NASA's Polar Orbiting Weather Satellites Reach End of an Era
NOAA-N Prime represents the final chapter in a long and productive series of polar-orbiting operational environmental satellites (POES) that stretch back to 1978, when the first modern weather satellite, TIROS-N, was launched. These satellites—designed and launched by NASA's Goddard Space Flight Center--have been the workhorses of the National Weather Service, producing a constant stream of data for meteorologists, climatologists, and other users.
Modern polar orbiting satellites can monitor cloud cover, atmospheric and sea surface temperatures, humidity, ozone levels, and aerosol levels with great precision. As such, they have become the primary data source for models that predict weather conditions three or more days in advance—including the path of hurricanes. Orbiting the Earth every 102 minutes, each satellite views each point on Earth's surface twice in 24 hours.
While early generations of weather satellites had focused mainly on capturing photographs of cloud cover, TIROS-N contained a full suite of instruments that allowed meteorologists to create robust quantitative observations of the atmosphere and to significant improve weather prediction. Some of the same instruments that flew on TIROS-N (though now in more sophisticated versions) can be found on NOAA N-Prime.
N Prime is the last in a long series of polar orbiting environmental satellites. A new program, called the National Polar Orbiting Operational Environmental Satellites System (NPOESS), will pick up where the current series leaves off. The first NPOESS satellite is slated to launch in 2013.
NASA’s very first weather satellite, TIROS-N, launched in April of 1960. "In the very early days of weather satellites, nobody had a clue about what a hurricane looked like," says James Greaves, an administrator at NASA's Goddard Space Flight Center who began his career as a contractor working on early weather satellites. "These days, it’s impossible for even a tropical storm to turn up without being immediately noticed."
While TIROS-N revolutionized weather satellites, subsequent years have brought more incremental improvements. NASA and the National Oceanic and Atmospheric Administration (NOAA) introduced an improved series of spacecraft in 1983, for example, that had more processing power and could support more instruments. NOAA 8, the first of these Advanced TIROS-N (ATN) satellites, added a new capability: a search-and-rescue beacon system that has saved the lives of more than 24,500 people to date. NOAA 15, launched in 1998, was the first environmental satellite to carry three advanced microwave instruments.
Over time, the mission of weather satellites has evolved. "We've seen a trend toward the inclusion of more instruments capable of studying both short-term weather conditions and the long-term climate system," said Bernard Seery, assistant director for advanced concepts at NASA Goddard. One example: NOAA 9, launched in 1984, was the first to carry an Earth Radiation Budget Experiment instrument, which helped meteorologists predict the weather but also provided useful information about how Earth's reflectivity—or albedo—influenced climate.
Most POES satellites have lasted significantly longer than their expected two-year lifespan, and only one has failed. (NOAA-B, launched in 1980, did not achieve a usable orbit because of a booster engine problem.) NOAA 12, the longest-lived of the series, operated for 16 years until it had to be decommissioned because its solar panels were actually producing more power than the spacecraft could handle.
NASA and NOAA built a close working relationship that has been critical to the program's success. Since the launch of the first weather satellite in 1960, NASA has managed the design, construction, and launch of spacecraft and then turned over control to NOAA. "It's been such a productive relationship that we can't help feeling a little nostalgic about seeing it change," said POES Deputy Project Manager Mary Walker.
A new generation of satellites is poised to pick up where the POES satellites will leave off. The new program, called the National Polar Orbiting Operational Environmental Satellites System (NPOESS), was created as a cost-saving measure in the 1990s. NPOESS will merge the nation's civilian weather satellite programs with the Department of Defense's Defense Meteorological Satellite Program (DMSP). An Integrated Program Office (IPO), located within NOAA, is charged with acquiring, managing, and operating this new series of weather satellites.
After the launch of N Prime, NOAA will remain responsible for operating NPOESS satellites through 2026. The Department of Defense will build and launch the series. NASA will be responsible for injecting cost-effective new technology into NPOESS satellites. NPOESS aims to launch its first satellite in 2013.
NASA engineers are preparing to launch a demonstration mission in 2010—the N-POESS Preparatory Project (NPP)—which will test critical sensors slated to fly on the NPOESS satellites. The NPP mission will also ensure that there are no gaps in key data sets started by NASA’s Terra and Aqua satellites.
"It's a busy time for environmental monitoring satellites," said NPP Project Manager Kenneth Schwer. "We're working very hard to ensure a smooth transition between the two programs."
NASA Goddard Space Flight Center