Space Science Topics to Be Covered at the AAAS Annual Meeting

Laser Interferometer Gravitational-Wave Observatory (LIGO)

Gravity was the first of the four fundamental forces of nature, the others being electromagnetic force, strong nuclear force, and weak nuclear force. The strong and weak nuclear forces operate only at the atomic scale. The remaining two—the gravitational force and the electromagnetic force—govern matter. These four fundamental forces were at work immediately following the Big Bang and resulted in the creation of atoms and matter.

And yet, nearly 350 years after Newton's insight, gravity remains a mystery of modern science. In 1915, Einstein developed his general theory of relativity, explaining that gravity is not a force between objects, but a force between mass and spacetime.

The presence of mass imposes a curvature on spacetime, while spacetime imposes constraints on how mass can behave. The general theory of relativity predicts that accelerating mass should radiate gravitational waves.

The U.S. effort in the search of gravitational waves is the Laser Interferometer Gravitational-Wave Observatory (LIGO), sponsored by the National Science Foundation.

An update on the data collected from LIGO will be presented at the 2003 AAAS Annual Meeting in Denver Colorado on February 17.

Gravity Recovery and Climate Experiment (GRACE)

The Gravity Recovery and Climate Experiment (GRACE) is a dedicated satellite mission whose objective is to map the global gravity field with unprecedented accuracy over a spatial range from 400 km to 40,000 km every thirty days. The measurement precision will provide a mean gravity field the accuracy of which in this frequency range is between 10 and 1000 times better than our current knowledge.

These results will be applicable to studies of the general ocean circulation and ocean-atmosphere heat and mass exchange. Measurements of continental aquifer mass change, polar ice mass change and ocean bottom currents are examples of a completely new remote sensing capability whereby we can use satellite measurements to look into the earth's interior.

The GRACE mission involves two identical satellites orbiting one behind the other at an approximate distance of 200 km. The primary measurement is provided by the High Accuracy Inter-satellite Ranging System (HAIRS), which measures range change between the two satellites. The range change will be measured with a precision better than 10 microns. A highly accurate three-axis accelerometer, located at the satellite mass center, will be used to measure the non-gravitational accelerations. Satellite GPS receivers will position the satellites over the earth with sub-centimeter level accuracy. With this set of measurements, GRACE will provide highly accurate measurements of the global gravity field once every thirty days. The two satellites were launched on March 17, 2002, and are designed to operate for a period of five years.

A presentation at the AAAS Annual Meeting in Denver Colorado will summarize the mission status, the satellite and instrument performance, and will describe some of the early data results and the impact of these results on global climate change investigations.

—Monica Amarelo

22 January 2003

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