AUSTIN, Texas—Researchers will be closer to answering questions about global warming, global climate change and El Niño after extraordinarily precise information is gathered by two NASA satellites to be launched March 16 in Russia under the direction of aerospace engineers from The University of Texas at Austin.
Working from a satellite operations center in Germany, Dr. Byron Tapley, director of the Center for Space Research at The University of Texas at Austin and a worldwide expert on precision orbit determination, will become the first non-NASA employee to direct a NASA mission when the project takes flight.
The launch of the Gravity Recovery and Climate Experiment (GRACE) will begin the journey for twin satellites to make at least a 100-fold improvement in current measurements of the Earth’s gravity field. This highly detailed map of Earth’s gravitational field will relate minute fluctuations of gravity to the planet’s physical features, such as ice caps, continental water storage, or environmental events such as storms. A new map of Earth’s gravity, which changes in time as well as by location, will be generated for every month during the mission’s expected five-year lifetime.
This improvement in the knowledge of Earth’s gravity will allow scientists to better trace the transport of water and heat between the oceans, atmosphere and land — information vital to the study of global climate change.
“Producing a precise model of the fluctuations in gravity, the invisible force that pulls two masses together, over the Earth’s surface has proven a formidable task,” Tapley said. “Currently, data from several dozen satellites must be combined to produce a model of Earth’s gravitational field. These models do a good job at replicating the large-scale features but cannot resolve finer-scale features or detail the small month-to-month variations in the gravity field associated with the water cycle.”Unlike former gravity measurements taken from the influence on a single satellite of Earth’s gravitational pull, GRACE will employ two satellites and measure their reactions to Earth’s pull as it varies the distance between them. Scientists are interested in the gravity variations on the earth and how gravity changes over time.
“The two GRACE satellites will be approximately 137 miles apart,” Tapley said. “We will be able to measure the distance between them with a precision better than 10 microns. That’s like measuring the distance between Bastrop and Houston to within the width of 1/10 of a human hair.”
Since the Earth has varied features such as mountains, valleys and underground caverns, the mass is not evenly distributed around the globe. The “lumps” observed in the Earth’s gravitational field result from an uneven distribution of mass inside the Earth. The GRACE mission will provide a global map of Earth’s gravity and how it changes as the mass distribution shifts.
The two GRACE satellites will travel in space 500 kilometers or about 300 miles above the Earth. As the front satellite approaches an area of higher gravity, such as a mountain, it will be pulled toward the area of higher gravity and speed up. This increases the distance between the two satellites. As the satellites straddle the area of higher gravity, the front satellite will slow down and the trailing satellite will speed up. As the trailing satellite passes the area of higher gravity, it will slow down and the lead satellite will not be affected. As the satellites move around the Earth, the speeding up and slowing down of the satellites will allow scientists to measure the distance between the two satellites and use this information to map the Earth’s gravity field.
The two satellites will provide scientists from around the world with an efficient and cost-effective way to map the Earth’s gravity field.
The GRACE satellites, set to launch from Eurockot’s dedicated launch facilities in Plesetsk, Russia aboard the Rockot, represents a four-year, $150 million international partnership between NASA in the United States and Deutsches Zentrum für Luft-und Raumfahrt (DLR) in Germany. Led by The University of Texas at Austin, the partners in the project include Jet Propulsion Laboratory in Pasadena, Calif., and GeoForschungsZentrum in Potsdam, Germany.
For more information, contact Margaret Baguio at the Center for Space Research (512) 471-6922 or Becky Rische at the College of Engineering (512) 471-7272. Photographs and more information are available at the GRACE mission Web site.
