GRACE Satellite Dies

from NASA

In September scientist lost contact with the GRACE-2 satellite. Contact was restored, but another battery cell had failed. GRACE is nearly out of fuel and the ability to store the energy collected by its solar panels when it is in earth shadow. Little power beyond the active solar collectors remains. The scientists put her on standby and in the next weeks she will complete her final data collection in full sun along the terminator line between night and day.

Launched in March of 2002 as the second mission under the NASA Earth System Science Pathfinder (ESSP) Program, the Gravity Recovery and Climate Experiment twin satellites were designed for a five years mission life. They have operated for 15 years far more than expected, though scientists had hoped they would continue to operate and collect data until their replacements, GRACE-FO (follow on), were launched, but GRACE-FO has been delayed.

The decommissioning of the GRACE satellites will begin in November when one of the satellites is moved to eliminate any chance it could collide with the other, followed by steps to render the spacecraft inert. The spacecraft will make an uncontrolled reentry (crash) in early 2018, with the exact time dependent on solar activity and its effects on the Earth’s atmosphere.

GRACE is a joint partnership between the National Aeronautics and Space Administration (NASA) in the United States and Deutsche Forschungsanstalt für Luft und Raumfahrt (DLR) in Germany. GRACE consists of two identical twin satellites that fly about 137 miles (220 kilometers) apart in a polar orbit 310 miles (500 kilometers) above Earth. GRACE maps Earth's gravity field by making accurate measurements of the distance between the two satellites, using GPS and a microwave ranging system. This allows scientists all over the world an efficient and accurate way to map Earth's gravity field. The replacement pair of satellites known as GRACE-FO will also be a joint German-American project, and are similar to the original GRACE spacecraft, but with the addition of a laser interferometer for more accurate measurements.

In January, NASA and the German Research Centre for Geosciences announced that a SpaceX Falcon 9 will carry the two GRACE-FO satellites as well as five Iridium Next communications satellites into low earth orbit. A launch date for the joint Iridium Next/GRACE-FO mission has not been set, but it is expected to occur in early 2018. NASA’s fiscal year 2018 budget proposal, published in May, projected a February 2018 launch of GRACE-FO.

The information gathered from the GRACE mission have allowed scientists to track the distribution and flow of mass within Earth and its surroundings- changes in water. The gravity variations studied by GRACE include: changes due to surface and deep currents in the ocean; runoff and ground water storage on land masses; exchanges between ice sheets or glaciers and the ocean; and variations of mass within Earth. Advances in hydraulic modeling with data from the satellites, make it possible to construct accurate and holistic picture of freshwater availability, across the globe as well as measure sea water.

GRACE data has provided a global picture of water storage trends for over a decade and could be an invaluable tool for understanding water resource availability. The GRACE mission is able to monitor monthly water storage changes within river basins and aquifers that are 77,000 square miles or larger. While this area may be too large for community water management, this information could someday be used to develop a unifying principal of cross border water resource allocation. The first use has been to study the trends on groundwater in various regions during this period.

Observing the groundwater buried beneath layers of soil and rock was almost impossible until, the twin satellites GRACE were launched in March 2002. At the time few believed the satellites could measure changes in groundwater, but thanks to work of Dr. Jay Famiglietti and his graduate student Matt Rodell, who were working at that time at the University of Texas at Austin (UT-Austin) the techniques for measuring groundwater using the GRACE satellites were developed and proven. Expanding on this earlier work is additional work by Alexandra S. Richey, Brian F. Thomas, Min-Hui Lo, John T. Reager, James S. Famiglietti, Katalyn Voss, Sean Swenson, and Matthew Rodell and I’m sure others that I have missed.