The unexpectedly long life of a pair of pioneering satellites that deepened scientific understanding of society’s influence on water and land is over. NASA and its project partners decided to end the GRACE satellite mission this week after the eighth of 20 battery cells on GRACE-2 failed. GRACE-1 was still working, but the mission, which measures fractional changes in Earth’s gravity based on the position of the satellites relative to each other, requires both to move in tandem. Losing one means losing all.