NASA says twin satellites end science mission after battery issue

A pair of U.S.-German satellites launched 15 years ago to map the Earth's ever-changing gravity field have ended their science operations, U.S. space agency NASA said Friday.

The twin Gravity Recovery and Climate Experiment (GRACE) satellites, GRACE-1 and GRACE-2, made science measurements only when the two were both fully functional, but an age-related battery issue occurred on GRACE-2 in September.

"It became apparent by mid-October that GRACE-2's remaining battery capacity would not be sufficient to operate its science instruments and telemetry transmitter," NASA said in a statement.

"Consequently, the decision was made to decommission the GRACE-2 satellite and end GRACE's science mission."

GRACE-2 has begun to slowly deorbit and atmospheric reentry is expected sometime in December or January, it said.

The other satellite, GRACE-1, will continue operating through the end of 2017 and its decommissioning and atmospheric reentry are expected in early 2018, the statement added.

The successor mission of GRACE, known as GRACE Follow-On, is scheduled to launch in early 2018.

GRACE, launched in March 2002 for a planned five-year mission, has revealed how water, ice and solid Earth mass move on or near Earth's surface due to its changing seasons, weather and climate processes, earthquakes and even human activities.