon, the VIIRS subcontractor, encountered significant problems that showed potential design deficiencies and manufacturing shortfalls. In late 2004, a cooling unit that is critical to the senor’s operation failed during tests. These problems prompted a complete review of the sensor’s design, development, and management and replacement of the whole Raytheon team. Sensor cost growth accounts for approximately 80 percent of current program cost overruns.

Northrop Grumman’s Ryan says VIIRS is now meeting all of its main performance requirements and has passed its vibration test, key to this instrument’s success. ”The sensor’s passive cooling system, which consists of a cryoradiator and other passive cooling elements, demonstrated better-than-required performance during recent thermal vacuum testing,” he states.

That testing is a critical development milestone, comments David Powner, director, IT management issues, U.S. Government Accountability Office. ”If the current design fails to meet its performance metrics, VIIRS could be in danger of falling further behind in cost and schedule.” VIIRS’s fate is critical because it is an integral part of the NPOESS Preparatory Project, a risk-reduction program; completion of VIIRS has now been moved back to 2008. CMIS, though a key component of NPOESS as well, is not part of that program.

Meeting that testing schedule, in turn, is crucial for two reasons. For one thing, the last of the POES satellites is scheduled to be launched in late 2007, the last DMSP satellite in 2011. The earliest the first of the NPOESS satellites could be launched, given the program’s three-year delay to date, is in late 2010. If that last POES satellite launched in 2007 were to fail during that three-year period, it would have ”a devastating effect on our national ability to forecast severe weather events,” states Powner.

A failure of that magnitude inevitably affects the reputations of all parties involved, posing threats to other critically needed Earth-sensing programs as well.

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