VANDENBERG AIR FORCE BASE, Calif. NASA launched its $1.3-billion Terra satellite on Saturday, sending it on a six-year mission to scrutinize how the Earths land, oceans and atmosphere operate as a system.

Terra lifted off aboard an Atlas-Centaur 2-AS rocket from Vandenberg Air Force Base, California at 1:57 p.m. Eastern Standard Time, just ten seconds before the close of the 25-minute launch window.

"We got off just in time," said Mike Benik, NASA's acting director of expendable launch vehicles at Kennedy Space Center (KSC). "It was a beautiful flight."

Terra, or EOS AM, is the first and likely flagship of a series of 10 satellites that make up NASAs Earth Observing System. The flotilla should contribute at least 15 years worth of data on the planet, providing a literal checkup of its health, including the effects of human activity.

"The Earth Observing System program has the idea of a 15-year observational period so we can begin to look at trends in the various aspects of the Earth system," said Jon Ranson, the Terra deputy project scientist at NASAs Goddard Space Flight Center.

EOS launches will continue through the next decade, with EOS PM, or Aqua, the next satellite scheduled.

None of the remaining satellites will be as large or complex as Terra, a virtual holdout from NASAs pre-"faster, better, cheaper" days. Ground operations alone, including support of a small army of 800 scientists for the mission, will cost $120 million, or about the price of the ill-fated Mars Climate Orbiter.

However, the complexity and grand scope of the mission dictate its cost, project members said. Terra and subsequent EOS satellites will look not at short-term weather, but at the much longer-term climate of the world, a view that is both global and dynamic.

"One of the big challenges for a climate mission is you have to be able to compare the numbers you take at the beginning of the mission and the numbers you take at the end of the mission and be confident that have the same meaning," said Ralph Kahn of NASAs Jet Propulsion Laboratory. Kahn is scientist for the Multi-angle Imaging Spectro-Radiometer (MISR), one of Terras five instruments.

"The way you do that is through calibration. Far more effort has been put into the calibration and verification of our instruments than ever before."

Terra will collect spectral data from the visible to the infrared from the entire surface of the globe every 16 days, amassing on a daily basis 850 gigabytes 100,000 encyclopedia volumes worth of measurements.

It will trail the Landsat 7 satellite, launched in April, by about 30 minutes, allowing the two to work virtually in unison in observing global phenomena. Terra will provide wide coverage; Landsat much finer.

"Landsat is kind of like youre zooming in to look at it in detail," said Darrel Williams, the Landsat 7 project scientist, during a talk at the American Geophysical Unions recent meeting in San Francisco.

Scientists expect to turn the raw data collected by Terra into literally dozens and dozens of types of global maps, detailing everything from cloud types to leaf density in forests to land cover.

Merely by working along, but in synch, Terras instruments will allow a multi-pronged attack on whatever the satellite spies.

The instruments are: 

• Clouds and the Earths Radiant Energy System (CERES): It measures the Earths radiation budget, or the difference between the energy received at the Earth from the sun and the amount radiated back into space. The planets surface and vegetation cover, atmosphere, aerosols and clouds affect that amount. CERES is the only one of Terra's five instrument packages that will not be the first of its kind to have flown aboard a spacecraft.
• Multi-angle Imaging Spectro-Radiometer (MISR): It looks in nine directions at once to measure the variation in the amount of light scattered by the Earths surface, clouds and particles in its atmosphere.
• Moderate-Resolution Imaging Spectrometer (MODIS): It measures surface temperatures, ocean color, global vegetation, cloud characteristics, snow cover and other phenomena at moderate resolutions.
• Measurements Of Pollution In The Troposphere (MOPITT): It measures methane and carbon monoxide concentrations in the lower atmosphere, or from the ground up to 10 miles (16 kilometers).
• Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER): It measures cloud properties, vegetation index, surface mineralogy, soil properties, surface temperature and topography.

Ranson gives the hypothetical example of a fire in the Amazon of a case where Terra could give scientists the tools to study the event more intensely than ever before imagined.

MODIS, Ranson said, could act as the fire spotter, its hot temperatures quickly noticed by the instrument. MISR, in turn, could measure the vertical profile any aerosols produced by the fire; MOPITT would look at the amounts of carbon monoxide produced. ASTER could observe the resulting burn scars and deforestation. And CERES could examine the effects on climate by the changes in the amounts of radiated energy from the burn area.

"All working together, thats a lot of information that can be applied to the problem," Ranson said.

Among the questions scientists hope Terra will answer is whether the growing season in the Northern Hemisphere is lengthening, a controversial theory with far-ranging implications for not only agriculture but all of human activity in that region of the world. Data collected from weather satellites seem to indicate that vegetation persists later and later in the year.

"The trends are apparent, but because of calibration issues, noisy data sets and maybe missing data, we cant verify it," Ranson said. "But if Terra cant verify it, then well come close."

V. Ramanathan, an atmospheric scientist at the Scripps Institute of Oceanography in La Jolla, California, said he plans to use CERES data to study global temperature change, including the warming effects of increased water vapor in the atmosphere and cooling effects of increased aerosol levels.

(Prior to about seven years ago, scientists did not recognize the importance of aerosols. They are now thought to play a key role in our understanding of climate prediction, Kahn said.)

CERES, Ramanathan said, will allow scientists to look at the so-called "thermal window" in the Earths atmosphere in fine detail to understand the amounts of energy it either traps or reflects back into space.

"Within a year of launch, we could get at this problem," Ramanathan said.