The transition from an all-U.S. system of polar-orbiting meteorological satellites to one where Europe now has responsibility for part of the coverage is going smoothly despite a still-unexplained failure aboard the new European Metop-A satellite, according to U.S. and European meteorological officials.

The principal instruments aboard Metop-A, which was launched in October 2006 and began preliminary operations in January, are all working well and being used by U.S. and European authorities alike.
Metop-A is part of a U.S.-European agreement on joint operation of weather satellites in polar low Earth orbit to provide weather data in the coming years. It represents the first time that the U.S. government has agreed to be dependent on Europe for part of the polar observation system, though European geostationary-orbiting spacecraft have been moved to cover gaps in U.S. coverage following a satellite failure.

The U.S. National Oceanic and Atmospheric Administration (NOAA) has performed the same service for Europe. The collaboration in polar orbit between NOAA and Europe’s Eumetsat meteorological satellite agency, has been especially welcome given the budget and schedule problems associated with the next generation of U.S. polar-orbiting satellites, now expected to enter service around 2013 years later than originally intended. “No one country can do it all,” said Gary Davis, head of the systems development office at NOAA’s satellite and information service. “International cooperation is a good thing, and Eumetsat and NOAA have a long history of working together.”

Davis said U.S. meteorological services have run into no serious problems integrating Metop-A data into their portfolio of weather-forecast tools. Up to now, NOAA has used its own satellites to manage the morning and afternoon polar orbits, so named because the spacecraft are timed to cross the equator at that time of day. Under the jointly run system taking shape, Metop, which is operated by Eumetsat, will take over the morning-orbit responsibility, with NOAA retaining responsibility for the afternoon orbit.

The NOAA-18 satellite, known as NOAA-N

Prime, is scheduled for launch in early 2009 to ensure continuous coverage of the afternoon orbit while waiting for the next-generation satellites. For the morning orbit, Metop-A will take over from the NOAA-17 satellite, which was launched in June 2002 and is nearing the end of its projected service life. Two more Metop satellites have been ordered to assure continuous coverage for the next 15 years.

A July failure of the Advanced High-Resolution Picture Transmission (AHRPT) payload on Metop-A forced Eumetsat and NOAA to rely on NOAA-17 to provide real-time, high-speed delivery.

Eumetsat and the Metop design authority, the European Space Agency, along with satellite prime contractor Astrium Satellites, formed a team to analyze the failure but as yet have not produced conclusive results, according to Mikael Rattenborg, Eumetsat’s director of operations.

Eumetsat concluded that it cannot recover the primary AHRPT instrument. Eumetsat is concerned that the problem might

lie with components inside the AHRPT power amplifier. Because this amplifier also serves the backup AHRPT, Eumetsat has not switched on the backup instrument, Rattenborg said Sept. 24.

Eumetsat encountered a similar problem on its MSG-1 geostationary-orbiting satellite in 2002 and was unable to recover the instrument’s functions. That failure forced Eumetsat to invent its Eumetcast data-transmission service. The emergency solution, which requires the lease of capacity aboard a conventional communications satellite, has proved superior to what the original instrument could have done, Eumetsat users say.

But that solution will not be so easily available to Eumetsat for a satellite in polar orbit, whose position relative to geostationary satellites is

changing constantly.

Rattenborg said the board of inquiry investigating the AHRPT failure is expected to issue conclusions in October. He said this issue is unrelated to the Sept. 18 shutdown of Metop-A for about a day, an event Eumetsat blamed on cosmic radiation that disturbed Metop-A’s electronics while the satellite was over the South Pole and out of ground station visibility. He said it is not expected to recur.