HURRICANE Emily's well monitored odyssey once again showed the power of weather satellites to track dangerous storms. At the same time, the loss of the new NOAA-13 satellite shortly after launch last month highlighted the vulnerability of the United States civil weather-satellite system to technical failures.
Forecasters who rely on the eye-in-the-sky perspective would also be vulnerable if they depended on only those US resources. Happily, that perspective is supplied internationally on a cooperative basis. One nation's system can call on other national systems for backup. Thus, the European Meteosat-3 has plugged the gap left by the loss of one of two US hurricane-watching satellites.
Now this cooperation is preparing to move into a more tightly coordinated phase. This should evolve, over the next decade, into a more integrated global system. National systems are likely to become part of a larger, mutually beneficial enterprise.
The National Oceanic and Atmospheric Administration (NOAA) maintains two complementary satellite networks for the United States. In one of these, a pair of GOES satellites travels in an orbit 22,300 miles (36,000 kilometers) above the equator. This is the Clarke orbit - named in honor of science-fiction writer Arthur C. Clarke - where a satellite travels at the same angular speed with which Earth turns. At this so-called geosynchronous speed, the satellite remains more or less over a given spot on the ground.
NOAA has had only one such satellite since GOES-6 failed in 1989. Its replacement was lost in a launch failure in 1986. Moreover, the development of a new GOES series has been repeatedly delayed. The first of these satellites won't be ready for launch until at least April.
These satellites track hurricanes, among other duties. And the American Meteorological Society has warned of the danger of relying on a single aging satellite - GOES-7 - during hurricane season. But thanks to international cooperation this hasn't happened. The European Organization for the Exploitation of Meteorological Satellites (Eumetsat) moved its Meteosat-3 into position to make up for NOAA's loss. It could, in fact, also cover for GOES-7 if that should fail. In doing this, Europe repays similar American aid when a GOES satellite backed up a Meteosat-2 failure in 1985.
NOAA also has two satellites orbiting over the poles at heights of about 500 miles. These provide daily atmospheric and ocean data on a global basis. The lost NOAA-13 satellite was to have been placed on standby in case the five-year-old NOAA-11 failed. There is no immediate loss of data for forecasters. Moreover, the Department of Defense maintains a parallel polar-orbiting system that could provide data if NOAA-11 does fail.
Thus American weather forecasters are less vulnerable to NOAA satellite failures than they might appear to be. International cooperation and military backup give the weather-satellite system a robustness that NOAA alone can't provide.
Now this situation is changing. International cooperation is maturing. And the role of military satellites is questionable.
There's general agreement among the Defense Department, NOAA, and Congress that the United States can no longer afford duplicate military and civil polar-orbiting systems. The next generation system probably will have NOAA satellites supply both civil and military needs. One military ``need'' NOAA may not meet is secrecy. Military data are encoded, whereas NOAA satellites are part of an open international system. Also, international partners may be uneasy about sharing data with what could look like a quasi-military operation. In the end, the military may have to settle for being one user among many of an open, world weather-satellite network.
Meanwhile, NOAA and Europe's 16-member Eumetsat are concluding an agreement to tighten mutual backup. This would include coordinating launch schedules to ensure that fresh satellites are always on orbit ready to cover for any satellite failure. Future cooperation will likely include polar-orbiting as well as geosynchronous systems.
Weather satellites are an aspect of space activity that obviously benefits all humankind on a daily basis. Although it lacks the glamour of manned missions, this is the area where a full global partnership in space is first likely to emerge.