FLURRY OF SATELLITES TO MONITOR EARTH AND EXAMINE GALAXY


By WARREN E. LEARY
12/10/2002
The New York Times
Page 2, Column 2
c. 2002 New York Times Company



WASHINGTON, Dec. 9   NASA will finish its year of space exploration by launching a small flurry of satellite missions to monitor the ice and sea winds of Earth and to look at the bubble of hot gas that surrounds the Milky Way.

The instruments, to be fired on two rockets this month, will expand the satellite system that studies the climate of Earth and look at a rarely studied region between nearby stars that was apparently cleared of much of its gas and dust by a supernova explosion 10 million to 12 million years ago.

Two missions, the Ice, Cloud and Land Elevation Satellite, or IceSat, and the Cosmic Hot Interstellar Plasma Spectrometer satellite, or ChipSat, are to be launched on Dec. 19 from Vandenberg Air Force Base, Calif., on the same Boeing Delta II rocket.

The third effort, a large microwave radar instrument, SeaWinds, is a major part of Japan's Advanced Earth Observing Satellite II. Adeos II is scheduled for launching by a Japanese H-IIA rocket on Friday at the Tanegashima Space Center.

ChipSat is the smallest mission, but it has the most distant reach. The 132-pound satellite, the size of a large Pullman suitcase, is hitching a ride on the IceSat rocket. In orbit, it will turn its gaze to deep space as its companion focuses on Earth.

The one-year ChipSat exploration, the first of NASA's streamlined University-Class Explorer missions, will focus on the interstellar medium, the area of hot low-density gas and dust that fills the vastness between stars. When cooled, the diffuse material in the medium forms clumps that scientists believe evolve into stars through a largely unknown process.

The $16 million ChipSat will look at an unusual part of this space where the solar system is situated, the Local Bubble. The region, 300 light-years in diameter, is filled with gas much less dense than the average interstellar medium, probably as a result of a supernova explosion millions of years ago.

Dr. Mark Hurwitz of the University of California at Berkeley, the principal mission scientist, said the gas in this region, although sparse, was extremely hot, at 1.8 million degrees Fahrenheit, and radiated most of its energy in the little-studied extreme ultraviolet region of the electromagnetic spectrum. ChipSat, from its orbit 367 miles above Earth, will measure the intensity and distribution of the extreme ultraviolet glow to test competing theories on how the gas forms into denser clouds, Dr. Hurwitz said.

The largest new mission, IceSat, is a major component of a program to study changes in the Earth's climate. The $282 million mission, intended to operate for three to five years, will use a laser instrument to measure precisely the changing elevations of large polar ice sheets from season to season.

In addition, the laser scanner will measure cloud height and distribution, particularly as related to ice sheets, as well as land elevation, sea ice and vegetation cover.

"This mission will provide revolutionary insight into changes in ice and the role ice plays in our Earth system, using a space-borne laser to look at the topography of ice both in the Antarctic and Greenland," said Dr. Ghassem Asrar, NASA's associate administrator for earth science.

"This information will help scientists determine whether the polar ice sheets are growing or shrinking, and how the ice masses may change under future climate conditions."

The altimeter system, measuring the time it takes light pulses to travel to a reflecting object and back to the satellite, will calculate the precise elevations and positions of ice sheets, icebergs, clouds and land formations. The satellite, 373 miles up, will perform the measurements 40 times a second.

The project scientist from the Goddard Space Flight Center, Dr. H. Jay Zwally, said the measurements would help determine the effects of global warming on the ice sheets and their role in rising sea levels. Historically, he said, about three inches of ocean surface water is transferred to the ice sheets as snowfall every 10 years, and the same amount comes out as icebergs and melting along the sheet edges. ''The mass of the two actions should balance,'' he said.

But over the last decade, Dr. Zwally said, sea levels have been rising 0.08 inches a year, or eight inches a century, and no one is certain where the added water comes from. Satellite and aircraft observations have measured the changing areas of ice sheets, but researchers need data on the changing heights, or elevations, to calculate their mass.

"IceSat should help us reduce the uncertainty of ice-melt estimates," he said.

The SeaWinds instrument on the Japanese satellite will map wind speed and direction across 90 percent of the Earth's ice-free oceans every two days. Winds play a major role in weather and climate, affecting the exchange of moisture, heat and greenhouse gases between the atmosphere and the oceans.

In addition to aiding long-term research, up to 15 times a day, SeaWinds will beam data for use by the National Oceanic and Atmospheric Administration and other agencies in improving forecasting and storm warnings, as well as helping generate ice maps to protect shipping lanes.

SeaWinds, which cost NASA $138 million to develop and build and will cost $16 million more to operate over its life of three to five years, is the third in a series of instruments that sense ripples caused by winds near the ocean surface, which scientists use to calculate wind speed and direction.

The 441-pound instrument will make 400,000 measurements a day by transmitting high-frequency microwave pulses to the ocean surface. They are to be echoed back to the satellite 500 miles above.

Measurements from an earlier SeaWinds instrument now operating aboard the NASA Quikscat satellite, launched in 1999, were instrumental in findings on typhoons' role in generating ocean life, reported on Saturday in San Francisco at the fall meeting of the American Geophysical Union.

Scientists from Taiwan and the United States said typhoons that swept over the South China Sea generated upwellings of nutrient-rich water from the deep ocean, stimulating vast blooms of algae, an important food for marine life.