GRACE-FO satellite image
GRACE-FO's new laser technology promises to make the measurement of the satellites' separation distance even more precise which could lead to enhanced gravity measurements. NASA-JPL image

The GRACE satellites, affectionately known as Tom and Jerry, have tirelessly orbited Earth for more than 15 years, collecting valuable information about the changes in the planet’s water, ice and land. Nearly 20 years ago, aerospace engineering professor Byron Tapley, director of The University of Texas at Austin Center for Space Research (UTCSR), encouraged NASA’s Jet Propulsion Laboratory (NASA-JPL) to use the twin satellites to measure small changes in the earth using its gravitational pull. This March, the satellites marked their 15th year in orbit.

Since the dawn of the space age, scientists have used measurements of large variations in the orbits or the paths of Earth satellites, based on the fundamental principles presented by Isaac Newton that explain tides and the earth’s structure through the studying the motion of the moon around the earth. The GRACE (Gravity Recovery and Climate Experiment) mission offered a paradigm-shifting implementation with its twin, co-orbiting satellites orbiting at 200 kilometers apart at 500 kilometers in altitude. This allows the continuous and highly precise measurements of the influence of never-before-seen variations in Earth’s gravitational field — for instance, due to the land-water cycle or ice-sheet changes — on the orbits of the twin satellites.

It its lifetime, the GRACE mission has helped researchers understand a variety of the climate trends taking place across continents. Once the satellites beam down data to CSR researchers, it is converted into useful information. Measurements from the GRACE satellites are analyzed through supercomputers at the university’s Texas Advanced Computing Center (TACC) and have provided important data such as measuring changes in sea level and revealing when aquifer levels are at a dangerous low.

“UTCSR has delivered maps of Earth’s gravitational field and mass variability that are now the established benchmark worldwide,” said Srinivas Bettadpur, who is an associate professor of aerospace engineering and engineering mechanics. “Because of our analyses, we have also delivered the now de-facto standards for the time-variable and mean gravitational field models for Earth.”

Additionally, Bettadpur said, geoscientists and engineers around the world have used GRACE data to show, for example, that water balance in river basins worldwide is quite variable, contrary to longstanding practices in the hydrology community, and can be indicative of the drought conditions in the past decade in places such as Texas and California. Across Greenland and Antarctica, GRACE data have also provided unprecedented measurements of ice-sheet-mass loss and helped spawn new research into the mechanics of ice-sheet evolution and the resulting societal impacts. Other GRACE outcomes include insights into the structure of the earth’s crust since the last ice age, the mechanics of some of the most major earthquakes and the delineation of the ocean currents and their variability.

While the twin GRACE satellites tripled their initial life expectancy, they will be retired and replaced by new twin satellites in the GRACE Follow-On mission, or GRACE-FO, in early 2018.

Bettadpur will spearhead the work at UT Austin for GRACE-FO, with UTCSR once again playing a key role in the mission; it will be jointly implemented by NASA-JPL and the GFZ German Geosciences Research Center. GRACE-FO is expected to not only fill the role of its predecessor, but potentially surpass its accuracy with new laser technology.

“GRACE-FO will provide continuity with GRACE, which is essential to understanding variations in the earth’s system at the decadal time scales that, in turn, are critical for our understanding of societal impacts of global climate change,” Bettadpur said. “At the same time, GRACE-FO will also fly a new laser interferometer demonstration system with highly precise data that will provide new insights into the earth’s system processes at finer spatial scales than ever before.”

GRACE-FO’s end date is scheduled for 2022, but the satellites have a potential lifespan of 10 years, allowing UT Austin to continue providing crucial data on the earth’s changing landmasses, ice sheets and water.

“With GRACE, scientists and engineers at UTCSR were instrumental in inventing a new remote-sensing technique and helping to establish it as the preferred technique among researchers studying globally connected climate processes,” Bettadpur said. “With GRACE-FO, we are able to use our initial insights to explore further, using more capable, upgraded satellites. On the technology front, we are also looking beyond GRACE-FO, seeing how the ideas and tools that might be confined to the lab today can be put to service for society in this way in the not too distant future.”

For more information on GRACE-FO, visit gracefo.jpl.nasa.gov/