In March, UT’s Center for Space Research celebrated the 15th anniversary of the Gravity Recovery and Climate Experiment, which has been taking detailed measurements of the Earth since its launch.

The GRACE mission consists of twin satellites that were originally meant to stay in space for only five years. However, due to the collaborative efforts of several institutions, including NASA, the German Aerospace Center and the University of Texas, the GRACE mission has stayed in orbit for the past 15 years. Himanshu Save, GRACE’s deputy science operations manager, said the satellites continue to provide insight about the Earth, including geological and oceanographic patterns.

“The way the mission works is brilliantly simple,” Save said. “GRACE is like a weighing scale in the sky that measures the mass distribution of water on the Earth. The orbit…is dependent on the gravity field of the planet…and that gravity is dependent on the distribution of mass.”

GRACE’s twin satellites measure mass changes on Earth by using the planet’s varying gravitational pulls. For instance, as the leading satellite approaches a mountain on the Earth’s surface, it is affected by the additional mass of the mountain and speeds up, according to Save. The distance between the leading and trailing satellite are closely linked to the measurement of mass.

“The change in distance measured by GRACE will change slightly from month to month,” Save said. “That change tells us how the mass under the satellites has changed over that time.”

The changing mass distribution of Earth due to rain, droughts and other climate events are then computed into a monthly map of regional variation used by scientists in their studies, Save said.

Byron Tapley, principal investigator and director of the Center for Space Research, said that the two satellites are able to capture the entirety of the Earth’s surface once every 30 days, which allows researchers to track changes over time. Researchers can use this information to track their regional aquifers and water resources.

“The scientific questions that arise depend on where you are,” Tapley said. “The dataset has a very large utilization. About 4,000 users accessed the data during this past year.”

Scientists have used GRACE to track the water cycle, including water movement in deep sea ocean currents, the changing ice sheets and underground aquifers and reservoirs.

“Water is going to be very important to us in the future for agriculture, drinking and a whole host of life-supporting functions,” Tapley said. “It’s given us the ability to measure underground aquifers… and find reservoirs for drinking and agriculture use.”

Save said GRACE’s potential to improve the quality of life for humans is fascinating, especially given the fact that freshwater is a limited resource. According to Save, there is no other mission that can track the global movement of water over time.

“GRACE has revolutionized how scientists look at this resource, and with the help of multi-disciplinary and multi-sensor studies, we should be able to make GRACE an invaluable resource,” Save said.