The loss of a weather satellite that a malfunctioning Delta rocket would have orbited last Saturday is a major blow for the United States weather observing program. ``We continue to operate at great risk with only one satellite capable of returning cloud images,'' says William Callicott, deputy director of the Office of Satellite Data Processing and Distribution of the National Oceanic and Atmospheric Administration (NOAA).
He explains that these pictures help forecasters track rapidly developing severe storms, as well as hurricanes. They would lose this valuable capability were the single orbiting weather eye now in service to fail.
Also, without a second satellite, Mr. Callicott's office can't provide full service. Two satellites are needed to give the kind of coverage US forecasters need -- one satellite located over the Pacific and one over the Atlantic.
The single satellite now available has been moved with the seasons to make the most of its capability. In winter, it views more of the Pacific. Then, during the Atlantic hurricane season, which starts next month, controllers move it eastward to monitor the development of tropical storms.
NOAA has lived with this unsatisfactory situation since one of a pair of satellites malfunctioned in July 1984. So loss of its replacement poses no immediate weather observing emergency. But, Callicott notes, the likelihood of losing the remaining working satellite increases as its components age.
The satellite in question is one of the GOES (Geostationary Operational Environmental Satellite) series of satellites, which orbit 22,300 miles above Earth's equator. Their height gives them a hemispheric view of weather.
Moreover, because their orbital speed matches the rate at which Earth spins, they hover over a given longitude -- hence the term geostationary.
A second type of weather satellite, traveling in a polar orbit, complements the GOES system.
Moving at a lower altitude of about 500 miles, it passes over a given location twice a day to give complete coverage of the planet.
While these complementary views of the polar orbiter are valuable for keeping track of large-scale weather globally, Callicott says they are no substitute for the continuous updating of weather over the western hemisphere that a full GOES two-satellite system provides.
Thus loss of the GOES-G satellite Saturday has been a bitter disappointment to NOAA. It was the seventh of the satellites and would have been designated GOES-7 had it reached orbit safely. NOAA has one more such satellite left in its inventory -- GOES-H. It was scheduled for launch in October and will be ready to go if the National Aeronautics and Space Administration (NASA) has recertified the Delta rocket design for use by that time.
Callicott says that he is cautiously optimistic about maintaining service. The current satellite -- GOES-6 -- is three years into its five-year design life and working well. Design defects that caused earlier GOES satellites to fail have been corrected. So GOES-6 may well outlast its nominal five years.
``We have a fairly high degree of confidence in the GOES-6 satellite,'' Callicott says.
If GOES-6 survives and if GOES-H can be orbited and put into operation later this year, there's a good likelihood that NOAA can offer full satellite service for the next several years.
Then, an improved GOES series is due to cut in. These satellites, now being built by Ford Aerospace & Communications Corporation, will offer better cloud pictures, relay data from buoys and other robot surface stations, and offer other information, such as temperatures at various heights in the atmosphere.
However, NOAA now has little operational margin as it shifts over to the new system. GOES-H was the backup for the satellite lost Saturday.
Now NOAA has nothing to fall back on if it were to lose another geostationary satellite either through launch failure or on orbit.
NASA, which is developing and testing the new GOES satellites for NOAA, has asked Ford Aerospace if it can speed delivery of the first of those satellites. ``If we can speed up our Ford Aerospace people by just six months, that would be a big boost,'' Callicott says.