The US and Germany's joint Gravity Recovery and Climate Experiment (GRACE) is coming to an end after 15 years of successful operation, according to a release from Nasa.
The mission, originally planned for five years, saw a pair of satellites – GRACE-1 and GRACE-2 – use different instruments to map the Earth's gravitational field and provide useful insights into how our planet is changing with the movement of water, ice, and solid Earth components due to natural as well as human-induced factors.
The movement or redistribution of water tweaked Earth's mass and gravitational pull from time to time – changes that the twin GRACE satellites kept monitoring to measure gravity field over the years. However, GRACE-2 suffered an age-related battery glitch in September, which meant lack of power to keep its scientific instruments and telemetry transmitter in operation.
As both satellites and their instruments had to be fully-functional for measurement of the gravity field, it was decided that the GRACE's mission had to be ended with the decommissioning of both satellites. According to Nasa, the fuel of GRACE-2 is being expended as the satellite has started deorbiting slowly. It will fall towards Earth and will re-enter its atmosphere sometime in January or December.
Meanwhile, GRACE-1 will continue its mission through the end of 2017 till its fuel runs out. "GRACE-1's remaining fuel will be used to complete previously planned manoeuvres to calibrate and characterize its accelerometer to improve the final scientific return and insights from the 15-year GRACE record," said GRACE Project Scientist Carmen Boening of Nasa's Jet Propulsion Laboratory (JPL). It is expected to renter in the early months of 2018.
"GRACE has provided paradigm-shifting insights into the interactions of our planet's ocean, atmosphere and solid Earth components," Byron Tapley, the primary investigator on the mission said. "It has advanced our understanding of the contribution of polar ice melt to global sea level rise and the amount of atmospheric heat absorbed by the ocean. Recent applications include monitoring and managing global water resources used for consumption, agriculture and industry; and assessing flood and earthquake hazards."
Moving ahead, the GRACE mission will be succeeded by 'GRACE Follow-On' in early 2018. The mission will see replacement satellites being positioned with a new laser-ranging interferometer for next-gen gravitational research satellites.